Response of the elastic properties of colloidal crystals to phase transitions and morphological changes

Abstract

We report on the shear modulus G of colloidal crystals formed from thoroughly deionized suspensions of charged latex spheres. G is measured as a function of particle number density n. Body- and face-centered-cubic (bcc and fcc) crystal structures are observed by simultaneously performed static light scattering, and a broad coexistence region is found between (2.7±0.1)×1018 m−3⩽n⩽(4.8±0.2)×1018 m−3. Below n=1019 m−3, G closely follows theoretical predictions for both bcc and fcc, while it stays constant throughout the transition region. Above n=1019 m−3, G still observes the predicted n-dependence but with values larger than expected. While in that region, an upper bound of particles per crystallite is estimated from scattering data to be on the order of 104; the abrupt change in G cannot be solely attributed to the gradual morphological transition from polycrystalline to nanocrystalline materials.

Effect of triplet attractions on the phase diagram of suspensions of charged colloids

“…For both cases we could only obtain quantitative agreement if we reduced the reported colloidal charges considerably. For instance, if we set Z = 480 instead of the reported Z = 700 [8], we find that the bcc-fcc coexistence region extends from η = 0.0026 ± 0.0004 to η = 0.0045 ± 0.0001 at κ σ ≈ 0.45. This matches the 'salt-free' observations of [8] quantitatively.…”

“…For instance, if we set Z = 480 instead of the reported Z = 700 [8], we find that the bcc-fcc coexistence region extends from η = 0.0026 ± 0.0004 to η = 0.0045 ± 0.0001 at κ σ ≈ 0.45. This matches the 'salt-free' observations of [8] quantitatively. Similarly, if we set Z = 350 instead of Z = 880 as reported in [5], the fluid-fcc coexistence is in the regime from η = 0.010 ± 0.005 to η = 0.030 ± 0.004 at κ σ ≈ 0.8, as observed experimentally in this low-salt regime [5].…”

“…The evidence of the breakdown stems from the large magnitude of the difference in densities between the coexisting phases in fluid-solid and bcc-fcc equilibrium. If one characterizes this difference by the ratio x (>1) of the two coexisting densities, one finds x 3 [5] and x = 1.5 [6] for fluid-solid coexistence and x 1.26 [7] and x = 1.78 [8] for bcc-fcc coexistence. To appreciate the large magnitude of these density jumps, one recalls that x = 1.1 for the fluid-fcc density jump in the hard-sphere system, that any repulsive softness tends to decrease x towards unity (a smaller jump) [10], that the density jump across the fcc-bcc transition in soft-sphere systems is so small that one usually does not bother to determine it, and that 'volume' terms (which can be seen as coarsegrained many-body potentials) tend to decrease density jumps in low-salt suspensions [11].…”

Effect of three-body interactions on the phase behavior of charge-stabilized colloidal suspensions

“…These experiments include the ones made by Monovoukas and Gast [13], Sirota et al [14], and Schöpe et al [15]. What all three of them have in common is the observation of a broad gas-solid or solid-solid coexistence in the low-salt regime.…”

Influence of the surface charge on the homogeneity of colloidal crystals

“…Both experiments and computer simulations have shown that low inter-particle repulsion and low volume fraction make colloidal crystals exhibit bcc structure and fcc structure is more favorable for higher repulsion and higher volume fraction. [37][38][39][40] For the five groups of PS particles investigated here, PS1 are bcc in the whole range of from 0.006 to 0.02. PS3, PS4, and PS5 which have larger effective charge exhibited fcc structures at the stable state, though bcc may be formed in the early stage of the crystallization process.…”