Construction of Infared-Excitation Nano-meter Scale Spectroscopic Surface Analyzer and Its Application to Polymer-Water Interfaces

The structure and hydrogen bonding of water in the vicinity of zwitterionic polymers such as PolyCMB (CMB, carboxybetaine monomer) and a random copolymer of CMB and n-butyl methacrylate, Poly(CMB-r-BMA), were analyzed in their aqueous solutions and thin film using vibrational spectroscopy. The number of hydrogen bonding collapsed by the presence of one monomer residue (N_<corr> value) of water-soluble zwitterionic polymers were much smaller than those for ordinary polyelectrolytes and close to those for nonionic water-soluble polymers. Furthermore, the O-H stretching band of vibrational spectra for the water incorporated in the film of zwitterionic copolymer with a large BMA content was similar to that for free water, which is in contrast with the drastic change in the O-H stretching band of water incorporated in polymer films such as poly(methyl methacrylate) (PMMA) and poly(n-butyl methacrylate) (PBMA). The observation with an atomic force microscope (AFM) confirmed the responsiveness of zwitterionic copolymer films to the sorption and desorption of water from the polymer films. The adhesion of platelets to zwitterionic copolymer films (Poly(CMB-r-BMA), for example) was much less than that to PMMA and PBMA. With an increase in the content of CMB residue, the number of human platelets adhered to the Poly(CMB-r-BMA) film drastically decreased and then gradually increased, probably due to the increase in the roughness of the film surface. These results suggest that the monomer residues with a zwitterionic structure do not significantly disturb the hydrogen bonding between water molecules in both aqueous solution and thin film systems, resulting in the excellent blood-compatibility of the zwitterionic polymers.