The ionic composition and pair correlations in fluid phases of realistically salt-free charged colloidal sphere suspensions are calculated in the primitive model. We obtain the number densities of all ionic species in suspension, including low-molecular weight microions, and colloidal macroions with acidic surface groups, from a self-consistent solution of a coupled physicochemical set of nonlinear algebraic equations and non-mean-field liquid integral equations. Here, we study suspensions of colloidal spheres with sulfonate or silanol surface groups, suspended in demineralized water that is saturated with carbon dioxide under standard atmosphere. The only input required for our theoretical scheme are the acidic dissociation constants pKa, and effective sphere diameters of all involved ions. Our method allows for an ab initio calculation of colloidal bare and effective charges, at high numerical efficiency.
The deviatoric stresses of colloidal suspensions are routinely calculated using the expression introduced by Batchelor [J. Fluid Mech. 83, 97--117 (1977)]. We show by example that the central feature in its derivation, the thermodynamic force driving particles down the density gradient, is inconsistent with the motion of the colloids. A new expression for the stress is proposed.
Hypothesis: Aging in colloidal suspensions manifests as a reduction in kinetic freedom of the colloids. In aqueous suspensions of charged colloids, the role of inter-particle electrostatics interactions on the aging dynamics is well debated. Despite water being the dispersion medium, the influence of water structure on the physicochemical properties of aging colloids has never been considered before. Laponite, a model hectorite clay, could be used to evaluate the relative contributions of medium structure and electrostatics in determining the physicochemical properties of aging colloidal suspe…
Bi-axial shear of confined colloidal suspensions: the structure and rheology of the vorticity-aligned string phase
利用一种新型的双轴共焦流变仪，我们研究了约束条件下剪切胶体悬浮液的结构和流变性。与以前的工作一致[X. Cheng \textit{et al., Proc. Natl. Acad. Sci. U. S. A.}，2011，109，63]，我们在单轴剪切下在中等浓度的胶体悬浮液中观察到涡旋对齐的弦相。使用双轴剪切协议，我们直接操纵的字符串结构的方向和形态。同时，我们使用双轴力测量装置测量了沿流动和涡度方向的悬浮液流变学。我们的研究结果表明，尽管高度各向异性的微观结构，悬浮液粘度保持各向同性和恒定的剪切速率探索。这些结果表明，流体动力学的贡献占主导地位的悬浮液响应。此外，他们强调双轴共焦流变仪的能力，阐明复杂流体的微观结构和流变学之间的关系。
We study self-diffusion and sedimentation in colloidal suspensions of nearly-hard spheres using the multiparticle collision dynamics simulation method for the solvent with a discrete mesh model for the colloidal particles (MD+MPCD). We cover colloid volume fractions from 0.01 to 0.40 and compare the MD+MPCD simulations to Brownian dynamics simulations with free-draining hydrodynamics (BD) as well as pairwise far-field hydrodynamics described using the Rotne--Prager--Yamakawa mobility tensor (BD+RPY). The dynamics in MD+MPCD suggest that the colloidal particles are only partially coupled to the…
Gas-Solid Coexistence in Highly Charged Colloidal Suspensions
采用静态光散射（SLS）和共聚焦激光扫描显微镜（CLSM）研究了不同体积分数的高电荷聚苯乙烯颗粒的水悬浮液的结构有序性和相行为。在去离子条件下，高电荷密度胶体颗粒的悬浮液保持无序，而相对低电荷密度的悬浮液通过对可见光表现出彩虹色而显示结晶。虽然对于肉眼结晶悬浮液出现均匀，静态光散射测量和CLSM观察揭示了其不均匀的性质，在共存的形式的空隙与致密有序的区域。CLSM调查无序悬浮液显示其不均匀性的形式共存的空隙与密集的无序（无定形）区域。我们对高电荷胶体的研究证实了气-固转变的发生，并且与使用具有长程吸引项的对势的蒙特卡罗模拟的预测一致[Mohanty和Tata，Journal of Colloid and Interface Science 2003，264，101]。基于我们的实验和模拟结果，我们认为，所报道的重入无序态[Yamanaka et al Phys. Rev. Lett. 1998，80，5806和Toyotama等人，Langmuir，2003，19，3236]在高电荷密度下观察到的带电胶体中存在气固共存状态。
We discuss the peculiarities of the Seebeck effect in stabilized electrolytes containing the colloidal particles. Its unusual feature is the two-stage character, with the linear increase of differential thermopower as the function of colloidal particles concentration $n_{\odot}$ during the first stage and dramatic drop of it at small $n_{\odot}$ during the second one (steady state). We show that the properties of the initial state are governed by the thermo-diffusion flows of the mobile ions of the stabilizing electrolyte medium itself and how the colloidal particles participate in formation o…
Self-Organized Velocity Pulses of Dense Colloidal Suspensions in Microchannel Flow
本文对压力驱动的微通道中稠密胶体悬浮液的二维流动进行了数值研究。胶体被模拟为弹性和摩擦球悬浮在牛顿流体中，我们模拟使用多粒子碰撞动力学的方法。该模型再现了周期性的速度和密度脉冲序列，在微通道中向上游行进，这是在L。Isa等人[Phys. Rev. Lett. 102，058302（2009）]。我们发现，胶体壁摩擦和合力链是至关重要的这些脉冲的形成。随着胶体密度的增加，首先出现孤立子阻塞，在中等密度下形成周期脉冲串，在高密度下形成不稳定的孤立子脉冲。我们制定了一个唯象的连续模型，并展示了如何这些时空流和密度分布可以被理解为同宿和周期轨道的行波方程。
We investigate the origin of yield stress aging in semi-dense, saline, and turbid suspensions in which structural evolution is rapidly arrested by the formation of thermally irreversible roll-resisting interparticle contacts. By performing optical tweezer (OT) three-point bending tests on particle rods, we show that these contacts yield by overcoming a rolling threshold, the critical bending moment of which grows logarithmically with time. We demonstrate that this time-dependent contact-scale rolling threshold controls the suspension yield stress and its aging kinetics. We identify a simple co…
The settling dynamics of falling spheres inside a Laponite suspension is studied. Laponite is a colloidal synthetic clay that shows physical aging in aqueous suspension due to the spontaneous evolution of inter-particle electrostatic interactions. In our experiments, millimeter-sized steel balls are dropped in aqueous Laponite suspensions of different ages (i.e., time elapsed since sample preparation). The motion of the falling balls are captured using a high-speed camera and the velocities of their centroids are estimated from the images. Interestingly, we observe that balls of larger diamete…
The performance of graphene oxide(GO)-based materials strongly depends on the lateral size and size distribution of GO nanosheets. Various methods are employed to prepare GO nanosheets with a narrow size distribution. One of the promising method was proposed recently by directionally freezing of a GO aqueous dispersion at a controlled growth rate of the freezing front. We develop a theoretic model of binary colloids suspension, incorporating both the moving freezing boundary and the preferential adsorption of colloidal particles to the ice phase. We numerically solve the coupled diffusion equa…
