Surface hydrophobicity: effect of alkyl chain length and network homogeneity

Abstract

Understanding the nature of hydrophobicity has fundamental importance in environmental applications. Using spherical silica nanoparticles (diameter= 369 ± 7 nm) as the model material, the current study investigates the relationship between the alkyl chain network and hydrophobicity. Two alkyl silanes with different chain length (triethoxymethylsilane (C1) vs. trimethoxy(octyl)silane (C8)) were utilised separately for the functionalisation of the nanoparticles. Water contact angle and inverse gas chromatography results show that the alkyl chain length is essential for controlling hydrophobicity, as the octyl-functionalised nanoparticles were highly hydrophobic (water contact angle= 150.6° ± 6.6°), whereas the methyl-functionalised nanoparticles were hydrophilic (i.e., water contact angle= 0°, similar to the pristine nanoparticles). The homogeneity of the octyl-chain network also has a significant effect on hydrophobicity, as the water contact angle was reduced significantly from 148.4° ± 3.5° to 30.5° ± 1.0° with a methyl-/octyl-silane mixture (ratio= 160:40 µL·g^–1 nanoparticles).

Graphical abstract

Keywords

hydrophobicity / surface energy / wettability / alkyl chain network / silica nanoparticle

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Acknowledgements

This study is part of the SCoBiC project funded by the UK’s EPSRC (EP/N015916/1). The authors declare no conflict of interests.

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ƒSupplementary material is available in the online version of this article at https://doi.org/10.1007/s11705-020-2003-0 and is accessible for authorized users.

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