ABSTRACT
This chapter addresses the influence of light on dynamic interfacial properties of aqueous solutions containing mixtures of 4,40-bis(trimethylammoniumhexyloxy) azobenzene bromide (BTHA) and sodium dodecylsulfate (SDS) by analyzing the shapes of pendant bubbles of air. The interfacial states of freshly created surfaces relax to equilibrium through two processes that
possess clearly distinguishable characteristic times. The first process, a fast process with a characteristics time <1 s, is independent of the state of illumination of the surfactant system and is associated with the transport of monomeric SDS to the surface. The second relaxation process, which is substantially slower than the first one, exhibits a characteristic time that is a strong function of the illumination of the surfactant system. Without prior or concurrent illumination with UV light, the characteristic time of the second process is 1500 s. With prior or concurrent illumination with UV light, the characteristic time of the second process is reduced to 50 s and 160 s, respectively. The second relaxation process is associated with the transport of BTHA to the interface and regulated through the influence of UV light on the state of aggregation of the surfactants in bulk solution. The characteristic time of the slow interfacial relaxation process is accelerated by five orders of magnitude by the addition of 1 : 1 electrolyte to mixtures of BTHA and SDS. Measurement of the intensity of visible light scattered from bulk solutions of BTHA and SDS reveals the presence of large vesicle-sized aggregates in bulk solution, independent of whether the process of assembly is triggered by the mixing of the two surfactants or by illumination with visible light.
