Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Physical Chemistry → Surface and colloidal chemistry ↓


Colloidal Stability


Colloidal stability refers to the ability of a colloidal system to remain uniformly dispersed over time. When discussing stability in this context, we are referring to resistance to processes such as aggregation, sedimentation, creaming, and fusion, which can lead to the separation of phases. Colloidal particles are typically in the range of 1 to 1000 nanometers and can be solid, liquid, or gas dispersed in a continuous phase.

Understanding colloidal systems

A colloid is a mixture consisting of finely dispersed insoluble particles of one substance suspended in another substance. Examples include:

  • Milk : A liquid colloid consisting of fat droplets dispersed in water.
  • Fog : A liquid-gas colloid consisting of tiny water droplets dispersed in the air.
  • Smoke : A solid-gas colloid whose solid particles are dispersed in the air.

Factors affecting colloidal stability

Colloidal stability is affected by a variety of factors, including:

  • Electrostatic forces : These are repulsive forces that arise due to the electrical double layers surrounding colloidal particles. When the particles have the same surface charge, they repel each other, thereby aiding in stability.
  • Van der Waals forces : These are attractive forces that exist between all molecules. They contribute to the aggregation of particles.
  • Static hindrance : The presence of large molecules adsorbed on the surface of colloidal particles can physically prevent aggregation by creating a barrier.
  • Hydration forces : Water molecules can form hydration shells around colloidal particles, which can stabilize the system.

DLVO principle

The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory explains colloidal stability by combining electrostatic repulsion and van der Waals attraction forces. According to this theory, the total potential energy of interaction between two colloidal particles is given by the sum of the attractive and repulsive forces.

    V t = V a + V r

Where:

  • V t is the total potential energy.
  • V A is the van der Waals attraction potential.
  • V R is the electrostatic repulsion potential.

Potential energy curve

    ,
    ,
    | Free |
    | Energy |
    ,
    ,
    ,
    ,
    +-----------------------> Separation

The potential energy curve shows the interplay of attractive and repulsive forces. The primary minimum corresponds to particle aggregation, while the secondary minimum can still lead to reversible aggregation. The maximum represents a barrier that must be overcome for the particles to come closer.

In practical terms, if the repulsion at the peak of the curve is greater than the thermal energy, the particles will remain at rest.

Types of colloidal stability

Based on different mechanisms, colloids can be stabilized through the following:

  • Electrostatic stability : This is achieved by ensuring that the particles have the same charge, causing repulsion.
  • Static stability : adsorption or grafting of polymers onto particle surfaces hinders close access.
  • Thermodynamic stability : This occurs when there is a decrease in free energy due to interactions between the colloid and the components of the medium, causing the system to become stable.

Visual diagram of electrostatic and steric stability

    ,
    ,
    , 
    ,
     electrostatic steric

Zeta potential

Zeta potential is a key indicator of colloidal stability. It is the electric potential across the sliding plane of a particle moving in a solution. It shows how strongly the particles will repel each other, hence their stability.

A high zeta potential (positive or negative) usually indicates stability, as the particles will repel each other and resist aggregation.

Measuring colloidal stability

There are several methods for measuring the stability of colloidal systems:

  • Dynamic light scattering (DLS) : measures particle size and distribution, estimates stability.
  • Electrophoretic light scattering (ELS) : This is used to measure zeta potential, assessing surface charge properties.
  • Observations over time : Visualization of sedimentation or other separation phenomena.

Applications of colloidal stability

Colloidal stability is important in a variety of industries:

  • Pharmaceuticals : Stable colloids are essential for drug delivery systems.
  • Food industry : Ensuring the stability of emulsions and controlling the texture and longevity of products such as mayonnaise and creams.
  • Cosmetics : Providing consistent dispersion in lotions and creams.

Challenges and strategies

Maintaining colloidal stability can be challenging due to changes in the environment, impurities, and fluctuations in concentration. Strategies to enhance stability include:

  • pH adjustment : Altering the pH to optimize charge repulsion.
  • Additives : Using surfactants and polymers to increase static and electrostatic stability.
  • Control of ionic strength : Modifying the concentration of ions to affect the electrostatic repulsion and compression of the electrical double layer.

Conclusion

Colloidal stability is important in many areas of science and industry. By understanding the underlying forces, including electrostatic and van der Waals forces, as well as techniques such as DLVO theory, professionals can create stable colloidal systems. Maintaining such stability requires a comprehensive understanding of physical chemistry and strategic interventions to ensure that products and applications that rely on colloidal systems work effectively and efficiently.


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Colloidal Stability

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