Cors Marian, Wrede Oliver, Wiehemeier Lars, Feoktystov Artem, Cousin Fabrice, Hellweg Thomas, Oberdisse Julian
Department of Physical and Biophysical Chemistry, Bielefeld University, Universitätsstr. 25, 33615, Bielefeld, Germany.
Laboratoire Charles Coulomb (L2C), University of Montpellier, CNRS, 34095, Montpellier, France.
Sci Rep. 2019 Sep 25;9(1):13812. doi: 10.1038/s41598-019-50164-6.
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.
核壳微凝胶特殊的线性温度依赖性溶胀现象据推测与结合了不同转变温度材料的核壳结构有关。在此，我们利用选择性氘化的小角中子散射研究了水相中聚N-异丙基丙烯酰胺核与聚N,N-二甲基丙烯酰胺壳微凝胶的结构随温度的变化。光子相关光谱用于仔细观察胶体颗粒的溶胀行为，并揭示了线性溶胀。此外，这些实验还用于检验氘化对溶胀的影响。使用无形式的多壳反向蒙特卡罗方法，将小角散射数据转换为径向单体密度分布。将由相同核组成的“仅核”颗粒与完全氢化的核壳微凝胶，最后与氢核/氘壳结构进行比较，明确表明核单体和壳单体呈现出具有强烈相互渗透的梯度分布，导致核嵌入比其孤立的“仅核”前体颗粒更大的壳中。这一惊人结果进一步推广到不同的核交联剂含量，以及涵盖两个转变温度的温度范围。我们的分析表明，聚N-异丙基丙烯酰胺核与聚N,N-二甲基丙烯酰胺壳微凝胶的内部结构是不均匀的且相互强烈渗透，大概仅允许在两个转变温度之间的温度下核逐渐溶胀，从而促进线性溶胀行为。
