Methacrylate based polymers are widely used in various industries. In many applications, polymers often get exposed to different liquid environments leading to the possibility of polymer dissolution. When exposed to solvents, polymers undergo structural deformation and molecular reorientation. This affects the usability and durability of polymers. In this work, two polymer thin films of poly(2-methoxy ethyl methacrylate) (polyMEMA) and poly (2-tertbutoxy ethyl methacrylate) were exposed to two solvents; D2O and CDCl3 simultaneously. Polymer thin films were prepared by spin coating 1% polymer solution in chloroform on quartz windows followed by annealing. Changes at the polymer – solvent interface were studied using sum frequency generation (SFG) spectroscopy and atomic force microscopy (AFM) supported with molecular simulation studies. SFG spectroscopy is a surface specific, non-linear optical technique which yields vibrational spectra of molecules at interfaces. By using this technique, the interfacial molecular organization of polymers before, during, and after exposure to solvent molecules was studied. AFM imaging was used to compare microscopic surface changes at polymer – solvent interface before, during, and after exposure to solvent molecules. Appropriate closed fluid cells were used in both techniques to ensure effective solvent exposure. Orientational analysis showed the -OCH3 group of polyMEMA (~2810 cm-1) positions itself closer to the surface normal at the polymer - solvent interface under D2O and points away from the surface normal when exposed to less polar CDCl3. AFM images and force measurements showed swelling and softening of polyMEMA surface while exposed to D2O. Upon removal of D2O, the swelled areas were imprinted on the surface as craters showing that the amorphous glassy structure of the polymer was disrupted due to solvent exposure. The chemical affinity and characteristics of the solvents define the conformational change at the interace. It had direct implications to interfacial processes involving adsorption, permeation eventually leading to swelling, aggregation, and possibly dissolution.

Polymer-solvent interaction and molecular reoreintation: Implication to solvent-assisted deformation and aggregation at the polymer surface using AFM and SFG spectroscopy

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