DYNAMIC CONTACT-ANGLE MEASUREMENT OF TEMPERATURE-RESPONSIVE SURFACE-PROPERTIES FOR POLY(N-ISOPROPYLACRYLAMIDE) GRAFTED SURFACES

We have investigated temperature modulation of surface properties for hydrophilic/hydrophobic changes using poly(N-isopropylacrylamide) (PIPAAm). Two types of PIPAAm were used as surface modifiers: an end-functionalized PIPAAm with a carboxyl end group and a poly(IPAAm-co-acrylic acid) copolymer. By means of dynamic contact angle measurements in water, the wettability of terminally polymer grafted surfaces using end-functionalized PIPAAm with a carboxyl end group were compared with that of multipoint polymer grafted surfaces using PIPAAm copolymers containing carboxyl groups along the polymer chain. Each PIPAAm grafted surface showed completely hydrophilic properties under 20 degrees C. Although multipoint grafted surfaces demonstrated surface property changes near 24 degrees C, the extent of decrease in the hydrophilic property was small compared to that of the terminal grafted surfaces. Terminal grafted surfaces demonstrated hydrophilic/hydrophobic surface property changes at 24 degrees C with small temperature increases. The value of cos theta changes from 0.63 at 20 degrees C to 0.05 at 26 degrees C. Temperature-responsive surface property changes which terminal grafted surfaces demonstrated were more rapid and significant than that of multipoint grafted surfaces;demonstrated. These features were suggested to be due to more effective restrited conformational freedom for PIPAAm graft chains which influence polymer dehydration and hydrogen bonding with water molecules.