Synthesis and thermal conductivity of monodisperse hollow silica nanoshperes

Monodisperse hollow silica nanospheres (HSNSs) with outer diameter of ~ 300 nm and shell thickness of ~ 50 nm were prepared via a spontaneous dissolution–regrowth process of solid silica nanospheres (SSNSs) in NaBH4 aqueous solution. Experimental results indicated that the as-prepared HSNSs have a reduced thermal conductivity of ~ 0.0519  0.0007 W/(m•K), compared to ~ 0.082  0.005 W/(m•K) of the corresponding SSNSs, from which the intrinsic solid thermal conductivity of individual SSNSs with a mean diameter of 200 nm can be calculated to be ~ 0.042 W/(m•K). Moreover, a small shell thickness and a small inner pore diameter are in general required to achieve HSNSs with low thermal conductivities.