In-Situ Self-Assembly of Silica Nanoparticles Into Microfibers With Potential to Reinforce Polymers

Abstract

Silica nanosphere with a diameter of 10-15 nm were organized into fibers with a lenght of 15 mm and an aspect ratio of 100 by self-assembly in 1,4-dioxane. Dioxane causes a positive zeta potential on the silica surface thus silica in dioxane may behave as an acceptor (base catalyzer) causing decomposition of dioxane to acetaldehyde and its consequent polymerization into oligomer or polymer (polyoxyethylene) chains that bond the particles together. This process was proved using a thermogravimetric analysis which showed that the amount of polymerized dioxane is in the rang 2-3.5 wt. %. Composition of the polymerized dioxane was elucidated employing FTIR. The formation of fibrillar structures was driven kinetically during solidification. The size of the fibers was controlled by the drying rate. Fast-drying results in longer and thinner fibers. Nanosilica fibers can also be formed in a polymer matrix (e.g. polycarbonate) via the solvent-casting method. Formation of fibers in-situ in a soft rubber polymer matrix in one-step processing can provide a polymer reinforcement at two hierarchical levels -at the nanoscale by immobilizing polymer chains due to the presence of nanoparticles and the microscale by strain transfer to the fibers. Elastic modulus of the fibers was determined by wrinkling technique by compression on the elastic surface and by thermal treatment in the polycarbonate matrix. Both techniques showed modulus 43-46 MPa.

Thermodynamic Parameters Controlling Nanoparticle Spatial Packing in Polymer Solutions

“…All of the investigated solvents except dioxane, on the other hand, acted as bases. Dioxane, acting as an acid, demonstrated the ambivalent character of the silica surface, which acted as a base, and led to the formation of spherical silica nanoparticles into anisotropic microfibers (Figure S7), as reported in our previous work . Oxygen is the only heteroatom present in the polymers investigated in this study (PMMA, PVAc, PC; PS contains no heteroatoms).…”