Phase Separation and Liquid Crystallinity in Mixtures of Rigid and Flexible Biopolymers

Structured soft materials have internal order that give rise to unusual mechanical properties and emergent organization of inclusions and defects. Here we present a composite structured liquid formed from biopolymers of distinct rigidities. Biopolymer filaments, such as actin and microtubules, behave as rigid rods when much shorter than their persistence length. These short, rigid filaments are known to crowd into a thin fluid layer that can form a nematic liquid crystal, where filaments have orientational order but not positional order. Here we investigate the phase space in a mixture of short, rigid, nematic forming filaments with more flexible biopolymers, which are much longer than their persistence length. Using fluorescence microscopy, we investigate the domain and defect formation as the phase separated polymer mixture evolves. Using a continuum model of lyotropic liquid crystal, we extract material properties of the liquid crystal. Our results suggest a novel structured soft composite, which potentially informs physical mechanisms of controlling material properties in structured fluids and templating functional polymeric materials.