Du Noiiy ring method

Interface by the du Noiiy Ring Method Basic Protocol 2 Dynamic Interfacial Tension Determination by the Drop D3.6.5... 

This unit will introduce two fundamental protocols—the Wilhelmy plate method (see Basic Protocol 1 and Alternate Protocol 1) and the du Noiiy ring method (see Alternate Protocol 2)—that can be used to determine static interfacial tension (Dukhin et al., 1995). Since the two methods use the same experimental setup, they will be discussed together. Two advanced protocols that have the capability to determine dynamic interfacial tension—the drop volume technique (see Basic Protocol 2) and the drop shape method (see Alternate Protocol 3)—will also be presented. The basic principles of each of these techniques will be briefly outlined in the Background Information. Critical Parameters as well as Time Considerations for the different tests will be discussed. References and Internet Resources are listed to provide a more in-depth understanding of each of these techniques and allow the reader to contact commercial vendors to obtain information about costs and availability of surface science instrumentation. 

The choice between the static methods (Wilhelmy plate method and the du Noiiy ring method) should primarily be based on the properties of the system being studied, in particular, the surfactant. As mentioned in UNITD3.5, the transport of surfactant molecules from the bulk to the surface requires a finite amount of time. Since static interfacial tension measurements do not yield information about the true age of the interface, it is conceivable that the measured interfacial tension values may not correspond to equilibrium interfacial tension values (i.e., the exchange of molecules between the bulk and the interface has not yet reached full equilibrium and the interfacial tension values are therefore not static). If the surfactant used in the experiment adsorbs within a few seconds, which is the case for small-molecule surfactants, then both the Wilhelmy plate method and the du Noiiy ring method are adequate. If the adsorption of a surfactant requires more time to reach full equilibrium, then the measurement should not be conducted until the interfacial tension values have stabilized. Since interfacial tension values are continuously displayed with... 

The basic setup to determine static interfacial tension based on either the Wilhelmy plate method or the du Noiiy ring method (see Alternate Protocol 2) is shown in Figure D3.6.1. It consists of a force (or pressure) transducer mounted in the top of the tensiometer. A small platinum (Wilhelmy) plate or (du Noiiy) ring can be hooked into the force transducer. The sample container, which in most cases is a simple glass beaker, is located on a pedestal beneath the plate/ring setup. The height of the pedestal can be manually or automatically increased or decreased so that the location of the interface of the fluid sample relative to the ring or plate can be adjusted. The tensiometer should preferably rest on vibration dampers so that external vibrations do not affect the sensitive force transducer. The force transducer and motor are connected to an input/output control box that can be used to transmit the recorded interfacial tension data to an external input device such as a monitor, printer, or computer. The steps outlined below describe measurement at a liquid/gas interface. For a liquid/liquid interface, see the modifications outlined in Alternate Protocol 1. Other variations of the standard Wilhelmy plate method exist (e.g., the inclined plate method), which can also be used to determine static interfacial tension values (see Table D3.6.1). 

The Wilhelmy plate and du Noiiy ring methods provide a single value for surface tension of a given surfactant at a given concentration. Examples are provided in unitd3.5 (see Figure D3.5.5). Examples of dynamic surface tension values are also provided in unitd3.5. 

Fig. 7. The increase in surface pressure of phospholipid monolayers as a function of signal-peptide concentration for the various E. coli LamB synthetic signal sequences (from Briggs, 1986). A monolayer of egg phosphatidylethanolamine and egg phosphatidylgly-cerol (65 35) was spread from a benzene solution onto 5 mM Tris buffer, pH 7.3, yielding a hnal surface pressure of 20 dyn/cm after evaporation of the benzene. The peptide was added by injecting a concentrated solution below the lipid-water interface. The surface pressure was measured by the du Noiiy ring method with a Fisher Autotensiomat equipped with a platinum-iridium ring. The plateau values are plotted as a function of the peptide concentration for the wild-type (O), Pro— Leu pseudorevertant (A), and deletion-mutant ( ) peptides.

The threshold of the equilibrium state can generally be reached slowly, and thus the surface tension values obtained by semi-static methods closely resemble those obtained by static ones. The rate of approaching the equilibrium state should be optimized in each system, in order to avoid lengthy measurements and to obtain surface tension values as close to the equilibrium ones as possible. Among the most common semi-static methods are the method of maximum pressure, the du Noiiy ring method and the drop-weight method. 

Our results also proved the correlation between foamability and surface tension gradient for aqueous nonionic surfactant solutions. Foam formation was estimated from a dynamic surface tension using the maximum bubble pressure method, and foam stability was estimated from a transfer distance of lamella using a laminometer. Laminometer measurements were made using the Du Noiiy ring method [1,78,96]. Force profile during the expansion of lamella was monitored using an electronic-balance with... 

The surface tension of a liquid can be measured in a variety of ways, including capillary tube rise, du Noiiy ring method, bubble pressure, and drop weight. These methods vary greatly in their applications. 

For emulsions, the interfacial tension is usually of most interest. Here, the du Noiiy ring, Wilhelmy plate, drop volume, pendant, or sessile drop methods are the most commonly used. The spinning drop or captive drop techniques are applicable to the very low interfacial tensions encountered in the enhanced oil recovery and microemulsion fields. The maximum droplet pressure technique can be used when there is little or no density contrast between the phases, such as in bitumen-water systems at elevated temperature. 

For foams, it is the surface tension of the foaming solution that is usually of most interest. For this, the most commonly used methods are the du Noiiy ring, Wilhelmy plate, drop weight or volume, pendant drop, and the maximum bubble pressure method. For suspensions it is again usually the surface tension of the continuous phase that is of most interest, with the same methods being used in most cases. Some work has also been done on the surface tension of the overall suspension itself using, for example, the du Noiiy ring and maximum bubble pressure methods (see Section 3.2.4). 

The du Noiiy ring surface tension method involves slowly raising a platinum ring through a liquid until it detaches from the surface (Figure 3.8, Lower). The force at the point of detachment is measured using a balance or torsion wire. If F is the force on the ring,... 

Another quite popular and rather simple method is the Du Noiiy ring detachment method (Figure 1.16) in which the force needed to pull the ring through the interface is measured. That force is given, within the first approximation, by F = 2 x where is the ring radius. If more precise measurements of the surface tension are needed, then proper corrections need to be introduced. This method can also be used to measure the interfacial tension between two liquids and is especially useful for interfacial tensions on the order of several mN/m. 

FIGURE1.16 Schematic illustration of Du Noiiy ring detachment method. 

Figure 4.7 Methods for measuring surface tension (a) capillary rise, (b) pendant drop, (c) du Noiiy ring, (d) Wilhelmy plate...

The most common methods used to measure surface tension of surfactant solutions using commercial instruments are the du Noiiy ring and Wilhelmy plate techniques (Fig. 4.7c and d). In the former, the force necessary to detach a ring or wire loop from a liquid surface is measured (for example using... 

A method that has been rather widely used involves the determination of the force to detach a ring or loop of wire from the surface of a liquid. It is generally attributed to du Noiiy [42]. As with all detachment methods, one supposes that a first approximation to the detachment force is given by the surface tension multiplied by the periphery of the surface detached. Thus, for a ring, as illustrated in Fig. II-ll,... 

Lecomte du Noiiy (1919) stated that there were large discrepancies in interfactial tension results obtained with previously available methods, which illustrated the need to develop better measurement methods. He therefore developed a new method in which a platinum ring... 

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