Liquid-glass transition in charge-stabilized colloidal dispersions

Abstract

Abstract. We model the inter-colloidal interactions in a charge-stabilized colloidal dispersion by a hard-core Yukawa potential 0(r)=ao7exp(-«r)/r, r> <JQ and apply the rescaled mean spherical approximation to calculate its static structure factor. In conjunction with the idealized mode-coupling theory, we determine the loci of the liquid-glass transition phase boundary for a salt-free suspension of charged colloids evaluated at different counter-ion environment (characterized by the K) in terms of the macro-ion parameters: volume fraction 77, charge ZQ and size CTQ. The calculated parametric phase diagrams are quite general since the results, with slight and straightforward modification, can be utilized to study the glass transition in a more realistic colloidal solution such as an aqueous monodisperse suspension of polystyrene charged spheres with an added electrolyte. Confining our discussion, then, to the simplest salt-free colloidal liquids, we extract from our analysis of the calculated liquid-glass transition boundaries some succinct features. Specifically, we show in this work that given a range of interaction X-KCJQ ^3.8, there is a possibility of observing the liquid^glass^liquid^glass (LGLG) re-entrant phenomenon in restrictive regions of the phase diagram r\-a § or ry-Zo for a monodisperse charge-stabilized solution. However, as the <TO increases above a critical size, the LGLG re-entrant behavior vanishes. To delve into this re-entrant phenomenon, we compare, for a given K, the glassy Debye-Waller factor, static structure factor and their spatial counterparts for two casesone for lower-Zo colloids at a high rj and the other for higher-Zo colloids at a low 77. For the former, the glassification is basically driven by the geometric restriction while that, for the latter, it is mainly induced by the Coulomb force. We conclude from this comparison that under the same screening environment both the excluded volume and the electrostatic effects are equally effective in impelling a charge-stabilized colloidal dispersion to undergo a structural arrest configuration and hence the liquid-glass transition.

Formation of a transient amorphous solid in low density aqueous charged sphere suspensions

“…This has been extensively demonstrated and detailed for hard sphere and charged colloidal systems 2 , 19 – 22 , 25 , 29 , 30 , 43 , 44 . Also for charged spheres at moderate to low densities, detailed predictions for the evolution of the intermediate scattering function with increasing number density exist 49 , 50 , 53 , 60 . Unfortunately, for the present samples, use of conventional dynamic light scattering (DLS) is inadequate due to multiple scattering effects that yield an ill-defined intercept and plateau value as well as the comparably fast structural evolution which hinders the determination of statistically valid time averages.…”

“…2,[19][20][21][22]25,29,30,43,44 Also for charged spheres at moderate to low densities, detailed predictions for the evolution of the intermediate scattering function with increasing number density exist. 49,50,53,60 Unfortunately, for the present samples, use of conventional dynamic light scattering (DLS) is inadequate due to multiple scattering effects that yield an illdefined intercept and plateau value as well as the comparably fast structural evolution which hinders the determination of statistically valid time averages. Note that such effects are practically absent in amorphous suspensions of clay platelets where the intermediate scattering function could be accessed and much information was obtained about the evolution of the sample dynamics.…”

“…40 However, experimental reports on the transition of charged spheres or charged platelets into an amorphous solid or "Wigner glass" [24][25][26][41][42][43][44][45][46] are much rarer than theoretical studies or simulations on these systems. [47][48][49][50][51][52][53][54][55][56][57][58][59][60] In systems of charged clay platelets, 25,61-63 also the glass transition at low packing fractions was addressed and demonstrated for sufficiently strong Coulomb-couplings. There, also the occurrence of ageing processes and the existence of a second slow relaxation process was demonstrated and interpreted in terms of dynamic heterogeneities known from previous studies on hard spheres glasses.…”

“…Systematic experimental studies of low density charged sphere glasses are so far missing even though predicted by Mode coupling Theory (MCT) approaches. 49,[51][52][53][54]60 In this work, we investigate low density amorphous solids formed from aqueous suspensions of charged spheres.Note that we intentionally denote the short-range ordered solid state of the present system as "amorphous solid" rather than as "glass", because we feel that i) many different colloidal glasses seem to co-exist in different experimental and theoretical approaches; ii) the issue of how exactly a glass can be unequivocally defined beyond being an amorphous solid therefore remains unsolved; and iii) we are not sure about the exact nature and the ways in and out of this state.Our amorphous solids are formed from standard polymer latex spheres (diameter 2ah = 117.6 nm, size polydispersity index PI = 0.05 (Fig. S1 in the supporting information), effective charge number Zeff,G = 379 ± 10) suspended in water at thoroughly deionized conditions yielding a residual ion concentration of 0.2 µmol/L.…”

“…Systematic experimental studies of low density charged sphere glasses are so far missing even though predicted by Mode coupling Theory (MCT) approaches. 49,[51][52][53][54]60 In this work, we investigate low density amorphous solids formed from aqueous suspensions of charged spheres.…”