This document provides information about liquid crystals and their structure and properties. It discusses different types of liquid crystals including thermotropic, lyotropic, and metallotropic phases. Thermotropic liquid crystals exhibit phase transitions based on temperature, while lyotropic phases transition based on both temperature and concentration. Common liquid crystal phases described include nematic, smectic, chiral, and discotic phases. The document also discusses the design of liquid crystalline materials and methods for analyzing mesophases including thermal optical microscopy and differential scanning calorimetry. Biological membranes are noted to exhibit lyotropic liquid crystalline properties.
Phase diagram of a one component system ( water system )ShahriarTipu1
This document discusses phase diagrams and the phase rule through the example of a one-component water system. It defines key terms like phase, component, degree of freedom, and phase rule. It then explains the different areas and curves in the phase diagram of water, including that the liquid-vapor, ice-vapor, and ice-liquid curves represent univariant systems while the areas represent bivariant systems. It also notes the unique properties of the ice-liquid curve and the triple point where ice, liquid water, and vapor coexist in equilibrium.
Diborane is prepared through several methods including reacting boron trifluoride with lithium aluminum hydride or oxidizing sodium borohydride with iodine. It is a colorless, toxic gas that spontaneously burns in air and is readily hydrolyzed by water. Diborane has a structure with two bridging hydrogen atoms between two boron atoms in a banana-like bond configuration, making it an electron deficient molecule. It has potential uses as a rocket propellant or in vulcanization and hydrocarbon polymerization processes.
Solid state chemistry- laws of crystallography- Miller indices- X ray diffraction- Bragg equation- Spectrophotometer- Determination of interplanar distance- Types of crystal
The document discusses various properties of liquids including intermolecular forces, vapor pressure, boiling point, surface tension, viscosity, refractive index, and optical activity. It describes three main types of intermolecular forces that exist in liquids: dipole-dipole interactions, London forces, and hydrogen bonding. Vapor pressure is defined as the pressure exerted by a liquid's vapor when in equilibrium, and it increases with temperature, affecting the boiling point. Methods for measuring properties like surface tension, viscosity, refractive index, and optical activity are also outlined.
1) The document discusses phase equilibria and phase diagrams, including definitions of key terms like phase, component, and degrees of freedom.
2) It provides examples of phase diagrams for one-component systems like water, which has three phases (ice, liquid water, vapor) in equilibrium, and sulphur, which has four phases.
3) Details are given on important features of phase diagrams like melting curves, vaporization curves, triple points, and how to apply Gibbs phase rule to analyze systems.
1. The document compares the properties of liquid ammonia and water, noting that liquid ammonia has lower melting and boiling points than water, weaker hydrogen bonding, and a lower dielectric constant.
2. It describes several reactions that occur in liquid ammonia, including autoionization, acid-base reactions where compounds forming NH4+ ions are acidic and NH2- ions are basic, and redox reactions where alkali metals dissolve to form strong reducing solutions.
3. Dinitrogen tetraoxide is also discussed as an alternative solvent, undergoing limited autoionization, with NO+ ions being acidic and NO3- ions basic, and allowing redox reactions through formation of NO gas.
This document defines liquid crystals as an intermediate state of matter between solids and liquids. It provides a brief history of liquid crystals, noting their discovery in 1888. It describes the four main types of liquid crystals - smectic, nematic, cholesteric, and columnar - and how they differ in molecular arrangement and mobility. Examples of thermotropic and lyotropic liquid crystals are given. The document outlines some key properties of liquid crystals and lists some pharmaceutical, food, and dermal applications that exploit these properties. Characterization techniques for liquid crystals are also summarized.
This document summarizes a seminar on crystal structures presented by Madhusmita Sethy at Dr. Hari Singh Gour Vishwavidyalaya University. It defines crystals as solids composed of atoms or molecules arranged periodically in three dimensions. Crystals are made up of basic building blocks including unit cells that repeat through translation, lattices consisting of periodic arrays of points, and motifs or basis of one or more atoms located in a specific way. The document outlines six major crystal systems and discusses crystal structures, Pauling's rules of crystal chemistry, polymorphism, and the significance of understanding crystal structures.
Phase diagram of a one component system ( water system )ShahriarTipu1
This document discusses phase diagrams and the phase rule through the example of a one-component water system. It defines key terms like phase, component, degree of freedom, and phase rule. It then explains the different areas and curves in the phase diagram of water, including that the liquid-vapor, ice-vapor, and ice-liquid curves represent univariant systems while the areas represent bivariant systems. It also notes the unique properties of the ice-liquid curve and the triple point where ice, liquid water, and vapor coexist in equilibrium.
Diborane is prepared through several methods including reacting boron trifluoride with lithium aluminum hydride or oxidizing sodium borohydride with iodine. It is a colorless, toxic gas that spontaneously burns in air and is readily hydrolyzed by water. Diborane has a structure with two bridging hydrogen atoms between two boron atoms in a banana-like bond configuration, making it an electron deficient molecule. It has potential uses as a rocket propellant or in vulcanization and hydrocarbon polymerization processes.
Solid state chemistry- laws of crystallography- Miller indices- X ray diffraction- Bragg equation- Spectrophotometer- Determination of interplanar distance- Types of crystal
The document discusses various properties of liquids including intermolecular forces, vapor pressure, boiling point, surface tension, viscosity, refractive index, and optical activity. It describes three main types of intermolecular forces that exist in liquids: dipole-dipole interactions, London forces, and hydrogen bonding. Vapor pressure is defined as the pressure exerted by a liquid's vapor when in equilibrium, and it increases with temperature, affecting the boiling point. Methods for measuring properties like surface tension, viscosity, refractive index, and optical activity are also outlined.
1) The document discusses phase equilibria and phase diagrams, including definitions of key terms like phase, component, and degrees of freedom.
2) It provides examples of phase diagrams for one-component systems like water, which has three phases (ice, liquid water, vapor) in equilibrium, and sulphur, which has four phases.
3) Details are given on important features of phase diagrams like melting curves, vaporization curves, triple points, and how to apply Gibbs phase rule to analyze systems.
1. The document compares the properties of liquid ammonia and water, noting that liquid ammonia has lower melting and boiling points than water, weaker hydrogen bonding, and a lower dielectric constant.
2. It describes several reactions that occur in liquid ammonia, including autoionization, acid-base reactions where compounds forming NH4+ ions are acidic and NH2- ions are basic, and redox reactions where alkali metals dissolve to form strong reducing solutions.
3. Dinitrogen tetraoxide is also discussed as an alternative solvent, undergoing limited autoionization, with NO+ ions being acidic and NO3- ions basic, and allowing redox reactions through formation of NO gas.
This document defines liquid crystals as an intermediate state of matter between solids and liquids. It provides a brief history of liquid crystals, noting their discovery in 1888. It describes the four main types of liquid crystals - smectic, nematic, cholesteric, and columnar - and how they differ in molecular arrangement and mobility. Examples of thermotropic and lyotropic liquid crystals are given. The document outlines some key properties of liquid crystals and lists some pharmaceutical, food, and dermal applications that exploit these properties. Characterization techniques for liquid crystals are also summarized.
This document summarizes a seminar on crystal structures presented by Madhusmita Sethy at Dr. Hari Singh Gour Vishwavidyalaya University. It defines crystals as solids composed of atoms or molecules arranged periodically in three dimensions. Crystals are made up of basic building blocks including unit cells that repeat through translation, lattices consisting of periodic arrays of points, and motifs or basis of one or more atoms located in a specific way. The document outlines six major crystal systems and discusses crystal structures, Pauling's rules of crystal chemistry, polymorphism, and the significance of understanding crystal structures.
Viscosity is a measure of a liquid's resistance to flow. It is defined as the shear stress divided by the rate of shear strain. There are several methods to measure viscosity, including using capillary tubes, rotating viscometers, and falling ball viscometers. The measurement involves determining the time required for liquid to flow through a capillary or for a ball to fall between marks in a viscometer tube, from which the dynamic viscosity in mPa·s can be calculated. Viscosity measurements require controlling the temperature accurately, usually within 0.1°C.
THE PHASE RULE
phase rule
degree of freedom in mixture
one component system
two component system
pressure temperature diagram sulfur hydrogen
eutectic eutectoid mixture
The document discusses the Kekule structure of benzene. August Kekule first proposed that benzene's structure contained a six-membered carbon ring with three alternating double and single bonds between carbons. This structure helped explain benzene's molecular formula of C6H6 but did not accurately predict its chemical behavior. The document then reviews the history of the Kekule structure and provides examples to illustrate benzene's actual delocalized bonding structure between carbons.
Chemical equilibrium is briefly discussed with following topics:
Free energy change in a chemical reaction. Thermodynamic derivation of the law of chemical equilibrium.
Definition of ΔG and ΔG◦
Le Chatelier’s principle.
Relationships between Kp, Kc and Kx
Crystal symmetry is defined by repeated patterns of atoms in a crystal structure. There are different types of symmetry operations including planes of symmetry, axes of symmetry, and centers of symmetry. Planes of symmetry divide the crystal into mirror images, axes of symmetry involve rotational symmetry, and centers of symmetry involve equidistance from a point. The six main crystal systems are defined by their unique combinations of symmetry elements and are classified from highest to lowest symmetry as isometric, tetragonal, orthorhombic, hexagonal, monoclinic, and triclinic. Miller indices and Weiss parameters are used to describe the orientation of crystal planes.
Thermodynamics is the branch of physics that studies heat, work, and energy. It is governed by four main laws:
1) The zeroth law establishes that thermal equilibrium is transitive.
2) The first law states that energy is conserved and the change in a system's internal energy equals heat added minus work done.
3) The second law specifies that entropy always increases for isolated systems undergoing spontaneous processes and heat cannot be fully converted to work.
4) The third law affirms that entropy reaches a minimum, zero for perfect crystals, as temperature approaches absolute zero.
This document outlines an experiment to determine the critical solution temperature of the phenol-water system. It describes the objective, requirements, theory, procedure, observations, calculations, results and precautions. The key steps are: mixing phenol and water in varying proportions, heating with stirring and noting the temperature at which the mixture becomes clear, then cooling and noting when turbidity reappears. By plotting the miscibility temperatures against phenol concentration, the maximum value on the curve gives the critical solution temperature, which is the temperature above which phenol and water are completely miscible in all proportions.
This document is a seminar presentation on boranes and carboranes presented by Arun Chikkodi. It introduces boranes as binary compounds of boron and hydrogen. Diborane is described as the simplest borane with two bridging hydrogen atoms. The different types of boranes and carboranes are defined based on their polyhedral structures. Bonding in boranes involves both 2c-2e and 3c-2e bonds. Wade's rule is used to predict borane and carborane structures based on skeletal electron pairs. Applications of boranes and carboranes include uses as rocket fuels and catalysts.
Silicones are a group of organosilicon polymers which are also known as siloxanes. Organosilicon compounds are those in which organic group is attached to silicon. preparations properties, types and applications of silicones.
references for study of silicones.
This document provides an overview of the application of phase rule to a three component system of acetic acid, chloroform, and water. It defines key terms like phases, components, and degrees of freedom. It explains Gibbs phase rule and how it applies to a three component system. Specifically, it discusses how the water-acetic acid-chloroform system can be represented on a triangular phase diagram, with acetic acid enhancing the miscibility of water and chloroform. The document outlines how the system transitions from two heterogeneous phases to a single homogeneous phase as the amount of acetic acid is increased.
Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals during bond formation. It involves combining orbitals of similar energy, such as an s orbital mixing with p orbitals. This leads to hybrid orbitals with different energies, shapes, and orientations compared to the original orbitals. The type of hybridization depends on the number and type of orbitals that mix, with common examples being sp, sp2, and sp3 hybridization. Hybridization helps explain molecular geometry and bonding properties.
1. There are 14 possible arrangements of points in 3D space known as Bravais lattices which describe the different crystal structures.
2. The unit cell is the smallest repeating unit that describes the structure of the crystal lattice. It is defined by the lattice parameters of length a, b, c and angles α, β, γ.
3. Atomic packing factors describe how efficiently atoms are packed within a unit cell structure, with metallic crystals having the closest packing in hexagonal close-packed and face-centered cubic structures.
4. Miller indices (hkl) are used to describe the orientation of crystal planes or faces based on their intercepts with the crystallographic axes.
The document discusses phase diagrams and the phase rule. It begins by defining key terms like phase, components, and degrees of freedom. It then explains Gibbs phase rule which relates the number of phases (P), components (C), and degrees of freedom (F) as F=C-P+2. Several examples of 1-component and 2-component phase diagrams are discussed. The document also covers concepts like true equilibrium, metastable equilibrium, and phase transitions. Phase diagrams show the conditions under which different phases can exist in equilibrium and include lines separating single phase and two phase regions.
Resonance structures represent different arrangements of electrons in a molecule that have the same positions of nuclei but different bonding patterns. Resonance contributes to the stability of molecules like benzene by delocalizing electrons across multiple equivalent structures. The actual structure of a molecule represented by resonance is a hybrid of the contributing structures, with bond lengths intermediate between single and double bonds. Delocalization of electrons is depicted using curved arrows between resonance structures.
This document discusses the molecular orbital theory presented by Dr. Farhat A. Ansari, Assistant Professor at JETGI. It introduces key concepts of molecular orbital theory including that atomic orbitals combine to form molecular orbitals belonging to the whole molecule. Molecular orbitals can be constructed through a linear combination of atomic orbitals. The document provides rules for linear combination and uses of molecular orbitals, and examples of applying molecular orbital theory to diatomic molecules including H2, He2, Li2, and B2.
This document discusses ligand substitution reactions in coordination compounds. It begins by defining ligand substitution and classifying the mechanisms as dissociative, associative, or interchange. For octahedral complexes, dissociative mechanisms are seen at high concentrations of the entering ligand and associative at low concentrations. Evidence for dissociative mechanisms includes little effect of the entering ligand on rate. Ligand substitution can also occur in octahedral complexes without breaking the metal-ligand bond. The document also discusses substitution in square planar complexes, factors affecting rate, and the trans effect, providing theories to explain it such as electrostatic polarization and pi bonding. Applications of the trans effect in synthesis are also mentioned.
The Pourbaix diagram plots the thermodynamically stable phases of an electrochemical system based on potential (EH) and pH values. It shows the boundaries between predominant chemical species in solution or as solids. Pourbaix diagrams are commonly given at room temperature and atmospheric pressure. They indicate regions of immunity, corrosion, and passivity for metals in various environments but do not account for kinetic effects.
GENERAL CHEMISTRY AS PART OF EDUCATIONSSAliceRivera13
The document discusses the kinetic molecular theory and intermolecular forces, explaining that solids and liquids behave differently due to the distances and interactions between their particles. It also examines properties of liquids like surface tension, viscosity, and capillary action that can be explained by intermolecular forces. Phase changes between solids, liquids, and gases occur at equilibrium points depending on temperature and pressure conditions according to a substance's phase diagram.
General Chemistry 2 - Chapter 1: The Kinetic Molecular Model and Intermolecul...marvinnbustamante1
The document discusses the properties of solids, liquids, and gases based on the kinetic molecular theory. It explains that in solids, particles are closely packed together in an ordered structure, while in liquids they are more spaced out but still in contact with each other. Liquids have stronger intermolecular forces than gases but weaker than solids. The document also discusses different types of intermolecular forces such as hydrogen bonding, dipole-dipole forces, and dispersion forces, and how these forces influence properties like boiling point, surface tension, and viscosity.
Viscosity is a measure of a liquid's resistance to flow. It is defined as the shear stress divided by the rate of shear strain. There are several methods to measure viscosity, including using capillary tubes, rotating viscometers, and falling ball viscometers. The measurement involves determining the time required for liquid to flow through a capillary or for a ball to fall between marks in a viscometer tube, from which the dynamic viscosity in mPa·s can be calculated. Viscosity measurements require controlling the temperature accurately, usually within 0.1°C.
THE PHASE RULE
phase rule
degree of freedom in mixture
one component system
two component system
pressure temperature diagram sulfur hydrogen
eutectic eutectoid mixture
The document discusses the Kekule structure of benzene. August Kekule first proposed that benzene's structure contained a six-membered carbon ring with three alternating double and single bonds between carbons. This structure helped explain benzene's molecular formula of C6H6 but did not accurately predict its chemical behavior. The document then reviews the history of the Kekule structure and provides examples to illustrate benzene's actual delocalized bonding structure between carbons.
Chemical equilibrium is briefly discussed with following topics:
Free energy change in a chemical reaction. Thermodynamic derivation of the law of chemical equilibrium.
Definition of ΔG and ΔG◦
Le Chatelier’s principle.
Relationships between Kp, Kc and Kx
Crystal symmetry is defined by repeated patterns of atoms in a crystal structure. There are different types of symmetry operations including planes of symmetry, axes of symmetry, and centers of symmetry. Planes of symmetry divide the crystal into mirror images, axes of symmetry involve rotational symmetry, and centers of symmetry involve equidistance from a point. The six main crystal systems are defined by their unique combinations of symmetry elements and are classified from highest to lowest symmetry as isometric, tetragonal, orthorhombic, hexagonal, monoclinic, and triclinic. Miller indices and Weiss parameters are used to describe the orientation of crystal planes.
Thermodynamics is the branch of physics that studies heat, work, and energy. It is governed by four main laws:
1) The zeroth law establishes that thermal equilibrium is transitive.
2) The first law states that energy is conserved and the change in a system's internal energy equals heat added minus work done.
3) The second law specifies that entropy always increases for isolated systems undergoing spontaneous processes and heat cannot be fully converted to work.
4) The third law affirms that entropy reaches a minimum, zero for perfect crystals, as temperature approaches absolute zero.
This document outlines an experiment to determine the critical solution temperature of the phenol-water system. It describes the objective, requirements, theory, procedure, observations, calculations, results and precautions. The key steps are: mixing phenol and water in varying proportions, heating with stirring and noting the temperature at which the mixture becomes clear, then cooling and noting when turbidity reappears. By plotting the miscibility temperatures against phenol concentration, the maximum value on the curve gives the critical solution temperature, which is the temperature above which phenol and water are completely miscible in all proportions.
This document is a seminar presentation on boranes and carboranes presented by Arun Chikkodi. It introduces boranes as binary compounds of boron and hydrogen. Diborane is described as the simplest borane with two bridging hydrogen atoms. The different types of boranes and carboranes are defined based on their polyhedral structures. Bonding in boranes involves both 2c-2e and 3c-2e bonds. Wade's rule is used to predict borane and carborane structures based on skeletal electron pairs. Applications of boranes and carboranes include uses as rocket fuels and catalysts.
Silicones are a group of organosilicon polymers which are also known as siloxanes. Organosilicon compounds are those in which organic group is attached to silicon. preparations properties, types and applications of silicones.
references for study of silicones.
This document provides an overview of the application of phase rule to a three component system of acetic acid, chloroform, and water. It defines key terms like phases, components, and degrees of freedom. It explains Gibbs phase rule and how it applies to a three component system. Specifically, it discusses how the water-acetic acid-chloroform system can be represented on a triangular phase diagram, with acetic acid enhancing the miscibility of water and chloroform. The document outlines how the system transitions from two heterogeneous phases to a single homogeneous phase as the amount of acetic acid is increased.
Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals during bond formation. It involves combining orbitals of similar energy, such as an s orbital mixing with p orbitals. This leads to hybrid orbitals with different energies, shapes, and orientations compared to the original orbitals. The type of hybridization depends on the number and type of orbitals that mix, with common examples being sp, sp2, and sp3 hybridization. Hybridization helps explain molecular geometry and bonding properties.
1. There are 14 possible arrangements of points in 3D space known as Bravais lattices which describe the different crystal structures.
2. The unit cell is the smallest repeating unit that describes the structure of the crystal lattice. It is defined by the lattice parameters of length a, b, c and angles α, β, γ.
3. Atomic packing factors describe how efficiently atoms are packed within a unit cell structure, with metallic crystals having the closest packing in hexagonal close-packed and face-centered cubic structures.
4. Miller indices (hkl) are used to describe the orientation of crystal planes or faces based on their intercepts with the crystallographic axes.
The document discusses phase diagrams and the phase rule. It begins by defining key terms like phase, components, and degrees of freedom. It then explains Gibbs phase rule which relates the number of phases (P), components (C), and degrees of freedom (F) as F=C-P+2. Several examples of 1-component and 2-component phase diagrams are discussed. The document also covers concepts like true equilibrium, metastable equilibrium, and phase transitions. Phase diagrams show the conditions under which different phases can exist in equilibrium and include lines separating single phase and two phase regions.
Resonance structures represent different arrangements of electrons in a molecule that have the same positions of nuclei but different bonding patterns. Resonance contributes to the stability of molecules like benzene by delocalizing electrons across multiple equivalent structures. The actual structure of a molecule represented by resonance is a hybrid of the contributing structures, with bond lengths intermediate between single and double bonds. Delocalization of electrons is depicted using curved arrows between resonance structures.
This document discusses the molecular orbital theory presented by Dr. Farhat A. Ansari, Assistant Professor at JETGI. It introduces key concepts of molecular orbital theory including that atomic orbitals combine to form molecular orbitals belonging to the whole molecule. Molecular orbitals can be constructed through a linear combination of atomic orbitals. The document provides rules for linear combination and uses of molecular orbitals, and examples of applying molecular orbital theory to diatomic molecules including H2, He2, Li2, and B2.
This document discusses ligand substitution reactions in coordination compounds. It begins by defining ligand substitution and classifying the mechanisms as dissociative, associative, or interchange. For octahedral complexes, dissociative mechanisms are seen at high concentrations of the entering ligand and associative at low concentrations. Evidence for dissociative mechanisms includes little effect of the entering ligand on rate. Ligand substitution can also occur in octahedral complexes without breaking the metal-ligand bond. The document also discusses substitution in square planar complexes, factors affecting rate, and the trans effect, providing theories to explain it such as electrostatic polarization and pi bonding. Applications of the trans effect in synthesis are also mentioned.
The Pourbaix diagram plots the thermodynamically stable phases of an electrochemical system based on potential (EH) and pH values. It shows the boundaries between predominant chemical species in solution or as solids. Pourbaix diagrams are commonly given at room temperature and atmospheric pressure. They indicate regions of immunity, corrosion, and passivity for metals in various environments but do not account for kinetic effects.
GENERAL CHEMISTRY AS PART OF EDUCATIONSSAliceRivera13
The document discusses the kinetic molecular theory and intermolecular forces, explaining that solids and liquids behave differently due to the distances and interactions between their particles. It also examines properties of liquids like surface tension, viscosity, and capillary action that can be explained by intermolecular forces. Phase changes between solids, liquids, and gases occur at equilibrium points depending on temperature and pressure conditions according to a substance's phase diagram.
General Chemistry 2 - Chapter 1: The Kinetic Molecular Model and Intermolecul...marvinnbustamante1
The document discusses the properties of solids, liquids, and gases based on the kinetic molecular theory. It explains that in solids, particles are closely packed together in an ordered structure, while in liquids they are more spaced out but still in contact with each other. Liquids have stronger intermolecular forces than gases but weaker than solids. The document also discusses different types of intermolecular forces such as hydrogen bonding, dipole-dipole forces, and dispersion forces, and how these forces influence properties like boiling point, surface tension, and viscosity.
GENERAL CHEMISTRY 2.pptxaaaaaaaaaaaaaaaaaaaaAliceRivera13
The document discusses the kinetic molecular theory and intermolecular forces, explaining how they influence the properties of solids, liquids, and gases. It describes how solids have a defined structure while liquids do not, and how properties like surface tension, viscosity, vapor pressure, and boiling point can be explained by the intermolecular forces between particles. Phase changes between solid, liquid, and gas are determined by a balance of kinetic energy and these attractive intermolecular forces.
Liquid crystals are a state of matter that have properties between those of a conventional liquid and solid crystal. They may flow like a liquid but their molecules can be oriented in a crystal-like way. There are different types of liquid crystal phases which can be distinguished by their optical properties when viewed under a polarized microscope. Liquid crystals can be divided into thermotropic, lyotropic, and metallotropic phases, with thermotropic and lyotropic phases consisting of organic molecules and exhibiting phase transitions depending on temperature and concentration. Examples of liquid crystals can be found naturally and in technologies like electronic displays.
Liquid crystals have properties of both liquids and crystals. They can be classified as thermotropic, lyotropic, or metallotropic based on what triggers their liquid crystalline phase. Thermotropic liquid crystals form phases based on temperature, while lyotropic phases depend on concentration in a solvent. Metallotropic phases are influenced by both inorganic-organic composition and temperature. Common liquid crystal phases include nematic, smectic, and cholesteric. Liquid crystals have many technological and natural applications, with most displays using liquid crystals and biological structures like membranes being forms of liquid crystals.
examples of materials that have directional properties as a single cry.docxtodd401
examples of materials that have directional properties as a single crystal but are isotropic in their polycrystalline form.
Solution
Liquid crystals (LCs) are matter in a state that has properties between those of conventional liquid and those of solid crystal. [1] For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of liquid-crystal phases, which can be distinguished by their different optical properties (such as birefringence). When viewed under a microscope using a polarized light source, different liquid crystal phases will appear to have distincttextures. The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in a liquid-crystal phase (just as water may turn into ice or steam).
Liquid crystals can be divided into thermotropic, lyotropic and metallotropic phases. Thermotropic and lyotropic liquid crystals consist of organic molecules. Thermotropic LCs exhibit a phase transition into the liquid-crystal phase as temperature is changed. Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of the liquid-crystal molecules in a solvent (typically water). Metallotropic LCs are composed of both organic and inorganic molecules; their liquid-crystal transition depends not only on temperature and concentration, but also on the inorganic-organic composition ratio.
Examples of liquid crystals can be found both in the natural world and in technological applications. Most contemporary electronic displays use liquid crystals. Lyotropic liquid-crystalline phases are abundant in living systems. For example, many proteins and cell membranes are liquid crystals. Other well-known examples of liquid crystals are solutions ofsoap and various related detergents, as well as the tobacco mosaic virus.
.
Liquid Crystals And Their ApplicationsMinhas Azeem
This document discusses liquid crystals, their phases and applications. It provides a history of liquid crystals, describing their discovery and classification into different phases like nematic, smectic and cholesteric based on molecular orientation. Common applications discussed include LCD displays, thermometers, imaging and protective gear. LCDs work by changing the polarization of light using liquid crystals between polarized filters. Future applications may include smart windows and 3D displays. In summary, the document covers the key topics of liquid crystal phases, LCD construction and various applications of liquid crystals.
The document discusses the kinetic molecular theory and intermolecular forces, explaining that solids and liquids behave differently due to the distances and interactions between their particles. It explores properties related to the phases of matter and phase changes, examining how increasing or decreasing energy can cause transformations between solid, liquid, and gas states depending on temperature and pressure conditions. Phase diagrams are introduced as a graphical representation of these relationships between physical states under varying temperature and pressure.
State of matter and properties of matter (Part-6)(Relative humidity, Liquid ...Ms. Pooja Bhandare
RELATIVE HUMIDITY, Humidity, Wet and Dry Hygrometer, LIQUID COMPLEX, LIQUID CRYSTALS, Types of liquid crystals, GLASSY STATES, Characteristics glassy state, Types of glassy state, What is the Glass Transition Temperature?
The document discusses liquid crystals and liquid crystal polymers. It notes that liquid crystals have properties between solids and liquids, with some positional and orientational order. They can exist in nematic, smectic, and cholesteric phases. Liquid crystal phases are important in biological systems like cell membranes and the brain. Liquid crystal polymers are highly resistant to heat and chemicals. They have applications in displays, body armor like Kevlar, and as heat sensors.
The document discusses liquid crystals and their properties. It begins by describing how cholesteryl benzoate undergoes two melting transitions, indicating an intermediate mesophase state. Liquid crystals are defined as materials that exhibit anisotropic properties between the solid and liquid states, without a 3D crystal lattice. They have orientational but not full positional order. Different types of liquid crystal phases are described, including nematic, smectic, columnar, and cubic. Common liquid crystal materials like calamitic and discotic molecules are also outlined. The document concludes by discussing some applications of liquid crystals like LCD displays.
Liquid crystals (LCs) are a state of matter that .pdfanokhijew
Liquid crystals (LCs) are a state of matter that have properties between those of a
conventional liquid and those of a solid crystal.[1] For instance, an LC may flow like a liquid,
but its molecules may be oriented in a crystal-like way. There are many different types of LC
phases, which can be distinguished by their different optical properties (such as birefringence).
When viewed under a microscope using a polarized light source, different liquid crystal phases
will appear to have distinct textures. The contrasting areas in the textures correspond to domains
where the LC molecules are oriented in different directions. Within a domain, however, the
molecules are well ordered. LC materials may not always be in an LC phase (just as water may
turn into ice or steam). Liquid crystals can be divided into thermotropic, lyotropic and
metallotropic phases. Thermotropic and lyotropic LCs consist of organic molecules.
Thermotropic LCs exhibit a phase transition into the LC phase as temperature is changed.
Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of
the LC molecules in a solvent (typically water). Metallotropic LCs are composed of both organic
and inorganic molecules; their LC transition depends not only on temperature and concentration,
but also on the inorganic-organic composition ratio.
Solution
Liquid crystals (LCs) are a state of matter that have properties between those of a
conventional liquid and those of a solid crystal.[1] For instance, an LC may flow like a liquid,
but its molecules may be oriented in a crystal-like way. There are many different types of LC
phases, which can be distinguished by their different optical properties (such as birefringence).
When viewed under a microscope using a polarized light source, different liquid crystal phases
will appear to have distinct textures. The contrasting areas in the textures correspond to domains
where the LC molecules are oriented in different directions. Within a domain, however, the
molecules are well ordered. LC materials may not always be in an LC phase (just as water may
turn into ice or steam). Liquid crystals can be divided into thermotropic, lyotropic and
metallotropic phases. Thermotropic and lyotropic LCs consist of organic molecules.
Thermotropic LCs exhibit a phase transition into the LC phase as temperature is changed.
Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of
the LC molecules in a solvent (typically water). Metallotropic LCs are composed of both organic
and inorganic molecules; their LC transition depends not only on temperature and concentration,
but also on the inorganic-organic composition ratio..
Liquid crystals are a state of matter between solid and liquid that form from organic compounds. They were discovered in 1888 by Austrian chemist Frederich Reinitzer. Liquid crystals exhibit ordered phases above melting points and have properties between solids and liquids. There are different types of liquid crystal phases including nematic, smectic, and blue phases that have distinct textures and properties. Liquid crystals find uses in devices like flat screen displays, watches, and thermometers.
The document discusses the properties of solids and liquids based on the kinetic molecular theory. It explains that solids have a defined structure with particles held closely together by strong intermolecular forces, while liquids lack a defined structure but their properties can be qualitatively understood by considering the intermolecular forces between their particles. The document then discusses several properties of liquids including surface tension, viscosity, vapor pressure, boiling point, and heat of vaporization, relating them to the intermolecular forces between the liquid particles.
States of matter can exist in different phases. The three most common states are solid, liquid, and gas. Solids maintain a fixed shape and volume, liquids maintain a volume but take the shape of their container, and gases expand freely to fill their container. Other states include plasma, which is an ionized gas, and Bose-Einstein condensates that form at very low temperatures. The state of matter depends on factors like temperature, pressure, and molecular interactions.
1.Distinguish the three states of matter in terms of movement of the particles
2.Relate the three states of matter with energy of movement of particles in them
3. Describe the changes of state using kinetic theory
Boiling, Vaporization, Melting, Fusion, Evaporation,
Condensation, Sublimation, Deposition,Freezing
The Kinetic Molecular Model and Intermolecular Forces of Attraction in Matter is one of the important topic in Grade 12, General Chemistry 2 subject. In here, it includes topics that discusses theory of solids and liquids, the different intermolecular and intramolecular forces such as covalent and ionic bonds, dipole- dipole, hydrogen bonds, london dispersion,
This document discusses complex fluids, which exhibit both liquid-like and solid-like properties. Complex fluids include polymeric solutions, gels, foams, and granular materials. They have heterogeneous structures with fluctuations across different length and time scales. When molecules in a polymeric solution or melt become sufficiently crosslinked, a gel transition occurs where a macroscopic cluster forms, localizing the molecules. The dynamics of particles in complex fluids are highly nonlinear and irregular, alternating between solid-like arrested states and fluid-like behavior depending on factors like density, temperature, and external forces inducing flow. While complex fluids are common in nature, their material properties are not fully understood and more research is still needed.
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Water can exist in three phases: gas, liquid, and solid. It has unique properties in each phase. As a liquid, water is able to dissolve nutrients and transport chemicals, making it perfect for life. If ice were denser than water, it would sink to the bottom of oceans when frozen and could freeze the entire planet, preventing the evolution of life. Water's ability to remain liquid over a wide range of temperatures and decrease in density when frozen allows life to thrive by keeping oceans from completely freezing.
Similar to B.Sc. I Year Physical Chemistry_Unit II_b_Lequid State (20)
Computers are now used almost everywhere from banks to homes. A computer is an electronic device that processes raw input data into useful output information. It consists of various components including hardware, software, and input/output devices. Hardware refers to the physical and tangible parts of a computer like processors, monitors, keyboards. Software includes computer programs and operating systems. Computers use binary numbers and arithmetic for processing. Programming allows users to provide computers with instructions to perform tasks.
Catalysis is the process by which a catalyst increases or decreases the rate of a chemical reaction without itself being consumed in the process. A catalyst remains chemically unchanged at the end of the reaction. Berzelius first coined the term "catalysis" in 1836 to describe substances that increase reaction rates by loosening the bonds between reacting molecules. Catalysts can either increase (positive catalysis) or decrease (negative catalysis) reaction rates. Characteristics of catalytic reactions include that the catalyst remains unchanged after the reaction, small amounts of catalyst are effective, finely divided catalysts work best, catalysts act specifically on certain reactions but cannot initiate new ones, and changing temperature can alter reaction rates both with and without a catalyst present
1. The document discusses theories of chemical kinetics including collision theory and the effect of temperature on reaction rates.
2. It introduces the Arrhenius equation and the concept of activation energy, which is the minimum energy required for a reaction to occur.
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1) The growth cycle phases - lag (adaptation), log (exponential growth), and plateau (confluence with reduced growth).
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B.Sc. I Year Physical Chemistry_Unit II_b_Lequid State
1. TEJASVI NAVADHITAMASTU
“Let our (the teacher and the taught) learning be radiant”
Let our efforts at learning be luminous and filled with joy, and endowed with the force of purpose
Paper III: PHYSICAL CHEMISTRY
Dr. Prabhakar Singh. D.Phil. Biochemistry
Department of Biochemistry, VBSPU, Jaunpur
Unit-II: B. Liquid State Inter molecular forces, structure of liquids (a qualitative description).
Structural differences between solids, liquids and gases; Liquid crystals Differences between liquid
crystals, solid and liquid, Classification, structure of nematic and cholestric phases, Thermbgraphy
and seven segment cells
2. Molecules in a gas are in constant random motion
and the spaces between them are large and the
intermolecular attractions negligible.
However, in a liquid the molecules are in contact
with each other. The forces of attraction between
the molecules are strong enough to hold them
together. All the same, the molecules are able to
move past one another through available
intermolecular spaces.
The molecules in a liquid move in a random fashion. At any instant the molecules may
form clusters, leaving vacant space or ‘hole’ here and there.
Most of the physical properties of liquids are actually controlled by the strengths of
intermolecular attractive forces.
LIQUID STATE
9. STRUCTURE OF LIQUIDS
Liquid is one of the four primary states of matter, with the others being solid, gas and plasma. A
liquid is a fluid. Unlike a solid, the molecules in a liquid have a much greater freedom to move.
The forces that bind the molecules together in a solid are only temporary in a liquid, allowing a
liquid to flow while a solid remains rigid.
A liquid, like a gas, displays the properties of a fluid. A liquid can flow, assume the shape of a
container, and, if placed in a sealed container, will distribute applied pressure evenly to every
surface in the container. If liquid is placed in a bag, it can be squeezed into any shape. Unlike a
gas, a liquid is nearly incompressible, meaning that it occupies nearly a constant volume over a
wide range of pressures; it does not generally expand to fill available space in a container but
forms its own surface, and it may not always mix readily with another liquid. These properties
make a liquid suitable for applications such as hydraulics.
Liquid particles are bound firmly but not rigidly. They are able to move around one another
freely, resulting in a limited degree of particle mobility. As the temperature increases, the
increased vibrations of the molecules causes distances between the molecules to increase.
When a liquid reaches its boiling point, the cohesive forces that bind the molecules closely
together break, and the liquid changes to its gaseous state (unless superheating occurs). If the
temperature is decreased, the distances between the molecules become smaller. When the
liquid reaches its freezing point the molecules will usually lock into a very specific order, called
crystallizing, and the bonds between them become more rigid, changing the liquid into its solid
state (unless supercooling occurs).
10.
11.
12.
13.
14. LIQUID CRYSTAL
Liquid crystals (LCs) are a state of matter which has properties between those of conventional liquids
and those of solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules may
be oriented in a crystal-like way. There are many different types of liquid-crystal phases, which can be
distinguished by their different optical properties. The contrasting areas in the textures correspond
to domains where the liquid-crystal molecules are oriented in different directions. Within a domain,
however, the molecules are well ordered. LC materials may not always be in a liquid-crystal state of
matter (just as water may turn into ice or water vapor).
Liquid crystals can be divided into thermotropic, lyotropic and metallotropic phases. Thermotropic
and lyotropic liquid crystals consist mostly of organic molecules, although a few minerals are also
known. Thermotropic LCs exhibit a phase transition into the liquid-crystal phase as temperature is
changed.
Lyotropic LCs exhibit phase transitions as a function of both temperature and concentration of the
liquid-crystal molecules in a solvent (typically water). Metallotropic LCs are composed of both organic
and inorganic molecules; their liquid-crystal transition depends not only on temperature and
concentration, but also on the inorganic-organic composition ratio.
Examples of liquid crystals can be found both in the natural world and in technological applications.
Widespread Liquid-crystal displays use liquid crystals. Lyotropic liquid-crystalline phases are abundant
in living systems but can also be found in the mineral world. For example, many proteins and cell
membranes are liquid crystals. Other well-known examples of liquid crystals are solutions of soap
and various related detergents, as well as the tobacco mosaic virus, and some clays.
15.
16.
17.
18.
19.
20.
21. LYOTROPIC LIQUID CRYSTALS
A lyotropic liquid crystal consists
of two or more components that
exhibit liquid-crystalline properties
in certain concentration ranges. In
the lyotropic phases, solvent
molecules fill the space around
the compounds to provide fluidity
to the system. In contrast to
thermotropic liquid crystals, these
lyotropics have another degree of
freedom of concentration that
enables them to induce a variety
of different phases.
A compound that has two immiscible hydrophilic and hydrophobic parts within the same
molecule is called an amphiphilic molecule. Many amphiphilic molecules show lyotropic
liquid-crystalline phase sequences depending on the volume balances between the
hydrophilic part and hydrophobic part. These structures are formed through the micro-phase
segregation of two incompatible components on a nanometer scale. Soap is an everyday
example of a lyotropic liquid crystal.
Structure of lyotropic liquid crystal. The red heads of
surfactant molecules are in contact with water,
whereas the tails are immersed in oil (blue): bilayer
(left) and micelle (right).
22. The content of water or other solvent molecules changes the self-assembled
structures. At very low amphiphile concentration, the molecules will be dispersed
randomly without any ordering. At slightly higher (but still low) concentration,
amphiphilic molecules will spontaneously assemble into micelles or vesicles. This is
done so as to 'hide' the hydrophobic tail of the amphiphile inside the micelle core,
exposing a hydrophilic (water-soluble) surface to aqueous solution.
These spherical objects do not order themselves in solution, however. At higher
concentration, the assemblies will become ordered. A typical phase is a hexagonal
columnar phase, where the amphiphiles form long cylinders (again with a hydrophilic
surface) that arrange themselves into a roughly hexagonal lattice. This is called the
middle soap phase. At still higher concentration, a lamellar phase (neat soap phase)
may form, wherein extended sheets of amphiphiles are separated by thin layers of
water. For some systems, a cubic (also called viscous isotropic) phase may exist
between the hexagonal and lamellar phases, wherein spheres are formed that create a
dense cubic lattice. These spheres may also be connected to one another, forming a
bicontinuous cubic phase.
The objects created by amphiphiles are usually spherical (as in the case of micelles),
but may also be disc-like (bicelles), rod-like, or biaxial (all three micelle axes are
distinct). These anisotropic self-assembled nano-structures can then order themselves
in much the same way as thermotropic liquid crystals do, forming large-scale versions
of all the thermotropic phases (such as a nematic phase of rod-shaped micelles).
23. THERMOTROPIC LIQUID CRYSTALS
Thermotropic phases are those that occur in a certain
temperature range. If the temperature rise is too high, thermal
motion will destroy the delicate cooperative ordering of the LC
phase, pushing the material into a conventional isotropic liquid
phase. At too low temperature, most LC materials will form a
conventional crystal.
Many thermotropic LCs exhibit a variety of phases as
temperature is changed. For instance, on heating a particular
type of LC molecule (called mesogen) may exhibit various
smectic phases followed by the nematic phase and finally the
isotropic phase as temperature is increased. An example of a
compound displaying thermotropic LC behavior is para-
azoxyanisole.
24.
25. NEMATIC PHASE
Most nematics are uniaxial: they have one axis (called directrix) that is longer and preferred, with the
other two being equivalent (can be approximated as cylinders or rods). However, some liquid crystals
are biaxial nematics, meaning that in addition to orienting their long axis, they also orient along a
secondary axis.
Nematics have fluidity similar to that of ordinary (isotropic) liquids but they can be easily aligned by an
external magnetic or electric field. Aligned nematics have the optical properties of uniaxial crystals and
this makes them extremely useful in liquid-crystal displays (LCD).
Scientists have discovered that electrons can unite to flow together in high magnetic fields, to create an
"electronic nematic" form of matter.
One of the most common LC phases is the nematic. The
word nematic comes from the Greek νήμα (Greek: nema),
which means "thread". This term originates from the
thread-like topological defects observed in nematics, which
are formally called 'disclinations'. Nematics also exhibit so-
called "hedgehog" topological defects. In a nematic phase,
the calamitic or rod-shaped organic molecules have no
positional order, but they self-align to have long-range
directional order with their long axes roughly parallel. Thus,
the molecules are free to flow and their center of mass
positions are randomly distributed as in a liquid, but still
maintain their long-range directional order.
Alignment in a nematic phase.
26.
27.
28. SMECTIC PHASES
Schematic of alignment in the
smectic phases. The smectic A
phase (left) has molecules
organized into layers. In the
smectic C phase (right), the
molecules are tilted inside the
layers.
The smectic phases, which are found at lower
temperatures than the nematic, form well-
defined layers that can slide over one another in a
manner similar to that of soap. The word
"smectic" originates from the Latin word
"smecticus", meaning cleaning, or having soap-
like properties.
The smectics are thus positionally ordered along
one direction. In the Smectic A phase, the
molecules are oriented along the layer normal,
while in the Smectic C phase they are tilted away
from it. These phases are liquid-like within the
layers.
There are many different smectic phases, all
characterized by different types and degrees of
positional and orientational order. Beyond organic
molecules, Smectic ordering has also been
reported to occur within colloidal suspensions of
2-D materials or nanosheets.
29. CHIRAL PHASES OR TWISTED NEMATICS
Schematic of ordering in chiral
liquid crystal phases. The chiral
nematic phase (left), also called
the cholesteric phase, and the
smectic C* phase (right).
The chiral nematic phase exhibits chirality (handedness).
This phase is often called the cholesteric phase because
it was first observed for cholesterol derivatives. Only
chiral molecules can give rise to such a phase. This
phase exhibits a twisting of the molecules perpendicular
to the director, with the molecular axis parallel to the
director. The finite twist angle between adjacent
molecules is due to their asymmetric packing, which
results in longer-range chiral order. In the smectic C*
phase (an asterisk denotes a chiral phase), the
molecules have positional ordering in a layered structure
(as in the other smectic phases), with the molecules
tilted by a finite angle with respect to the layer normal.
The chirality induces a finite azimuthal twist from one
layer to the next, producing a spiral twisting of the
molecular axis along the layer normal.
30. The chiral pitch, p, refers to the distance over which the
LC molecules undergo a full 360° twist (but note that the
structure of the chiral nematic phase repeats itself every
half-pitch, since in this phase directors at 0° and ±180°
are equivalent). The pitch, p, typically changes when the
temperature is altered or when other molecules are
added to the LC host (an achiral LC host material will
form a chiral phase if doped with a chiral material),
allowing the pitch of a given material to be tuned
accordingly.
CHIRAL NEMATIC PHASE; P
REFERS TO THE CHIRAL PITCH
Discotic phases: Disk-shaped LC molecules can orient themselves in a layer-like
fashion known as the discotic nematic phase. If the disks pack into stacks, the phase is
called a discotic columnar. The columns themselves may be organized into rectangular or
hexagonal arrays. Chiral discotic phases, similar to the chiral nematic phase, are also
known.
Conic phases: Conic LC molecules, like in discotics, can form columnar phases.
Other phases, such as nonpolar nematic, polar nematic, stringbean, donut and onion
phases, have been predicted. Conic phases, except nonpolar nematic, are polar phases.
31.
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33.
34. DESIGN OF LIQUID CRYSTALLINE MATERIALS
A large number of chemical compounds are known to exhibit one or several liquid crystalline
phases. Despite significant differences in chemical composition, these molecules have some
common features in chemical and physical properties.
There are three types of thermotropic liquid crystals: discotic, conic (bowlic), and rod-shaped
molecules. Discotics are flat disc-like molecules consisting of a core of adjacent aromatic rings; the
core in a conic LC is not flat, but is shaped like a rice bowl (a three-dimensional object). This allows
for two dimensional columnar ordering, for both discotic and conic LCs. Rod-shaped molecules have
an elongated, anisotropic geometry which allows for preferential alignment along one spatial
direction.
1. The molecular shape should be relatively thin, flat or conic, especially within rigid molecular
frameworks.
2. The molecular length should be at least 1.3 nm, consistent with the presence of long alkyl group
on many room-temperature liquid crystals.
3. The structure should not be branched or angular, except for the conic LC.
4. A low melting point is preferable in order to avoid metastable, monotropic liquid crystalline
phases. Low-temperature mesomorphic behavior in general is technologically more useful, and
alkyl terminal groups promote this.
An extended, structurally rigid, highly anisotropic shape seems to be the main criterion for liquid
crystalline behavior, and as a result many liquid crystalline materials are based on benzene rings.
35. METALLOTROPIC LIQUID CRYSTALS
Liquid crystal phases can also be based on low-melting inorganic phases like ZnCl2 that have a
structure formed of linked tetrahedra and easily form glasses. The addition of long chain soap-like
molecules leads to a series of new phases that show a variety of liquid crystalline behavior both as a
function of the inorganic-organic composition ratio and of temperature. This class of materials has
been named metallotropic.
LABORATORY ANALYSIS OF MESOPHASES
Thermotropic mesophases are detected and characterized by two major methods-
Original method was use of thermal optical microscopy, in which a small sample of the material was
placed between two crossed polarizers; the sample was then heated and cooled. As the isotropic
phase would not significantly affect the polarization of the light, it would appear very dark, whereas
the crystal and liquid crystal phases will both polarize the light in a uniform way, leading to brightness
and color gradients. This method allows for the characterization of the particular phase, as the
different phases are defined by their particular order, which must be observed.
The second method, differential scanning calorimetry (DSC), allows for more precise determination of
phase transitions and transition enthalpies. In DSC, a small sample is heated in a way that generates a
very precise change in temperature with respect to time. During phase transitions, the heat flow
required to maintain this heating or cooling rate will change. These changes can be observed and
attributed to various phase transitions, such as key liquid crystal transitions.
Lyotropic mesophases are analyzed in a similar fashion, though these experiments are somewhat
more complex, as the concentration of mesogen is a key factor. These experiments are run at various
concentrations of mesogen in order to analyze that impact.
36. BIOLOGICAL LIQUID CRYSTALS
Lyotropic liquid-crystalline phases are abundant in living systems, the study of which is
referred to as lipid polymorphism. Accordingly, lyotropic liquid crystals attract particular
attention in the field of biomimetic chemistry. In particular, biological membranes and cell
membranes are a form of liquid crystal. Their constituent molecules (e.g. phospholipids) are
perpendicular to the membrane surface, yet the membrane is flexible. These lipids vary in
shape . The constituent molecules can inter-mingle easily, but tend not to leave the
membrane due to the high energy requirement of this process. Lipid molecules can flip from
one side of the membrane to the other, this process being catalyzed by flippases and
floppases (depending on the direction of movement). These liquid crystal membrane phases
can also host important proteins such as receptors freely "floating" inside, or partly outside,
the membrane, e.g. CCT.
Many other biological structures exhibit liquid-crystal behavior. For instance, the
concentrated protein solution that is extruded by a spider to generate silk is, in fact, a liquid
crystal phase. The precise ordering of molecules in silk is critical to its renowned strength.
DNA and many polypeptides, including actively-driven cytoskeletal filaments, can also form
liquid crystal phases. Monolayers of elongated cells have also been described to exhibit
liquid-crystal behavior, and the associated topological defects have been associated with
biological consequences, including cell death and extrusion. Together, these biological
applications of liquid crystals form an important part of current academic research.
37.
38. CHOLESTERIC LIQUID CRYSTALS
He found that cholesteryl benzoate does not melt in the same manner as other compounds, but has
two melting points. At 145.5 °C (293.9 °F) it melts into a cloudy liquid, and at 178.5 °C (353.3 °F) it
melts again and the cloudy liquid becomes clear. The phenomenon is reversible. Seeking help from a
physicist, on March 14, 1888, he wrote to Otto Lehmann, at that time a Privatdozent in Aachen. They
exchanged letters and samples. Lehmann examined the intermediate cloudy fluid, and reported seeing
crystallites. Reinitzer's Viennese colleague von Zepharovich also indicated that the intermediate "fluid"
was crystalline. The exchange of letters with Lehmann ended on April 24, with many questions
unanswered. Reinitzer presented his results, with credits to Lehmann and von Zepharovich, at a
meeting of the Vienna Chemical Society on May 3, 1888.
In 1888, Austrian botanical physiologist
Friedrich Reinitzer, working at the Karl-
Ferdinands-Universität, examined the
physico-chemical properties of various
derivatives of cholesterol which now belong
to the class of materials known as cholesteric
liquid crystals. Previously, other researchers
had observed distinct color effects when
cooling cholesterol derivatives just above the
freezing point, but had not associated it with
a new phenomenon. Reinitzer perceived that
color changes in a derivative cholesteryl
benzoate were not the most peculiar feature.
Chemical structure of cholesteryl
benzoate molecule
39. MINERAL LIQUID CRYSTALS
Examples of liquid crystals can also be found in the mineral world, most
of them being lyotropics. The first discovered was Vanadium(V) oxide,
by Zocher in 1925. Since then, few others have been discovered and
studied in detail.
The existence of a true nematic phase in the case of the smectite clays
family was raised by Langmuir in 1938, but remained open for a very
long time and was only solved recently.
With the rapid development of nanosciences, and the synthesis of
many new anisotropic nanoparticles, the number of such mineral liquid
crystals is quickly increasing, with, for example, carbon nanotubes and
graphene. A lamellar phase was even discovered, H3Sb3P2O14, which
exhibits hyperswelling up to ~250 nm for the interlamellar distance.
40. LED SEVEN SEGMENT DISPLAY
The arrangement of a LED Seven Segment Display is shown in Fig. (a). The actual
LED devices are very small, so, to enlarge the lighted surface, solid plastic light
pipes are often employed, as shown. Any desired numeral from 0 to 9 can be
indicated by passing current through the appropriate segments, [Fig (b)]. Part (c) in
Fig. shows three LED Seven Segment Display together with a two-segment display
referred to as a half digit. The whole display, termed a three-and-a-half digit display,
can be used to indicate numerical values up to a maximum of 1999.
41. LIQUID CRYSTAL CELLS:
Liquid crystal material is a
liquid that exhibits some of
the properties of a solid.
The molecules in ordinary
liquids normally have
random orientations. In
liquid crystals the molecules
are oriented in a definite
crystal pattern.
A liquid crystal cell consists of a very thin layer of liquid crystal material sandwiched
between glass sheets, as illustrated. The glass sheets have transparent metal film
electrodes deposited on the inside surfaces. In the commonly used twisted nematic cell
two thin polarizing optical filters are placed at the surface of each glass sheet. The liquid-
crystal material employed twists the light passing through when the cell is not energized.
This twisting allows the light to pass through the polarizing filters, so that the cell is semi-
transparent. When energized, the liquid molecules are reoriented so that no twisting
occurs, and no light can pass through. Thus, the energized cell can appear dark against a
bright background. The cells can also be manufactured to appear bright against a dark
background.
42. Seven-segment numerical (and other type) displays made from liquid crystal cells are
referred to as liquid crystal displays (LCDs). Two types of LCDs are illustrated in Fig. 20-8.
The reflective-type shown in Fig. 20 (a) relies on reflected light. The cell is placed on a
reflective surface, so that when not energized it is just as reflective as the surrounding
material, consequently, it disappears. When energized, no light is reflected from the cell,
and it appears dark against the bright background. The transmittive cell in Fig. 20 (b)
allows light to pass through from the back of the cell when not energized. When
energized, the light is blocked, and here again the cell appears dark against a bright
background. The trans-reflective cell is a combination of transmittive and reflective
types.
43. LCD SEVEN-SEGMENT DISPLAY:
Because liquid-crystal cells are light reflectors or transmitters rather than light generators, they
consume very small quantities of energy. The only energy required by the cell is that needed to
activate the liquid crystal. The total current flow through four small LED Seven Segment Display is
typically about 20 μA. However, LCDs require an ac voltage supply, either in the form of a sine
wave or a square wave. This is because a continuous direct current flow produces a plating of the
cell electrodes that could damage the device. Repeatedly reversing the current avoids this
problem.
A typical LCD supply is a 3 V to 8 V peak-to-peak square wave with a frequency of 60 Hz. Figure 20-
9 illustrates the square wave drive method. The back plane, which is common to all of the cells, is
supplied with a square wave, (with peak voltage VP). Similar square wave applied to each of the
other terminals are either in phase or in antiphase with the back plane square wave. Those cells
with waveforms in phase with the back plane waveform (cells e and f in Figure 20-9) have no
voltage developed across them. Both terminals of the segment are at the same potential, so they
are not energized. The cells with square waves in antiphase with the back plane input have a
square wave with peak voltage 2VP developed across them, consequently, they are energized.
Unlike LED displays, which are usually quite small, LCDs can be fabricated in almost any convenient
size. The major advantage of LCDs is their low power consumption. Perhaps the major
disadvantage of the LCD is its decay time of 150 ms (or more). This is very slow compared to the
rise and fall times of LEDs. In fact, the human eye can sometimes observe the fading out of LCD
segments switching off