Heat flux sensors used to measure thermal conductivity of a new type of hollow silica

greenTEG AG: greenTEG’s heat flux sensors were used to measure the thermal conductivity of a new type of hollow silica. Recently, hollow silica particles have attracted great attention due to their unique structural properties and possible applications as efficient catalysts, in optical devices, as drug delivery carriers, as thermal and electrical insulators. Researchers from ETH Zurich and Hiroshima University now developed an improved synthesis route to hollow silica particles starting from tetramethyl orthosilicate (TMOS) instead of ethyl ester. The new synthesis results in a higher quality of hollow silica and reduces production costs. The research has been published in Langmuir, 2016, 32 (1), pp 338–345.

Abstract

We present an improved synthesis route to hollow silica particles starting from tetramethyl orthosilicate (TMOS) instead of the traditionally used ethyl ester. The silica was first deposited onto polystyrene (PS) particles that were later removed. The here introduced, apparently minor modification in synthesis, however, allowed for a very high purity material. The improved, low density hollow silica particles were successfully implemented into polymer films and permitted maintaining optical transparency while significantly improving the heat barrier properties of the composite. Mechanistic investigations revealed the dominant role of here used methanol as a cosolvent and its role in controlling the hydrolysis rate of the silicic ester, and subsequent formation of hollow silica particles. Systematic experiments using various reaction parameters revealed a transition between regions of inhomogeneous material production at fast hydrolysis rate and reliable silica deposition on the surface of PS as a core–shell structured particle. The shell-thickness was controlled from 6.2 to 17.4 nm by increasing TMOS concentration and the diameter from 95 to 430 nm through use of the different sizes of PS particles. Hollow silica particle with the shell-thickness about 6.2 nm displayed a high light transmittance intensity up to 95% at 680 nm (length of light path ∼ 1 cm). Polyethersulfone (PES)/hollow silica composite films (35 ± 5 μm thick) exhibited a much lower thermal conductivity (0.03 ± 0.005 W m·K–1) than pure polymer films. This indicates that the prepared hollow silica is able to be used for cost and energy effective optical devices requiring thermal insulation.