Packing Polydisperse Colloids into Crystals: When Charge-Dispersity Matters

Abstract

Monte-Carlo simulations and small-angle x-ray scattering experiments were used to determine the phase diagram of aqueous dispersions of titratable nano-colloids with a moderate size polydispersity over a broad range of monovalent salt concentrations, 0.5 mM ≤ cs ≤ 50 mM and volume fractions, φ. Under slow and progressive increase in φ, the dispersions freeze into a face-centered-cubic (fcc) solid followed unexpectedly by the formation of a body centered cubic (bcc) phase before to melt in a glass forming liquid. The simulations are found to predict very well these observations. They suggest that the stabilization of the bcc solid at the expense of the fcc phase at high φ and cs results from the interaction (charge) polydispersity and vibrational entropy. arXiv:1909.02774v1 [cond-mat.soft]

Coadsorption of Counterionic Colloids at Fluid Interfaces: A Coarse-Grained Simulation Study of Gibbs Monolayers

“…For instance, at Π* = 0.07, in the expansion sequence, the crystalline structure is stable (snapshot 3F in Figure ), while a gel-like structure is obtained in the compression case (snapshot 3E in Figure ). Further insights into gel–crystal coexistence curves would require advanced simulation techniques beyond the scope of this study, plausibly involving an improved sampling of configurational space and ideally also free-energy calculations . Such techniques should help to rationalize the hysteresis observed in computations and experiments in terms of the metastability regimes for each of the two phases.…”

“…Further insights into gel−crystal coexistence curves would require advanced simulation techniques beyond the scope of this study, plausibly involving an improved sampling of configurational space and ideally also free-energy calculations. 65 Such techniques should help to rationalize the hysteresis observed in computations and experiments in terms of the metastability regimes for each of the two phases. The reduction of the magnitude of the pair interactions changes the qualitative clustering behavior of the system.…”

Kinetic Phase Diagram for Nucleation and Growth of Competing Crystal Polymorphs in Charged Colloids

“…However, the crystallization mechanism in charged colloids is not clearcut and numerous experimental observations are hitherto unexplained. For instance, the observation of broad fluidsolid and fcc-bcc coexistences in various experiments [4,5] is inconsistent with the theoretical phase diagrams [6] that predict narrow phase coexistences. Furthermore, a wide variety of crystallization mechanisms has been observed in experiments, ranging from a simple one-step nucleation mechanism of fcc crystals [7,8] to the emergence of metastable bcc crystals that subsequently transform into fcc [9,10], as well as the emergence of hexagonal closepacked (hcp) before fcc is formed [11].…”

Designing Multicomponent Polymer Colloids for Self-Stratifying Films

“…The main objective in this work is to understand self-stratification in film-forming colloidal particles, which differs from related studies on structural characterization in hard sphere colloidal suspensions. Colloidal suspensions show a rich variety of structures in their dispersed state depending on particle size, polydispersity, and surface charges. − In addition, colloidal particles can be patterned into various complex structures after carrier fluid evaporation depending on the nature of the substrate, particle properties, and interparticle interactions. , Although such patterned colloidal structures are technologically relevant, − in this work, we are mainly focused on understanding the film formation and self-stratification process, rather than quantifying the evolution of the colloidal suspension structure during solvent evaporation. Film-forming soft latex particles typically lose their discrete particle identity upon coalescence, which facilitates film formation on a substrate.…”