Tensiometry surface tension

Wilhelmy plate tensiometry is also commonly used in Langmuir troughs (sec. 3.3). The difference between the surface tensions on the two sides of the barrier is identical to the surface pressure. 

On the other hand, the powder tensiometry method can be applied with any Wilhelmy type tensiometer. A special thin glass tube, which has a porous plug at the bottom, is filled with the powder which will be tested and the powder column is then brought into contact with the testing liquid. The mass of liquid absorbed into the porous solid is measured as a function of time by means of an electrobalance. The amount absorbed is a function of the viscosity, density and surface tension of the liquid, the material constant of the solid, and the contact angle of the interaction, as given in the following relationship ... 

Tensiometry" as the surface tension passes a maximum due to the superposition of area expansion and adsorption rate of surfactants. Similar behaviour is observed at the surface of growing drops, discussed in the next paragraph. 

About 150 years ago Simon [174] proposed the maximum bubble pressure method for measurements of surface tensions of liquids. Due to technical problems, this method was believed to be unreliable. During the last 20 years, however, more than 200 publications have been published on theoretical and experimental aspects of the bubble pressure tensiometry making this method to the most frequently used one for the very short adsorptions times from few milliseconds to some seconds. One of the advantages of this technique is the small amount of liquid required for the surface tension measurements, which is particularly important in studies of biological liquids [175]. 

Typically, narrow capillaries are used in the bubble pressure tensiometry (reap <0.01 cm), so that no correction with respect to the sphericity of the bubble is needed and the equation for the calculation of surface tension reads... 

In the applications of the capillary pressure tensiometry deseribed, an equivalent to Eq. (4.119) is used in the two particular cases in which either the surface tension (pressure derivative method) or the drop curvature (expanded drop method) are constant. In other applications, like the expanding or growing drop methods developed respectively by Nagarajan and Wasan and McLeod and Radke, respectively [25, 154], the capillary pressure is monitored while the surface area is increasing continuously. In these methods APcap changes due to the variation of the drop radius and of the interfacial tension caused by the dilation of the surface which put the system in a state out of the adsorption equilibrium. The problem is that area change, flow in the bulk phases, and the adsorption kinetics of the present surface active compounds have to be considered in a model simultaneously. 

The general application of tensiometry was shown in [241] and it was impressively demonstrated how large the capacity of interfacial studies for medical research is. For example, selected dynamic surface tension values of serum or urine correlate with the health state of patients suffering from various diseases. In the course of a medical treatment these values then change from a pathological level back to the normal values determined as standard for a certain group of people (age and sex). 

The miceUization of binary surfactant solutions is studied by the method of tensiometry at the variation of the fraction of ionic surfactant within the range 0-1.0. The quantitative treatment of the surface tension isotherms within the framework of the phase separation modeP showed that the values of the interaction parameter p in these systems lay within the range (-0.85)-(-. 6). This indicates that in these systems synergetic behaviour occurs, i.e. the mixed aggregates are formed. The surface potential is calculated for all the systems. A decrease in the potential is shown to occur with a decrease in In... 

The two methods maximum bubble pressure and profile analysis tensiometry complement each other experimentally and cover a total time range of nine orders of magnitude from about lO" seconds up to 10 seconds (many hours). The example given in Fig. 33 shows the dynamic surface tension of two Triton X-100 solutions measured with the instruments BPA and PAT (SINTERFACE Technologies) over the time interval of 7 orders of magnitude. As one can see, the experiments cover the beginning of the adsorption process and the establishment of the equilibrium state. 

The HT voltammetry with gold electrodes was also recently used to measure the surface partitioning constant of a soluble, redox-active surfactant at the air/water interface [25]. Malec and coworkers modified the surface of gold electrodes by self-assembly of short alkane chain thiols in order to mimic the thermodynamic properties of the air/water interface. They relied on the fact that the surface tensions of the air/water interface and of the liquid alkane/water interface are similar [8]. Indeed, the HT measurements of the Gibbs monolayer formation constant were in agreement with their surface tensiometry and Brewster angle microscopic measurements [25]. 

Contact angle measurements or surface tensiometry allow determination of surface energy or surface tension on polymer brushes (85). It also gives information on differences in morphology and fiinctional group distribution... 

FIGURE 19.1 Dynamic surface-tension data for n-alkyldimethylphosphine oxides, as measured by maximum bubble-pressure technique (O), drop-volume tensiometry ( ), and de Nolly ring tensiometry (A), and model fit ignoring reorientation (dotted line) and incorporating reorientation (solid line). (From Fainerman, V. B., et al. 2000. Adv. Colloid Interface Sci. 86 (1-2) 83-101. With permission.)... 

Moore et al. measured the surface tension of oceanic dissolved organic matter (DOM) from Atlantic Ocean samples off the coast of Georgia, USA [197]. Using pendant drop tensiometry at 24 C they saw clear surface tension depression from surface-active organics, which followed the Szyszkowski-Langmuir equation, = ffo — 2.9527 In (1 -i- 2 x 10 C), where C is in units mg L . Surface tension as inferred using KTA also showed excellent agreement with the direct measurements. 

Frosch and coworkers studied the surface tension of binary solutions of adipic, citric, oxalic, succinic, and cis-pinonic acids in either ammonium sulfate or sodium chloride aqueous solutions using tensiometry at room temperature [205]. They observed no surface tension depression in solutions containing oxalic acid, and cis-pinonic acid had the highest surface activity among the compounds studied. 

Tensiometry The balance of forces at the free boimdary of liquids reveals a net inward force toward the bulk, known as siuface tension /.Thus,surface tension is a property intimately related to both the bulk and the interface. To modify the surface tension of a given liquid, siufactants are often used as additives, primarily because the bulk properties of the liquid remain relatively unchanged. Other approaches to changing surface tension (e.g., temperature, solvent mixing) have the undesired effect that they alter both interfacial and bulk properties simultaneously. 

Gunde R, Hartland S, Mader R. (1995) Sphere tensiometry A new approach to simultaneous and independent determination of surface tension and contact zn e. J of Colloid... 

H. Nakanishi, K. Nakazato, K. Terashima, Surface tension variation of molten silicon measured by ring tensiometry technique and related temperature and impurity dependence. Japan. J. Appl. Phys. Part 1-ReguL Pap. Short Notes Rev. Pap. 39(12A), 6487-6492 (2000)... 

Like surfactants, block copolymers form micelles above a critical concentration. The critical micelle concentration can be located by a variety of techniques [112], the most commonly used being surface tensiometry where the cmc is located as the point at which the surface tension becomes essentially independent of concentration. The primary methods to determine micelle size and shape are light scattering and small-angle X-ray and neutron scattering. The thermodynamic radius (from the thermodynamic volume, which is one eighth... 

Kjellin, U.R.M., Reimer, J., Hansson, P. An investigation of dynamic surface tension, critical micelle concentration, and aggregation number of three nonionic surfactants using NMR, time-resolved fluorescence qnenching, and maximum bubble pressure tensiometry. J. Colloid Interface Sci. 2003, 262, 506-515. 

A range of fluorinated anionic surfactants, which are structural relatives of Aerosol-OT, were synthesized and characterized, with the aim of investigating the effects of chemistry on the structure and stability of water-in-carbon dioxide microemulsions. The dilute aqueous phase behavior was studied to check for chemical purity and fuUy characterize the compounds. Once appropriate measures were taken to achieve sufficient purity, the surface excesses measured by both tensiometry and neutron reflection measurements agreed well, and the surface tensions were consistent with a prefactor of 2 in the Gibbs equation. 

A.I. Rusanov, V.A. Prokhorov, Interfacial Tensiometry, Elsevier (1996). (Although this book emphasizes measurements of surface and interfacial tensions, it also contains much interesting information on thermodyncimic backgrounds and interpretations.)... 

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