Measurements of the forces in water between neutral hydrophobic surfaces prepared by covalent modification of glass are presented. The surfaces are stable under a variety of conditions including high temperature, high salt concentrations and with added ethanol. The forces between these surfaces have been studied under all of these different conditions. In water the force is attractive at very large surface separations, and discontinuities or steps are present in the force curves. It is suggested that the steps at the onset of the force are due to the bridging of submicroscopic bubbles or cavities between the surfaces and that it is their consequent growth with decreasing separation that causes the long-range attraction between hydrophobic surfaces. Electrolyte has a negligible effect on the range and strength of the measured forces, except at very high salt concentrations where the strength of the attractive forces and the adhesion between the surfaces increases slightly. The addition of ethanol reduces both the strength of the long range forces and the adhesion between the surfaces. On the basis of the comparison between these results and earlier measurements, it appears that the attraction does not obey the Derjaguin approximation. Forces were also measured in the presence of a microscopic vapor cavity created by first bringing the surfaces into contact. IntroductionDirect measurements of the interactions between macroscopic hydrophobic surfaces have revealed the presence of strong attractions of much longer range than the classical van der Waals force.'-14 The force is in some cases measurable at separations greater than 100 nm. The existence of an interaction at such distances challenges fundamental notions of liquid structure and surface forces, and despite considerable theoretical effort the molecular origin of this long-range attraction remains controversial.A number of explanations of the range and the strength of the interaction have been proposed. It has been shown that the force might originate from a perturbation in the ordering of water propagating through the liquid between two hydrophobic surfaces,lS a hypothesis that is difficult to test by experimental or

Highly active and low-cost electrocatalysts for water oxidation are required due to the demands on sustainable solar fuels; however, developing highly efficient catalysts to meet industrial requirements remains a challenge. Herein, we report a monolayer of nickel–vanadium-layered double hydroxide that shows a current density of 27 mA cm−2 (57 mA cm−2 after ohmic-drop correction) at an overpotential of 350 mV for water oxidation. Such performance is comparable to those of the best-performing nickel–iron-layered double hydroxides for water oxidation in alkaline media. Mechanistic studies indicate that the nickel–vanadium-layered double hydroxides can provide high intrinsic catalytic activity, mainly due to enhanced conductivity, facile electron transfer and abundant active sites. This work may expand the scope of cost-effective electrocatalysts for water splitting.

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The interaction in water of neutral hydrocarbon and fluorocarbon surfaces, prepared by Langmuir-Blodgett deposition of surfactant monolayers, has been investigated. The attraction between these hydrophobic surfaces can be measured at separations of 70 to 90 nanometers and thus is of considerably greater range than previously found. Spontaneous cavitation occurred as soon as the fluorocarbon surfaces were brought into contact but occurred between the hydrocarbon surfaces only after separation from contact. The very long range forces measured are a consequence of the metastability of water films between macroscopic hydrophobic surfaces. Thus the hydrophobic interaction between macroscopic surfaces may not be related to water structure in the same way that the hydrophobic effect between nonpolar molecules is related to water structure.

The effect of inert salt concentration on polyelectrolyte adsorption from aqueous solutions onto oppositely charged surfaces and the interactions between such surfaces were studied experimentally using a surface force technique and compared to theoretical predictions from Monte Carlo simulations. At a polyelectrolyte concentration of 10 ppm and a low inert salt concentration (10-4 M), the polyelectrolytes adsorb in a flat conformation and the force acting between the surfaces is close to zero down to a separation of 10-1 5 nm, where the surfaces jump inward. The attractive force observed at separations below 10 nm is stronger than the expected van der Waals force. The magnitude and range of the attraction agree with forces obtained from Monte Carlo simulation, and we interpret the attraction as being due to bridging polyelectrolytes. When the salt concentration is increased, additional polyelectrolyte adsorption takes place. This again gives rise to a repulsive force, which is significantly larger than what is observed between bare surfaces. The extra repulsion is due to adsorbed polyelectrolytes stretching out from the surfaces and is also predicted from simulations.