The assembly of small molecules into hierarchical networks is advantageous for guiding both material properties and stimuli-responsive behavior. In isolation, a single small molecule can arrange itself across molecular, nanometer, and micrometer length scales to form a robust network. However, these networks are typically only functional in the solution state, traditionally as gelatinous materials swollen with organic solvents. Although many of the networks can stand alone, short chain polymeric materials have been utilized to influence the nucleation modes of the small molecule gelators and guide their rheological behavior and mechanics. The addition of short chain polymers inspired us to investigate the impact of introducing long chain polymers, or polymers above their entanglement molecular weight, to these molecular gel systems.<br/>Utilization of polymers above their entanglement molecular weight allows us to explore both the solution and solid-state properties by fabricating molecular gel-reinforced composites. In this work, we explore the union of either shear thickening or shear thinning long-chain polymers with molecular gels and the resulting effects on nucleation and rheological behavior. We observed that the shear thickening polymer behaves as a physical barrier to gelation, and the rheological behavior of the gel network is highly concentration dependent. In contrast, the gel network formed in the presence of the shear-thinning polymer is not as sensitive to concentration fluctuations. <i>In-situ</i> small and wide angle X-ray experiments indicated that two different networks were formed, and the shear-thinning polymer exhibited a difference in structure than the one formed by the isolated molecular gel. Additionally, with the shear-thickening polymer the molecular gel seems to be forced into permanent network junctions, but with the shear thinning polymer the network is comprised of transient junctions. Interestingly, this difference in network seems to dictate thermomechanical behavior and whether the gel can dissociate in solid-state composites.

Molecular gel composites: From solution to solid-state reversibility

255th National Meeting (2018)

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