Structure of the Laves Phase Observed in Polystyrene Latexes

Abstract

This paper describes the light-microscopic observations of polystyrene latexes with spherical particles of two different diameters, d and 1.4-1.9d. Polystyrene latexes are available for simulating real structures in intermetallic compounds. An amorphous state appeared for a few hours after stirring or vibrating the latexes, and subsequently, the Laves phase structure nucleated and grew by the Brownian motion of the particles whose diameters were d and 1.4-1.7d. The structures of the observed Laves phase were classified into the MgCu2 and the MgZn2 types, containing such lattice defects as grain boundaries, dislocations, vacancies or mis-arranged particles.

Stability of LS and LS2 crystal structures in binary mixtures of hard and charged spheres

“…The last observation is in agreement with experiments on charged colloids where Laves structures MgCu 2 and MgZn 2 were reported in the size-ratio range of 0.59-0.71. 3,13,14 We also find that soft repulsion greatly favors the CsCl phase over Laves phases, thus making the stable pockets of Laves phases smaller. For the system of oppositely charged spheres, the Laves phases are metastable with respect to CsCl and fluid phases.…”

“…In the equally charged system we find regions of stability for both the Laves phases as well as CsCl, while in the oppositely charged case we find only CsCl. The work on charged colloids is interesting as it connects with the experimental observations of the Laves structures MgCu 2 and MgZn 2 in mixtures of large and small charged colloids 3,13,14 and also with recent work on binary mixtures of oppositely charged nanoparticles. 15 To calculate the stability of the phases, both for the hardcore interactions and the charged systems, we calculate the Gibbs free energy using MC simulations.…”

“…The first experimental observations of binary crystal structures of hard-sphere-like particles were made by Sanders 2 in natural gem opals. Later, other authors [3][4][5] observed binary crystals with the large ͑L͒ and small ͑S͒ spheres arranged in LS 2 ͑atomic analog AlB 2 ͒ and LS 13 ͑atomic analog NaZn 13 ͒ structure. It has since been shown that both of these structures are stabilized by entropy alone.…”

“…The observation of stable Laves phases in a system of screened-Coulomb particles at a size ratio below the size-ratio range where Laves phases are stable for hardsphere mixtures is in agreement with experiments on charged colloids where MgCu 2 and MgZn 2 structures were observed at size ratios of 0.59-0.71. 3,13,14 In the phase diagram of the oppositely charged spheres in Fig. 17, the Laves phases are not stable and the phase diagram is dominated by CsCl-fluid and CsCl-fcc coexistence regions.…”

Melting and freezing lines for a mixture of charged colloidal spheres with spindle-type phase diagram

“…At size ratios between 0.4 and 0.8 they develop stoichiometric compounds with peritectics at certain size ratios or compositions. The predicted and experimentally confirmed structures include AB, AlB 2 , the Laves-Phase MgZn 2 as well as NaZn 13 [22,23,24,25,26,27,28,29,30]. Simple eutectics, azeotropes and spindle-type phase diagrams are found only for very similar components with Γ approaching unity [25,31].…”