Capillary Rise Technique Research Articles

Capillary Rise: A Simple Tool for Simultaneous Determination of Porosity and Thickness of Thin Silica Coatings

Coating porosity is an important property that supports solid-gas and solid-liquid exchange that can either enhance various science and technological applications or promote damage if not properly controlled. However, non-destructive instrumental techniques for the measurement of porosity on coated walls or surfaces can be quite challenging. Here, a seamless capillary rise technique has been used to determine both the thickness and porosity of a thin silica coating. Uniform coatings were prepared from 5 wt% hydrophobic fumed silica in absolute ethanol and spin-coated at 500–8000 rpm on glass slides. Capillary imbibition of squalane was then controlled into known areas of the resulted hydrophobic nano-porous coatings. The mass of the solid (silica) and the infiltrated oil (squalane) were gravimetrically measured. The porosity of the material was calculated as the percentage fraction of the pore volume while the film thickness was determined as the ratio of the total volume to the area of coverage. Mean values of the porosity and coating thickness calculated from capillary impregnation technique were 86 ± 2% and 3.7 ± 0.2 μm, respectively. The coating thickness obtained was comparable with those revealed by SEM and Dektak profiler measurements. This study highlights the effectiveness of capillary rise as a simple and cost-effective non-destructive technique for assessment of coating thickness and porosity.

Mathematical Models to Follow the Dyeing of Cotton Knitted Garment Using the Capillary Rise Technique

Mathematical Models to Follow the Dyeing of Cotton Knitted Garment Using the Capillary Rise Technique

Surface tension of seawater at low temperatures including supercooled region down to – 25 °C

The experimental apparatus used for the measurement of surface tension of supercooled water using a capillary rise technique [Hrubý et al. J. Phys. Chem. Lett 5 (2014) 425 and Vinš et al. J. Phys. Chem. B 119 (2015) 5567] was modified for the measurements with seawater. New data for the surface tension of IAPSO seawater standard were collected for a salinity range from 10 g/kg to 38 g/kg and at temperatures from 30 °C down to −25 °C. The reported measurements are relative to the surface tension of pure water at the reference temperature of 15 °C. The combined standard uncertainty of the relative surface tension is better than 0.30%. The new data do not indicate any anomaly in the temperature trend of the surface tension of low-temperature and supercooled seawater down to temperature of −25 °C. The data agree with other literature data measured at stable conditions above 0 °C. Recent correlation by Nayar et al. [J. Phys. Chem. Ref. Data 43 (2014) 043103], considered as a potential standard for the surface tension of seawater, shows a very good agreement with the new data both in the stable region and under the metastable supercooled conditions. The differences between the correlation and the experimental data are entirely within the experimental uncertainty. Consequently, the recommended range of validity of the correlation by Nayar et al. can be extended into the supercooled region down to −25 °C for salinity up to 38 g/kg. In addition, an alternative correlation for the surface tension of seawater compatible with the recent correlation by Pátek et al. [J. Chem. Eng. Data 61 (2016) 928] for pure water is introduced. The new correlation has the same form as that by Nayar et al., however with slightly modified coefficients. Both correlations for seawater provide comparable results over the temperature and salinity ranges of the available experimental data.

Development of a simple and practical method for estimating the liquid absorption of pharmaceutical porous materials using a capillary rise technique

Porous materials are attractive substances for designing pharmaceutical particulates. However, understanding the behavior of liquid absorption into the intra-pores and interstices of porous carrier particles is important to effectively manufacture active pharmaceutical ingredients (APIs) using these carriers. In this study, we established a simple and practical method for evaluating the liquid absorption behavior of porous carriers using force tensiometry and a capillary rise technique. Different-sized tablets of porous materials were prepared and evaluated by this method using various solvents to estimate liquid absorption into the intra-particle pores and interstices of the particles. The amount of liquid trapped in the interstices of the particles decreased with decreasing tablet volume, after which the amount of liquid in the intra-particle pores could be estimated. Finally, API-loaded particles were prepared by absorbing the API solution into porous carriers based on the intra-capacity revealed above. No free API was found on the surface of the prepared particles, as it was well absorbed into the intra-particle pores. Collectively, this tensiometer method using different-sized tablets of porous materials appears to be a promising technique for evaluating the liquid absorption characteristics of porous pharmaceutical materials.

Surface tension of aqueous binary mixtures under the supercooled conditions – Development of the measuring technique and preliminary data for water + lower alcohols

An experimental apparatus originally developed for the measurement of surface tension of supercooled water was modified such that it allows for measurement of binary aqueous mixtures. The measuring principle based on the capillary rise technique is similar to that employed in the previous measurements with pure water [J. Hrubý et al., J. Phys. Chem. Lett. 5 (2014) 425 and V. Vinš et al., J. Phys. Chem. B 119 (2015) 5567]. The temperature dependence of the surface tension is determined from the measured height of the liquid column elevated in a vertical capillary tube with an inner diameter of 0.32 mm. The aqueous liquid rises to a height of 60 mm to 95 mm depending on the solute concentration and the temperature. Preliminary tests performed with the binary mixtures of water with methanol, ethanol, and n-propanol at various concentrations and temperatures down to –28 °C approved functionality of the measuring technique. Some difficulties, such as influence of impurities on the liquid column elevation or formation of bubbles in the liquid column, were observed. The experimental apparatus is further being modified in order to obtain more accurate data for various aqueous mixtures.

Surface properties and morphology of selected polymers and their blends designed to mucoadhesive dosage forms

In the mucoadhesive drug delivery systems the controlling mechanism is initiated by the wetting and swelling of the polymer matrix. In view of the above, the aim of our study was to analyze the effect of model saliva and gastric fluids on the wetting properties and sorption of selected mucoadhesive (Carbopol 974P NF, HEC) and film-forming (Kollidon VA 64) polymers as well as their blends. We considered two types of examined materials: individual polymers and their blends in the form of powders as well as in the form of compressed discs (blanc tablets). The contact angle measurements for powders were performed according to the Washburn method, using the capillary rise technique, whereas the sessile drop method was applied to the compressed discs of mucoadhesive polymers. The surface energy was determined by the OWRK method. The influence of composition of the polymer blends and pH of model fluids on the wetting properties and sorption of the polymer formulations was evaluated. Moreover, significant differences in the morphology, surface roughness and surface properties of mucoadhesion polymers considered were discussed.

Surface properties and surface free energy of cellulosic etc mucoadhesive polymers

The paper presents the sorption and wettability properties for several mucoadhesive polymers (Carbopol 974P NF (carbomer polymer; carboxy polymethylene), Noveon AA-1, (polycarbophil; acrylic acid polymer crosslinked with divinyl glycol) HPMC (hypromellose; cellulose 2-hydroxyethyl methyl ester) and HEC (cellulose 2-hydroxyethyl ether) and a film-forming polymer Kollidon VA 64 (polyvinylpyrrolidone-vinyl acetate copolymer)) commonly used in controlled drug delivery systems. Moreover, the surface energy of powders was determined using the data obtained according to the three types of experimental investigation. The contact angle measurements for powders were performed according to the Washburn method and using the capillary rise technique. Whereas the sessile drop method was performed on the compressed discs of mucoadhesive polymers. For the surface characterization the IGC technique was also applied. The results obtained by different methods, for both: wettability and surface energies, were compared and correlated. The presented study showed significant differences in the morphology and surface properties of mucoadhesion polymers considered. It was confirmed that for the accurate quantification of the free surface energy (and its components), for mucoadhesive polymers considered, not only the IGC in finite concentration, but also the Washburn method should be used.

An Investigation of the Robustness of Physical and Numerical Vanishing Interfacial Tension Experimentation in Determining CO2 + Crude Oil Minimum Miscibility Pressure

Different experimental and theoretical methods are used for predicting the minimum miscibility pressure (MMP) of complex CO2 + reservoir crude oil systems that are of particular interest to petroleum industry. In this paper, published physical and numerical vanishing interfacial tension (VIT) experimentations are critically examined for identifying best practices to reliably predict the CO2 + crude oil MMP. Some of the reported physical VIT experimentation studies appear to follow a portion of full scale VIT experimentation (i.e., a combination of the pendent drop method and the capillary rise technique). The physical VIT experimentation method in which the IFT measurements are made at varying pressures but with the same initial load of live oil and gas phases in the optical cell seems to be the most robust mechanistic procedure for experimentally studying the pressure dependence of IFT behaviors of complex CO2 + crude oil systems and thus determining the MMP using the VIT technique. The results presented here suggest that a basic parachor expression based on numerical VIT experimentation can reasonably follow the physical VIT experimentation in low IFT region, provided measured input data such as equilibrium phase densities and compositions are used in calculations.

Measurements of the wettability of catalyst support materials using the Washburn capillary rise technique

The penetration of porous solids by organic solvents is a technologically important phenomenon, relevant to a wide variety of fields including heterogeneous catalysis. Selecting the most appropriate solvent is a critical, albeit sometimes overlooked, step in such processes. In this study, the Washburn capillary rise technique was used to determine the wetting rates and contact angles of fifteen different organic solvents on some typical catalyst support materials, with the aim of better reaction design. This technique relates the rate at which a solvent is imbibed vertically through a bed of powder to the contact angle of the analyte solvent on the powder's surface. Experiments conducted on a range of catalyst support types indicated that contact angles were consistently low on silica and alumina supports regardless of the nature of the imbibed solvent, but were significantly higher on hydroxyapatite and microcrystalline cellulose-type supports. Oven drying of the powders only induced statistically significant changes in the wetting behaviour of some systems. The solvents with the most consistent wetting properties were those with moderate polarity such as tetrahydrofuran or ethyl acetate, making them the most versatile group of solvents for reactions involving the tested powdered supports.

Characterization of Glass Beads Surface Modified with Ionic Surfactants

Knowledge of the wetting characteristic of mineral surfaces is very important in enhancing the efficiency of separation of valuable minerals from gangue using froth flotation or oil agglomeration. In this paper a capillary rise technique was used to characterize the glass beads surface modified with cationic surfactant. The glass microspheres were used as model particles with a spherical shape and smooth surface to eliminate the roughness effect. The value of the contact angle for water was found to be 21.5 for unmodified beads, and 61.8, 89.7, 68.4 for 0.1, 1.0, 10 mg/gsolid of CTAB, and 39.8, 68.6, 87.9 for 0.1, 1.0, 10 mg/gsolid of DDAHCl, respectively. Data revealed that the adsorption of surfactant onto glass beads decreased the value of the electron donor component, γ-, which defines the hydrophobicity of the surface. Also, the property of the surface was investigated by flotation and oil agglomeration experiments. It was observed that particles with low value of contact angle for water and high for 1-bromonaphthalene and low value of γ- were floated with a recovery equal to 91.1 and 83.1% for CTAB and DDAHCl, respectively, and effectively agglomerated. This indicates that the capillary rise method can be successfully used to predict the wetting properties of solid particles in mineral processing.

Imaging surface water waves for the determination of surface tension and spatial attenuation

We propose the use of the image analysis technique to determine the surface tension of water and the attenuation coefficients of surface water waves in terms of frequency. Tap water from two different locations is used in our experiments. Water waves are continuously generated at various frequencies in a ripple tank by a plastic blade driven by a function generator. Images of the water waves are then captured by a digital camera and analyzed by using Tracker. As a result, we obtain the surface tension of water at 25 °C from both locations that are in good agreement with those resulting from the capillary rise technique. In addition, a linear relationship between the attenuation coefficient of the water waves and driven frequencies, ranging from 40 to 90 Hz, can be observed. Our results indicate that the greater the surface tension the longer distance the water wave takes before its amplitude decreases to 1/e of its original value. This work brings forward a relatively simple technique that can be applied to determine the surface tension and attenuation coefficients of surface water waves in a ripple tank with notable results.

Wettability study for pigmentary titanium dioxide

Wetting is the first step in the dispersion process of any powder. Understanding how the powder surface and the liquid properties affect the speed and intensity of the wetting process provides a set of tools to determine the dispersion efficiency as a whole, and an effective dispersion allows the reduced use of the powder to achieve the specified final properties. This article reports experimental results on the wetting behavior of five different TiO2 samples by liquids with different values of surface tension [deionized (DI) water and DI water containing surfactants] and its effect on the dispersion process. The selection of the TiO2 samples was based on different particles sizes with similar surface properties, and similar sizes with different surface properties. The samples were characterized in terms of their specific surface area and particle size distribution. The wetting behavior was evaluated by a capillary rise technique (Washburn) to measure liquid penetration height and rate, and the time evolution of the particle size distribution. The results show that larger particles presented faster wettability and that liquids with lower surface tension facilitate the wetting of the powder. The energy required to deagglomerate the powder is inversely proportional to the wetting speed: the faster the wetting the easier it will be to disperse the particles, with less energy required.

Measurements of contact angle between fine, non-porous particles with varying hydrophobicity and water and non-polar liquids of different viscosities

The three phase contact angle (θ) between liquids and fine solids is a key design parameter used in the control of the mineral separation, foam stabilisation or antifoaming processes, and therefore the accurate determination of θ is critical. Commonly used techniques produce variable results and are sensitive to the liquid type or viscosity. Different size ranges of non-porous, spherical glass beads were used to determine the applicability of the sessile drop method on particles forming ‘flat’ surfaces using different adhesives. Also investigated were the capillary rise and thin layer wicking techniques for the measurements of the contact angle between particles and water or oils of variable viscosity. The measured contact angles between particles and all liquids were compared with the contact angles obtained on the flat glass, made of the same material as the particles. Additionally, some of the particles were chemically modified in order to produce variable range of particle hydrophobicity for further comparison of the technique applicability. The measured contact angles were also qualitatively verified with the particle attachment to the bubble formed in the investigated liquids. Very good agreement between the measured water contact angles on particles using the sessile drop method and the water contact angles measured on flat glass was found for both degrees of glass hydrophobicity. The water contact angles measured of the particles with the capillary rise and thin layer wicking methods were found to be consistently larger, although reliable if considered as advancing contact angles. The contact angles between particles and three different viscosity oils were measured correctly only with the sessile drop method. By comparison, the thin layer wicking and the capillary rise technique produced significant errors. To conclude, the sessile drop on the adhesive slide is the most accurate technique for the measurements of contact angles between particles and water or oils, demonstrating that the technique is independent of the particle size or degree of hydrophobicity.

Effect of chemical modification on surface free energy components of Aerosil silica powders determined with capillary rise technique

Abstract The knowledge about interfacial energy interactions and surface free energy is necessary for understanding and modeling many surface and interface processes. The aim of this paper is to study the effect of the chemical modification on the surface free energy components of Aerosil OX50. This fumed silica is chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The modification process is studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid silica samples. The combination of these two techniques allows the determination of the adsorption isotherm of HTS onto silica showing the formation of a plateau for an initial concentration of 3 mM. The quantity adsorbed of HTS at maximum coverage is 2.14 μmol/m 2 . However, the chemical modification does not elaborate a compact layer. The HTS density is approximately 1.2 molecules/nm 2 which is close to the density of hydroxyl groups on the surface. A recent method, developed by Chibowski and Perea-Carpio, based on imbibition of probe liquids into a thin porous layer (capillary rise), is used for the determination of the surface free energy components. The surface free energy γ s decreases continuously from 54.2 mJ/m 2 for bare silica to 46.7 mJ/m 2 for silica treated at an initial concentration of 4 mM following a linear diminution of γ s with the HTS adsorbed amount. The apolar Lifshitz-van der Waals component γ s LW is reduced from 41.1 mJ/m 2 to 35.8 mJ/m 2 . The electron-donor parameter γ s − drops from 53.9 mJ/m 2 to 27.5 mJ/m 2 while the electron-acceptor parameter γ s + remains roughly constant (1 mJ/m 2 ). Trends in the surface free energy components are notably linked to observations in infrared spectra and give additional information about the structure of the HTS layer.

Applicability of Washburn capillary rise for determining contact angles of powders/porous materials

The Washburn capillary rise (WCR) technique has been widely utilized for determining contact angles of powders or porous materials; however, there are concerns regarding powder size and powder packing, especially for materials that exhibit large contact angle hysteresis. In this paper, some of these concerns were addressed. Due to the large water contact angle hysteresis on flat nylon 6/6 films, these films were ground into powders of different sizes and then used as model packing materials. The powders were packed in glass tubes to result in various packing structures that affected the penetration (i.e. advancing) rate of the test liquids. While all advancing contact angles obtained from WCR were found to be overestimated, more reasonable values were resulted when relatively large powders (e.g. 500–2000μm) were used to pack the tubes. With larger powders, the packing contained bigger voids and consequently lead to slower penetration rates of the liquids, hence a relatively smaller advancing contact angle. The smaller advancing contact angle obtained from the slower advancing rate was also observed by using the sessile drop method. To verify the applicability of using large powders (500–2000μm) for contact angle determination by using WCR, the advancing water contact angles of a bacterial cellulose/alginate composite sponge (BCA) with and without UV/ozone treatment were measured. The results showed that by using relatively large powders, WCR could be applied to obtain a reasonable advancing contact angle and assess the wettability change of complex porous materials.

Plasma treatment as a method for functionalising and improving dispersion of carbon nanotubes in epoxy resins

This study reports on the results of plasma-treated carbon nanotubes (CNTs) in the presence of oxygen and ammonia which can be scaled up for relatively large quantities of nanomaterials. The plasma treatment has been shown to change the surface chemistry and energy as well as the morphology of the carbon nanotubes. X-ray photoelectron spectroscopy analysis shows increases in oxygen and nitrogen groups on the oxygen- and ammonia-treated CNTs, respectively. Titration of the enhanced oxygen plasma-treated CNTs reveals an increased presence of carboxylic acid groups at 2.97 wt% whilst bulk density decreases from 151 kg/m3 for untreated carbon nanotubes to 76 kg/m3 after the enhanced oxygen treatment. The free surface energy has also been shown to increase from 33.70 up to 53.72 mJ/m2 determined using a capillary rise technique. The plasma-treated carbon nanotubes have been mixed in epoxy and have shown an improvement in dispersion, which was quantitatively evaluated using an optical coherence tomography (OCT) technique shown to be suitable for nanocomposite characterisation. This research has demonstrated that it is possible to surface functionalise large quantities of carbon nanotubes in a single process, and that this process improves the dispersion of the carbon nanotubes in epoxy.

The anisotropic characteristics of natural fibrous sepiolite as revealed by contact angle, surface free energy, AFM and molecular dynamics simulation

In this study, the anisotropic character of natural sepiolite was revealed by a combination of techniques involving contact angle measurements, Atomic Force Microscopy (AFM), and molecular dynamics (MD) simulations. Capillary rise technique was used to determine the change in contact angle values for several wetting liquids and calculate the surface free energy and acid/base components of sepiolite. The surface heterogeneity of sepiolite for a single fiber surface corresponding to roughness parameters was calculated from the AFM images. Finally, the interactions between water molecules and sepiolite mineral surfaces were also computationally analyzed using MD simulation to understand the interfacial water structure and the configuration of water molecules at the basal surface of sepiolite. It was found that due to the absence of hydrogen bonding sites, the hydrophobic sepiolite basal plane is not in close contact with water molecules, thus leaving a 3Å void space at the basal plane.

Measurement of the Surface Tension of Liquid Marbles

The capillary rise and Wilhelmy plate methods have been used to study the "surface tension" of water marbles encapsulated with polytetrafluoroethylene (PTFE) powders of 1-, 35-, and 100-μm particle size. With the capillary rise technique, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the heights of the capillary rise from the marble and from a flat water surface in a beaker. An equation based on Marmur's model was proposed to calculate the water marble surface tension. This method does not require the water contact angle with the supporting solid surface to be considered; it is therefore a simple but efficient method for determining liquid marble surface tension. The Wilhelmy method was used to measure the surface tension of a flat water surface covered by PTFE powder. This method offers a new angle for investigating liquid marble shell properties. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.

The effect of particle shape and hydrophobicity in flotation

The effect of particle shape on the flotation process has been investigated in laboratory experiments with monosized spherical ballotini and ground ballotini. The particles were treated by partial methylation with trimethylchlorosilane to achieve varying degrees of hydrophobicity. In flotation, the process of film thinning and liquid drainage is critical in the formation of stable bubble–particle attachments and this is affected by the particle shape and surface hydrophobicity. Flotation tests with different particle sizes were conducted in a modified batch Denver cell. Predictions from a computational fluid dynamic model of the flotation cell that incorporates fundamental aspects of bubble–particle attachment were compared with data from flotation tests. Contact angles of the particles were measured using a capillary rise technique to indicate surface hydrophobicity. Ground ballotini generally has higher flotation rates than spherical ballotini; the results are consistent with effects from faster film thinning and rupture at rough surfaces and are well correlated by the sphericity index.

Ternary solution of sodium chloride, succinic acid and water; surface tension and its influence on cloud droplet activation

Abstract. Surface tension of ternary solution of sodium chloride, succinic acid and water was measured as a function of both composition and temperature by using the capillary rise technique. Both sodium chloride and succinic acid are found in atmospheric aerosols, the former being main constituent of marine aerosol. Succinic acid was found to decrease the surface tension of water already at very low concentrations. Sodium chloride increased the surface tension linearly as a function of the concentration. Surface tensions of both binary solutions agreed well with the previous measurements. Succinic acid was found to lower the surface tension even if sodium chloride is present, indicating that succinic acid, as a surface active compound, tends to concentrate to the surface. An equation based on thermodynamical relations was fitted to the data and extrapolated to the whole concentration range by using estimated surface tensions for pure compounds. As a result, we obtained an estimate of surface tensions beyond solubility limits in addition to a fit to the experimental data. The parameterization can safely be used at temperatures from 10 to 30°C. These kinds of parameterizations are important for example in atmospheric nucleation models. To investigate the influence of surface tension on cloud droplet activation, the surface tension parameterization was included in an adiabatic air parcel model. Usually in cloud models the surface tension of pure water is used. Simulations were done for characteristic marine aerosol size distributions consisting of the considered ternary mixture. We found that by using the surface tension of pure water, the amount of activated particles is underestimated up to 8% if particles contain succinic acid and overestimated it up to 8% if particles contain only sodium chloride. The surface tension effect was found to increase with increasing updraft velocity.