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Coatings from carboxymethylated dextrans (CMDs) were fabricated, analyzed by XPS, and investigated for their ability to inhibit corneal epithelial tissue outgrowth and bovine corneal epithelial cell attachment and growth. CMDs with differing degrees of carboxymethyl substitution and various molecular weights were synthesized by the solution reaction of dextrans with bromoacetic acid under different reactant ratios. The CMD compounds thus obtained were attached onto aminated surfaces produced in two ways: by the plasma deposition of a coating from n-heptylamine vapour, and by the plasma deposition of an acetaldehyde coating onto whose surface aldehyde groups the polyamine compounds polylysine, polyethyleneimine and polyallylamine were immobilized to provide platforms for CMD immobilization. XPS spectra showed that the latter route produced thicker coatings than the former approach. CMD molecules attached directly onto the plasma-fabricated amine surface supported some tissue migration; the extent of carboxymethyl substitution and the molecular weight of the CMDs had little influence. For CMDs immobilized via polyamine spacers, on the other hand, tissue outgrowth was completely inhibited, and again there were no discernible effects from the extent of carboxymethyl substitution and the molecular weight of the CMDs. In assays involving cell attachment and growth, analogous observations were found. Thus, the mode of immobilization of these polysaccharide coatings is the dominant factor in their anti-fouling performance, suggesting that optimization of the architecture of polysaccharide coatings may be an important factor for maximizing their cell-repellent abilities.

Lysozyme, lactoferrin, trypsin and myoglobin were bound onto thin carboxymethyl-dextran coatings in two ways: by physisorption, and by an intended carbodiimide interfacial linking reaction. XPS analyses recorded substantial protein loadings on all the samples. In some cases, the protein coverages achieved by physisorption were larger than on covalent binding, indicating substantial affinity of the proteins for spontaneous adsorption onto the coatings. The observation of significant physisorption raised the question of to what extent physisorption competed with covalent binding when the intended covalent linking reaction was performed. The technique of Surface-MALDI mass spectrometry was found to be rapid, convenient, sensitive, and eminently suitable for probing for the presence of a physisorbed population among the covalently linked proteins. Control experiments with physisorbed samples showed that all the four proteins investigated gave rise to strong signals. On samples produced using carbodiimide linking, however, no protein signals were detected while photomatrix signals attested to successful evaporation of the matrix. Covalently linked proteins evidently were immune to desorption and detection by Surface-MALDI-MS. Using signal-to-noise ratios of spectra recorded on samples with approximate monolayer coverage of physisorbed proteins, it was estimated that a signal should have been detectable if, among the covalently coupled protein molecules, >1–2% of the total protein coverage present after intended covalent immobilization were physisorbed. Therefore, Surface-MALDI analyses suggest that within experimental accuracy, the carbodiimide chemistry used led to complete covalent interfacial immobilization of all four protein layers.

Approaches are described for the analysis of XPS signals from samples comprising thin conformal coatings on substrates with non-ideal surface topography. In particular, attention is focused on arbitrarily shaped rough or curved substrates. Relations are derived for the relative x-ray photoelectron intensities emitted from various elements in such non-ideal samples. The surface topography of arbitrarily rough samples is analysed by atomic force microscopy to provide a frequency histogram of the local slopes, which is incorporated into a global, multi-element analysis method for interpretation of the observed XPS elemental intensities. An analogous approach is used for the analysis of curved samples. Our algorithms also enable simultaneous analysis of successively coated multilayer structures. When the elemental composition of the individual layers is known, the fit procedure enables determination of the thickness values of single-layer and multilayer coatings. The range of validity of the theory is discussed. © 1997 by John Wiley & Sons, Ltd.

In the course of plasma deposition of organic-polymeric thin films, radicals are incorporated into the growing film. These radicals initiate spontaneous oxidation reactions that continue over many weeks when the plasma polymers are stored in air. The resultant changes to the composition with time were monitored by XPS for ethylene diamine plasma polymer samples in order to improve understanding of the products of the oxidative reactions. The broadness of all the peaks, and the multitude of functional groups expected to be present, precluded the obtainment of detailed compositional information by curve fitting for components, but shifts in the binding energies (BEs) of the N 1s and O 1s peaks with time provided useful evidence of compositional changes. As the oxygen content of the plasma polymer increased upon oxidation, the binding energy of the N 1s photoelectrons increased from 399.1 to 399.8 eV. Concurrently, the amount of nitrogen in relation to carbon (N/C) decreased from 0.42 to 0.34. As the nitrogen content of the plasma polymer decreased, the binding energy of the O 1s photoelectrons increased from 531.1 to 531.8 eV. The BE values and their shifts with time/compositional changes suggested that the oxidation process predominantly caused oxidation of the carbon atoms that had amine groups attached to them, leading to the formation of amide groups and perhaps also some imides.

A protocol for global analysis of x-ray photoelectron spectra of plasma-deposited polymer films is presented. These materials are difficult to analyse because of the multitude of different chemical groups present. The combination of different primary and secondary binding energy shifts results in relatively broad, featureless photoelectron peaks. The protocol is based on fitting a series of spectra obtained by monitoring the surface composition of a plasma polymer film over extended periods of time after deposition. Information obtained from this first round of curve-fitting is used in the form of additional constraints for a second round of fitting. This leads to a self-consistent procedure which is akin to a global approach to curve-fitting. To illustrate application of this method, results of a study of ann-heptylamine plasma polymer are described. The spectral changes on ageing provided clear evidence for radical-initiated oxidation reactions. These reactions generated additional radicals, which sustained the oxidation process for many months and not only led to substantial incorporation of oxygen into the material (forming a variety of carbon–oxygen functionalities) but also to conversion of most of the existing carbon–nitrogen functionalities to an oxidized form.

A theoretical description is presented for the macroscopic contact angle (θ) of a solid/vapor/aqueous solution interface when the solid surface is ionizable and relatively hydrophobic. The contact angle is related to the free energy of formation of the ionizable surface in aqueous solution. Therefore, the theoretical approach takes into account the electrostatic free energy of charging the surface and the change in the free energy associated with the acid-base reactions of the surface sites. It is shown that the dependence of θ on pH depends on the number ofionizable surface sites per unit area, the intrinsic acid-base dissociation constant (K a i ) of the surface sites, and the background electrolyte. The negative free energy change which accompanies the acid-base reactions dominates over the positive electrostatic free energy of charging the surface ; therefore, the overall free energy of ionization is negative, and the ionized surfaces are more wettable than the uncharged surfaces. The theoretical description is applied to experimental values of θ as a function of pH, measured on heptylamine plasma polymer surfaces in the presence of either 1 or 10 mM NaCl. The theoretical fit to the advancing and sessile contact angles indicates that the plasma polymer surface contains ca. 4±1x10 17 amines/m 2 and the pK a i of the amine groups is ca. 6. The surface site density is in accord with values obtained by derivatization techniques, and the pK a i is consistent with a low effective dielectric constant for the polymer-water interfacial microenvironment.

Polymer surfaces can adapt to surrounding media by reorientation of surface segments ; such motions can produce changes in contact angles (CAs). Building on two existing formalisms for time-independent CAs of heterogeneous surfaces, treatments are derived for the analysis of time-dependent CAs, enabling quantitative evaluation of the restructuring of polymer surfaces. In particular, we treat the case of air/water CAs on polymers which contain some polar surface groups that are immobile and others that are mobile and can migrate away from the surface by rotational and/or translational motions of polymer chains. A first-order process is assumed for the rate-limiting reorientation motion. The resulting equations have three parameters, viz., the fraction of the surface area covered by mobile polar groups, the fraction of the surface area covered by immobile polar groups, and the characteristic time constant (lifetime) of the reorientation process. The theoretical descriptions were applied to sets of contact angles measured on various plasma-modified polymer surfaces over extended periods oftime, enabling quantitative comparison of the effects of identical plasma treatments on the surface restructuring of different polymers.

Using X-ray photoelectron spectroscopy for quantification, the adsorption has been studied of chicken egg lysozyme, human serum albumin (HSA), bovine colostrum lactoferrin, and γ-globulin (IgG) from single solutions onto surface-immobilised polysaccharide coatings, which were produced by the covalent attachment of a series of carboxymethyldextrans (CMDs) onto aminated fluoropolymer surfaces. CMDs with differing degrees of carboxymethyl substitution were synthesized by the reaction of dextran with bromoacetic acid under different reactant ratios. Substantial amounts of protein adsorption onto these coatings were observed with the majority of the coating/protein combinations. On the most extensively substituted CMD (1 carboxyl group per 2 dextran units), lysozyme and lactoferrin adsorbed to approximately monolayer amounts whereas there was minimal adsorption of HSA, indicating the importance of electrostatic interfacial interactions. CMD 1:14 was similar whereas the least substituted, least dense coating, from CMD 1:30, adsorbed less lysozyme and lactoferrin but more HSA. Adsorption of the large multidomain protein IgG varied little with the coating. Grazing angle XPS data indicated that for the CMD 1:30 coating there occurred significant in-diffusion of the lower molecular weight proteins. The data suggest that elimination of adsorption of a broad spectrum of proteins is not straightforward with negatively charged polysaccharide coatings; elimination of protein accumulation onto/into such coatings may not be achievable solely with a balance of electrostatic and steric–entropic interfacial forces.

A theoretical description is presented for the equilibrium capillary height (heq) of a solution between parallel,flat,solidsurfaceswhichcontainionizablegroups. Theheqisrelatedtothechangeingravitational potential energy, the intrinsic wettability of the un-ionized surface, and the free energy of formation of theionizablesurfaceinaqueoussolution. Thetheoreticalapproachtakesintoaccountboththeelectrostatic free energy of charging the surface and the change in the free energy associated with the acid-base reactions of the surface sites. It is shown that the dependence of heq on pH depends on the number of ionizable surface sites per unit area, the intrinsic acid-base dissociation constant (Ka i ) of the surface sites, andthebackgroundelectrolyte. Thenegativefreeenergychangewhichaccompaniestheacid-basereactions dominates over the positive electrostatic free energy of charging the surface. Consequently, the overall free energy of ionization is negative, and an ionized surface is more wettable than an un-ionized surface. The theoretical description is applied to experimental values ofheqas a function of pH, measured between two heptylamine plasma polymer surfaces in the presence of 1 mM NaCl. The theoretical fit to the data indicates that the plasma polymer surface contains ca. 1017 amines/m2 and the pKa i of the amine groups is ca. 5. The surface site density is in reasonable accord with values obtained by both derivatization techniquesandcontactanglemeasurements. ThepKa i isconsistentwithaloweffectivedielectricconstant for the polymer-water interface.

Fluorinated ethylene-propylene (FEP) surfaces modified by ammonia or water vapor plasmas under a range of conditions were stored in contact with air and their surface restructuring on aging was monitored by periodic determination of air/water contact angles (CAs). By use of formalisms for the analysis of time-dependent CAs, the fraction of the surface area initially covered by mobile polar groups, the fraction of the surface area covered by immobile polar groups, and the characteristic time constant (lifetime) of the reorientation process were calculated. For ammonia-plasma-modified FEP surfaces, the fraction of mobile polar groups increased with increasing plasma treatment time up to an optimal treatment time of 45 s, probably due to plasma-induced chain cleavage. This indication of increasing mobility upon extended plasma treatment was, however, not accompanied by a decrease in the lifetime of the reorientation process, implying that the rate-limiting step for surface reorientation may not be associated with the inward motions of plasma-modified surface chains, but instead may depend on the slower outward migration of FEP chains to the surface.

Treatment of fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE) in ammonia plasmas produced surfaces with very high wettability by water, but on storage in air at ambient tempe...