Equilibrium and kinetic aspects of the uptake of poly(ethylene oxide) by copolymer microgel particles of N-isopropylacrylamide and acrylic acid
Equilibrium and kinetic aspects of the uptake of poly(ethylene oxide) by copolymer microgel particles of N-isopropylacrylamide and acrylic acid
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DOI：
10.1021/la047966z
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发表时间：
2005-02-15
期刊：
影响因子：
3.9
通讯作者：
Vincent, B
中科院分区：
文献类型：
--
作者：
Bradley, M;Ramos, J;Vincent, B
使用微凝胶进行受控摄取和释放多年来一直是活跃的研究领域。在这项工作中，N-异丙基丙烯酰胺（NIPAM）和丙烯酸（AAc）的共聚物微凝胶，含有不同浓度的AAc和交联单体，已制备和表征。这些微凝胶对pH和温度有反应。除了监测对这些变量的变化的平衡响应之外，还研究了微凝胶颗粒在改变pH或温度时的溶胀/去溶胀速率。结果表明，适当改变pH值，含AAc的微凝胶颗粒的去溶胀速率比溶胀速率快得多。这是解释的H+和Na+离子的相对迁移率，进出的颗粒。观察到含有AAc的微凝胶在pH 8下在从20 ℃加热至50 ℃时相对缓慢地去溶胀。这归因于与微凝胶颗粒内的抗衡离子浓度的大幅增加相关的抗塌陷性。这些共聚物微凝胶的溶胀和去溶胀性能也进行了研究，在聚（环氧乙烷）（PEO）的水溶液中，不同的MW（2000-300 000）。也已经使用耗尽法确定了从溶液到微凝胶上的PEO的相应吸收量。作为AAc含量、交联剂浓度、PEO MW、pH和温度的函数的结果，已经在PEO链渗透到各种微凝胶颗粒中的容易程度和深度以及PEO与AAc部分的-COOH和/或酰胺基团的H（弱得多）之间的H-键合关联方面被合理化。最后，与聚合物吸附到刚性表面上的正常扩散时间尺度相比，PEO分子在微凝胶颗粒中的吸附和解吸已经显示出极其缓慢。
The use of mierogels for controlled uptake and release has been an area of active research for many years. In this work copolymer microgels of N-isopropylacrylamide (NIPAM) and acrylic acid (AAc), containing different concentrations of AAc and also cross-linking monomer, have been prepared and characterized. These microgels are responsive to pH and temperature. As well as monitoring the equilibrium response to changes in these variables, the rates of swelling/de-swelling of the microgel particles, on changing either the pH or the temperature, have also been investigated. It is shown that the rate of de-swelling of the microgel particles containing AAc is much faster than the rate of swelling, on changing the pH appropriately. This is explained in terms of the relative mobilities of the H+ and Na+ ions, in and out of the particles. It was observed that the microgels containing AAc, at pH 8, de-swelled relatively slowly on heating to 50 degreesC from 20 degreesC. This is attributed to the resistance to collapse associated with the large increase in counterion concentration inside the microgel particles. The swelling and de-swelling properties of these copolymer microgels have also been investigated in aqueous poly(ethylene oxide) (PEO) solutions, of different MW (2000-300 000). The corresponding absorbed amounts of PEO from solution onto the microgels have also been determined using a depletion method. The results, as a function of AAc content, cross-linker concentration, PEO MW, pH, and temperature, have been rationalized in terms of the ease and depth of penetration of the PEO chains into the various microgel particles and also the H-bonding associations between PEO and either the -COOH of the AAc moeities and/or the H of the amide groups (much weaker). Finally, the adsorption and desorption of the PEO molecules in to and out of the microgel particles have been shown to be extremely slow compared to normal diffusion time scales for polymer adsorption onto rigid surfaces.