Network domain structure in phase-separating polymer solutions

Abstract

The Soret effect in dilute polymer solutions: Influence of chain length, chain stiffness, and solvent quality Results from molecular dynamics simulations of phase separation in a quenched polymer solution are presented for both two-and three-dimensional systems. Simulations clearly demonstrate the existence of a networklike pattern formation at an early to intermediate time regime for sufficiently dense polymer solutions. This network structure, however, relaxes at late times as the minimization of the interface energy wins over the elastic stress of the network. A crossover of domain growth exponent from a smaller value at intermediate times to the Lifshitz-Slyozov value of 1/3 at late times is seen in three-dimensional ͑3D͒ simulations of network breakup. Our results for the late-time growth exponent and dynamical scaling of the structure factors strongly indicate that the late-time growth kinetics of quenched polymer solutions belong to the same universality class of small molecular mixtures.

Poly(N‐isopropylacrylamide) Phase Diagrams: Fifty Years of Research

“…[53] Thev iscoelastic effect as discussed above with regard to mesoglobules is expected to occur upon quenching of solutions below the overlap threshold, f < f*. [69,70] Such effects were also invoked in discussing relatively long-lived transient structures occurring upon quenching of solutions at higher concentrations below the critical composition f c i.e., initial states with f* < f < f c .Inthis case the quench initially resulted in network-like structure formed by the minority, polymer-rich phase and the solvent rich domains. [53,57] The structure and its evolution was discussed in terms of at ransient gel arising because of entanglements and intrachain attraction in poor solvents.O ns hort time scales the overall volume of the gel is basically constant and chain-chain attraction in concert with connectivity constraints leads to microphase separation.…”

Poly(N‐isopropylacrylamid)‐Phasendiagramme: 50 Jahre Forschung

“…Sie argumentierten, dass das Wachstum der Mesokügelchen als Reptationsprozess aufzufassen ist, dessen Dynamik durch die charakteristische Zeit t rep % (h a 3 /k B T)N 0 a pr bestimmt ist. [69,70] Solche Effekte spielten auch eine Rolle bei der Diskussion relativ langlebiger transienter Strukturen, die beim "Quench" von hçher konzentrierten Lçsungen unterhalb der kritischen Konzentration f c ,also für Anfangszustände mit f* < f < f c ,auftauchten. [14] Man beachte,d ass t rep mit zunehmender "Quench"-Tiefe DT,d ie ihrerseits das zeitabhängige f pr beeinflusst, ansteigt.…”

Shear effects on phase separating polymer solutions: A molecular dynamics study

“…The -temperature for this model in two dimensions is known to be T (r c ϭ2.5)Ϸ0.9 in reduced units. 11,12 A quench of a polymer solution from a high temperature single phase to a temperature below T should produce a phase separation of the polymer chains from the solution. Rather than carrying out such a temperature quench we have prepared the solution as a good solvent for the polymer chains by using a cutoff distance r c ϭ2 1/2 .…”

“…In the absence of any external shear field such a quench produces a network domain structure at early and intermediate times which relaxes at very late times. 11,12 In the present work, we performed the quench in the presence of an applied shear field to the system. The imposed shear flow is along x direction, while the shear gradient is along the y direction, i.e., the external shear velocity can be written as…”

“…Such a spongelike network structure of domains has been observed in some recent experiments [3][4][5] and numerical simulations. [10][11][12][13] For a proper understanding of this most unusual pattern formation, one needs to incorporate polymer-specific effects such as conformation and entanglement of the chain molecules in the theoretical study of the dynamic process, 14 in addition to the inherent nonlinearity present in the coarsening of quenched binary liquid mixtures. 8,9 In this context, our recent molecular dynamics ͑MD͒ simulations 11,12 of phase separation in quenched polymer solutions have been quite useful in characterizing the formation and subsequent relaxation of the network domain structure.…”