Wetting and Spreading

Les interactions entre molécules des diverses phases impliquées dans les phénomènes de mouillage engendrent des interactions entre interfaces, qui influencent de façon profonde l'existence et la nature des transitions de mouillage. Cet ouvrage contribue à la compréhension de ce lien complexe entre interactions et transitions de mouillage, à partir de l'étude expérimentale du mouillage des alcanes sur l'eau et de considérations théoriques.
La thèse dont est issu cet ouvrage a été récompensée par le prix Ilya Prigogine 2001 de la meilleure thèse en thermodynamique.
Les toutes premières pages de l'ouvrage sont téléchargeables ici.

Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculiarities of nanopore-confined condensed matter are also discussed with regard to applications.
A particular emphasis is put on texture formation upon crystallisation in nanoporous media, a topic both of high fundamental interest and of increasing nanotechnological importance, e.g. for the synthesis of organic/inorganic hybrid materials by melt infiltration, the usage of nanoporous solids in crystal nucleation or in template-assisted electrochemical deposition of nano structures.

Spatial confinement in nanoporous media affects the structure, thermodynamics and mobility of molecular soft matter often markedly. This article reviews thermodynamic equilibrium phenomena, such as physisorption, capillary condensation, crystallisation, self-diffusion, and structural phase transitions as well as selected aspects of the emerging field of spatially confined, non-equilibrium physics, i.e. the rheology of liquids, capillarity-driven flow phenomena, and imbibition front broadening in nanoporous materials. The observations in the nanoscale systems are related to the corresponding bulk phenomenologies. The complexity of the confined molecular species is varied from simple building blocks, like noble gas atoms, normal alkanes and alcohols to liquid crystals, polymers, ionic liquids, proteins and water. Mostly, experiments with mesoporous solids of alumina, gold, carbon, silica, and silicon with pore diameters ranging from a few up to 50 nm are presented. The observed peculi...

ABSTRACT Experiments to understand the effect of surface wettability on impact characteristics of water drops onto solid dry surfaces were conducted. Various surfaces were used to cover a wide range of contact angles (advancing contact angle from 48 • to 166 • , and contact angle hysteresis from 5 • to 56 •). Several different impact conditions were analyzed (12 impact velocities on 9 different surfaces, among which 2 were superhy-drophobic). Results from impact tests with millimetric drops show that two different regimes can be identified: a moderate Weber number regime (30 < W e < 200), in which wettability affects both drop maximum spreading and spreading characteristic time; and a high Weber number regime (W e > 200), in which wettability effect is secondary, because capillary forces are overcome by inertial effects. In particular, results show the role of advancing contact angle and contact angle hysteresis as fundamental wetting parameters to allow understanding of different phases of drop spreading and beginning of recoiling. It is also shown that drop spreading on hy-drophilic and superhydrophobic surfaces occurs with different time scales. Finally, if the surface is superhydrophobic, eventual impalement, i.e., transition from Cassie to Wenzel wetting state, which might occur in the vicinity of the drop impact area, does not influence drop maximum spreading. C 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4757122]

The effects of adding silver and indium to lead-free solders was investigated through an experiment. The solder alloys used for this study included Sn-0.7Cu-1.01n-xAg, where x = 0, 0.1, 0.3, and 0.5. Thermal analysis of the solder alloys was performed using a DSC-50 differential scanning calorimetry. The heating rate was 5°C/min from room temperature to 350°C in 50mL/min argon gas flow. The wetting balance test was conducted using a SAT5100 Rhesca, and the parameters used for wetting balance test were 5 mm/s of dipping speed with a dipping depth of 10 mm. The Vickers hardness number of the solder alloy was determined by conducting a microhardness test. The curve obtained from DSC analysis shows the onset temperature of Sn-0.7Cu is 227.4°C. Indium was observed distributed in primary grain because of its similar atomic size. Higher Ag contents produced better wettability by lowering wetting time and increasing maximum wetting force.

www.aws.org/bsmc/wj0409-45.pdf

Abstract: There were some problems that face continuous drip irrigation system in Egypt, such as emitter clogging, due to the narrow paths of water which give small discharge and in sandy soil, the depth of wetting pattern is relatively higher than the width. They cause deep percolation beyond root zone. Thus the need to increase the width of wetting pattern and use of high emitter discharge suggest the use of pulse drip irrigation.
The information on depths and widths of wetted zone of soil plays the greatest role in design and management of drip irrigation system. There is a lack of models to predict wetting pattern under pulse and intermittent flow regime, since the applicability of the available models were limited to continuous flow regime only. Therefore, the objective of this research was to develop a dimensional analysis model to estimate both depth and width of wetting pattern under different flow regimes. Thus, a model was developed using semi-empirical approach and dimensional analysis method for determining geometry of wetted root zone under. The predicted values of wetted depth and width were compared with those obtained through laboratory experiments conducted in same soil. Experiment included determination of maximum depths and widths of wetted zone after 1, 2, 3, 4 h of water application under different flow regimes. Predicted and observed values were compared to test model applicability in laboratory conditions. On the basis of root mean square, mean error and model efficiency parameters model performance was found good. Thus, developed models can be used to predict wetting pattern under continuous, intermittent and pulse flow with line source of water application. Pulse flow results showed that the wetted width increased and wetted depth decreased as the operating on-time decreased for the same amount of applied water. As the pulsed flow was increased from six to twelve times the continuous flow, deep percolation was reduced and horizontal spread increased. This result shows the advantage of pulse flow, for reducing the deep percolation of water under the crop root zone, while obtaining a wide horizontal spread of wetting. This enables using a highly discharge emitter with the same amount of water.

Three aluminium metal matrix composites containing reinforcing particles of B4C, SiC and Al2O3 (0-20vol.%) were processed. The stir-casting manufacturing route followed by hot extrusion was utilized, being one of the cost-effective industrial methods. A clear interfacial reaction product/layer was found at Al-SiC interface for composites held for a relatively long processing time (>30 min). No reaction product was observed at Al-B4C and Al-Al2O3 interfaces at the resolution limit of the SEM used. On the other hand, two secondary phases (alumina and another phase containing aluminium, boron and carbon) were found in the aluminum matrix away from the interface in Al-B4C composites. From the fracture surface analysis, B4C reinforced Al composite seemed to exhibit a better interfacial bonding compared to the other two composites.

TECHNICAL FIELD - This application relates to the field of coatings that prevent fogging on solid surfaces without altering the characteristics of the covered surface. The coatings may be used on devices and equipment for sports and recreation, the medical field, military and industrial safety
applications. Such devices and equipment include windows and mirrors of automobiles, motorcycles, boats, airplanes, and trains. In industrial and instrumentation application: protective windows, domes, and lenses of gauges, dials, meters. In medical applications: intraocular lenses, endoscopic/laparoscopic lenses, protective eyewear, contact lenses for visual correction, medical implants, surfaces, and medical and surgical tools.
BACKGROUND
The problem of condensation with fogging: Hydrophobic versus hydrophilic surfaces. Protective eyewear, glasses, sunglasses, swimming goggles, diving goggles, helmet visors, windshields, intraocular lenses, medical scopes, and high-precision instrumentation are just several applications where visual distortion due to fogging with condensation poses a problem.
Control of fogging due to condensation on polymer and glass surfaces has seen development, testing and patenting of solutions for a broad spectrum of optical, vision, visor, goggle and lens materials, including optical glasses, borosilicate glass, polycarbonates, tinted thin film coatings, and other polymers for athletic visor and vision-wear. These can require optimization of the robustness and resiliency to create permanent anti-fog coatings, and optimization of adhesion on polycarbonates and surfaces with difficult geometries such as very high curvature. Therefore, anti-fog technologies and their applications have to be conceived and optimized by
adapting to a broad range of specifications for use, use duration, etc., and require working directly with a variety of end users to create such adaptability. End users for anti-fog technology include, but were not limited to: surgeons, professional athletes, recreational users, professional safety users, fire-workers, emergency personnel, biohazard handlers, medical and surgical personnel, and instrumentation dials and domes manufacturers.
Control of fogging should be tested using the specific conditions of condensation experienced by each group end users, such as body or outdoor temperatures, and water vapor pressures and various fluids present during use, such as bodily fluids, sweat, blood, skin oils and human tears or fluids produced from machinery. U.S. patent application Ser. No. No. 13/674,307 (hereinafter '307 application) describes an emulsion that physically changes the surface topography so that condensation behavior can be controlled. The result in the '307 application is a hydrophilic surface that manipulates water droplets so that the water droplets form a thin translucent film on the hydrophilic surface. The'307 application describes a  wet anti-fog technology, where the emulsion is applied when the
surface requires an antifogging coating and should not be dried on the surface. When the emulsion of the '307 application is dried, the polymers come out of the solution and precipitate so that the coated surface is no longer optically transparent and fails to maintain optical quality.
Specifically, the emulsion described in the '307 application is optimized for temporary application and for ease of application. The emulsion described in the '307 application was designed for medical applications, including but not limited to vitro-retinal surgery as well as endoscopic and laparoscopic procedures and surgeries. Thus the emulsion described in the '307
application does not permanently coat the surfaces with anti-fog technology. Accordingly, there is need for a dry permanent anti-fog technology that manipulates water so the water droplets form a thin translucent film on a surface rather than produce fogging on the surface while maintaining optical quality. First, the invention consists of permanent anti-fog coatings, including but not limited to their materials components, composition, adaptive formulation and several methods of fabrication.
The permanent anti-fog is referred to as “FogKnox™”. It includes but is not limited to very high quality optical transmission films that are distortion-free, and exhibit a very high degree of transparency. FogKnox™ includes but is not limited to dry, permanent and very highly uniform optical anti-fog coatings, which can be delivered in wet (fluid) or solid from. Both wet and solid form preserve and improve instantaneously visualization on edges of lenses, dials and surfaces and wide-angle lens. Only after drying is the anti-fog a permanent, non-removable solid film. In a separate embodiment, the anti-fog coatings can be made removable for applications where
lenses and devices on which they are applied need to be resurfaced, called KnoxFog™. The antifoam coatings can also be made semi-permanent, so it can be scrubbed, thus removable by scrubbing, detergent washing and/or sonication, for medical applications, and are then called
VitreOx™. Second, the invention includes, for all above mentioned anti-fog coatings, their method of application in large scale, medium scale or small scale manufacturing, via several possible coating processes, adaptive compositions, adjustments of physical properties and surface
preparation procedures, which are disclosed as the second part of the invention. Third, all the above coatings can also be applied on existing, already manufactured optical devices, tools, dials, goggles, vials, bottles and scopes, via the third element of the invention, specific delivery device and its cartridge of anti-fog coatings materials. The delivery device
includes a coating delivery and element to allow for quick drying element attachment to the metered delivery automated mechanism to apply the coating in a few seconds, and let it dry within minutes.

Interfacial reactions during Si die attachment with Zn-Al-Mg-Ga high-temperature lead (Pb)-free solder on bare Cu lead-frame (Tamac 4) and Ni metallized Cu lead-frame were investigated using an optical microscope, scanning electron microscope (SEM) and energy dispersive x-ray (EDX). Die attachment was performed in an automatic die attach machine in a forming gas environment at temperature 380C. The back side of the die was metallized with Ti/Ni/Ag layers. Comparative studies of die attach properties such as wetting, void and die shear strength on bare and Ni metallized Cu lead-frame was made. Cross sectional microstructural investigation revealed that as many as three intermetallic compound (IMCs) layers form at the solder/lead-frame interface for bare Cu lead-frame. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn4 forms at the solder side, while Cu5Zn8 forms at the middle. At the interface with Si die, IMC layer could not be detected by SEM. With Ni metallized Cu lead-frame, no IMC layer was observed at the solder/lead-frame as well as Si die/solder interface by SEM. Wetting on Ni metallized Cu lead-frame was found to be lower as compared to that at bare Cu lead-frame. Die shear strength was found to be higher on bare Cu lead-frame (24.2 MPa) as compared to Ni metallized Cu lead-frame (20.5 MPa). Die shear strength of standard Pb-5Sn solder was also measured for comparison and found to be 28.2 MPa. © 2010 IEEE.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5746721&tag=1

We examine the motion of a liquid-air meniscus advancing into a microchannel with chemically heterogeneous walls. We consider the case where a constant flow rate is imposed, so that the mean velocity of the interface is kept constant, and study the effects of the disorder properties on the apparent contact angle for each microchannel surface. We focus here on a large diffusivity regime, where any possible advection effect is not taken into account. To this end, we make use of a phase-field model that enables contact line motion by diffusive interfacial fluxes and takes into account the wetting properties of the walls. We show that in a regime of sufficiently low velocities, the contact angle suffers a hysteresis behavior which is enhanced by the disorder strength. We also show that the contact line dynamics at each surface of the microchannel may become largely coupled with each other when different wetting properties are applied at each wall, reflecting that the dynamics of the interface is dominated by nonlocal effects.

Zn-Al based alloys have been suggested as high temperature lead-free solder for Si die attach by different researchers. But, so far, these alloys have not been tested in the industrial environment. In this study, Zn-Al-Ge alloy solder wire was used for Si die attachment on Cu substrate in an automatic die attach machine. The back side of the die was metalized with Ti/Ni/Ag layers. Die attachment was performed in a forming gas environment at temperatures ranging from 370°C to 390°C. Interfacial structure at the Si die and Cu substrate interfaces, and the bulk solder microstructure were investigated using an optical microscope, scanning electron microscope (SEM), energy dispersive x-ray (EDX) and electron probe microanalyzer (EPMA). Wetting characteristics and die shear strength were also studied. Cross sectional microstructural investigation revealed that as many as three intermetallic (IMCs) layers form at the solder/copper interface. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5Zn 8 forms at the middle. At the Si die-solder interface, with Ti/Ni/Ag metallization, no IMC layer was detected. Microstructural evidence suggests that Ni layer did not react with the Zn-Al-Ge solder. The microstructure of the bulk solder consists of mainly two phases: one with a lighter contrast and the other one being darker under the SEM. The phase with lighter contrast is a zinc rich phase containing an average of about 70.9% Zn. The darker one is found to be an aluminum rich phase containing an average of about 54.9% Al. In addition, some particles with brighter appearance are observed at different places in the bulk solder. These particles are rich in zinc and their composition closely resembles that of scallop type CuZn 4 IMC which forms at the solder side of the copper-solder interface. It is suggested that these particles are CuZn 4 IMC which have been spalled from the interface during soldering. Wetting of Zn-Al-Ge solder on Cu substrate was found to be lower at 370°C as compared with that at 390°C. Voids were found in the solder which were more in number at higher die attach temperatures. Die shear strength was found to be higher at the die attached temperature of 390°C (22.3 MPa) as compared with those obtained at 370-380°C (15.5-17.4 MPa). Die shear strength of standard Pb-Sn solder was also measured for comparison and was found to be 28.2 MPa. The microstructure and properties of the solder joint are discussed.

ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5643009

Purpose - The purpose of this paper is to investigate the effects of addition Co nanoparticles on the characteristic properties of Sn-3.8Ag-0.7Cu solder. Design/methodology/approach - Cobalt (Co) nanoparticles were added to Sn-Ag-Cu solders by thoroughly blending various weight percentages (0-2.0 wt%) of Co nanoparticles with near eutectic SAC387 solder paste. Blending was done mechanically for 30 min to ensure a homogeneous mixture. The paste mixture was then reflowed on a hot plate at 250 degrees C for 45s. The melting points of nanocomposite solder were determined by differential scanning calorimetry. Spreading rate of nanocomposite was calculated following the JIS Z3198-3 standard. The wetting angle was measured after cross-sectional metallographic preparation. Findings - No significant change in melting point of the solder was observed as a result of Co nanoparticle addition. The wetting angles of the solder increased with the addition of nanoparticles, while the spreading rate decreased. Although the wetting angle increased, the values were still within the acceptable range. Scanning micrograph observations revealed that the as-solidified microstructure of the composite solder was altered by the addition of Co nanoparticles. Microhardness of the solders slightly increased upon Co nanoparticles addition to SAC387. Originality/value - The paper demonstrates that a simple process like paste mixing can be used to incorporate nanoparticles into solder.

http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=23&issue=1&articleid=1905669&show=pdf

Measurements of contact angles are conventionally used to describe the wetting behavior of nanoscopic liquid droplets on a flat substrate, where the dissimilar molecular interface is vague. Considering this issue, we performed an atomistic simulation of the spherical nano-droplets of pure and ion-water on a bare solid substrate to determine the relationship between the contact angle and the boundary position residing at the solid–liquid interface. In this exploration, the existence of the correlation between the contact angle and the associated boundaries is observed using classical Young’s equation. Our study reveals that the effects of the variable wettability and boundary positions have a significant impact on the contact angle. In addition, we investigate the contact angle based on boundary positions for different ion-water nano-droplets with varying ion concentrations. Interestingly, the contact angles of pure and ion-water droplets are almost identical in a specific boundary position for both varying wettability and ion concentrations. Finally, we compare the estimated contact angle for different boundary positions with the solid substrate experimental contact angle. Atomistic simulations indicate that the interfacial boundary concept for measuring contact angle using classical Young’s equation gives a certain convergence to experimental evaluation.

Capillary filling dynamics of liquid n-tetracosane (n-C24H50) in a network of cylindrical pores with 7 and 10 nm mean diameter in monolithic silica glass (Vycor) exhibit an abrupt temperature-slope change at Ts approx. 54 deg
C, 4 deg
C above bulk and 16
degC, 8 deg
C, respectively, above pore freezing. It can be traced to a
sudden inversion of the surface tension’s T slope, and thus to a decrease in surface entropy at the advancing pore menisci, characteristic of the formation of a single solid monolayer of rectified molecules, known as surface freezing from macroscopic, quiescent tetracosane melts. The imbibition speeds, that are
the squared prefactors of the observed square-root-of-time Lucas-Washburn invasion kinetics, indicate a conserved bulk fluidity and capillarity of the nanopore-confined liquid, if we assume a flat lying, sticky hydrocarbon backbone monolayer at the silica walls.

We have studied how carboxylic modified latex (CML) microparticles adsorb at liquid surfaces and the preferred type of emulsion they can stabilise depending on the particle size and the surface density of carboxylic groups. We measured the particle contact angle by using the gel trapping technique (GTT) for CML particles adsorbed at air–water and oil–water interfaces. Using this method we obtained scanning electron microscopy (SEM) micrographs of polydimethylsiloxane (PDMS) replicas of the liquid interface with the particles, where the PDMS replicates the non-polar phase and measured the particle contact angle. We discovered that the particle wettability correlates well with the surface density of the carboxylic groups but is not very sensitive to the presence of electrolyte in the aqueous phase and the value of the particle zeta potential. We demonstrated that CML microparticles with a high surface density of COOH groups stabilise oil-in-water (O/W) emulsions while those with the lowest coverage of COOH groups favour the formation of water-in-oil (W/O) emulsions. We found that this corresponds to a change of the CML particle contact angle from lower than 90° to higher than 90° upon decrease of the surface density of COOH groups. The findings confirm that the surface density of polar groups has a much bigger effect on the particle wettability and the preferred emulsion than the particle surface charge and zeta potential. Our results on the type of stabilised Pickering emulsion agree with other experimental studies with different particle materials. We propose an alternative explanation for the link between the particle contact angle and the type of stabilised Pickering emulsion.

Capillary driven surface oscillations of liquid argon (Tsat = 87.3 K at 1,013 hPa) have been investigated in a partly filled right circular cylinder under non-isothermal boundary conditions. The oscillations take place during the reorientation from the normal gravity surface position towards a new position upon step reduction of gravity. The situation is similar to the end of thrust in a rocket tank when the cold propellant moves along the warmer tank wall driven by capillary forces. The aim was to investigate the influence of the temperature difference between the slightly subcooled cryogenic liquid and the superheated cylinder wall on the oscillations and their characteristics in a single-component, two-phase system. Axial wall temperature gradients of averaged 0.15 K/mm − 1.93 K/mm above the normal gravity surface position were implemented. A general dependence of the reorientation behavior on the gradient value was observed, concerning the apparent contact line behavior, the frequency and damping of the oscillations of the free surface center point, and the apparent contact angle. The behavior of the ullage pressure was found to follow the behavior of the contact line.

Interfacial reactions during Si die attachment with Zn-Al-Mg-Ga high-temperature lead (Pb)-free solder on bare Cu lead-frame (Tamac 4) and Ni metallized Cu lead-frame were investigated using an optical microscope, scanning electron microscope (SEM) and energy dispersive x-ray (EDX). Die attachment was performed in an automatic die attach machine in a forming gas environment at temperature 380C. The back side of the die was metallized with Ti/Ni/Ag layers. Comparative studies of die attach properties such as wetting, void and die shear strength on bare and Ni metallized Cu lead-frame was made. Cross sectional microstructural investigation revealed that as many as three intermetallic compound (IMCs) layers form at the solder/lead-frame interface for bare Cu lead-frame. A CuZn intermetallic layer forms close to copper, a scallop shaped CuZn 4 forms at the solder side, while Cu 5Zn 8 forms at the middle. At the interface with Si die, IMC layer could not be detected by SEM. With Ni metallized Cu lead-frame, no IMC layer was observed at the solder/lead-frame as well as Si die/solder interface by SEM. Wetting on Ni metallized Cu lead-frame was found to be lower as compared to that at bare Cu lead-frame. Die shear strength was found to be higher on bare Cu lead-frame (24.2 MPa) as compared to Ni metallized Cu lead-frame (20.5 MPa). Die shear strength of standard Pb-5Sn solder was also measured for comparison and found to be 28.2 MPa.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5746721

The effect of magnesium and silicon additions to aluminum, free silicon on the SiC substrate, nitrogen gas in the atmosphere, and process temperature on the wetting characteristics of SiC by aluminum alloys are investigated using the sessile drop technique. The contribution of each of these parameters and their interactions to the contact angle, surface tension, and driving force for wetting are determined. In addition, an optimized process for enhanced wetting is suggested and validated. Results show that the presence of free silicon on the surface of SiC significantly reduces the contact angle between the molten alloy and the substrate. The positive effect of silicon on the contact angle is attributed to a chemical reaction in which both SiC and aluminum are active participants. The results also indicate that nitrogen gas in the atmosphere positively influences the liquid/vapor surface tension, and the presence of magnesium in the aluminum alloy favorably affects the overall driving force for wetting. A mechanism is proposed to explain the beneficial role that the interaction of nitrogen with magnesium plays in enhancing wetting. Magnesium significantly reduces the surface tension of aluminum melts but has a low vapor pressure. Consequently, it readily volatilizes during holding at the processing temperature and is lost from the alloy. It is proposed that a series of chemical reactions in the system Al-Mg-N are responsible for reintroducing magnesium into the melt, thus, maintaining a low melt surface tension. Interactions between the aluminum alloy and the silicon carbide substrate that may lead to the dissolution of the substrate and the formation of undesirable reaction products, particularly Al 4 C 3 , are examined, and means for mitigating their formation are outlined.

Gold is a standard surface for attachment of thiol-based self-assembled monolayers (SAMs). To achieve uniform defect free SAM coatings, which are essential for bio/chemical sensing applications, the gold surface must have low roughness, and be highly orientated. These requirements are normally achieved by either heating during Au deposition or post deposition Au surface annealing. This paper shows that room temperature deposited gold, can afford equivalent gold surfaces, if the gold deposition parameters are carefully controlled. This observation is an important result as heating (or annealing) of the deposited gold can have a detrimental effect on the mechanical properties of the silicon on which the gold is deposited used in microsensors. The paper presents the investigation of the morphology and crystalline structure of Au film prepared by thermal evaporation at room temperature on silicon. The effect of gold deposition rate is studied, and it is shown that by increasing the deposition rate from 0.02 nm s-1 to 0.14 nm s-1 the gold surface RMS roughness decreases, whereas the grain size of the deposited gold is seen to follow a step function decreasing suddenly between 0.06 and 0.10 nm s-1. The XRD intensity of the preferentially [111] orientated gold crystallites is also seen to increase as the deposition rate increases up to a deposition rate of 0.14 nm s-1. Formation and characterization of 1-dodecanethiol on these Au coated samples is also studied using contact angle. It is shown that by increasing the Au deposition rate the contact angle hysteresis (CAH) decreases until it plateaus, for a deposition rate greater than 0.14 nm s-1, where the CAH is smaller than 9 degrees which is an indication of homogeneous SAM formation, on a smooth surface.

The aim of this study is to formulate and solve the equiiibrium shape of a liquid droplet of contact radius r. in the middle of anelastic isotropic thin solid sheet of radius I, by using the different surface concepts such as surface free energy and surface stress.
This is achieved by determining the form of the interfaces as a result of minimization of the total free energy of the system. The profiles are obtained from integration of Euler’s differential equations. An interpretation of these equations is given in terms of mechanical forces. In the domain 0 < r < ro, normal to the sheet there act two shearing forces. One of them derives from Laplace’s overpressure inside the drop. It is uniformly distributed over the area rrg. The other one, coming from the total surface stress of
the sheet, leads to shearing forces proportional to the local slope. Outside the drop (rc < r < I), there are at the same two types of normal shearing forces, one due to tbe surface stress, the other type acting on the triple line of length 2rrr,. Each of these mechanical forces acts on distinct domains of the sheet. Therefore it is not allowed to superpose these forces acting on the entire sheet 0 < r < 1. If such a superposition is unduly made, a ridge appears at the triple line. The liquid drop is found to be spherical as
expected in the absence of gravity. If gravity acts, qualitative modifications are discussed. The profile of the sheet is pseudo-parabolic with an inflection circle of radius ri changing within 0 < ri < 1 according to the fastening ratio l/r, of the sheet. The sag under the drop depends on the Lapiace overpressure and the flexure rigidity D of the sheet. Our general result is easily brought to the special cases where the droplet lies either on a
membrane or on another liquid surface.

Amongst vertebrates, the avian egg is unique in its structure and form.  Bird eggs show a large range in shape, size and colour, the diversity of which has inspired much interest and debate. We have identified a new biological structure present in the surface of the eggshell, which is seemingly specific to one group of birds whose breeding ecology is unique within the avian kingdom. The guillemot group (Uria sp.) of the Alcidae family breed on exposed marine cliff faces, and with no nest used, the eggs are laid directly on the rock surface.  The eggs are constantly exposed to sea-salt spray and guano from the incubating parents. The conical-like structural protrusions present in the eggshell surface of guillemot eggs are analogous with the nano-scale hierarchical arrangements identified in lotus leaves (Nelumbo sp.), the purpose of which is self cleaning. These structures are entirely absent in the eggs of 217 other birds species studied, including those nesting in similar environments, and those closely related to the guillemots from a phylogenetic perspective. Through comparative experiments we demonstrate how the guillemot eggshells exhibit hydrophobicity, have increased surface roughness and surface area, and a high rate of gas exchange under constant conditions. We conclude that these differences, a result of the conical protrusions in the eggshell surface, are an adaptation to the unusual breeding environment of the guillemot, in particular the salt and guana exposure.

The effect of wetting on the ability of solid millimetre-sized and smaller particles to float on a liquid of lower density than the particle material has been considered theoretically and investigated experimentally. The contribution of capillary force towards particle buoyancy is assessed for a range of systems, as well as the range of diameters of particles which could be buoyant for each combination of solid and liquid. The critical parameters in this evaluation of particle buoyancy were considered to be (i) solid density, (ii) liquid density, (iii) liquid surface tension, and (iv) interfacial wetting between solid and liquid phases.