“…For surface pressure less than 15 mN/m the data are more or less the same, however, for surface pressures larger than 15 mN/m, the viscoelasticity modulus depends on the method used: with the drop profile method, we obtain higher values than with the bubble profile method. Similar findings have been discussed in [115, 116]. Fig.…”
Surface tension and dilational viscoelasticity of solutions of various surfactants measured with bubble and drop profile analysis tensiometry are discussed. The study also includes experiments on the co-adsorption of surfactant molecules from a solution drop and alkane molecules from saturated alkane vapor phase. Using experimental data for 12 surfactants with different surface activities, it is shown that depletion due to adsorption of surfactant from the drop bulk can be significant. An algorithm is proposed quantitatively to take into consideration the depletion effect which is required for a correct description of the co-adsorption of alkanes on the solution drop surface and the correct analysis of experimental dynamic surface tension data to determine the adsorption mechanism. Bubble and drop profile analysis tensiometry is also the method of choice for measuring the dilational viscoelasticity of the adsorbed interfacial layer. The same elasticity moduli are obtained with the bubble and drop method only when the equilibrium surface pressures are sufficiently small (Π < 15 mN m−1). When the surface pressure for a surfactant solution is larger than this value, the viscoelasticity moduli determined from drop profile experiments become significantly larger than those obtained from bubble profile measurements.
“…For surface pressure less than 15 mN/m the data are more or less the same, however, for surface pressures larger than 15 mN/m, the viscoelasticity modulus depends on the method used: with the drop profile method, we obtain higher values than with the bubble profile method. Similar findings have been discussed in [115, 116]. Fig.…”
Surface tension and dilational viscoelasticity of solutions of various surfactants measured with bubble and drop profile analysis tensiometry are discussed. The study also includes experiments on the co-adsorption of surfactant molecules from a solution drop and alkane molecules from saturated alkane vapor phase. Using experimental data for 12 surfactants with different surface activities, it is shown that depletion due to adsorption of surfactant from the drop bulk can be significant. An algorithm is proposed quantitatively to take into consideration the depletion effect which is required for a correct description of the co-adsorption of alkanes on the solution drop surface and the correct analysis of experimental dynamic surface tension data to determine the adsorption mechanism. Bubble and drop profile analysis tensiometry is also the method of choice for measuring the dilational viscoelasticity of the adsorbed interfacial layer. The same elasticity moduli are obtained with the bubble and drop method only when the equilibrium surface pressures are sufficiently small (Π < 15 mN m−1). When the surface pressure for a surfactant solution is larger than this value, the viscoelasticity moduli determined from drop profile experiments become significantly larger than those obtained from bubble profile measurements.
“…As a consequence of coalescence the droplet size distribution tends to be enlarged and moves towards larger sizes, eventually favoring creaming and destabilization of the emulsion. Among the most important effects relevant for the hindering of droplet coalescence, it is worth to mention the repulsive interaction between adsorbed layers, the interfacial coverage, the steric effects and the high dilational viscoelasticity of the interfacial layers [24,25]. The repulsive interactions are particularly relevant when ionic surfactants are concerned.…”
Section: Background On Emulsions and Droplet Interfacial Propertiesmentioning
A comparative study is reported on the interfacial properties of a set of surfactants and is discussed in terms of the effects on the features of the corresponding oil-water emulsions. The surfactants are saponin, Tween 80 and citronellol glucoside (CG), while the oil is Miglyol 812N—A Medium Chain Triglyceride (MCT) oil. Due to their high biocompatibility, all these compounds are variously utilized in food, cosmetic or pharmaceutical products. Among the surfactants, which are all soluble in water, CG presents also an important solubility in oil, as shown by the measured partition coefficient. For these systems, dynamic and equilibrium interfacial tensions and dilational viscoelasticity are measured as a function of the surfactant concentration and analyzed according to available adsorption models. In order to compare these results with the time evolution of the corresponding emulsions, the actual surfactant concentration in the matrix phase of the emulsion is accounted for. This may differ significantly from the nominal concentration of the solutions before dispersing them, because of the huge area of droplets available for surfactant adsorption in the emulsion. Using this approach allows the derivation of the correlations between the observed emulsion behavior and the actual surfactant coverage of the droplet interface.
“…The main elements of the method are dosing system, light source, CCD camera, frame grabber, cuvette with needle for drop ( -decane) formation. The drop ( -decane) was formed at the tip of a bent stainless steel needle immersed The slope from the plot of vs concentration can be used to calculate the maximum interfacial excess concentration ( max , in mol cm −2 ) by the Gibbs adsorption isotherm equation [30]:…”
Section: Measurements Of Interfacial Tension and Dilational Rheologicmentioning
confidence: 99%
“…Therefore, the interfacial dilational rheological properties of the adsorbed layers have been extensively studied in recent years [22][23][24][25].…”
The dilational rheological properties of series branched betaine surfactants: Guerbet p-(n-tetradecyl)-benzyl carboxybetaine (C 14 GCB), Guerbet p-(n-dodecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C 12 GE 2 CB), Guerbet p-(n-tetradecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C 14 GCB) and Guerbet p-(n-hexadecyl)-benzyl polyoxyethylene ether(2) carboxybetaine (C 16 GCB), were investigated by drop shape analysis method at the water-decane interface. The dilational properties of surfactants were investigated as a function of time, frequency and concentration. The experimental results show that the time dependence was complex. It was also found that the dilational modulus were almost independent of frequency in the experimental concentration range for C 14 GE 2 CB and C 16 GE 2 CB, while the dilational modulus of C 14 GCB and C 12 GE 2 CB increased with the increase of frequency, sharing the same results with conventional zwitterionic surfactants. The results indicated the appearance of a more elastic film for the C 14 GE 2 CB and C 16 GE 2 CB due to the internal compression and expansion of oxyethylene units (EO). On the other hand, the surfactant with branched alkyl chain came forth a higher maximum value of dilational modulus compared with the straight chain surfactants with the increase of concentration, which means the branching of alkyl chain was another important factor to control the interfacial film.
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