Hybrid xerogel films as novel coatings for antifouling and fouling release

Abstract

Hybrid sol-gel-derived xerogel films prepared from 45/55 (mol ratio) n-propyltrimethoxysilane (C3-TMOS)/tetramethy lorthosilane (TMOS), 2/98 (mol ratio) bis [3-(trimethoxysilyl)propyl]-ethylenediamine (enTMOS)/tetraethylorthosilane (TEOS), 50/50 (mol ratio) n-octyltriethoxysilane (C8-TEOS)/TMOS, and 50/50 (mol ratio) 3,3,3-trifluoropropyltrimethox ysilane (TFP-TMOS)/TMOS were found to inhibit settlement of zoospores of the marine fouling alga Ulva (syn. Enteromorpha) relative to settlement on acid-washed glass and give greater release of settled zoospores relative to glass upon exposure to pressure from a water jet. The more hydrophobic 50/50 C8-TEOS/TMOS xerogel films had the lowest critical surface tension by comprehensive contact angle analysis and gave significantly greater release of 8-day Ulva sporeling biomass after exposure to turbulent flow generated by a flow channel than the other xerogel surfaces or glass. The 50/50 C8 TEOS/TMOS xerogel was also a fouling release surface for juveniles of the tropical barnacle Balanus amphitrite. X-ray photon electron data indicated that the alkylsilyl residues of the C3-TMOS-, C8-TEOS-, and TFP-TMOS-containing xerogels were located on the surface of the xerogel films (in a vacuum), which contributes to the film hydrophobicity. Similarly, the amine-containing silyl residues of the enTMOS/TEOS films were located at the surface of the xerogel films, which contributes to the more hydrophilic character and increased critical surface tension of these films.

Antifouling character of ‘active’ hybrid xerogel coatings with sequestered catalysts for the activation of hydrogen peroxide

“…Values of K SV were 4200 M 71 for these xerogels (xerogel 2 of Figure 1). In contrast, the 50/50 C3TMOS/TMOS xerogel (Tang et al 2005) gave K SV of 520 M 71 . Values of K SV for the B5 and B6 xerogels suggest that the B5 and B6 coatings are much more permeable to I 7 and presumably other halide salts relative to the hydrophobic 50/50 C3TMOS/TMOS xerogel (Tang et al 2005).…”

“…In glass, the ratio of the C(1s)/Si(2p3) signals is 0.2 (Tang et al 2005), suggesting a relatively carbon-free surface with any carbon found at the ostensibly SiO 2 surface presumably arising from adventitious/ adsorbed carbon-containing species from the atmosphere. The ratio of the C(1s)/Si(2p3) signals for the B6 xerogel surface is 1.75 + 0.30 for the surface treated with ASW and 2.0 + 0.5 for the surface treated with 0.9 M H 2 O 2 in ASW for 24 h prior to XPS analysis.…”

“…The assay followed the principles outlined in Tang et al (2005): 10 ml aliquots [1.5 6 10 6 spore ml 71 in ASW with and without 100 mM H 2 O 2 ] were pipetted into individual compartments of polystyrene quadriperm culture dishes (Fisher), each containing a test surface. After incubation for 1 h in darkness at *208C, all slides were washed in ASW to remove zoospores that had not attached.…”

“…A screening campaign showed that there was significant I 7 quenching of [Ru(dpp) 3 ] 2þ within the 50% APTES/ 50% TEOS (B5) and the 10% APTES/90% TEOS xerogel (B6) formulations. Figure 1 compares 2þ sequestered within a hydrophobic xerogel film prepared from a 50/50 npropyltriethoxysilane (C3TMOS)/TMOS) sol, which has been described as an AF/foul-release surface (Tang et al 2005). The hydrophobic 50/50 C3TMOS/ TMOS-[Ru(dpp) 3 ] 2þ formulation did not show significant quenching, suggesting that the I 7 cannot partition/diffuse within this film.…”

“…Hybrid xerogel coatings with critical surface energies near 20 mN m 71 , which is in the range where minimal bioadhesion is observed due to the formation of weak boundary layers (Baier et al 1968;Baier 1984), reduce the settlement of cyprids of the barnacle B. amphitrite and, for one xerogel coating, display excellent fouling-release properties for juvenile barnacles (Tang et al 2005).…”