Polysiloxane coatings containing chemically-bound ("tethered") quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.

Polymer surface properties are controlled by the molecular surface structures. Sum frequency generation (SFG) vibrational spectroscopy has been demonstrated to be a powerful technique to study polymer surface structures at the molecular level in different chemical environments. In this research, SFG has been used to study the surface segregation of biocide moieties derived from triclosan (TCS) and tetradecyldimethyl (3-trimethoxysilylpropyl) ammonium chloride (C-14 QAS) that have been covalently bound to a poly(dimethylsiloxane) (PDMS) matrix. PDMS materials are being developed as coatings to control biofouling. This SFG study indicated that TCS-moieties segregate to the surface when the bulk concentration of TCS-moieties exceeds 8.75% by weight. Surface segregation of C-14 QAS moieties was detected after 5% by weight incorporation into a PDMS matrix. SFG results were found to correlate well with antifouling activity, providing a molecular interpretation of such results. This research showed that SFG can aid in the development of coatings for controlling biofouling by elucidating the chemical structure of the coating surface.

Siloxane-polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol⁻¹) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.

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In order to facilitate a semi-high throughput approach to the evaluation of novel fouling-release coatings, a 'spinjet' apparatus has been constructed. The apparatus delivers a jet of water of controlled, variable pressure into the wells of 24-well plates in order to facilitate measurement of the strength of adhesion of algae growing on the base of the wells. Two algae, namely, sporelings (young plants) of the green macroalga Ulva and a diatom (Navicula), were selected as test organisms because of their opposing responses to silicone fouling-release coatings. The percentage removal of algal biofilm was positively correlated with the impact pressure for both organisms growing on all the coating types. Ulva sporelings were removed from silicone elastomers at low impact pressures in contrast to Navicula cells which were strongly attached to this type of coating. The data obtained for the 24-well plates correlated with those obtained for the same coatings applied to microscope slides. The data show that the 24-well plate format is suitable for semi-high throughput screening of the adhesion strength of algae.

Strategically designed amphiphilic invertible polymers (AIPs) are capable of (i) self-assembling into invertible micellar assemblies (IMAs) in response to changes in polarity of environment, polymer concentration, and structure, (ii) accommodating (solubilizing) substances that are otherwise insoluble in water, and (iii) inverting their molecular conformation in response to changes in the polarity of the local environment. The unique ability of AIPs to invert the molecular conformation depending on the polarity of the environment can be a decisive factor in establishing the novel stimuli-responsive mechanism of solubilized drug release that is induced just in response to a change in the polarity of the environment. The IMA capability to solubilize lipophilic drugs and deliver and release the cargo molecules by conformational inversion of polymer macromolecules in response to a change of the polarity of the environment was demonstrated by loading IMA with a phytochemical drug, curcumin. It was demonstrated that four sets of micellar vehicles based on different AIPs were capable of delivering the curcumin from water to an organic medium (1-octanol) by means of unique mechanism: AIP conformational inversion in response to changing polarity from polar to nonpolar. The IMAs are shown to be nontoxic against human cells up to a concentration of 10 mg/L. On the other hand, the curcumin-loaded IMAs are cytotoxic to breast carcinoma cells at this concentration, which confirms the potential of IMA-based vehicles in controlled delivery of poorly water-soluble drug candidates and release by means of this novel stimuli-responsive mechanism.

High throughput combinatorial characterization was performed on thermosetting siloxaneurethane coatings in order to find a correlation between the characterization techniques, surface topography, and adhesion strength of barnacles. A series of coatings having microtopographical surfaces with different domain sizes were prepared based on a thermosetting siloxane-urethane system. This microtopography was formed spontaneously during the filmformation process. These surfaces were characterized by atomic force microscopy (AFM), surface energy, dynamic contact angle, and pseudo barnacle pull-off adhesion and were compared to pure polyurethane (PU) and silicone rubber control. Surface energy and dynamic contact angles were measured by an automated surface energy measurement system and pull-off adhesion values were obtained from a high throughput pull-off adhesion measurement unit. The results were compared with the adhesion strength of barnacles.