Showing papers on "Surface modification published in 1994"

Electrochemical oxidation of amine-containing compounds. A route to the surface modification of glassy carbon electrodes

Abstract: A method for the modification of glassy carbon electrodes (GCEs) with amine-containing compounds for electrocatalytic and biosensor purposes is investigated. The method utilizes the electrooxidation of amines to their analogous cation radicals to form a chemically stable covalent linkage between the nitrogen atom of the amine and edge plane sites at the GCE surface. By use of X-ray photoelectron spectroscopy (XPS) for coverage assessment, the capability of this route is demonstrated by the immobilization of a simple primary amine at the GCE surface. An investigation of the influence of substituents on the nitrogen atom (e.g., primary, secondary, tertiary amines) revealed that the surface coverage of primary amines was [approximately] 3 times higher than that of secondary amines, whereas tertiary amines were not immobilized at a detectable level. This behavior is attributed to a strong steric effect whereby bulky substituents on the nitrogen atom binder accessibility of the reactive amine cation radical to surface binding sites. Amine salts and amides also showed no detectable coverage by XPS. The utility of the method for creation of a GCE with electrocatalytic activity is demonstrated by the immobilization of dopamine (DA) at the GCE surface. 48 refs., 9 figs., 1 tab.

Surface modification of poly(lactide-co-glycolide) nanospheres by biodegradable poly(lactide)-poly(ethylene glycol) copolymers.

Abstract: The modification of surface properties of biodegradable poly(lactide-co- glycolide) (PLGA) and model polystyrene nanospheres by poly(lactide)-poly(ethylene glycol) (PLA:PEG) copolymers has been assessed using a range of in vitro characterization methods followed by in vivo studies of the nanospheres biodistribution after intravenous injection into rats. Coating polymers with PLA:PEG ratio of 2:5 and 3:4 (PEG chains of 5000 and 2000 Da. respectively) were studied. The results reveal the formation of a PLA:PEG coating layer on the particle surface resulting in an increase in the surface hydrophilicity and decrease in the surface charge of the nanospheres. The effects of addition of electrolyte and changes in pH on stability of the nanosphere dispersions confirm that uncoated particles are electrostatically stabilized, while in the presence of the copolymers, steric repulsions are responsible for the stability. The PLA:PEG coating also prevented albumin adsorption onto the colloid surface. The evidence that this effect was observed for the PLA:PEG 3:4 coated nanospheres may indicate that a poly(ethylene glycol) chain of 2000 Da can provide an effective repulsive barrier to albumin adsorption. The in vivo results reveal that coating of PLGA nanospheres with PLA:PEG copolymers can alter the biodistribution in comparison to uncoated PLGA nanospheres. Coating of the model polystyrene nanospheres with PLA:PEG copolymers resulted in an initial high circulation level, but after 3 hours the organ deposition data showed values similar to uncoated polystyrene spheres. The difference in the biological behaviour of coated PLGA and polystyrene nanospheres may suggest a different stability of the adsorbed layers on these two systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Biofunctional surface modified ocular implants, surgical instruments, medical devices, prostheses, contact lenses and the like

Abstract: A method for modifying the surface of a material adapted for contact with tissue of a human or non-human animal to impart biofunctional, bioactive or biomimetic properties to the surface comprising: (a) exposing the surface to a solution comprising (1) an ethylenically unsaturated monomer or mixture thereof capable, via the ethylenic unsaturation, of gamma irradiation or electron beam induced polymerization, and (2) at least one biofunctional agent; and (b) irradiating the surface with gamma or electron beam irradiation in the presence of the solution to thereby form on the surface a graft polymerized coating, the coating having physically entrapped therein or chemically bonded thereto molecules of the at least one biofunctional agent which imparts biofunctional or biomimetic properties to the surface; wherein the gamma or electron beam irradiation induced polymerization is conducted under one of the following conditions: A. (i) monomer concentration in the solution in the range of from about 0.1% to about 50%, by weight; (ii) total gamma or electron beam dose in the range of from about 0.001 to less than about 0.50 Mrad; and (iii) gamma dose rate in the range of from about 10 to about 2,500 rads/min., or electron beam dose rate in the range of from about 10 to about 10 8 rads/min.; B. (i) hydrophilic monomer(s) graft under conditions which may include monomer pre-soak or plasma gamma surface modification (especially for metal or glass substrates in latter case); and (ii) graft polymerization of monomer(s) with bioactive/biofunctional molecules using (i) as substrate; C. (i) Hydrograft™ as in A or B above followed by dehydration and adsorption of bioactive/biofunctional molecules into the hydrophilic polymer graft; wherein the biological properties of the biofunctional agent are substantially maintained.

Surface and Interface Stresses

Abstract: Perhaps the most fundamental difference (from a thermodynamic point of view) between a solid surface and a liquid surface involves the distinction between the surface free energy and the surface stress. The reversible work per unit area involved in forming a surface, which exposes new atoms, is the surface free energy y. This parameter describes the reversible work to form a new solid surface by a process such as cleavage. The surface stress I is the reversible work per unit area required to elastically stretch a surface. When a fluid surface is stretched, new atoms or molecules arrive at the surface such that the number of atoms per unit area remains constant. As a result, it can be considered that for a fluid the surface free energy is the same as the surface stress. On the other hand, when a solid surface is elastically stretched, the actual number of atoms per unit area is altered and, in general, I =f. y. When a solid of finite size is elastically deformed, work is performed against both volume and surface forces. Under most conditions the volume term will strongly dominate over the surface term. However, for solids of small enough extent, the surface term can become important and induce a bulk stress of order I/t that elastically changes the eqUilibrium lattice spacing. Here t corresponds to the characteristic length

Preparation of zeolite filled glassy polymer membranes

Abstract: The incorporation of zeolite particles in the micrometer range into polymeric matrices was investigated as a way to improve the gas separation properties of the polymer materials used in the form of membranes. The adhesion between the polymer phase and the external surface of the particles appeared to be a major problem in the preparation of such membranes when the polymer is in the glassy state at room temperature. Various methods were investigated to improve the internal membrane structure, that is, surface modification of the zeolite external surface, preparation above the glass-transition temperature, and heat treatment. Improved structures were obtained as observed by scanning electron microscopy, but the influence on the gas separation properties was not in agreement with the observed structural improvements.

Preparation of high porosity xerogels by chemical surface modification

Abstract: This invention provides an extremely porous xerogel dried at vacuum to below-supercritical pressures but having the properties of aerogels which are typically dried at supercritical pressures. This is done by reacting the internal pore surface of the wet gel (e.g. alkoxide-derived silica gel) with an organic surface modification agent (e.g. trimethylchloro-silane in benzene) in order to change the contact angle of the fluid meniscus in the pores during drying. Shrinkage of the gel (which is normally prevented by the use of high autoclave pressures, such that the pore fluid is at temperature and pressure above its critical value) is avoided even at vacuum or ambient pressures. The figure 4 shows a change in sample weight and sample length during drying for surface modified, ambient pressure gel processed in accordance with the invention, illustrating the initial shrinkage followed by expansion of the gel during the final stages of drying. The extremely low density finely pored gel products have useful insulating and other properties.

Chemical modification of polymer surfaces: a review

Abstract: The main approaches that have been taken to chemically modify polymer surfaces are introduced and reviewed. These are wet chemical oxidation, plasma treatment, classical organic chemistry, and attachment of polymer chains. The extent to which each of these approaches can produce the specific modifications desired is discussed, and any unwanted effects that commonly occur are cited. Finally, the need for using several methods of surface analysis in concert to obtain adequate surface characterization is described.

The effect of surface modification by an organosilane on the electrochemical properties of kaolinite

Abstract: The electrochemical properties of kaolinite before and after modification with chlorodimethyl- octadecylsilane have been studied by electrophoretic mobility, surface charge titration, and extrapolated yield stress measurements as a function of pH and ionic strength. A heteropolar model of kaolinite, which views the particles as having a pH-independent permanent negative charge on the basal planes and a pH- dependent charge on the edges, has been used to model the data. The zeta potential and surface charge titration experimental data have been used simultaneously to calculate acid and ion complexation equi- librium constants using a surface complex model of the oxide-solution interface. The experimental data were modeled following subtraction of the basal plane constant negative charge, describing only the edge electrical double layer properties. Extrapolated yield stress measurements along with the electrochemical data were used to determine the edge isoelectric points for both the unmodified and modified kaolinite and were found to occur at pH values of 5.25 and 6.75, respectively. Acidity and ion complexation constants were calculated for both sets of data before and after surface modification. The acidity constants, pKat = 5.0 and pKa2 = 6.0, calculated for unmodified kaolinite, correlate closely with acidity constants determined by oxide studies for acidic sites on alumina and silica, respectively, and were, therefore, assigned to pH-dependent specific chemical surface hydroxyl groups on the edges of kaolinite. The parameters calculated for the modified kaolinite indicate that the silane has reacted with these pH- dependent hydroxyl groups causing both a change in their acidity and a concomitant decrease in their ionization capacity. Infrared data show that the long chain hydrocarbon silane is held by strong bonding to the kaolinite surface as it remains attached after washing with cyclohexane, heating, and dispersion in an aqueous environment.

Hydrophilic films by plasma polymerisation

Abstract: The invention describes a process for the surface modification of a polymer, which comprises treating a polymer with a working gas comprising hydrogen peroxide and an organic compound in plasma form.

Lubricious silicone surface modification

Abstract: Lubricious silicone surface modifying treatments and/or coatings for modifying the frictional or slip surface characteristics of shaped elastomeric articles are provided in surface modifications including a coating or surface modifying composition comprising: a crosslinkable silane having the formula: wherein R is selected from unsubstituted and halogen-substituted aliphatic, cycloaliphatic, aromatic and alkyl aromatic groups having less than or equal to about ten carbon atoms, R¹ is independently selected from hydrogen, hydroxyl, halogen, alkoxy and acyloxy groups, R² is independently selected from hydrogen, alkyl and halogen-substituted alkyl groups, n is an integer of 1 to 3 inclusive, and m = 3 - n . The cured, highly crosslinked, three dimensional silicone coatings are effective at reducing the coefficient of friction of surfaces of shaped elastomeric articles, such as those frequently used in medical devices, by a factors of from about 50% to about 80% as compared with the same uncoated substrates.

Surface modification of fluoropolymers with vacuum ultraviolet irradiation

Abstract: Amorphous fluoropolymers (AF) have recently been developed to provide several favorable characteristics not present in the more crystalline materials However, these polymers have not been fully characterized and reports of surface modification are not extensive This work presents results of surface analysis and modification with vacuum ultraviolet (VUV) irradiation of Teflon‐AF‐2400 using contact angle measurements, x‐ray photoelectron spectroscopy (XPS), and laser‐assisted Fourier transform mass spectroscopy (FTMS) Results are compared to those for other, more crystalline, fluoropolymers, namely, poly(tetrafluoroethylene) (PTFE) and the copolymer of tetrafluoroethylene and perfluoroalkoxyvinyl ether (PFA) These three fluoropolymers differ in structure and amount of oxygen that they contain Samples were irradiated for sixty minutes downstream from a helium microwave plasma, in some instances through a LiF crystal filter In the latter case, modification is due solely to photons with wavelengths great

Surface modification of polyethylene fiber by graft polymerization

Abstract: To improve the wettability and adhesion, graft polymerization of acrylamide (AAm) and glycidyl methacrylate (GMA) was performed onto the surface of ultra-high modulus polyethylene (UHMPE) fiber pretreated with Ar plasma. Following the plasma treatment and the subsequent exposure to air to introduce peroxides onto the fiber surface, graft polymerization onto the UHMPE fiber was allowed to proceed from the polymer peroxides either in deaerated monomer solution at an elevated temperature (degassing method), or in aerated monomer solution containing riboflavin at 30°C under UV irradiation (photoinduction method). The monomer solution was prepared from water and dioxane for AAm and GMA, respectively. After rigorous removal of homopolymers, surface analysis of the grafted fibers was performed with ATR-FTIR and XPS, which revealed that PAAm and PGMA chains were grafted in the surface region of fibers. The grafting rate of PAAm by the photoinduction method was much higher than that by the degassing method when compared at the same concentration of the AAm solution. The amount of PGMA grafted was greatly affected by UV irradiation time, but depended on plasma treatment time to an insignificant extent if the treatment was carried out for longer than 30 s. Reaction of propylamine with the PGMA-grafted surface resulted in the appearance of a nitrogen peak in the XPS spectrum, suggesting the presence of epoxy groups on the surface of PGMA grafted fiber. © 1994 John Wiley & Sons, Inc.

Surface Modification of Polymers by Blending Siloxane Block Copolymers

Abstract: The surface modification of a series of homopolymers is accomplished through mixing an AB block copolymer, where B is a poly(dimethylsiloxane) (PDMS) block and A is the block of the same chemical identity as of the homopolymers. The homopolymers are polystyrene, poly(α-methylstyrene), and Bisphenol A polycarbonate. The surface composition of PDMS is measured by angle-dependent ESCA. The PDMS blocks are segregated in the topmost surface region and constitute up to 90 wt% of the surface of the AB/A blends, even though the overall bulk PDMS concentrations of the blends are 6% or less

Surface modification of aluminum by electrical discharge alloying

Abstract: Surface modification of aluminum was carried out using a new method named electrical discharge alloying. Deposition of titanium contained in electrodes and carbon decomposed from hydrocarbon working fluid occurs on aluminum substrates. With an electrode of a Ti-36mass%Al premixed green compact, in situ composite layers mainly consisting of TiC and TiAl are formed. The process makes it possible not only to coat the in situ composite layers with a thickness of 100 μm within a few minutes but also to obtain different TiC volume ratios by changing the process parameters. The formation of fine dendritic TiC precipitates can be considered to be a result of rapid solidification during the process. The volume ratio of TiC decreases with increasing distance from the surface, which means that the modified layers are composed of gradient constituents. The hardness close to the surface can be controlled to a value of 3.5–10.5 GPa changing the process parameters, such as the pulse width and working time.

Enhanced Surface Crystallization of β‐Barium Borate on Glass Due to Ultrasonic Treatment

Abstract: β-Barium borate (BBO) surface crystallized glass composites were prepared for a glass of composition 40BaO·15Tio2–45B2O3 (in mol%). Enhanced nucleation was attained by ultrasonic surface modification with an aqueous suspension of BBO particles, resulting in dense BBO thin films on the glass surfaces. Second harmonic generation signals were observed for samples subjected to ultrasonic treatment.

Patterned neuronal attachment and outgrowth on surface modified, electrically charged fluoropolymer substrates.

Abstract: Fluorinated ethylenepropylene copolymer (FEP) and polyvinylidene fluoride (PVDF) can generate static and transient electrical charges, respectively, after bulk molecular rearrangements induced by electrical charging techniques. Neurons cultured on electrically active FEP and PVDF show increased levels of nerve fiber outgrowth compared to electrically neutral material. The purpose of the present study was to determine if the addition of charged surface groups to the surfaces of FEP and PVDF would modify the influence of bulk electrical charges on cultured neurons. Mouse neuroblastoma (Nb2a) cells were cultured on electrically charged and uncharged FEP and PVDF substrates with covalently modified surfaces containing hydroxyl (OH) and amine (NH2) groups. Surface chemical modification was performed on the entire surface or in discrete striped regions. Nb2a cells cultured on electrically active FEP and PVDF showed greater levels of differentiation than cells on electrically neutral substrates. The presence of ...

Wet-process surface modification of dielectric polymers: adhesion enhancement and metallization

Abstract: For many electronic applications, the surface of a dielectric polymer must be modified to obtain the desired surface properties, such as wetting, adhesion, and moisture barrier, without altering the bulk properties. This paper reviews wet- process modifications of dielectric polymer surfaces and also presents unpublished results related to fluorinated polyimides. In a typical wet process, a substrate is immersed in or sprayed with a chemical solution, rinsed with a solvent to remove the excess reagents, and then dried if necessary. Wet processing can provide greatly enhanced adhesion and reliability of the adherate (top) layer to the modified polymer surface (adherend). We discuss a) the wet-process modification of various polymers (e.g., PMDA-ODA, BPDA-PDA, 6FDA-ODA, PTFE, PCTFE); b) polyimide/polyimide and PCTFE/glass adhesion, and c) the surface chemistry and the adhesion at a fluorinated polyimide (6FDA-ODA) surface. Entanglement of polymer chains plays an important role in polyimide/polyimide adhesion, while chemical reactions are the major contributors to PCTFE/glass adhesion strength. The metallization of dielectric substrates often requires surface pretreatments or conditioning by wet processes to sensitize a polymer surface for deposition of a metal seed layer. After seeding, a thick layer of a conducting metal (e.g., Cu) is deposited by electroless or electrolytic plating. Unlike dry or high-vacuum processing of polymer surfaces, the chemistry of a wet-processed polymer surface can be well characterized and often defined at a molecular level. A relationship can be established between a polymer's surface chemical (or morphological) structure and its surface properties such as adhesion and metallization.

Surface modification of UHMWPE fibers

Abstract: Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a high specific strength, high specific modulus, and outstanding toughness, but their poor adhesive properties has limited their use for composite material applications. In this research, the effects of chemical etching on the surface chemistry and topography have been explored using chromic acid, potassium permanganate, and hydrogen peroxide etching. The smooth surface observed on the as-received fiber was rich in ether and/or hydroxyl oxygen. This smooth surface resulted from the presence of an outer layer, a weak boundary layer, that was removed by all the etchants. A fibrillar structural hierarchy was revealed beneath this outer layer and the fiber was relatively unchanged by further etching. Chromic acid, the strongest etchant studied, produced a rough and oxidized UHMWPE surface with both ether and carbonyl oxygen. The combination of outer layer removal, roughness, and changes in oxygen bonding helps explain the improved adhesion on chromic acid etching in spite of the reduction in surface oxygen. Neither hydrogen peroxide nor potassium permanganate etching roughened or oxidized the surface to a great extent and neither yielded improved adhesion. © 1994 John Wiley & Sons, Inc.

Fluoropolymer surface modification for enhanced evaporated metal adhesion

Abstract: Adhesion of evaporated Cu to Teflon PFA (polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether) was greatly enhanced by plasma pretreatment. The efficiency of the treatment decreased in the following order: N2 > O2 > (N2 + H2) > (O2 + H2) > H2. X-ray photoelectron spectroscopy (XPS) showed the loss of fluorine and the incorporation of oxygen and nitrogen at the polymer surface. Among the gases, H2 was found to be the most efficient for fluorine elimination, and (N2 + H2) for surface functionalization. Based on this investigation, it is proposed that Cu reacts with both oxygen and nitrogen to form, respectively, Cu-O and Cu-N bonds at the interface but no reaction occurs with carbon and fluorine. While greater enhancement in polymer surface wettability and stronger interfacial reactions can account for the higher performance of N2 over O2 in improving adhesion, these effects cannot explain the lower efficiency of H2. Several possibilities are discussed, including surface cleaning, oxygen incorporation and...

Novel Surface Graft Copolymerization Method with Micron-Order Regional Precision

Abstract: A novel graft copolymerization method which allows for surface modification with micron-order regional precision is presented. The essential feature of the method is based on surface photoprocessing leading to immobilization of radical initiators. This method consists of the following steps: (1) derivatization of amino groups onto a polymer surface via photochemical fixation of poly(allylamine) partially derivatized with photoreactive phenylazido groups, (2) chemical fixation of carboxylated radical copolymerization initiators via condensation reaction with poly(allylamine), and (3) surface radical graft copolymerization under reduced pressure. Two examples were demonstrated to verify the effectiveness of this method. One was surface graft copolymerization of styrene on poly(vinyl alcohol) (PVA) film, and the other was surface graft copolymerization of acrylamide on poly(ethylene terephthalate) (PET) film. ESCA and water contact angle measurement before and after sequential surface reactions provided evidence that graft copolymerization proceeded successfully. The microprocessing of a substrate surface using a photomask with micron-level spaces was demonstrated. Atomic force microscopy showed that surfaces were grated on only UV-irradiated regions, resulting in the formation of a micropatterned graft polymer, which was clearly visualized by staining of hydrolyzed acrylamide units with a dye. The scope of potential applications is discussed

Novel Hybrid Inorganic-Organic Abrasion-Resistant Coatings Prepared by a Sol-Gel Process

Abstract: Novel abrasion-resistant coatings prepared by a sol-gel process have been developed and applied on the polymeric substrate Bisphenol A polycarbonate. In general, coatings utilize either 4,4′-diaminodiphenyl sulfone (DDS) or diethylenetriamine (DETA) that are then functionalized at their amine groups with 3-isocyanatopropyltriethoxysilane. Following functionalization, these coating materials are then spin coated onto bisphenol A polycarbonate sheet and cured. These reactants undergo a comparable sol-gel reaction similar to typical metal alkoxide chemistry, thereby producing an insoluble network material containing a good dispersion of the functionalized organic along with the hydrolyzed and condensed silicon alkoxide groups. The final coating is transparent and of a few microns in thickness. Following curing, an index of the abrasion resistance is assessed by an optical method, and the adhesion behavior of the coatings is investigated and quantified. It is demonstrated that these thin transparent ...

The interaction of surface engineering and high temperature corrosion protection

Abstract: The interaction between surface engineering and corrosion resistance of high temperature materials is reviewed. A brief description is given of high temperature corrosion, while criteria for surface engineering are outlined. The most important classes of surface treatments utilized technologically to provide high temperature corrosion protection, namely surface alloying, diffusion coatings and also metallic and ceramic overlay coatings, are discussed. The various ways in which surface engineering can interact with high temperature corrosion resistance are considered. Thus, the main purpose of the surface layer can be solely to afford protection, but in other cases, such as with thermal barrier coatings, the surface layers have another primary task, but additionally provide corrosion resistance. Finally, the important role of surface modification techniques, in particular ion implantation, as a research tool for corrosion science is highlighted.