We performed a combined calorimetric and molecular modeling investigation of poly(vinyl acetate) (PVAc) on silica to characterize the intermolecular interactions and the behavior of the adsorbed polymer. From temperature-modulated differential scanning calorimetry experiments, different regions of thermal activity suggested a gradient of mobility in the adsorbed polymer. Polymer segments in more direct contact with silica (tightly bound) showed a significantly elevated and broadened glass transition relative to the bulk polymer, while polymer further away (loosely bound) showed only a slightly elevated transition relative to the bulk polymer. A thermal transition for PVAc at the air interface (more-mobile) was also observed and was at lower temperatures than the bulk polymer. Density profiles from molecular dynamics studies suggested a structure of the adsorbed polymer similar to that experimentally observed. These studies were consistent with the presence of a motional gradient in the polymer segments, and concomitant glass transition changes from the silica to the air interfaces. These results also demonstrate that hydrogen-bonding interactions, at the PVAc/silica interface, are critical to the high-temperature shifts in the glass transition. ■ INTRODUCTIONAdsorbed polymer−substrate interactions usually lead to differences in properties of bulk and adsorbed polymers. 1−10 Interactions between adsorbed polymers and solid surfaces have been shown to provide advantageous physical, mechanical, and thermal properties, making these materials suitable as lubricants, adhesives, coatings, and corrosion-resistant agents. 11−17 These properties are closely related to those that determine the glass transition, which for small amounts of adsorbed polymers depend on film thickness, polymer molecular mass, intermolecular interactions, and the mobility of macromolecular chains. 18−20 For example, the T g will be elevated if the interactions between the polymers and the substrate are attractive and strong. 21 Strong attractive interactions, covalent or hydrogen bonding, between polymer segments and the substrate can potentially reduce the mobility of the adsorbed polymer segments. This reduction in mobility due to restrictions from attachment points has been proposed as the main reason for T g elevation. 22−24 Differential scanning calorimetry (DSC) is the most common technique used to investigate thermal characteristics of bulk polymers and composites. 25−27 Temperature-modulated DSC (TMDSC) is a variant of DSC that, in addition to providing the same information as conventional DSC, provides additional insight into the thermal behavior of materials by separating the heat flow data into reversing and nonreversing events. 28,29 TMDSC and its derivatives have been used to resolve both weak and multicomponent transitions that would be difficult to distinguish in a conventional DSC scan. 30−34 Molecular dynamics (MD) simulations have also been used to investigate the dynamics and thermodynamics of thin-film polymer coatings. 35−5...

In this study, we report that the antimicrobial and hemolytic activities of ternary statistical methacrylate copolymers consisting of cationic ammonium (amino-ethyl methacrylate: AEMA), hydrophobic alkyl (ethyl methacrylate: EMA), and neutral hydroxyl (hydroxyethyl methacrylate: HEMA) side chain monomers. The cationic and hydrophobic functionalities of copolymers mimic the cationic amphiphilicity of naturally occurring antimicrobial peptides (AMPs). The HEMA monomer units were used to separately modulate the compositions of cationic and hydrophobic monomers, and we investigated the effect of each component on the antimicrobial and hemolytic activities of copolymers. Our data indicated increasing the number of cationic groups of copolymers to be more than the 30 mole % did not increase their antimicrobial activity against Escherichia coli. The number of cationic side chains in a polymer chain at this threshold is 5.5 −7.7, which is comparable to those of natural antimicrobial peptides such as maginin (+6). On the other hand, the MIC values of copolymers with > 30 mole % of AEMA depend on only the mole % of EMA, indicating that the hydrophobic interactions of copolymers with E. coli cell membranes determine the antimicrobial activity of copolymers. These results suggest that the roles of cationic and hydrophobic groups can be controlled independently by design in the ternary copolymers studied here.

Polymer−substrate interactions can directly affect the thermal properties of adsorbed polymers, such as the glass transition temperature. Using temperature-modulated differential scanning calorimetry (TMDSC) and molecular modeling, we performed direct comparisons of the thermal properties and intermolecular interactions of adsorbed poly-(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) with similar molecular masses and adsorbed amounts on silica. Compared to their bulk counterparts, adsorbed PMMA showed a larger change in glass transition and a larger amount of tightly bound polymer compared to adsorbed PVAc. These observations suggested that the interactions between PMMA and silica were stronger than those between PVAc and silica. Molecular modeling of these surface-adsorbed polymers showed that PMMA associates more strongly with silica than does PVAc through additional hydrogen-bonding interactions. Additionally, simulations show that the polymer−polymer interactions are stronger in PMMA than PVAc, helping explain why a PMMA mobile component is not observed in TMDSC thermograms.

Modification of diatomaceous earth (DE) was performed using alkyltrimethoxysilanes of different chain lengths (C3, C8, C12, C16, and C18), and their resultant properties were determined. The thermal properties of these alkyltrimethoxysilane-treated DE powders were probed using thermogravimetric analysis and temperature-modulated differential scanning calorimetry, and the surface/porosity was studied using nitrogen adsorption and electron microscopy. Crystallinity of the hydrocarbon tails occurred when the chain lengths were C12 or larger, and the adsorbed hydrocarbon amounts were 1.6 mg/m or more. The wettability of functionalized DE-containing surfaces was studied using water contact angle measurements. At larger adsorbed amounts of 2.2 mg/m or more, the treated DE formed superhydrophobic coatings (with water contact angles ≥150°) with a polyurethane binder. These coatings required a minimum of 30% particle loadings, which allowed the DE particles to dominate the surface. At loadings larger than approximately 50%, there was a decrease in the contact angles corresponding to a reduction in roughness on the surface. Samples with adsorbed amounts less than 2.2 mg/m or chain lengths shorter than C12 were only hydrophobic. These results were in agreement with scanning electron microscopy and Brunauer-Emmett-Teller specific surface area and pore volume measurements.

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Superhydrophobic coatings were prepared using fluorosilane-treated diatomaceous earth (DE) with either polyurethane or epoxy binders. The surface wettability and morphology of the films were analyzed using contact angle measurements and scanning electron microscopy (SEM), respectively. The water contact angles were studied as a function of the fluorocarbon fraction on DE and the particle loadings of treated DE in the coating. The contact angles exceeded 1508 for coatings with at least 0.02 fluorocarbon fraction (mass of fluorosilane/mass of particle) on the DE and with 0.2 particle loadings (mass of treated particles/mass of coating). The water contact angles of the surfaces were dependent on the nature of the binder below 0.2 particle loadings of the superhydrophobic DE particles, but were independent of the binder type after attaining superhydrophobicity. The results were consistent with the superhydrophobicity resulting from the migration of the superhydrophobic DE moving to and covering the surfaces completely. It was also shown that the treatment with fluorosilanes restricted the pores in DE and reduces the specific surface area of the material. However, these changes had effectively no effect on the superhydrophobicity of the coatings. The results of this work clearly identify some important considerations relative to producing superhydrophobic coatings from inexpensive diatomaceous earth. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44072.

In this report, we demonstrate the pH-dependent, in vitro antimicrobial activity of a cationic, amphiphilic random copolymer against clinical isolates of drug-resistant Staphylococcus aureus. The polymer was developed toward a long-term goal of potential utility in the treatment of skin infections. The proposed mechanism of action of the polymer is through selectively binding to bacterial membranes and subsequent disruption of the membrane structure/integrity, ultimately resulting in bacterial cell death. The polymer showed bactericidal activity against clinical isolates of methicillin-resistant or vancomycin-intermediate S. aureus. The polymer was effective in killing S. aureus at neutral pH, but inactive under acidic conditions (pH 5.5). The polymer did not exhibit any significant hemolytic activity against human red blood cells or display cytotoxicity to human dermal fibroblasts over a range of pH values (5.5–7.4). These results indicate that the polymer activity was selective against bacteria over human cells. Using this polymer, we propose a new potential strategy for treatment of skin infections using the pH-sensitive antimicrobial polymer agent that would selectively target infections at pH-neutral wound sites, but not the acidic, healthy skin.

Monocyte transendothelial migration is a multi-step process critical for the initiation and development of atherosclerosis. The chemokine monocyte chemoattractant protein-1 (MCP-1) is overexpressed during atheroma and its concentration gradients in the extracellular matrix (ECM) is critical for the transendothelial recruitment of monocytes. Based on prior observations, we hypothesize that both free and bound gradients of MCP-1 within the ECM are involved in directing monocyte migration. The interaction between a three-dimensional (3D), cell-free, collagen matrix and MCP-1; and its effect on monocyte migration was measured in this study. Our results showed such an interaction existed between MCP-1 and collagen, as 26% of the total MCP-1 added to the collagen matrix was bound to the matrix after extensive washes. We also characterized the collagen-MCP-1 interaction using biophysical techniques. The treatment of the collagen matrix with MCP-1 lead to increased monocyte migration, and this phenotype was abrogated by treating the matrix with an anti-MCP-1 antibody. Thus, our results indicate a binding interaction between MCP-1 and the collagen matrix, which could elicit a haptotactic effect on monocyte migration. A better understanding of such mechanisms controlling monocyte migration will help identify target cytokines and lead to the development of better anti-inflammatory therapeutic strategies.