Relaxation dynamics in a transient network fluid with competing gel and glass phases

Abstract

We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics.

Interference between the glass, gel, and gas-liquid transitions

“…4 of 11 and Fig. 11 of 13 ). Although not shown here (see, however, the SM), the corresponding two-step relaxation is also exhibited by the self-intermediate scattering function (self-ISF) F S ( k , τ ; t w ) ≡ <exp i k · [R( t w + τ ) − R( t w )]>.…”

“…Such fundamental knowledge would allow us to systematically build an understanding (even at “van der Waals” level) of the exploding experimental and computational information 8,9 on the general phenomenology of these non-equilibrium phases. One of the most illustrative examples is the amazing behavior observed when the ordinary equilibrium gas-liquid phase transition interferes with the non-equilibrium glass transition 10 , leading to remarkable multistep relaxation processes 11–13 and puzzling delay (or “latency”) effects 14–16 during the formation of gels by arrested spinodal decomposition.…”

“…When applied to LJ-like simple liquids, the same NE-SCGLE equations predict new dynamically-arrested phases, identified with gels and porous glasses 20 , and provides a kinetic perspective of the irreversible evolution of the structure of the system after being instantaneously quenched to the interior of its spinodal region 21,22 . The main aim of the following discussion is to illustrate the NE-SCGLE prediction that the seemingly complex interplay between spinodal decomposition, gelation, glass transition, and their combinations 11–13 , may be simply understood in terms of two kinetically competing limiting behaviors, associated with the two underlying dynamic arrest transitions predicted to exist 20 in the gas-liquid spinodal region by the very same NE-SCGLE Equation.…”

Connectivity, dynamics, and structure in a tetrahedral network liquid

“…At intermediate times, we reach a maximum that indicates the time at which the distribution of displacements is farthest from the Gaussian behavior. The position and height of this maximum increases upon cooling the system, reaching values at low T which are significantly higher than those reported for both fragile and strong glass forming-liquids such as binary mixtures of Lennard-Jones particles [60], models of supercooled water [61], or viscous silica [62] but comparable to other recently reported in network liquids with competing gel-glass phases [63]. Finally, at long times, α 2 (t) decreases, and the distribution seems to recover the Gaussian statistics, α 2 (t) = 0.…”

Relaxation functions and dynamical heterogeneities in a model of chemical gel interfering with glass transition

“…However, the distinction between gels and glasses may be still elusive when the two transitions coexist, as in some polymer or colloidal systems, where a crossover from gel-like to glass-like behaviour is observed on varying the control parameters (see, for instance, the P L64/D 2 O AHS micellar system studied in [17]). In this case, the relaxation functions may exhibit complex decays, such as multi-step and logarithmic decays [18,19].…”