Introduction
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 is vital for developing drug delivery systems that offer optimal therapeutic outcomes.
Key Concepts of Surface and Interfacial Phenomena
Liquid Interfaces
Occur between immiscible liquids (e.g., oil and water) and are crucial for emulsions and suspensions.
Surface and Interfacial Tensions
Surface Tension: Force minimizing liquid surface area.
Interfacial Tension: Force between two immiscible phases, impacting emulsion and foam stability.
Surface Free Energy
Energy needed to increase surface area; affects wetting and stability of coatings and films.
Measuring Tensions
Methods include Wilhelmy Plate, Drop Weight, and Capillary Rise techniques to control formulation behavior.
Spreading Coefficient
Influences the ability of one liquid to spread over another, impacting ointment spreadability.
Adsorption at Liquid Interfaces
Accumulation of molecules (e.g., surfactants) stabilizes emulsions and enhances drug solubility.
Surface-Active Agents (Surfactants)
Reduce tensions and stabilize emulsions, essential in formulations for solubilization.
Hydrophile-Lipophile Balance (HLB) Scale
Determines surfactant suitability for water-in-oil or oil-in-water emulsions.
Solubilization
Incorporates poorly soluble substances into solutions using surfactants, enhancing drug bioavailability.
Detergency
Surfactants remove unwanted substances from surfaces, relevant in equipment and skin cleaning.
Adsorption at Solid Interfaces
Molecules accumulate on solids, affecting drug stability and interactions with packaging.
Importance in Pharmaceutical Sciences
These surface and interfacial phenomena are essential for designing stable, effective drug delivery systems such as emulsions, suspensions, and ointments.
By controlling these interactions, pharmaceutical scientists can optimize drug release, improve bioavailability, and ensure the therapeutic efficacy of formulations.