Correspondence between the rigid amorphous fraction and nanoconfinement effects on glass formation

Abstract

Semicrystalline polymers' properties are strongly influenced by the presence of a "rigid amorphous fraction" (RAF) of material with enhanced glass transition temperature and suppressed mobility. Here, we review striking similarities between this domain and near-interface regions of altered dynamics in other nanostructured polymers, including thin films, nanocomposites, layered films, and ionomers. Building on these observations, we present results of molecular simulations of model nanolayered polymers in which one layer is crystalline. The results of these simulations, which bear close similarities to semicrystalline homopolymers while providing a well-defined equilibrium crystal size, suggest that the RAF shares the same phenomenology and mechanism as dynamic interphases in these other polymeric systems. Specifically, the fraction of rigid amorphous material is driven by the scale of cooperative rearrangements characteristic of dynamics in polymers and other supercooled liquids. These results situate the RAF as a specific instance of a general tendency towards broad dynamic interphases in polymers and other glass-forming materials. V C 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 907-918

Crystallization-induced formation of rigid amorphous fraction

“…The RAF has been discovered in almost all semicrystalline polymers, as well as in a large array of interfacially‐rich polymeric systems that exhibit alterations in dynamics and glass formation behavior . This large array includes nanolayered polymers, block copolymers, as well as polymer nanocomposites .…”

“…The RAF has been discovered in almost all semicrystalline polymers, [1] as well as in a large array of interfacially-rich polymeric systems that exhibit alterations in dynamics and glass formation behavior. [3,4] This large array includes nanolayered polymers, [5][6][7] block copolymers, [8,9] as well as polymer nanocomposites. [10][11][12][13][14][15][16][17][18] Like the RAF of semicrystalline polymers, all these systems exhibit evidence of a domain near internal or external interfaces in which dynamics and glass formation behavior are profoundly altered.…”

“…II-Form I transformation of PB-1 is connected with densification of the chains, as the crystal density increases from 0.91 g/cm3 in Rigid amorphous fraction (w RA ) of poly[(R)-3-hydroxybutyrate] after cooling from the melt at the indicated rates and annealing at 25 C, plotted as a function of crystallinity (w C ).…”

Structure, nanomechanics, and dynamics of dispersed surfactant‐free clay nanocomposite films

“…TEM analysis suggests clay tactoids have aspect ratios around 2‐2.4. Based on the Halpin‐Tsai (HT) Model's prediction , these aspect ratio values can give rise to a nominal 1.08% increase in Young's modulus. Our results are in rough agreement with this prediction.…”

“…First, it has long been known that interfacial interactions between amorphous and crystalline domains in semicrystalline polymers can induce the formation of a “rigid amorphous fraction” of amorphous material with suppressed dynamics . Simulation results indicate that this effect is likely physically equivalent to alterations in dynamics near nanoparticles and in thin films . Second, as discussed above the nanofillers can also induce spatially varying alterations in dynamics.…”