The Osuji group (where I did my Ph.D.) had a very strong and fruitful relationship with the former Gin group of the University of Colorado-Boulder. One collaboration that was particularly fun was a mechanical analysis study performed with Dr. Lauren Bodkin. The paper, entitled “Effect of localized control of cross-link density on mechanical properties of bicontinuous cubic lyotropic networks via copolymerization with different singly-polymerizable monomers,” investigated several different chemical moieties that were similar in their general chemistries, but had different crosslinking modes. One of the investigated monomers could only crosslink at its polar head, one in the nonpolar tail, and one in both the head and tail regions. We made gyroid networks (what a wonderful structure, the gyroid) and investigated the tensile strength of each.
We found that by increasing our nonpolar crosslinking, we strengthened the tensile properties of the material, which helps support the assertion that nonpolar crosslinking groups in aqueous lyotropic species are necessary for overall stability. There was a turning point, though, as when we only incorporated the two crosslinking-mode species, we found that the films became more brittle due to a depletion of reacted crosslinking groups at the polar heads. The nonpolar groups interacted so fast that it harmed the overall tensile strength of the material. Incorporating only tail-based groups also upset the phase stability. We see in this paper the balancing act that all lyotropic liquid crystal films have to undergo when optimizing properties and structure.
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