Unraveling the Polymer Chain-Adsorbed Constrained Interfacial Region on an Atomistically Thin Carbon Sheet

Thermal evolution of a polymer-nanoparticle binary mixture

We experimentally probe the microscopic variations in a model polymer-nanoparticle (NP) binary mixture (mixture of polybutadiene and clay nanoplatelets) across a thermal evolution path for which Tevolution > Tg(polymer). The evolution of the NP dispersion, NP crystallinity, polymer chain-NP interface, and nature of polymer chain-NP interaction are mapped for a spectrum of temperatures and NP concentrations constrained by experiments. Multiple pieces of evidence indicate that thermal evolution does not influence the nature of interparticle dispersion and is also independent of NP concentration in the binary mixture. However, the NP crystalline order significantly reduces across the thermal evolution path. Thermal evolution induces a transition of a sharp polymer chain-NP interface to a diffuse interfacial layer. In contrast, an already diffuse polymer-NP interface existing in the binary mixture due to particle crowding at high NP concentrations undergoes no significant change in its nature across the evolution path. At all particle concentrations, thermal evolution changes the dominant interaction from polymer chain-polymer chain to polymer chain-NP. These insights aid in explaining the molecular origins of unique and anomalous behaviors shown by polymer-nanoparticle binary mixtures while undergoing thermal evolution.

Hydration influences on the phase heterogeneity of segmented copolymers

We elucidate the influences of hydration on the morphological heterogeneity of the class of hard-soft segmented copolymers by experimenting on three model members selected from this group. For influences on phase segmentation, we quantify the degree of phase separation, segment boundary diffusiveness and extent of interphase mixing. Qualitative variations induced by hydration in hydrogen bonding within the phases are also mapped. An inverse relationship between the degree of segmentation and inherent water miscibility of the polymer backbones is observed, that is, high miscibility reducing the degree of segmentation, whereas poor miscibility increasing it. We then quantify hydration induced variations in the size, volume fraction and interaction pair potentials of individual hard segments. The influences on hard segment assemblies are assessed by quantifying their size, volume fraction, interaction pair potential and intrasegment adhesion. This quantification reveals a complex interplay between the volume expansion of individual hard segments and simultaneous swelling and disassembly of their assemblies. Finally, we integrate the segmentation parameters with observed alterations in hydrogen bonding and the inherent polarizability of segments to present a mechanism that reasonably describes the hydrated state morphology. Besides revealing the influences of hydration on the morphological heterogeneity of this class of polymers, our insights give strategies for new synthesis methods for water contact applications and aids in predicting their hydration induced thermomechanical property alterations.