PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Physical Chemistry → Surface and Colloid Chemistry ↓


Colloidal Stability


Colloidal stability is an important topic in surface and colloid chemistry, and it refers to the ability of colloidal systems to remain uniformly distributed without the particles aggregating or settling. Colloidal systems, such as sols, emulsions, and foams, consist of finely dispersed insoluble particles suspended in another substance. The stability of these colloids is important in a wide range of scientific and industrial applications such as pharmaceuticals, food production, and cosmetics.

Introduction to colloids

Colloids are mixtures where one substance is dispersed evenly throughout another substance. The particles dispersed in a colloid range in size from 1 to 1000 nanometers. These particles may be solid, liquid, or gas, while the medium in which they are dispersed may also be in one of these states. For example, emulsions such as milk contain droplets of liquid fat dispersed throughout the liquid water phase. Other examples include aerosols, foams, gels, and sols.

Milk (Emulsion): Liquid fat in water Smoke (Aerosol): Solid particles in air Jelly (Gel): Liquid in solid

Forces affecting colloidal stability

The stability of colloidal systems is affected by various forces acting on the particles. These include:

1. Van der Waals force

Van der Waals forces are attractive forces that occur between molecules. These forces arise due to temporary fluctuations in electron density that induce dipoles. In colloids, van der Waals forces cause particles to attract one another, which can lead to aggregation. The strength of these forces depends on the size of the particles and their distance.

Van der Waals attraction

2. Electrostatic force

Colloidal particles often carry electrical charges. The electric potential around charged particles can act as a barrier to aggregation. The electrical double layer, consisting of a rigid layer and a stretched layer, contributes to these electrostatic forces. Charged particles repel each other, maintaining stability by preventing close approach.

Stern Layer: Strongly bounded ions Diffuse Layer: Loosely associated counter ions

3. Static force

Static immobilization occurs when polymers are attached to the surface of colloidal particles. These polymer chains form a physical barrier that prevents the particles from coming close enough to experience attractive forces. This type of immobilization is especially useful in non-aqueous systems.

Polymer Chain

Mechanisms of stability

DLVO principle

The DLVO theory, developed by Derjaguin, Landau, Verwey, and Overbeek, describes the stability of colloidal dispersions by considering the balance between van der Waals attractive forces and repulsive electrostatic forces. The theory predicts whether particles will aggregate based on the potential energy as a function of the distance between the particles.

The total potential energy, V_total, is given by:

V_total = V_attractive + V_repulsive

Where V_attractive is the energy due to van der Waals forces and V_repulsive is the energy due to electrostatic forces. According to this theory the stability of a colloid is determined by the presence of an energy barrier. If the kinetic energy of the particles is less than this energy barrier, the system remains stable.

collected steady

Stokes' Law and sedimentation

Another factor affecting colloidal stability is sedimentation due to gravity. Stokes' law describes the settling velocity of spherical particles in a fluid. According to Stokes' law, the terminal velocity v is given by:

v = (2/9) * (r^2 * (ρ_particle - ρ_fluid) * g) / η

where r is the radius of the particle, ρ_particle and ρ_fluid are the densities of the particle and fluid, g is the acceleration due to gravity, and η is the dynamic viscosity of the fluid. The smaller the particles in a colloid sediment, the slower they settle, and stability is often increased by reducing particle size and increasing the viscosity of the fluid.

Factors affecting colloidal stability

Several factors affect the stability of a colloid:

pH

The pH of a colloidal system affects the charge on the particle surface because it affects the ionizable groups. Changes in pH can neutralize charges and lead to instability. For example, amino acid-based proteins in colloids can lose stability if the pH is adjusted to their isoelectric point where their net charge is zero.

Temperature

Increasing the temperature can provide the kinetic energy needed to overcome repulsion forces, leading to aggregation. In addition, changes in temperature can affect solubility, viscosity, and reaction rates that indirectly affect colloidal stability.

Ionic strength

The concentration of ions in the medium affects the thickness of the electric double layer. An increase in ionic strength compresses the double layer thereby reducing repulsion, which can result in coagulation or flocculation. The slight presence of certain multivalent ions can have significant destabilizing effects.

Ways to increase sustainability

Several measures can be taken to ensure the stability of colloidal systems:

Surface modification

Chemically modifying the surface of colloidal particles can enhance stability. Coating the particles with surfactants or adding functionality to bind polymers aids in steric stabilization.

Use of surfactants

Surfactants can be added to change the charge of the particles and increase the repulsion between the particles. This is a common way to stabilize emulsions and foams.

pH adjustment

By adjusting the pH to prevent the particles from reaching their isoelectric point, which would maximize the net surface charge, aggregation can be prevented.

Conclusion

Colloidal stability is subtle and is governed by a balance between attractive and repulsive forces. Understanding these forces and environmental factors plays a vital role in the design and application of stable colloidal systems in various industries. Techniques such as DLVO theory, control of ionic strength, and surface modification provide insights into the design of new colloidal materials. Continuing research and technological advancement in colloid chemistry are expanding the capabilities and applications of these fascinating materials.


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Colloidal Stability

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