Hydrophobic, ultra-low refractive index films prepared by sol-gel process

• Published in: Materials letters Vol. 184; pp. 305 - 307
• Main Authors: Yuan, Ye, Yan, Genghua, Liu, Shaozhe, Lu, Xiaodi, Hong, Ruijiang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2016
• Subjects: Annealing; Hydrophobicity; Porous materials; Refractive index; Refractivity; Silicon dioxide; Sol gel process; Sol-gel preparation; Sols; Thin films; Triton; Ultra-low refractive index; Sol-gel preparation; Thin films; Porous materials; Ultra-low refractive index
• ISSN: 0167-577X; 1873-4979
• DOI: 10.1016/j.matlet.2016.08.057

Hydrophobic silica films with ultra-low refractive index were prepared by a simple sol-gel process. Triton X-100 (TX-100) was added into the alkaline silica sols to decrease the refractive index of the films. Polymethylhydrosiloxane (PMHS), with a tiny amount of platinum divinyltetramethyldisiloxane complex (Karstedt catalyst), was introduced into the sols to improve the films' hydrophobicity. The dependence of the films' properties on the additives contents, sols' aging time and the post annealing temperature were investigated. The refractive index values of the as-prepared films decreased with the increase of TX-100 content. To some extent, the values also increased with the PMHS content. FT-IR analysis on the composition of the films showed that the TX-100 was almost removed after the post annealing process at 500°C for 15min. Though the methyl groups on the film's surface were partly destroyed during the annealing process, its water contact angle (WCA) remained over 100°. The film with refractive index of 1.120 was obtained by controlling the process parameters. [Display omitted] •Silica films with refractive index as low as 1.120 were prepared.•Triton X-100 was first added into the alkaline silica sol to increase porosity.•Polymethylhydrosiloxane was added to enhance the hydrophobicity of the films.•The water contact angle of films could be increased from 10° to over 110°.