Investigation of Short-Time Particle Dynamics near an Interface in the Presence of Nonadsorbed Macro-ions

Abstract

The optical technique of total internal reflection microscopy was used to study the normal Brownian motion of a single colloidal particle near an interface. The measurements were made using a recently developed technique in which the diffusion coefficient was determined by the variance of the short-time (Deltat --> 0) motion of the particle. Experiments were performed in solutions containing either silica nanospheres or clay platelets (Laponite RD) to investigate the effect of nonadsorbed material on the dynamics of near-contact particle motion. The change in the diffusion coefficient with separation distance between the particle and plate in solutions containing nonadsorbed macro-ions was well-described by the theory developed for simple fluids. These results suggest that, in dilute solutions of nonadsorbed material in which the bulk rheological properties remain similar to those of the pure fluid, the mobility and diffusion coefficient correction factors developed for simple fluids remain valid.

Effect of small particles on the near-wall dynamics of a large particle in a highly bidisperse colloidal solution

“…Examples include dairy products, polymeric gels and nearly all complex fluids in biological organisms. Since the dynamics of colloidal systems is often influenced by their confining boundaries [1,2], the confining effects are important in many emerging applications, e.g., in self-assembly technology involving colloidal crystals [3,4] and in chemical deposition processes on patterned wall [5]. Hence, it is necessary to understand how polydisperse suspensions behave in the proximity of a bounding surface.…”

Correlated Brownian motions and the depletion effect in colloids

“…Oetama and Walz [34] report the result of a study of short-time dynamics with a focus on determining the diffusion coefficient of the large particles in the presence of the small particles.…”

“…Consequently, we start with the following. 34 32 See Walsh [47] 33 If ψ(r) is a differentiable scalar-valued isotropic function of position r, then its gradient ∇ r ψ(r) is a isotropic vector-valued function of position. In particular, ∇ r γ(|r| 2 ) = 2γ ′ (|r| 2 )r. The converse is also true.…”

“…In particular, ∇ r γ(|r| 2 ) = 2γ ′ (|r| 2 )r. The converse is also true. 34 For convenience, we suppress the subscript ε of g in Section 3 except when a specific form of the forcing kernel is used.…”

“…Total internal reflection microscopy (TIRM) has the advantage of using an evanescent wave to interrogate the position of a large particle with respect to an optical surface, see Tuinier et al [41] for a brief description of the technique and see references [2], [36], [34] and [5] for reports of depletion effects observed. Also, see Figure (4).…”