Determination Of Contact Angle Research Articles

Surface Energetics of Protein Adsorption on to Chromatographic Supports

Protein separation behavior during adsorption chromatography is governed by system thermodynamics and kinetic factors. Hydrophobic interaction chromatography (HIC) is widely utilized since many important biological products present a quite hydrophobic character. In this work, the interaction between a set of model proteins (n = 9) and a commercial adsorbent (Phenyl Sepharose FF, high substitution, GE Healthcare) was studied via extended DLVO (XDLVO) calculations. Psychochemical properties of both separand and adsorbent were gathered by contact angle determination and zeta potential measurements. Proteins were subjected to the mentioned measurements in the hydrated and the dehydrated state, so as to simulate protein properties in a low vs. high salt concentration milieu, respectively. In HIC, protein adsorption usually take place at high concentrations of ammonium sulphate (up to 1.7M) and protein desorption occurs by decreasing salt concentration in the mobile phase. The mentioned XDLVO approach allowed the calculation of the free energy of interaction vs. distance profiles between the interacting surfaces, in the aqueous environment provided by the operating mobile phase. XDLVO calculations were correlated with the actual chromatography behavior of the studied model proteins. This correlation revealed that these proteins can be segregated in two main groups, according to surface energy calculations and elution position during chromatography: i) strong binding showing a deeper secondary minimum energy >|0.20| kT ii) and weak binding having a small secondary minimum energy <|0.12| kT, thus calculations were able to predict early or late elution from a gradient chromatography experiment; the more the calculated interaction energy, the stronger will be protein binding and the later will be the elution time. The knowledge generated from these studies will generate a better understanding of real downstream bioprocess behavior which could, in turn, facilitate process design and optimization.

A simple apparatus for the determining contact angle of water repellent fabrics

A simple apparatus for the determination of fabric-water contact angle of water repellent fabrics is described. It is based on the tilting plate principle and the additional advantage that the end point can be sharply ascertained by optical means.

Wettability Evaluation of a CO2/Water/Bentheimer Sandstone System: Contact Angle, Dissolution, and Bubble Size

The success of CO2 storage in deep saline aquifers and depleted oil and gas reservoirs is largely controlled by interfacial phenomena among fluid phases and rock pore spaces. Particularly, the wettability of the rock matrix has a strong effect on capillary pressure, relative permeability, and the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. Precise understanding of wettability behavior is therefore fundamental when injecting CO2 into geological formations to sequestrate CO2 and/or to enhance gas/oil production. In this study, the contact angles of Bentheimer sandstone/water/CO2 or flue gas have been evaluated experimentally using the captive-bubble technique in the pressure range from 0.2 to 15 MPa. The experiments were conducted using different compositions of aqueous phase with respect to CO2, i.e., unsaturated and fully saturated. It has been shown that a reliable contact-angle determination needs to be conducted using a pre-equilibrat...

Polyethersulfone/Poly(D,L‐lactide) Blend Membranes: Preparation, Characterization, and Performance

AbstractPolyethersulfone (PES) was blended with poly(D,L‐lactide) (PDLLA) to prepare asymmetric membranes using the phase inversion method. The effects of the blend ratios and poly(ethylene glycol) (PEG) as additive on the membrane structure, properties, and performance were investigated. The membranes were characterized by contact angle determination, scanning electron microscopy, porosity measurement, thermogravimetric analysis, degradation tests in compost, and dynamic tests for pure water flux and bakery product wastewater treatment. PES and PEG slightly reduced the membrane contact angle. Increasing the PDLLA concentration in the blend membranes enhanced the membrane degradation in compost and also the membrane porosity. The permeate flux of the membranes was improved, but the rejection of pollution indices did not change noticeably.

Study of sulfur heterogeneous nucleation from supersaturated vapor on tungsten oxide and sodium chloride seed particles. Determination of contact angle of critical sulfur nuclei

A procedure has been developed for determining the contact angle of a critical nucleus formed on seed particles during the heterogeneous nucleation of a vapor in a flow chamber. The procedure comprises the determination of the fraction of enlarged particles, as well as the selective separation of nanoparticles over sizes to locate the zone of intense nucleation. The concentration and size distribution of aerosol particles have been measured with a diffusion spectrometer of aerosols. Vapor concentration distributions and supersatura� tion fields have been determined by solving the masstransfer problem. The calculated supersaturation fields are in good agreement with the location of the intense nucleation zone experimentally found with the help of selective separation. The fractions of enlarged particles have been determined as functions of supersaturation in the chamber. A formula has been derived for calculating the fraction and size distribution function of enlarged particles at known supersaturation and temperature fields and a preset contact angle. The contact angles are selected in a manner such that the calculated fraction of enlarged particles coincides with that mea� sured experimentally. It has been revealed that the contact angle of critical sulfur nuclei formed on tungsten oxide seed particles with average radii 〈Rp〉 ≈ 5.8-4.4nm is in a range of 21.2-20.5°, while, in the case of sodium chloride seed particles with 〈Rp〉 ≈ 6.0-4.4 nm, the contact angle is 20.4-17.4°. The size of a critical nucleus has been found to be proportional to calculated average radius of a seed particle 〈R p 〉 in both cases.

Surface changes of biopolymers PHB and PLLA induced by Ar+ plasma treatment and wet etching

Polymers, especially group of biopolymers find potential application in a wide range of disciplines due to their biodegradability. In biomedical applications these materials can be used as a scaffold or matrix. In this work, the influence of the Ar+ plasma treatment and subsequent wet etching (acetone/water) on the surface properties of polymers were studied. Two biopolymers – polyhydroxybutyrate with 8% polyhydroxyvalerate (PHB) and poly-l-lactic acid (PLLA) were used in these experiments. Modified surface layers were analyzed by different methods. Surface wettability was characterized by determination of water contact angle. Changes in elemental composition of modified surfaces were performed by X-ray Photoelectron Spectroscopy (XPS). Surface morphology and roughness was examined using Atomic Force Microscopy (AFM). Gravimetry method was used to study the mass loss. It was found that the modification from both with plasma and wet etching leads to dramatic changes of surface properties (surface chemistry, morphology and roughness). Rate of changes of these features strongly depends on the modification parameters.

A Rapid One-Step Fabrication of Patternable Superhydrophobic Surfaces Driven by Marangoni Instability

We present a facile and inexpensive approach without any fluorinated chemistry to create superhydrophobic surface with exceptional liquid repellency, transportation of oil, selective capture of oil, optical bar code, and self-cleaning. Here we show experimentally that the control of evaporation is important and can be used to form superhydrophobic surface driven by Marangoni instability: the method involves in-situ photopolymerization in the presence of a volatile solvent and porous PDMS cover to afford superhydrophobic surfaces with the desired combination of micro- and nanoscale roughness. The porous PDMS cover significantly affects Marangoni convection of coating fluid, inducing composition gradients at the same time. In addition, the change of concentration of ethanol is able to produce versatile surfaces from hydrophilic to superhydrophobic and as a consequence to determine contact angles as well as roughness factors. In conclusion, the control of evaporation under the polymerization provides a convenient parameter to fabricate the superhydrophobic surface, without application of fluorinated chemistry and the elegant nanofabrication technique.

Investigation on nanoadhesive bonding of plasma modified titanium for aerospace application

Physico-chemical changes of the plasma modified titanium alloy [Ti-6Al-4V] surface were studied with respect to their crystallographic changes by X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM).The plasma-treatment of surface was carried out to enhance adhesion of high performance nano reinforced epoxy adhesive, a phenomenon that was manifested in subsequent experimental results. The enhancement of adhesion as a consequence of improved spreading and wetting on metal surface was studied by contact angle (sessile drop method) and surface energy determination, which shows a distinct increase in polar component of surface energy. The synergism in bond strength was established by analyzing the lap-shear strength of titanium laminate. The extent of enhancement in thermal stability of the dispersed nanosilica particles reinforced epoxy adhesive was studied by Thermo Gravimetric Analysis (TGA), which shows an increase in onset of degradation and high amount of residuals at the high temperature range under study. The fractured surfaces of the joint were examined by Scanning electron microscope (SEM).

Hydrolysis time influence in obtaining hybrid film with addition of cerium ions for protecting galvanized steels

The hybrid films act as a barrier layer between the substrate and the environment. This kind of coating reduces the electrolyte permeability, decreasing the corrosion rate of the substrate. However, many variables influenced the corrosion resistance of hybrid coating. The main factors that influence the thickness of the films are: temperature, curing time, the concentration alcooxide precursors on the bath, the pH of the hydrolysis and the hydrolysis time. In this study, the galvanized steel was coated with and hybrid film obtained from precursors consisting of a sol alcooxide 3-(trimetoxisililpropil) methacrylate (TMSPMA) and tetraethoxysilane (TEOS) with cerium nitrate addition [0,01 M]. The hydrolysis time was varied in four levels of (1, 3, 24 and 48 hours). The characterization of the films was performed by SEM, profilometry, contact angle determination, polarization and electrochemical impedance spectroscopy measurements. Results showed that the hydrolysis time presented influence on the hybrid film properties and consequently on the protection.

Modifications induced by gamma irradiation to Makrofol polymer nuclear track detector

The aim of the present study was extended from obtaining information about the interaction of gamma rays with Makrofol DE 7-2 track detector to introduce the basis that can be used in concerning simple sensor for gamma irradiation and bio-engineering applications. Makrofol polymer samples were irradiated with 1.25MeV 60Co gamma radiations at doses ranging from 20 to 1000kGy. The modifications of irradiated samples so induced were analyzed using UV–vis spectrometry, photoluminescence spectroscopy, and the measurements of Vickers’ hardness. Moreover, the change in wettability of irradiated Makrofol was investigated by the contact angle determination of the distilled water. UV–vis spectroscopy shows a noticeable decrease in the energy band gap due to gamma irradiation. This decrease could be attributed to the appearance of a shift to UV spectra toward higher wavelength region after irradiation. Photoluminescence spectra reveal a remarkable change in the integrated photoluminescence intensity with increasing gamma doses, which may be resulted from some matrix disorder through the creation of some defected states in the irradiated polymer. The hardness was found to increase from 4.78MPa for the unirradiated sample to 23.67MPa for the highest gamma dose. The contact angle investigations show that the wettability of the modified samples increases with increasing the gamma doses. The result obtained from present investigation furnishes evidence that the gamma irradiations are a successful technique to modify the Makrofol DE 7-2 polymer properties to use it in suitable applications.

Molecular Simulation of Carbon Dioxide, Brine, and Clay Mineral Interactions and Determination of Contact Angles

Capture and subsequent geologic storage of CO2 in deep brine reservoirs plays a significant role in plans to reduce atmospheric carbon emission and resulting global climate change. The interaction of CO2 and brine species with mineral surfaces controls the ultimate fate of injected CO2 at the nanoscale via geochemistry, at the pore-scale via capillary trapping, and at the field-scale via relative permeability. We used large-scale molecular dynamics simulations to study the behavior of supercritical CO2 and aqueous fluids on both the hydrophilic and hydrophobic basal surfaces of kaolinite, a common clay mineral. In the presence of a bulk aqueous phase, supercritical CO2 forms a nonwetting droplet above the hydrophilic surface of kaolinite. This CO2 droplet is separated from the mineral surface by distinct layers of water, which prevent the CO2 droplet from interacting directly with the mineral surface. Conversely, both CO2 and H2O molecules interact directly with the hydrophobic surface of kaolinite. In the presence of bulk supercritical CO2, nonwetting aqueous droplets interact with the hydrophobic surface of kaolinite via a mixture of adsorbed CO2 and H2O molecules. Because nucleation and precipitation of minerals should depend strongly on the local distribution of CO2, H2O, and ion species, these nanoscale surface interactions are expected to influence long-term mineralization of injected carbon dioxide.

Measuring contact angle and meniscus shape with a reflected laser beam

Side-view imaging of the contact angle between an extended planar solid surface and a liquid is problematic. Even when aligning the view perfectly parallel to the contact line, focusing one point of the contact line is not possible. We describe a new measurement technique for determining contact angles with the reflection of a widened laser sheet on a moving contact line. We verified this new technique measuring the contact angle on a cylinder, rotating partially immersed in a liquid. A laser sheet is inclined under an angle φ to the unperturbed liquid surface and is reflected off the meniscus. Collected on a screen, the reflection image contains information to determine the contact angle. When dividing the laser sheet into an array of laser rays by placing a mesh into the beam path, the shape of the meniscus can be reconstructed from the reflection image. We verified the method by measuring the receding contact angle versus speed for aqueous cetyltrimethyl ammonium bromide solutions on a smooth hydrophobized as well as on a rough polystyrene surface.

Experimental study on advantages of foam–sol in coal dust control

In China, more than 2.65 million coal mine workers are exposed to coal dust. Every year, new pneumoconiosis cases amount to 25,000, among which 6000 cases die of this disease. The figure is twice the death toll in production safety accidents. Occupational diseases seriously endanger life and health of coal mine workers, and restrict the healthy growth of the coal industry.The paper presented a study of foam–sol-based coal dust control. This was an experimental study of characteristics of foam–sol-based coal dust control, which features dust capture, suppression, and isolation. Comparative wettability experiments were carried out to determine contact angles of water, aqueous foam, and foam–sol solution. A new foam–sol generating system with a conical diffuser outlet was proposed.The experiment results clearly showed that the foam–sol features dust capture, suppression, and isolation. The wettability of the aqueous foam solution was better than the foam–sol solution, but the foam–sol technology had the better ability to capture the airborne dust, suppress the static dust and enclose the dust source, due to the excellent surface viscosity, strong cohesiveness and less volatile property. The paper concluded that the foam–sol could greatly improve the dust control efficiency and did not have main deficiencies that the aqueous foam technology had.

Preparation and characterization of bipolar membranes modified by cystine-modified TiO2 visible-light photocatalyst

A cystine-modified TiO2 visible-light photocatalyst was prepared by the sol–gel method and characterized by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and X-ray photoelectron spectroscopy (XPS). The XRD results showed the cystine-modified TiO2 was in the anatase phase, but with reduced size. UV–Vis DRS indicated that cystine-modification could reduce the band gap of TiO2 and enhance the absorption of visible light. The XPS spectra showed that the cystine-modified TiO2 sample contained C, N, and S, and that some of the C, N, and S entered the TiO2 lattice. The cystine-modified TiO2 visible-light photocatalyst was added to a chitosan (CS) anion-exchange layer to prepare PVA–CMC/modified TiO2–PVA–CS bipolar membrane (BPM; here, PVA denotes poly(vinyl alcohol), CMC denotes carboxymethylcellulose, and the solidus “/” denotes the interlayer) by a paste method. The membrane was characterized by determination of contact angle, J–V characteristics, and AC impedance spectroscopy, among other techniques. Experimental results showed that the cystine-modified TiO2 visible-light photocatalyst was a better photocatalyst than TiO2 for splitting of water at the interlayer of the BPM. The membrane impedance and trans-membrane voltage drop (IR drop) of the modified BPM clearly decreased under sunlight irradiation. At a current density of 60 mA/cm2, the cell voltage of the PVA–CMC/modified TiO2–PVA–CS BPM decreased by 0.9 V. Moreover, the hydrophilicity of the modified BPM was increased and its mechanical properties were improved.

High-precision drop shape analysis on inclining flat surfaces: Introduction and comparison of this special method with commercial contact angle analysis

Drop shape analysis is one of the most important and frequently used methods to characterise surfaces in the scientific and industrial communities. An especially large number of studies, which use contact angle measurements to analyse surfaces, are characterised by incorrect or misdirected conclusions such as the determination of surface energies from poorly performed contact angle determinations. In particular, the characterisation of surfaces, which leads to correlations between the contact angle and other effects, must be critically validated for some publications. A large number of works exist concerning the theoretical and thermodynamic aspects of two- and tri-phase boundaries. The linkage between theory and experiment is generally performed by an axisymmetric drop shape analysis, that is, simulations of the theoretical drop profiles by numerical integration onto a number of points of the drop meniscus (approximately 20). These methods work very well for axisymmetric profiles such as those obtained by pendant drop measurements, but in the case of a sessile drop onto real surfaces, additional unknown and misunderstood effects on the dependence of the surface must be considered. We present a special experimental and practical investigation as another way to transition from experiment to theory. This procedure was developed to be especially sensitive to small variations in the dependence of the dynamic contact angle on the surface; as a result, this procedure will allow the properties of the surface to be monitored with a higher precession and sensitivity. In this context, water drops onto a 111 silicon wafer are dynamically measured by video recording and by inclining the surface, which results in a sequence of non-axisymmetric drops. The drop profiles are analysed by commercial software and by the developed and presented high-precision drop shape analysis. In addition to the enhanced sensitivity for contact angle determination, this analysis technique, in combination with innovative fit algorithms and data presentations, can result in enhanced reproducibility and comparability of the contact angle measurements in terms of the material characterisation in a comprehensible way.

On the Calculation of Solid-Fluid Contact Angles from Molecular Dynamics

A methodology for the determination of the solid-fluid contact angle, to be employed within molecular dynamics (MD) simulations, is developed and systematically applied. The calculation of the contact angle of a fluid drop on a given surface, averaged over an equilibrated MD trajectory, is divided in three main steps: (i) the determination of the fluid molecules that constitute the interface, (ii) the treatment of the interfacial molecules as a point cloud data set to define a geometric surface, using surface meshing techniques to compute the surface normals from the mesh, (iii) the collection and averaging of the interface normals collected from the post-processing of the MD trajectory. The average vector thus found is used to calculate the Cassie contact angle (i.e., the arccosine of the averaged normal z-component). As an example we explore the effect of the size of a drop of water on the observed solid-fluid contact angle. A single coarse-grained bead representing two water molecules and parameterized using the SAFT-γ Mie equation of state (EoS) is employed, meanwhile the solid surfaces are mimicked using integrated potentials. The contact angle is seen to be a strong function of the system size for small nano-droplets. The thermodynamic limit, corresponding to the infinite size (macroscopic) drop is only truly recovered when using an excess of half a million water coarse-grained beads and/or a drop radius of over 26 nm.

Wettability of Supercritical Carbon Dioxide/Water/Quartz Systems: Simultaneous Measurement of Contact Angle and Interfacial Tension at Reservoir Conditions

Injection of carbon dioxide in deep saline aquifers is considered as a method of carbon sequestration. The efficiency of this process is dependent on the fluid-fluid and rock-fluid interactions inside the porous media. For instance, the final storage capacity and total amount of capillary-trapped CO2 inside an aquifer are affected by the interfacial tension between the fluids and the contact angle between the fluids and the rock mineral surface. A thorough study of these parameters and their variations with temperature and pressure will provide a better understanding of the carbon sequestration process and thus improve predictions of the sequestration efficiency. In this study, the controversial concept of wettability alteration of quartz surfaces in the presence of supercritical carbon dioxide (sc-CO2) was investigated. A novel apparatus for measuring interfacial tension and contact angle at high temperatures and pressures based on Axisymmetric Drop Shape Analysis with no-Apex (ADSA-NA) method was developed and validated with a simple system. Densities, interfacial tensions, and dynamic contact angles of CO2/water/quartz systems were determined for a wide range of pressures and temperatures relevant to geological sequestration of CO2 in the subcritical and supercritical states. Image analysis was performed with ADSA-NA method that allows the determination of both interfacial tensions and contact angles with high accuracy. The results show that supercritical CO2 alters the wettability of quartz surface toward less water-wet conditions compared to subcritical CO2. Also we observed an increase in the water advancing contact angles with increasing temperature indicating less water-wet quartz surfaces at higher temperatures.

Adaptation of the Hydrocarbonoclastic Bacterium Alcanivorax borkumensis SK2 to Alkanes and Toxic Organic Compounds: a Physiological and Transcriptomic Approach

The marine hydrocarbonoclastic bacterium Alcanivorax borkumensis is able to degrade mixtures of n-alkanes as they occur in marine oil spills. However, investigations of growth behavior and physiology of these bacteria when cultivated with n-alkanes of different chain lengths (C6 to C30) as the substrates are still lacking. Growth rates increased with increasing alkane chain length up to a maximum between C12 and C19, with no evident difference between even- and odd-numbered chain lengths, before decreasing with chain lengths greater than C19. Surface hydrophobicity of alkane-grown cells, assessed by determination of the water contact angles, showed a similar pattern, with maximum values associated with growth rates on alkanes with chain lengths between C11 and C19 and significantly lower values for cells grown on pyruvate. A. borkumensis was found to incorporate and modify the fatty acid intermediates generated by the corresponding n-alkane degradation pathway. Cells grown on distinct n-alkanes proved that A. borkumensis is able to not only incorporate but also modify fatty acid intermediates derived from the alkane degradation pathway. Comparing cells grown on pyruvate with those cultivated on hexadecane in terms of their tolerance toward two groups of toxic organic compounds, chlorophenols and alkanols, representing intensely studied organic compounds, revealed similar tolerances toward chlorophenols, whereas the toxicities of different n-alkanols were significantly reduced when hexadecane was used as a carbon source. As one adaptive mechanism of A. borkumensis to these toxic organic solvents, the activity of cis-trans isomerization of unsaturated fatty acids was proven. These findings could be verified by a detailed transcriptomic comparison between cultures grown on hexadecane and pyruvate and including solvent stress caused by the addition of 1-octanol as the most toxic intermediate of n-alkane degradation.

Durable Hydrophobic Treatment of Cotton Fabrics with Glycidyl Stearate

Glycidyl stearate (GS) obtained by reaction of sodium stearate with epichlorohydrin in the presence of dimethylformamide (DMF) was used for durable hydrophobic finishing of cotton fabrics. The presence of glycidyl stearate on hydrophobic treated cellulose fiber was put into evidence by FTIR, SEM, and EDX analyses. The hydrophobicity of the treated sample was assessed by determination of the water contact angles and absorption times of the water drops. The effects of glycidyl ester concentration, temperature, and duration of curing treatment on hygroscopicity, air permeability, whiteness, and tensile strength were evaluated. The best results regarding the use of glycidyl stearate as a hydrophobization agent (water contact angle is 152, absorption time of water drop is 200 min) were obtained for the samples treated with 60 g/L glycidyl stearate and 10 g/L NaOH at 120 °C condensation temperature for 20 min. The durability of hydrophobic treatment was also examined.

Determination of contact angle of polymer compositions for irrigators of cooling towers

The authors studied the contact angles of polymer compositions with a different content of a woodflour. It has been established that with increasing of concentrations of woodflour in the polymer composition, the contact angle decreases substantially, i.e. increases the hydrophilicity of the sprinkler which leads to slow movement of the water film, increasing its ability to spread. The results can be applied to improve the efficiency of cooling towers.