Wang Peixi, Geiger Christina, Kreuzer Lucas P, Widmann Tobias, Reitenbach Julija, Liang Suzhe, Cubitt Robert, Henschel Cristiane, Laschewsky André, Papadakis Christine M, Müller-Buschbaum Peter
Lehrstuhl für Funktionelle Materialien, Physik Department, Technische Universität München, James-Franck-Street 1, Garching 85748, Germany.
Institut-Laue-Langevin, 6 rue Jules Horowitz, Grenoble 38000, France.
Langmuir. 2022 Jun 7;38(22):6934-6948. doi: 10.1021/acs.langmuir.2c00451. Epub 2022 May 24.
The water swelling and subsequent solvent exchange including co-nonsolvency behavior of thin films of a doubly thermo-responsive diblock copolymer (DBC) are studied via spectral reflectance, time-of-flight neutron reflectometry, and Fourier transform infrared spectroscopy. The DBC consists of a thermo-responsive zwitterionic (poly(4-((3-methacrylamidopropyl) dimethylammonio) butane-1-sulfonate)) (PSBP) block, featuring an upper critical solution temperature transition in aqueous media but being insoluble in acetone, and a nonionic poly(-isopropylmethacrylamide) (PNIPMAM) block, featuring a lower critical solution temperature transition in water, while being soluble in acetone. Homogeneous DBC films of 50-100 nm thickness are first swollen in saturated water vapor (HO or DO), before they are subjected to a contraction process by exposure to mixed saturated water/acetone vapor (HO or DO/acetone-d6 = 9:1 v/v). The affinity of the DBC film toward HO is stronger than for DO, as inferred from the higher film thickness in the swollen state and the higher absorbed water content, thus revealing a pronounced isotope sensitivity. During the co-solvent-induced switching by mixed water/acetone vapor, a two-step film contraction is observed, which is attributed to the delayed expulsion of water molecules and uptake of acetone molecules. The swelling kinetics are compared for both mixed vapors (HO/acetone-d6 and DO/acetone-d6) and with those of the related homopolymer films. Moreover, the concomitant variations of the local environment around the hydrophilic groups located in the PSBP and PNIPMAM blocks are followed. The first contraction step turns out to be dominated by the behavior of the PSBP block, whereas the second one is dominated by the PNIPMAM block. The unusual swelling and contraction behavior of the latter block is attributed to its co-nonsolvency behavior. Furthermore, we observe cooperative hydration effects in the DBC films, that is, both polymer blocks influence each other's solvation behavior.
通过光谱反射率、飞行时间中子反射仪和傅里叶变换红外光谱，研究了一种双热响应性二嵌段共聚物（DBC）薄膜的水溶胀及随后的溶剂交换，包括共非溶剂行为。该DBC由一个热响应性两性离子（聚（4 - （（3 - 甲基丙烯酰胺基丙基）二甲基铵）丁烷 - 1 - 磺酸盐））（PSBP）嵌段和一个非离子聚（N - 异丙基甲基丙烯酰胺）（PNIPMAM）嵌段组成。PSBP嵌段在水性介质中具有上临界溶液温度转变，但不溶于丙酮；PNIPMAM嵌段在水中具有下临界溶液温度转变，且可溶于丙酮。首先将厚度为50 - 100 nm的均匀DBC薄膜在饱和水蒸气（H₂O或D₂O）中溶胀，然后通过暴露于混合饱和水/丙酮蒸气（H₂O或D₂O/丙酮 - d₆ = 9:1 v/v）使其经历收缩过程。从溶胀状态下较高的膜厚度和较高的吸水含量推断，DBC薄膜对H₂O的亲和力强于对D₂O的亲和力，从而揭示出明显的同位素敏感性。在水/丙酮混合蒸气引起的共溶剂诱导转变过程中，观察到薄膜有两步收缩，这归因于水分子的延迟排出和丙酮分子的吸收。比较了两种混合蒸气（H₂O/丙酮 - d₆和D₂O/丙酮 - d₆）以及相关均聚物薄膜的溶胀动力学。此外，跟踪了位于PSBP和PNIPMAM嵌段中亲水性基团周围局部环境的伴随变化。结果表明，第一步收缩由PSBP嵌段的行为主导，而第二步收缩由PNIPMAM嵌段主导。后一个嵌段异常的溶胀和收缩行为归因于其共非溶剂行为。此外，我们在DBC薄膜中观察到协同水合效应，即两个聚合物嵌段相互影响彼此的溶剂化行为。
