Hydrophobic Polymer surface modification

PFM experiments performed with surface-modified tips allow steady imaging of polymer blends with respect to the pull-off forces. Comparing non-modified, hydrophilic tips with modified hydrophobic tips reveals the inversion of the difference between the adhesive forces, indicating even an inversion of the strength of interactions between hydrophilic and hydrophobic polymer surfaces and the SFM tip or silica particles. It could also be shown that the hardness of the silane layer influences the measured pull-off forces. The harder HMDS modification leads to lower adhesive forces, like the softer PDMS modification, confirming the results obtained for toner-silica particles. 

In this study, we describe the modification of PTFE by a chemical method in combination with a biochemical method leading to an improved cell adhesion. The modification was first developed with punched disks from PTEE film, and was then transferred to commercially available vascular grafts made of PTEE. The aim was to retain the mechanical properties of the polymer so that only the biological properties of the inner surface of the graft were changed. Thus it would become possible to couple adhesion proteins to the previously inert and hydrophobic polymer surface to favor adhesion and attachment of endothelial cells (ECs) withstanding shear stress as it occurs in small-diameter vascular grafts. 

For this reason, the polymer substrate treatment represents a very important step in the technology of metallic or ceramic coating on the polymer substrate. Therefore, noble metals and other low reactivity metals do not wet the untreated polymer surfaces, forming three-dimensional spherical clusters growing in a Volmer-Weber mode. Surface modification of the hydrophobic polymer surface onto a hydrophilic one can be achieved by wet (acid, alkali), dry (plasma), and radiation treatments (ultraviolet radiation and laser), without affecting the bulk properties. Consequently, application of different pretreatment methods represents an efficient way to improve wettability and thin metal adhesion. 

Surface modifiers change the physical chemistry of mineral and fiber surfaces. Hydrophilic surfaces, as commonly found with many mineral fillers, can be made hydrophobic by surface modification. Mineral and glass fibers can be treated so that the polymers they reinforce will wet their surfaces. Surface modifiers are chemically bound to one surface and physically attracted to another surface or material. They... 

Polymer degradation by hydrolysis will be governed by the amount of water present in the formulation. The degradation rate is thus influenced by Ihe hydro-phobicity of the polymeric side chains and their ability to take on water. The hydrophobicity of the polymeric structure must strike a balance with the optimal hydrophobicity needed for protein adsorption and cellular attachment. In order for cells to adhere to a polymeric scaffold, the scaffold must be hydrophilic. However, many of the polymers utilized for scaffold fabrication are highly hydrophobic. Thus, surface modifications or pre-wetting the scaffold with a solvent is typically needed for successful cell adherence. 

Polymer Surface Modification to Attain Blood Compatibility of Hydrophobic Polymer... 

Chain-Growth Associative Thickeners. Preparation of hydrophobically modified, water-soluble polymer in aqueous media by a chain-growth mechanism presents a unique challenge in that the hydrophobically modified monomers are surface active and form micelles (50). Although the initiation and propagation occurs primarily in the aqueous phase, when the propagating radical enters the micelle the hydrophobically modified monomers then polymerize in blocks. In addition, the hydrophobically modified monomer possesses a different reactivity ratio (42) than the unmodified monomer, and the composition of the polymer chain therefore varies considerably with conversion (57). The most extensively studied monomer of this class has been acrylamide, but there have been others such as the modification of PVAlc. Pyridine (58) was one of the first chain-growth polymers to be hydrophobically modified. This modification is a post-polymerization alkylation reaction and produces a random distribution of hydrophobic units. 

A second surface modification has been reported by Yamamoto et al. These workers added stearic acid to their carbon paste mixture. This produced an electrode which was relatively insensitive to ascorbic acid and DOPAC relative to dopamine. It is theorized that this electrode works because of electrostatic repulsion of the anionic ascorbate and DOPAC by surface stearate groups. Ionic repulsion has also been employed by covering the surface of the working electrode with an anionic polymer membrane. Gerhardt et al. used Nafion, a hydrophobic sulfonated perfluoro-polymer, to make a dopamine selective electrode. This electrode exhibited selectivity coefficients as large as 250 1 for dopamine and norepinephrine over ascorbic acid, uric acid, and DOPAC. 

The improvement of its activity and stability has been approach by the use of GE tools (see Refs. [398] and [399], respectively). A process drawback is the fact that the oxidation of hydrophobic compounds in an organic solvent becomes limited by substrate partition between the active site of the enzyme and the bulk solvent [398], To provide the biocatalyst soluble with a hydrophobic active site access, keeping its solubility in organic solvents, a double chemical modification on horse heart cytochrome c has been performed [400,401], First, to increase the active-site hydrophobicity, a methyl esterification on the heme propionates was performed. Then, polyethylene glycol (PEG) was used for a surface modification of the protein, yielding a protein-polymer conjugates that are soluble in organic solvents. 

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Avseenko et al. (2001) immobilized antigens onto aluminum-coated Mylar films by electrospray (ES) deposition. Various surface modifications of the metallized films were studied to determine their abilities to enhance sensitivity. The plastic surfaces were firsf cleaned by plasma discharge treatment, followed by coating with proteins (BSA and casein) or polymers such as poly (methyl methacrylate) or oxidized dextran, or they were exposed to dichlorodimethyl silane to create hydrophobic surfaces. Protein antigen was prepared in 10-fold excess sucrose and sprayed onto the surfaces to form arrays with spot diameters between 7 and 15 pm containing 1 to 4 pg protein. 

Modifications of monodisperse colloidal silica, of 10 or 500 nm in diameter, were carried out using trialkoxysilane-terminated polymer in a low polar solvent, such as acetone or 1,2-dimethoxyethane. without coagulation during the coupling reaction (35,37-42). In this modification, the hydrophobic polymer can be efficiently bound to hydrophilic colloidal silica surface. The reaction mechanism of the binding... 

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