Polydispersity and gelation in concentrated colloids with competing interactions

Abstract

In colloids with competing short-range attractions and long-range repulsions, microcrystalline gels are experimentally formed under conditions where computer simulations point to a lamellar phase as the ground state. Here, upon applying a low-frequency alternating electric field, we bring the system from an initial gel state to a columnar-like state. While molecular dynamics simulations on monodisperse colloids reveal that a columnar structure spontaneously evolves towards a lamellar phase, the columnarlike state in experiments relaxes back to the initial disordered gel state once the electric field is switched off. Similarly, a columnar phase in molecular dynamics simulations decomposes into finite-size crystalline clusters as the relative polydispersity of the colloids is around 1.0%. We conclude that the experimentally observed melting of the columnar structure is driven by polydispersity. Moreover, further simulations reveal that the critical polydispersity required to destabilize a long-range ordered structure increases with the attraction range, pointing to the possibility of observing periodic structures in experiments if the attraction range is sufficiently long compared to the polydispersity of the colloids.

Living islands of driven two-dimensional magnetic colloids on the disordered substrate

“…where T is the system temperature and the subscripts a and b indicate the components of F i T and F , j T respectively. The total interaction potential between colloidal particles U cc is the sum of a repulsive potential U rp [28,29,[47][48][49] and an attractive potential U ap [7,8,43], i.e.,…”

“…It is known that there is a self-propelled interaction between active colloidal particles [4,5]. Thanks to this property, they could present a series of novel behaviors that are not attainable in the passive systems, such as living clusters and living islands [6][7][8], which are closely related to the biological self-organization [5,7,9,10]. In addition, the selfpropelled property can also be used to design the micro/nanomachines that operate in microscopic environments, such as micro/nanomotors [1,[11][12][13][14][15], single particle pumps [14,16], nanorotors [17], and so forth [18][19][20][21].…”

“…Using an external field, we can control and track the motion of colloidal particles, and thereby probing the microscopic rheological properties and viscous elastic responses of the biological cells. But an external field will cause an equilibrium system into a non-equilibrium moving state, and thus there will exhibit a series of unusual phenomena, such as self-assembly [5,6,10,30], clustering [7][8][9][10][31][32][33][34][35], swarming [36,37], phase separation [25,38,39], odd rheological and phase behaviors [8,40,41].…”

Friction of two-dimensional colloidal particles with magnetic dipole and Lennard–Jones interactions: A numerical study

“…Active systems can actively absorb energy from the environment and overcome resistance (i.e., energy barrier) through energy storage [14], as in the case of bacterial colonies of fish and birds and tissues of cells; such systems are different from passive systems that acquire energy from the surrounding environment and subsequently restore energy to the environment. It is known that the abovementioned activity originates from weak attractive interactions between individuals in the systems [15][16][17][18][19][20], for, e.g., van der Waals interaction between colloidal particles. Such self-propelling interactions between individual members of active systems [21] drive the systems to non-equilibrium states, which leads the systems exhibiting a series of novel behaviors that cannot be observed under equilibrium [20][21][22][23][24][25].…”

Gelation in mixtures of polymers and bidisperse colloids

“…Particle polydispersity in these mixtures shifts the equilibrium phase behavior, affecting both the number of phases and the location of boundaries between them [43,48]. Indeed, these shifts may be significant enough to reveal [49,50] or suppress [50,51] the concentrated equilibrium phases predicted for monodisperse suspensions. High particle polydispersity can also disrupt non-equilibrium phases, such as the re-entrant glass transition observed at high particle concentrations [52].…”