Fig. 2 Bubble solution preparation. (a) Mixing of NTs dispersed in THF with epoxy to make a uniform solution. (b) Different concentration SiNW– epoxy solutions: From left to right are 0.01, 0.03, 0.15 wt%, respectively. (c) Viscosity versus curing time for an epoxy solution, where the range suitable for bubble expansion is highlighted (hatched area).