INTERFACIAL PHENOMENA Kuncoro Foe
REFERENCES Martin, Physical Pharmacy Remington’s Pharmaceutical Science Sprowl, Prescription Pharmacy Husa’s Dispensing of Medication Burlage, Physical Pharmacy
Interface The boundary between two or more phases (liquid-gas, liquid-liquid, liquid-solid, solid-gas, solid-solid) Liquid interfaces (liquid-gas, liquid-liquid, liquid-solid) Solid interfaces (solid-gas, solid-liquid) Interfacial tension () : dyne/cm (cgs)
Surface The boundary between other phases with gas phase Surface: gas-solid or gas-liquid interface Every surface is interface Phases: solid, liquid, gas Solid-solid is less important in pharmaceutical science Surface tension () : dyne/cm (cgs)
Utilization in Pharmacy (1) Drug adsorption in dosage form Incompatibilities (undesirable) Deodorant (desirable) Mechanism of therapeutic efficacy Antidotum Drug penetration through biological membrane, eg. anthelmintics
Utilization in Pharmacy (2) Formulation: stability and effectiveness Liquid dosage form Homogeneous system (solution) Heterogeneous system (emulsion, suspension) Interfacial phenomena should be considered, since drug absorption until the site of action
Liquid Interfaces (1) A liquid drop suspended in air tends to form a spherical shape, since (a) cohesive force adhesive force, (b) to attain the smallest surface area
Liquid Interfaces (2) Surface tension (s.t.): gaya pada permukaan untuk mempertahankan bentuknya Interfacial tension (i.t.): gaya per satuan panjang pada interface antara 2 fase zat cair yang saling tidak campur i.t. = 0, completely miscible liquid (no interfacial tension, no boundaries)
Liquid Interfaces (3) = tegangan permukaan f b = bobot maksimum supaya film tidak pecah (force to break the film) 2 L = the length of the movable bar in contact with the film
Surface & Interfacial Tension Surface Free Energy Surface & Interfacial Tension Pada umumnya untuk cairan, apabila suhu meningkat maka tension menurun karena energi kinetik molekul meningkat
Measurement Methods Du Nouy ring method/tensiometer Capillary rise method Drop weight Bubble pressure Sessile drop Wilhelmy plate
Spreading Coefficient (1) Koefisien penyebaran spreading liquid dan sublayer liquid, tergantung pada: Gaya kohesi Gaya adhesi Apabila minyak diteteskan di atas cairan: Sebagian minyak tetap dalam bentuk globul Sebagian minyak menyebar membentuk ‘film’ pada permukaannya
Spreading Coefficent (2) Contoh soal: heksana = 18 dyne/cm, air = 72,8 dyne/cm, LS = 50,8 dyne/cm Apa yang terjadi apabila heksana diteteskan pada air? Apa yang terjadi apabila air diteteskan pada heksana?
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