The effect of polyhedral oligomeric silsesquioxane dispersant and low surface energy additives on spectrally selective paint coatings with self-cleaning properties

摘要

Thickness-Insensitive Spectrally Selective (TISS) paint coatings were made of fluoropolymer resin binder (Lumiflon (LF), Asahi Glass Co., Ltd., Japan) and their water- and oil-repellent properties were obtained (contact angle: θ_(water)～150°, θ_(n-hexadecan)～55°) by the addition of Polyhedral Oligomeric Silsesquioxane (POSS) characterized by amino (AP), isooctyl (IO) and perfluoro (PF) groups (i.e.AP_2IO_4PF_2) attached on the silsesquioxane cube (–SiO_(3/2))_8. Paint dispersions were made by modifying of black spinel pigment with trisilanol isobutyl (IB_7T-7(OH)_3) POSS dispersant and with a single-capped silane isobutyltrimethoxysilane (IBTMS). Infrared and ~(29)Si NMR spectra measurements were used for the identification of the structural characteristic of the corresponding POSS compounds. Surface free energy values of the pure cross-linked (no pigment added) LF binder which was determined from the measured contact angles for water, diiodomethane and formamide revealed the γ~(tot) value of the LF unpigmented resin with added AP_2IO_4PF_2 T_8 POSS was about 16.4mN/m, which led to the θ_(water)～110°,indicating enhancement of the hydrophobicity of the pure LF resin binder (θ_(water)～89°).SEM micrographs, which were used for the assessment of the TISS paint coating surface morphology confirmed the beneficial dispersive effect of IB_7 T_7(OH)_3 dispersant as compared to the IBTMS silane.The presence of large Aluminium flake pigment and finely ground black pigment led to the formation of TISS paint coating surface, which exhibited bi-hierarchical roughness, resulting in water sliding angles of less than 10°, indicating the possible self-cleaning effect (θ_(water)>150° and θ_(n-hexadecane)～55°). The use of POSS dispersant and POSS low surface energy additive also enhanced spectral selectivity, which became the highest known so far for the black TISS paint coatings (e_T～0.24 and a_s～0.93). The use of simple silane IBTMS dispersant even in the presence of the AP_2IO_4PF_2 T_8 POSS did not lead to the oil-repellent effect confirmed by spreading of n-hexadecane on the surface of the corresponding TISS paint coating.