A liquid jams into an amorphous solid, e.g. glass, when it is quickly quenched or compressed. At zero temperature and shear stress, packings of frictionless spheres undergo the jamming transition at a critical-like point J in the framework of the jamming phase diagram. The criticality of Point J has been extensively studied recently.

Recent experiments and simulations have shown that in the vicinity of Point J at T > 0, the first peak of the pair distribution function exhibits a maximum at a crossover volume fraction (pressure) varying with the temperature. We find that this crossover is accompanied with apparent changes of material properties. Surprisingly, multiple quantities show critical scaling collapse, implying the criticality of Point J. Therefore, the structural signature shown at the crossover contains important physics. We also find that isostaticity still controls the flattening of the density of vibrational states, a special feature of the T = 0 jamming transition, in thermal colloidal systems. We thus propose a phase diagram to state the complexity during the formation of amorphous solids such as glasses. 

Polymer glasses are ubiquitous “thermoplastic” materials that are widely employed in industry and daily life. Fundamental understanding of their ultraslow nonequilibrium dynamics and nonlinear mechanical properties remains a challenging problem. Recently, we have developed a microscopic nonlinear Langevin equation theory of segmental relaxation and elasticity of polymer glasses and then extended it to address many important issues including physical aging, mechanical rejuvenation, stress-accelerated relaxation, yielding, strain softening, strain hardening, etc. The key structural variable of the theory is the amplitude of long wave length density fluctuations which is directly observable in scattering experiment.