Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour
Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour
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DOI：
10.1038/s41598-019-50164-6
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发表时间：
2019-09-25
影响因子：
4.6
通讯作者：
Oberdisse, Julian
中科院分区：
文献类型：
--
作者：
Cors, Marian;Wrede, Oliver;Oberdisse, Julian
核壳微凝胶特殊的线性温度依赖性溶胀被认为与核壳结构结合了不同转变温度的材料有关。本文利用小角中子散射法研究了水中pNIPMAM核和pNNPAM壳微凝胶的结构随温度的变化。用光子相关光谱分析了胶体颗粒的膨胀行为，发现了线性膨胀。此外，这些实验也被用来检验氢气对膨胀的影响。利用一种无格式的多壳层逆蒙特卡罗方法，将小角散射数据转换为径向单体密度分布。与完全氢化的核-壳微凝胶以及H-核/D-壳结构的比较清楚地表明，核和壳单体呈梯度分布，具有很强的相互穿透性，导致核嵌入壳中的核大于其孤立的‘核-壳’前体粒子。这一令人惊讶的结果进一步推广到不同的核心交联剂含量，因为温度范围包括这两个转变。我们的分析表明，pNIPMAM-核和pNNPAM-壳微凝胶的内部结构是非均相的，并且相互渗透很强，在中间到两个转变温度的温度下，可能只允许渐进的核膨胀，从而促进了线性膨胀行为。
The peculiar linear temperature-dependent swelling of core-shell microgels has been conjectured to be linked to the core-shell architecture combining materials of different transition temperatures. Here the structure of pNIPMAM-core and pNNPAM-shell microgels in water is studied as a function of temperature using small-angle neutron scattering with selective deuteration. Photon correlation spectroscopy is used to scrutinize the swelling behaviour of the colloidal particles and reveals linear swelling. Moreover, these experiments are also employed to check the influence of deuteration on swelling. Using a form-free multi-shell reverse Monte Carlo approach, the small-angle scattering data are converted into radial monomer density profiles. The comparison of 'core-only' particles consisting of identical cores to fully hydrogenated core-shell microgels, and finally to H-core/D-shell architectures unambiguously shows that core and shell monomers display gradient profiles with strong interpenetration, leading to cores embedded in shells which are bigger than their isolated 'core-only' precursor particles. This surprising result is further generalized to different core cross-linker contents, for temperature ranges encompassing both transitions. Our analysis demonstrates that the internal structure of pNIPMAM-core and pNNPAM-shell microgels is heterogeneous and strongly interpenetrated, presumably allowing only progressive core swelling at temperatures intermediate to both transition temperatures, thus promoting linear swelling behaviour.