Abstract
Some polymer gels are capable of undergoing large volume changes and significant density changes under the influence of solvent composition and temperature. Such characteristics are of interest in the design of small underwater devices. Studies have been conducted on the effects of temperature on the density and volume of poly(N-isopropylacrylamide) (NIPA) gels. The gels were investigated in solutions of distilled water and solutions of natural seawater, which has an approximate salinity of 35 parts per thousand (ppt). For each solution, the effect of temperature from 5 to 50°C was investigated. Such gels contract significantly when heated above their phase transition temperatures. The transition temperature for gels in seawater, 26-28°C, was found to be lower than for gels in distilled water, 33-34°C. Gels in seawater become more dense at higher temperatures, whereas gels in distilled water decrease in density. Short-term tests reveal that such NIPA gels realize full contraction after 4-6 h, but re-swelling takes longer. Density values fluctuate greatly in the first few hours due to phase coexistence. Mechanical tests on the NIPA gels showed a marked increase in mechanical strength and elastic modulus as temperature was increased above the phase transition temperature.
