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The surface stress f , a capillary force at solid surfaces, has important implications for the behavior of nanomaterials. Surface stress is known to vary considerably when atoms adsorb on the surface, yet the underlying mechanisms are poorly understood. Our in situ dilatometry study of H adsorption on porous nanocrystalline Pd provides quantitative data for the response of f to changes in the adsorbate coverage. The porous body is immersed in aqueous electrolyte and H adsorption is controlled and measured electrochemically. The surface stress response is quantified by means of the electrocapillary coupling parameter, ς , defined as the derivative of f with respect to the superficial charge density. The results support previous, more indirect, findings for ς . We show that ς is precisely predicted by a model based on the continuum mechanics of superficial layers containing misfitting solute.

The length change in response to changes in the surface stress during scans of the electrode potential was measured for nanoporous platinum samples immersed in aqueous NaF, an electrolyte with weak ion adsorption. The surface stress–charge response may be characterized separately for four different processes, selected by the potential range and by the surface pretreatment: hydrogen adsorption/desorption, oxygen adsorption/desorption (and/or surface oxidation/reduction), and nominally capacitive charging of the Pt surface in two different states, clean and oxide-covered. While each process exhibits a roughly linear response, the magnitude and even the sign of the slope, which determines the surface stress–charge coefficient, ζ, differ. We suggest that the sign of ζ depends on the penetration depth of the excess charge: for strong screening the electronic charge is located outside of the surface, and ζ is negative as found previously for clean metal surfaces. For weaker screening, the wider space charge layer implies a trend for the excess charge to fill bulk-like unoccupied states. These states are here antibonding, giving positive-valued ζ.

We report the preparation of composite foils consisting of two layers, one solid gold and one nanoporous gold. Tip displacements of several millimeters are observed when the foils are immersed in aqueous electrolytes and the electrochemical potential varied. This suggests that nanoporous metals could be used as the active component in actors, and it demonstrates for the first time that changes in the surface stress f of the metal−electrolyte interface can induce a macroscopic strain, orders of magnitude larger than the amplitudes which are reached in conventional cantilever bending experiments used to measure f.

We present a study of the magnetic-field dependence of the small-angle neutron scattering of the nanocrystalline soft magnet Vitroperm (Fe73Si16B7Nb3Cu1), which was treated so as to exhibit a macroscopic magnetic anisotropy. We show how the field dependences of i) the radial average of the scattering cross-section dΣ/dΩ and ii) the variation of dΣ/dΩ as a function of the orientation of the scattering vector can be analysed to supply separately information on the orientation of the net magnetisation of the domains and on the internal spin disorder within the domains. As the applied magnetic field is decreased starting from saturation, we find that two processes occur independently: the formation of a domain structure with the net magnetisation of the domains aligned along the macroscopic easy axis and the increase in magnitude of static, nanometer-scale fluctuations of the spin orientation.

The mechanical response to the electrochemical charging of nanoporous metals with their pore space wetted by electrolyte have been studied in-situ using dilatometry and wide angle x-ray diffractometry techniques. The actuation strain reported in this manuscript is purely elastic and completely reversible. The capacitive double layer charging became more effective near to the potential to zero charge (pzc) and contribute significantly to the variations of surface stress and crystal strain. In a suitable experimental setup, the actuator effect from porous metals can be amplified, where deliberate movements of the actuator parts are desirable with minimum external force, suggesting that metallic foam-like materials with high surface to volume ratio could be used to mimic natural muscles.

We report an experimental study of the variation of surface stress with surface charge density for nanoporous Pt immersed in aqueous solutions of NaF of various concentration. As the concentration is reduced, we find initially an increase in the magnitude of the surface stress-charge coefficient, followed by saturation at a value of -1.9 V. Since specific adsorption is expected to be reduced as the solution becomes more dilute, the results support the notion that changes in the bonding at the metal surface play a decisive role in determining the change in the surface stress during double-layer charging.