Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Hoboken, New Jersey 07030, USA.
ACS Nano. 2009 Nov 24;3(11):3595-605. doi: 10.1021/nn900655z.
We report on reversible temperature-triggered swelling transitions in hydrogen-bonded multilayer films of a polycarboxylic acid and stimuli-responsive block copolymer micelles (BCMs). A neutral hydrogen-bonding temperature-responsive diblock copolymer, poly(N-vinylpyrrolidone)-b-poly(N-isopropylacrylamide) (PVPON-b-PNIPAM), was synthesized by macromolecular design via the interchange of xanthates (MADIX). The block copolymer exhibited reversible micellization, forming PNIPAM-core micelles with PVPON coronae in 0.01 M buffer solutions at temperatures higher than 34 degrees C, or in solutions with high salt concentrations (C(NaCl) > 0.4 M) at 20 degrees C. The PVPON-b-PNIPAM BCMs were then assembled with poly(methacrylic acid) (PMAA) at acidic pH and higher temperature using the layer-by-layer (LbL) technique. Within the hydrogen-bonded multilayer, BCMs were stabilized through hydrogen bonding between PVPON and PMAA units and, unlike in solution, did not dissociate into unimers in low-salt solution at T < 34 degrees C. Instead, PVPON-b-PNIPAM BCMs reversibly swelled within film in response to temperature- or salt-concentration variations, reflecting collapse and dissolution of the BCM PNIPAM cores. The capacity of BCM/PMAA films to retain hydrophobic molecules was also dramatically dependent on temperature and/or ionic strength. The characteristic release time of pyrene from a BCM/PMAA film decreased from 80 to 10 min upon a decrease in temperature from 37 to 20 degrees C. In addition, at 20 degrees C, ionic strength was also capable of controlling the collapse of PNIPAM micellar cores and the subsequent film swelling and pyrene release rate. Incorporation of stimuli-responsive BCM micelles within LbL films opens new opportunities in designing nanoscale films capable of controlling molecular swelling, transport, and diffusion in response to environmental stimuli.
我们报告了氢键多层膜中羧酸和刺激响应嵌段共聚物胶束（BCM）可逆的温度触发溶胀转变。通过黄原酸酯（MADIX）的交换，通过大分子设计合成了中性氢键温度响应两亲性嵌段共聚物聚（N-乙烯基吡咯烷酮）-b-聚（N-异丙基丙烯酰胺）（PVPON-b-PNIPAM）。该嵌段共聚物在高于 34°C 的温度下或在 20°C 下盐浓度（C（NaCl）> 0.4 M）较高的溶液中，表现出可逆的胶束化，形成以 PVPON 为壳的 PNIPAM 核胶束。然后，在酸性 pH 值和较高温度下，通过层层（LbL）技术将 PVPON-b-PNIPAM BCM 与聚（甲基丙烯酸）（PMAA）组装在一起。在氢键多层膜中，BCM 通过 PVPON 和 PMAA 单元之间的氢键稳定，与溶液不同，在 T < 34°C 的低盐溶液中不会解离成单体。相反，PVPON-b-PNIPAM BCM 在膜内可逆溶胀，响应温度或盐浓度的变化，反映了 BCM PNIPAM 核的塌陷和溶解。BCM/PMAA 薄膜保留疏水分子的能力也强烈依赖于温度和/或离子强度。当温度从 37°C 降至 20°C 时，从[BCM/PMAA]（10）薄膜中芘的特征释放时间从 80 分钟降至 10 分钟。此外，在 20°C 时，离子强度也能够控制 PNIPAM 胶束核的塌陷以及随后的膜溶胀和芘释放速率。在 LbL 薄膜中引入刺激响应 BCM 胶束为设计能够响应环境刺激控制分子溶胀、传输和扩散的纳米级薄膜开辟了新的机会。
