Thermal, Mechanical, and Acoustic Properties of Polydimethylsiloxane Filled with Hollow Glass Microspheres

Abstract

Polydimethylsiloxane (PDMS) is the most widely used silicon-based polymer due to its versatility and its various attractive properties. The fabrication of PDMS involves liquid phase cross-linking to obtain hydrophobic and mechanically flexible material in the final solid form. This allows to add various fillers to affect the properties of the resulting material. PDMS has a relatively low Thermal Conductivity (TC), in the order of 0.2 W/mK, which makes it attractive for thermal insulation applications such as sealing in construction. Although a further decrease in the TC of PDMS can be highly beneficial for such applications, most research on the thermal properties of PDMS composites have focused on fillers that increase the TC rather than decrease it. In the present work, we propose a simple and reliable method for making a PDMS-based composite material with significantly improved thermal insulation properties, by adding hollow glass microspheres (HGMs) to the mixture of the liquid base and the cross-linker (10:1 ratio), followed by degassing and heat-assisted crosslinking. We obtained a 31% reduction of thermal conductivity and a 60% increase in the elastic modulus of samples with HGM content of 17% by weight. At the same time, the sound insulation capacity of the PDMS-HGM composite is slightly decreased in comparison to pure PDMS, as a result of its lower density. Finally, the wettability of the samples had no dependence on HGM content.

Polydimethylsiloxane/Glass-Based Composite Elastomer for Thermophysical Applications

“…Less steep linear decrease is observed from 2.5 wt% to 10 wt% HGM content leading to the total decrease in thermal conductivity down to 0.059 W/m•K (or by 57% relative to the pristine PDMS), which is already between the thermal conductivity of asbestos (0.08 W/m•K [22]) and mineral wool (0.04 W/m•K [23]). This is a significantly more pronounced effect than the one reported for PDMS-HGM composite by Vlassov et al [12] (approximately 22% decrease for 10 wt%). Possible reason may be related to structural integrity of the spheres during the mixing stage.…”

“…The essential difference between materials used in this work and Ref. [12] is that Vlassov et al used HGM produced by other maker (Q-CEL 300, Potters). It is possible that HGM used in our study may be more resistant to mechanical damage during the mixing stage.…”

“…The ratio of base and curing agent for mixing, according to the documentation, is 10:1. This set was chosen as the basis (matrix) in many scientific articles [1,2,12,21], which made it a widely used model elastomer. HGM (Graphite PRO, Russia) with a bulk density of 0.19 g/cm 3 were used as a filler.…”

“…Possible methods include the formation of pores in the matrix (material) [9], and the introduction of more heat-insulating or heat-reflecting materials into the volume of the material [10]. At the moment, only few works [11][12][13] are available on reducing thermal conductivity of PDMS by filler addition, which is probably due to the initial relatively low thermal conductivity of PDMS (λ ≈ 0.17 W/m•K) [9].…”

“…Nevertheless, care should be taken to avoid damaging of HGMs that otherwise may result in opposite effect on heat conductivity [20]. In a recent study by Vlassov et al [12] authors prepared PDMS-HGMs composites using commercially available HGMs (Q-CEL 300, Potters) and achieved 31% reduction of thermal conductivity (from 0.16 to 0.11 W/m•K) at 17 wt% HGM content. This is significantly less than results obtained by Lee et al [13] with aerogel filler, but PDMS-HGMs composite benefits from simplicity of preparation and more user-friendly cost.…”