Nucleation effects of high molecular weight polymer additives on low molecular weight gels

Abstract

Polymeric species have been introduced to low molecular weight gelators to tailor their nucleation and rheological behavior. This work combines polymers and molecular gels (MGs) in a different manner by using polymers as the major component in a solution. Additionally, using polymers above their entanglement molecular weight is a step towards building polymer–MG composite materials. Specifically, a cholesterol-pyridine (CP) molecular gel was introduced to poly(ethylene oxide-co-epichlorohydrin) (EO-EPI) and poly(vinyl acetate) (PVAc), which have dissimilar chain conformations in anisole. Dynamic light scattering, scanning electron microscopy, and temperature-dependent small- and wide-angle X-ray studies were utilized to investigate the influence of the solution properties of high molecular weight EO-EPI and PVAc on the CP network structure. The collapsed chain conformation and aggregation of EO-EPI led to isolated, branched CP fiber networks, resulting in unexpectedly high dissociation temperatures. In contrast, PVAc gels displayed transient fiber networks, as evidenced by fiber wrapping and bundling. Cooperative interactions between PVAc and CP resulted in gels with dissociation temperatures higher than those of pure CP gels. These structural characteristics significantly influenced the gel mechanics. The collapsed chain conformation of EO-EPI led to weaker, more viscous gels, and the freely extended PVAc chain conformation led to interconnected, elastic gels independent of the molecular gel concentration. Polymer chain conformation was utilized to control the nucleation of a cholesterol-pyridine molecular gel. Collapsed chain conformations influence gel structure and dissociation behavior by acting as physical barriers that lead to confinement effects and permanent networks. An extended polymer chain conformation allowed for polymer–molecular-gel interactions and increased dissociation temperatures due to its highly ordered structure, resulting in transient networks. Additionally, the high molecular weight polymer solution behavior guided solution mechanics, where collapsed chains lead to viscous solutions and gels and extended chains led to elastic gel networks.