Plasma Copolymers Research Articles

Stress Transfer Function for Interface Assessment in Composites with Plasma Copolymer Functionalized Carbon Fibres

Radio-frequency-induced plasma copolymerization of acrylic acid/1,7-octadiene was used to produce a range of functionalized plasma copolymer coatings with controlled degree of adhesion. The single-fibre fragmentation test was used to characterize the adhesion of plasma copolymer coated fibres to epoxy resin. The cumulative stress transfer function (CSTF) and Kelly-Tyson approaches were used to evaluate the degree of adhesion. By continuous monitoring of the fragmentation process, it was found that the mechanical performance of a composite material could be evaluated using the CSTF methodology at strain well below saturation. The degree of debonding was a good measure of relative interface/interphase adhesive strength. The trend in the CSTF is consistent with the propagation of interfacial debonds during the test. For a completely debonded fibre a normalized CSTF value, referred as stress transfer efficiency (STE), was found to provide a more consistent analysis that was able to differentiate between fibres with similar degrees of debonding. The calculated values of interfacial shear strength (IFSS) were only valid for a fully debonded fibre (1,7-octadiene plasma homopolymer coating) where the assumption of a constant shear stress, as in the Kelly-Tyson model, applied. However, IFSS did not provide the same ranking. Where debonding does not occur, the stress transfer efficiency also provides a sensitive measure of the interface/interphase performance. Improved adhesion over the untreated-unsized carbon fibre was observed for both of the plasma copolymer-coated and commercially treated carbon fibres. Since there is a concentration dependence of carboxyl groups on adhesion, the mechanism appears to relate to covalent bond formation with the epoxy group. Plasma copolymer coatings on carbon fibres also causes an increased tensile strength and Weibull modulus.

Application of Variable-Temperature Ellipsometry to Plasma Polymers: The Effect of Addition of 1,7-Octadiene to Plasma Deposits of Acrylic Acid

New insight is given into the complex molecular structure and composition of thin-film deposits of acrylic acid (AA) and 1,7-octadiene (OD) by variable-temperature ellipsometry. An AA plasma polymer is shown to contain nonbound, volatile material, which includes water, AA monomer, and oligomers thereof. The addition (0.25 molar fraction) of OD to an AA plasma is sufficient to cross-link most of these volatiles into the plasma copolymer deposit.

Comparison of proliferation and growth of human keratinocytes on plasma copolymers of acrylic acid/1,7-octadiene and self-assembled monolayers

Human keratinocytes were cultured on plasma copolymers (PCPs), self-assembled monolayers (SAMs), and tissue culture poly(styrene) (TCPS). Plasma copolymerization was used to deposit films with controlled concentrations of carboxylic acid functional groups (<5%). Human keratinocytes were cultured onto these PCP surfaces, TCPS, and collagen I. A hydrocarbon plasma polymer surface was used as the negative control. Keratinocyte attachment was measured at 24 h and cell proliferation and growth at 3 and 7 days using optical microscopy and DNA concentrations. The PCP surfaces were compared with two SAM systems comprising pure acid and pure hydrocarbon functionalities, and pure gold was used as a control surface. PCP surfaces containing carboxylic acid functionalities promoted keratinocyte attachment. The level of attachment on these surfaces was comparable to that seen on collagen I, a preferred substratum for the culturing of keratinocytes. After several days in culture the cells were well attached and proliferative, forming confluent sheets of keratinocytes. This result was confirmed by DNA assays that suggested the acid PCP surfaces were performing as well as collagen I. Keratinocytes attached well to gold and acid-terminated SAMs but attached poorly to methyl-terminated SAMs. The acid functionality also promoted proliferation and growth of keratinocytes after several days in culture. DNA assays revealed that keratinocyte growth on the acid surface was higher than on collagen I.

Comparison of proliferation and growth of human keratinocytes on plasma copolymers of acrylic acid/1,7‐octadiene and self‐assembled monolayers

Comparison of proliferation and growth of human keratinocytes on plasma copolymers of acrylic acid/1,7‐octadiene and self‐assembled monolayers

Surface characterization and platelet adhesion studies of plasma polymerized phosphite and its copolymers with dimethylsulfate.

Due to its capability for using a wide variety of organic and inorganic compounds as the monomer source, including those which are not polymerizable by conventional methods, plasma polymerization has been used to incorporate various functional groups onto the substrates of interest. Plasma polymerization of trimethylphosphite and triisopropylphosphite was attempted with an aim to deposit a thin film with phosphorous-containing functional groups such as phosphate or phosphite onto the glass substrate. Sulfur-containing functional groups, such as sulfonate, were incorporated as well with the addition of dimethylsulfate to the phosphite monomer inlet. These plasma polymers and plasma copolymers were very hydrophilic. Incomplete surface coverage was noticed under the processing conditions of low phosphite flow rate, low RF input power and shorter deposition time. Extended deposition duration and higher power input resulted in the formation of voids and pits on the plasma polymer surface. In addition, the surface coverage of the plasma copolymers becomes discontinuous if the flow rate ratio of dimethylsulfate to triisopropylphosphite is too high. In vitro platelet adhesion studies indicated the plasma polymers and plasma copolymers with continuous surface coverage are less platelet activating than the glass control. Moreover, the addition of dimethylsulfate into the phosphite monomer flow led to a further reduction in platelet adhesion and activation than the comparable one. This may be attributed to the effect of the sulfur-containing functionalities, such as sulfonate or sulfate, found on the plasma copolymers.

Molecular Engineering of Surfaces by Plasma Copolymerization and Enhanced Cell Attachment and Spreading

The plasma copolymerization of acrylic acid and methyl vinyl ketone with 1,7-octadiene is reported. A range of surfaces including hydrocarbon plasma polymer, carbonyl-containing plasma copolymer and carboxyl-containing plasma copolymers have been prepared and characterized by means of X-ray photoelectron spectroscopy. The stability of these surfaces in water has been assessed at 37°C. The influence of their functional group chemistries on the attachment and spreading of osteoblast-like (ROS 17/2.8) and bone marrow stromal cells (BMSC) has been explored. The data reported show a strong correlation between the carboxyl group and the attachment and spreading of both ROS cells and BMSC. This relationship has been explored in some detail with the ROS cells. Actin-staining by direct immunofluorescence was used to visualize changes in cytoskeleton of ROS cells with substratum chemistry. As the concentration of the carboxyl groups increased cell number and cell spreading were notably enhanced. As few as 5 carboxyls per 100 carbons were sufficient to support good attachment and with cells showing well-defined polygonal cell morphology. Although cells attached to a hydrocarbon plasma polymer surface these cells had failed to spread. The attachment and spreading of BMSC were compared on a carboxyl-containing surface and on a hydrocarbon surface. There was a more marked difference in the number of cells that had attached to these two surfaces (cf. ROS cells). The spreading on the carboxyl surface was much more typical of BMSC. Results from an extended culture using primary cultures of bone marrow cells (BMC) are reported. These cells were not trypsinized and appear to be less sensitive to differences in surface chemistry (cf. BMSC). Even so, the results at 10 days indicate much greater biosynthetic activity on the carboxyl-containing surface.

Plasma copolymer surfaces of acrylic acid/1,7 octadiene: Surface characterisation and the attachment of ROS 17/2.8 osteoblast-like cells

The purpose of this study was: (a) to examine the effect of plasma-gas composition on plasma polymer oxygen/carbon (O/C) ratio, functional group composition and stability in water, and then (b) to examine cell attachment to surfaces containing different concentrations of O/C and functional groups. Oxygen-functionalised surfaces were deposited by means of the plasma copolymerisation of acrylic acid/1,7-octadiene. The use of a diluent hydrocarbon allowed the deposition of surfaces with a range of O/C concentrations. Plasma copolymer surfaces were characterised by X-ray photoelectron spectroscopy (XPS). Changes in functional group composition with % acrylic acid monomer and the non-dispersive and dispersive parts of the surface energy of these plasma copolymers were measured. The solubility of the plasma copolymers was assessed by means of XPS. The degree of attachment of ROS 17/2.8 osteoblast-like cells to plasma copolymer surfaces deemed to be ‘stable’ in aqueous medium was measured. Tissue culture polystyrene (TCPS) was included as a control. Attachment was found to be greatest to the plasma copolymer surface with an O/C of 0.11. This surface had a carboxylic acid concentration of ca. 3%. Attachment did not correlate with increased surface wettability (i.e. the non-dispersive component of the surface energy).

Plasma Copolymerization of Allyl Alcohol/1,7-Octadiene: Surface Characterization and Attachment of Human Keratinocytes

Plasma copolymers (PCPs) of allyl alcohol/1,7-octadiene were prepared and characterized using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and contact angle measurements. The use of a hydrocarbon diluent in the monomer feed allowed the deposition of films with controlled concentrations of hydroxyl groups. ToF-SIMS data have shown these PCPs to be rich in unsaturation. Dimeric allyl alcohol species were observed in the ToF-SIMS spectra, which reduced in intensity with the proportion of hydrocarbon diluent in the monomer feed. Contact angle measurements have shown the nondispersive component of surface energy to increase with hydroxyl group concentration, while the dispersive component remained approximately constant. Human keratinocytes were cultured on these PCP surfaces and collagen I. The level of keratinocyte attachment over 24 h was measured. Keratinocyte attachment increased with hydroxyl group concentration (the nondispersive component of surface...

Attachment of human keratinocytes to plasma co-polymers of acrylic acid/octa-1,7-diene and allyl amine/octa-1,7-diene

Plasma co-polymers (PCPs) of acrylic acid/octa-1,7-diene and allyl amine/octa-1,7-diene have been prepared and characterised using X-ray photoelectron spectroscopy (XPS). The use of a hydrocarbon diluent in the monomer feed allowed the deposition of films with controlled concentrations of carboxylic acid and nitrogen-containing functional groups. Human keratinocytes were cultured on these PCP surfaces, tissue culture poly(styrene) (TCPS) and collagen I. The level of keratinocyte attachment over 24 h was measured. PCP surfaces containing low concentrations of carboxylic acid groups (2.3%) were found to promote keratinocyte attachment. The performance of these PCPs was similar to collagen I, a well established substratum for attachment. Nitrogen-containing PCP surfaces were found to promote attachment at higher functional group concentrations, although the attachment did not attain the level achieved on the acid functionalised PCP surfaces.

Comparison of Proliferation and Growth of Human Keratinocytes on Plasma CO-Polymers of Acrylic acid/1,7- Octadiene and Self Assembled Monolayers

AbstractHuman keratinocytes have been cultured on plasma co-polymers (PCPs), self assembled monolayers (SAMs), tissue culture poly(styrene) (TCPS) and collagen I. The degree of keratinocyte attachment was measured over 24 hours and cell proliferation and growth monitored over 7 days using optical microscopy and DNA concentrations. Cell attachment and proliferation and growth on the PCP surfaces were compared with 2 self assembled monolayer (SAM) systems. PCP surfaces containing carboxylic acid functionalities promoted keratinocyte attachment, with optimum attachment levels seen on surfaces containing less than 5% acid groups. The level of attachment on these surfaces was comparable to that seen on collagen I, a preferred substratum for the culturing of keratinocytes. After several days in culture the cells were well attached and proliferative. Keratinocytes attached well to acidterminated SAMs but attached poorly to methyl-terminated SAMs.

Relative rates for plasma homo- and copolymerizations of olefins in a homologous series of fluorinated ethylenes.

It is well known that the rate of plasma polymerization, or deposition rate, of a given monomer depends on various plasma process parameters, e.g., monomer flow rate, pressure, power, frequency (DC, rf or microwave), location of the substrate in the reactor, reactor geometry or configuration, and temperature. In contrast, little work has been done to relate deposition rates to monomer structures for a homologous series of monomers where the rates are obtained under identical plasma process parameters. For the particular series of fluorinated ethylenes (C2HxF4-x; x = 0-4), deposition rates were reported for ethylene (ET), vinyl fluoride, vinylidene fluoride and tetrafluoroethylene (TFE), but for plasma polymerizations carried out under different discharge conditions, e.g., pressure, current density, and electrode temperature. Apparently, relative deposition rates were reported for only two members of that series (ET, x = 4, and TFE, x = 0) for which the plasma polymerizations were conducted under identical conditions. We now present relative deposition rates for both homopolymerizations and copolymerizations of the entire series of fluorinated ethylenes (x = 0-4). Our interest in such rates stems from prior work on the plasma copolymerization of ET and TFE in which it was found that the deposition rates for the plasma copolymers, when plotted versus mol % TFE in the ET/TFE feed stock, followed a concave-downward curve situated above the straight line joining the deposition rates for the plasma homopolymers. This type of plot (observed also for an argon-ET/TFE plasma copolymerization) indicated a positive interaction between ET and TFE such that each monomer apparently "sensitized" the plasma copolymerization of the other. Since the shape of that plot is not altered if mol % TFE is replaced by F/C, the fluorine-to-carbon ratio, this paper aims (1) to show how the relative deposition rates for plasma copolymers drawn from all pairs of monomers in the C2HxF4-x series, as well as the deposition rates for the individual plasma homopolymers, vary with F/C ratios of the monomers or monomer blends, and (2) to see if those rates give rise to a common plot.

A comparative study of cell attachment to self assembled monolayers and plasma polymers

The first comparative study of cell attachment to self-assembled monolayers (SAMs) and plasma-deposited films is reported. Osteoblast-like cells attached extensively to acid-terminated alkyl thiol SAMs and to a plasma co-polymer of acrylic acid and octa-1,7-diene (acid-PCP). However, they attached poorly to methyl-terminated SAMs and a plasma polymer of octa-1,7-diene (OD-PP).

Plasma homo- and copolymerizations of tetrafluoroethylene and chlorotrifluoroethylene

The plasma homo- and copolymerizations of tetrafluoroethylene (TFE) and chlorotrifluoroethylene (CTFE) in a capacitively coupled tubular reactor (TR) with external electrodes were studied by means of microgravimetry and FT-IR and XPS analyses. The deposition rates for CTFE/TFE plasma copolymers, as well as the ratios of IR absorbances at 1180 and 1225 cm−1, and the XPS-derived Cl/C and F/C ratios, varied regularly with mol % CTFE in the feed, all of which results were dependent upon the rf power at which the plasma copolymerizations were conducted. The deposition rates for the plasma homopolymers of TFE (PPTFE) and CTFE (PPTCFE) depended markedly on rf power (W) and monomer molar flow rate (F). The F/C ratio for PPTFE was nearly independent of the composite parameter,W/FM (whereM is the monomer molecular weight), while for PPCTFE, the F/C ratio decreased significantly and the Cl/C ratio increased slightly with increase inW/FM. The percentage of carbon as CF3 was 20–24% in PPTFE and 7–14% in PPCTFE. Plots of deposition rate versusW/FM for PPTFE and PPCTFE obtained in a TR differed considerably from corresponding plots in the literature for the same homopolymers prepared in a glass-cross or bell-jar reactor.

Plasma copolymerization of ethylene and tetrafluoroethylene

AbstractThe plasma copolymerization of ethylene (ET) and tetrafluoroethylene (TFE) was investigated by means of IR and XPS analyses. The deposition rates for plasma ET/TFE copolymers, when plotted versus mol % TFE in the feed gas, gave a concave‐downward curve situated above the straight‐line joining the deposition rates for the respective plasma polymers, PPET and PPTFE, with the maximum rate at ∼ 70‐80 mol % TFE. This result, coupled with the finding that normalized absorbances of the CH and CF IR bands of ET/TFE copolymers had maxima at ∼ 20 and 80 mol % TFE, respectively, indicated a positive interaction between ET and TFE such that each monomer “sensitized” the plasma copolymerization of the other. As analyzed by XPS, CF groups dominated over CF2 and CF3 groups at 5‐70 mol % TFE, but at ≥ 80 mol % TFE, these moieties approached the relative proportions in PPTFE (CF2 &gt; CF3 &gt; CF). The plot of F/C ratio versus mol % TFE was concave‐upward and situated below the hypothetical straight‐line plot representing noninteracting, independent polymerization of ET and TFE, while the % F in the plasma copolymers was linear with mol % TFE. The F1s mean binding energies of the ET/TFE plasma copolymers, which increased monotonically with % F, were consistently higher than those for several commercial polymers of fluorinated olefins at comparable values of % F. This result suggested clustering of CFn moieties in the plasma copolymers or the presence of F atoms in highly fluorinated environments. © 1992 John Wiley &amp; Sons, Inc.

Plasma‐substrate interaction: Effect of volatile oligomers in silicone rubber on plasma polymerization of fluorine‐containing monomers

AbstractThe cause of the conspicous Si content consistently observed on plasma polymers deposited on silicone rubber was investigated in this study. Plasma polymers of tetrafluoroethylene and of hexafluoroethane were deposited on the inside surface of Silastic tubings with and without oligomers by using a semicontinuous plasma polymerization reactor. This tube coating reactor is unique in the sense that the only surface which interacts with the plasma is the substrate surface (i.e., inside wall of tubing) and that plasma polymerization occurs in a very small volume of 3.3‐mm‐I.D. and 2‐cm‐long section of tubing at any given time. These two factors render the reactor a suitable system for the investigation of plasma‐substrate surface interaction. Silastic tubings free of oligomers were prepared by extracting the tubings as received with distilled n‐hexane for 3 h which yielded a 3% weight loss. It was found that the conspicuous Si content noted previously was not occasioned by the migration of oligomers through the plasma polymers but was caused by the redeposition of plasma copolymers formed from a mixture of the feed‐in monomer and the silicon‐containing volatile components evolved from the silicone rubber when exposed to the plasma. The presence of Si‐containing compounds in the plasma evidently interfered with the plasma polymerization of tetrafluoroethylene and hexafluoroethane. Without volatile oligomers (the extracted samples), ESCA analysis indicated that the plasma polymers contained large amounts of CF3, CF2, and CF moieties, just like most typical plasma polymers of these monomers deposited on nonreactive substrates. With the presence of volatile oligomers, the fluorine content decreased drastically and a significant increase of oxygen‐containing and silicon‐containing moieties was observed. The influence of the volatile oligomers in the substrate on the balance between ablation and polymerization in plasma polymerization and its energy input level dependence (manifested by W/FM) were studied as well. The results were also discussed in relation to the bicyclic rapid step‐growth polymerization mechanism.