Department of Mechanical Engineering, The University of Texas at Austin, 204 East Dean Keeton Street, Austin, Texas 78712, USA.
Langmuir. 2013 Jun 25;29(25):8116-24. doi: 10.1021/la401072d. Epub 2013 Jun 5.
Poly(N-isopropylacrylamide) (PNIPAM) is expected to find utility in tissue engineering and drug delivery, among other biomedical applications. These applications capitalize on the intrinsic lower critical solution temperature (LCST) of the polymer: below the LCST, enthalpic gain from intermolecular hydrogen bonding between PNIPAM and water molecules dominates the solvation; above the LCST, entropic effects resulting from the intramolecular hydrogen bonding between the carboxyl and amide groups of PNIPAM lead to water expulsion. The dependence of the LCST upon the molecular weight, solvent, and solution activity (i.e., solute concentration) has been studied extensively. However, what has not been previously explored is the effect of humidity on the characteristic properties of the polymer. Herein, we show that the relative humidity affects the water adsorption dynamics of PNIPAM as well as the magnitude of the transition that occurs at the LCST of the polymer. In short, the magnitude of the LCST transition decreases with an increasing relative humidity, and the time period over which adsorption occurs decreases with the temperature.
聚（N-异丙基丙烯酰胺）（PNIPAM）有望在组织工程和药物输送等生物医学应用中得到应用。这些应用利用了聚合物的固有低临界溶液温度（LCST）：在 LCST 以下，PNIPAM 与水分子之间的分子间氢键的焓增益主导着溶剂化；在 LCST 以上，PNIPAM 中羧基和酰胺基团之间的分子内氢键导致水分子排出，从而产生熵效应。LCST 对分子量、溶剂和溶液活度（即溶质浓度）的依赖性已经得到了广泛的研究。然而，以前尚未探索的是湿度对聚合物特性的影响。在此，我们表明相对湿度会影响 PNIPAM 的水吸附动力学以及聚合物 LCST 处发生的转变的幅度。简而言之，LCST 转变的幅度随相对湿度的增加而减小，而吸附发生的时间段随温度的升高而减小。
