"Tuning Colloidal Interactions with Adsorbed Functional Polymers"


Sven Behrens

Abstract: Colloidal dispersions are fascinatingly versatile materials; they are ubiquitous in nature and form the basis of many industrial products we encounter every day.  The stability, transport and optical properties of colloidal dispersions hinge on the interaction between the particle surfaces. This interaction can be modified by adsorbed polymer and further tuned by the polymer?s response to changes in the surrounding solution. We have studied the effects of charged and neutral polymer adsorbates on the interaction of a colloidal particle with a flat substrate, using the uncommon but particularly sensitive method of total internal reflection microscopy (TIRM). The results reveal a subtle interplay of steric, electrostatic, and van der Waals forces.  The same principles govern the behavior of emulsions, another type of colloidal systems. Additional emulsion-specific properties like the instability against coalescence and ripening can also be addressed through adsorbed polymeric species. As an example, novel surfactant-free emulsions stabilized by pH and temperature switchable microgels shall be discussed, which offer unprecedented stability control.