(276b) Phase Diagrams for Mixtures of Dipolar Rods and Disks

Colloidal self-assembly is a powerful tool that can be used to create new materials with a wide range of applications. Anisotropic particles, in particular, offer a way to precisely control the structure that forms during the self-assembly process. Binary mixtures that contain anisotropic, interacting particles have been proposed as a way to introduce multiple functionalities into the self-assembled structure. We simulate binary mixtures of dipolar rods and dipolar discs in two-dimensions using discontinuous molecular dynamics to determine how the assembled structures of these mixtures differs from those seen in single component systems. Two different binary mixtures are investigated: a mixture of an equal number of dipolar rods and dipolar discs (“equal number”), and a mixture where the area fraction of dipolar rods was equal to the area fraction of dipolar discs (“equal area”). Phase boundaries between fluid, string-fluid, and “gel” phases are calculated and compared to the phase boundaries of the pure components. The equal number mixture displays phase changes from a fluid to a string-fluid and from a string-fluid to a “gel” at a slightly lower temperature than occur for single component dipolar rods. The equal area mixture shows these phase changes occurring at approximately the same temperature as single component dipolar discs. Looking deeper at the underlying structure of the mixture reveals complex interplay between the rods and discs and the formation of states where the two components are in different phases. The mixtures exhibit phases where both rods and discs are in the fluid phase, where rods form a string fluid while discs remain in the fluid phase, a rod string-fluid coexisting with a disc string-fluid, a “gel” that consists primarily of rods while the discs form either a fluid or string fluid phase, and a “gel” that contains both rods and discs. Our results give insight into how binary mixtures can be utilized to create complex aggregates by varying the relative composition of the two components. By manipulating the properties of one of the components it should be possible to fabricate bifunctional, thermally responsive self-assembled materials.