The grafting of pH-responsive poly(acrylic acid) (PAA) brushes was carried out on the surface of a commercial TFC-PA membrane using surface-initiated atom transfer radical polymerization (SI-ATRP). Poly(t-butyl acrylate) was polymerized through the SI-ATRP method followed by its acid hydrolysis to form PAA hydrophilic polymer brushes. Surface morphology, permeation flux, salt rejection, and pore sizes were investigated. The contact angle for water was reduced from 50° for a pristine membrane to 27° for the modified membrane due to a modification with the hydrophilic functional group and its brush on membrane surfaces. The flux rate also increased noticeably at lower pH values relative to higher pH for the modified membranes, while the flux remains stable in the case of pristine TFC-PA membranes. There is slight transition in the water flux rate that was also observed when going from pH values of 3 to 5. This was attributed to the pH-responsive conformational changes for the grafted PAA brushes. At these pH values, ionization of the COOH group takes place below and above to influence the effective pore dimension of the modified membranes. At a lower pH value, the PAA brushes seem to permit tight structure conformation resulting in larger pore sizes and hence more flux. On the other hand, at higher pH values, PAA brushes appeared to be in extended conformation to induce smaller pore sizes and result in less flux. Further, pH values were observed to not significantly affect the NaCl salt rejection with values observed in between 98.8% and 95% and close to that of the pristine TFC-PA membranes. These experimental results are significant and have immediate implication for advances in polymer technology to design and modify the “switchable membrane surfaces” with controllable charge distribution and surface wettability, as well as regulation of water flux and salt.

中文翻译：

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通过接枝亲水性 pH 可调聚（丙烯酸）刷对 TFC-PA RO 膜进行表面改性

使用表面引发的原子转移自由基聚合（SI-ATRP）在商业 TFC-PA 膜的表面上进行 pH 响应性聚（丙烯酸）（PAA）刷的接枝。聚（丙烯酸叔丁酯）通过 SI-ATRP 方法聚合，然后进行酸水解，形成 PAA 亲水聚合物刷。研究了表面形态、渗透通量、盐截留率和孔径。由于亲水性官能团的修饰及其在膜表面的刷子，水的接触角从原始膜的 50° 降低到改性膜的 27°。与改性膜的较高 pH 值相比，较低 pH 值下的通量率也显着增加，而原始 TFC-PA 膜的通量保持稳定。当从 3 到 5 的 pH 值时，也观察到水通量速率的轻微转变。这归因于接枝 PAA 刷的 pH 响应构象变化。在这些 pH 值下，COOH 基团的电离发生在下方和上方，以影响改性膜的有效孔尺寸。在较低的 pH 值下，PAA 刷似乎允许紧密的结构构象，从而导致更大的孔径和更多的通量。另一方面，在较高的 pH 值下，PAA 刷似乎处于扩展构象中，以诱导较小的孔径并导致较小的通量。此外，观察到 pH 值不会显着影响 NaCl 盐截留率，观察到的值介于 98.8% 和 95% 之间，接近原始 TFC-PA 膜的值。