Characterization of the Topography and Wettability of English Weed Leaves and Biomimetic Replicas

The topography and wettability of the underside of English weed （Oxalis pes-caprae） leaves and of their biomimetic replicas are investigated. Polyvinyl siloxane molds were cast from the leaves and then filled with an epoxy pre-polymer to produce replicas. The particular topographical structures of leaves and replicas were evaluated by optical microscopy and Scanning Electron Microscopy （SEM） analysis. The static wettability of leaves and replicas was assessed by contact angle measurements, while the dynamic wettability was characterized by estimating contact angle hysteresis and studying the dynamic behavior of impacting water droplets. A smooth glass slip and its replica were used as control surfaces. The replica moulding method used was able to transfer the characteristic pattern of irregular 100 μm - 200 μm × 60 μm convex papillae interspersed with stomata of the original leaf to the epoxy replicas. The static contact angle of 143°± 3° and the contact angle hysteresis of 2~ indicate that the underside of the English weed leaf is close to superhydrophobic. The lower contact angles （130° ± 4°） and higher hysteresis （31°） observed for the replica when compared with the original leaves were associated to an inaccurate replication of the chemistry and structures of the three-dimensional wax projections covering the plant surface. Also, trichomes in the original leaves could not be accurately reproduced due to their flexibility and fragility. Differences in wetting behavior were also evident from droplet impact experiments, with rebound regimes prevailing in the original leaves and regimes characterized by higher adhesion and larger dissipation predominating in the replicas. Nevertheless, the morphological features of the leaf transferred to the replica were sufficient to promote a clear hydrophobic behavior of the replica when compared with the smooth epoxy reference surface.     

Controlled Cell Patterning on Bioactive Surfaces with Special Wettability

The ability to control cell patterning on artificial substrates with various physicochemical properties is of essence for important implications in cytology and biomedical fields.Despite extensive progress,the ability to control the cell-surface interaction is complicated by the complexity in the physiochemical features ofbioactive surfaces.In particular,the manifestation of special wettability rendered by the combination of surface roughness and surface chemistry further enriches the cell-surface interaction.Herein we investigated the cell adhesion behaviors of Circulating Tumor Cells (CTCs) on topographically patterned but chemically homogeneous surfaces.Hamessing the distinctive cell adhesion on surfaces with different topography,we further explored the feasibility of controlled cell patterning using periodic lattices of alternative topographies.We envision that our method provides a designer's toolbox to manage the extracellular environment.     

植物叶表面的润湿性及其生态学意义

植物叶表面的润湿性是各种生境中常见的一种现象,表现了叶片对水的亲和能力。叶面的润湿性可以通过测定气、固、液界面的接触角大小确定,接触角θ＜110°的为润湿,θ＞130°的为不润湿,表现出斥水性。影响叶片润湿性的主要因素有叶面蜡质含量与形态,叶面绒毛数量、质地、形态和分布方式,气孔和表皮细胞形态和大小,叶水分状况等。叶表面的化学组成和形态是影响叶润湿性的主要内在原因,但外界环境的变化通过影响表面的结构和形态来影响叶润湿性。叶面的润湿性是植物叶片截流降水的微观基础,水分在润湿性强的叶面上铺展呈膜;在不润湿的叶面上形成水珠,容易在风和重力的作用下离开叶面;铺展的水膜,又会对叶的光合作用产生重要的影响。不同润湿性的叶面,滞留、吸附、过滤各种大气污染物数量不同;这些污染物沉降在叶片表面,与叶面发生相互作用,从而改变叶面的润湿性。植物叶含水量的高低对叶感染病菌有重要的影响,在病菌感染期间如果叶表面完全润湿则有利于病菌侵染;一旦病菌侵染,又会对叶面结构造成破坏,需要考虑润湿性能对防治病虫害的农药液滴持留的影响。对于润湿性小、斥水性大的植物,其叶表面表现出一定的自清洁功能;根据这些高疏水性、具有自清洁性的植物叶面特征,可利用或借鉴生物学信息进行仿生设计或制造新的功能材料。润湿性作为固、气、液三相作用的综合结果,是认识植物界面关系的微观基础,对于植物叶面生态功能的认识具有重要的意义。     

Factors influencing initial larval settlement: temporal, spatial and surface molecular components

The impact of initial surface chemistry on settlement of barnacle, bryozoan, and hydroid larvae was assessed. Temporal (on a scale of weeks to months) and fine scale spatial (centimeter to meter) variation in settlement were quantified. Four arrays of silanized glass surfaces, deployed at ≈2-wk intervals, were monitored after 1 and 3 days of immersion. Settlement of all larval types exhibited strong temporal variation. There was a 25, 22- and 18-fold difference between the highest and lowest Day 1 settlement for barnacles, bryozoans and hydroids, respectively. Bryozoan and hydroid settlement was spatially variable, barnacle settlement was not. Barnacle and bryozoan settlement was influenced by inttial surface chemistry, hydroid settlement was not. For barnacles, there was a 2-fold difference between total settlement over the four arrays on untreated glass and diphenyl-silanized surfaces; for bryozoans, there was a 51-fold difference, and in the opposite direction. There was a negative correlation between barnacle and bryozoan settlement with respect to surface. This result was independent of the presence of the other species. Bryozoan settlement was also spatially and temporally quantified in a separate, single surface 56-h array, and total bryozoan settlement ·h⁻¹ was found to be correlated with light intensity. Patterns of initial colonization were strongly influenced by surface chemistry and spatial temporal variation in larval supply. These effects on initial colonization may influence subsequent community development.     

Molecular dynamics simulation of the spreading of the nanosized droplet on a graphene-coated substrate: the effect of the contact line forces

Surface characteristics of graphene have an important impact on its performance. Substantial attention has been devoted to studying the static wetting behaviour of a graphene-coated substrate with little attention to the dynamic wetting behaviour. The impact of contact line forces (CLFs) on the droplet-spreading process has not been revealed completely yet. A series of molecular dynamics (MD) simulation is performed to investigate the spreading process of the water droplet on the graphene-coated substrate in this research. The increase of interaction potential parameter between substrate and water droplet makes the spreading radius getting bigger and the final static contact angle smaller. Apart from that, the higher hydrophilicity of underlying substrate can lead to the greater averaged forces of atoms near contact line. CLFs correlate well with the variation of kinetic energy of water molecules located in the contact line region. Surface tensions of water droplets on graphene-coated substrates are also examined. The liquid-vapour and solid-vapour surface tensions are constant. An increase in the surface tension of liquid-solid lead to the increase of balanced contact angles of water on the substrate. The results are useful for understanding the effect of CLFs on the dissipation of kinetic energy of water molecules.     

Molecular dynamics study on explosive boiling of ultra-thin liquid over solid substrate: considering interface wettability of Argon/MoS2

A molecular dynamics (MD) study is carried out to reveal the phenomenon about the normal and explosive boiling of ultra-thin liquid argon film absorbed on MoS₂ surface with different wetting conditions. The three-phase molecular system is composed of a solid MoS₂ wall, a liquid argon film and a vapour argon region. Initially, the three-phase simulated system is thermally equilibrated at a low temperature. Then the MoS₂ heat source is suddenly heated up to two different high temperatures those far above critical point of liquid argon, and the argon experienced a phase transition process in the NVE ensemble. The simulation results show that the good wetting properties and high heat source temperature dramatically enhance phase transition efficiency, accelerating the heat transfer rate, shortening the boiling time, and increasing the evaporation rate, and they have remarkable effects on temperature and pressure histories, density distribution during whole boiling process. Explosive boiling is more likely to occur at high superheated degree, but evaporation occurs at low superheated degree. In addition, at a high superheated degree, it can be conclude from the simulation results that the better wetting properties of the solid-liquid interface is, the shorter time of the explosive boiling is needed.     

Foliar water and solute absorption: an update

The absorption of water and solutes by plant leaves has been recognised since more than two centuries. Given the polar nature of water and solutes, the mechanisms of foliar uptake have been proposed to be similar for water and electrolytes, including nutrient solutions. Research efforts since the 19th century focussed on characterising the properties of cuticles and applying foliar sprays to crop plants as a tool for improving crop nutrition. This was accompanied by the development of hundreds of studies aimed at characterising the chemical and structural nature of plant cuticles from different species and the mechanisms of cuticular and, to a lower extent, stomatal penetration of water and solutes. The processes involved are complex and will be affected by multiple environmental, physico-chemical and physiological factors which are only partially clear to date. During the last decades, the body of evidence that water transport across leaf surfaces of native species may contribute to water balances (absorption and loss) at an ecosystem level has grown. Given the potential importance of foliar water absorption for many plant species and ecosystems as shown in recent studies, the aim of this review is to first integrate current knowledge on plant surface composition, structure, wettability and physico-chemical interactions with surface-deposited matter. The different mechanisms of foliar absorption of water and electrolytes and experimental procedures for tracing the uptake process are discussed before posing several outstanding questions which should be tackled in future studies.     

Endowing antifouling properties on metal substrata by creating an artificial barrier layer based on scalable metal oxide nanostructures

Abstract

Here, by creating different types of artificial barrier layer against bacterial attachment, anti-biofouling properties were endowed on three metallic surfaces – aluminum, stainless steel and titanium. To each metallic surface, a tailored chemical oxidation process was applied to grow scalable oxide structures with an additional appropriate coating, resulting in three different types of anti-biofouling barrier, a thin water film, an air layer and an oil layer. Fluorescence images of the attached bacteria showed that the water layer improved the anti-biofouling performance up to 8–12?h and the air layer up to 12–24?h, comparable with the lifetime of the air layer. In comparison, the oil layer exhibited the best anti-biofouling performance by suppressing the fouled area by < 10% up to 72?h regardless of the substratum type. The present work provides simple, low-cost, scalable strategies to enhance the anti-biofouling performance of industrially important metallic surfaces.