Frenzel Lara, Lehmkühler Felix, Lokteva Irina, Narayanan Suresh, Sprung Michael, Grübel Gerhard
Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany.
The Hamburg Centre for Ultrafast Imaging (CUI), Luruper Chaussee 149, 22761 Hamburg, Germany.
J Phys Chem Lett. 2019 Sep 5;10(17):5231-5236. doi: 10.1021/acs.jpclett.9b01690. Epub 2019 Aug 23.
We present the structure and dynamics of highly concentrated core-shell nanoparticles composed of a silica core and a poly(-isoproylacrylamide) (PNIPAm) shell suspended in water. With X-ray photon correlation spectroscopy, we are able to follow dynamical changes over the volume phase transition of PNIPAm at LCST = 32 °C. On raising the temperature beyond LCST, the structural relaxation times continue to decrease. The effect is accompanied by a transition from stretched to compressed exponential shape of the intensity autocorrelation function. Upon further heating, we find a sudden slowing down for the particles in their collapsed state. The dependence of the relaxation time shows an anomalous change from τ ∝ to τ ∝ . Small angle X-ray scattering data evidence a temperature-induced transition from repulsive to attractive forces. Our results indicate a temperature-induced phase transition from a colloidal liquid with polymer-driven dynamics toward a colloidal gel.
我们展示了由二氧化硅核和悬浮在水中的聚（N-异丙基丙烯酰胺）（PNIPAm）壳组成的高浓度核壳纳米颗粒的结构和动力学。通过X射线光子相关光谱，我们能够跟踪PNIPAm在最低临界溶液温度（LCST）= 32°C时体积相变过程中的动态变化。当温度升高超过LCST时，结构弛豫时间持续下降。这种效应伴随着强度自相关函数从拉伸指数形状到压缩指数形状的转变。进一步加热后，我们发现处于塌陷状态的颗粒突然减速。弛豫时间的依赖性显示出从τ ∝ 到τ ∝ 的异常变化。小角X射线散射数据证明了温度诱导的从排斥力到吸引力的转变。我们的结果表明存在温度诱导的相变，从具有聚合物驱动动力学的胶体液体转变为胶体凝胶。
