Surface and interfacial tension measurement theory and applications pdf

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surface and interfacial tension measurement theory and applications pdf

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Surface and Interfacial Tension: Measurement, Theory, and Applications (eBOOK)

All liquids — water, organic solvents, oils, and so on — have strong intermolecular cohesive forces. Molecules in the bulk experience this attractive force in all directions. However, liquid molecules at the surface formed between the liquid and a gas, such as air, do not have neighbors of the same kind on all sides like in Fig.

When an interface forms between two immiscible liquids, a similar situation occurs. In this case it is called interfacial tension. Thus, surface and interfacial tension can be interpreted in two ways: as a tension force acting along all directions of the surface per unit length, or as the energy required to increase the surface area.

In both interpretations, the surface wants to minimize its surface area or potential energy. Therefore, a surface with no or negligible external forces will form a sphere which has the smallest surface area to volume ratio.

Techniques to measure surface and interfacial tension are separated here into two main categories: force tensiometry where the force the surface imparts on a probe is directly measured; and optical tensiometry where the profile of a drop or bubble extracted from an image is fit to a theoretical equation.

In force tensiometry the force experienced by a probe at the liquid surface is directly measured. With the Attension Sigma tensiometers , three techniques are available: the Du Nouy ring method, the Wilhelmy plate method, and the platinum rod. In each technique, the respective probe is hung from a sensitive balance while being brought in contact with the liquid. The size and shape of the probe, contact angle between the probe and liquid, and in some cases liquid density, are incorporated into models to relate the measured force to surface or interfacial tension.

The Du Nouy ring method brings a platinum ring in contact with the surface or interface [1]. First, the ring is fully submerged and then slowly lifted up to form a meniscus-like in Fig. During this process, the force of the meniscus pulling on the ring is measured with the balance as shown in the plot in Fig.

Prior to the meniscus tearing, the meniscus will exert a maximum force point 7 in Fig. This maximum force is used in determining the surface tension in the OneAttension software.

While the original theory assumed a ring with infinite diameter and neglected excess liquid pulled up in the circular meniscus, current methods include correction factors in software calculations [2,3].

These correction factors require the liquid density to be known. The Wilhelmy plate method brings a platinum plate into contact with the surface as in Fig. In this case, the model assumes the plate is fully wetted and the plate is in contact with, but not submerged in, the liquid. Therefore, the position of the plate relative to the surface is critical. The plate is then completely lowered into the liquid and raised back to the zero depth of immersion. At this point the force recorded by the balance is used to determine the surface tension according to the equation:.

Note that the contact angle between the plate and the liquid is assumed to be zero. In contrast to the Du Nouy ring method, the density of the liquid is not necessary to measure surface tension.

Optical tensiometry uses drop or bubble profiles to indirectly measure surface and interfacial tension. In the literature, this technique is commonly referred to as axisymmetric drop shape analysis or ADSA [5].

The technique revolves around extracting a drop or bubble shape from the Young-Laplace equation,. Equation 2 describes the balance between gravity pulling the drop down in Fig. Discretizing with respect to arc length along the drop surface, s, leads to three coupled differential equations shown in Fig. In practice the drop shape extracted from Eq.

Thus, the quality of the measurement hinges heavily on the quality and proper calibration of the image. This quantity is also sometimes referred to as the Bond number [8]. The pendant drop method and ADSA, in general, has several advantages including the small sample size on the order of tens of microliters , non-invasive measurements, and capability of measuring very low interfacial tensions.

Surface and interfacial tension are sensitive to temperature and pressure. In the case of temperature, surface tension has been shown experimentally to decrease nearly linearly with temperature. The increase in temperature causes a corresponding decrease in cohesive intermolecular forces and this surface tension decreases. For example, the surface tension of water and air is Figure 5 plots the surface tension of water and air for a range of temperatures from ref.

As for pressure, surface tension is relatively unaffected by pressure changes until reaching high pressures as would be found in enhanced oil recovery and supercritical fluids. The increasing pressure causes dissolution of gas in the liquid, thereby decreasing the surface tension. Surfactants lower surface and interfacial tension by adsorbing to the surface or interface.

In general, surfactants are amphiphilic molecules, meaning they have both hydrophobic water-fearing and hydrophilic water-loving components. In the presence of a water-air or water-oil interface, for example, the surfactant aligns itself at the interface such that the hydrophilic component is in the water and the hydrophobic component is in the other phase. The presence of the surfactant disrupts the cohesive forces between water molecules at the interface and reduces the surface or interfacial tension.

The relationship between bulk concentration and surface tension at a constant temperature is called an isotherm, and an equation describing this relationship can be derived from the Gibbs adsorption isotherm. One commonly used and relatively simple example is the Szyskowski equation [10],.

In Fig. As the bulk concentration continues to increase, a point is reached where the surface concentration no longer increases. Instead surfactants in the bulk begin aggregating into structures called micelles. This point is called the critical micelle concentration or CMC and is driven by thermodynamics.

The bottom of Fig. After the CMC, surface tension tends to not vary significantly with bulk concentration. When a new surface or interface is formed, such as when a pendant drop is generated, a dynamic process involving surfactant adsorption from the bulk to the surface and desorption from the surface back to the bulk begins. Additional bulk transport processes such as diffusion and convection impact the net rate of adsorption to the surface.

The net adsorption rate, and similarly the change in surface or interfacial tension with time, is dependent on the surfactants involved and the fluid properties.

The time it takes for the surface tension to reach an equilibrium can be as short as minutes and as long as days. When taking surface and interfacial tension measurements, particularly when performing a surface tension isotherm, it is important to consider this time dependence. A new apparatus for measuring surface tension. Physiol 1 p. Huh, S.

A rigorous theory of ring tensiometry. Colloid Polymer Sci. Zuidema, G. Ring method for the determination of interfacial tension. W Neumann, R. Good, R. Surface and Colloid Science, Vol. Saad, A. Colloid Interface Sci. Bashforth, J. Adams, An attempt to test the theories of capillary action. Cambridge University Press.

London, England, Rotenberg, L. Borkuva, A. Determination of surface tension and contact angles from the shapes of axisymmetric fluid interfaces. Alvarez, L. Walker, S. A non-gradient based algorithm for the determination of surface tension from a pendant drop: Application to low Bond number drops. Vargaftik, B. Volkov, L. International tables of the surface tension of water.

Data 12 p. Prosser, E. Adsorption and surface tension of ionic surfactants at the air-water interface: review and evaluation of equilibrium models. Colloids Surf. A p. Hsu, M. Shao, S. Adsorption kinetics of C12E4 at the air-water interface: adsorption onto a fresh interface.

Langmuir 16 p. What is surface and interfacial tension? How is surface and interfacial tension measured? Force Tensiometry Du Nouy ring method Wilhelmy Plate Optical Tensiometry Effect of temperature and pressure on surface and interfacial tension Effect of surfactants on the surface and interfacial tension Surface tension isotherms and the critical micelle concentration CMC Surfactant adsorption and time dependent surface tension Related Contact Angle Goniometry.

Surface Free Energy. Advancing and Receding Contact Angles.

measurement of surface and interfacial tension pdf

Published By On January 28, Surface and Interfacial Phenomenon: HLB classification, measurement of surface and interfacial tensions, surface free energy, surface and interfacial tensions, solid-gas and solidliquid interfaces, surface active agents detergency, adsorption at solid interfaces, complex films, solubilization, electrical prope of interface, liquid interface. Interfacial tension on the other hand is important parameter in emulsion stability. Boon-Beng Lee. Surface tension is a direct measure of this energy loss per unit area of surface. Forces acting on liquid 6. Interfacial tension is measured the measurement is typically done upside down, meaning that the droplet will rise rather than hang on the tip of the needle.

Surface and interfacial tension play a key role in several industrial processes including, for example, detergents, coatings and oil recovery to name a few. Surface tension measurements are carried out when new coating formulations are developed, or when the quality of a detergent is being evaluated. There are three main methods used to measure equilibrium surface and interfacial tensions. The platinum ring is placed on a measurement hook connected to highly sensitive balance. The ring is submerged below the interface by moving the platform on which the liquid container is placed. After immersion, the height of the platform is decreased, and the ring pulls through the interface bringing meniscus of liquid with it. If the container is lowered further, the meniscus will tear from the ring.

measurement of surface and interfacial tension pdf

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measurement of surface and interfacial tension pdf

Static measurements are usually more accurate and it is possible to measure the surface tension to an accuracy of 0. Interfacial tension on the other hand is important parameter in emulsion stability. Chemical Engineering Communications, A short summary of this paper.

Wettability alteration and interfacial tension IFT reduction are two important mechanisms for enhanced oil recovery EOR. The introduction of nanotechnology from the fields of Biology and Material Science to the application in EOR is emerging because nanoparticles have the potential to alter formation factors like wettability and fluid properties like IFT and viscosity. However, a systematic literature review shows that ambiguity exists regarding whether nanoparticles can change wettability and IFT or not and which component in nanofluid plays a role. In this work, we investigated the effects of bare silica nanoparticles on wettability and IFT using a contact angle goniometer. The results showed that the contact angle measurement on quartz plates had relatively large uncertainty while those on calcite plates showed a clear trend that the smaller the nanoparticle size and the larger the nanofluid concentration, the smaller the contact angle. In addition, silica nanoparticles did not have an effect on IFT.


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