Nanoscale Effects on Phase Separation

Abstract

Classical nucleation theory predicts that a binary system which is immiscible in the bulk should become miscible at the nanoscale when lowering its size below a critical size. Here we tackle the problem of miscibility in nanoalloys with a combination of ab initio and atomistic calculations, developing a statistical-mechanics approach for the free energy cost of forming phase-separated aggregates. We apply it to the controversial case of AuCo nanoalloys. AuCo is immiscible in the bulk, but a rich variety of nanoparticle configurations, both phase-separated and intermixed, have been obtained experimentally. Our calculations strongly point to the permanence of an equilibrium miscibility gap down to the nanoscale and to the nonexistence of a critical size below which phase separation is impossible. We show that this is due to nanoscale effects of general character, caused by the existence of preferred nucleation sites in nanoparticles, which lower the free-energy cost for phase separation with respect to bulk systems.

Advances in thermodynamic modelling of nanoparticles

“…This is effect becomes nonnegligible for very small nanoparticles (~2-3 nm in size) i.e. clusters [82][83][84]. The large curvature of small nanoparticles is responsible of the strain which gives a volume contribution into the excess Gibbs energy of nanoparticles.…”

First principles global optimization of metal clusters and nanoalloys

“…Hence, in early GO studies of clusters, generally only empirical (or semi-empirical) potentials (EP) were used [58][59][60][61][62][63][64][65][66]. Even today, many studies employ this EP-GO approach, which is usually followed by geometry refinement with more rigorous first principle methods [67][68][69][70][71][72][73][74][75][76][77][78][79]. The main advantage of this approach is that it can also be applied to large clusters, of several hundreds or a few thousands of atoms.…”

Microphase separation of a miscible binary liquid mixture under confinement at the nanoscale

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Many new properties have been then discovered such as the giant diffusion of liquids, [16][17][18] the apparition of new phases and new transitions, [19][20][21][22] giant dielectric properties, 11,12,[23][24][25] the increase of optical properties, 26 and the possible mixing of non-miscible mixtures. 27 These observations indicated that the classical understanding of the physics of liquids should be revisited in confined geometry. Whereas these effects have been largely investigated in the case of confined single components [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and immiscible binary mixtures, [28][29][30] less works have been devoted to the confinement of miscible liquid mixtures.…”