title: Hollow Silica as an Optically Transparent and Thermally Insulating Polymer Additive.
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.
authors.affiliation: Department of Chemical Engineering, Hiroshima University , 1-4-1 Kagamiyama, Hiroshima 739-8527, Japan.
authors.forename: Lusi
authors.initials: L
authors.lastname: Ernawati
authors.affiliation: Department of Chemical Engineering, Hiroshima University , 1-4-1 Kagamiyama, Hiroshima 739-8527, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ogi
authors.affiliation: Department of Chemical Engineering, Hiroshima University , 1-4-1 Kagamiyama, Hiroshima 739-8527, Japan.
authors.forename: Ratna
authors.initials: R
authors.lastname: Balgis
authors.affiliation: Department of Chemical Engineering, Hiroshima University , 1-4-1 Kagamiyama, Hiroshima 739-8527, Japan.
authors.forename: Kikuo
authors.initials: K
authors.lastname: Okuyama
authors.affiliation: Institute for Chemical and Bioengineering, ETH Zurich , Wolfgang-Pauli-Strasse. 10, CH-8093 Zürich, Switzerland.
authors.forename: Mario
authors.initials: M
authors.lastname: Stucki
authors.affiliation: Institute for Chemical and Bioengineering, ETH Zurich , Wolfgang-Pauli-Strasse. 10, CH-8093 Zürich, Switzerland.
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Hess
authors.affiliation: Institute for Chemical and Bioengineering, ETH Zurich , Wolfgang-Pauli-Strasse. 10, CH-8093 Zürich, Switzerland.
authors.forename: Wendelin J
authors.initials: WJ
authors.lastname: Stark