Non-equilibrium cluster states in colloids with competing interactions

Abstract

Cluster formation and gelation are studied in a colloidal model system with competing short-range attractions and long-range repulsions. In contrast to predictions by equilibrium theory, the size of clusters spontaneously formed at low colloidal volume fractions decreases with increasing strength of the short-range attraction. Moreover, the microstructure and shape of the clusters sensitively depend on the strength of the short-range attraction: from compact and crystalline clusters at relatively weak attractions to disordered and quasi-linear clusters at strong attractions. By systematically varying attraction strength and colloidal volume fraction, we observe gelation at relatively high volume fraction. The structure of the gel depends on attraction strength: in systems with the lowest attraction strength, crowding of crystalline clusters leads to microcrystalline gels. In contrast, in systems with relatively strong attraction strength, percolation of quasi-linear clusters leads to low-density gels. In analyzing the results we show that nucleation and rearrangement processes play a key role in determining the properties of clusters and the mechanism of gelation. This study implies that by tuning the strength of short-range attractions, the growth mechanism as well as the structure of clusters can be controlled, and thereby the route to a gel state.

Self-Assembly of Heterogeneously Charged Particles under Confinement

“…Similar structures have been only observed in the bulk of colloidal systems with competing short-range attractions and long-range repulsions. 30,32 The crucial parameter driving the self-assembly into ordered domains, as opposed to disordered aggregates, was proven to be the patch extension: bigger patches were found to give rise to extended structures consisting of ordered triangular domains; in contrast, smaller patches were shown to favor the formation of several ring-like particle arrangements, which consequently led to the formation of an open gel network. It is also worth noting that for IPCs with relatively smaller patches bonding contacts occur between only one patch and one equator, whereas for IPCs with bigger patches, one patch often overlaps with two neighboring equators.…”

The role of quench rate in colloidal gels

“…This feature of crystallisation suppressed by five-fold symmetric clusters is found also in experiments on colloidal gels [28], simulations of molecular gels [15], and isolated clusters [37] where in the case of the latter, the ground state is one of the clusters considered by the TCC. However, suppression of crystallisation is not universal, experiments in which locally crystalline clusters are found have also been reported [38].…”

Communication: Microphase equilibrium and assembly dynamics

“…Beyond their mere aesthetic value, some of the resulting ordered and disordered structures of diblock copolymers have found uses as nanoscale templates and filters 4,5 . Colloidal analogues, however, have thus far only given rise to disordered microphases, such as clusters and gels [6][7][8] . Recent advances describing the equilibrium behavior of model colloidal microphaseformers 9,10 confirm that such ordering should be thermodynamically possible 2,3 , but whether it is dynamically accessible remains an open question.…”