Colloids are crucial to both ordinary living and pharmacological formulations. the study of both big molecules
and intricately divided multiphase systems is known as colloidal science. the intersection of colloid and
surface science is the multi-phase system. a colloid is a mixture in which one material is suspended within
another substance and has insoluble particles scattered over a tiny scale. between genuine solutions and
suspensions, colloidal solutions or colloidal dispersions represent a middle ground. the dispersed phase of
colloids is distributed throughout the dispersion medium. in many facets of chemistry, colloidal chemistry
knowledge is necessary. this article provides information on what colloids are, their types, sizes, forms,
qualities, and uses.
Physical Pharmaceutics-IUnit-IIISurface and Interfacial tension (Part-1)(Li...Ms. Pooja Bhandare
This document discusses liquid interfaces and surface and interfacial tension. It defines a liquid interface as the boundary between phases in contact, with surface referring specifically to the boundary between a liquid and gas. Surface tension is the force per unit length acting at right angles to the liquid surface and arises from cohesive intermolecular forces being imbalanced at the surface. Molecules in the bulk liquid experience equal attractive forces from all sides, while surface molecules only experience inward attraction. This imbalance causes the surface to contract and results in surface tension. Interfacial tension similarly describes the imbalance of forces at the boundary between immiscible liquids. Some examples of liquid surface tensions are provided.
This document discusses pH, buffers, and isotonic solutions. It begins by defining pH as a measure of hydrogen ion concentration in water using Sorensen's pH scale. It then describes two methods for determining pH: the calorimetric method which compares a solution's color to standard buffers and indicators, and the electrometric method which uses a pH meter. The document also discusses buffers and their importance in biological and pharmaceutical systems like blood, tears, and injections to maintain optimal pH levels. Factors that can influence a buffer's pH like temperature, dilution, and ionic strength are also covered.
Solvation and association (Solubility of drug Part -3)Ms. Pooja Bhandare
The document discusses solvation and association as factors that influence drug solubility. It defines solvation as the interaction of a solute with solvent molecules that leads to stabilization. Solvation is quantified by its dissolution rate. Solubility depends on an equilibrium between dissolution and precipitation rates. Solvent-solute interactions like hydrogen bonding, ion-dipole interactions, and van der Waals forces affect solvation. Solvation energy is determined by a balance of enthalpy, entropy, and temperature factors. Association occurs via chemical reactions where oppositely charged ions or molecules come together to form distinct chemical entities in solution. The extent of association depends on the dielectric constant of the solvent.
This document discusses coarse dispersions and provides information on suspensions and emulsions. It defines coarse dispersions as heterogeneous dispersed systems where the dispersed phase particles are larger than 1000 nm. Suspensions are defined as heterogeneous biphasic liquid systems containing insoluble solid particles suspended in a liquid medium. Emulsions are defined as biphasic liquid dosage forms containing two immiscible liquids mixed with force and stabilized by surfactants. The document also discusses interfacial properties of suspended particles, formulation of suspensions and emulsions, and theories of emulsification.
The document summarizes key information about pharmaceutical suspensions. It defines suspensions as coarse dispersions of insoluble solids suspended in a liquid medium. Suspensions consist of two phases, with the internal solid phase dispersed throughout the external liquid phase using mechanical agitation and excipients. Suspensions are advantageous for stable delivery of drugs that are insoluble or unstable in solution. The document outlines factors that influence sedimentation of particles in suspensions and methods for achieving physical stability, including controlling particle size and flocculation.
This document provides an overview of suspensions, including their classification, properties, formulation, and stability. Key points include:
- Suspensions are heterogeneous systems with an insoluble dispersed phase distributed throughout a continuous phase. They can be classified based on their intended use, concentration of solids, particle size, and electrokinetic properties.
- Interfacial properties like surface tension affect particle flocculation and sedimentation. Surfactants can reduce surface tension to promote deflocculation.
- Particle size, concentration, and Brownian motion influence sedimentation rates. Flocculated particles settle faster but are easier to redisperse than deflocculated particles.
- Stable suspensions are formulated using vehicles to
Complexation and Protein Binding [Part-2](Method of analysis, Complexation a...Ms. Pooja Bhandare
This document discusses various methods for analyzing complexes, including continuous variation (Job's) method, distribution method, solubility method, pH titration method, and spectroscopy. The continuous variation method analyzes changes in physical properties like dielectric constant when complexes form to determine stoichiometric ratios. The distribution method examines how the distribution of a solute between immiscible liquids changes with complexation to estimate stability constants. The solubility method observes whether solubility increases or decreases with the addition of a complexing agent. pH titration is reliable for complexes that affect pH upon formation. Spectroscopy techniques like UV and NMR are also used to determine rate constants and equilibrium constants.
Physical Pharmaceutics-IUnit-IIISurface and Interfacial tension (Part-1)(Li...Ms. Pooja Bhandare
This document discusses liquid interfaces and surface and interfacial tension. It defines a liquid interface as the boundary between phases in contact, with surface referring specifically to the boundary between a liquid and gas. Surface tension is the force per unit length acting at right angles to the liquid surface and arises from cohesive intermolecular forces being imbalanced at the surface. Molecules in the bulk liquid experience equal attractive forces from all sides, while surface molecules only experience inward attraction. This imbalance causes the surface to contract and results in surface tension. Interfacial tension similarly describes the imbalance of forces at the boundary between immiscible liquids. Some examples of liquid surface tensions are provided.
This document discusses pH, buffers, and isotonic solutions. It begins by defining pH as a measure of hydrogen ion concentration in water using Sorensen's pH scale. It then describes two methods for determining pH: the calorimetric method which compares a solution's color to standard buffers and indicators, and the electrometric method which uses a pH meter. The document also discusses buffers and their importance in biological and pharmaceutical systems like blood, tears, and injections to maintain optimal pH levels. Factors that can influence a buffer's pH like temperature, dilution, and ionic strength are also covered.
Solvation and association (Solubility of drug Part -3)Ms. Pooja Bhandare
The document discusses solvation and association as factors that influence drug solubility. It defines solvation as the interaction of a solute with solvent molecules that leads to stabilization. Solvation is quantified by its dissolution rate. Solubility depends on an equilibrium between dissolution and precipitation rates. Solvent-solute interactions like hydrogen bonding, ion-dipole interactions, and van der Waals forces affect solvation. Solvation energy is determined by a balance of enthalpy, entropy, and temperature factors. Association occurs via chemical reactions where oppositely charged ions or molecules come together to form distinct chemical entities in solution. The extent of association depends on the dielectric constant of the solvent.
This document discusses coarse dispersions and provides information on suspensions and emulsions. It defines coarse dispersions as heterogeneous dispersed systems where the dispersed phase particles are larger than 1000 nm. Suspensions are defined as heterogeneous biphasic liquid systems containing insoluble solid particles suspended in a liquid medium. Emulsions are defined as biphasic liquid dosage forms containing two immiscible liquids mixed with force and stabilized by surfactants. The document also discusses interfacial properties of suspended particles, formulation of suspensions and emulsions, and theories of emulsification.
The document summarizes key information about pharmaceutical suspensions. It defines suspensions as coarse dispersions of insoluble solids suspended in a liquid medium. Suspensions consist of two phases, with the internal solid phase dispersed throughout the external liquid phase using mechanical agitation and excipients. Suspensions are advantageous for stable delivery of drugs that are insoluble or unstable in solution. The document outlines factors that influence sedimentation of particles in suspensions and methods for achieving physical stability, including controlling particle size and flocculation.
This document provides an overview of suspensions, including their classification, properties, formulation, and stability. Key points include:
- Suspensions are heterogeneous systems with an insoluble dispersed phase distributed throughout a continuous phase. They can be classified based on their intended use, concentration of solids, particle size, and electrokinetic properties.
- Interfacial properties like surface tension affect particle flocculation and sedimentation. Surfactants can reduce surface tension to promote deflocculation.
- Particle size, concentration, and Brownian motion influence sedimentation rates. Flocculated particles settle faster but are easier to redisperse than deflocculated particles.
- Stable suspensions are formulated using vehicles to
Complexation and Protein Binding [Part-2](Method of analysis, Complexation a...Ms. Pooja Bhandare
This document discusses various methods for analyzing complexes, including continuous variation (Job's) method, distribution method, solubility method, pH titration method, and spectroscopy. The continuous variation method analyzes changes in physical properties like dielectric constant when complexes form to determine stoichiometric ratios. The distribution method examines how the distribution of a solute between immiscible liquids changes with complexation to estimate stability constants. The solubility method observes whether solubility increases or decreases with the addition of a complexing agent. pH titration is reliable for complexes that affect pH upon formation. Spectroscopy techniques like UV and NMR are also used to determine rate constants and equilibrium constants.
This document discusses an introduction to rheology and its importance in pharmacy. It begins by outlining the topics to be covered, which include the importance of rheology in pharmacy applications, definitions and fundamentals, types of fluids, viscosity, measurements of viscosity, instrumentation, and viscoelasticity. The first section defines rheology and describes its importance in areas like manufacturing dosage forms, handling drugs for administration, topical applications, and more. The introduction provides definitions of key terms like shear stress and rate of shear. It also describes Newton's laws of viscous flow. The document goes on to classify fluids as Newtonian or non-Newtonian and describes different types of non-Newtonian fluids.
This document provides information about colloidal dispersions. It defines colloids as mixtures where one substance is dispersed as very small particles (1-1000 nm) throughout another substance. Colloids are classified based on properties of the dispersed and continuous phases. Key characteristics include particle size, shape, surface area, and charge. Colloids exhibit optical properties like Tyndall effect and kinetic properties such as Brownian motion and electrophoresis. The stability of colloids can be impacted by the addition of electrolytes or other charged particles/colloids.
This document discusses adsorption at liquid surfaces and interfaces. It defines positive and negative adsorption, where some solute molecules are partitioned in favor of the surface/interface (positive adsorption) while others favor the bulk liquid (negative adsorption). Surfactant molecules that reduce surface/interfacial tension through positive adsorption are also introduced. The document then describes how surfactant molecules have both a polar head and nonpolar tail, and how they orient at interfaces. It discusses micelle formation above the critical micelle concentration and how this affects physical properties. In summary, the document provides an overview of adsorption phenomena at liquid surfaces/interfaces with a focus on surfactant molecules and micelle formation.
Suspension, type of suspension, interracial property of suspended particles Dheeraj Saini
Here you find
Suspension , types of suspension, difference between flocculated and deflocculated suspension and interfacial properties of suspended particles
The document discusses coarse dispersions and suspensions. It defines a suspension as an insoluble solid dispersed in a liquid medium where the particles are larger than 0.1 μm. Common types of suspensions include orally administered, ophthalmic, and injectable suspensions. Desirable qualities include minimal settling, uniform distribution, and appropriate viscosity. The document outlines factors that influence particle interactions like surface energy and interfacial tension. It also discusses strategies to achieve stability including controlled flocculation, use of surfactants, polymers, and structured vehicles.
Solid State of matter,
Crystalline, Amorphous & Polymorphism Forms,
Classification of solid state of matter On the basis of Internal Structure,
PHYSICAL PHARMACEUTICS-I,
Habet,
B.Pharm,
Surface and Interfacial tension [Part-6]( Solubilization, Detergency, Adsorp...Ms. Pooja Bhandare
This document discusses three topics related to surface and interfacial tension: solubilization, detergency, and adsorption at solid interfaces. Solubilization is the process of increasing the solubility of organic compounds in water using surfactants. Detergency is the removal of dirt from surfaces using detergents, which are surfactants. Adsorption at solid interfaces is when substances deposit on the surface of solids, with the deposited substance called the adsorbate and the surface called the adsorbent. Adsorption depends on factors like the nature of the adsorbent and adsorbate, temperature, and can be physical or chemical in nature.
Surface and Interfacial tension [Part-5](HLB System, Solubilization )Ms. Pooja Bhandare
This document discusses the HLB (hydrophilic lipophilic balance) system for classifying surfactants. It explains that HLB values indicate whether a surfactant is more hydrophilic or lipophilic. Methods for estimating a surfactant's HLB value involve assigning group numbers to different parts of the molecule. Required HLB values can predict whether a surfactant will form a stable oil-in-water or water-in-oil emulsion with a given oil. However, the HLB system has limitations and does not consider surfactant concentration which also impacts emulsion stability.
Physical pharmacy i third semester (unit-i) solubility of drugMs. Pooja Bhandare
Physical pharmaceutics is the study of physicochemical properties of drug molecules in designing dosage forms. This document discusses the definitions and concepts related to solubility of drugs. It defines key terms like solute, solvent, saturated solution, and explains how solubility is expressed quantitatively and qualitatively. The mechanisms of solute-solvent interactions are discussed based on the nature of solvents being polar, non-polar or semi-polar. Specific examples are provided to illustrate solubility principles for different classes of solvents.
This document discusses solubility, solvation, and association. It defines solvation as the interaction between solute and solvent molecules, with hydration referring specifically to water as the solvent. Solvation of ions involves electrostatic interactions, while solvation of molecules involves weaker intermolecular forces. Factors that affect solvation include surface area, agitation, and temperature. Association refers to the joining of oppositely charged ions and is explained by Coulomb's law. Factors that impact association include the magnitude of electric charges, dielectric constant, and distance between charges. The key factors affecting solubility are outlined as the nature of solute and solvent, surface area, temperature, pressure, and pH.
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?
This document discusses colloids and their properties. It defines colloids as dispersed systems with particle sizes between 1 nm and 1000 nm. Colloids have large surface areas and include systems like sols, emulsions, and foams. They are classified as lyophilic, lyophobic, or association colloids based on particle interactions. Common preparation methods are milling, peptization, and condensation. Colloids exhibit optical properties like Tyndall effect and can be viewed under electron microscopes. They have applications in therapy, stability, absorption, and targeted drug delivery due to their unique size.
The document discusses Hydrophilic-Lipophilic Balance (HLB), which is a numerical scale used to represent the hydrophilicity and lipophilicity of surfactants. The HLB scale ranges from 0 to 20 for non-ionic surfactants and up to 50 for ionic surfactants. Surfactants with higher HLB values are more water-soluble and hydrophilic, while those with lower values are more oil-soluble and lipophilic. The HLB concept allows emulsifiers to be selected and blended to produce stable oil-in-water or water-in-oil emulsions for a given oil based on its required HLB value. Formulas are provided to calculate required H
Surface Tension is defined as the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.
It is due to the phenomena of surface tension that the drops of water tend to assume a spherical shape to attain minimum surface area. the presentation gives a brief description of the methods to measue this important property of the interface of two fluid.
State of matter and properties of matter (Part-3) (Eutectic mixture)Ms. Pooja Bhandare
This document discusses eutectic mixtures, which are mixtures of two or more phases that have the lowest melting point. A eutectic mixture is formed at a specific composition where the phases simultaneously crystallize from a molten solution. The term comes from the Greek word meaning "easily melted". Eutectic mixtures can be formed between APIs, APIs and excipients, or excipients. Below the eutectic temperature, the mixture exists as a solid, while above it exists as a liquid. Eutectic mixtures have various applications in the pharmaceutical industry, such as improving drug solubility and bioavailability for different routes of administration like oral, transdermal, parental, and nasal delivery.
The document discusses various techniques used for size separation of particles in pharmaceutical processes. It defines different powder sizes according to mesh aperture sizes. Some common size separation methods described are sieving, sieve shaker, cyclone separator, air separator, filter bags, and elutriation tank. Sieving involves agitation of powders on mesh screens to separate particles by size. A sieve shaker uses vibration to quickly separate particles. A cyclone separator and air separator use centrifugal forces and air currents respectively to separate particles. Filter bags apply suction to separate fine powders, while an elutriation tank separates particles based on density differences in water.
1. A colloid is a heterogeneous system with one substance dispersed as very fine particles in another substance. Colloids are classified based on the physical state, interaction between phases, and type of dispersed particles.
2. Common colloids include sols, gels, and emulsions. Soaps form micelles above a critical micelle concentration when hydrocarbon chains aggregate.
3. Colloids can be purified through dialysis, electrodialysis, or ultrafiltration to remove electrolytes and impurities. Colloidal particles exhibit properties like Tyndall effect, Brownian motion, and surface charge.
This document provides information about colloidal dispersions. It defines a colloid as a substance microscopically dispersed throughout another substance, with particle sizes between 1-1000nm. Colloids can be classified based on their physical state, nature of interactions, size, appearance, or electric charge. Key properties of colloids include Brownian motion, diffusion, sedimentation, viscosity, light scattering, and electrical behaviors like electrophoresis and electrosmosis. Colloids find applications in areas like therapy, absorption, solubility, stability, and drug targeting.
This document discusses an introduction to rheology and its importance in pharmacy. It begins by outlining the topics to be covered, which include the importance of rheology in pharmacy applications, definitions and fundamentals, types of fluids, viscosity, measurements of viscosity, instrumentation, and viscoelasticity. The first section defines rheology and describes its importance in areas like manufacturing dosage forms, handling drugs for administration, topical applications, and more. The introduction provides definitions of key terms like shear stress and rate of shear. It also describes Newton's laws of viscous flow. The document goes on to classify fluids as Newtonian or non-Newtonian and describes different types of non-Newtonian fluids.
This document provides information about colloidal dispersions. It defines colloids as mixtures where one substance is dispersed as very small particles (1-1000 nm) throughout another substance. Colloids are classified based on properties of the dispersed and continuous phases. Key characteristics include particle size, shape, surface area, and charge. Colloids exhibit optical properties like Tyndall effect and kinetic properties such as Brownian motion and electrophoresis. The stability of colloids can be impacted by the addition of electrolytes or other charged particles/colloids.
This document discusses adsorption at liquid surfaces and interfaces. It defines positive and negative adsorption, where some solute molecules are partitioned in favor of the surface/interface (positive adsorption) while others favor the bulk liquid (negative adsorption). Surfactant molecules that reduce surface/interfacial tension through positive adsorption are also introduced. The document then describes how surfactant molecules have both a polar head and nonpolar tail, and how they orient at interfaces. It discusses micelle formation above the critical micelle concentration and how this affects physical properties. In summary, the document provides an overview of adsorption phenomena at liquid surfaces/interfaces with a focus on surfactant molecules and micelle formation.
Suspension, type of suspension, interracial property of suspended particles Dheeraj Saini
Here you find
Suspension , types of suspension, difference between flocculated and deflocculated suspension and interfacial properties of suspended particles
The document discusses coarse dispersions and suspensions. It defines a suspension as an insoluble solid dispersed in a liquid medium where the particles are larger than 0.1 μm. Common types of suspensions include orally administered, ophthalmic, and injectable suspensions. Desirable qualities include minimal settling, uniform distribution, and appropriate viscosity. The document outlines factors that influence particle interactions like surface energy and interfacial tension. It also discusses strategies to achieve stability including controlled flocculation, use of surfactants, polymers, and structured vehicles.
Solid State of matter,
Crystalline, Amorphous & Polymorphism Forms,
Classification of solid state of matter On the basis of Internal Structure,
PHYSICAL PHARMACEUTICS-I,
Habet,
B.Pharm,
Surface and Interfacial tension [Part-6]( Solubilization, Detergency, Adsorp...Ms. Pooja Bhandare
This document discusses three topics related to surface and interfacial tension: solubilization, detergency, and adsorption at solid interfaces. Solubilization is the process of increasing the solubility of organic compounds in water using surfactants. Detergency is the removal of dirt from surfaces using detergents, which are surfactants. Adsorption at solid interfaces is when substances deposit on the surface of solids, with the deposited substance called the adsorbate and the surface called the adsorbent. Adsorption depends on factors like the nature of the adsorbent and adsorbate, temperature, and can be physical or chemical in nature.
Surface and Interfacial tension [Part-5](HLB System, Solubilization )Ms. Pooja Bhandare
This document discusses the HLB (hydrophilic lipophilic balance) system for classifying surfactants. It explains that HLB values indicate whether a surfactant is more hydrophilic or lipophilic. Methods for estimating a surfactant's HLB value involve assigning group numbers to different parts of the molecule. Required HLB values can predict whether a surfactant will form a stable oil-in-water or water-in-oil emulsion with a given oil. However, the HLB system has limitations and does not consider surfactant concentration which also impacts emulsion stability.
Physical pharmacy i third semester (unit-i) solubility of drugMs. Pooja Bhandare
Physical pharmaceutics is the study of physicochemical properties of drug molecules in designing dosage forms. This document discusses the definitions and concepts related to solubility of drugs. It defines key terms like solute, solvent, saturated solution, and explains how solubility is expressed quantitatively and qualitatively. The mechanisms of solute-solvent interactions are discussed based on the nature of solvents being polar, non-polar or semi-polar. Specific examples are provided to illustrate solubility principles for different classes of solvents.
This document discusses solubility, solvation, and association. It defines solvation as the interaction between solute and solvent molecules, with hydration referring specifically to water as the solvent. Solvation of ions involves electrostatic interactions, while solvation of molecules involves weaker intermolecular forces. Factors that affect solvation include surface area, agitation, and temperature. Association refers to the joining of oppositely charged ions and is explained by Coulomb's law. Factors that impact association include the magnitude of electric charges, dielectric constant, and distance between charges. The key factors affecting solubility are outlined as the nature of solute and solvent, surface area, temperature, pressure, and pH.
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?
This document discusses colloids and their properties. It defines colloids as dispersed systems with particle sizes between 1 nm and 1000 nm. Colloids have large surface areas and include systems like sols, emulsions, and foams. They are classified as lyophilic, lyophobic, or association colloids based on particle interactions. Common preparation methods are milling, peptization, and condensation. Colloids exhibit optical properties like Tyndall effect and can be viewed under electron microscopes. They have applications in therapy, stability, absorption, and targeted drug delivery due to their unique size.
The document discusses Hydrophilic-Lipophilic Balance (HLB), which is a numerical scale used to represent the hydrophilicity and lipophilicity of surfactants. The HLB scale ranges from 0 to 20 for non-ionic surfactants and up to 50 for ionic surfactants. Surfactants with higher HLB values are more water-soluble and hydrophilic, while those with lower values are more oil-soluble and lipophilic. The HLB concept allows emulsifiers to be selected and blended to produce stable oil-in-water or water-in-oil emulsions for a given oil based on its required HLB value. Formulas are provided to calculate required H
Surface Tension is defined as the tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.
It is due to the phenomena of surface tension that the drops of water tend to assume a spherical shape to attain minimum surface area. the presentation gives a brief description of the methods to measue this important property of the interface of two fluid.
State of matter and properties of matter (Part-3) (Eutectic mixture)Ms. Pooja Bhandare
This document discusses eutectic mixtures, which are mixtures of two or more phases that have the lowest melting point. A eutectic mixture is formed at a specific composition where the phases simultaneously crystallize from a molten solution. The term comes from the Greek word meaning "easily melted". Eutectic mixtures can be formed between APIs, APIs and excipients, or excipients. Below the eutectic temperature, the mixture exists as a solid, while above it exists as a liquid. Eutectic mixtures have various applications in the pharmaceutical industry, such as improving drug solubility and bioavailability for different routes of administration like oral, transdermal, parental, and nasal delivery.
The document discusses various techniques used for size separation of particles in pharmaceutical processes. It defines different powder sizes according to mesh aperture sizes. Some common size separation methods described are sieving, sieve shaker, cyclone separator, air separator, filter bags, and elutriation tank. Sieving involves agitation of powders on mesh screens to separate particles by size. A sieve shaker uses vibration to quickly separate particles. A cyclone separator and air separator use centrifugal forces and air currents respectively to separate particles. Filter bags apply suction to separate fine powders, while an elutriation tank separates particles based on density differences in water.
1. A colloid is a heterogeneous system with one substance dispersed as very fine particles in another substance. Colloids are classified based on the physical state, interaction between phases, and type of dispersed particles.
2. Common colloids include sols, gels, and emulsions. Soaps form micelles above a critical micelle concentration when hydrocarbon chains aggregate.
3. Colloids can be purified through dialysis, electrodialysis, or ultrafiltration to remove electrolytes and impurities. Colloidal particles exhibit properties like Tyndall effect, Brownian motion, and surface charge.
This document provides information about colloidal dispersions. It defines a colloid as a substance microscopically dispersed throughout another substance, with particle sizes between 1-1000nm. Colloids can be classified based on their physical state, nature of interactions, size, appearance, or electric charge. Key properties of colloids include Brownian motion, diffusion, sedimentation, viscosity, light scattering, and electrical behaviors like electrophoresis and electrosmosis. Colloids find applications in areas like therapy, absorption, solubility, stability, and drug targeting.
1. A colloid is a mixture of one substance dispersed evenly throughout another substance where at least one dimension of the dispersed particles is between 1-1000 nanometers.
2. Colloids can be classified as lyophilic or lyophobic depending on whether the dispersed particles are attracted to or repel the dispersion medium.
3. Common methods for preparing lyophobic colloids include mechanical dispersion, arc discharge, and chemical reactions like reduction or hydrolysis, while lyophilic colloids are often prepared by simple mixing.
Colloids are mixtures where one substance is microscopically dispersed throughout another. They consist of two phases - a dispersed phase made of very tiny particles 1nm to 1um in size suspended in a continuous dispersion medium. Common examples are milk, fog, and blood. Colloids can be classified based on the physical state of the phases and the interactions between them. Preparation methods include mechanical grinding, electrical dispersion, peptization of precipitates, and condensation by changes in conditions. The interactions between colloidal particles, such as excluded volume repulsion, electrostatic forces, van der Waals forces, and steric effects influence colloid stability and properties.
Colloids are substances microscopically dispersed throughout another substance. The dispersed particles range in size from 1-100 nm. Colloids exhibit properties between true solutions and suspensions due to their intermediate particle size. They are able to pass through filters but not semipermeable membranes. Common examples include milk, fog, mayonnaise and paints. Colloids can be classified based on factors like the physical state of the phases, the interaction between the phases, the size and nature of dispersed particles, and the electrical charge on particles. They are purified using techniques like dialysis, electrodialysis, and ultrafiltration which separate colloidal particles from dissolved substances.
Colloidal dispersions are heterogeneous systems where one substance is divided into small particles, between 1 nm and 1 μm, dispersed throughout a second substance. They can be classified based on the dispersed and dispersion medium, such as sols where the medium is a liquid. Colloidal particles exhibit properties like Brownian motion, diffusion, and Tyndall effect. Their size, shape, and surface charge affect characteristics like stability, flowability, and pharmacological effects. Purification methods remove electrolytes and impurities through dialysis, ultrafiltration, or electrodialysis.
This document provides information about colloids, including:
1. It defines colloids and distinguishes them from true solutions and suspensions based on particle size and other properties.
2. It describes the phases in a colloidal solution and different classification methods for colloids.
3. It explains various preparation methods for lyophobic colloidal solutions and properties of colloids such as Brownian motion, Tyndall effect, and coagulation.
4. It discusses purification techniques like dialysis and ultrafiltration and industrial applications of colloids.
Colloids have particle sizes between 1 nm and 1000 nm. They are classified as lyophilic, lyophobic, or association colloids based on particle interactions with the dispersion medium. Lyophilic colloids readily disperse in the medium, lyophobic colloids resist dispersion, and association colloids form micelles above a critical concentration. Colloids demonstrate optical properties like Tyndall effect, kinetic properties like Brownian motion and diffusion, and electric properties due to particle charge. Their stability depends on preventing particle aggregation.
This document discusses colloids and their properties. It defines colloids as dispersed systems with particle diameters between 1 nm and 1000 nm. Colloids have large surface areas and can be classified as lyophilic, lyophobic, or association colloids. Common examples and methods of preparation are provided. The document also discusses optical properties like Tyndall effect and use of electron microscopes to view colloids, as well as comparisons between types of colloids.
Colloids have particle sizes between 1 nm and 1000 nm. They are classified as lyophilic, lyophobic, or association colloids based on particle interactions with the dispersion medium. Lyophilic colloids readily disperse in the medium while lyophobic colloids do not. Association colloids form micelles above a critical micelle concentration. Colloids demonstrate optical properties like Tyndall effect and can be imaged with electron microscopes. They also exhibit kinetic properties including Brownian motion, diffusion, osmotic pressure, and sedimentation. Colloidal particles are often electrically charged, leading to electrokinetic phenomena like electrophoresis and electroosmosis. Stability is important for preventing
Colloidal Dispersion, Its Types and Method of PreparationChitralekhaTherkar
Dispersion
Definition of Colloids
Shapes and Sizes of Colloids
Classification of Colloids
Properties of Colloids
1. Optical Properties.
2. Electrical Properties.
3. Kinetic Properties
Purification of Colloids
Method of Preparation of Colloids.
Physical Stability of Colloids.
Factors affecting Colloidal Dispersion.
This document provides an overview of colloids, including:
1) What colloids are and the difference between lyophobic and lyophilic colloids
2) Methods for preparing colloidal solutions, including dispersion and condensation methods
3) Properties of colloidal systems like optical properties related to light scattering and the electrical double layer
The document discusses colloids and their properties. It defines colloids as dispersed systems with particle sizes between 1-1000 nm. Colloids can be lyophilic, lyophobic, or association colloids depending on interactions between particles and dispersion medium. Key properties of colloids include optical effects like Tyndall scattering, Brownian motion, diffusion, osmotic pressure, and electrokinetic phenomena that are influenced by particle size, temperature, and viscosity. Colloids find applications in pharmaceuticals for solubilization, increasing bioavailability, and as therapeutic or diagnostic agents.
6. Colloidal properties of any colloidal substanceManteeKumari
This document discusses colloidal systems and their properties. It begins by defining colloids as mixtures where one substance is divided into minute particles dispersed throughout a second substance. The particles in a colloid are larger than atoms or molecules in solutions, but smaller than particles in suspensions.
It then discusses some key properties of colloids, including that colloidal particles do not diffuse through membranes, they scatter light and exhibit the Tyndall effect, and they undergo constant random motion called Brownian movement. Colloidal particles also acquire and maintain a net electric charge via preferential adsorption of ions from the dispersion medium. This charge prevents the particles from aggregating due to electrical repulsions between them.
In
The document discusses colloidal dispersions, which are systems with particulate matter dispersed in a continuous medium. Colloidal dispersions have particle sizes between 1-500 nm. They are classified as lyophilic, lyophobic, or association colloids based on particle interactions. Lyophilic colloids are stable and interact with the solvent, while lyophobic colloids are less stable and do not interact well with water. Association colloids form micelles above a critical concentration of amphiphilic molecules. Colloids have various properties related to their kinetics, optics, and electrical characteristics that depend on factors like particle size, shape, and surface charge.
Here almost full every topics interrelated with colloid chemistry has been discussed.The slides have been made showing question pattern taking Begum Rokeya University Chemistry Department previous year questions to appear the slides easy towards the viewers.Stay join with me.Thank you.
A colloid is a substance microscopically dispersed throughout another substance.
The word colloid comes from a Greek word 'kolla', which means glue thus colloidal particles are glue like substances.
These particles pass through a filter paper but not through a semipermeable membrane.
Colloids can be made settle by the process of centrifugation.
This document provides an overview of colloidal dispersions. It defines colloids as micro-heterogeneous dispersed systems with particle sizes between 1 nm and 1 μm. Colloids differ from molecular and coarse dispersions based on particle size, appearance, visibility, and ability to pass through membranes. Colloidal particles take on various shapes and their properties depend on shape. Colloids are classified as lyophilic or lyophobic based on particle-solvent interactions. The document discusses purification, association, optical, kinetic, electrical, and stability properties of colloids.
1. The document discusses methods for preparing and purifying colloidal solutions.
2. There are two main methods for preparing lyophobic colloidal sols: dispersion methods, which break down larger particles, and peptization, which breaks down freshly precipitated particles.
3. Purification methods remove electrolyte impurities from colloidal solutions and include dialysis, electrodialysis, ultrafiltration, and ultracentrifugation.
This document defines and classifies colloids. Colloids have particle sizes between 1-1000 nm, which are larger than true solutions and smaller than suspensions. Colloids are classified based on the physical state of the dispersed and dispersion medium (solid-liquid, liquid-liquid, etc.), interaction between the phases (lyophobic or lyophilic), and particle type (multimolecular, macromolecular, associated). Common colloids include emulsions, gels, sols, and foams. Properties include the Tyndall effect, Brownian motion, and coagulation with electrolytes. Colloids find applications in products like rubber, soaps, and medicines.
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2. Dispersed systems consist of particulate
matter, known as the dispersed phase, distributed
throughout a continuous or dispersion medium.
The dispersed material may range in size from
particles of atomic and molecular dimensions to
particles whose size is measured in millimeters.
Accordingly, a convenient means of classifying
dispersed systems is on the basis of the mean
particle diameter of the dispersed material.
3. Types of dispersed systems
1. molecular dispersions.
2. Colloidal dispersions.
3. coarse dispersions.
1. Molecular dispersions (less than 1 nm)
Particles invisible in electron microscope
Pass through semipermeable membranes
and filter paper, Particles do not settle
down on standing Undergo rapid
diffusion E.g. ordinary ions, glucose
4. 2. Colloidal dispersions (1 nm - o.5 um)
Particles not resolved by ordinary microscope, can
be detected by electron microscope. Pass through
filter paper but not pass through semipermeable
membrane. Particles made to settle by
centrifugation Diffuse very slowly E.g. colloidal
silver sols, natural and synthetic polymers,
cheese, butter, jelly, paint, milk, shaving cream.
3- Coarse dispersions (> 0.5 um)
Particles are visible under ordinary microscope.
Do not pass through filter paper or semipermeable
membrane. Particles settle down under gravity do
not diffuse E.g. emulsions, suspensions, red blood
cells.
5. Size and Shape of Colloidal
Particles
Particles in the colloidal size range possess a
surface area that is enormous compared with the
surface area of an equal volume of larger particles.
Thus, a cube having a 1-cm edge and a volume of
1 cm3 has a total surface area of 6 cm2. If the
same cube is subdivided into smaller cubes each
having an edge of 100 μm, the total volume
remains the same, but the total surface area
increases to 600,000 cm2. This represents a 105-
fold increase in surface area.
6. specific surface is defined as the surface
area per unit weight or volume of material. In the
example just given, the first sample had a specific
surface of 6 cm2/cm3, whereas the second sample
had a specific surface of 600,000 cm2/cm3. The
possession of a large specific surface results in
many of the unique properties of colloidal
dispersions. For example, platinum is effective as
a catalyst only when in the colloidal form as
platinum black. This is because catalysts act by
adsorbing the reactants onto their surface. Hence,
their catalytic activity is related to their specific
surface.
7. The color of colloidal dispersions is related to the
size of the particles present. Thus, as the particles
in a red gold sol increase in size, the dispersion
takes on a blue color. Antimony and arsenic
trisulfides change from red to yellow as the
particle size is reduced from that of a coarse
powder to that within the colloidal size range.
Because of their size, colloidal particles can be
separated from molecular particles with relative
ease. The technique of separation, known as
dialysis, uses a semipermeable membrane of
collodion or cellophane, the pore size of which will
prevent the passage of colloidal particles, yet
permit small molecules and ions, such as urea,
glucose, and sodium chloride, to pass through.
The principle is illustrated in Figure 16-1,
8. Fig. 16-1.Sketch showing the removal of
electrolytes from colloidal material by diffusion
through a semipermeable membrane. Conditions
on the two sides, A and B, of the membrane are
shown at the start and at equilibrium. The open
circles are the colloidal particles that are too
large to pass through the membrane. The solid
dots are the electrolyte particles that pass
through the pores of the membrane.
9. at equilibrium, the colloidal material is retained in
compartment A, whereas the subcolloidal material
is distributed equally on both sides of the
membrane. By continually removing the liquid in
compartment B, it is possible to obtain colloidal
material in A that is free from subcolloidal
contaminants. Dialysis can also be used to obtain
subcolloidal material that is free from colloidal
contamination—in this case, one simply collects
the effluent.
10. Dialysis occurs in vivo. Thus, ions and small
molecules pass readily from the blood, through a
natural semipermeable membrane, to the tissue
fluids; the colloidal components of the blood
remain within the capillary system. The principle of
dialysis is utilized in the artificial kidney, which
removes low–molecular-weight impurities from the
body by passage through a
semipermeable membrane.
11. The shape of colloidal particles in
dispersion is important:
The more extended the particle the greater its
specific surface the greater the attractive force
between the particles of the dispersed phase and
the dispersion medium.
Flow, sedimentation and osmotic pressure of the
colloidal system affected by the shape of
colloidal particles.
Particle shape may also influence the
pharmacologic action.
12. Fig. 16-2.Some shapes that can be assumed by
colloidal particles: (a) spheres and globules, (b)
short rods and prolate ellipsoids, (c) oblate
ellipsoids and flakes, (d) long rods and threads,
(e) loosely coiled threads, and (f) branched
threads.
13. Types of Colloidal Systems
A. on the basis of the interaction of the
particles, molecules, or ions of the
dispersed phase with the molecules of the
dispersion medium.
1.Lyophilic Colloids
Systems containing colloidal particles
that interact to an appreciable extent with
the dispersion medium are referred to as
lyophilic (solvent-loving) colloids. Owing
to their affinity for the dispersion
medium, such materials form colloidal
dispersions, or sols with relative ease.
14. lyophilic colloidal sols are usually obtained
simply by dissolving the material in the solvent
being used. For example, the dissolution of
acacia or gelatin in water.
The various properties of this class of colloids
are due to the attraction between the dispersed
phase and the dispersion medium, which leads
to solvation, the attachment of solvent molecules
to the molecules of the dispersed phase.
In the case of hydrophilic colloids, in which
water is the dispersion medium, this is termed
hydration.
15. Most lyophilic colloids are organic molecules, for
example, gelatin, acacia, insulin, albumin,
rubber, and polystyrene.
gelatin, acacia, insulin, albumin produce
lyophilic colloids in aqueous dispersion media
(hydrophilic sols). Rubber and polystyrene form
lyophilic colloids in nonaqueous, organic
solvents. These materials accordingly are
referred to as lipophilic colloids.
16. 2. Lyophobic Colloids
The second class of colloids is composed of
materials that have little attraction, if any, for the
dispersion medium. These are the lyophobic
(solvent-hating) colloids.
Lyophobic colloids are generally composed of
inorganic particles dispersed in water. Examples
of such materials are gold, silver, sulfur,
arsenous sulfide, and silver iodide.
In contrast to lyophilic colloids, it is necessary to
use special methods to prepare lyophobic
colloids. These are (a) dispersion methods, in
which coarse particles are reduced in size,
17. Dispersion can be achieved by the use of high-
intensity ultrasonic generators operating at
frequencies in excess of 20,000 cycles per second.
A second dispersion method involves the
production of an electric arc within a liquid. Owing
to the intense heat generated by the arc, some of
the metal of the electrodes is dispersed as vapor,
which condenses to form colloidal particles.
Milling and grinding processes can be used,
although their efficiency is low. So-called colloid
mills, in which the material is sheared between two
rapidly rotating plates set close together, reduce
only a small amount of the total particles to the
colloidal size range.
18. (b) condensation methods, in which materials of
subcolloidal dimensions are caused to aggregate
into particles within the colloidal size range. The
required conditions for the formation of lyophobic
colloids by condensation or aggregation involve a
high degree of initial supersaturation followed by
the formation and growth of nuclei.
Supersaturation can be brought about by change
in solvent or reduction in temperature. For
example, if sulfur is dissolved in alcohol and the
concentrated solution is then poured into an
excess of water, many small nuclei form in the
supersaturated solution. These grow rapidly to
form a colloidal sol.
19. Other condensation methods depend on a
chemical reaction, such as reduction, oxidation,
hydrolysis, and double decomposition. Thus,
neutral or slightly alkaline solutions of the noble
metal salts, when treated with a reducing agent
such as formaldehyde or pyrogallol, form atoms
that combine to form charged aggregates.
20. 3. Association Colloids
Association or amphiphilic colloids form
the third group in this classification. As
shown in the Interfacial Phenomena
chapter, certain molecules or ions,
termed amphiphiles or surface-active
agents, are characterized by having two
distinct regions of opposing solution
affinities within the same molecule or
ion. When present in a liquid medium at
low concentrations, the amphiphiles exist
separately and are of such a size as to be
subcolloidal. As the concentration is
increased, aggregation occurs over a
narrow concentration range. These
aggregates, which may contain 50 or
21. Because the diameter of each micelle is of the
order of 50 Å, micelles lie within the size range we
have designated as colloidal. The concentration of
monomer at which micelles form is termed the
critical micelle concentration(CMC). The number of
monomers that aggregate to form a micelle is
known as the aggregation number of the micelle.
22. In the case of amphiphiles in water, the
hydrocarbon chains face inward into the
micelle to form, in effect, their own
hydrocarbon environment. Surrounding this
hydrocarbon core are the polar portions of the
amphiphiles associated with the water
molecules of the continuous phase.
Aggregation also occurs in nonpolar liquids.
The orientation of the molecules is now
reversed, however, with the polar heads facing
inward while the hydrocarbon chains are
associated with the continuous nonpolar
phase. These situations are shown in Figure
16-4, which also shows some of the shapes
postulated for micelles.
23. Fig. 16-4.Some probable shapes of micelles: (a)
spherical micelle in aqueous media, (b)
reversed micelle in nonaqueous media, and (c)
laminar micelle, formed at higher amphiphile
concentration, in aqueous media.
24. It seems likely that spherical micelles exist at
concentrations relatively close to the CMC. At
higher concentrations, laminar micelles have an
increasing tendency to form and exist in
equilibrium with spherical micelles.
As with lyophilic sols, formation of association
colloids is spontaneous, provided that the
concentration of the amphiphile in solution
exceeds the CMC. Amphiphiles may be anionic,
cationic, nonionic, or ampholytic (zwitterionic),
and this provides a convenient means of
classifying association colloids.
25.
26. Types of Colloidal Systems
B. On the base of the original states of their
constituent parts:
31. Optical Properties of Colloids
1. The Faraday–Tyndall Effect
when a strong beam of light is passed through a
colloidal sol, the path of light is illuminated (a
visible cone formed).
This phenomenon resulting from the scattering
of light by the colloidal particles.
32.
33. The same effect is noticed when a beam of
sunlight enters a dark room through a slit when
the beam of light becomes visible through the
room. This happens due to the scattering of light
by particles of dust in the air.
34. 2- Electron microscope
Ultra-microscope has declined in recent years as it
does not able to resolve lyophilic colloids. so
electron microscope is capable of yielding
pictures of actual particles size, shape and
structure of colloidal particles. Electron
microscope has high resolving power, as its
radiation source is a beam of high energy
electrons, while that of optical microscope is
visible light.
36. 3- Light Scattering
depend on tyndall effect. used to give information
about particle size and shape and for
determination of molecular weight of colloids.
Used to study proteins, association colloids and
lyophobic sols. Scattering described in terms of
turbidity, T Turbidity: the fractional decrease in
intensity due to scattering as the incident light
passes through 1 cm of solution. Turbidity is
proportional to the molecular weight of lyophilic
colloid.
37. Hc / T = 1/M + 2Bc
T: turbidity
C: conc of solute in gm / ml of
solution
M: molecular weight
B: interaction constant
H: constant for a particular
system
38. Kinetic Properties of Colloids
Grouped under this heading are several properties
of colloidal systems that relate to the motion of
particles with respect to the dispersion medium.
The motion may be thermally induced (Brownian
movement, diffusion, osmosis), gravitationally
induced (sedimentation), or applied externally
(viscosity).
39. 1. Brownian Motion
Brownian motion describes the random
movement of colloidal particles. The erratic
motion, which may be observed with particles as
large as about 5 μm, was explained as resulting
from the bombardment of the particles by the
molecules of the dispersion medium.
The zig-zag movement of colloidal
particles continuously and
randomly
40. The motion of the molecules cannot be
observed, of course, because the molecules are
too small to see.
The velocity of the particles increases with
decreasing particle size.
Increasing the viscosity of the medium, which
may be accomplished by the addition of glycerin
or a similar agent, decreases and finally stops
the Brownian movement.
41. 2. Diffusion
Particles diffuse spontaneously from a region
of higher concentration to one of lower
concentration until the concentration of the
system is uniform throughout. Diffusion is a
direct result of Brownian movement.
According to Fick's first law, the amount, dq,
of substance diffusing in time, dt, across a
plane of area, S, is directly proportional to the
change of concentration, dc, with distance
traveled, dx.
Fick's law is written as
42. D diffusion coefficient the amount of the
material diffused per unit time across a unit area
when dc/dx (conc. gradient) is unity.
The measured diffusion coeffecient can be used
to determine the radius of particles or molecular
weight.
3. Osmotic Pressure
The osmotic pressure, π, of a dilute colloidal
solution is described by the van't Hoff equation:
where c is molar concentration of solute. This
equation can be used to calculate the molecular
weight of a colloid in a dilute solution. Replacing c
with cg/M in equation (16-9), in which cg is the
grams of solute per liter of solution and M is the
molecular weight, we obtain
43. 𝝅 osmotic pressure
R molar gas constant
4- Sedimentation
The velocity, v, of sedimentation of
spherical particles having a density
ρ in a medium of density ρ0 and a
viscosity η0 is given by Stokes's
law:
44. where g is the acceleration due to gravity. If the
particles are subjected only to the force of gravity,
then the lower size limit of particles obeying
Stokes's equation is about 0.5 μm. This is because
Brownian movement becomes significant and
tends to offset sedimentation due to gravity and
promotes mixing instead. Consequently, a
stronger force must be applied to bring about the
sedimentation of colloidal particles in a
quantitative and measurable manner. This is
accomplished by use of the ultracentrifuge, which
can produce a force one million times that of
gravity.
45. 5. Viscosity
Viscosity is an expression of the resistance to
flow of a system under an applied stress. The
more viscous a liquid is, the greater is the
applied force required to make it flow at a
particular rate.
The shapes of particles of the disperse phase
affect the viscosity of colloidal dispersions.
Spherocolloids form dispersions of relatively low
viscosity, whereas systems containing linear
particles are more viscous.
46. Colloids
Particles dispersed in liquid media may become
charged mainly in one of two ways :
The first involve selective adsorption of a
particular ionic species present in solution. This
may be an ion added to the solution or, in the
case of pure water, it may be the hydronium or
hydroxyl ion. The majority of particles dispersed
in water acquire a negative charge due to
preferential adsorption of the hydroxyl ion.
Second : charges on particles arises from
ionization of groups (such as COOH) that may be
situated at the surface of the particles.
47. The Electric Double Layer
Consider a solid surface in contact with a polar
solution containing ions, for example, an aqueous
solution of an electrolyte. Furthermore, let us
suppose that some of the cations are adsorbed
onto the surface, giving it a positive charge.
Remaining in solution are the rest of the cations
plus the total number of anions added. These
anions are attracted to the positively charged
surface by electric forces.
In addition to these electric forces, thermal motion
tends to produce an equal distribution of all the
ions in solution.
48. An equilibrium situation is set up in which some of
the excess anions approach the surface, whereas
the remainder are distributed in decreasing
amounts as one proceeds away from the charged
surface.
At a particular distance from the surface, the
concentrations of anions and cations are equal,
that is, conditions of electric neutrality prevail.
49. Fig. 15-28. The electric double layer at the surface
of separation between two phases,showing
distribution of ions. The system as a whole is
electrically neutral.
50. in figure 15-28 aa′ is the surface of the solid.
The adsorbed ions that give the surface its
positive charge are referred to as the potential-
determining ions.
Immediately adjacent to this surface layer is a
region of tightly bound solvent molecules,
together with some negative ions, also tightly
bound to the surface. The limit of this region is
given by the line bb′ in Figure 15-28.
51. These ions, having a charge opposite to that
of the potential-determining ions, are known
as counterions or gegenions.
The degree of attraction of the solvent
molecules and counterions is such that if the
surface is moved relative to the liquid, the
shear plane is bb′ rather than aa′.
In the region bounded by the lines bb′ and
cc′, there is an excess of negative ions. The
potential at bb′ is still positive because, as
previously mentioned, there are fewer anions
in the tightly bound layer than cations
adsorbed onto the surface of the solid.
Beyond cc′, the distribution of ions is uniform
52. Thus, the electric distribution at the interface is
equivalent to a double layer of charge, the first
layer(extending from aa′ to bb′) tightly bound and
a second layer (from bb′ to cc′) that is more
diffuse. The so called diffuse double layer
therefore extends from aa′ to cc′.
53. Two situations other than that represented by
Figure 15-28 are possible:
(a) If the counterions in the tightly bound, solvated
layer equal the positive charge on the solid
surface, then electric neutrality occurs at the plane
bb′ rather than cc′.
(b) Should the total charge of the counterions in
the region aa′– bb′ exceed the charge due to the
potential-determining ions, then the net charge at
bb′ will be negative rather than less positive, as
shown in Figure 15-28.
This means that, in this instance, for electric
neutrality to be obtained at cc′, an excess of
positive ions must be present in the region bb′–cc′.
54. Nernst and Zeta Potentials
The potential at the solid surface aa′ due to the
potential-determining ion is the
electrothermodynamic Nernst potential, E, and
is defined as the difference in potential between
the actual surface and the electroneutral region
of the solution.
potential located at the shear plane bb′ is
known as the electrokinetic, or zeta, potential,
δ. The zeta potential is defined as the difference
in potential between the surface of the tightly
bound layer (shear plane) and the electroneutral
region of the solutiona.
55. The zeta potential has practical application in the
stability of systems containing dispersed
particles because this potential, rather than the
Nernst potential, governs the degree of repulsion
between adjacent, similarly charged, dispersed
particles.
If the zeta potential is reduced below a certain
value (which depends on the particular system
being used), the attractive forces exceed the
repulsive forces, and the particles come
together. This phenomenon is known as
flocculation.
56. The movement of a charged surface with respect
to the adjacent liquid phase is the basic principle
underlying four electrokinetic phenomena :
Electrophoresis
Electroosmosis
Sedimentation Potential
Streaming Potential
57. Electrophoresis
Electrophoresis is the most known
electrokinetic phenomena. It refers to the
motion of charged particles related to the fluid
under the influence of an applied electric field.
If an electric potential is applied to a colloid,
the charged colloidal particles move toward
the oppositely charged electrode.
58. Electro-osmosis
It is the opposite in principal to that of
electrophoresis.
If the solid is rendered immobile ( by making
particles into a porous plug), the liquid moves
relative to the charged surface. When
potential is applied
59. Sedimentation Potential
The sedimentation potential also called the
(Donnan effect).
It is the potential induced by the fall of a
charged particle under an external force field.
if a colloidal suspension has a gradient of
concentration (such as is produced in
sedimentation or centrifugation), then a
macroscopic electric field is generated by the
charge imbalance appearing at the top and
bottom of the sample column.
60.
61. Streaming Potential
Differs from electro-osmosis in that the
potential is created by forcing a liquid to flow
through a bed or plug of particles.
63. The presence and magnitude, or absence, of a
charge on a colloidal particle is an important
factor in the stability of colloidal systems.
Stabilization is accomplished essentially by two
means:
1. providing the dispersed particles with an
electric charge.
2. surrounding each particle with a protective
solvent
sheath that prevents mutual adherence when the
particles collide as a result of Brownian
movement.
This second effect is significant only in the case
of lyophilic sols.
64. A lyophobic sol is thermodynamically unstable. The
particles in such sols are stabilized only by the
presence of electric charges on their surfaces. The
like charges produce a repulsion that prevents
coagulation of the particles. If the last traces of ions
are removed from the system by dialysis, the
particles can agglomerate and reduce the total
surface area, and, owing to their increased size, they
may settle rapidly from suspension. Hence, addition
of a small amount of electrolyte to a lyophobic sol
tends to stabilize the system by imparting a charge to
the particles. Addition of electrolyte beyond that
necessary for maximum adsorption on the particles,
however, sometimes results in the accumulation of
opposite ions and reduces the zeta potential below
its critical value.
Coagulation also result from mixing of oppositely
65. Lyophilic and association colloids are
thermodynamically stable and The addition of an
electrolyte to a lyophilic colloid in moderate
amounts does not result in coagulation, as was
evident with lyophobic colloids. If sufficient salt
is added, however, agglomeration and
sedimentation of the particles may result. This
phenomenon, referred to as salting out.
66. This is obtained by:
1- Addition of large amounts of electrolytes
- Anions arranged in a decreasing order of
precipitating power: citrate > tartrate > sulfate >
acetate > chloride> nitrate > bromide > iodide
- The precipitation power is directly related to the
hydration of the ion and its ability to separate
water molecules from colloidal particles
2- addition of less polar solvent
- e.g. alcohol, acetone
- The addition of less polar solvent renders the
solvent mixture unfavourable for the colloids
solubility
67. Coacervation:
the process of mixing negatively and positively
charged hydrophilic colloids, and hence the
particles separate from the dispersion to form a
layer rich in the colloidal aggregates (coacervate)
68. Sensitization and protective
colloidal action:
Sensitization: the addition of small amount of
hydrophilic or hydrophobic colloid to a
hydrophobic colloid of opposite charge tend
to sensitize (coagulate) the particles.
Polymer flocculants can bridge individual
colloidal particles by attractive electrostatic
interactions.
For example, negatively-charged colloidal
silica particles can be flocculated by the
addition of a positively-charged polymer.
69. Protection: the addition of large amount of
hydrophilic colloid (protective colloid) to a
hydrophobic colloid tend to stabilize the system.
This may be due to:
The hydrophile is adsorbed as a monomolecular
layer on the hydrophobic particles.