Analysis of Machinable Structures and Their Wettability of Rotary Ultrasonic Texturing Method

Tailored surface textures at the micro- or nanoscale dimensions are widely used to get required functional performances.Rotary ultrasonic texturing(RUT) technique has been proved to be capable of fabricating periodic micro- and nanostructures. In the present study, diamond tools with geometrically defined cutting edges were designed for fabricating different types of tailored surface textures using the RUT method. Surface generation mechanisms and machinable structures of the RUT process are analyzed and simulated with a 3D-CAD program. Textured surfaces generated by using a triangular pyramid cutting tip are constructed. Different textural patterns from several micrometers to several tens of micrometers with few burrs were successfully fabricated, which proved that tools with a proper two-rake-face design are capable of removing cutting chips efficiently along a sinusoidal cutting locus in the RUT process. Technical applications of the textured surfaces are also discussed. Wetting properties of textured aluminum surfaces were evaluated by combining the test of surface roughness features. The results show that the real surface area of the textured aluminum surfaces almost doubled by comparing with that of a flat surface, and anisotropic wetting properties were obtained due to the obvious directional textural features.

Molecular dynamics simulations on the wet/dry self-latching and electric fields triggered wet/dry transitions between nanosheets:A non-volatile memory nanostructure

We design a nanostructure composing of two nanoscale graphene sheets parallelly immersed in water.Using molecular dynamics simulations,we demonstrate that the wet/dry state between the graphene sheets can be self-latched;moreover,the wet→dry/dry→wet transition takes place when applying an external electric field perpendicular/parallel to the graphene sheets(E;/E;).This structure works like a flash memory device(a non-volatile memory):the stored information(wet and dry states)of the system can be kept spontaneously,and can also be rewritten by external electric fields.On the one hand,when the distance between the two nanosheets is close to a certain distance,the free energy barriers for the transitions dry→wet and wet→dry can be quite large.As a result,the wet and dry states are self-latched.On the other hand,an E;and an E;will respectively increase and decrease the free energy of the water located in-between the two nanosheets.Consequently,the wet→dry and dry→wet transitions are observed.Our results may be useful for designing novel information memory devices.

Superhydrophobic Surfaces Produced by Applying a Self- Assembled Monolayer to Silicon Micro/Nano-Textured Surfaces

A novel way of producing superhydrophobic surfaces by applying a self-assembled monolayer(SAM)to silicon micro/nano-textured surfaces is presented in this paper.The micro/nano-textured surfaces on silicon substrates were generated by the aluminum-induced crystallization(AIC)of amorphous silicon(a-Si)technique.Octadecyltrichlorosilane(OTS)SAMs were then applied to the textured surfaces by dip coating.The topography and wetting properties of the resulting surfaces were characterized using scanning electron microscopy(SEM)and a video-based contact angle measurement system.The results show that by introducing OTS SAMs on the silicon micro/nano-textured surfaces,superhydrophobic surfaces with water contact angles(WCAs)of 155°were obtained,as compared to the WCAs of OTS-modified smooth silicon surfaces of about 112°.Surface topography was found to directly influence the WCA as predicted by the Cassie-Baxter model.

How polar hydroxyl groups affect surface hydrophobicity on model talc surfaces

Based on molecular dynamics simulations,we have studied the wetting behaviors of water on the talc-like surface with different surface polarity by modifying the charge distribution of surface hydroxyl(–OH)groups.With the change of the charge of the hydrogen atom(denoted asδq)in–OH group,the contact angle decreases from 91°to 50°and then remains constant.On the surfaces with the larger charge of hydrogen atoms(δ_(q)≥0.2 e),a water droplet is formed above a water monolayer,which is exactly contacted on the surface.Each water molecule in the monolayer forms one hydrogen bond(H bond)with surface–OH groups,without participating in any H bond with the water molecules within the monolayer or with the water molecules above the monolayer.The polarity of the–OH group also has a great influence on the dynamic behaviors of the interface water,such as residence time,hydrogen bond lifetime and selfdiffusion coefficient.The diffusion of water molecules in the water monolayer near the highly polar surface is greatly suppressed,and the residence time of water molecules in the water monolayer even exceeds 12 ns.