lInvestigation on the structure of temperature-responsive N-isopropylacrylamide microgels containing a new hydrophobic crosslinker
lInvestigation on the structure of temperature-responsive N-isopropylacrylamide microgels containing a new hydrophobic crosslinker
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DOI：
10.1080/23312009.2015.1012658
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发表时间：
2015-01-01
期刊：
影响因子：
--
通讯作者：
Pedersen, Jan Skov
中科院分区：
文献类型：
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作者：
Deen, G. Roshan;Pedersen, Jan Skov
采用表面活性剂介导的沉淀乳液聚合法制备了一种新型疏水化学交联剂交联的聚N-异丙基丙烯酰胺温敏性微凝胶。利用光散射和小角X射线散射（SAXS）研究了微凝胶的温敏特性以及交联剂对微凝胶溶胀行为的影响。随着温度的升高，微凝胶的回转半径（R-g）和流体动力学半径（R-h）减小，这是由于微凝胶从溶胀状态向坍塌状态的体积相变。由于微凝胶的交联密度较低，在转变温度以下的R-g/R-h比低于硬球。SAXS数据进行了分析，其中微凝胶被建模为具有梯度界面的核-壳颗粒的模型。在中间温度下的模型包括一个中央核心和一个更分散的外层描述挂起的聚合物链与低交联密度。在完全溶胀状态下，微凝胶被建模为具有宽梯度表面的单一组分。在坍缩状态下，它们被建模为均匀且相对紧凑的颗粒。微凝胶内的聚合物体积分数也来自基于该模型，并被发现随着温度的增加，作为结果的微凝胶的崩溃紧凑的颗粒。在微凝胶的核心中的聚合物体积分数在塌陷状态下是约60%，这是高于类似的微凝胶与亲水性和柔性交联剂交联。
Temperature-responsive poly(N-isopropylacrylamide) microgels crosslinked with a new hydrophobic chemical crosslinker were prepared by surfactant-mediated precipitation emulsion polymerization. The temperature-responsive property of the microgel and the influence of the crosslinker on the swelling behaviour was studied systematically by light scattering and small-angle X-ray scattering (SAXS). The radius of gyration (R-g) and the hydrodynamic radius (R-h) of the microgels decreased with increase in temperature due to the volume-phase transition from a swollen to a collapsed state. The ratio of R-g/R-h below the transition temperature was lower than that of hard-spheres due to the lower crosslinking density of the microgels. The SAXS data were analysed by a model in which the microgels were modelled as core-shell particles with a graded interface. The model at intermediate temperatures included a central core and a more diffuse outer layer describing pending polymer chains with a low crosslinking density. In the fully swollen state, the microgels were modelled with a single component with a broad graded surface. In the collapsed state, they were modelled as homogeneous and relatively compact particles. The polymer volume fraction inside the microgel was also derived based on the model and was found to increase with increase in the temperature as a result of collapse of the microgel to compact particles. The polymer volume fraction in the core of the microgel in the collapsed state was about 60% which is higher than that of similar microgels crosslinked with hydrophilic and flexible crosslinkers.