Superhydrophobicity of Bionic Alumina Surfaces Fabricated by Hard Anodizing

Bionic alumina samples were fabricated on convex dome type aluminum alloy substrate using hard anodizing technique. The convex domes on the bionic sample were fabricated by compression molding under a compressive stress of 92.5 MPa. The water contact angles of the as-anodized bionic samples were measured using a contact angle meter （JC2000A） with the 3μL water drop at room temperature. The measurement of the wetting property showed that the water contact angle of the unmodi- fied as-anodized bionic alumina samples increases from 90° to 137° with the anodizing time. The increase in water contract angle with anodizing time arises from the gradual formation of hierarchical structure or composite structure. The structure is composed of the micro-scaled alumina columns and pores. The height of columns and the depth of pores depend on the ano- dizing time. The water contact angle increases significantly from 96° to 152° when the samples were modified with self-assembled monolayer of octadecanethiol （ODT）, showing a change in the wettability from hydrophobicity to su- per-hydrophobicity. This improvement in the wetting property chemical modification. is attributed to the decrease in the surface energy caused by the

Microstructures and mechanical properties of extruded Mg-2Sn-xYb(x=0,0.1,0.5 at.%)sheets

Microstructures and mechanical properties of extruded Mg-2Sn-xYb(x=0,0.1,0.5 at.%)sheets were investigated.The grain size of as-cast Mg-2Sn alloy is significantly reduced with increasing Yb concentration.In addition toα-Mg and Mg_(2)Sn phase,some fine Mg_(2)(Sn,Yb)particles are observed in as-cast Mg-2Sn-0.5Yb alloy,but these fine particles are not observed in as-cast Mg-2Sn-0.1Yb alloy due to a high solubility of Yb in Mg matrix.Tensile tests demonstrated that extruded Mg-2Sn-0.5Yb sheet exhibited the highest tensile strength and available elongation to failure at room temperature,while extruded Mg-2Sn-0.1Yb alloy exhibited the highest tensile properties at 100°C and 200°C.The difference in the tensile properties of extruded sheets mainly arises from the different strengthening roles of grain refinement,solid solution strengthening and precipitation strengthening of particles.

Strain-hardening and warm deformation behaviors of extruded Mg-Sn-Yb alloy sheet

Strain-hardening and warm deformation behaviors of extruded Mg-2Sn-0.5Yb alloy(at.%)sheet were investigated in uniaxial tensile test at temperatures of 25-250 ℃ and strain rates of 1×10^(−3) s^(−1)-0.1 s^(−1).The data fit with the Kocks-Mecking type plots were used to show different stages of strain hardening.Besides III-stage and IV-stage,the absence of the II-stage strain hardening at room temperature should be related to the sufficient dynamic recrystallization during extrusion.The decrease of strain hardening ability of the alloy after yielding was attributed to the reduction of dislocation density with increasing testing temperature.Strain rate sensitivity(SRS)was significantly enhanced with increasing temperature,and the corresponding m-value was calculated as 0.07-0.12,which indicated that the deformation mechanism was dominated by the climb-controlled dislocation creep at 200 ℃.Furthermore,the grain boundary sliding(GBS)was activated at 250 ℃,which contributed to the higher SRS.The activation energy was calculated as 213.67 kJ mol^(−1),which was higher than that of lattice diffusion or grain boundary self-diffusion.In addition,the alloy exhibited a quasi superplasticity at 250 ℃ with a strain rate of 1×10^(−3) s^(−1),which was mainly related to the fine microstructure and the presence of the Mg2Sn and Mg2(Sn,Yb)particles.

A Biomimetic Tooth Replicate That Is Hard,Damage-Tolerant,and Self-Healable

Hard materials typically lack the mechanism of energy dissipation and cannot self-heal.Nature addresses this challenge by creating multiscale interfaces between high-contrast materials,namely minerals and biopolymers.Inspired by the enamel-dentin junction in nature,an enamel-like crown consisting ofβFeOOH nanocolumns is interdigitated with a flexible self-healing layer.The iron oxide top layer has exceptionally high modulus and hardness,which is more resistant to cyclic deformation than the bottom layer.The latter however provides an additional pathway for viscous and plastic energy dissipation and enables self-healing by allowing upward polymer diffusion to seal the damage.Picture-frame crack patterns were observed under large loading conditions using microindentation,which localizes the damage at the indentation site.The bending properties can be optimized by varying the thickness of the bottom layer,and the crack induced by bending can be effectively captured at the interface without any delamination.The biomimetic tooth replicate is highly adhesive to a ceramic surface and shows an obvious inhibition effect against Streptococcus mutans,a significant contributor to tooth decay.Combined with ultralow thermal diffusivity,this has great potential as dental material.Learning from nature,our work thus provides a powerful pathway to broadening the scope of synthetic materials for dental replicates.

Role of Multi-scale Hierarchical Structures in Regulating Wetting State and Wetting Properties of Structured Surfaces

Amplifying the intrinsic wettability of substrate material by changing the solid/liquid contact area is considered to be the main mechanism for controlling the wettability of rough or structured surfaces.Through theoretical analysis and experimental exploration,we have found that in addition to this wettability structure amplification effect,the surface structure also simultaneously controls surface wettability by regulating the wetting state via changing the threshold Young angles of the Cassie-Baxter and Wenzel wetting regions.This wetting state regulation effect provides us with an alternative strategy to overcome the inherent limitation in surface chemistry by tailoring surface structure.The wetting state regulation effect created by multi-scale hierarchical structures is quite significant and plays is a crucial role in promoting the superhydrophobicity,superhydrophilicity and the transition between these two extreme wetting properties,as well as stabilizing the Cassie-Baxter superhydrophobic state on the fabricated lotus-like hierarchically structured Cu surface and the natural lotus leaf.