Variation Of Surface Energy Research Articles

Surface Energy Variation Effect on the Onset of Thermocapillary Instability of a Thin Liquid Layer Heated from the Side

A general interfacial energy balance equation taking into account surface energy variation is derived for viscous two-layer flows. Application of this interfacial energy equation to a thin liquid layer heated from one side using a one-layer model shows that thermocapillary induced surface energy variation has a tendency to stabilize the system, resulting in an increase in the critical Marangoni number for the onset of thermocapillary instability. Thermocapillary induced surface energy variation tends to decrease the temperature of hot surface spots and increase the temperature of cold surface spots through an absorb-release mechanism. This absorb-release mechanism increases the free surface’s capability to convect thermal energy from hot spots to cold spots and thus redistributes the disturbance energy evenly across the free surface. This new stabilizing effect becomes stronger at high surface temperature and at high surface dilatation rate.

Alternative Method for Determining Surface Energy by Utilizing Polymer Thin Film Dewetting

Contact angle and contact mechanics, the most common estimating methods for surface energy, exhibit intrinsic drawbacks when determining surface energy or surface energy variation of micron-scaled areas. In this study, the dewetting of a polymer thin film was explored as a means for surface energy determination. In particular, two empirical plots were generated through modification of silicon wafers with various organosilanes and organosilane mixtures. One plot correlated dewetting velocity of a polystyrene thin film as a function of surface energy for both polar and nonpolar surfaces; the other plot consisted of variation of dewetting hole diameters with surface energy for strictly nonpolar surfaces. The empirical plots were then applied to deduce surface energies of micron-scaled areas of gradient and heterogeneous-patterned surfaces. This approach resulted in reasonable values with less than 1% difference as compared to those expected for perfluorodecyl-1H,1H,2H,2H-trichlorosilane/n-decyltrichlorosilane surfaces. But the difference was slightly higher (35%) for the n-octadecyltrichlorosilane (OTS) contact-printed surfaces, which might be a result of better contact with the surface and higher OTS concentration on the stamps when smaller stamps were used.

Characterization of SiO2 Surface Treated by HMDS Vapor and O2 Plasma with AFM Tip.

In order to prepare hydrophobic and hydrophilic surfaces, silane coupling treatment with hexamethyldisilazane (HMDS) and exposing to oxygen plasma are carried out to silicon oxide substrates, respectively. Surface force measurement indicates that the attractive force F of the AFM tip is more sensitive to surface energy variation of the solid surface. The adhesion work W mainly depends on polar component of surface energy. Positive correlation between elastic energy Ee of the cantilever tip and adhesion work W can be confirmed. By using two kinds of tips which have different component values of surface energy, surface property in lithography process can be analyzed.

Multifunctional ToF-SIMS: combinatorial mapping of gradient energy substrates

We present a simple method for chemical modification of chlorosilane self-assembled monolayers (SAMs) on Si surfaces by exposure to a gradient of UV-ozone radiation to create stable substrates with a range of contact angles ( θ H 2O ≈5–95°) and surface energies on a single substrate. These gradient energy substrates are developed to potentially generate libraries for combinatorial studies of thin film phenomenology, where a systematic variation of interfacial surface energy represents one of the significant parameters along one axis. The graded oxidation process presents a systematic variation of surface chemical composition. We have utilized contact angle measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS) to investigate this variation for a series of ions, among which are SiCH 3 +, SiOH + and COOH −. We show that the macroscopic measurements of surface free energy/contact angle correlate with the detailed analysis of surface chemistry (as assessed by ToF-SIMS) on these test substrates.

Micromechanical measurement of active sites on silicon nitride using surface free energy variation

We have investigated chemical reactions between adsorbed water and active sites on a silicon nitride surface as a function of temperature and relative humidity using microcantilevers. Effects that might produce a change in the response of the microcantilever, such as a mass adsorption, surface tension of the adsorbed water, and changes in thermal conductivity, were systematically investigated. It is shown that the judicious choice of experimental conditions could make these effects essentially inconsequential in comparison with the instrument response produced by the change in free surface energy of the microcantilever due to the chemical reactions. Using this method, the variation in free surface energy when changing from dry to high humidity conditions was found and the number of active sites that reacted was estimated. This method may be extended to other problems for use in determining surface free energy change and thus the density of reactant sites under different conditions of interest.

Combinatorial Methods for Investigations in Polymer Materials Science

AbstractWe review recent advances in the development of combinatorial methods for polymer characterization. Applied to materials research, combinatorial methodologies allow efficient testing of structure–property hypotheses (fundamental characterization) as well as accelerated development of new materials (materials discovery). Recent advances in library preparation and high-throughput screening have extended combinatorial methods to a wide variety of phenomena encountered in polymer processing. We first present techniques for preparing continuous-gradient polymer “libraries” with controlled variations in temperature, composition, thickness, and substrate surface energy. These libraries are then used to characterize fundamental properties such as polymer-blend phase behavior, thin-film dewetting, block-copolymer order–disorder transitions, and cell interactions with surfaces of biocompatible polymers.

EFFECT OF SURFACE PROPERTIES ON THE WETTABILITY OF IRON CONTAINING AMORPHOUS CARBON FILMS

Ta-C and iron containing amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe contents on the wettability of the films were investigated in terms of surface energy. The surface energy of a-C:Fe films was determined by the contact angle measurement. Atomic force microscopy (AFM), Raman spectroscopy and X-ray induced photoelectron spectroscopy (XPS) were employed to analyze the origin of the variation of surface energy with various Fe content. It is found that the contact angle for water increases significantly after incorporating Fe into the films and the films become hydrophobic. The roughness of these films has a little effect on the contact angle. The surface energy is reduced after incorporating Fe into the a-C film which is due to the reduction of both dispersive and polar component. The reduction in dispersive component is ascribed to the decrease of atomic density of the a-C:Fe films due to the increase in sp2 bonded carbon. The absorption of oxygen on the surface play an important role in the reduction of polar component for the a-C:Fe films. It is proposed that such network as (Ca-O-Fe)-O-(Fe-O-Ca) may be formed and responsible for the reduction of polar component.

Wettability and surface energy of oxidized and hydrogen plasma-treated diamond films

The wettability of CVD diamond films with liquids of different physico-chemical natures (water, glycerin, tin melt) was investigated by measuring the contact angles using the sessile drop method. The translucent diamond films of 0.5-mm thickness were grown in a microwave plasma CVD using CH4–H2 mixtures as the source gas, and separated from Si substrates. The growth surfaces have been polished to a roughness of Ra≤10 nm, and then exposed to microwave hydrogen plasma or thermal oxidation in air at 500 °C. Raman and Auger/XPS spectroscopies, optical and atomic force microscopies have been used to characterize the diamond films. Based on the wettability data, the variations in surface energy induced by hydrogenation and oxidation of polycrystalline diamond have been evaluated by the Fowkes equation. The hydrogenation of the films in the plasma essentially increases hydrophobic properties (contact angle for water increases up to θ=93°) as compared to oxidation (θ=32°). This is attributable to a reduction in a polar component of the surface energy due to hydrogen adsorption-induced reconstruction of the film surface. For comparison, the wettability of HPHT diamond single crystal, diamond ceramics and pyrolytic graphite have been measured and the differences observed will be discussed in this paper.

Surface energy of amorphous carbon films containing iron

Iron containing diamond-like amorphous carbon (a-C:Fe) films were deposited by filtered cathodic vacuum arc technique. The influences of Fe content and substrate bias on the surface energy of the films were investigated. The surface energy of a-C:Fe films was determined by the contact angle measurement. Atomic force microscopy, Raman spectroscopy, and x-ray induced photoelectron spectroscopy were employed to analyze the origin of the variation of surface energy with various Fe content and substrate bias. It is found that the contact angle for water increases significantly after incorporating Fe into the films and the films become hydrophobic. The roughness of these films has no effect on the contact angle. The surface energy is reduced from 42.8 to 25 dyne/cm after incorporating Fe into the a-C film (10% Fe in the target), which is due to the reduction of both dispersive and polar component. The reduction in dispersive component is ascribed to the decrease of atomic density of the a-C:Fe films due to the increase in sp2 bonded carbon. When sp2 content increases to some extent, the atomic density remains constant and hence dispersive component does not change. The absorption of oxygen on the surface plays an important role in the reduction of the polar component for the a-C:Fe films. It is proposed that such network as (Cn–O–Fe)–O–(Fe–O–Cn) may be formed and responsible for the reduction of polar component.

The effect of Al addition on the gas sensing properties of Fe 2O 3-based sensors

Gas sensors based on α-Fe 2O 3(Al) have been studied experimentally and theoretically. Those with 9 mol% Al-added, sintered at 850°C, exhibit good gas sensing responses to CO and CH 4. Well formed polycrystalline particles, essential to good gas sensing properties, are observed. XRD data show that the Al is dissolved into the material. The improvement in the gas sensing performance is attributed to the increase of the specific surface area caused by this aluminum addition. Variation of surface energy due to the Al-doped iron(III) oxide is modeled with two- and three-dimensional periodic structures. The results show that stronger relaxation leads to a stabilization of the surface in the case of Al addition compared to that without Al addition. Without relaxation, the non Al-added surface has a much lower surface energy than the Al-added surface. Although the energy difference between the relaxed surfaces is small, it indicates that the growth of Al-added iron oxide is less exothermic than that of pure iron oxide, which would explain the smaller particle size and hence the increased surface area observed after Al addition.

Combinatorial Mapping of Polymer Film Wettability On Gradient Energy Surfaces

AbstractCombinatorial methods were used for studying dewetting of thin hydrophobic polystyrene (PS) and hydrophilic poly(DL-lactic acid) (PDLA) films on chemically modified gradient energy surfaces. Substrate libraries were prepared by immersing passivated Si (Si-H surface functionality) in Piranha solution (H2SO4/H2O2/H2O) at acontrolled rate, yielding a systematic variation of solvent contact angles across the surface. Additionally, chlorosilane-treated Si surfaces were exposed to UV radiation in a gradient fashion under ozone atmosphere such that a range from hydrophobic to hydrophilic conditions was obtained across the surface (≈ 3 cm). Solvent droplet contact angles of water and diiodo methane were used to quantify the spatial variation of surface energy along one axis across the surface. Libraries of thin films of PS or PDLA coatings on gradient energy surfaces orthogonal to gradients in film thickness were screened for dewetting behavior using automated optical microscopy. Contrasting trends in the wettability of PS and PDLA were visibly apparent as a function of surface energy of the substrate. The number density of polygons of the dewet PS films was found to obey a power law relationship with both film thickness and substrate surface hydrophilicity.

Stepwise adsorption of a long trichlorosilane and a short aminosilane

A mixed film of microscopic heterogeneity was formed by stepwise deposition of a long-chain organosilane n-octadecyltrichlorosilane (OTS) and a short-chain organosilane aminobutyldimethylmethoxysilane (ABS). The amount of silane deposited on an oxidized silicon substrate was controlled kinetically by varying the dip time in each silane solution. The binary film was characterized by the atomic force microscopy (AFM), infrared attenuated total internal reflection (IR-ATR), and contact angle goniometry. OTS forms a monolayer structure whose fractional surface coverage and surface energy can be precisely controlled. ABS agglomerates slowly to form island structure and is ineffective in surface energy or composition variation. The contact angles on sub-monolayers of OTS follows the Cassie equation, while the contact angle of the binary OTS and ABS film deviates positively from the equation.

A computational model for incompressible flow including surface tension

In this communication a computational model for incompressible flow with the effect of surface tension is briefly described. The formulation for calculating surface tension is developed based on a variational approach. It is assumed that the variations in surface energy, which may contribute to the fluid motion, should not change the total energy. A formulation expressed in the colour function is then derived. The colour function is computed by an advection scheme that predicts the first order spatial derivatives of the colour function as well. The first order derivative computed directly from the advection equation is then used to find the surface tension related quantities.

Isothermal microcalorimetry and inverse phase gas chromatography to study small changes in powder surface properties

It is known that processing can alter the surface energetics of powders. In this study a sample of drug has been processed by use of different drying techniques. The samples were then assessed using inverse phase gas chromatography. It was seen that the original material had a highest surface energy and the tray-dried sample had the lowest energy surface, other samples were intermediate. The use of isothermal microcalorimetry to study water sorption to the powders revealed that the surface of the original material was unstable, as the water sorption response changed on repeat cycling. The tray-dried sample did have a stable surface which gave the same sorption response on repeat exposure to water vapour. It was concluded that the drug had minor variations in surface energy, with the as received material being in a high energy unstable state, which could be due to it being partially amorphous. The tray-dried sample had a lower energy stable surface. In certain applications differences in surface energetics could be expected to lead to changes in processing nature of the powder, so these vapour sorption techniques offer a good way of providing an assurance of the same surface energy between batches of nay material which may be at risk.

Variation De L'énergie Superficielle D'une Bentonite Par Traitement Chimique Et Thermique

Variation of surface energy of a bentonite by chemical and thermal treatments. The effect of an attack by hydrochloric acid and of thermal treatments on the dispersive surface energy, γ d s, and on the morphology index of a bentonite has been studied by inverse gas chromatography at infinite dilution. The results show that γ d s is very sensitive to two parameters: one is the atomic scale morphology of the clay material, the other one is the mineral impurity contents, mainly composed of alkaline and alkaline-earth oxides. The large increase of γ d s after a moderate treatment [t < 10 h, HC1 < 2N and thermal treatment temperature (TTT)≤300°C] is attributed to the bentonite purification and to the lateral surface appearence. However, a more severe treatment (t>10h, HC1 >3N et TTT > 500°C) destroys the lamellar structure of the montmorillonite and in this case the measured γ d s is attributed to the basal surface.

Stress Concentration Induced by Variation of Surface Energy in Half-Anisotropic Materials.

The author has performed the analyses of stress and deformation taking into account a surface energy, which exists at the surface and interface dividing phases. In the present paper, the equilibrium formulation considering the surface energy previously deduced by author is used for calculating the stress and deformation. The problem that the surface energy in a half region of a half-infinite anisotropic materials varies is analyzed by using the theory of elasticity. This problem relates with the surface of contaminating, oxidizing or polluting by other materials. Hilbert transform techniques was used for solving an integral equation with respect to an unknown Fourier transform function in the analysis. Consequently, all stress components and displacements were deduced in a closed form. The shear components of bulk stress become infinite at the edge of discontinuity of the surface energy, and then the free suface deforms alike a step. This result may be suggest that cracking occurs easier in a chemically contaminated surface than in a clean one.

Interfacial Energy Balance Equation for Surface-Tension-Driven Bénard Convection

Existing theories for the surface-tension-driven B\'enard convection (Marangoni convection) have considered only thermocapillary effects through the shear stress balance equation at the interface via the surface-tension-gradient-induced shear stresses. Thermocapillary induced surface energy variation has been ignored altogether in these theories. A formulation taking into account this surface energy variation shows that it can have a non-negligible effect on the onset of B\'enard convection cells.

Shape change of a pore in a stressed solid via surface diffusion motivated by surface and elastic energy variation

When a solid is stressed at a high temperature, atoms may move along various paths, causing a pore preexisting in the solid to change shape. This paper assumes that atoms only diffuse on the pore surface and the solid is elastic. Both surface energy and elastic energy vary as the pore changes shape. When the surface energy variation dominates, the pore evolves to an equilibrium shape close to an ellipse. When the elastic energy variation dominates, the pore never reaches equilibrium; noses emerge and sharpen into crack tips. We describe the pore shape with a conformal mapping of many terms, determine the elastic field by a complex variable method, and evolve the mapping coefficients (and thereby the pore shape) by a set of ordinary differential equations. The numerical simulation gives the threshold for the shape instability, the time for a supercritical pore to grow crack tips, and the crack size when it just forms. Also explored are the effects of the applied stress state and surface tension anisotropy. We discuss the implications of the results for the lifetime of crystals stressed at elevated temperatures.

Theoretical aspects of self-stratification

In order to predict whether a system of two polymers or resins in a common solvent mixture will ‘self-stratify’, two predictive models, one based on UNIFAC and the other on surface tension relationships, have been developed. The UNIFAC model can predict phase behaviour, vapour pressure, evaporation rates and surface tensions for systems containing two polymers or resins in a solvent mixture. Comparisons between experimental and calculated data are made for acrylic/acrylic, epoxn/acrylic and alkyd/acrylic resin combinations. The prediction of phase separation during solvent evaporation from a thin film is satisfactory in most cases, especially when the difference in molecular weight between the two polymers is not too large. For epoxy/acrylic resin combinations, the calculated evaporation profiles are in reasonable agreement with observed values. The evaporation rate decreases with increasing epoxy molecular weight, but is almost independent of the acrylic resin and the resin ratio. The tendency of epoxy/acrylic resin combinations to undergo self stratification is predicted to increase as the molecular weight of the epoxy resin increases. The degree of phase separation is increased as the molecular weight of the acrylic resin is increased. These predictions agree with experimental observation but for acrylic/alkyd resin combinations, no phase separation is predicted which is not in agreement with experiment. This is probably because the model cannot allow for the broad molecular weight distribution of the alkyd resin. A second predictive model based on surface energy variation with concentration of two polymer solution phases in contact has been developed. This model can be used to predict which resin combinations will give rise to self-stratifying systems given the surface energy/concentration relationship of the pure resins in solution and assuming the systems have phase separated. For solutions of epoxy resins combined with a second resin the model correctly predicts the observed tendency for the resins to stratify provided the system phase separates at some point.

Electronic surface properties of alkali-metal alloys

A generalization of the stabilized jellium model (Perdew et al 1990, Phys. Rev. B 42 11 627) to random alkali-metal alloys is given and applied to calculations of the surface energy and the work function changes due to the concentration in the presence of surface segregation. The calculated variations in surface energy and work function against the concentration of the constituents are in good agreement with measurements.