Controlling crystallization of responsive microgel particles via cyclic stimuli

微凝胶粒子可以通过外界刺激(如温度或光线)改变其体积和物理化学特性，为胶体结晶提供了良好的可控模型体系。当被限制在液体界面上时，这种粒子代表了二维强相互作用的经典多体系统，这使得对自组装现象的基础研究成为可能。该项目的目标是通过周期性的，即时间周期的方式施加刺激来控制结晶过程和缺陷的动力学。基本假设是，通过使用优化的循环刺激，可以更快地对缺陷进行退火，以产生长程有序的晶体阵列。在第一个资助期，这一假设得到了一项概念验证研究的支持，该研究使用了在空气/水界面形成的单组分二维胶体晶体，这些晶体暴露在声波驻留表面波中。这种周期性增加有效界面面积的循环呼吸运动对缺陷和晶界的退火是有效的，并显著提高了系统的整体有序性。此外，对刺激响应型微凝胶和二元混合物在液体界面的行为的基础研究为研究受限条件下的体积相变和相变的确定性预测提供了新的见解。在第二个资助期，我们将在三个不同的方向利用这些见解：i)干燥过程中发生的毛细作用力及其在结构形成中的作用，ii)弯曲歧管上的颗粒，如Pickering乳液中的球面，以及iii)新颖的、奇异的结构，可从双组分和多组分的颗粒混合物中获得。为了实现这些目标，我们将以互补的方式利用实验和理论进行成功的合作。

Microgel particles, which can change their volume and physicochemical characteristics by external stimuli, such as temperature or light, provide excellent controllable model systems for colloidal crystallization. When confined to a liquid interface, such particles represent two-dimensional strongly interacting classical many-body systems, which allow fundamental studies of self-assembly phenomena. The goal of the project is to control the crystallization process and the defect dynamics by applying stimuli in a cyclic, i.e. time-periodic, way. The basic hypothesis is that, by using optimized cyclic stimuli, defects can be annealed more quickly to produce crystalline arrays with long range order. In the first funding period, this hypothesis was supported by a proof-of-concept study using one-component, two dimensional colloidal crystals formed at the air/water interface, which were exposed to acoustic standing surface waves. This cycling breathing motion, in which the available interfacial area was periodically increased, proved effective in annealing defects and grain boundaries and significantly increased the overall order in the system. In addition, fundamental investigations on the behaviour of stimuli-responsive microgels and binary mixtures at liquid interfaces provides new insights into the volume phase transition under confinement and the deterministic predictions of phase transitions. In the second funding period, we will capitalize on these insights into three different directions: i) capillary forces occurring during drying and their role in structure formation, ii) particles on curved manifolds such as spherical surfaces in Pickering emulsions, and iii) novel, exotic structures obtainable from bi- and multinary mixtures of particles. To achieve these goals, we shall pursue our successful collaboration using experiments and theory in a complementary way.