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We study the statistical properties of the potential energy landscape of a system of particles interacting via a very short-range square-well potential (of depth $-u_0$), as a function of the range of attraction $\Delta$ to provide thermodynamic insights of the Noro and Frenkel [ M.G. Noro and D. Frenkel, J.Chem.Phys. {\bf 113}, 2941 (2000)] scaling. We exactly evaluate the basin free energy and show that it can be separated into a {\it vibrational} ($\Delta$-dependent) and a {\it floppy} ($\Delta$-independent) component. We also show that the partition function is a function of $\Delta e^{\beta u_o}$, explaining the equivalence of the thermodynamics for systems characterized by the same second virial coefficient. An outcome of our approach is the possibility of counting the number of floppy modes (and their entropy)., Comment: 4 pages, 4 figures accepted for publication on PRE

We discuss features of simple inter-particle potentials which are able to generate low-packing fraction arrested states, i.e. gels, in the absence of a macroscopic phase separation phenomenon. We suggest that the ratio between surface and bulk free energy is crucial in favoring ideal gel states. Two possible models for gels, one based on the competition of short range attraction and long range repulsions and the other on local constraints disfavoring packed local structures are discussed. © 2005 Elsevier B.V. All rights reserved.

We studied the phase behavior of a model binary mixture of eye lens crystallin proteins using first-order thermodynamic perturbation theory. The instability boundary, or spinodal surface, was found to be very sensitive to the strength of the attraction between the two proteins, and also to respond to this interprotein attraction strength in a non-monotonic fashion. In particular, in the case of either weak or strong attractions, these eye lens solutions become thermodynamically unstable. Interestingly, attraction strengths that correspond closely to those of proteins isolated from the living lens fall right within the stable region of the phase diagram. This non-monotonic stability suggests new molecular mechanisms for eye lens opacification in cataract.

Extensive molecular dynamics simulation studies of particles interacting via a short-ranged attractive square-well potential arc reported. The calculated loci of constant diffusion coefficient D in the temperature-packing fraction plane show a reentrant behavior, i.e., an increase of diffusivity on cooling, confirming an important part of the high volume-fraction dynamical-arrest scenario earlier predicted by theory for particles with short-ranged potentials. The more efficient localization mechanism induced by the short-range bonding provides, on average, additional free volume as compared to the hard-sphere case and results in faster dynamics. © 2002 The American Physical Society.

We derive an analytical expression for the effective force between a pair of macrospheres immersed in a sea of microspheres, in the case where the interaction between the two unlike species is assumed to be a square well or a square shoulder of given range and depth (or height). This formula extends a similar one developed in the case of hard core interactions only. Qualitative features of such effective force and the resulting phase diagram are then analyzed in the limit of no interaction between the small particles. Approximate force profiles are then obtained by means of integral equation theories (PY and HNC) combined with the superposition approximation and compared with exact ones from direct Monte Carlo simulations., 34 pages