Nano Superfine Poly(N- isopropylacrylamide)/PVA Composite Fibrous and Its Thermal-switching Function

摘要

Shape memory polymers are intelligent or smart materials, which represent a promising class of materials that can be responsive to a variety of environmental stimuli, such as change of pH, temperature, ionic strength, or electric field, and the presence of a specific chemical substrate. When they are stimulated, their volume phase transits from swollen to shrunk or vice versa. Thermally activated polymer, poly(N-isopropylacrylamide) (PNIPAAm), has been of great interest because its aqueous solution can undergo fast, reversible switching around its lower critical solution temperature (LCST) at about 29?38°C (according to its structure). In water, PNIPAAm polymer chains show an extended conformation below the LCST because of strong hydration, but change to a compact form when it is above the LCST due to sudden dehydration. The special structures formed with water molecules, and the hydrophilic groups on PNIPAAm chains lead to a reversible formation and cleavage of hydrogen bonds between the hydrophilic groups and surrounding water molecules upon a change in temperature, i.e., the reversible switching effect from hydrophilic to hydrophobic.