Synthesis and rheological behavior of shear thickening fluids (STFs) for liquid armor applications

Abstract

Shear thickening is a phenomenon which is generally observed in concentrated colloidal dispersions and defined as the increase in viscosity with increasing shear stress or shear rate. This property brings many drawbacks for general use and restrict their application areas as well as makes them beneficial in protective applications. Liquid armor is the most widely studied field of shear thickening fluids (STFs). The goal of this study is to produce STFs and measure their rheological behavior as well as preparing STF/aramid fabric composites and testing their mechanical properties in terms of stab, flexibility and ballistic tests.for liquid armor applications. For this purpose, fumed silica and polyethylene glycol (PEG) based dispersions were prepared by sonochemical method. The effect of filler concentration and molecular weight of continuous phase was observed by using 5-30 wt% fumed silica and PEGs having 200, 300, 400 and 600 g/mole molecular weight, respectively. Also, microstructural and thermal characterization of raw materials and STFs were performed. According to the collected rheological data, viscosity increment of STFs is increased with concentration. The maximum available viscosity was obtained for STF30-PEG 200 as 1622 Pa.s and the lowest critical shear rate was measured for STF30-PEG 300 as 11.1 s-1. Moreover, it was found that the viscous property dominates the elastic property of STFs with greater viscous modulus (G†) values than the elastic (G’) modulus. Both moduli values were also reflected the thickening property with varying angular frequency and strain %. Stab and ballistic tests showed that STF impregnation enhances the resistance property of neat fabrics. The maximum load was supported by aramid fabric/STF30-PEG200 composite as 137 N whereas the highest stiffness was measured as 9o for aramid fabric/STF30-PEG 600 composite. Also, in ballistic tests, the highest result was obtained as 623m/s for the sample which composed of a configuration of STF impregnated aramid and Ultrahigh molecular weight polyethylene (UHMWPE) fabrics with neat polyethylene (PE) laminae.