Dimethyl phosphine oxide

To demonstrate the applicability of the criterion, given by Eqs (5.8) - (5.10), Ay(t )-values of aqueous solutions containing decyl dimethyl phosphine oxide as the main component and dodecyl dimethyl phosphine oxide as the simulated impurity were measured. The results, shown in Fig. 5.4, confirm that the assumption works well. 

Comparison of theoretical (lines) and experimental results (symbols) for a system containing decyl dimethyl phosphine oxide as main component and dodecyl dimethyl phosphine oxide as... 

Fig. 6.13 shows the agreement between the elasticity modulus, derived form the adsorption isotherm and from relaxation experiments with n-dodecyl dimethyl phosphine oxide solutions. 

Fig. 6.13 Dilational elasticity modulus of n-dodecyl dimethyl phosphine oxide determined for oscillating bubble experiments ( ), and calculated from the adsorption isotherm ( ) according to Wantke etal.(1993)...

The dynamics of mixtures of surfactants with proteins is of great importance for many practical processes, such as coating of photographic films, where gelatine in mixtures with surfactants and surface active dyes adsorb at the interface. Hempt et al. (1985) studied the relaxation behaviour of gelatine solutions in presence and absence of surfactants (SDS, tetradecyl dimethyl phosphine oxide, cetyltrimethyl ammonium bromide, n-decanoic acid, perfluoro octanoic acid tetraethyl ammonium salt). 

The adsorption kinetics of a surfactant to a freshly formed surface as well as the viscoelastic behaviour of surface layers have strong impact on foam formation, emulsification, detergency, painting, and other practical applications. The key factor that controls the adsorption kinetics is the diffusion transport of surfactant molecules from the bulk to the surface [184] whereas relaxation or repulsive interactions contribute particularly in the case of adsorption of proteins, ionic surfactants and surfactant mixtures [185-188], At liquid/liquid interface the adsorption kinetics is affected by surfactant transfer across the interface if the surfactant, such as dodecyl dimethyl phosphine oxide [189], is comparably soluble in both liquids. In addition, two-dimensional aggregation in an adsorption layer can happen when the molecular interaction between the adsorbed molecules is sufficiently large. This particular behaviour is intrinsic for synergistic mixtures, such as SDS and dodecanol (cf the theoretical treatment of this system in Chapters 2 and 3). The huge variety of models developed to describe the adsorption kinetics of surfactants and their mixtures, of relaxation processes induced by various types of perturbations, and a number of representative experimental examples is the subject of Chapter 4. 

Let us consider another example in order to emphasise the extraordinary importance of the dilational elasticity for the understanding of the adsorption state of surfactant molecules. The experimental values of the viscoelasticity for two homologues of alkyl dimethyl phosphine oxides (C 4 and Cio) measured using the oscillating bubble method [96] are presented in Fig. 2.12. The existence of the maxima in the experimental curves are due to the finite magnitude of the oscillations of the bubble surface (-10%) resulting in an over-saturation of the surface layer at higher surfactant concentrations in the bulk phase and at the interface. 

The surface tension isotherms for alkyl dimethyl phosphine oxides (C DMPO) in the interval from Cj to Ci6 at 25 °C are shown in Fig. 3.11. It should be noted that the experimental data reported in [36] for Cj, Ciq, Cp and C[4 are in a good agreement with the data presented in [37, 38], and therefore the results for these experimental data are also shown in Fig. 3.11. The parameters of the Frumkin and reorientation models are summarised in Tables 3.6 and 3.7. Both isotherms agree well with the experimental data. Small differences between the calculated isotherms exist only for nc > 13, while for lower nc the curves for the two models perfectly coincide. It follows then that neither of the two models can be preferred if one takes into account only the agreement between the experimental and theoretical data. However, the negative values of the Frumkin constant a for lower homologues, and the unusual shape of this dependence on nc (cf Fig. 3.12) indicate that for the Frumkin model the coincidence with the experiment is only formal. 

Similar to the alkyl dimethyl phosphine oxides discussed in the previous section, the minimum area co2 per mole (molecule) of CnBHB is almost independent of n, while the area co] per... 

It is seen that the coj value remains almost unchanged with increasing n. This feature is characteristic also for other homologous series of non-ionic surfactants. The quite small (as compared with the alkyl dimethyl phosphine oxides or betains) increase of co, with n is due to the fact that the main contribution to co, comes from the oxyethylene groups. 

In the thermodynamic model derived by Fainerman et al. [49, 64], which has been described in detail in the preceding Chapter 2, it was supposed that, depending on the surface coverage, surfactant molecules can adsorb in two different states. These states are characterised respectively by two different molar surface areas coi and CO2 and by the parameters bi and b2, which are related to the respective surface activities. Then it was demonstrated in Chapter 3 that n-alkyl dimethyl phosphine oxides [65] and poly-oxyethylated surfactants at the water/air and water/alkane interfaces could be described by this model perfectly [66, 67,68]. 

To estimate this coefficient K, first the value of K can be determined experimentally, and the ratio D2/D1 calculated using the equation proposed by Wilke and Chang [229]. For CioEOg we obtain K = 1.8. For Tritons at the water/nonane interface the following values have been given [230] K = 1.5 for Triton X-45, and K = 0.5 for Triton X-100. For decyl dimethyl phosphine oxide (CioDMPO) the adsorption activity of which is close to that of CioEOg, a value of K = 1.3 was found by Ferrari et al. [133]. 

Harmonic and transient relaxation experiments for dodecyl dimethyl phosphine oxide solutions were performed with the elastic ring method by Loglio [240]. This methods allows oscillation experiments in the frequency range from about 0.5 to 0.001 Hz and is suitable for comparatively slow relaxing systems. Slow oscillation experiments can be performed much easier now with the pendent drop apparatus [186]. Both techniques are also able to perform transient relaxation experiments. The two types of experiments have a characteristic frequency defined in the same way by Eq. (4.110). 

The easiest penetration experiments are those with a monolayer of an insoluble component spread on a subphase which contains a soluble component of the same homologous series. An example is the study by Fainerman et al. [115] of the penetration of the soluble dodecyl dimethyl phosphine oxide (C,2DMPO) into a monolayer of the insoluble eicosyl dimethyl phosphine oxide (CjqDMPO). The monolayer isotherm of C20DMPO at 20 °C shows a break... 

Decyl dimethyl phosphine oxide solution in water at 25 C [9]. The experimental data n vs t for this system measured at bulk concentrations 0.1 molW, 0.3 mol/m and 1.0 mol/m using MPT, TE and TVT methods are contained in the files C10DMPO-01R.txt, C10DMPO-03R.txt and C10DMPO-10R.txt, respectively. Figure 7.9 illustrates the results obtained for the system by calculations with WardTordai program. It is clearly seen that the experimental data obtained by various methods can be adequately approximated by the Frumkin model. 

Thiazolidinyl phosphine oxide (67) can be prepared by the addition of dimethyl phosphine oxide to 3-thiazolines (66) <97HAC207>. 

More recently (114, 115, 176), the adsorption dynamics of C 3 dimethyl phosphine oxide (Cj3DMPO), and C qDMPO at freshly formed water-hexane interfaces has been investigated as a funetion of the initial partition conditions and of the relative volumes between the two liquids. As shown in Table 1 some of these surfactants have large values for the partition eoeffieients, which enhances the influence of the transfer. 

First of all, we see that the data of the two experimental methods complement each other adequately. The dotted line refers to the diffusion model with a diffusion coefficient of D= 3 10 cm /s, which corresponds to the physically reasonable value for this surfactant. One can see that this line does not fit the experimental data very well, however, the solid line does. This solid line was calculated for D = 1 10 cm /s, a value slightly smaller than expected. The reason could be that we used here a mixed adsorption isotherm based on a Frumkin model, while it was shown that alkyl dimethyl phosphine oxides are better described by the reorientation model. This could explain the lower value of the diffusion coefficients. 

There are some informations about monotonous decrease of the equilibrium surface tension, dilatational elasticity, and adsorption of lysozyme for non-ionic surfactant decyl dimethyl phosphine oxide (Cj DMPO) as the concentration of surfactant increases in the mixture. However, in the case of mixtures of non-ionic surfactants with more flexible proteins like P-casein, the elasticity of the interfacial layer decreases before passing through a maximum as the concentration of surfactant increases [7], Possibly, the weaker interfacial network formed by P-casein as compared to globular proteins determines the dilatational response of the mixtures. The same picture was shown for the system P-casein mixed with dodecyl dimethyl phosphine oxide (C,2DMPO). For all studied frequencies (0.005-0.1 Hz) the elasticities for adsorption layers have a maximum about 4x10" mol/1 Cj2DMPO concentration. It was shown the obtained values are very close to those measured for the surfactant alone. Thus, in this concentration region the surfactant dominates the surface layer. In our case we have... 

Oscillation experiments with the elastic ring method in the frequency range from about 0.5 to 0.001 Hz for dodecyl dimethyl phosphine oxide solution were first conducted by Loglio [68]. 

The values of k , calculated from Eiquation 5.13, are almost independent of [CioE4]j. - However, the inhibition by dodecyl(dimethyl)phosphine oxide (C12PO) is less than that by C,oE4, for example, with 0.05 M CTABr and 0.05 M C12PO, W kobs = 4.83 sec as compared to 10 k bs = 3.0 sec with added 0.05 M C10E4, and rate differences are similar over a range of conditions. These qualitative observations indicate that the simple treatment with constant kM probably does not fit the effects of C,2PO. The simplest explanation of this failure is that the rate constant k increases on addition of C,2PO, and this increase is found to fit the following empirical equation ... 

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