Prior research established that P[AB]-copolyoxetane polyurethanes with soft blocks having A = trifluoroethoxy (CF(3)CH(2)-O-CH(2)-, 3FOx) and B = dodecylammonium-butoxy (C12) are highly effective as polymer surface modifiers (PSMs). These PSMs displayed high contact antimicrobial efficiency against spray challenge that was attributed to surface concentration of quaternary charge. Herein, using a novel cell design and polymer coating process, streaming potential (SP) measurements are reported for estimating accessible surface charge density. Fused-silica capillaries were embedded in flat polypropylene sheets, and the inner capillary walls were coated with neat HMDI-BD(30)-P[(3FOx)(C12)-87:13-5100] (PU-1) and 1 wt % PU-1 in HMDI-BD(50)-PTMO-1000 (base polyurethane 2). Effects of annealing (60 degrees C) and electrolyte flow cycles on near-surface quaternary charge concentration were determined. Neat PU-1 had a constant SP that was cycle-independent and actually increased on annealing. As-cast 1 wt % PU-1 showed initial SPs about half those for neat PU-1, with substantial attenuation over 16 measurement cycles. SPs for annealed 1 wt % PU-1 displayed lower initial values that attenuated rapidly over multiple cycles. Zeta potentials and surface charge densities were calculated from SPs and discussed relative to contact antimicrobial properties. Tapping mode atomic force microscopy (TM-AFM) imaging was employed for investigation of 1 wt % PU-1 surface morphology. Microscale phase separation occurs on annealing 1 wt % PU-1 for 24 h at 60 degrees C. Surprisingly, phase separation was also observed after short immersion of 1 wt % PU-1 coatings in water. The morphological changes are correlated with instability of near-surface charge found by SP measurements. A model is proposed for near-surface spinodal decomposition of metastable as-cast 1 wt % PU-1. The formation of a fluorous modifier rich phase apparently sequesters near-surface quaternary charge and accounts for temporal instability of antimicrobial properties. The results are important in providing a facile method for screening polycation-based, contact antimicrobial coatings for accessible charge density and in assessing durability.
Free-standing porous silica microstructures have been made via the electroassisted deposition of silica in an appropriately patterned array of recessed electrodes consisting of hydrophilic and hydrophobic domains. The 100 nm deep recessed indium tin oxide (ITO) electrodes were prepared by a photolithographic/chemical etching process on Glass/ITO/Au substrates. Hydrophobic areas were formed by passivation of unetched gold with a self-assembled monolayer of 1-octadecanethiol. Application of sufficiently negative potentials produced thick layers of silica that extended across the whole substrate; however, because of adhesion differences of silica on hydrophilic (ITO) and hydrophobic (thiol-modified gold) surfaces, selective removal of silica from the more hydrophobic areas of the substrate was achieved. The surface morphology, porosity, and thickness of resultant microstructures depended on the concentration of tetramethoxysilane in the sol, the electrolysis time, and the applied potential, all of which have been varied. Free-standing silica features of different geometries including bands, squares, and circles, ranging in width from 60 to 500 μm and heights >1 μm, have been prepared using this approach. Scanning electron microscopy (SEM) images showed the materials to consist of aggregates of colloidal particles that extend tens to thousands of nanometers above the surface. Such film-like materials have important characteristics that make them ideally suited as a platform for chemical sensors; most notably, an open framework and the presence of interconnected pores within individual microstructures.
A composite surface was prepared on cyclic olefin copolymer (COC) microchannels by UV-photografting of polyethylene glycol acrylate (PEGA) and poly(acrylic acid) (PAA) films. A PEGA layer of globular particles with average thickness of 60 nm was formed after 15 min of polymerization. Real time monitoring by pulsed streaming potentials demonstrated the ability of the PEGA layer to inhibit the adhesion of five different nonspecific adsorbing proteins when compared with pristine COC. Roughness determined by atomic force microscopy (AFM) after PAA grafting on COC-PEGA at different UV illumination times suggests that PAA formation is initiated at the free space in between the PEGA particles. Carboxylic groups activated with N-hydroxysuccinimide and N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide were used to bind anti-lysozyme polyclonal antibodies. The composite COC-PEGA-PAA-anti-lysozyme surface demonstrated its ability to detect lysozyme with a dynamic range between 140 and 860 nM. Linearity was maintained even when samples were spiked with 250 nM of cytochrome as interfering species. The equilibrium constant K(eq) for the adsorption of Ly on COC-PEGA-PAA-anti-Ly was estimated to be 2.7 × 10(6) M(-1), and it shows that this kinetic approach of monitoring the surface charge is also useful to estimate affinity interactions for proteins in label free fashion. The regeneration of the surface exhibited an average percentage of recovery of ∼97% for each of six adsorption-regeneration cycles. This feature enables curve calibration on a single microfluidic chip because each point of the curve has a reproducible and renewable surface.
Biocomposites are materials formed by mixing a polymer matrix and a filler or reinforcement, with the characteristic that at least one should be of biological origin. For this study, biocomposites were obtained from natural fibers of cane bagasse and polypropylene, using bagasse from postindustrial sources, originating from the production of sugarcane from the Valle-Cauca region in Colombia. In addition, cane bagasse fibers were treated chemically, with the purpose of improving the interfacial relationship. Polypropylene homopolymer was used as a polymeric matrix, which was mixed in a twin screw extruder, obtaining different materials as biocomposites. Finally, it was possible to obtain a suitable biocomposite for application in injection molding processes and studying its mechanical, viscoelastic, and thermal behaviors, through DSC, TGA, DMA, and SEM techniques.
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