Soft colloidal objects, such as microgels, are known to have phase behaviors that are quite different from their hard-sphere counterparts. For example, phenomena such as overpacking, self-healing, defect tolerance, and stimulus-induced annealing have all been demonstrated in colloidal crystals composed of microgels. In this contribution, we describe the phase behavior and defect tolerance of colloidal crystals composed of the softest microgels yet prepared. Using a synthetic approach that does not rely upon cross-linking monomers, but instead uses rare chain-transfer events to create the network, one can prepare "ultra-low cross-linked" (ULC) microgels. A combination of dynamic light scattering, optical microscopy, and atomic force microscopy are used to characterize the microgels and the resultant phases. Colloidal crystals prepared from these ULC microgels display all the properties described above, but in many cases the magnitude of the observed properties is significantly greater than those observed with standard cross-linked microgels. Surprisingly, observations of non-close-packed phases have also been made, suggesting that the extreme softness of the ULC microgels leads to packing phenomena not accessible using more rigid microgels.

Packing and defect tolerance of ultra-low cross-linked microgel assemblies

255th National Meeting (2018)

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