DuNouy ring

Several other methods for determining 7 —notably, the maximum bubble pressure, the drop weight, and the DuNouy ring methods (see Section 6.2) —all involve measurements on surfaces with axial symmetry. Although the Bashforth-Adams tables are pertinent to all of these, the data are generally tabulated in more practical forms that deemphasize the surface profile. 

RH and at 25°C. using the sessile drop method. Surface tensions were measured at 25°C. using the duNouy ring method. Unless otherwise noted in the text, the contact angles were reproducible to 2° and the critical surface tensions to 0.5 dynes/cm. 

Surface Tension. Measurements were carried out by the duNouy ring method, and the corrections of Harkins and Jordan (12) were applied. Aging effects in the measured surface tensions were negligible. Each surface tension point corresponded to a solution individually prepared by weighing. 

Aqueous viscosity was measured at room temperature with a Brookfield and Ubbelohde viscometer. Intrinsic viscosities were measured by a five-point dilution method no shear-rate corrections were made for the data. Interfacial tension was measured with a DuNouy ring tensiometer against toluene at various polymer concentrations. The formulations used to evaluate the HMHECs for latex paints have been described elsewhere (5). 

The interfacial tension, y, in the Gibbs adsorption equation is used for equilibrium conditions as bitumen components are adsorbed. Measurement techniques available are extensive. Some of these methods are duNouy ring, maximum bubble pressure, drop volume, Wilmhelmy plate, sessile drop, spinning drop, pendant drop, capillary rise, oscillating jet, and capillary ripples. These and many others are referenced extensively by Malhotra and Wasan (153). These authors also showed that there is no correlation between emulsion stability and interfacial tension. The nature of the film dominates stability. Some relationships between interfacial tensions and crude oil properties follow. 

FIGURE 1.12 Schematic diagram of the DuNouy ring method for measuring interfacial tension. 

The surface tension of the 70°C agarose solution was measured with a DuNouy ring surface tension balance. 

The surface tension of the samples was determined by a DuNouy ring method using a KSV Sigma 70 tensiometer (Braumann, Germany). The equipment is useful for determination the dynamic surface tension of liquids, the wetting contact angle and the water uptake or swelling of solid samples. 

Critical micelle concentrations were determined at 25 °C from the intersection of lines in surface tension-log (surfactant concentration) data plots. Surface tensions were measured with a platinum duNouy ring using an automated apparatus. These curves did not show minima, which indicates that impurities more surface active than the surfactant were absent. 

C Naggiar [44], radii of curvature (drop profile m od) D Schwarz and Moseley [9], DuNouy ring method E Krishnaswamy and Shashidhar [17], pendant drop method. 

Ring = DuNouy ring method RC = radii of cur iture (drq) profile method) ... 

Employing different methods always means different solid-nematic intoractions which are particularly dominant for the methods of capillary height, DuNouy ring, Wilhelmy plate and sessile drop [28]. In fact, even under identical experimental conditions, the different history of the nematic samples can lead to a considerable dispersion of the data [57,58]. The effect of impurities is the most frequently... 

Measurement of Pituitousness Value (2). The pituitousness (stringiness) values were obtained with a conventional duNouy tensiometer. The wire ring was lowered into the solution and then raised above the surface. The time required for the solution to break all contact with the ring was recorded as the pituitousness value, thus giving an empirical measure of the stringiness of the solutions. 

In principle, by measuring the force needed to extend the film, the wire frame shown in Fig. 18.1 could be used to measure the surface tension. In practice, other devices are more convenient. The ring-pull device (called the duNouy tensiometer) shown in Fig. 18.2 is one of the simplest of these. We can calibrate the torsion wire by adding tiny masses to the end of the beam and determining the setting of the torsion scale required to keep the beam level. To make the measurement, we place the ring on the beam and raise the liquid to be... 

In the duNouy tensiometer, the force required to pull up a ring of fine wire lying in the surface of the liquid is measured. If the diameter of the ring is 1.0 cm and the force needed to pull the ring up (with the surface of the liquid attached to the inner and outer periphery of the ring) is 6.77 mN, what is the surface tension of the liquid ... 

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