Polyhedral oligomeric silsesquioxane trisilanols as pigment surface modifiers for fluoropolymer based Thickness Sensitive Spectrally Selective (TSSS) paint coatings I. Jerman a , M. Mihelc ˇic ˇ a , D. Verhovˇ sek b , J. Kovac ˇ c , B. Orel a,n a National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia b Cinkarna—METALUR ˇ SKO KEMI ˇ CNA INDUSTRIJA CELJE, d.d. Kidric ˇeva 26, 3001 Celje, Slovenia c Joz ˇef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia article info Article history: Received 22 April 2010 Accepted 4 August 2010 Available online 12 October 2010 Keywords: Pigment surface modification Open POSS Selective paint abstract Thickness Insensitive Spectrally Selective (TISS) paint coatings based on black pigment (PK 3060, Ferro Company) dispersed in a fluoropolymeric resin binder (Lumiflon, Asahi Company, Japan) have recently been made without added aluminium flakes and their properties have been reported for the first time. In this study we investigated in more detail the effect of trisilanol isobutyl (IB 7 T 7 (OH) 3 ) polyhedral oligomeric silsesquioxane (trisilanol POSS) on the surface modification of PK 3060 pigment. Infrared spectral analysis of the surface modified pigment particles provided firm evidence for the formation of a POSS layer on the surface of the pigment particles, substantiated by the corresponding TEM and Energy Dispersive X-ray Spectroscopy (EDXS) measurements of functionalized and as-received pigments. SEM micrographs of the diluted dispersions in fluoropolymeric resin binder revealed uniform distribution of pigment particles with an average size of 300 nm and the beneficial effect of the pigment functionalization was assessed from the measured spectral selectivity of coatings of various thicknesses. & 2010 Elsevier B.V. All rights reserved. 1. Introduction High-quality dispersion of pigments in organic phases is prerequisite in the fabrication of homogeneous hybrid composite materials used as plastics, adhesives, restorative biomaterials, electronic packages [1,2] and solar absorber paints used for making spectrally selective paint coatings for solar absorbers in solar thermal collectors [3]. Only finely grained pigment particles that are uniformly dispersed in the polymer resin binder can provide spectrally selective paint coatings exhibiting high solar absorption (a s ) and low thermal emittance (e T ) [4], because such pigment dispersions enable the formation of coating with closely packed assembly of particles bounded with the smallest amount of polymer resin binder. In order to overcome the problem of incompatibility of organic or polymeric phases with high-surface- area nanosized mineral fillers or commercial pigments, the surface of the particles must first be modified, which means altered from hydrophilic to organophilic. Many organic systems have been investigated for surface modification. Functionalization is usually achieved by intense mixing or ball milling of the pigment in the presence of a surfactant or macro-molecules [5], which become attached to the pigment surface by preferential adsorption of the polar groups via electrostatic interactions. Alternatively, the pigment surface can be modified by chemical reactions relying on chemical interac- tions between the modifiers and the pigment surface. In this case, modifiers are usually bifunctional alkoxysilanes (X-Si(OR) n ) with hydrolysable (–Si(OR) n – usually alkoxy) and organo-functional ends (X-functional head group) [6] used since 1966 [7]. The non- hydrolysable group, X, can be used to tune the chemical and physical properties of the layers, while the hydrolysable alkoxy groups in the presence of acid catalysts give reactive silanol (Si–OH) groups, enabling the condensation of hydrolyzed silanes to gels by the establishment of siloxane (Si–O–Si) bonds and ensure adequate interactions with the other metal centres on the surface of the pigments by forming covalent M–O–Si bonds (M¼ Al, Sn,y). The functionalization of nanosilicas [8], magnetic nanoparticles [9], TiO 2 nanoparticles [10], WS 2 fullerene-like particles [11] and composite of antimony doped tin oxide conductive nanoparticles and acrylate by grafting 3-methacrylox- ypropyltrimethoxysilane [12] are typical examples of using silanes for modification of the particle surface in order to provide stable and non-agglomerated dispersion of nanoparticles and for tailoring their properties, such as viscosity [13], and for better Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/solmat Solar Energy Materials & Solar Cells 0927-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.solmat.2010.08.005 n Corresponding author. E-mail address: boris.orel@ki.s (B. Orel). Solar Energy Materials & Solar Cells 95 (2011) 423–431