NQPI Seminar | Polymer-solvent interaction and molecular reorientation: Implication to solvent-assisted deformation at the polymer surface using AFM and SFG spectroscopy, Oct. 20

The Nanoscale and Quantum Phenomena Institute (NQPI) 's Seminar Forum series features Tharushi Ambagaspitiya discussing "Polymer-solvent interaction and molecular reorientation: Implication to solvent-assisted deformation at the polymer surface using AFM and SFG spectroscopy" Oct. 20 at 4:10 p.m. in Walter 245.

Ambagaspitiya is a graduate student in Chemistry & Biochemistry at Ohio University.

Abstract : 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; D ₂ O and CDCl ₃ 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). 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. Methoxy group (-OCH ₃ ) of polyMEMA shows the symmetric stretch vibration at ~2810 cm ^-1 . The changes in the relative intensity of the peak on fitted spectra showed the polyMEMA surface undergoes molecular reorganization when exposed to D ₂ O and CDCl ₃ . Orientational analysis showed the -OCH ₃ group positions itself closer to the surface normal at the polymer-liquid interface under D ₂ O. However, -OCH ₃ group points away from the surface normal when polyMEMA is exposed to less polar CDCl _3. AFM images and force measurements showed swelling and softening of polyMEMA surface while exposed to D ₂ O. Upon removal of D ₂ O, 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. Dissolution of the polymer when exposed to CDCl ₃  was also evident from AFM studies.