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ABSTRACT: Polydimethylsiloxane (PDMS) materials have extensively shown to function as excellent fouling-release (FR) coatings in the marine environment. The incorporation of biocide moieties, such as quaternary ammonium salts (QAS), can impart additional anti-biofouling properties to PDMS-based FR coating systems. In this study, the molecular surface structures of two different types of QAS-incorporated PDMS systems were investigated in different chemical environments using sum frequency generation vibrational spectroscopy (SFG). Specifically, a series of PDMS coatings containing either a QAS with a single ammonium salt group per molecule or quaternary ammonium-functionalized polyhedral oligomeric silsesquioxane (Q-POSS) were measured with SFG in air, water, and artificial sea water (ASW) to investigate the relationships between the interfacial surface structures of these materials and their antifouling properties. Although previous studies have shown that the above-mentioned materials are promising contact-active antifouling coatings, slight variations of the QAS structure can lead to substantial differences in antifouling performance. Indeed, the SFG results presented here indicated that the surface structures of these materials depend on several factors, such as the extent of quaternization, the molecular weight of the PDMS component, and the functional groups of the QAS used for incorporation into the PDMS matrix. It was concluded that in aqueous environments, a lower extent of POSS quaternization and the use of ethoxy (instead of methoxy) functional groups for QAS incorporating facilitated the extension of the alkyl chains away from the nitrogen atom of the QAS on the surface. The SFG results correlated well to the antifouling activity studies which indicated that the coatings exhibiting a lower concentration of longer alkyl chains protruding out from the surface can neutralize microorganisms more effectively, ultimately leading to better antifouling performance. Furthermore, the results of this study provide additional evidence that incorporated QAS exert their antimicrobial activity through a two-step interaction. The first step is the adsorption of the bacteria on the surface due to the electrostatic attraction between the negatively charged microorganisms and the positively charged QAS nitrogen atoms on the surface. The second step is the disruption of the cell membranes by the penetration of the QAS long, extended alkyl chains.
Langmuir 02/2013; · 4.19 Impact Factor
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ABSTRACT: An array of quaternary ammonium functionalized-polyhedral oligomeric silsesquioxane (Q-POSS) compounds with different alkyl
chain lengths and counter ions were synthesized using a two-step process. First, octasilane POSS was functionalized with dimethylamino
groups by hydrosilylation with allyldimethylamine. Next, partial quaternization of the tertiaryamino-functional POSS was achieved
using an alkyl halide to produce the Q-POSS. Alkyl chain length of the Q-POSS compounds varied from –C12H25 to –C18H37 and the counter ions varied between chlorine, bromine, and iodine. Moisture-cured polysiloxane coatings were prepared by
dispersing Q-POSS molecules into a solution blend of silanol-terminated polydimethylsiloxane, methylacetoxysilane, and a catalyst.
To evaluate the utility of the Q-POSS molecules as a broad-spectrum antimicrobial additive, the antimicrobial activity of
the coatings toward the Gram-negative bacterium, Escherichia coli, the Gram-positive bacterium, Staphylococcus aureus, and the opportunistic fungal pathogen, Candida albicans, was determined using an agar plating method. The results obtained showed that both the composition of the Q-POSS and the
composition of the polysiloxane matrix affected antimicrobial properties. Compositions were identified that inhibited the
growth of all three microorganisms on the coating surface. Surface Raman spectroscopic analysis was performed on selected
set of coatings to understand the relative concentration of Q-POSS molecules at the coating surface.
KeywordsPolyhedral oligomeric silsesquioxane (POSS)-Polydimethylsiloxane-Antimicrobial additive
Journal of Coatings Technology and Research 04/2012; 7(4):455-467. · 1.12 Impact Factor
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ABSTRACT: High throughput combinatorial characterization was performed on thermosetting siloxane–urethane 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 film-formation 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.
Journal of Coatings Technology and Research 04/2012; 4(2):131-138. · 1.12 Impact Factor
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ABSTRACT: Moisture-curable polysiloxanes were modified with ionic groups to enable specific interactions between the polysiloxane matrix
and silica nanoparticle reinforcement. A trimethoxysilane-functional quaternary ammonium salt (QAS) was used to modify the
polysiloxane matrix. A comparison of the mechanical properties of coatings containing QAS modification to analogous coatings
without QAS modification showed that QAS modification resulted in a dramatic improvement in mechanical properties of silica
nanoparticle-reinforced coatings. QAS modification provided major enhancements in both tensile modulus and toughness. The
coatings were characterized using positron annihilation spectroscopy, photo-acoustic FT-IR, differential scanning calorimetry,
transmission electron microscope, and atomic force microscopy. The characterization results suggested that the QAS moieties
present in the polysiloxane matrix undergo specific interactions with the surface of silica nanoparticles enabling an enhancement
in interfacial adhesion between the polymer matrix and the nanoparticles. Most likely, the specific interaction that provided
the enhanced mechanical properties was an ion–dipole interaction involving silanol groups present on the surface of the silica
nanoparticles. The enhanced modulus and toughness of these polysiloxane materials may enable their application as a fouling-release
coating for ship hulls, since current polysiloxane-based fouling release coatings suffer from poor mechanical properties and
durability.
KeywordsPolysiloxanes-Quaternary ammonium salts-Silica nanoparticle-Positron annihilation spectroscopy
Journal of Coatings Technology and Research 04/2012; 7(2):239-252. · 1.12 Impact Factor
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ABSTRACT: The concept of tethering quaternary ammonium salts (QASs) to a crosslinked polysiloxane matrix to produce a hybrid antifouling/fouling-release
coating was investigated. A statistical experimental design was used to determine the effect of QAS concentration on biocidal
activity toward a marine bacterium, Cellulophaga lytica (C. lytica). In addition to measuring biocidal activity, coating film quality as well as stability upon water immersion were evaluated.
The results of the study showed that biocidal activity was strongly dependent on QAS concentration. For addition-curable coatings,
the presence of 4wt% QAS moieties resulted in approximately 50% reduction in C. lytica biofilm retention without any leachate toxicity. Attempts to increase the level of QAS moieties to increase biocidal activity
resulted in coating delamination from the substrate and unacceptable film quality upon artificial seawater immersion due to
excessive swelling. As a result, a moisture-curable system based on tethered QASs was investigated since moisture curing allows
for higher crosslink densities to be achieved which would be expected to minimize swelling upon artificial seawater immersion.
The moisture-curable coating developed showed enhanced stability upon artificial seawater immersion, greater than 80% reduction
in C. lytica biofilm retention, and greater than 90% reduction in biofilm growth for the marine algae, Navicula incerta.
Journal of Coatings Technology and Research 04/2012; 5(4):405-417. · 1.12 Impact Factor
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ABSTRACT: As part of ongoing efforts aimed at the development of extensive structure−property relationships for moisture-curable polysiloxane coatings containing tethered quaternary ammonium salt (QAS) moieties for potential application as environmental friendly coatings to combat marine biofouling, a combinatorial/high-throughput (C/HT) study was conducted that was focused on four different compositional variables. The coatings that were investigated were derived from solution blends of a silanol-terminated polydimethylsiloxane (HO-PDMS-OH), QAS-functional alkoxysilane, and methyltriacetoxysilane. The compositional variables investigated were alkoxysilane functionality of the QAS-functional silane, chain length of the monovalent alkyl group attached to the QAS nitrogen atom, concentration of the QAS-functional alkoxysilane, and molecular weight of the HO-PDMS-OH. Of these variables, the composition of the alkoxysilane functionality of the QAS-functional silane was a unique variable that had not been previously investigated. The antifouling (AF) and fouling-release (FR) characteristics of the 24 unique coating compositions were characterized using HT assays based on three different marine microorganisms, namely, the two bacteria, Cellulophaga lytica and Halomonas pacifica, and the diatom, Navicula incerta. Coatings surfaces were characterized by surface energy, water contact angle hysteresis, and atomic force microscopy (AFM). A wide variety of responses were obtained over the compositional space investigated. ANOVA analysis showed that the compositional variables and their interactions significantly influenced AF/FR behaviors toward individual marine microorganisms. It was also found that utilization of the ethoxysilane-functional QASs provided enhanced AF character compared to coatings based on methoxysilane-functional analogues. This was attributed to enhanced surface segregation of QAS groups at the coating-air interface and confirmed by phase images using AFM.
ACS combinatorial science. 05/2011; 13(3):298-309.
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ABSTRACT: Poly(dimethylsiloxane) (PDMS) materials containing chemically bound (''tethered'') quaternary ammonium salt (QAS) moieties are being developed as new contact-active antimicrobial coatings. Such coatings are designed to inhibit the growth of microorganisms on surfaces for a variety of applications which include ship hulls and biomedical devices. The antimicrobial activity of these coatings is a function of the molecular surface structure generated during film formation. 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. SFG was successfully used to characterize the surface structures of PDMS coatings containing tethered QAS moieties that possess systematic variations in QAS chemical composition in air, in water, and in a nutrient growth medium. The results indicated that the surface structure was largely dependent on the length of the alkyl chain attached to the nitrogen atom of the QAS moiety as well as the length of alkyl chain spanning between the nitrogen atom and silicon atom of the QAS moiety. The SFG results correlated well with the antimicrobial activity, providing a molecular interpretation of the activity. This research showed that SFG can be effectively used to aid in the development of new antimicrobial coating technologies by correlating the chemical structure of a coating surface to its antimicrobial activity.
Langmuir 03/2010; 26(21):16455-62. · 4.19 Impact Factor
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ABSTRACT: High-throughput biological assays were used to develop structure - antimicrobial relationships for polysiloxane coatings containing chemically bound (tethered) quaternary ammonium salt (QAS) moieties. The QAS-functional polysiloxanes were derived from solution blends of a silanol-terminated polydimethylsiloxane, a trimethoxysilane-functional QAS (QAS-TMS), and methylacetoxysilane. Since the QAS moieties provide antimicrobial activity through interaction with the microorganism cell wall, most of the compositional variables that were investigated were associated with the chemical structure of the QAS-TMS. Twenty different QAS-TMS were synthesized for the study and the antimicrobial activity of sixty unique polysiloxane coatings derived from these QAS-TMS determined toward Escherichia coli , Staphylococcus aureus , and Candida albicans . The results of the study showed that essentially all of the compositional variables significantly influenced antimicrobial activity. Surface characterization of these moisture-cured coatings using atomic force microscopy as well as water contact angle and water contact angle hysteresis measurements indicated that the compositional variables significantly affected coating surface morphology and surface chemistry. Overall, compositional variables that produced heterogeneous surface morphologies provided the highest antimicrobial activity suggesting that the antimicrobial activity was primarily derived from the relationship between coating chemical composition and self-assembly of QAS moieties at the coating/air interface. Using data modeling software, a narrow region of the compositional space was identified that provided broad-spectrum antimicrobial activity.
Journal of Combinatorial Chemistry 10/2009; 11(6):1115-27. · 3.41 Impact Factor
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ABSTRACT: 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.
Langmuir 10/2008; 24(17):9686-94. · 4.19 Impact Factor
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Partha Majumdar,
Elizabeth Lee,
Nehal Patel,
Kaley Ward,
Shane J Stafslien,
Justin Daniels,
Bret J Chisholm,
Philip Boudjouk,
Maureen E Callow,
James A Callow,
Stephanie E M Thompson
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ABSTRACT: 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.
Biofouling 02/2008; 24(3):185-200. · 4.43 Impact Factor
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06/2005;
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ABSTRACT: An array of quaternary ammonium-functionalized POSS (Q-POSS) compounds were synthesized and their antimicrobial properties toward the Gram-negative bacterium, Escherichia coli, and the Gram-positive bacterium, Staphylococcus aureus, determined in aqueous solution. Using Q-POSS compositions that exhibited broad spectrum antimicrobial activity in solution, the utility of the Q-POSS compounds as an antimicrobial additive for polysiloxane coatings was determined. The results of the investigation showed that Q-POSSs possessing a relatively low extent of quaternization and longer alkyl chain lengths provided the highest antimicrobial activity in solution. For polysiloxane coatings containing Q-POSS molecules as an antimicrobial additive, coating surface energy, surface morphology, and antimicrobial properties were found to be strongly dependent on Q-POSS composition. Coatings based on Q-POSSs possessing the lowest extent of quaternization displayed antimicrobial activity while analogous coatings produced using Q-POSSs possessing the highest extent of quaternization showed no antimicrobial activity. The lack of antimicrobial activity exhibited by coatings possessing Q-POSSs with a relatively high extent of quaternization was attributed to agglomeration of Q-POSS molecules through the formation of intermolecular interactions involving the quaternary ammonium moieties. Agglomeration would be expected to reduce diffusivity and inhibit interaction of the Q-POSS molecules with microbial cells.Graphical abstract
Polymer. 50(5):1124-1133.
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ABSTRACT: Optimization of coating film deposition using an automated combinatorial film deposition system was carried out using an experimental design approach. In this study, a D-optimal response surface design was used. Numerical factors (dispense volume, doctor blade speed, contact time between doctor blade, and coating materials) and categorical factors (doctor blade movement, pattern of drops, and number of drops for each patch) were used as input variables. The models obtained for dry film thickness difference for model coating formulations having two different viscosities (90 mPa·s and 220 mPa·s) were significant. Optimum combinations of these factors were used to minimize dry film thickness variation to 7.5 μm and to 2.5 μm for formulations with viscosity 90 mPa·s and 220 mPa·s, respectively, and for both formulations the coatings obtained were acceptable with respect to length and width.
Progress in Organic Coatings.
