微结构表面润湿模式转换的实验研究

采用等离子体刻蚀技术及表面硅烷化处理制备了一组硅基方柱阵列样品,测量了其表面与水的表观接触角,简要分析了表面微结构几何参数对润湿模式转换的影响,探讨了方柱阵列微结构表面发生润湿模式转换的原因.结果表明,微结构表面润湿模式转换受微结构几何参数的影响,原因是微结构几何参数的改变会引起表面上的液滴能量的变化,最终导致液滴的润湿状态发生变化.     

Neurite outgrowth on microstructured surfaces functionalized by a neural adhesion protein

Designed networks of neurons are potentially very useful to investigate neural activities. Using photolithography microgrooves suited in size for single neurons have been produced on glass chips. Two conducting gold lanes ending in each microgroove allow extracelluar stimulation of the neurons and recording of their activity. A cell adhesive surface was created by functionalization of glass with the adhesion peptide RGDC. In addition, in order to optimize the contact of the neuronal cell membrane to the electrode surface axonin-1, a specific neural adhesion protein was used. A recombinant form of axonin-1 was produced and immobilized in a correct orientation on protected gold surfaces through a C-terminal cysteine residue. Neurite outgrowth of neurons cultured on chips derivatized with RGDC or axonin-1 were compared. The developed materials and methods represent a first step towards establishing designed functionalized glass surfaces for neurophysiological investigations.     

Physical mechanism of the wetting of solid surfaces

This article examines physical principles in the theory of wetting. Wetting angles are calculated by using isotherms of the disjoining pressure of wetting liquid films on solid substrates.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 795–802, November, 1987.     

Spreading characteristics of droplets impact on microstructured surfaces with gradient wettability

Journal of Materials Science - Manipulating droplet motion using gradient wettability surfaces has attracted much attention in recent years. In this paper, four kinds of microstructured surfaces...     

Proliferation of osteoblasts and fibroblasts on model surfaces of varying roughness and surface chemistry

Physical and chemical properties of the surfaces of implants are of considerable interest for dental and orthopedic applications. We used self-assembled monolayers (SAMs) terminated by various functional chemical groups to study the effect of surface chemistry on cell behavior. Cell morphology and proliferation on silicon wafers of various roughnesses and topographies created by chemical etching in caustic solution and by corundum sandblasting were analyzed as well. Water contact angle data indicated that oxidized wafer surfaces displayed high hydrophilicity, modification with poly(ethylene glycol) (PEG) created a hydrophilic surface, and an amino group (NH₂) led to a moderately wettable surface. A hydrophobic surface was formed by hydrocarbon chains terminated by CH₃, but this hydrophobicity was even further increased by a fluorocarbon (CF₃) group. Cell proliferation on these surfaces was different depending primarily on the chemistry of the terminating groups rather than on wettability. Cell proliferation on CH₃ was as high as on NH₂ and hydrophilic oxidized surfaces, but significantly lower on CF₃. Precoating of silicon wafers with cell culture serum had no significant influence on cell proliferation. Scanning electron microscopy indicated a very weak initial cell-surface contact on CF₃. The cell number of osteoblasts was significantly lower on sandblasted surfaces compared with other rough surfaces but no differences were detected with 3T3 mouse fibroblasts. The different surface roughnesses and topographies were recognized by MG-63 osteoblasts. The cells spread well on smooth surfaces but appeared smaller on a rough and unique pyramid-shaped surface and on a rough sandblasted surface.     

Control of wetting on Ti-based bulk metallic glass surfaces by a hydrothermal method

The surfaces of the Ti-based bulk metallic glasses (Ti₅₀Ni₂₀Cu₂₅Sn₅) were modified by a hydrothermal method using sodium hydroxide (NaOH) solution, and the surface wettability was investigated. No reflections were observed in the XRD patterns of the NaOH-treated samples even though there was a clear change of the color, indicating formation of amorphous oxide phases. The Raman spectra showed peaks attributed to sodium titanate compounds (Na–O–Ti) and titanium oxide. Some of the samples were observed to have a very rough surface microstructure such as a “house-of-cards” or leaf-like structure. The water contact angle of the treated samples decreased with increasing treatment temperature and time. These results indicate that the wettability of the sample surface was able to be controlled from hydrophobic to hydrophilic by changing the conditions of the hydrothermal treatment.     

飞秒激光不锈钢表面陷光微结构的制备与性能研究

利用飞秒激光在高真空环境下,在316L不锈钢表面两次交叉扫描制备了周期性微纳结构,并研究了微纳结构对波长范围200~900nm的光波的吸收增强能力。样品表面微结构形貌与成分采用扫描电子显微镜(SEM)和X射线衍射仪测试。第1次扫描采用高能流激光,获得了微米级锥状钉结构,表面覆盖了典型的激光诱导周期性表面结构(LIPSS)。然后将样品旋转90°,采用能流为0.02J/cm2的激光进行第2次扫描,路径与第1次扫描相交。第1次扫描的结构中的LIPSS被第2次低能流激光打断纳米颗粒,从而与锥状钉结构结合形成双尺度微结构。反射率测试结果表明,这种双尺度微结构表面的平均反射率约为2.28%,为光滑表面平均反射率的3.42%。结合XRD分析结果,不锈钢表面获得强陷光性能主要归因于飞秒激光制备的微结构。     

Analytical modeling of wetting dependence on surface nanotopography

An analytical model was developed to describe the mechanism of wetting dependence on surface nanotopography. This model relates the contact angle formation with the asperity geometry for application to a hydrophilic wafer surface, which is derived based on liquid-solid interfacial contact over the contact line. Experimental investigations were performed to verify the model. For much of the examined parameter room in the hydrophilic silicon wafer surface, it was found that the contact angle was strongly dependent on the ratio of asperity height to length, and the sharper asperity led to the higher contact angle. The observations are well consistent with Gibbs' contact-line theory.     

Some effects of anisotropic roughening on the wetting of metal surfaces

The wetting of aluminium, copper and steel workpieces by drops of water, tin, copper or silver-copper braze was found to be affected by anisotropic roughening. Two types of behaviour were exhibited; wetting and flow in well-wetted systems with contact angles below about 20° was enhanced by the roughening, but that of poorly or moderately wetting systems was impeded. The anisotropy of the roughening was reflected in the eccentricity of the drops which increased with roughening, particularly so for well-wetting systems. Similarly, the area covered by a drop was little affected by roughening for most systems, but increased rapidly for those that wetted well. These experimental effects were in accord with models that regard roughening surfaces as presenting a series of energy barriers impeding the flow of all but the most energetic liquids, as defined by their enthalpy.     

Lattice Boltzmann simulations of incompressible liquid-gas systems on partial wetting surfaces

A three-dimensional Lattice Boltzmann two-phase model capable of dealing with large liquid and gas density ratios and with a partial wetting surface is introduced. This is based on a high density ratio model combined with a partial wetting boundary method. The predicted three-dimensional droplets at different partial wetting conditions at equilibrium are in good agreement with analytical solutions. Despite the large density ratio, the spurious velocity around the interface is not substantial, and is rather insensitive to the examined liquid and gas density and viscosity ratios. The influence of the gravitational force on the droplet shape is also examined through the variations of the Bond number, where the droplet shape migrates from spherical to flattened interface in tandem with the increase of the Bond number. The predicted interfaces under constant Bond number are also validated against measurements with good agreements.     

Singularity of the electric field at the wetting line of a dielectric surface

An electric field is considered in the vicinity of the wetting line of a dielectric plate of a conducting or a dielectric liquid. It is shown that the electric field is, at the wetting line, a feature where the modulus of the field tends to infinity when the distance from the wetting line tends to zero. At a wetting angle differing from zero, the giving feature is integrated, and the full volume and density of electric energy remain finite. The results of calculations make it possible to conclude that the singularity of the electric field exists at any wetting angles differing from zero and 180 degrees, as well as at any positive values of dielectric permeabilities.     

Spectral control of thermal emission by periodic microstructured surfaces in the near-infrared region.

Thermal emissive properties of microstructured surfaces are measured in the near-infrared region. Two-dimensional periodic microstructured surfaces with metal coatings are fabricated with Si anisotropic etching and laser ablation techniques. The structural periods of the samples are 2.0 and 1.5 microm. Clear selective-emission bands are observed experimentally. This selective emission is attributed to the resonance effect between the emissive field and the surface microstructures. In addition, numerical calculation computed with rigorous coupled-wave analysis (RCWA) is performed on the microstructured samples. The selective-emission peaks measured through experiments can be reproduced well by RCWA, and this result suggests strongly that the thermal radiation from periodic structures may have spatial coherence. It is confirmed that the surface microstructure can be applied to the control of spectral emission from high-temperature materials.     

Enhanced repair of a critical-sized segmental bone defect in rabbit femur by surface microstructured porous titanium

Repair of load-bearing bone defects remains a challenge in the field of orthopaedic surgery. In the current study, a surface microstructured porous titanium (STPT) successively treated with H₂O₂/TaCl₅ solution and simulated body fluid was used to repair the critical-sized segmental bone defects in rabbit femur, and non-treated porous titanium (NTPT) and porous biphasic calcium phosphate ceramics (PBCP) were used as control, respectively. A 15 mm long implant was positioned in the femoral defect and stabilized by a plate and screws fixation. After implantation into the body for 1, 3 and 6 months, X-ray observation confirmed that porous titanium groups (NTPT and STPT) provided better mechanical support than PBCP group at the early stage. However, there was no obvious difference in the formed bony callus between PBCP and STPT groups in the later stage, and they both showed better shape of bony callus than NTPT group. Micro-CT and histomorphometric analysis for the samples of 6-month implantation demonstrated that more new bone formed in the inner pores of PBCP and STPT groups than that in NTPT group. Moreover, the biomechanical tests revealed that STPT group could bear larger compressive load than NTPT and PBCP groups, almost reaching the level of the normal rabbit femur. STPT exhibited the enhanced repairing effect on the critical-sized segmental bone defect in rabbit femur, meaning that it could be an ideal material for the repair of large bone defect in load-bearing site.     

Mixed alkylsilane functionalized surfaces for simultaneous wetting and homeotropic anchoring of liquid crystals

Surfaces functionalized with a self-assembled monolayer (SAM) formed from a mixture of two alkylsilanes with different chain lengths have been designed to simultaneously improve the liquid crystal (LC) wettability and promote homeotropic anchoring of the LC. Most chemically functionalized surfaces (e.g., long alkyl chain SAMs) that promote homeotropic alignment of LC possess low surface energy and result in poor LC wettability, inhibiting LC infiltration into microstructured surfaces and sometimes resulting in LC dewetting from the surface. However, a surface modified with a mixed SAM of octadecyltriethoxysilane (C18) and ethyltriethoxysilane (C2) exhibited very low LC contact angle while providing homeotropic anchoring. Ellipsometry was used to correlate the bulk concentration of C18 in the deposition solution to the surface coverage of C18 in the mixed monolayer; these bulk and surface concentrations were found to be equal within experimental uncertainty. The LC contact angle was found to depend nonmonotically with the surface coverage density, with a minimum (14.4 ± 0.1°) at a C18 surface coverage of 0.26 ± 0.08. Homeotropic LC anchoring was achieved at a C18 surface coverage of ≥0.11 ± 0.04, in the regime where a minimum in the LC contact angle was observed. The practical application of this approach to surface modification was demonstrated using a micropillar array sensor substrate. When the array was functionalized with a conventional C18 SAM, the LC did not infiltrate the array and exhibited a contact angle of 47.4 ± 0.5°. However, the LC material successfully infiltrated and wetted the same microstructured substrate when functionalized with a C18/C2 mixed SAM, while still exhibiting the desired homeotropic anchoring.