Department of Chemistry, Texas A&M University, College Station, TX 77842-3012, USA.
ACS Appl Mater Interfaces. 2010 Feb;2(2):452-8. doi: 10.1021/am9007006.
Stimuli-responsive surfaces grafted with thermoresponsive polymers switch from hydrophilic to hydrophobic thermally, making these surfaces attractive in applications such as in microfluidics devices, as antifouling surfaces, and in cell culture and tissue engineering. These materials exhibit changes in wettability as the polymer undergoes a phase transition above its lower critical solution temperature (LCST). Because the presence of salts affects LCSTs in accordance to the Hofmeister series, salt effects on the wettability of these thermoresponsive surfaces will dramatically impact device performance. Prior studies of such effects have focused on the influence of anions. Detailed studies of the effects of cations have not been carried out. Here, the influence of varying cation identity in a series of mono-, di-, and trivalent sulfate salts on the wettability of a stimuli-responsive grafted surface was investigated by measuring advancing water contact angle (Theta(a)) changes. The cation-induced changes in Theta(a) were correlated with corresponding changes in surface morphology examined by AFM. The results showed that the effects of varying cations on surface wettability are as large as the effects of varying anion identity and concentration (i.e., Theta(a) changes of up to 90 degrees). Parallel studies of the effects of varying the cation identity and concentration for these same cation sulfate salts in solution show that cation variation also has a large effect on the LCST of PNIPAM, the stimuli responsive polymer component of the nanocomposite grafts that were studied. Moreover, analyses of the Theta(a) and LCST data using activity showed that the Theta(a) or LCST versus cation activity/concentration could be readily grouped by charge. Such differences are not seen in similar studies where anion identity, charge, and concentration are changed.
刺激响应表面接枝有温敏聚合物，从亲水变为疏水性，从而使这些表面在微流控设备、防污表面以及细胞培养和组织工程等应用中具有吸引力。这些材料的润湿性会发生变化，因为聚合物在其低临界溶液温度（LCST）以上发生相转变。由于盐的存在会根据豪夫迈斯特序列影响 LCST，因此这些温敏表面的润湿性对盐的影响将极大地影响器件性能。以前对这些影响的研究主要集中在阴离子的影响上。尚未对阳离子的影响进行详细研究。在这里，通过测量前进水接触角（Theta(a)）的变化，研究了一系列一价、二价和三价硫酸盐盐中阳离子种类变化对刺激响应接枝表面润湿性的影响。Theta(a)的阳离子诱导变化与通过 AFM 检查的相应表面形貌变化相关联。结果表明，阳离子对表面润湿性的影响与阴离子种类和浓度的变化一样大（即 Theta(a)变化高达 90 度）。对于这些相同的阳离子硫酸盐盐在溶液中阳离子种类和浓度变化的平行研究表明，阳离子变化对 PNIPAM 的 LCST 也有很大影响，PNIPAM 是所研究的纳米复合接枝的刺激响应聚合物成分。此外，使用活性对 Theta(a)和 LCST 数据进行分析表明，Theta(a)或 LCST 与阳离子活性/浓度之间的关系可以通过电荷进行分类。在研究阴离子种类、电荷和浓度发生变化的类似研究中，不会出现这种差异。
