For some twenty years the marine coatings industry has been intrigued by polymer surfaces with low adhesion to other materials, especially to the biological glues used by marine organisms. Polymers with fouling release surfaces have been made from sundry materials, and their resistance to marine fouling in both static and dynamic tests has been evaluated in the world's oceans. Although the polymer surface property most frequently correlated with bioadhesion is its critical surface tension (γ(?)), resistance to fouling is also influenced by other bulk and surface properties of the polymer. This paper reviews the types of bonding associated with polymeric materials used in fouling resistant coatings, describes the removal process in terms of fracture mechanics, and discusses the importance of surface energy, elastic modulus and coating thickness in the release of biofoulants.

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Friction coefficients were measured for bearing materials slid in dry air against sputter-deposited MoS2-coated substrates. Ball versus flat tests were performed over a wide range of initial Hertzian pressures (200–1500 MPa) by varying loads (1–50 N), elastic moduli (70–615 GPa), and ball diameters (1.6–12.7 mm). The friction coefficient μ decreased as load L increased according to μ∝ L(−0.32), in agreement with the Hertzian contact model. Regression analysis of over 600 data points for friction coefficient versus Hertzian pressure (PH), fitted to μ=(S0/PH)+α, gave mean values of the shear strength S0=24.8 MPa±0.5 and α= 0.001±0.001, with S0 in good agreement with values in the literature.

The friction behavior of a diamond-like carbon coating was studied in reciprocating sliding contact at speeds from 0.01 to 5 mm/s, in dry nitrogen. ''Superlow'' friction coefficients of 0.003-0.008 were obtained in continuous sliding at the higher speeds ͑Ͼ1 mm/s͒. However, friction coefficients rose to values typical of diamond-like carbon in dry and ambient air ͑0.01-0.1͒ at lower speeds ͑Ͻ0.5 mm/s͒ as well as in time-delayed, higher speed tests. The rise of the friction coefficients in both speed and time-delay tests was in good quantitative agreement with gas adsorption kinetics predicted by the Elovich equation for adsorption onto carbon. More generally, superlow friction could be sustained, suppressed, and recovered as a function of exposure time, demonstrating that duty cycle cannot be ignored when predicting performance of superlow friction coatings in devices. The past 10 years has seen a steady lowering of the friction coefficient thanks to innovations in applied surface science and coating technology. Friction coefficients below 0.01 have been observed for certain MoS 2 and diamond-like carbon ͑DLC͒ coatings, but only in ultrahigh vacuum. [1][2][3] Coatings with friction coefficients in this range can eliminate the need for liquid lubrication and enable new classes of sliding devices. However, friction coefficient is not a materials parameter; rather, it depends on factors like contact stress, sliding speed, environment, and tribochemical properties of the sliding interface.4-6 For example, it is known that the friction of graphite in vacuum is reduced by exposure to O 2 or H 2 O, 7 while for DLC, exposure to these gases increases friction. 8,9 Moreover, conditions for maintaining low friction coefficients are not very well understood, and what works in one application may be useless in another. Thus, the success of DLC in the hard disk industry as a protective, friction reducing coating, for example, has not been readily translated to microelectromechanical or pointing-andtracking devices, where operating conditions such as speed and environment are vastly different.In this letter we introduce a methodology for assessing the friction behavior of coatings for low speed sliding applications. DLC coatings that give friction coefficients down to 0.001 at atmospheric pressure in dry nitrogen were investigated.10,11 By systematically varying speed and environmental exposure times, superlow friction could be sustained or lost, but always recovered. The friction behavior is explained in terms of gas adsorption. DLC coatings were prepared by low temperature, plasma assisted chemical vapor deposition in a hydrogen and hydrocarbon rich environment.11 Coatings were deposited to 1 m thickness on 6.35 mm diameter sapphire balls, 12.7 mm diameter steel balls, and on H13 steel flats. Friction tests were performed with a reciprocating, ball-on-flat tribometer in a nominally dry nitrogen environment ͑RHр1%, O 2 Ͻ1%͒. 12The coated ball was loaded against the coated flat to 9.8 N ͑0.6-1.1 GPa Hertzian mean pressure͒ and...

Silicone coatings are currently the most effective non-toxic fouling release surfaces. Understanding the mechanisms that contribute to the performance of silicone coatings is necessary to further improve their design. The objective of this study was to examine the effect of coating thickness on basal plate morphology, growth, and critical removal stress of the barnacle Balanus amphitrite. Barnacles were grown on silicone coatings of three thicknesses (0.2, 0.5 and 2 mm). Atypical (''cupped'') basal plate morphology was observed on all surfaces, although there was no relationship between coating thickness and i) the proportion of individuals with the atypical morphology, or ii) the growth rate of individuals. Critical removal stress was inversely proportional to coating thickness. Furthermore, individuals with atypical basal plate morphology had a significantly lower critical removal stress than individuals with the typical (''flat'') morphology. The data demonstrate that coating thickness is a fundamental factor governing removal of barnacles from silicone coatings.