Excess Entropy Scaling Law in Quasi-Two-dimensional 'Attractive' Colloidal Fluids

摘要

Understanding the relation between structure and dynamics in colloidal suspensions is important to both fundamental science and industrial applications. We employ quasi-two-dimensional (2D) colloidal fluids and video microscopy to systematically study how short-range attractions between colloidal particles affect their structures and self-diffusion dynamics. The 2D colloidal fluid was formed by confinement near a water/glass interface. The short-range attraction is induced by the rod-shape surfactant micelles composed of hexaethylene glycol monododecyl ether. The lengths of the micelles grow with temperature, which enables us to tune attraction strength in situ using an objective heater. Pair correlation function, g(r), and two-body excess entropy, S2, were used to characterize the fluidic structure of the 2D colloidal suspensions and mean squared displacement and long-time diffusivity were employed to quantify the dynamics. We observe that, with stronger attractions, colloidal fluids exhibit more ordered structures due to transient colloidal clusters. Meanwhile, diffusion dynamics becomes more heterogeneous and more hindered when attraction is stronger. Interestingly, the normalized long-time diffusivity exhibits an excess entropy scaling law, D*?exp(0.85S2),which is universal for all samples with different packing fractions and attraction strengths.