Stallard, Charlie P.
Stallard, Charlie P.
Stallard, Charlie P.
Now showing 1 - 7 of 7
- PublicationThree Dimensional Coupled Fluid-Droplet Model For Atmospheric Pressure PlasmasA three-dimensional coupled fluid-droplet model is developed specifically to characterize the significance of droplet-plasma interaction at atmospheric pressure. The liquid droplet introduces a perturbation in atmospheric pressure plasma (APP) and under many conditions, the behavior of this perturbation is not clear during transport in PlasmaStream system. In this study, we identify the importance of ionization mechanism in two-phase flow. The affect and spatial expansion of vaporization in discharge plasma depend on the flow rate of liquid precursors. Penning ionization is recognized as the leading process along the pulse of evaporating droplets as compared to other ionization processes that explain the relevance of small nitrogen impurities in an APP. The influence of different precursors, such as Hexamethyldisiloxane, Tetraethyl orthosilicate and water is described by contrasting the implication of the evaporation process along the pulse of droplets in the APP. Finally, we validate the numerical simulation by comparison with the experimental observations of droplet size distributions using a laser diffraction particle size analysis technique as a part of atmospheric pressure plasma jet deposition system.
- PublicationDeposition of nano and micron thick aligned fiber plasma polymerised coatings using an atmospheric plasma jet techniqueThis paper reports on the deposition of siloxane coatings exhibiting ‘aligned’ and ‘non-aligned’ fibrous structures using an atmospheric plasma jet system called PlasmaStreamTM. The coatings were deposited from both liquid HMDSO and TCFS (tetramethyl cyclotetrasiloxane / fluorosiloxane) precursors. These precursors were nebulized into a helium / nitrogen plasma and the coatings were deposited onto silicon wafer substrates. By controlling the deposition conditions superhydrophobic coatings exhibiting a needle-like coating morphology was obtained from both precursors. Initial fibre lengths were in the nm range but after longer deposition time’s coatings with micron long fibre lengths were obtained. In the case of the HMDSO precursor individual aligned fibres with diameters of up to 300 nm and lengths of up to 12 μm were observed. The TCFS coatings were structurally different as they exhibited a non-aligned, more densely packed, fibrous structures. For the same deposition time as used with HMDSO, the TCFS coatings exhibited fibre lengths of up to 10 microns. Coating morphology, water contact angle and functional chemistry were examined using optical profilometry, contact angle and FTIR techniques respectively. The micron thick fibrous coatings both exhibited superhydrophobic properties with contact angles of over 150°.
- PublicationInfluence of coating properties on the adhesion of proteins to atmospheric plasma modified surfacesProtein adhesion is of key importance for the biocompatibility of medical devices. This study investigates the adsorption of protein, bovine serum albumin (BSA), onto both uncoated silicon wafers and nanometre thick fluorosiloxane coated wafers. A plasma polymerised coating was deposited from a mixture of tetramethylcyclotetrasiloxane (TC) and perfluorooctyltriethoxysilane (FS) (1:1 by vol. ratio). The liquid precursor mixture was nebulised into an atmospheric plasma jet formed using the PlasmaStreamTM system. The adsorption of protein on the plasma polymerised coatings was evaluated under dynamic flow conditions using a spectroscopic ellipsometry technique. The rate of protein adsorption onto coated and uncoated silicon wafer substrates was monitored over time after the BSA solution was introduced into a flow cell. These measurements indicated the adsorption of a 2 nm thick BSA protein layer on the uncoated silicon wafers. The ellipsometry thickness measurements of adsorbed protein on silicon wafer were confirmed using quartz crystal microbalance measurements (QCM). The BSA adsorption studies were then repeated with a fluorosiloxane coating. These coatings exhibited a highly textured surface morphology with low surface energy and a high water contact angle of 156 . The ellipsometry flow cell tests with BSA indicated almost no adsorption of protein onto the superhydrophobic fluorosiloxane coating. This study demonstrated the ability of ellipsometry to measure protein adsorption under dynamic flow 2 conditions and the influence of surface properties on protein adsorption.
- PublicationEvaluation of Protein Adsorption on Atmospheric Plasma Deposited Coatings Exhibiting Superhydrophilic to Superhydrophobic PropertiesProtein adsorption is one of the key parameters influencing the biocompatibility of medical device materials. This study investigates serum protein adsorption and bacterial attachment on polymer coatings deposited using an atmospheric pressure plasma jet system. The adsorption of bovine serum albumin and bovine fibrinogen (Fg) onto siloxane and fluorinated siloxane elastomeric coatings that exhibit water contact angles (θ) ranging from superhydrophilic (θ < 5°) to superhydrophobic (θ > 150°) were investigated. Protein interactions were evaluated in situ under dynamic flow conditions by spectroscopic ellipsometry. Superhydrophilic coatings showed lower levels of protein adsorption when compared with hydrophobic siloxane coatings, where preferential adsorption was shown to occur. Reduced levels of protein adsorption were also observed on fluorinated siloxane copolymer coatings exhibiting hydrophobic wetting behaviour. The lower levels of protein adsorption observed on these surfaces indicated that the presence of fluorocarbon groups have the effect of reducing surface affinity for protein attachment. Analysis of superhydrophobic siloxane and fluorosiloxane surfaces showed minimal indication of protein adsorption. This was confirmed by bacterial attachment studies using a Staphylococcus aureus strain known to bind specifically to Fg, which showed almost no attachment to the superhydrophobic coating after protein adsorption experiments. These results showed the superhydrophobic surfaces to exhibit antimicrobial properties and significantly reduce protein adsorption.
Scopus© Citations 128 388
- PublicationA comparison between gas and atomised liquid precursor states in the deposition of functional coatings by pin corona plasmaThis work directly compares vapour and liquid aerosol states for the deposition of perfluorocarbon coatings using an atmospheric pressure, non-thermal equilibrium plasma jet system. The objective of the study is to evaluate how the physical state of the precursor (gas or liquid), influences the fragmentation of the monomer molecules in the plasma and the subsequent coating properties. Specifically the effect of gas or liquid aerosol precursor feed on the ability to achieve a soft plasma polymerisation (SPP) is assessed with a view to producing a coating that exhibits minimal fragmentation, while being well crosslinked. The precursor (Perfluoro–1–Decene) was introduced into a helium plasma and coatings deposited at rates of up to 50 nm/min. The deposited coatings were examined using XPS, FTIR, contact angle and ellipsometric measurements. These indicated that a controlled polymerization reaction through the vinyl group of the monomer had taken place in the case of the gas deposited samples with only minor fragmentation of the functional perfluoro chain. Furthermore, a high level of cross-linking was achieved and the perfluorocarbon coatings were stable to a toluene wash. In contrast, while 2 coatings deposited using the liquid deposition technique showed good retention of monomer molecular structure, they exhibited poor stability when immersed in toluene. This is attributed to lower levels of cross-linking of the liquid precursor in the plasma, compared with coatings deposited using the gaseous precursor technique.
363Scopus© Citations 19
- PublicationCan attenuated total internal reflection-fourier transform infrared be used to understand the interaction between polymers and water? A hyperspectral imaging studyThis study investigates the potential use of attenuated total internal reflection-Fourier transform infrared (ATR-FT-IR) imaging, a hyperspectral imaging modality, to investigate molecular level trends in the interaction of water with polymeric surfaces of varying hydrophobicity. The hydrophobicity of two categories of polymeric biomaterials is characterised using contact angle (CA) measurements and their relationship with the band area of the OH stretching v S vibration of water over time is presented. This is supported with correlations between CA data and single wavenum-ber intensity values (univariate analysis). Multivariate analysis of the spectra captured at the OH stretch for all polymers is carried out using principal component analysis to study the spatial variation in the interaction between the polymeric surfaces and water. Finally, a comparison between the univariate and multivariate strategies is presented to understand the interaction between polymeric biomaterials and water.
170Scopus© Citations 6
- PublicationFabrication of nano-structured TiO2 coatings using a microblast deposition techniqueMicron thick titanium dioxide (TiO2) coatings exhibiting a nano-structured, anatase, meso-porous structure were successfully deposited across a range of polymer, conductive glass and metallic substrates at low velocities using a microblasting technique. This process was conducted at atmospheric pressure using compressed air as the carrier gas and commercially available agglomerated nano particles of TiO2 as the feedstock. An examination of the effect of impact kinetics on the agglomerated powder before and after deposition was undertaken. A further examination of the coating microstructure along with photocurrent density measurements before and after thermal treatments was explored. Owing to the low temperature and velocity of the powder during deposition no change in phase of the powder or damage to the substrate was observed. The resulting TiO2 coatings exhibited relatively good adhesion on both titanium and FTO coated glass substrates with coating thickness of approximately 1.5 μm. Photo-catalytic performance was measured under solar simulator illumination using a photo-electrochemical cell (PEC) with a 5-fold increase in performance observed after thermal treatment of the TiO2 coated substrates. Microblasting was demonstrated to be a rapid and cost effective method for the deposition of nano-structured, photo-catalytic, anatase TiO2 coatings.
Scopus© Citations 10 1623