Ross-Miles testing

The foaming properties of sodium symmetrical secondary alcohol sulfates, sodium secondary alcohol sulfates, isomeric sodium secondary pentanol sulfates, and sodium linear alcohol sulfates were studied by Dreger et al. [72] via the Ross-Miles test [150] at 46°C. Within the linear series sodium tetradecyl sulfate produces the largest amount of foam. The influence of several electrolytes was also studied. 

Maurer et al. [57] determined the foaming power of octadecyl sulfuric acid and several of its salts, such as sodium, triethylamine, triethanolamine, and some amino acids. Foam capacity, measured by the Ross-Miles test [150] at 60°C, was in the range of 180-210 mm showing comparatively few differences. 

TABLE 24 Foaming Power of AOS and Reference Surfactants According to a Modified Ross-Miles Test at 40°C and 1 g/L Surfactant Concentration... 

Foaming plays an important part for many applications. Figure 8 shows foaming behavior of sulfosuccinates expressed as foam height in the Ross-Miles test. 

The quantity xp is a much better defined characteristic of foam stability (since the pressure in the borders along the height of the foam column remains constant during its destruction). This parameter is also much more sensitive to the kind of surfactant, electrolyte concentration and other additives, compared to the lifetime of the foam in gravitational field, with an averaged pressure value from 0 to pgH. Estimation of the stability of foams from different surfactants by xp and by the Ross-Miles test has been reported in [16]. The results are discusses in Section 7.6.1. The advantages of the Foam Pressure Drop Technique and, respectively, xp as a characteristic of the foam stability, are clearly shown. 

It depicts the H(i) dependence for NaDoS foams. Curve 1 refers to common thin films, curve 2 to CBF and curve 3 to NBF. It is clearly seen that the curves differ from one another. This indicates that the Ross-Miles test can be used to distinguish foams constituted of the different types of foam films. This is in agreement with the xp(Ap) dependence for NaDoS foams (seeFig. 7.6). As mentioned in the beginning of this Section a quantitative comparison of the results by the two techniques cannot be done. 

Analogous tp(Ap) and H(x) relations were obtained for foams from non-ionic surfactants (Fig. 7.14). Here the Ross-Miles test cannot be used to distinguish foams with common thin and black films by H (the non-ionic surfactants form only one type of black films see Section 3.4). xp(Ap) dependence indicates that at low pressures (< 3103 Pa) the foam with common thin films has longer lifetime (curve 2) while in the range of higher pressures the foam with black films (curve 1) lives longer. The differences in Tp at Ap = 5-... 

Foam formation also plays a certain role in the washing process. The persistent conviction of consumers expressed as no foaming, no washing compels the producers to manufacture a wide spectrum of detergents with an obligatory possibility of foam formation in the washing solution. As a result, tests on determination of volume and stability of foams in the solution (e.g. Ross-Miles test) are included in many standards for efficacy characterisation of detergents [6]. 

Dynamic foam test. Here, foam is generated by flowing gas through a porous orifice into a test solution as shown in Figure 2.17. The steady-state foam volume maintained under constant gas flow into the column is then measured. This is usually done in a column, but there are many variations of this kind of test [62, 99,100]. This technique is frequently used to assess the stabihty of evanescent foams. Another kind of dynamic foam test, the continuous plunging jet method [101], is a modification ofthe Ross-Miles test, described later. 

Ross-Miles Test. A method for assessing foam stability in which one measures the rate of collapse of a (static) column of foam that has been generated by allowing a certain quantity of foaming solution to fall a specified distance into a separate volume of the same solution contained in a vessel. 

Pour test method (the Ross-Miles test)... 

Many other test methods and standards are available. Ross-Miles testing is another important test though it is often criticized for not being representative of real life foaming. In this test, a dilute solution of surfactant is dropped from a fixed height into a pool of the same dilute solution and the foam volume developed is measured. 

To check whether the preceding estimates, Eqs. (9) and (10), described real foams, we performed a series of parallel experiments with various surfactant-antifoam couples for determination of the entry barrier, P , by FTT and of the final foam height, Hp, by the Ross-Miles test. The results are summarized in Fig. 10, where Hp is shown as a function of P (see the figure caption for the specific systems). The results show that the theoretical linear relationship between Hp and P , Eq. (10a), holds very well for P ... 

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