Entropic Mixing of Ring/Linear Polymer Blends

Abstract

The topological constraints of nonconcatenated ring polymers force them to form compact loopy globular conformations with much lower entropy than unconstrained ideal rings. The closed-loop structure of ring polymers also enables them to be threaded by linear polymers in ring/linear blends, resulting in less compact ring conformations with higher entropy. This conformational entropy increase promotes mixing rings with linear polymers. Here, using molecular dynamics simulations for bead-spring chains, ring/linear blends are shown to be significantly more miscible than linear/linear blends and that there is an entropic mixing, negative χ, for ring/linear blends compared to linear/ linear and ring/ring blends. In analogy with small angle neutron scattering, the static structure function S(q) is measured, and the resulting data are fit to the random phase approximation model to determine χ. In the limit that the two components are the same, χ = 0 for the linear/linear and ring/ring blends as expected, while χ < 0 for the ring/linear blends. With increasing chain stiffness, χ for the ring/linear blends becomes more negative, varying reciprocally with the number of monomers between entanglements. Ring/ linear blends are also shown to be more miscible than either ring/ring or linear/linear blends and stay in single phase for a wider range of increasing repulsion between the two components.

Miscibility and exchange chemical potential of ring polymers in symmetric ring–ring blends

“…In this study, symmetric blends of noncocatenated ring polymers with molecular weights near the entanglement molecular weight were investigated by using molecular dynamics (MD) and SGMC simulations. As mentioned above, it has been already reported in the preceding works 42,48 that the critical temperature of symmetric ring–ring blends is lower than that of the corresponding linear–linear blends. Sakaue and Nakajima model does not predict the phase behavior obtained by the simulations for symmetric ring–ring blends.…”

“…As mentioned in the introduction, the same conclusion that symmetric ring–ring blends are more compatible has been obtained in the study. 48 It was also pointed out that the miscibility increase for ring–ring blends was attributed to the fewer inter-molecular contacts.…”

“…For symmetric linear–linear blends of the bead-spring models, χ can be considered independent of the composition as studied in the literatures. 48,56,57 For symmetric ring–ring and linear–linear blends, we applied the same formula to evaluate χ as an effective miscibility parameter represented aswhere the superscript (L) and (R) represent the linear–linear blends and the ring–ring blends, respectively. We evaluated χN instead of χ by fitting the simulation data to eqn (3) because χN is scale invariant of coarse-grained models.…”

“…31,37,38 In addition to the rheological and mechanical properties, the phase diagrams of polymer blends and block copolymer melts are expected to be affected by ring topology. 13,[39][40][41][42][43][44][45][46][47][48] When ring polymers are used as additives to alter material properties, miscibility is an important factor for their applicability. In studies focusing on phase behavior within the framework of the random phase approximation, 49 scattering functions derived from the assumption of Gaussian statistics for ring polymers have often been used 40,41 while ignoring topological constraints.…”

Modular Software for Generating and Modelling Diverse Polymer Databases

“…[1][2][3][4][5][6][7][8][9][10] In order to optimize their aforementioned properties for this range of applications, the role of polymer constitution and topology has been widely explored, with a range of architectures including homopolymers, block copolymers, branched and ring polymers. [11][12][13][14][15][16][17] As a result of contemporary research activities, the chemical and structural domains of synthetic polymers are continuously growing. [18][19][20] Polymeric materials have been the focus of a significant amount of scientific research for many decades.…”