Surface microstructures of solids play a significant role in producing superhydrophobic surfaces. In the present paper, the Cassie-Baxter and Wenzel models on a rough substrate are examined from the viewpoints of geometry and energy. The result shows that if the air beneath a droplet on a sinusoidal substrate is open to the atmosphere, the superhydrophobic state can exist only when the substrate is hydrophobic, and that the geometric parameters of the microstructure have a great influence on the wetting behavior. Two mechanisms that may lead to a superhydrophobic property from a hydrophilic substrate are addressed. Firstly, for closed or airproof microstructures (e.g. honeycomb structures), a negative Laplace pressure difference caused by the trapped air under the drop can keep the balance of the liquid/vapor interface. Secondly, some special topologies of surface structures satisfying a certain geometric condition may also lead to the formation of a Cassie-Baxter state even if the microstructures are open to the air. Therefore, some surface morphologies may be designed to obtain superhydrophobic properties on hydrophilic surfaces. The present study is also helpful to understand some superhydrophobic phenomena observed in experiments and in nature.

A relation on electric field dependent surface stress, or alternatively surface piezoelectricity, is proposed in this paper. Based on such relation, a piezoelectric ring under prescribed potential has been studied and the results show that the surface piezoelectricity may play an important role in the electromechanical behavior of piezoelectric nanostructures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Mechanical behaviour analysis plays an important role in the design of micro/nano-electromechanical system (MEMS/NEMS) devices for reliability. In this paper, the size-dependent mechanical properties of nanostructures are numerically studied with the finite element method (FEM) by developing a kind of surface element to take into account the surface elastic effect. This method is then applied to the investigation of the interaction between two pressurized nanovoids and the effective moduli of two-dimensional nanoporous material. The numerical results indicate that surface elasticity can significantly alter the nature of interaction forms and the effective moduli by inducing a strong size dependence in conventional results.

Coupled magnetic–mechanical–electric effects in a composite with ferromagnetic rare-earth–iron alloys (e.g., Tb1−xDyxFe2) filled in ferroelectric polymers [e.g, poly(vinylidene-fluoride–trifluoroethylene) copolymer] are studied by using the Green’s function technique. Numerical results suggest a possible giant linear magnetoelectric effect in the ferroic polymer–matrix composite, which is markedly larger than that in the best-known magnetoelectric materials. In addition, the mechanically flexible composite exhibits large magnetostriction. The present results may stimulate further interest in the area of magnetoelectric materials for technological applications.

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