Enhanced heat dissipation and hydrophobicity of PDMS/silver nanoshells nanocomposites

Abstract Enhancing the heat transfer properties of PDMS is critical for advancing its application in microfluidic systems, despite its inherent advantages of flexibility and biocompatibility. The study aims to augment PDMS's heat dissipation characteristics by incorporating silver nano-shells (SNS), synthesised by coating amine functionalized silica nanoparticles (NPs) with silver. The thermal conductivity of PDMS/SNS nanocomposites increases with higher SNS concentrations (1, 2, and 3 wt.%), reaching up to 0.357 W/(m·K), higher than 0.175 W/(m.K) value for pristine PDMS. Sessile water drop evaporation tests demonstrated more than 50% increase in drop evaporation rate on PDMS nanocomposites as compared to pristine PDMS at 3 wt.% SNS loadings, suggesting improved heat transfer pathways. The evaporation behaviour is quantitatively analysed and fitted using a theoretical framework for drop drying. Thermogravimetric and differential thermogravimetric analysis of the PDMS/SNS nanocomposites show that nanofillers have improved the thermal stability of the PDMS matrix in the temperature range of 300–460 °C and the decomposition temperature of pristine PDMS is lower as compared to PDMS nanocomposites. Theoretical calculations revealed that the oxygen atoms in PDMS, exhibit affinity for the silver atoms, indicating that SNS is likely to adsorb onto the polar oxygen sites of the PDMS chains without covalent bond formation. Electrostatic potential contour plots showed that the polarity of Si-O bond reduces due to delocalisation of charge density over the entire molecule, as a consequence of silver atom affinity towards polar oxygen sites. Therefore, the hydrophobicity of PDMS surface is significantly affected, resulting in higher contact angle as observed experimentally. In addition, incorporation of 3% SNS into PDMS matrix decreases the transmittance from 90% to 10% in the wavelength range of 350 nm to 900 nm.