Interfacial self-assembly of polysaccharide rods and platelets bridging over capillary lengths

Generation of long-range ordering of colloidal particles through anisotropic interactions is of growing interest in material designing. At submicron-scale, routine works use synthetic spheres or rods but the knowledge pertaining to assembly of binary combination of particles is severely restricted. Improved understanding of the fundamental aspects that drive self-assembly, can lead to robust strategies for fabrication of topographically oriented films.

The fluidical geometry of a liquid crystalline (LC) solution of polysaccharide consisting of micron-sized rod and platelet units was explored. The solutions, characterized for their rheological behavior, were evaporated from a rectangular cavity. The assembly and orientation of the units was monitored by polarizing microscopy and the interparticle capillary forces approximated mathematically.

The units deposited into an uninterrupted membrane upon interfacial evaporation, forming a bridge along the 8 mm gap, linking the substrates. The membrane, composed of a lamellar structure, was uniaxially oriented along the direction of the gap. The rheological estimations corroborated an extremely high value of viscosity with the presence of crosslinking junctions in this solution when compared to a solution with only rod units, capable of bridging a maximum of 1 mm. It has been demonstrated for the very first time that the presence of platelet-units contributes lateral capillary interactions and assist rod-units towards a wider, self-assembled structure.