Specific Ion Effects in Thermo-Responsive Polymer Solutions

Stimuli-responsive polymers are macromolecules that undergo a significant change in conformation and interactions in response to an external stimulus such as temperature and addition of salts. The applications of these materials are numerous ranging from biomedical applications to fabrication of smart surfaces.

The present PhD thesis deals with understanding the fundamentals and mechanisms, which control the physiochemical properties of stimuli-responsive polymers in aqueous saline solutions. The whole study can be divided into two sections: (i) polymers in bulk solution and (ii) polymers adsorbed/grafted to a solid/aqueous interface.

The first research approach comprises of three subprojects mainly concerned with understanding the mechanisms through which the salts can affect the polymer stability in solution, an effect that is widely known as the Hofmeister effect. The second research approach includes two subprojects that address adsorption and behavior of homo- and copolymers at solid/aqueous interfaces.

Besides understanding the fundamentals of polymer properties at the interfaces, this part aims to indicate how changing the structure of the polymers or addition of salts can affect the structure of the polymer layer. The experimental methods that have been used in this project can also be divided into bulk-related and surface-related measurements.

Differential scanning calorimetry was used in order to obtain the phase transition temperature of the polymer solutions, as well as thermodynamics of the transition. Dynamic light scattering was employed to assess the hydrodynamic size of the polymer coils and interchain aggregates. To study adsorption, hydration and conformation of the polymers at the solid/aqueous interfaces, quartz crystal microbalance with dissipation monitoring was used.

Ultimately, atomic force microscopy imaging and colloidal probe measurements were conducted to study the topography of the polymer layers and the interactions between the polymer-coated surfaces.