Dispersion of Gold Nanoparticles in UV-Cured, Thiol-Ene Films by Precomplexation of Gold-Thiol
Alkyl thiols and alkenes (enes) polymerize via an extremely rapid step-growth, free-radical chain process, uninhibited by air, to give high-density networks with excellent mechanical and physical properties. These thiol-ene coatings are potentially useful for a wide variety of coatings, adhesives, and optical applications. In this work, a series of nanogold-containing UV-cured, thiol-ene coatings were prepared from trimethylol propane tris(3-mercaptopropionate) (trithiol) and pentaerythritol ally ether (triene) monomers using a unique procedure which facilitates precomplexation of the gold-thiol prior to photocuring. Irgacure 651 (1 wt %) was used as a photoinitiator, and nano-old was incorporated at 0-1 wt %, average similar to 10 nm size particles by TEM. Physical and mechanical properties were characterized using bulk tack analysis and other standard techniques: DSC, TGA, pencil hardness, and gel fractions. In general, films were found to be low absorbing, in the visible range and highly uniform and to contain well-dispersed nanogold particles. Although the rate of polymerization was modestly retarded by the presence of gold nanoparticles, functional group conversions (C=C and S-H) and gel fractions were high. Increasing nanogold content resulted in an, increase in T-g measured by DSC (-15 to -8 degrees C for 0-1 wt % nanogold, respectively) due to the increasing number of physical gold-thiol cross-links created. TGA analysis revealed a small negative impact of increasing nanogold composition on relative thermal stability. The 1 wt % nanogold-containing samples possessed appreciable electrostatic discharge (ESD) character, with ESD times of 1-10 s measured using a commercial charge plate analyzer.