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.
Intermediate state of mesophases & halfway between isotropic liquid &solid crystal.
In solid crystal, basic unit display translational long range order, with center of molecule located on crystal lattice &display orientational order.
In isotropic liquid, basic unit do not preset positional or orientational long rang order.
Intermediate state of mesophases & halfway between isotropic liquid &solid crystal.
In solid crystal, basic unit display translational long range order, with center of molecule located on crystal lattice &display orientational order.
In isotropic liquid, basic unit do not preset positional or orientational long rang order.
Silicone polymers structure, prepartion, properties, uses
INORGANIC POLYMERS
Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybridpolymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber.
Of synthetic polymers whose backbone is made of repeating silicone to oxygen bonds (siloxane bonds) with organic side groups, such as methyl, phenyl or vinyl.The basic repeating unit became known as siloxane and the most common available silicone is polydimethylsiloxane
Organo-silicone polymers contain chains or network of alternating silicone and oxygen atoms in their structures ,that is exhibited in some natural silicone minerals
Polymeric molecules in silicones held together by weak van der waals force results, they are liquids of varying viscosity or gums or solids containing polymeric molecules which generally soluble in organic mediaHydrolysis of dichloro dimethyl silane (CH3)2SiCl2 gives long chain polymers.As there is active OH group at each end .The length of the chain increasing.so it is called chain building unit
properties
1.The si-o-si bond in silanes is shorter than the expected si-o-si bond as calculated from the their radii.This indicates that there is some ionic character in si-o bond due to which it becomes quite stable.
2.This the the reason for why polysiloxanes are thermally stable and do not decompose even upto 350-400`C.
1. Highly polar character of si-o bond and the ability of si to expand its valency shell by utilizing its d-orbitals renders polysiloxanes susceptible to attack by several reagents.
2.The siloxanes may undergo hydrolysis and alcoholysis at elevated temperature in the presence of strong acids and bases
to give silanols and alkaxysilanes .In general, the greater the extent of substitution on Si atom, the greater is the case of hydrolysis in the presence of acids and greater is the difficulty of hydrolysis in the presence of bases.
thankingyou
ESWARAN .M -inboxeswaran@gmail.com
Silicone polymers structure, prepartion, properties, uses
INORGANIC POLYMERS
Polymers containing inorganic and organic components are sometimes called hybrid polymers, and most so-called inorganic polymers are hybridpolymers. One of the best known examples is polydimethylsiloxane, otherwise known commonly as silicone rubber.
Of synthetic polymers whose backbone is made of repeating silicone to oxygen bonds (siloxane bonds) with organic side groups, such as methyl, phenyl or vinyl.The basic repeating unit became known as siloxane and the most common available silicone is polydimethylsiloxane
Organo-silicone polymers contain chains or network of alternating silicone and oxygen atoms in their structures ,that is exhibited in some natural silicone minerals
Polymeric molecules in silicones held together by weak van der waals force results, they are liquids of varying viscosity or gums or solids containing polymeric molecules which generally soluble in organic mediaHydrolysis of dichloro dimethyl silane (CH3)2SiCl2 gives long chain polymers.As there is active OH group at each end .The length of the chain increasing.so it is called chain building unit
properties
1.The si-o-si bond in silanes is shorter than the expected si-o-si bond as calculated from the their radii.This indicates that there is some ionic character in si-o bond due to which it becomes quite stable.
2.This the the reason for why polysiloxanes are thermally stable and do not decompose even upto 350-400`C.
1. Highly polar character of si-o bond and the ability of si to expand its valency shell by utilizing its d-orbitals renders polysiloxanes susceptible to attack by several reagents.
2.The siloxanes may undergo hydrolysis and alcoholysis at elevated temperature in the presence of strong acids and bases
to give silanols and alkaxysilanes .In general, the greater the extent of substitution on Si atom, the greater is the case of hydrolysis in the presence of acids and greater is the difficulty of hydrolysis in the presence of bases.
thankingyou
ESWARAN .M -inboxeswaran@gmail.com
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.
.
Web- Liquid Crytals and Liquid Crystal Polymers-2015malcolmmackley
This presentation gives an overview of the microstructure for liquid crystals (LC) and liquid crystal polymers (LCP). Both LC and LCPs contain disclination singularities which normally control local ordering within the material. The microstructure can be explored using birefringent optical microscopy.
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..
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?
Solid state of matter has a definite volume and definite shapes.
Molecules of solids have lowest kinetic energies but they possess vibrational energies. Solids can be classifies as crystalline and amorphous solids.
This slide describes about Hydrogen Evolution Reaction and effect of Cu substitution in enhancing the activity. Deconvolution of strain and ligand effect is explained in the slide and in the respective paper.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
The increased availability of biomedical data, particularly in the public domain, offers the opportunity to better understand human health and to develop effective therapeutics for a wide range of unmet medical needs. However, data scientists remain stymied by the fact that data remain hard to find and to productively reuse because data and their metadata i) are wholly inaccessible, ii) are in non-standard or incompatible representations, iii) do not conform to community standards, and iv) have unclear or highly restricted terms and conditions that preclude legitimate reuse. These limitations require a rethink on data can be made machine and AI-ready - the key motivation behind the FAIR Guiding Principles. Concurrently, while recent efforts have explored the use of deep learning to fuse disparate data into predictive models for a wide range of biomedical applications, these models often fail even when the correct answer is already known, and fail to explain individual predictions in terms that data scientists can appreciate. These limitations suggest that new methods to produce practical artificial intelligence are still needed.
In this talk, I will discuss our work in (1) building an integrative knowledge infrastructure to prepare FAIR and "AI-ready" data and services along with (2) neurosymbolic AI methods to improve the quality of predictions and to generate plausible explanations. Attention is given to standards, platforms, and methods to wrangle knowledge into simple, but effective semantic and latent representations, and to make these available into standards-compliant and discoverable interfaces that can be used in model building, validation, and explanation. Our work, and those of others in the field, creates a baseline for building trustworthy and easy to deploy AI models in biomedicine.
Bio
Dr. Michel Dumontier is the Distinguished Professor of Data Science at Maastricht University, founder and executive director of the Institute of Data Science, and co-founder of the FAIR (Findable, Accessible, Interoperable and Reusable) data principles. His research explores socio-technological approaches for responsible discovery science, which includes collaborative multi-modal knowledge graphs, privacy-preserving distributed data mining, and AI methods for drug discovery and personalized medicine. His work is supported through the Dutch National Research Agenda, the Netherlands Organisation for Scientific Research, Horizon Europe, the European Open Science Cloud, the US National Institutes of Health, and a Marie-Curie Innovative Training Network. He is the editor-in-chief for the journal Data Science and is internationally recognized for his contributions in bioinformatics, biomedical informatics, and semantic technologies including ontologies and linked data.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
2. Liquid Crystal and Life
Liquid crystals are also fundamentally
important to life. DNA and cell
membranes have liquid crystal phases.
Our brains are around 70% liquid
crystal, and liquid crystals are also
found in muscles, the amazing
iridescent colours of some insects, and
also slug slime!
Liquid crystals are beautiful and mysterious; I am fond of them for both reasons.
- P.G. De Gennes
3. Liquid crystals (LCs) are matter in a state that has properties between
those of conventional liquid and those of solid crystal.
For instance, an LC’s may flow like a liquid, but its molecules may be
oriented in a crystal like way.
There are many different type of LC phases, which can be distinguish
by their different “optical properties” (such as birefringence.
Which viewed under a microscope using a polarized light source,
different liquid crystal phases will appear to have distinct textures.
Introduction
4. Positional Order + Orientational Order = Crystal Phase
Positional Order + No Orientational Order = Plastic Phase
Varying Positional Order + Orientational Order = Liquid Crystal Phase
No Positional Order + No Orientational Order = Isotropic Phase
Liquid crystals are classified in terms of following criterion:
(1) Translational order/ Positional Order
(2) Bond orientational order
(3) Correlation between smectic layers
(4) With chirality?
(5) Cubic structure?
5. Liquid Crystal-Is it a Solid or Liquid..???
The amount of energy required to cause the phase transition is called latent
heat of the transition and is useful to measure of how different the two phases are.
In the case of cholesteryl myristate, the latent heat of solid to liquid crystal is 65
calories/gram,while the latent heat for liquid crystal to liquid transition is 7
calories/gram.
The smallness the latent heat of liquid crystal to liquid phase transition is evidence
that liquid crystal are more similar to liquids than they are to solids.
6. Mesophase: a phase lying between solid (crystal)
and isotropic (liquid) states.
Liquid crystals: fluid (l) but also show birefringence (c);
have properties associated with both crystals and liquids.
Thermotropic: liquid crystalline phase is formed
when the pure compound is heated.
Lyotropic: liquid crystalline phase forms
when the molecules are mixed with a solvent (solution).
Liquid Crystalline Phases
7. Liquid Crystals
Thermotropic Lyotropic
High molecular
(molar) mass
[ polymers]
Low molecular
(molar) mass
Main-chain
polymers
Side-chain
polymers
Rod-like or
lath-like
molecules
Calamitic
Disc-like
molecules
Discotic
Single or multicomponent
systems
Homo- or co-polymers
Figure 9.1 The liquid crystal family tree.
8. No translational order—Nematics
The word “Nematic" is derived from the
Greek word for thread-like structure.
It is the only liquid crystal phase with no
long range translational order.
It is the least ordered mesophase
Preferred Orientation is denoted by the
‘Director’ n.
This phase has a symmetrical axis C∞ along
the director
Point Group D∞h.
It has thread like structure when seen
under polarizing microsope.
9. One-dimensional translational order—Smectic
The word "Smectic" is derived from the Greek word for soap
Liquid-like motion of the rods in each layer
No correlation of the molecular positions from one layer to
the next
The layers can easily slide
In the smectic A phase, molecules tend to be perpendicular to
the smectic layers
In the smectic C phase, the molecules in the layers are parallel
and tilted in arrangement with respect to the normal of the
layers by a tilt angle θ.
10. Chiral Liquid Crystal- Cholesteric
Also known as “Chiral nematic”
Molecules have non-symmetrical carbon
atoms and thus lose mirror symmetry
Shows a helical structure.
In general the helical pitch of cholesteric
liquid crystals is of the order of visible light’s
wavelength—about a few hundreds nm and
so shows different color.
11. Lyotropic Liquid Crystal
Lyotropic LCs are two-component systems where an amphiphile is dissolved in a
solvent.
Lyotropic mesophases are concentration and solvent dependent.
13. Thermotropic Liquid Crystal
The essential requirement for a molecule to be a thermotropic LC is a structure
consisting of a central rigid core (often aromatic) and a flexible peripheral moiety
(generally aliphatic groups). This structural requirement leads to two general
classes of LCs:
1. Calamitic LCs: Calamitic or rod-like LCs are
those mesomorphic compounds that possess an
elongated shape.
Divided into 2 groups:
Nematic and Smectic
2. Discotic LCs:
14. Order Parameter
To quantify just how much order is present in a
material, an order parameter (S) is defined.
Theta is the angle between the director and the long
axis of each molecule
The brackets denote an average over all of the
molecules in the sample.
In an isotropic liquid, the average of the cosine terms
is zero, and therefore the order parameter is equal to
zero.
For a perfect crystal, the order parameter evaluates
to one
Typical values for the order parameter of a liquid
crystal range between 0.3 and 0.9, with the exact
value a function of temperature, as a result of kinetic
molecular motion.
S=(1/2)<3Cos2q -1>
Nematic LC
15. External influences on Liquid Crystals
External perturbation can cause significant changes in the macroscopic properties of
the liquid crystal system. The order of liquid crystals can be manipulated by
mechanical, electric or magnetic forces.
Electric and Magnetic field effect:
Due to the effect of electric field permanent electric
dipole results which aligns the director along the
electric field.
The effect of magnetic field is analogous to the electric
field.
Surface Preparations: It is possible, however, to force the director to point in a
specific direction by introducing an outside agent to the system.
For example, when a thin polymer coating (usually a polyimide) is rubbed in
a single direction,on a glass substrate, with a cloth, it is observed that liquid crystal
molecules in contact with that surface align with the rubbing direction.
16. Birefringence in Liquid Crystals
When light enters a birefringent material, such as a nematic liquid crystal
sample, the process is modeled in terms of the light being broken up into the
fast (called the ordinary ray) and slow (called the extraordinary ray)
components. Because the two components travel at different velocities, the
waves get out of phase. When the rays are recombined as they exit the
birefringent material, the polarization state has changed because of this phase
difference
17. Liquid Crystal Textures
The term texture refers to the orientation of liquid crystal molecules in the vicinity
of a surface. Each liquid crystal mesophase can form its own characteristic
textures,which are useful in identification. We consider the nematic textures here.
If mesogenic materials are confined between closely spaced plates with rubbed
surfaces (as described above) and oriented with rubbing directions parallel, the
entire liquid crystal sample can be oriented in a planar texture, as shown in the
following diagram
18. Defects Under the Microscope:
• The abrupt changes in brightness seen in the pictures signal a rapid change in
director orientation in the vicinity of a line or point singularity known as a
disclination. A disclination is a region where the director is undefined. The
following is a diagram that shows the orientation of the director around a
disclination.
Defects in Liquid Crystal
20. Experimental Identification of Liquid
Crystals
Differential Scanning Calorimetry (DSC): It
provides valuable information like the exact
transition temperatures and the enthalpies of
the different phases
Polarizing Microscope: When a liquid crystal
material is placed on a microscope slide with a
cover slip and the slide is heated and viewed
using a polarizing microscope, textures
characteristic of each type of liquid crystal can
be seen.
21. Experimental Identification of Liquid
Crystals
X-ray Crystallography: This can be used to study the extent of
translational or positional order, and thus infer the type of liquid crystal
phase
Extended X-ray absorption fine structure spectroscopy
(EXAFS): EXAFS was used to investigate the local structure of the polar
spines of metal ion soaps in the columnar liquid crystalline state
22. Applications of liquid crystals
Display application of liquid
crystals: The most common
application of liquid crystal
technology is liquid crystal displays
(LCDs.)
Thermal mapping and non-
destructive testing
Medicinal Uses: Cholesteric liquid
crystal mixtures have also been
suggested for measuring body skin
temperature, to outlines tumours
etc.
Optical Imaging and Liquid Crystal
Interactions with Nanostructure
Liquid Crystal in
Chromatography
Liquid Crystal as Solvents in
Spectroscopy
23. Characteristics:
• These are a class of aromatic polymer.
• Extremely unreactive and inert.
• Highly resistant to fire.
Liquid crystallinity in polymers can be obtained :
By dissolving in a solvent. (Thermotropic)
By heating above melting transition point. (Lyotropic)
Liquid Crystal Polymer (LCP)
26. Advantage of LCP
High heat resistance
Flame retardant
Chemical resistance
Dimensional stability
Mold ability
Heat aging resistance
Adhesion
Low viscosity
Wieldable
Low cost
Disadvantage of LCP
Form weak weld lines
Highly anisotropic properties
Drying required before
processing
High Z-axis thermal expansion
coefficient
27. • Soap
• Conducting foams
• Heat Sensitive cameras use liquid crystal screens
that respond to heat.
Applications
28. • Kevlar, the most widely used body armor is made up of
intertwined liquid crystal polymers.
Applications
Editor's Notes
Liquid crystals are found to be birefringent, due to their anisotropic nature. That is, they demonstrate double refraction (having two indices of refraction). Light polarized parallel to the director has a different index of refraction (that is to say it travels at a different velocity) than light polarized perpendicular to the director. In the following diagram, the blue lines represent the director field and the arrows show the polarization vector.
Thus, when light enters a birefringent material, such as a nematic liquid crystal sample, the process is modeled in terms of the light being broken up into the fast (called the ordinary ray) and slow (called the extraordinary ray) components. Because the two components travel at different velocities, the waves get out of phase. When the rays are recombined as they exit the birefringent material, the polarization state has changed because of this phase difference.
The birefringence of a material is characterized by the difference, Dn, in the indices of refraction for the ordinary and extraordinary rays. To be a little more quantitative, since the index of refraction of a material is defined as the ratio of the speed of light in a vacuum to that in the material, we have for this case, ne = c/V| | and no = c/V^ for the velocities of a wave travelling perpendicular to the director and polarized parallel and perpendicular to the director, so that the maximum value for the birefringence, Dn = ne – no. We won’t deal here with the general case of a wave travelling in an arbitrary direction relative to the director in a liquid crystal sample, except to note that Dn varies from zero to the maximum value, depending on the direction of travel. The condition ne > no describes a positive uniaxial material, so that nematic liquid crystals are in this category. For typical nematic liquid crystals, no is approximately 1.5 and the maximum difference, Dn, may range between 0.05 and 0.5.
The length of the sample is another important parameter because the phase shift accumulates as long as the light propagates in the birefringent material. Any polarization state can be produced with the right combination of the birefringence and length parameters.
It is convenient here to introduce the concept of optical path in media since for the above two wave components travelling with different speeds in a birefringent material, the difference in optical paths will lead to a change in the polarization state of the wave as it progresses through the medium. We define the optical path for a wave travelling a distance L in a crystal as nL so that the optical path difference for the two wave components mentioned above will be L (ne – no) = LDn. The resultant phase difference between the two components (the amount by which the slow, extraordinary component lags behind the fast, ordinary one) is just 2p LDn/lv where lv is the wavelength in vacuum.
The following simulation demonstrates the optical properties of a birefringent material. A linearly polarized light wave enters a crystal whose extraordinary (slow) index of refraction can be controlled by the user. The length of the sample can also be varied, and the outgoing polarization state is shown. The concept of optical path difference and its influence on polarization state can also be explored here. This leads to a discussion of optical retardation plates or phase retarders, in the context of the simulation.