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.

Deducing Multiple Interfacial Dynamics during Polymeric Foaming.

Several interfacial phenomena are active during polymeric foaming, the dynamics of which significantly influence terminal stability, cell structure, and in turn the thermomechanical properties of temporally evolved foam. Understanding these dynamics is important in achieving desired foam properties. Here, we introduce a method to simultaneously portray the time evolution of bubble growth, lamella thinning, and plateau border drainage, occurring during reactive polymeric foaming. In this method, we initially conduct bulk and surface shear rheology under polymerizing and nonfoaming conditions. In a subsequent step, foaming experiments were conducted in a rheometer. The microscopic structural dimensions pertaining to the terminal values of the dynamics of each interfacial phenomena are then measured using a combination of scanning electron microscopy, optical microscopy, and imaging ellipsometry, after the foaming is over. The measured surface and bulk rheological parameters are incorporated in time evolution equations that are derived from mass and momentum transport occurring when a model viscoelastic fluid is foamed by gas dispersion. Analytical and numerical solutions to these equations portray the dynamics. We demonstrate this method for a series of reactive polyurethane foams generated from different chemical sources. The effectiveness of our method is in simultaneously obtaining these dynamics that are difficult to directly monitor because of short active durations over multiple length scales.