KINETICS OF CONTACT-ANGLE FORMATION AT THE GAS-LIQUID SOLID INTERPHASE

An apparatus is described which allows both the thin film profile and the bubble profile to be determined as a function of time in the interphase region of a solid substrate approaching a gas bubble in an aqueous solution of a cationic surface active agent. The apparatus allows the rate of approach of the solid substrate to the bubble to be carefully controlled. Results obtained with the equipment are given for experiments carried out using cleaved mica, a molecularly smooth surface, as a substrate and aqueous solutions of dodecyltrimethylammonium bromide. The contact angle was determined as a function of time after bubble-substrate contact. In the concentration region 10(-5) to 10(-4) mol dm-3 it was found that contact angle formation occurred as a single rate process, whereas in the concentration region 10(-4) to ca 10(-2) mol dm(-3) a two-step process was observed with a fast initial step.