Structure and stability of charged colloid-nanoparticle mixtures

Abstract

Physical properties of colloidal materials can be modified by addition of nanoparticles. Within a model of like-charged mixtures of particles governed by effective electrostatic interactions, we explore the influence of charged nanoparticles on the structure and thermodynamic phase stability of charge-stabilized colloidal suspensions. Focusing on salt-free mixtures of particles of high size and charge asymmetry, interacting via repulsive Yukawa effective pair potentials, we perform molecular dynamics simulations and compute radial distribution functions and static structure factors. Analysis of these structural properties indicates that increasing the charge and concentration of nanoparticles progressively weakens correlations between charged colloids. We show that addition of charged nanoparticles to a suspension of like-charged colloids can induce a colloidal crystal to melt and can facilitate aggregation of a fluid suspension due to attractive van der Waals interactions. We attribute the destabilizing influence of charged nanoparticles to enhanced screening of electrostatic interactions, which weakens repulsion between charged colloids. This interpretation is consistent with recent predictions of an effective interaction theory of charged colloid-nanoparticle mixtures.

Selective Entropy Gain-Driven Adsorption of Nanospheres onto Spherical Bacteria Endows Photodynamic Treatment with Narrow-Spectrum Activity

“…Note that, compared with our nanospheres, the spherical bacteria are appreciably larger and significantly less negatively charged. We hence propose entropy gain, which drives the adsorption of nanoparticles onto like-charged colloids, 32,33 as the driving force for the observed adsorption of nanospheres onto spherical bacteria and suggest the following scenario to describe this process. The electrostatic repulsion between the highly negatively charged nanospheres pushes some nanospheres onto the spherical bacterial cells, which provides more space for the free planktonic nanospheres, and the entropy gains that resulted from this process are huge enough to overcome the Coulombic repulsion between the nanosphere and bacterium and that between the adsorbed nanospheres.…”

“…In the presence of negatively charged polyelectrolytes, bacteria aggregate due to entropy gain-driven depletion − as do synthetic colloids . Note that, in the like-charged nanoparticle/colloid mixtures, the nanoparticles undergo entropy gain-driven adsorption − to form “halos” around the weakly charged colloids . We naturally ask the following question.…”

Electrostatic interactions in soft particle systems: mesoscale simulations of ionic liquids

“…where q is the wave vector magnitude, x a = N a /N is the concentration of species a, d(r) is the Dirac delta function, d ab is the Kronecker delta function, the star on the sum implies the exclusion of selfinteractions, and the angular brackets represent an ensemble average over all ionic species in the model IL simulation systems. [72][73][74][75] A scaled static structural factor for the same type of ionic species is given as S aa ðqÞ…”

Charge Regulated Diffusion of Silica Nanoparticles into Wood for Flame Retardant Transparent Wood

“…Many commercially available NP dispersions are surface stabilized by repulsive charges. [25][26][27] Very few studies have investigated the diffusion of NPs in wood related to their surface chemistry. Segmehl et al studied the diffusion pattern of water in the cell wall based on the migration behavior of ultrasmall europium-doped hafnium dioxide particles traced by Raman microscopy.…”