微凝胶通常用作溶质载体,尺寸在哪里,密度,微凝胶的功能取决于溶质结合。作为对微凝胶具有高亲和力的离子溶质的代表,我们在这里通过光散射技术和小角度X射线散射研究了超离液Keggin多金属氧酸盐(POMs)PW12O403-(PW)和SiW12O404-(SiW)对非离子聚(N-异丙基丙烯酰胺)(PNiPAM)微凝胶的水溶胀和内部结构的影响。由于它们的水合作用较弱,这些POM以毫摩尔浓度自发地结合到微凝胶上。因此,微凝胶在低POM浓度下带电并膨胀,令人惊讶的是,没有强烈增加体积相变温度,并在较高的POM浓度下放松。由于POM的解离抗衡离子的渗透压而引起膨胀,而去溶胀是由于POM在NaCl或过量POM溶液中的静电下在微凝胶中充当物理交联。与较低的电荷密度相关的PW比SiW的溶胀/去溶胀转变更尖锐。较弱的水合作用,和PW更强的结合。POM在定性和定量上引起离子表面活性剂和经典盐的不同溶胀作用。此外,网络柔软度和拓扑结构控制POM结合时的溶胀响应。微凝胶越软,肿胀反应越强,while,在微凝胶里面,在充电/交联时,高聚合物密度的区域比具有低聚合物密度的区域膨胀/收缩更多。因此,POM结合使得能够微调微凝胶性质并突出网络拓扑在微凝胶溶胀中的作用。因为POM在碱性pH下分解,除了PNiPAM微凝胶的典型温度响应性之外,这些POM/微凝胶系统还表现出pH响应性溶胀。
Microgels are commonly applied as solute carriers, where the size, density, and functionality of the microgels depend on solute binding. As representatives for ionic solutes with high affinity for the microgel, we study here the effect of superchaotropic Keggin polyoxometalates (POMs) PW12O403- (PW) and SiW12O404- (SiW) on the aqueous swelling and internal structure of nonionic poly(N-isopropylacrylamide) (pNiPAM) microgels by light scattering techniques and small-angle X-ray scattering. Due to their weak hydration, these POMs bind spontaneously to the microgels at millimolar concentrations. The microgels thus become charged and swell at low POM concentration, surprisingly without strongly increasing the volume phase transition temperature, and deswell at higher POM concentration. The swelling arises because of the osmotic pressure of dissociated counterions of the POMs, while the deswelling is due to POMs acting as physical cross-links in the microgels under screened electrostatics in NaCl or excess POM solution. This swelling/deswelling transition is sharper for PW than for SiW related to the lower charge density, weaker hydration, and stronger binding of PW. The POMs elicit qualitatively and quantitatively different swelling effects from ionic surfactants and classical salts. Moreover, the network softness and topology govern the swelling response upon POM binding. The softer the microgel, the stronger is the swelling response, while, inside the microgel, regions of high polymer density swell/contract more upon electric charging/cross-linking than regions with low polymer density. POM binding thus enables fine-tuning of microgel properties and highlights the role of network topology in microgel swelling. Because POMs decompose at an alkaline pH, these POM/microgel systems also exhibit pH-responsive swelling in addition to the typical temperature responsiveness of pNiPAM microgels.