Shape-Stable Composites of Electrospun Nonwoven Mats and Shear-Thickening Fluids

Abstract

To improve the flexibility of the fabric stacks used in protective clothing, shear-thickening fluids (STFs) have previously been incorporated into woven microfiber fabrics to enhance their impact resistance. However, the microfiber−STF composites can exhibit loss of the STF from the composite over time due to the large interstitial spaces between fibers, resulting in limited long-term shape stability. In this study, nonwoven mats of electrospun ultrafine fibers (UFFs) were used in place of woven microfiber fabrics to improve the STF retention within the fiber−STF composites by taking advantage of high specific surface area, small pore size, and large capillary force. The UFF−STF composite, comprising an electrospun polyamide (PA 6,6) UFF mat and a fumed silica (FS) STF, exhibited excellent shape stability with high breakthrough pressure and improved STF retention compared to composites based on conventional microfiber fabrics. The mechanical response of the composite is shown to depend on the rate of deformation. At strain rates lower than the shear-thickening threshold of the STF, the introduction of STF resulted in no stiffening or strengthening of fiber mats, allowing the composite to remain flexible. At high deformation rates above the onset of shear thickening, the incorporation of STF improved both the elasticity and the viscosity of the material. In addition, the shape stability and the mechanical properties of the composite were influenced by the STF viscosity and the UFF morphology. STF with high particle loading and UFF with small fiber diameter resulted in a more pronounced enhancement to membrane performance.

Shear Thickening Fluid and Its Application in Impact Protection: A Review

“…A new composite consisting of electrospun ultrafine fibers and STF was developed to improve the shape stability of STF-impregnated fabrics. The composites were demonstrated to be shape-stable with high breakthrough pressure due to the small effective pore size and the high capillary force of UFF membranes [ 154 ]. Chen et al proposed a direct microencapsulation of Ionic-Liquid-based STF and designed a circuit made of Ionic-Liquid-based STF microcapsules-incorporated conductor.…”

Shear thickening fabric composites for impact protection: a review

“…Test results showed that the applied impact force on treated STF-impregnated fabric was less than that on pure STF-impregnated fabric, and thereby the STF properties could affect the cushioning effects of fabrics. Hao et al 74 introduced a new composite consisting of electrospun polyamide ultrafine fiber (UFF) non-woven mats and STF to improve the shape stability of fabrics (Figure 8(b)). Drop impact tests were conducted to characterize the viscoelastic response under a high deformation rate.…”

“…(a) Low-velocity drop-weight impact testing (Copyright 2019, Elsevier), 84 drop-weight tests on (b), (c) electrospun a non-woven mat/shear thickening fluid (STF) composite (Copyright 2020, American Chemical Society), 74 and (d), (e) a warp-knitted spacer fabric (WKSF)/STF composite (Copyright 2013, Elsevier). 59 …”

“…Hao et al. 74 introduced a new composite consisting of electrospun polyamide ultrafine fiber (UFF) non-woven mats and STF to improve the shape stability of fabrics (Figure 8(b)). Drop impact tests were conducted to characterize the viscoelastic response under a high deformation rate.…”

Warp-knitted spacer fabric flexible composites with high stability and low-velocity impact resistance infused by flock-reinforced shear thickening gel

“…Shear thickening gel (STG) is a colloidal functional material whose modulus increases instantaneously with increasing shear rate, and its state transforms from viscous liquid to solid. 4,5 Compared to shear thickening fluid (STF), which is also stimuli-responsive and has been extensively studied, [6][7][8][9] STG is more viscous in its natural state and exhibits better stability. 10 When subjected to impact, the shear thickening effect and viscoelastic deformation of STG results in a massive expansion of the impacted area, while the impact force and energy are diffused and absorbed, 11 and thereby a variety of STG composites have been prepared for impact protection.…”