Relation between Polymer Conformational Structure and Dynamics in Linear and Ring Polyethylene Blends

Abstract

Flory theorem," stating that polymers in the melt are nearly "ideal," [28] in the specific sense that they should have similar excluded volume (EV) interactions as polymers at their theta point, i.e., ν = 1/2, simply does not hold for ring melts. Instead, ν for ring melts has often been reported to be near 2/5 [11,12,21,24] which is consistent with the theoretical estimate of Cates and Deutsch. [29] Recent computational studies [16][17][18]30,31] have suggested that very long rings in the melt should be in a collapsed globular state for which ν equals 1/3. On the other hand, Lang et al. [32] have argued for a value of ν = 3/8 for high mass rings, an exponent close, but not equal to the value for collapsed chains. Despite the uncertainty in the exact exponent value, it seems safe to conclude that ν is significantly less than 1/2 so that the conformation of melt rings does not conform to random walk (RW) chains with screened excluded volume interactions.The absence of screening of excluded volume in rings implies that the addition of solvents and linear polymers to ring melts should lead to different effects than adding these molecular species to linear polymer chain melts. This phenomenon has been considered in previous work, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] but the nature of this swelling process is not yet entirely clear, and the present work is devoted to further elucidating this problem from a new perspective not relying on the reptation model. There have admittedly been numerous arguments, [29,33,34] experiments, [33][34][35][36][37][38][39][40][41] and simulations [42][43][44][45][46][47][48] pertaining to the configurational properties and dynamics of rings diluted by linear chains. Originally, Cates and Deutsch [29] suggested that the topologically induced EV interactions in the ring melt are relieved upon diluting the rings by linear chains so that the rings in the melt should become "ideal" upon dilution by linear chains. Recent simulations [44][45][46][47][48] and experiments [40,41] on ring-linear polymer blends have reported that rings increase their size upon the dilution and their conformational structure resembles ideal rings in a theta solvent, clearly supporting a change in the EV interactions in ring melts upon adding linear chains. Moreover, the rate of diffusion of tracer ring polymers in the melt was found to be greatly slowed by adding linear chains, an effect interpreted as arising from the ring-linear polymer threadings. [33,[35][36][37][38][39]43,48] Although there have been many attempts at quantifying this physically appealing "threading effect," [7,[35][36][37][38][43][44][45][46]48] the validity of the threading model has not yet been established. In this communication, we consider an alternative explanation of the slowing down of Ring-Linear Chain BlendsAtomistic molecular dynamics simulations of ring-linear polyethylene blends are employed to understand the relationship between chain conformational structure and the melt dynamics of these blends. As o...

Influence of Branching on the Configurational and Dynamical Properties of Entangled Polymer Melts

“…We emphasize that this asymptotic large mass scaling of Rg∼Mnormalw1/2 has only been established for linear polymer chains . Recent simulation and experimental work has indicated that Rnormalg for unknotted rings scales with polymer mass with a power of approximately 1/3 with increasing polymer mass [51,52,53]. This scaling would imply that p should diverge to infinity as Mw→∞ for polymers having this non-linear molecular topology.…”

Composite entanglement topology and extensional rheology of symmetric ring-linear polymer blends

“…Blending rings with linear chains produces even more intriguing viscoelastic behaviors due to the interplay of arXiv:2107.01491v1 [cond-mat.soft] 3 Jul 2021 their distinct topologies. The closed-loop structure of rings enables them to be threaded by other chains [19,20,21,22,23,24,25,26,27], which can significantly alter chain conformations [28,29,30], segmental dynamics [19,12,31,32], and blend viscosity [33,34,21,35]. Roovers showed for ring-linear blends of polybutadiene with approximately 15.3 entanglements per chain that there was a maximum in zero-shear viscosity for a ring fraction φ R ∼ 0.4 [36].…”

“…These analysis enable us to directly quantify and visualize the flow-driven unthreading of rings from the linear network during elongation. While prior simulation studies have separately characterized some of these quantities for different ring-linear systems [47,23,30,43,32], these results are difficult to aggregate due to variations and limitations in system size, concentration, polymer size, and the degree of ring-linear threading. Thus, in order to build a fuller and clearer picture of topological threading in ring-linear blends, we have generated systems of well-entangled chains with system sizes that are a factor 5-10 times larger than typically found in the literature.…”

Ring and Linear Copolymer Blends under Confinement

“…Although the change of size within the considered interaction range is small its overall effect on the domain size is significant as indicated by the significant shift in the peak position of S(q). Note that the swelling of ring polymers upon addition of small molecules/solvents and linear polymers in the case of homopolymers has been observed in earlier studies, [15][16][17] however it is reported that the nature of swelling is not clear. And in a recent study by Jeong and Douglas it is shown that the swelling arises from altered self-excluded volume interactions which amplifies in the entangled regime.…”

“…For example, sufficiently long ring polymers are shown to behave as compact object (i.e., size ∼ N 1/3 with N chain length), also unexpected power-law stress relaxation is observed in entangled ring polymers, [8][9][10][11] and smaller diffusion coefficient [12]. Interesting observations are made in case of ring-linear blends, e.g., it shows enhancement of miscibility due to the topological entropy gain of rings upon mixing with linear chains, [13,14] swelling of rings and unusual dynamics of rings in the matrix of linear chains, [15][16][17] and dramatic increase of viscosity of linear melts by adding rings [18]. Recent efforts in understanding the equilibrium and out-of-equilibrium properties of ring * slenin2001@gmail.com polymers focus mainly on homopolymers.…”