Experimental and theoretical investigation of the interfacial phenomenon associated with wetting of trisiloxane surfactant solutions

Abstract

Surface active agents have been successfully employed in numerous industrial, agricultural and biomedical applications for decades. Trisiloxane surfactants in particular have proved to be exceptionally effective as wetting enhancers; hence the name ‘superspreaders’. Since the early ‘90s these extraordinary surfactants have become an irreplaceable component in various products and processes. However, the true nature of their specific wetting behaviour has not been fully revealed and their underlying wetting mechanisms are still poorly understood despite substantial scientific interest during the last decades. In this thesis is an attempt to shed light on specific wetting and spreading behaviour of trisiloxane solutions. Commercial superspreader products were tested in various environments in order to get further insight into their performance in specific practical applications. Experimental investigation of wetting of superspreader solutions on surfaces of different hydrophobicity and comparison to that of a conventional surfactant revealed superiority of trisiloxanes. Exceptional interfacial activity was explained in terms of the specific chemical structure and ‘T’-shape of the molecule. However, sensitivity of the trisiloxane head to low pH and long-time ageing in aqueous environment was revealed. Performance of binary mixtures of commercial superspreaders and conventional surfactant was also assessed. Behaviour of trisiloxanes in the capillary action was studied. Finally, a comprehensive mathematical model for trisiloxane wetting, which incorporates diffusion as the governing factor of the wetting process, was developed.