| Environmentally responsive, water-soluble polymers have a wide variety of uses ranging from drug delivery to viscosity modifiers. Their utility lies in the ability to use environmental perturbations to dramatically alter the material properties. Here, we describe the interfacial properties of two types of polymers---poly (N-isopropylacrylamide) (PNIPAM) which is temperature responsive and the copolymer of N-isopropylacrylamide and glycinylacrylamide (NIPAM-N-Gly-(C 18)2), which is both temperature and pH responsive.; The interfacial properties of end-grafted temperature responsive poly (N-isopropylacryamide) (PNIPAM) were quantified by direct force measurements above and below the lower critical solution temperature of 32°C. One study was on the PNIPAM films prepared using surface initiated Atom Transfer Radical Polymerization (ATRP) to achieve higher grafting density and molecular weight. The other study was on lipid membrane supported PNIPAM chains. At the low grafting densities and molecular weights investigated, the thickness of the polymer films did not change significantly above the LCST. In contrast, significant chain collapse was observed at high grafting density and molecular weight.; Direct force measurements quantified the substantial pH-dependent change in the molecular properties of end-grafted NIPAM-N-Gly-(C18) 2 monolayers. At pH 8.0, where the glycine side chains are ionized, the polymers exhibit stereotypical polyelectrolyte behavior. Side chain neutralization at pH 5.0 causes a substantial decrease in the film thickness, and the polymer films adhere strongly. The adhesion is presumably through H-bonding between the glycine side chains. Our findings revealed the likely molecular basis of pH-dependent changes in the copolymer films and identified clear design criteria for tuning the interfacial properties of these polymer films. In addition to the study of the interfacial properties of NIPAM-Gly copolymer, we also investigated the mucoadhesive properties using SFA and Surface Plasmon Resonance (SPR), and identify key parameters that control the interaction between hydrogen bonding polymers and soluble mucin. |
