Effects of particle size and oxide shell on variable stiffness performance of phase-changing materials

Abstract

Phase-changing materials have recently found use as particulate fillers to engender stiffness-changing behavior in composites. In the transition from solid to liquid particles, the composite modulus can be significantly reduced, and then raised again as the particles are allowed to solidify. While the general effect of stiffness tuning in phase-changing composites has been demonstrated in a range of studies and applications, the most drastic stiffness ranges are provided by fusible metallic alloys, which are commonly subject to the formation of oxide shells on their surfaces. In this work, we examine the effect these oxide surfaces have on variable-stiffness performance, and investigate the corresponding role of particle size. In particular, we study particles of a low-melting-point metallic alloy, Field’s Metal, and we also present a facile method of manufacture that allows for control of particle size. We then manufacture a set of stiffness-changing composites using these particles and characterize mechanical performance, with the aim of controlling particle size to increase the total stiffness ratio while resisting material failure.

Augmentation of Liquid Metal Particle Mechanics via Non‐Native Oxide Nanoshells

“…[ 44 ] In the case of core‐shell particles, geometrical considerations are taken into account when determining the stiffness values of particles with different sizes and shell thicknesses. [ 66 ] Assuming constant values for the elastic modulus and Poisson's ratio for the shell, the stiffness of the compressed particle should be proportional to 1/ D as observed in Figure 4b. [ 35 ]…”

Liquid Metal + x: A Review of Multiphase Composites Containing Liquid Metal and Other (x) Fillers

“…Bartlett et al [198] reported that by dispersing eGaIn in silicone elastomer, the value obtained from Equation ( 2) was E i = 129 kPa, but they found agreement between their experimental data and Equation ( 1) when E i = 320 kPa (Figure 4B). The difference in the elastic modulus of inclusions could be attributed to the presence of stiff oxide skin around the liquid metal inclusions, as studied by Lear et al [156] and Buckner et al, [202] and also the interaction between adjacent inclusions, which was not predicted in Eshelby's theory.…”

“…[197] The reinforcing effect of the liquid-solid interface has been shown for single liquid-filled microcapsules [35] and also dispersed liquid inclusions in elastomers. [198][199][200][201][202][203] Style et al [196] postulated that to include the surface tension effect in the Eshelby equation for predicting composite elastic modulus E c , the liquid inclusions can be considered as soft elastic inclusions:…”

“…[204] In this double inclusion model (Figure 4D), the elasticity of the LM inclusions is actively tuned according to the relative shell thickness of gallium oxide surrounding each inclusion, where it is known that as the size of droplets decreases the oxide shell becomes more mechanically dominant. [156,202] Bury and Koh [69] employed a microcapacitor model in their work to study the electrical behavior of multiphase composites. Therein, the composite is modeled as a network of randomly distributed microcapacitors in the host matrix.…”

“…[ 197 ] The reinforcing effect of the liquid–solid interface has been shown for single liquid‐filled microcapsules [ 35 ] and also dispersed liquid inclusions in elastomers. [ 198–203 ] Style et al. [ 196 ] postulated that to include the surface tension effect in the Eshelby equation for predicting composite elastic modulus E c , the liquid inclusions can be considered as soft elastic inclusions: $$$$\begin{equation} E_c = E\frac{1+\frac{2}{3}\frac{E_i}{E}}{(\frac{2}{3}-\frac{5\phi}{3})\frac{E_i}{E}+(1+\frac{5\phi}{3})} \end{equation}$$$$where E i is the effective elastic modulus obtained from the properties of the dispersed and continuous phases as follows: $$$$\begin{equation} E_i = E\frac{24\frac{\gamma}{ER}}{10+9\frac{\gamma}{ER}} \end{equation}$$$$…”