Impact of long range repulsive interactions on the stochastic dynamics in ensembles of active and passive particles

在这个实验项目中，我们将研究在粒子分布和热噪声的涨落影响下，由主动粒子和被动粒子组成的准二维胶体系综中的集体行为。活性粒子是光敏的，可以产生长程排斥相互作用，其强度可以根据需要在很大范围内进行调节，从与其他有吸引力的粒子相互作用的弱排斥竞争，到强烈排斥完全控制的图案或相的形成。长程排斥相互作用的起源本质上是扩散渗透的(光驱动扩散渗透流，LDDO)，并与每个活性胶体周围局部流动的产生有关。活性粒子既可以用径向流场完全“覆盖”，也可以通过部分钝化表面来呈现Janus类型的自推进胶体。我们方法的独特之处在于，可以通过方便的外部光刺激(强度、照射波长)来调节远程互斥力和自推力，从而实现各种不同的实验情况。目前，有一些理论研究和预测涉及到主动粒子和主动/被动混合粒子系综的相分离行为，但实验还不能捕捉到这些行为，例如运动诱导相分离。由于我们可以使相互作用和自推进的强度可调和依赖于时间，所以人们可以在实验研究中显著扩展胶体系综的非平衡行为的现象学，特别是解决与本项目中的中心问题有关的涨落方面：流动模式的非平衡、耗散性质如何决定相互作用的胶体系综中的颗粒分布？

In this experimental project we are going to study the collective behavior in a quasi-two dimensional colloidal ensemble consisting of active and passive particles under the impact of fluctuations both with respect to particle distribution and thermal noise. The active particles are photo-responsive and can generate long-range repulsive interactions, the strength of which can be tuned on demand and over a broad range, from weakly repulsive competing with other attractive particle interactions, to strongly repelling fully governing pattern or phase formation. The origin of the long-range repulsive interactions is diffusioosmotic in nature (light driven diffusioosmotic flow, LDDO) and related to generation of local flow around each active colloid. Active particles can either be fully "dressed" with a radially directed flow field, or rendered Janus-type, self-propelling colloids by partially inactivating their surface. The unique feature of our approach is that the long range mutual repulsion and also self-propulsion can be tuned by convenient external optical stimuli (intensity, irradiation wavelength) such that a broad variety of experimental situations can be realized. Currently, there are some theoretical studies and predictions related to phase separation behaviour of ensembles of active and active/passive particle mixtures that could not yet be captured by experiment, for instance motility induced phase separation. Since we can make the strength of mutual interaction and self-propulsion tuneable and time-dependent, one can significantly extend the phenomenology of non-equilibrium behaviour of colloidal ensembles in experimental study and in particular address the aspect of fluctuations, related to the central question in this project: how does the non-equilibrium, dissipative nature of the flow patterns dictate the particle distribution in mutually interacting colloidal ensembles?