Restricting Molecular Mobility in Polymer Nanocomposites with Self-Assembling Low-Molecular-Weight Gel Additives.

Multiscale investigation of molecular gel additives in polymer matrices guides understanding of how solution-state assemblies result in mechanically enhanced, solid-state nanocomposites. Model polymers, poly(ethylene oxide- co-epichlorohydrin) (EO-EPI) and poly(vinyl acetate) (PVAc), were utilized as matrices and reinforced by cholesterol-pyridine (CP) nanofiber networks. The CP nanofillers suppress ethylene oxide segment melting for EO-EPI composites, whereas for PVAc nanocomposites, cause a polymer-gel dissociation transition. Incorporation of crystalline CP fiber networks led to an order of magnitude increase in tensile storage modulus due to restrictions on polymer chain mobility. This decrease in molecular mobility was confirmed by decreased loss moduli for both EO-EPI and PVAc composites. Excitingly, PVAc nanocomposites display an additional relaxation mode caused by release of PVAc chains from the transient molecular gel assembly. For both EO-EPI and PVAc composites, bulk flow can be suppressed to temperatures up to 100 °C by simply increasing the CP concentration.