Impact of co-nonsolvency effects on dynamic wetting

点击翻译按钮获取中文摘要

The primary goal of this project continues to be the investigation of the dynamic wetting behavior of the polymer brushes showing cononsolvency effects. This proposal for the second funding period (FP2) heavily builds on the results of the first funding period (FP1). For this purpose, we keep the same model system: PNiPAAm brushes prepared by a grafting-to method with water and ethanol as solvent and cosolvent. In FP1 we have identified at couple of important features that suggest a coupling of dynamic wetting behavior and the cononsolvency of PNiPAAm brushes. (i) Intense (not necessarily long) prewetting with water or ethanol changes the wetting properties strongly but reversibly and in a long-time stable way. (ii) Repeated wetting and the composition of the gas phase can change the wetting properties. (iii) The changes of the wetting properties are correlated to the structural changes in the PNiPAAm-brush surface as seen with sum frequency generation spectroscopy.These results posed several important questions that we plan to address in FP2. (a) Which are the parameters of the prewetting procedure that mainly control the static and dynamic wetting properties for a successive wetting? (b) Which storage and (pre)wetting conditions strengthen or reduce the long-time stability of the induced wetting state? (c) Regarding its influence on wetting, how is cononsolvency interrelated to thermo-sensitivity of PNiPAAm? (d) Do polymer brushes exhibiting a cosolvency effect show similar features in their wetting behavior as those with cononsolvency effects? To address these questions, we will use a set of complementary experimental techniques (partially in cooperation with other groups within the SPP), see the Methods section in 2.3. (i) Dynamic wetting experiments in a broad range of well-defined contact lines velocities (from μm/s to tens of cm/s). (ii) Analytic methods like spectroscopic VIS-ellipsometry (brush layer thickness), AFM-based techniques for the mechanical characterization, SFG spectroscopy for structural information. (iii) Systematic variations of the experimental parameters, like the properties of the polymer brush (molar mass, brush thickness, cononsolvency vs. cosolvency effect), the time scales and contact-lines velocities, and the composition of the wetting liquid and gas phase In the combination of these methods, we aim for a fundamental understanding on how the wetting of polymer brushes is interrelated with the cononsolvency of the brush.