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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
Definition of Dissociation Constant: It is a measure of the extent to which a compound separates into its components in solution. For a general reaction: $\text{AB} \leftrightarrow \text{A} + \text{B}$ the dissociation constant is given by :$K_d = \frac{[A][B]}{[AB]}$ Properties of Dissociation Constant: Equilibrium: Indicates the position of equilibrium for dissociation reactions. Strength of Interaction: … Read more
Definition of Dipole Moment: It is a measure of the separation of positive and negative charges in a molecule. It is given by: $\mu = q \cdot d$ where q is the charge and d is the distance between the charges. Measured in Debye units (D), the dipole moments indicate the polarity of a molecule. … Read more
Definition: Dielectric Constant is a measure of a material’s ability to store electrical energy in an electric field. It is the ratio of the permittivity of the material (ε) to the permittivity of free space (ε0) $\kappa = \frac{\varepsilon}{\varepsilon_0}$ Properties: Capacitance: The dielectric constant affects the capacitance of a capacitor, given by: $C = \kappa … Read more
Definition of Optical Rotation Optical Rotations refers to the rotations of the plane of polarization of polarized light as it passes through an optically active substance. It is quantified as $\alpha = [\alpha] \cdot l \cdot c$ where: α is the observed rotation (degrees). [α] is the specific rotation (degrees·dm⁻¹·g⁻¹·mL). l is the path length … Read more
