Contact Angle Data Research Articles

Dilute surfactants for wettability alteration and enhanced oil recovery in carbonates

The effectiveness of dilute nonionic surfactant was evaluated in this study for wettability alteration and enhanced oil recovery (EOR) in carbonates by performing a suite of measurements such as aqueous stability, surface tension, phase behavior, interfacial tension (IFT), zeta potential, contact angle, and microscopic dynamic oil liberation. Two different brines, low salinity and high salinity, were used at 0.1 wt% surfactant concentration. These measurements were conducted at elevated temperature using the rock and crude oil samples from a carbonate reservoir. The dilute concentration of polymer has also been used together with surfactant in both high salinity and low salinity brines to quantify the effects of wettability alteration on microscopic oil liberation efficiency in carbonates.The compatibility of nonionic surfactant was demonstrated in high salinity brine at reservoir temperature. The critical micelle concentrations were found to be very low in both low salinity and high salinity brines. The phase behavior results showed the formation of middle phase microemulsion and correspondingly low interfacial tensions in high salinity brine. The contact angle data indicated the ability of nonionic surfactant to significantly alter the wettability of carbonate from oil-wet to either intermediate wet or less oil-wet in high salinity brine whereas only marginal wettability alterations from oil-wet to less oil-wet were obtained in low salinity brine. The increasing negative zeta potentials and the alteration of charge polarity from positive to negative were observed at crude oil-brine and calcite/brine interfaces, respectively due to surfactant in the high salinity brine. The microscopic equilibrium degree of crude oil liberation from carbonate surface was found to be about 20% higher with high salinity surfactant-polymer solution when compared to the low salinity surfactant-polymer solution. Such higher oil release efficiency obtained with high salinity surfactant-polymer solution can be attributed to the beneficial effects of surfactant induced wettability alteration and IFT reduction mechanisms in the high salinity brine to favorably alter both capillary and adhesion forces for efficient EOR in carbonates.

The effect of attached tetracycline and hydrophilic groups on the enhancement of antibacterial effectiveness and low temperature flexibility of polyurethane

Tetracycline was chemically attached to polyurethane (PU) to enhance its antimicrobial activity, and a carboxyl group or polyol was also attached to PU to enhance the hydrophilicity. The attached groups affected cross‐linking, viscosity of PU solution, glass transition of soft segment, breaking tensile stress, reliable shape recovery capability, flexibility at very low temperature, surface hydrophilicity, and antibacterial effectiveness. The glass transition temperature could go up from −67.5°C for unmodified PU to −48.8°C due to the attached tetracycline. The attachment of tetracycline boosted breaking tensile stress and shape recovery by 345% and 186%, respectively, relative to unmodified PU. The attached carboxyl group and polyol improved the hydrophilicity as confirmed by water swelling and water contact angle data. Finally, PU samples with the attached tetracycline demonstrated excellent flexibility at freezing temperature compared with ordinary PU and absolutely inhibited the bacterial growth of S. aureus and K. pneumoniae on PU.

Surface Morphologies and Durability on Water Contact Angle of Titanium Dioxide Nanoparticle Thin Films

Titanium dioxide nanoparticle thin films on the glass slide of 5x20 cm2 as substrate were prepared by sparking method. The sparking system was modified by using titanium wires as an anode of 9 pieces and a cathode of 9 pieces which set the gap between the electrodes of 1 mm and connected a high voltage power supply. The sparking method was controlled a surface temperature of substrate as 26, 100 and 150 OC and a sparking time of 1-5 h in air atmosphere. The as-deposited thin films were analyzed by a scanning electron microscope, measured the water contact angle of 180 days and studied the durability of thin films on glass substrate to the drop water. The result indicated that the optimum condition of the as-deposited thin films was shown at the sparking time of 4 h and surface temperature of 150 OC which shown the homogeneity surface, the hydrophilic properties. The water contact angle increased with increasing the sparking time whereas the increasing surface temperature was found the decreasing of water contact angle. The optimum durability of thin films was used a minimum of a standard deviation (S.D.) at 4.27 which calculated from the water contact angle data from 1-180 days.

Antibiofouling Performance by Polyethersulfone Membranes Cast with Oxidized Multiwalled Carbon Nanotubes and Arabic Gum

Despite extensive research efforts focusing on tackling membrane biofouling, one of the biggest problems associated with membrane technology, there has been little headway in this area. This study presents novel polyethersulfone (PES) membranes synthesized via a phase inversion method at incremental loadings of functionalized oxidized multiwalled carbon nanotubes (OMWCNT) along with 1 wt. % arabic gum (AG). The synthesized OMWCNT were examined using scanning electron microscopy and transmission electron microscopy for morphological changes compared to the commercially obtained carbon nanotubes. Additionally energy-dispersive X-ray spectroscopy was carried out on the raw and OMWCNT materials, indicating an almost 2-fold increase in oxygen content in the latter sample. The cast PES/OMWCNT membranes were extensively characterized, and underwent a series of performance testing using bovine serum albumin solution for fouling tests and model Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial species for anti-biofouling experiments. Results indicated that the composite PES membranes, which incorporated the OMWCNT and AG, possessed significantly stronger hydrophilicity and negative surface charge as evidenced by water contact angle and zeta potential data, respectively, when compared to plain PES membranes. Furthermore atomic force microscopy analysis showed that the PES/OMWCNT membranes exhibited significantly lower surface roughness values. Together, these membrane surface features were held responsible for the anti-adhesive nature of the hybrid membranes seen during biofouling tests. Importantly, the prepared membranes were able to inhibit bacterial colonization upon incubation with both Gram-positive and Gram-negative bacterial suspensions. The PES/OMWCNT membranes also presented more resilient normalized flux values when compared to neat PES and commercial membrane samples during filtration of both bacterial suspensions and real treated sewage effluents. Taken together, the results of this study allude to OMWCNT and AG as promising additives, for incorporation into polymeric membranes to enhance biofouling resistance.

Impact of the Interfacial Energy and Density Fluctuations on the Shift of the Glass-Transition Temperature of Liquids Confined in Pores

The behavior of the low- and high-molecular weight glass formers confined in nanoporous templates remains an unsolved puzzle despite the intensive long-term studies in this matter. Special effort is taken to understand the enhancement of segmental or structural dynamics and the depression of the glass-transition temperatures, Tgs in materials infiltrated in pores of the nanometric size. In this paper, we have analyzed dielectric, calorimetric, and contact angle data collected for various systems to determine which factors are responsible for these effects. It turned out that with increasing interfacial energy, molecules attached to the pore walls (interfacial layer) vitrify at higher temperatures. Moreover, the dynamics of core molecules starts to deviate from bulk-like behavior. Therefore, a greater depression of the glass-transition temperature, Tg, of this fraction of molecules is noted. Also, it was found that the sensitivity of structural dynamics to the density fluctuations, quantified by the pressu...

Statistical Analysis of the Accuracy of Solid Surface Tensions Calculated from Error-Included Contact Angle and Liquid Surface Tension Data by the Multi-component Approach

Both exclusive and synergetic effects of errors in contact angle (CAEs) and liquid surface tension data (LSTEs) on the accuracy and statistics of solid surface tension components and parameters (SSTCPs)/square roots of SSTCPs (SQSSTCPs) were investigated. The calculations were done by Monte Carlo simulations covering the whole ranges of CAs or SSTCPs that can be determined by the most widely used liquid triplets. The results showed that on most part of valid domains the multi-component approach determined SSTCPs/SQSSTCPs at moderate accuracy even when both input errors were involved. However, the approach should be applied with caution on domains where the relative-root-mean-square errors of SSTCPs were higher than 20 % due to the reduced accuracy and skewed distributions of SSTCPs which made sample mean no longer a preferred measure of central tendency of the distribution. The results revealed the necessity of statistical consideration in evaluation and application of the multi-component approach.

Evaporation and instability of an unbounded-axisymmetric liquid bridge between chemically similar and different substrates

HypothesisIn this manuscript we examine the stability of an evaporating-unbounded axisymmetric liquid bridge confined between parallel-planar similar or chemically different substrates using both theory and experiments. With a quasistatic assumption we use hydrostatics to estimate the minimum stable volume Vmin via the Young-Laplace equation for Bond numbers 0⩽Bo⩽1, and top/bottom wall contact angles 5°<θ<175° although the primary focus is on wetting and partial wetting fluids. Solving the Young-Laplace equation requires knowledge of appropriate capillary pressure values, which appear as a constant, and may not provide unique solution. To examine uniqueness of numerical solutions and volume minima determined from the Young-Laplace equation for unbounded-axisymmetric liquid bridges we analyzed capillary pressure for large and small liquid volume-asymptotic limits at zero Bond number. ExperimentsExperiments were performed to compare with the volume minima calculations for Bond numbers 0.04⩽Bo⩽0.65. Three substrates of varying surface energy were used, with purified water as the primary liquid. Volume estimates and contact angle data were extracted via image analysis and evaporation rates measured from this data are reported. FindingsVolume minima were in the range 0.1<Vmin<20 μl depending on Bond number. There was good agreement when comparing predicted volume minima and those determined from experiments for the range of parameters studied.

Hydrophobicity and resistance against microorganisms of heat and chemically crosslinked poly(vinyl alcohol) nanofibrous membranes

Poly(vinyl alcohol) (PVA) is a water-soluble, semi-ionic and biocompatible polymer with excellent chemical and thermal stability. The chemical crosslinking of PVA membrane improve its stability towards humidity and water. In the present work, PVA nanofibrous membranes were fabricated using roller electrospinning techniques. The prepared membranes were crosslinked by heat treatment, glutaraldehyde dipping, and glutaraldehyde vapour. Furthermore, octadecyltrichlorosilane (OTS) treatment was used for hydrophobization of the crosslinked membranes. The prepared crosslinked membranes were analysed by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). The hydrophobization of PVA nanofibrous membranes were analysed by employing optical goniometer and auto-dynamic vapour sorption (AVS) techniques. Further, the PVA membranes were tested against algae and mould growth at in-vitro laboratory conditions. The SEM and FTIR results revealed significant differences in the morphology of the PVA nanofibrous membranes and in chemical bond formation due to crosslinking treatments. Water contact angle and AVS data confirmed a hydrophobization of PVA membranes by the treatments.

Analytical derivation of a pH dependent contact angle equation and the relationship to industrial processes of energy concerns

Regarding Young's equation, three fundamental interfacial energies of interfacial tensions can be identified. One of these interfacial energies relevant to our purpose is that related to the solid-liquid interface and it can be pH dependent. Intermolecular theory of surface tension links the solid-liquid interfacial tension or energy to surface charge species of solids. These species are electrostatic and depend on the pH of the aqueous medium in contact with the solid surface. Therefore, a theoretical relationship between contact angle and pH of some kind is worth exploring based on the fundamental theories of pH dependent solid-liquid interfacial tension, given the pH dependent electric double layer.A review of the literature dealing with the pH-dependent contact angle shows that polynomial curves have been fitted to contact angle versus pH data. Based on established theoretical works dealing with surface charge theories related to the electric double layer found in the literature, we have derived a pH dependent contact angle equation that describes trends in published experimental data with a high degree of regression coefficient. We have also theoretically and experimentally validated our model. The industrial significance of our model lies in the fact that the solution for pH, when the derivative is equated to zero, gives the point of zero charge pH of solid surface, which is an approach that has already been used in published works without any theoretical justification. The relationship of our model to industrial operations of energy and environmental significance has been discussed.

Modeling Oil Recovery in Mixed-Wet Rocks: Pore-Scale Comparison Between Experiment and Simulation

To examine the need to incorporate in situ wettability measurements in direct numerical simulations, we compare waterflooding experiments in a mixed-wet carbonate from a producing reservoir and results of direct multiphase numerical simulations using the color-gradient lattice Boltzmann method. We study the experiments of Alhammadi et al. (Sci Rep 7(1):10753, 2017. https://doi.org/10.1038/s41598-017-10992-w) where the pore-scale distribution of remaining oil was imaged using micro-CT scanning. In the experiment, in situ contact angles were measured using an automated algorithm (AlRatrout et al. in Adv Water Resour 109:158–169, 2017. https://doi.org/10.1016/j.advwatres.2017.07.018), which indicated a mixed-wet state with spatially non-uniform angles. In our simulations, the pore structure was obtained from segmented images of the sample used in the experiment. Furthermore, in situ measured angles were also incorporated into our simulations using our previously developed wetting boundary condition (Akai et al. in Adv Water Resour 116(March):56–66, 2018. https://doi.org/10.1016/j.advwatres.2018.03.014). We designed six simulations with different contact angle assignments based on experimentally measured values. Both a constant contact angle based on the average value of the measured values and non-uniform contact angles informed by the measured values gave a good agreement for fluid pore occupancy between the simulation and the experiment. However, the constant contact angle assignment predicted 54% higher water effective permeability after waterflooding than that estimated for the experimental result, whereas the non-uniform contact angle assignment gave less than 1% relative error. This means that to correctly predict fluid conductivity in mixed-wet rocks, a spatially heterogeneous wettability state needs to be taken into account. The novelty of this work is to provide a direct pore-scale comparison between experiments and simulations employing experimentally measured contact angles, and to demonstrate how to use measured contact angle data to improve the predictability of direct numerical simulation, highlighting the difference between the contact angle required for the simulation of dynamic displacement process and the contact angle measured at equilibrium after waterflooding.

Non‐Destructive Surface Energy Measurements on (1 0 0) Galfenol

AbstractDeveloping protocols for making thin sheet FeGa (Galfenol) with abnormally grown Goss or Cube grains, which provide maximum magnetostriction, is challenging because the mechanisms that regulate grain boundary mobility and texture development in these alloys are not yet understood. Grain boundary energy models do not account for forces caused by the control of surface energy from atmospheric annealing conditions. By characterizing the surface energy of specific Galfenol grains, we can develop a more accurate thermodynamic framework for modeling abnormal grain growth and texture development. To non‐destructively measure surface energy of specific crystal orientations and overcome passivation layer difficulties in previous studies, a two‐liquid‐phase contact angle method is utilized. A single‐crystal (1 0 0) Fe82Ga18 is used as a proof of concept for its isotropic surface crystal orientation. The resultant contact angle data shows a high dependence on the use of Ar‐plasma surface preparation to remove native oxides exposing a true interaction between a sessile drop and the Galfenol surface. Experimentally measured surface energy values are in agreement with density functional theory simulations. Surface texture and composition are confirmed using EBSD and XPS measurements. This non‐destructive technique paves the way towards studying surface energies of bare metal surfaces.

Nanofiltration composite membranes of polyethersulfone and graphene oxide and sulfonated graphene oxide

AbstractIn the present study, the polyethersulfone (PES) mixed matrix nanofiltration membranes with the embedding of the graphene oxide (GO) and sulfonated graphene oxide (s‐GO) nanoparticles were fabricated via phase inversion method. The effect of GO and s‐GO on the morphology and performance‐fabricated PES membrane was evaluated in terms of pure water flux, dye retention, salt rejection, heavy metal removal, and antifouling properties. The fabricated membranes were characterized using FE‐SEM, AFM, and water contact angle and porosity measurement. As a result, by adding GO and s‐GO nanoparticles, the pure water flux (PWF) of mentioned membranes significantly improved due to the higher hydrophilicity. The increased hydrophilicity of the mentioned membranes was proved by the water contact angle data. The evaluation of nanofiltration performance was assessed by rejection measurement of cationic and anionic dyes. The rejection of heavy metals in the following order 97.5%, 87.8%, 76.3%, and 60.6% for Cr, Cd, Cu, and Ni, respectively, was obtained for the sample that contains 1 wt% s‐GO. Moreover, other nanocomposite membranes showed relatively good results. The rejection results showed that GO and s‐GO nanoparticles embedded membranes have higher dye retention ability than the bare PES. Fouling resistance of the membranes was evaluated by filtration of bovine serum albumin (BSA) solution. The results of antifouling properties showed that the membrane containing 0.5 wt% s‐GO had the best fouling resistance.

Effect of additional polishing methods on the physical surface properties of different nanocomposites: SEM and AFM study.

This evaluated the arrangement of filler particles in depth of nanocomposites, and surface roughness, wettability, microtopography, and micromorphology following additional polishing step. Forty samples of each composite tested [Filtek Z350XT (FZ), IPS Empress Direct (IP)] were fabricated and finished/polished/additionally polished using one of the following methods (n = 10/group): no finishing/polishing (NFP), Sof-Lex Pop-On + no additional polishing (SP), Sof-Lex Pop-On + Astropol rubber polisher (SP+A), and Sof-Lex Pop-On + felt disc with polishing paste (SP+FP). Surface roughness (Ra) and contact angles were measured using a profilometer and goniometer, respectively. Microtopography and micromorphology were evaluated using atomic force microscopy and scanning electron microscopy, respectively. Ra and contact angle data were examined by two-way analysis of variance and Tukey's test (p < .05). Organic matrix, lower and larger filler particles were disposed in depth. Mean Ra values were lowest and contact angles were smallest in the NFP group for both composite resins. SP+A and SP+FP decreased mean Ra in comparison with SP for FZ, whereas only SP+FP decreased mean Ra in comparison with SP for IP. Only SP+FP increased contact angles in comparison with SP for FZ, whereas contact angles in the SP+A, SP+FP, and SP groups were similar for FZ. Both composites presented more uniform topography and smother surfaces following SP+A and SP+FP in comparison with SP. Therefore, additional polishing improved surface smoothness and decreased wettability of the composite resins studied. SP+FP produced smoother and less wettable surfaces for FZ and IP.

CNT/PVP blend PVDF membranes for the removal of organic pollutants from simulated treated wastewater effluent

In this work, we established a simple and effective way of immobilizing CNT onto polyvinylidene fluoride (PVDF) membrane by casting dual-layer membranes. We explored two different methods of dual-layer casting: (i) layer by layer and (ii) simultaneous dual layer fabrication. The influence of these methods on the characteristics of the prepared membranes were investigated. The hydrophilicity of the top surface was ensured by blending appropriate quantity of polyvinyl pyrrolidone (PVP) into the polymer dope so that the feed water and its organic pollutant content have adequate contact with the membrane surface containing the CNT. Dynamic contact angle data revealed that CNT blend PVDF membranes were highly hydrophilic when compared to their pristine counterparts. Single layer and simultaneous cast double layer blend membranes showed bigger pores (∼10 μm), whereas layer-by-layer cast double layer blend membrane showed acceptable lower mean pore size (∼0.25 μm). Adsorption experiments were done using methylene blue (MB) as a model adsorbate. Composite membranes performed better in the removal of MB, while also showing high rate of filtration. This was achieved due to better membrane wettability, more open structure and higher concentration of CNT on the top surface of the blend membranes. An almost complete desorption of MB off the membrane surface was successfully accomplished using ethanol solution at a pH of 2, indicating the possible cyclic application of these membranes.

Preparation and characterization of modified ultrafiltration nylon 6 membrane modified by poly (acrylamide-co-maleic anhydride)

In attempt to prepare modified ultrafiltration (UF) Nylon 6 membrane and improve its hydrophilicity and anti-fouling performance, poly (acrylamide-co-maleic anhydride)(AM-MA) was utilized as hydrophilic copolymer additive in the dope solution. The UF Nylon 6/AM-MA membranes were synthesized through blending Nylon 6 with poly(AM-MA) using a phase inversion process. Characterization of the prepared membranes for morphological studies and thermal behavior was carried out by SEM and DSC instruments respectively. The SEM photos demonstrated that by increasing the copolymer density in the dope solution, the morphology was changed from spongy to bi-continuous, composed of small interlocked and stick-like crystallites. FTIR/ATR and water contact angle data also confirmed the existence of AM-MA copolymer on the blend membranes surface. Furthermore, the effect of different molecular weights and concentration of hydrophilic copolymer on filtration performance and antifouling properties were experimentally studied. The results exhibited that the blend UF membranes possessed better water flux permeability than pure Nylon 6 membrane due to the increased surface hydrophilicity and porosity. Fouling resistance experiments revealed that the surface anti-fouling ability of the blend membranes was improved via the addition of AM-MA copolymer with lower MW (co1) to the cast solution, while this parameter was weakened in higher MW of copolymer (co2).

Alignment of liquid crystal molecules on self-assembled monolayer with fluorinated alkyl chain at different deposition time

We demonstrated a homeotropic liquid crystal (LC) alignment state on fluorinated self-assembled monolayers (FSAMs) deposited by gas-phase method as a function of deposition time. The gas-phase method to deposit FSAMs was simple process and cost-effective. Contact angle data and surface energy analyses of the FSAMs showed that film formation occurs, and showed a correlation with the homeotropic alignment of LC molecules on the FSAMs. Stable LC alignments on FSAMs were achieved at deposition time over 60 min. In addition, high transparency and thermal stability of FSAM further enhanced its possibility as a LC alignment layer.

Production and characterization of hydrophilic and hydrophobic sunflower protein isolate nanofibers by electrospinning method

In the present study, sunflower protein isolate (SPI) was extracted and applied for production of nanofiber using polyvinyl alcohol (PVA) in different SPI:PVA volume ratios (0:100, 20:80, 40:60, 60:40, 80:20 and 100:0) under two voltages (18 and 23 kV) and two flow rates (0.5 and 0.75 ml/h). Nanofibers with average diameters ranging from 304 to 400 nm were achieved. SPI:PVA volume ratio of 40:60 at voltage of 18 kV and flow rate of 0.75 ml/h were determined as the optimum conditions for electrospinning which produced bead-free and uniform nanofibers with average diameter of 398 nm. The effects of heating (150 °C, for 24 h) and calcium chloride (1% W/V) solution solely and together on nanofibers hydrophobicity were also examined. SEM images after 24 h soaking in lactate buffer (pH 5.5) showed that only heat treatment could make nanofibers hydrophobic, which was proved by contact angle data. FTIR analysis showed denaturation of protein and interactions between protein and PVA after heat treatment. Moreover, DSC and TGA results indicated miscibility of protein and PVA, and higher thermal stability of heat treated sample. This study showed the potential application of soy protein as a byproduct for production of both hydrophobic and hydrophilic nanofibers.

Experimental Investigation of the System Nonmetallic Inclusion-Molten Steel-Refractory System at High Temperatures

In continuous casting, the buildup of particles in the flow control system is called clogging. Clogging may be caused by preexisting nonmetallic inclusions attached to the refractory wall, interrupting or disturbing the fluid flow conditions. The interfacial properties of the nonmetallic inclusion-molten steel-refractory system are believed to play a key role in the clogging tendency of selected steel grades in contact with ceramics. The combination of a high-temperature laser scanning confocal microscope (HT-LSCM), which is employed for in situ observation of inclusions’ behavior in the liquid steel or at the steel/ceramic interface, and a high-temperature drop shape analyzer (HT-DSA), which is utilized for contact angle measurements, enabled the investigation of reactions and interactions in the described system at experimental temperatures of approximately 1600 °C. The objective of this study was to develop a method to obtain qualitative information on the deposition of nonmetallic inclusions (NMIs) in the submerged entry nozzle (SEN) during casting. The behavior of solid NMIs from a calcium-treated steel at the interface between liquid steel and Al2O3 or MgO was investigated by means of HT-LSCM. During the test evaluation, inclusions were found to separate at the steel/ceramic interface due to an attractive force. This force increased with the NMIs’ size as well as with the ceramic particle change. The HT-DSA provided contact angle data between molten steel and the ceramic used for implementation into the theoretical capillary force model. A clear correspondence between the estimated and calculated capillary forces was observed. The change in the wettability of the system, as induced by the change in the ceramic from MgO to Al2O3, showed a reduction of the attractive forces, indicating a weaker separation toward the SEN for the same inclusion type. This study confirmed the strong potential of wettability investigations to predict the clogging tendency of certain steel grades.

Molecular dynamics simulations of the wetting behavior of carbon nanotubes in liquid copper

Although it is generally agreed that carbon is not wetted by liquid copper, the degree of rejection for a Single Wall Carbon Nanotube (SWCNT) has not been quantified. This paper presents Molecular Dynamics (MD) simulations to quantify the magnitude of resistance liquid copper imposes on a (5,5) SWCNT under static and dynamic intrusion scenarios. Two new sets of coefficients for the Morse potential model are proposed that better predict interfacial behavior between liquid copper and carbon. The proposed models, after being validated using empirically observed contact angle data for liquid copper and carbon, are used to investigate the wettability of a (5,5) single-walled carbon nanotube in liquid copper. It was found that the force required to submerge an initially un-wetted SWCNT into liquid copper under static conditions is higher than the expected force calculated from macro-scale fluid dynamic theory. The results indicate that a perturbation in the liquid copper surface reduces the force required for the SWCNTs to become incorporated in the liquid copper.

An approximate analytical approach to estimate the diffusivity of toxic chemicals in polymer barrier materials from the time evolution of sessile drop profiles

Any practical technique to determine the diffusivity of chemical warfare agents in protective barrier materials should require handling only miniscule volume of the chemicals and also require data analysis methods that are not computationally burdensome. Such an approach is described here based on imaging the time evolution of ~ 1 μL sessile drop profiles on the barrier surface and using an approximate analytical approach to analyze the time-dependent drop volume and contact angle data for extracting the diffusivity. The approximate analytical approach is validated by comparison against results from computationally intensive finite element simulations available in the literature. The domain of reliable use of the sessile drop technique in terms of the relative importance of the simultaneous evaporation and absorption is assessed using measurements on three challenging toxic chemicals in air and in butyl rubber. The ability of this approach to provide reasonable diffusivity estimates even if the substrate undergoes swelling is explored by studying water sessile drops on a Nafion membrane. The results allow one to conclude that the sessile drop technique coupled to the approximate analytical approach can be reliably used for rapid screening of new barrier materials for protection against chemical warfare agents if the screening is implemented using simulants with low vapor pressures.