Kenneth J. Wynne

Thickness dependence of ice removal stress for a polydimethylsiloxane nanocomposite: Sylgard 184.

Minimizing adhesion of ice has been the subject of extensive studies because of importance to applications such aircraft wings, spacecraft, and power transmission wires. A growing interest concerns coatings for wind turbine blades and refrigeration. Herein, a new laboratory test was employed to obtain the thickness dependence of ice adhesion for Sylgard 184-a filled polydimethylsiloxane elastomer. A correlation between ice adhesion and coating thickness (t) was found that follows a relationship developed by Kendall over 40 years ago for removal of a rigid object from an elastomer. With a 0.05 mm/s probe speed a nearly linear relationship between peak removal stress (Ps) and 1/t(1/2) was obtained with Ps ∼ 460 kPa for an 18 μm coating, decreasing to ∼120 kPa for 533 μm. Preliminary results suggest that below ∼10 μm Ps departs from the 1/t(1/2) correlation while above ∼500 μm a limiting value for Ps may be reached. We previously reported that probe speed has negligible effect on the glassy polymer PMMA. In contrast, probe speed is identified as an important variable for testing ice release on elastomeric Sylgard 184 coatings. While work of adhesion, which is related to surface free energy, is recognized as an important factor that can affect ice release, the results reported herein show that coating thickness can override this single parameter for elastomeric substrates.

Preparation and characterization of electrostrictive polyurethane films with conductive polymer electrodes

All-polymer electrostrictive soft films were developed for the first time by depositing conductive polymer (polypyrrole) directly on both sides of solution-cast electrostrictive polyurethane elastomer films. The final composite films are flexible with strong adhesion between the polyurethane film and the conductive polymer electrode. The conductivity (sheet resistivity ∼1000 Ω/□), of the polymer electrode is appropriate for its intended use. The compatible interface between the polypyrrole electrode polymer and the electrostrictive polyurethane significantly improves the acoustic and optical transparency of these composite films, compared with using a metal electrode film. The all-polymer films also exhibit comparable dielectric properties to gold-electroded polyurethane films in the temperature range from −40°C to +80°C. The temperature range covers the soft segment glass transition temperature of the polyurethane elastomers, which is about −20°C. The films also show large electric field induced strain responses which are dependent on film thickness and measurement frequency. The electrostrictive characteristics in the all-polymer films show similarities to those of the films with gold electrodes under identical measurement conditions.

Two silicone nontoxic fouling release coatings: Hydrosilation cured PDMS and CaCO3 filled, ethoxysiloxane cured RTV11

Two silicone coatings have been evaluated for barnacle adhesion. One coating is an unfilled hydrosilation cured polydimethylsiloxane (PDMS) network, while the other is a room temperature vulcanized (RTV), filled, ethoxysiloxane cured PDMS elastomer, RTV11†. The adhesion strength of one species of barnacle, Balanus eburneus, to the hydrosilation coatings is in the range of 0.37–0.60 kg cm‐2 while the corresponding range for RTV11 is 0.64–0.90 kg cm‐2. The easier release of B. eburneus from the hydrosilation cured network compared to RTV11 is discussed in relationship to differences in bulk and surface properties. Preliminary results suggest bulk modulus may be the most important parameter in determining barnacle adhesion strength. In light or mechanical property analysis, a re‐evaluation of surface properties and chemical stability is presented.

Synthesis of unsymmetrical tellurides and selenaditellurides

Abstract Unsymmetrical tellurides may be prepared by the reaction of arenetellurenyl halides, generated in situ, with Grignard reagents. Selenaditellurides, RTeSeR, are prepared from the reaction of arenetellurenyl halides with ArSeMgBr.

Surface Characterization of Biocidal Polyurethane Modifiers Having Poly(3,3-substituted)oxetane Soft Blocks with Alkylammonium Side Chains

This paper focuses on surface characterization of P[ AB] copolyoxetane soft block polyurethanes having either fluorous (3FOx, -CH2OCH 2CF3) or PEG-like (ME2Ox, -CH2(OCH2CH2) 2OCH3), A side chains and alkylammonium, B side chains. Physical surface characterization data were analyzed in light of the previously observed order of antimicrobial effectiveness for a set of four surface modifiers. Ample physical evidence for surface concentration of fluorous 2 wt % P[ AB]-polyurethane modifiers was obtained from XPS, contact angles, ATR-IR spectroscopy, and TM-AFM. In TM-AFM phase imaging, the most effective biocidal surface modifier, 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU, showed a nanoscale phase-separated structure consisting of 200 nm domains with background features about 10 times smaller. Despite similar surface characterization data, the 2 wt % fluorous C6 analog ranked third in contact biocidal effectiveness. Physical evidence for surface concentration of 2 wt % P[(ME2Ox)(C12)-0.86:0.14]-PU was modest, considering that antimicrobial effectiveness was second only to 2 wt % HMDI-BD(30)/P[(3FOx)(C12)-0.89:0.11]-PU. In this set of surface modifiers, nanoscale morphology is largely driven by the fluorous component, whereas antimicrobial effectiveness is more strongly influenced by alkylammonium chain length. The effect of alkylammonium side chain length on surface concentration and antimicrobial behavior is more pronounced for ME2Ox polyurethanes compared to the 3FOx analogs.

Highly effective, water-soluble, hemocompatible 1,3-propylene oxide-based antimicrobials: poly[(3,3-quaternary/PEG)-copolyoxetanes].

This study focuses on the solution antimicrobial effectiveness of a novel class of copolyoxetanes with quaternary ammonium and PEG-like side chains. A precursor P[(BBOx-m)(ME2Ox)] copolyoxetane was prepared by cationic ring-opening copolymerization of 3-((4-bromobutoxy)methyl)-3-methyloxetane (BBOx) and 3-((2-(2-methoxyethoxy)ethoxy)methyl)-3-methyloxetane (ME2Ox) to give random copolymers with 14-100 (m) mol % BBOx. Reaction of P[(BBOx-m)(ME2Ox)] with dodecyl dimethylamine gave the corresponding quaternary P[(C12-m)(ME2Ox)] polycation salts, designated C12-m, as viscous liquids in 100% yield. BBOx/ME2Ox and C12/ME2Ox ratios were obtained by (1)H NMR spectroscopy. C12-m molecular weights (M(n), 3.5-21.9 kDa) were obtained from (1)H NMR end group analysis. DSC studies up to 150 °C showed only thermal transitions between -69 and -34 °C assigned to T(g) values. Antibacterial activity for the C12-m copolyoxetanes was tested by determining minimum inhibitory concentrations (MICs) against Gram(+) Staphylococcus aureus and Gram(-) Escherichia coli and Pseudomonas aeruginosa . MIC decreased with increasing C12 mol percent, reaching a minimum in the range C12-43 to C12-60. Overall, the antimicrobial with consistently low MICs for the three tested pathogenic bacteria was C12-43: (bacteria, MIC, μg/mL) E. coli (6), S. aureus (5), and P. aeruginosa (33). For C12-43, minimum biocidal concentration (MBC) to reach 99.99% kill in 24 h required 1.5× MIC for S. aureus and 2× MIC for E. coli and P. aeruginosa . At 5× MIC against a challenge of 10(8) cfu/mL, C12-43 kills ≥99% S. aureus , E. coli , and P. aeruginosa within 1 h. C12-m copolyoxetane cytotoxicity toward human red blood cells was low, indicating good prospects for biocompatibility. The tunability of C12-m copolyoxetane compositions, effective antimicrobial behavior against Gram(+) and Gram(-) bacteria, and promising biocompatibility offer opportunities for further modification and potential applications as therapeutic agents.

High Antimicrobial Effectiveness with Low Hemolytic and Cytotoxic Activity for PEG/Quaternary Copolyoxetanes

The alkyl chain length of quaternary ammonium/PEG copolyoxetanes has been varied to discern effects on solution antimicrobial efficacy, hemolytic activity and cytotoxicity. Monomers 3-((4-bromobutoxy)methyl)-3-methyloxetane (BBOx) and 3-((2-(2-methoxyethoxy)ethoxy)methyl)-3-methyloxetane (ME2Ox) were used to prepare precursor P[(BBOx)(ME2Ox)-50:50–4 kDa] copolyoxetane via cationic ring opening polymerization. The 1:1 copolymer composition and Mn (4 kDa) were confirmed by 1H NMR spectroscopy. After C–Br substitution by a series of tertiary amines, ionic liquid Cx-50 copolyoxetanes were obtained, where 50 is the mole percent of quaternary repeat units and “x” is quaternary alkyl chain length (2, 6, 8, 10, 12, 14, or 16 carbons). Modulated differential scanning calorimetry (MDSC) studies showed Tgs between −40 and −60 °C and melting endotherms for C14–50 and C16–50. Minimum inhibitory concentrations (MIC) were determined for Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa. A systematic dependence of MIC on alkyl chain length was found. The most effective antimicrobials were in the C6–50 to C12–50 range. C8–50 had better overall performance with MICs of 4 μg/mL, E. coli; 2 μg/mL, S. aureus; and 24 μg/mL, P. aeruginosa. At 5 × MIC, C8–50 effected >99% kill in 1 h against S. aureus, E. coli, and P. aeruginosa challenges of 108 cfu/mL; log reductions (1 h) were 7, 3, and 5, respectively. To provide additional insight into polycation interactions with bacterial membranes, a geometric model based on the dimensions of E. coli is described that provides an estimate of the maximum number of polycations that can chemisorb. Chain dimensions were estimated for polycation C8–50 with a molecular weight of 5 kDa. Considering the approximations for polycation chemisorption (PCC), it is surprising that a calculation based on geometric considerations gives a C8–50 concentration within a factor of 2 of the MIC, 4.0 (±1.2) μg/mL for E. coli. Cx-50 copolyoxetane cytotoxicity was low for human red blood cells, human dermal fibroblasts (HDF), and human foreskin fibroblasts (HFF). Selectivities for bacterial kill over cell lysis were among the highest ever reported for polycations indicating good prospects for biocompatibility.

Conducting Polymers: Partially Oxidized Bridge-Stacked Metallophthalocyanines

Abstract The synthesis and characterization of a novel class of polymeric phthalocyanines (Pc), (PcMX)n (M-Al, Ga, Cr; X[dbnd]F and M-Si, Ge, Sn; X[dbnd]0) of exceptional thermal stability are summarized. These materials possess a linear MX backbone surrounded by a sheath of cofacial M-centered Pc rings. (PcAlF)n and (PcGaF)n are sublimable (10−3mmHg,540°C and 430°C, respectively) allowing for thin film formation. Iodine-doping leading to compositions (PcMXIy)n with y ranging from 0.06 to 5.5 is reported. Thermogravimetric analysis has proven useful for iodine analyses and has revealed that the order of thermal stability with regard to loss of iodine is (PcCrFIy)n < (PcGaFIy)n< (PcAlFIy)n < (PcSioIy)n. Raman spectra point to I3-and I5-as the principle polyiodide species, though their relative proportions vary depending on M and doping level. Increases in the electrical conductivity by as much as 109 with maximum conductivities in the range of 0.01–1 ohm−1cm−1 result from iodine doping. Conduction appears ...

Laboratory test for ice adhesion strength using commercial instrumentation.

A laboratory test method for evaluating ice adhesion has been developed employing a commercially available instrument normally used for dynamic mechanical analysis (TA RSA-III). This is the first laboratory ice adhesion test that does not require a custom-built apparatus. The upper grip range of ∼10 mm is an enabling feature that is essential for the test. The method involves removal of an ice cylinder from a polymer coating with a probe and the determination of peak removal force (Ps). To validate the test method, the strength of ice adhesion was determined for a prototypical glassy polymer, poly(methyl methacrylate). The distance of the probe from the PMMA surface has been identified as a critical variable for Ps. The new test provides a readily available platform for investigating fundamental surface characteristics affecting ice adhesion. In addition to the ice release test, PMMA coatings were characterized using DSC, DCA, and TM-AFM.

Synthesis of water-soluble camptothecin-polyoxetane conjugates via click chemistry.

Water-soluble camptothecin (CPT)-polyoxetane conjugates were synthesized using a clickable polymeric platform P(EAMO) that was made by polymerization of acetylene-functionalized 3-ethyl-3-(hydroxymethyl)oxetane (i.e., EAMO). CPT was first modified with a linker 6-azidohexanoic acid via an ester linkage to yield CPT-azide. CPT-azide was then click coupled to P(EAMO) in dichloromethane using bromotris(triphenylphosphine)copper(I)/N,N-diisopropylethylamine. For water solubility and cytocompatibility improvement, methoxypolyethylene glycol azide (mPEG-azide) was synthesized from mPEG 750 g mol(-1) and click grafted using copper(II) sulfate and sodium ascorbate to P(EAMO)-g-CPT. (1)H NMR spectroscopy confirmed synthesis of all intermediates and the final product P(EAMO)-g-CPT/PEG. CPT was found to retain its therapeutically active lactone form. The resulting P(EAMO)-g-CPT/PEG conjugates were water-soluble and produced dose-dependent cytotoxicity to human glioma cells and increased γ-H2AX foci formation, indicating extensive cell cycle-dependent DNA damage. Altogether, we have synthesized CPT-polymer conjugates able to induce controlled toxicity to human cancer cells.