SiO
x
-like coatings were deposited on glass slides from a hexamethylsiloxane precursor by plasma-assisted CVD (PACVD). Surface energies (23.1-45.7 mJ m
−1
) were correlated with the degree of ...surface oxidation and hydrocarbon contents. Tapping mode AFM revealed a range of surface topologies with Ra values 1.55-3.16 nm and RMS roughness 1.96-4.11 nm. Settlement of spores of the green alga Ulva was significantly less, and detachment under shear significantly more on the lowest surface energy coatings. Removal of young plants (sporelings) of Ulva under shear was positively correlated with reducing the surface energy of the coatings. The most hydrophobic coatings also showed good performance against a freshwater bacterium, Pseudomonas fluorescens, significantly reducing initial attachment and biofilm formation, and reducing the adhesion strength of attached bacterial cells under shear. Taken together the results indicate potential for further investigation of these coatings for applications such as heat exchangers and optical instruments.
Summary
In order to study the haemocompatibility of metal and carbon coatings, fibrinogen adsorption and platelet adhesion to various coatings have been investigated.Two metallic coatings titanium ...and zirconium, and two carbon coatings isotropic diamondlike and isotropic graphite-like coatings, were prepared by plasma vapour deposition onto stainless steel substrate. It has been shown that the adsorption of fibrinogen to metal and carbon coatings and its post-adsorptive transition are dependent on both the material properties and the fibrinogen environment. The adsorption of fibrinogen from human plasma on titanium and zirconium coatings is similar to that on uncoated stainless steel surface. Both carbon coatings adsorb much greater amount of fibrinogen from plasma, and fibrinogen retention by carbon surfaces is also greater than by metal surfaces. Increased numbers of adhered platelets have been found on both carbon coatings in comparison to the metal materials, although this does not correlate with the amount of adsorbed fibrinogen.
Recent work using an improved design of an unbalanced magnetron in a four-magnetron closed-field arrangement has resulted in exceptionally high ion current densities at the substrates during both ion ...cleaning and deposition. The ion current at the electrically biased substrate is increased by a factor of close to 100 as compared to balanced magnetrons of the same polarity. The absolute ion current is dependent on a number of factors which are discussed, the most important being the power applied to the magnetrons. The relationship between substrate bias and ion current is presented. It is found that it is possible to achieve very high ion currents at bias voltages as low as −50
V. The effect of the substrate bias voltage and the substrate ion current on the coating structure have been studied, and it is found that the optimum conditions for the deposition of dense coherent coatings with low internal stresses are a high ion current at a low bias voltage. These conditions are readily achieved using the closed-field unbalanced magnetron technique. It is shown that coating structure is almost independent of deposition rate, which is extremely important for the deposition of coatings with excellent structures at low temperatures. Ion cleaning prior to deposition is carried out with the magnetrons operating at low power. This allows the plasma discharge to strike and be maintained at low argon pressures, thus avoiding contamination from the chamber walls, etc. The enhancement of the ion current under these conditions is similar to that achieved during deposition, i.e. around 100×, and so the efficiency of ion cleaning is considerably enhanced, producing a “clean” surface which results in excellent adhesion. Scratch adhesion testing has been used to compare the critical loads for coatings deposited with different cleaning conditions and the excellent adhesion achievable is demonstrated.
Many current surface technologies apply coatings at temperatures which are too high for materials such as polymers, aluminium alloys and constructional steels. In the present work, recent advances ...are discussed whereby these materials can be surface-hardened at lower temperatures to improve the wear resistance without loss of their mechanical properties. The techniques presented are metal ion implantation where hardening is found well beyond the zone where the implanted material resides, pulsed intense beam technology where hardening is achieved by a ultra-rapid melt and resolidification of the surface leading to a very fine grain size, and low-temperature deposition of TiN accompanied by ion bombardment which produces dense, wear-resistant coatings at temperatures in the order of 160
°C.
Si- and N-doped diamond-like carbon (DLC) coatings with various Si and N contents were deposited on glass slides using magnetron sputter ion-plating and plasma-enhanced chemical vapour deposition. ...Surface energy analysis of the DLC coatings revealed that with increasing Si content, the electron acceptor
value decreased while the electron donor
value increased. The antifouling property of DLC coatings was evaluated with the bacterium, Pseudomonas fluorescens, which is one of the most common microorganisms forming biofilms on the surface of heat exchangers in cooling water systems. P. fluorescens had a high value of the
component (69.78 mN m
−1
) and a low value of the
component (5.97 mN m
−1
), and would be negatively charged with the zeta potential of −16.1 mV. The experimental results showed that bacterial removal by a standardised washing procedure increased significantly with increasing electron donor
values and with decreasing electron acceptor
values of DLC coatings. The incorporation of 2%N into the Si-doped DLC coatings further significantly reduced bacterial attachment and significantly increased ease of removal. The best Si-N-doped DLC coatings reduced bacterial attachment by 58% and increased removal by 41%, compared with a silicone coating, Silastic® T2. Bacterial adhesion strength on the DLC coatings is explained in terms of thermodynamic work of adhesion.
Plasma-assisted chemical vapour deposition (PACVD) siloxane coatings from a mixture of hexamethyldisiloxane (HMDSO) and O
2, and hybrid coatings deposited by simultaneous sputtering of silicon and ...plasma polymerisation of HMDSO
+
O
2 were prepared on glass and steel substrates. The effect of the addition of sputtered silicon was investigated for coatings with different HMDSO/O
2 ratios. The microstructure and composition of coatings were affected by the coating parameters used. Silicon content was roughly the same for all coatings; carbon content decreased while oxygen content and surface energy increased with decreasing HMDSO/O
2 ratio in hybrid coatings. Hardness and modulus were higher for hybrid coatings and increased with decreasing HMDSO/O
2 ratio. Hybrid coatings showed much better scratch and wear resistance than PACVD coatings. All coatings showed good fouling-release performance with the freshwater bacterium
Pseudomonas fluorescens.
A range of SiO
x
-like coatings was deposited on glass slides from a hexamethylsiloxane precursor by plasma-assisted CVD. The effect of varying deposition parameters, specifically ion cleaning time ...and HMDSO/O
2 ratios, on the coating properties and antifouling performance was investigated. At low HMDSO/O
2 ratios, the resulting coatings were close to SiO
2. Carbon content in the bulk of the coatings increased with increasing HMDSO/O
2 ratio. Coatings deposited at high HMDSO/O
2 ratios and with the longest cleaning time (30
min), elevated the relative carbon content to 25 atomic %. Surface energies (22–43
mJ/m) were correlated with the degree of surface oxidation and hydrocarbon content. With the exception of the most polar coatings the apolar component of the surface energy (
γ
LW) was the dominant component. In the most hydrophilic coatings, the Lewis base component of the surface energy (
γ
−) was dominant. Significantly improved antifouling performance was detected with the most reduced coatings deposited using the extended ion cleaning times. For both, the removal of sporelings of the marine green alga,
Ulva
linza and the initial adhesion of the freshwater bacterium,
Pseudomonas fluorescens, there was a strong, positive correlation between strength of attachment and ion cleaning time. Increased ion cleaning time will elevate the deposition temperature, increasing decomposition rates and thus the crosslinking of the polymer. Increased cross-linking may render these coatings less permeable to penetration and mechanical interlocking by the adhesive polymers used by these organisms, thus reducing their adhesion. Films with improved biological performance have potential for use as coatings in the control of biofouling in applications such as heat exchangers, where thin films are important for effective thermal transfer, or optical windows where transparency is important.
The deployment of a vascular stent during angioplasty has greatly reduced the risks of restenosis. However, the presence of the device still induces a host response as well as a mechanical action on ...the blood vessel wall and an alteration of the haemodynamics. Platelet and inflammatory cells can adhere on the stent surface and be activated to produce biochemical signals able to stimulate an excessive proliferation of the smooth muscle cells with the consequent obstruction of the vessel lumen. For these reasons, the host response to two of the materials used in stent manufacture, stainless steel and diamond-like carbon, was investigated in vitro. The data showed that stainless steel induced a higher level of host response both in terms of platelet aggregation and macrophage activation. However, the spreading of inflammatory cells was more accentuated on diamond-like carbon. The inflammatory cells produced levels of platelet-derived growth factor, a key signal in smooth muscle cell proliferation, similar to stainless steel thus suggesting that carbon coatings may not be able to prevent restenosis.
Nano-structured superhard coatings represent the state-of-the-art in the rapidly increasing worldwide market for protective coatings. In this study, the combination of nano-composite and ...nano-multilayered structures into the same coating was attempted. Nano-multilayered coatings of TiN/TiSiN and CrN/CrSiN were deposited on tool steel substrates by closed-magnetic-field unbalanced DC magnetron sputter ion plating. The coating structures were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Mechanical characterizations were performed including nano-hardness measurement, progressively-increasing-load scratch test, and wear test. TiN/TiSiN coatings have a nano-hardness of 40.2 GPa, whereas CrN/CrSiN coatings have a hardness of 30.9 GPa. TiN/TiSiN coatings also showed a higher critical failure force and scratch fracture toughness as well as better wear resistance and lower acoustic emission signal, indicating less total damage to the coatings.
