Polysulfone and polyacrylate-based zwitterionic coatings for the prevention and easy removal of marine biofouling.

A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1-2 µm) relative to commercial coating standards (>200 µm).

Spontaneous aryldiazonium film formation on 440C stainless steel in nonaqueous environments.

The ability of three aryldiazonium salts to spontaneously assemble onto the surface of type 440C stainless steel is investigated in acetonitrile (ACN) and the model hydraulic fluids tributyl phosphate (TBP) and hexamethyldisiloxane (HMDS). Competition between native oxide formation and organic film growth at different diazonium salt concentrations is monitored by electrochemical impedance spectroscopy. At 1 mM diazonium salt, 70% of total assembly is complete within 10 min, though total surface coverage by organics is limited to ≈0.15 monolayers. Adding HCl to the electrolyte renders native oxide formation unfavorable, yet the diazonium molecules are still unable to the increase surface coverage over 1 M-10 µM HCl in solution. X-ray photoelectron spectroscopy confirms preferential bonding of organic molecules to iron over chromium, while secondary ion mass spectroscopy reveals the ability of these films to self-heal when mechanically removed or damaged. Aging the diazonium salts in these nonaqueous environments demonstrates that up to 90% of the original diazonium salt concentration remains after 21 days at room temperature, while increasing the temperature beyond 50 °C results in complete decomposition within 24 h, regardless of solvent-salt combination. It is concluded that the investigated diazonium molecules will not spontaneously form a continuous monolayer on 440C stainless steel immersed in ACN, TBP, or HMDS.

Identification of Multiple Diffusion Rates in Mixed Solvent Anion Exchange Membranes Using High Resolution MAS NMR.

High resolution magic angle spinning (HRMAS) 1H NMR in combination with 2D exchange NOESY and pulsed field gradient (PFG) NMR diffusion experiments have been used to characterize 1 N methanol swollen polymer anion exchange membranes (AEM) presently being developed for alkaline fuel cells. Standard static 1H NMR experiments on these materials have proven unsuccessful due to severe signal broadening. New experimental methods for increased resolution are needed to determine distinct solvent environments and transport properties. Using HRMAS NMR, resonances from water and methanol in both a free (bulk-like) environment and membrane-associated environment within the AEM were observed. 1H HRMAS PFG NMR experiments identified different molecular diffusion environments in the solvent, while 1H 2D NOESY exchange NMR experiments confirmed spatial contacts between membrane-associated species and the membrane. These results demonstrate that 1H HRMAS is an ideal technique for the characterization of individual environments and diffusion rates in polymer membranes with mixed solvent systems.

New multi-electron high capacity anodes based on nanoparticle vanadium phosphides.

Nanoscale vanadium phosphides can serve as new high capacity anodes in alkaline aqueous electrolytes. Competing corrosion reaction(s) are mitigated with the novel use of an anion exchange membrane providing for capacities as high as 2800 mAh g(-1) @ 100 mA g(-1) discharge rate.