Definition of Adsorption at Solid Interfaces Adsorptions at solid interfaces involves the accumulation of molecules from a liquid or gas onto a solid surface. Types of Adsorption: Physical Adsorption (Physisorption) Forces: Weak van der Waals forces; reversible. Characteristics: Occurs at low temperatures; decreases with heat. Forms multilayers as molecules are loosely held. Example: Adsorption of … Read more
Definition of Detergency Detergency is the process by which surfactants clean surfaces by removing dirt, oils, and other contaminants. Mechanism Wetting: Surfactants lower surface tension, allowing cleaning solutions to spread. Emulsification: Oils and greases are emulsified and suspended. Dispersion: Particulate soils are dispersed and prevented from re-deposition. Factors Influencing Detergency Surfactant Concentration: Must be above … Read more
Definition of Solubilization Solubilization is the process of dissolving a solute into a solvent with the aid of surfactants, forming a thermodynamically stable isotropic solution. Mechanism Micellar Solubilization: Incorporation of hydrophobic solute molecules into the hydrophobic core of micelles. Phase Behavior: Surfactants above the CMC facilitate solubilization. Factors Affecting Solubilization Surfactant Structure: Tail length and … Read more
Definition of Surfactants Surfactants are compounds that reduce surface and interfacial tensions by concentrating at the interface due to their amphiphilic nature. Classification of Surfactant Anionic Surfactants Charge: Negative in water. Functional Groups: Sulfate, sulfonate, or carboxylate. Example: Sodium lauryl sulfate (SLS) – used in shampoos, toothpaste, detergents. Characteristics: High detergency and foaming; can be … Read more
Definition of Adsorption at Liquid Interfaces Adsorptions at liquid interfaces involves the accumulation of molecules (adsorbates) at the boundary between two phases, reducing surface or interfacial tension. Mechanism of Adsorption at Liquid Interfaces Surface Activity: Molecules with both hydrophilic and hydrophobic regions orient themselves at interfaces. Gibbs Adsorptions Isotherm: Describes the relationship between surface tension … Read more
Definition of Spreading Coefficient The spreading coefficient (S) indicates the ability of one liquid to spread over another. It is defined as: $S = \gamma_S – (\gamma_L + \gamma_{SL})$ where: γS is the surface tension of the sublayer liquid. γL is the surface tension of the spreading liquid. γSL is the interfacial tension between the … Read more
Surface Tensions Surface tension is the force per unit length existing at the interface between a liquid and a gas (usually air), arising from the imbalance of intermolecular forces at the surface layer of the liquid. Molecules at the surface experience a net inward force, leading to minimized surface area. Units: Dynes per centimetre (dyn/cm) … Read more
Definition of Surface Free Energy Surface Free Energies is the excess energies at the surfaces of a material compared to the bulk. It quantifies the work required to create a unit area of surface. Relationship with Surface Tension: Numerically equal to surface tension in liquids. Concepts of Surface Free Energy Thermodynamics: Surfaces free energy arises because … Read more
Definition of Liquid Interface A liquid interfaces is the boundary between two immiscible liquid phases or between a liquid and another phase (solid or gas). At this boundary, the physical and chemical properties differ from those in the bulk phases due to molecular interactions unique to the interface. Types of Liquid Interface Liquid-Gas Interface: Examples … Read more
Introduction of Surface and Interfacial Phenomena Surface and Interfacial Phenomena are critical in pharmaceutical sciences as they impact the formulation, stability, and effectiveness of dosage forms like emulsions, suspensions, foams, and ointments. These phenomena describe the interactions at the boundaries (interfaces) between different phases of matter—solid, liquid, and gas. A thorough understanding of these interactions … Read more
