Stabilization of Colloidal Suspensions: Competing Effects of Nanoparticle Halos and Depletion Mechanism

Abstract

Bimodal colloidal mixtures of nanoparticles and microparticles may show different phase behaviors depending upon the interparticle interaction of both species. In the present work, we examined the stabilization of spherical microparticles using highly charged, spherical nanoparticles. Total internal reflection microscopy (TIRM) was used to measure the interaction forces between a charged microparticle and flat glass substrate in aqueous solutions at varying volume fractions of nanoparticles of the same sign. We found that, in the system containing of highly charged nanoparticles, microparticle, and glass substrate, non-adsorbing charged nanoparticles in solution did not lead to depletion attraction. Instead, the addition of nanoparticles was to consistently create a repulsive force between the microparticle and glass substrate even at a very low nanoparticle volume fraction. This result might attributed to the formation of thin shells (halos) with a high local nanoparticle volume fraction to the region near the glass surface, resulting in electrostatic repulsion between the decorated surfaces. This study demonstrates that nanoparticle halos can also arise in binary systems of mutually but highly repulsive microparticle/nanoparticle dispersions.

Experimental investigation on the use of highly charged nanoparticles to improve the stability of weakly charged colloidal system

“…In corroboration to the results obtained by Ji et al [30], Xing et al [43] discovered that the haloing phenomena could also manifest in a highly charged nanoparticle-microparticle/plate system in contrast to the previously known attractive depletion force. They reasoned that the nanoparticle may have converged on the plate due to its low charge potential resulting into effective repulsive force which becomes more pronounced with decreasing separation distance.…”

Effective electrostatic interactions in colloid-nanoparticle mixtures

“…These authors postulated that the suspensions were stabilized by the formation of nanoparticle halos around the colloidal particles. Their observations and interpretation have been supported by independent measurements [53][54][55][56][57][58][59][60][61][62][63] confirming that attraction and adsorption of strongly charged nanoparticles onto weakly-charged colloids can result in formation of nanoparticle halos. With increasing concentration, nanoparticles first confer charge stabilization by amplifying the colloid zeta potential, but ultimately destabilize the suspension by screening repulsive electrostatic interactions.…”

Investigation on the use of graphene oxide as novel surfactant to stabilize weakly charged graphene nanoplatelets

“…It is evident that the change in zeta potential value strongly signifies the existence of a unique interaction between the particles. Further, while previous studies focus on understanding the stabilizing effect of low charged microparticles with highly charged nanoparticle [108][109][110][111][112], the present study embarked on the opposite configuration wherein the GnP particles become highly attracted to a much larger GO sheet, but the repulsive nature of both elements prevents their permanent contact within the bimodal system. This result coupled with the imagery evidences may strongly suggest that the hybrid composite mixture exhibits the prevalent characteristic of highly stable colloid which is mutually attractive in a long range but sufficiently repulsive as both particles are drawn closer within the Dybe length zone [113].…”