Surfactant-Polymer interaction at the Liquid-Solid Interface

The scientific study of colloidal interactions gocs back to the nincteenth century, although colloids have been used by humanity since the beginning of time. Noncthcless, our level of understanding of colloidal interactions is still insufficient to predict many phenomena. This thesis is an attempt to build a colloidal toolbox for a wide extent of applications starting from the different colloidal interactions that take place during the removal of proteic "dirt" from hard surfaces. The toolbox contains experimental techniques applied to the study of a range of surfaces and colloidal solutions. We have deepened our comprehension in the use of polymer coatings and surfactants to remove and repel proteic dirt or bacterial attachment, taking bovine serum albumin (BSA) as a protein model for dirt. To this purpose, we have chosen a range of inexpensive hydrophilic polymers and surfactants with different headgroups. Equally important for scientists are suitable model systems to study the phenomena of interest. We have found the use of nano-sized colloidal surfaces to be comparable to that of flat-macroscopic surfaces as model systems to study dirt-removal applications. Using colloidal surfaces could present many potential advantages since the surface area is considerably increased in a small volume of sample. Also, the requisites for sample preparation and measurements are timesaving when compared to the main techniques used to investigate these systems in flat-macroscopic surfaces: SPR and QCM-D. The mechanisins of colloidal interaction in the cases of gold nanoparticle - vesicles and bacteria - polymer-coated surfaces have been investigated by building an extended DLVO model for objects of different shapes and sizes. For the first time, our model foretells an attractive interaction berween the bacterial cells and clean glass also in deionised water. The models previously proposed in the literature, neglecting the large difference in 5-potential between bacteria and glass, predicted repulsion and could not explain the experimental evidence of increased attachment to glass at low ionic strength. However, there are aspects of the mechanisins of "dirt" removal or repellency that also involve the more subtle hydrophobic interactions and, presently, cannot be managed by models. In these cases, we opted for a mainly experimental approach. We studied the interaction berween polymers and surfactants in solution since this interaction can ultimately affect dirt deposition. On the other hand, we followed the effect of surfactants on the BSA protein both in solution and on protein deposited on a hard surface. In solution, the overall order of surfactant interaction affinitics towards BSA has been found to be in accordance to literature: ncutral < zwitterionic ‹ cationic ‹ anionic. This order of interaction changes upon surfactant interaction on a BSA coated surface; which becomes zwitterionic