Depletion-Mediated Potentials and Phase Behavior for Micelles, Macromolecules, Nanoparticles, and Hydrogel Particles

Abstract

We report a simple depletion potential that captures measured potentials and phase behavior for micrometer-sized colloids in the presence of unadsorbing charged micelles, charged nanoparticles, nonionic macromolecules, and nonionic hydrogel particles. Total internal reflection microscopy (TIRM) is used to measure net potentials between colloids and surfaces, and video microscopy (VM) is used to measure quasi-2D phase behavior in the same material systems. A modified Asakura-Oosawa (AO) depletion potential is developed to accurately quantify particle-wall potentials and interfacial crystallization via particle-particle potentials in Monte Carlo (MC) simulations. The modified AO potential includes effective depletant sizes, accurate osmotic equations of state, and partition coefficients. Partition coefficients are used as the sole adjustable fitting parameter, although an approach to their theoretical prediction from depletant density profiles is also presented. Our results demonstrate a model that accurately captures depletion interactions and phase behavior in a variety of material systems.

Direct measurements of particle–surface interactions in aqueous solutions with total internal reflection microscopy

“…This equation also ignores the shape, polydispersity of the depletants, as well as interactions between the depletants. Therefore, a number of theoretical methods have been developed to describe the depletion interactions induced by different types of depletants 15,30,38,39 .…”

“…While TIRM is not being widely used in laboratories worldwide, it is probably fair to state that TIRM is ideally suited to measuring extremely weak and dynamic interactions that are most relevant to the stability of colloidal dispersions and interaction of biomacromolecules. Moreover, recent advancements such as the integration of TIRM and video microscopy (VM) enables the simultaneous measurements of many particles at many different surface locations, which generates significantly more statistical information and allows measurements of colloid-surface and colloid-colloid interactions in the same ensemble 29,30 . Furthermore, magnetic tweezers has been incorporated in the TIRM that enables measuring of viscoelastic properties of soft materials near solid surface 31 .…”

Thermal Optofluidics: Principles and Applications

“…This creates a concentration gradient ∇ c , which gives rise to an osmotic pressure proportional to ∇ c , which tends to push the particles from the low‐ to the high‐temperature region. Such depletion forces have been studied extensively as a means of controlling the trapping and assembling of colloidal particles by tailoring the characteristics of the depletant molecules or nanoparticles …”

“…Such depletion forces have been studied extensively as a means of controlling the trap ping and assembling of colloidal particles by tailoring the char acteristics of the depletant molecules or nanoparticles. [25,26,99,100]…”

Optical tracking of nanoscale particles in microscale environments

“…Scanning probe techniques would otherwise introduce additional potentials that could confound the measurement. This technique allows the inference of excluded volume interactions 139 between charged species that are of interest in biological systems and in self-assembly processes mediated by fluids. Sec.…”