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Graphical abstract Highlights • The dilational visco-elasticity of C n Eo m adsorption layers is changing with the adsorption time. • The observed changes are caused by the surface layer composition. • Minor compounds present as admixtures in the studied samples can be higher surface active. • However, these admixtures adsorb slower due to their lower concentration. • The proposed admixture effects are supported by model calculations. Abstract Harmonic surface oscillations of drops are used to study the dilational surface rheology of solutions of the oxyethylated alcohols C 10 ЕO 8 , C 12 ЕO 5 and C 14 ЕO 8 at the fixed oscillation frequency of 0.1 Hz for adsorption times between 200 and 5000 s. It was found that at shorter adsorption times the visco-elasticity modulus is lower than its value at longer adsorption times or in the equilibrium state of the adsorption layer at the same surface pressure. This mechanism is explained by the fact that an actual surfactant, characterized by a certain number of EO groups, is in fact a mixture of compounds with a quite wide range of these groups. As molecules with a smaller number of EO groups exhibit a higher visco-elasticity modulus, the changes in the composition of the adsorbed layer during the adsorption lead to the given situation. These considerations are supported by theoretical calculations of the adsorption for mixed surfactants solution. [ABSTRACT FROM AUTHOR]

Dynamic surface tensions and dilational visco-elasticity are easy accessible parameters of liquids. For human body liquids, such as urine, blood serum, amniotic fluid, gastric juice, saliva and others, these parameters are very characteristic for the health status of people. In case of a disease the composition of certain liquids specifically changes and the measured characteristics of dynamic surface tension of the dilational surface elasticity and viscosity reflect these changes in a clear way. Thus, this kind of physico-chemical measurements represent sensitive tools for evaluating the severity of a disease and can serve as control tool for the efficiency of applied therapies. The overview summarises the results of a successful work over about 25 years on this subject and gives specific insight into a number of diseases for which the diagnostics as well as the therapy control have been significantly improved by the application of physico-chemical experimental techniques. [ABSTRACT FROM AUTHOR]

The adsorption of proteins (β-lactoglobulin, β-casein) and the oxyethylated non-ionic surfactants C 10 EO 8 and C 14 EO 8 at the aqueous solution/air interface is strongly enhanced and accelerated by the presence of hexane vapour in the air phase caused by the co-adsorption of hexane molecules. Due to this hexane co-adsorption, the dependence of dilational visco-elasticity modulus on surface pressure is shifted towards larger surface pressure values. The adsorption kinetics of the studied non-ionic surfactants shows the same picture as that observed for the two proteins. In contrast, the desorption process of the hexane molecules from a pre-adsorbed mixed adsorption layer is very slow. This decelerated desorption is explained by a rather large desorption energy required by the hexane molecules. The experimental data are compared with several theoretical models developed earlier. The results allow estimating the activation energy for the hexane desorption from adsorption layers of the two studied non-ionic surfactants. [ABSTRACT FROM AUTHOR]

The dynamic surface tension of aqueous solutions of C 10 EO 8 at the interfaces with air and saturated hexane vapor was measured by the maximum bubble pressure tensiometer BPA for adsorption times t ≥ 0.01 s. It can be shown that the dynamic surface pressure of C 10 EO 8 solutions in a saturated hexane atmosphere increases at short adsorption times with increasing surfactant concentration. The theory of diffusion controlled adsorption of two surfactants from the water and gas phases, respectively, was used for data analysis. The obtained experimental results agree with a model based on a reorientation of the C 10 EO 8 molecules, assuming a strong intermolecular interaction between hexane and C 10 EO 8 molecules in the surface layer. Alternatively, an additional enhancement of C 10 EO 8 adsorption activity can be assumed due to the presence of hexane molecules at the interface. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption kinetics, adsorption isotherm and the dilational surface rheology at low oscillation frequencies of sodium dodecyl sulphate (SDS) were studied by drop and bubble profile, and bubble pressure tensiometry. The effect of the inevitably present dodecanol in any SDS solution is taken into account by interpreting the experimental data with theoretical models valid for mixed surfactant solutions. In particular the dilational rheology method appears to be very suitable for demonstrating the continuously on-going hydrolysis reaction in a SDS solution, as the resulting dilational elasticities and viscosities change from a frequency dependencies characteristic to SDS to those expected for dodecanol adsorption layers. For surfactants as active as dodecanol, it turns out that all adsorption and rheological quantities depend significantly on the use of drop or bubble profile tensiometry, i.e. the small reservoir of available surface active molecules in a single droplet has to be considered quantitatively to obtain reliable data. [Copyright &y& Elsevier]

Abstract: The presence of micelles in the solution accelerates the adsorption dynamics of Tritons at the solution/air interface, depending on the micelle dissolution rate. Micellar solutions (at CMC and up to about 10× CMC) are studied by maximum bubble pressure tensiometry and oscillating bubble profile tensiometry. The dynamic surface tensions in the time range between 0.1ms up to 50s are analysed by a diffusion controlled mechanism. At very short times the effect of molecular reorientation of the Triton molecules at the surface is observed. The dilational elasticity data at low frequencies (0.005–0.2Hz) provide good agreement with a respective model assuming a very fast micelle dissolution. While for Triton X-45 and X-100 a quantitative agreement with existing theories is observed, the results for Triton X-165 and X-405 agree only qualitatively. This discrepancy is obviously due to the respective composition of the technical surfactants and a quantitative understanding would require an accurate knowledge on the sample composition. [Copyright &y& Elsevier]

Abstract: Exact knowledge of the dead time as part of the bubble lifetime in the maximum bubble pressure method is an important prerequisite for accurate dynamic surface tension measurements. The duration of the dead time depends essentially on the capillary geometry and affects significantly the measured surface tensions of concentrated surfactant solutions. Increase of the dead time leads to a significant surface tension decrease of a freshly formed bubble surface due to the significantly higher residual adsorption of the surfactant molecules. It is shown that correct dynamic surface tensions are obtained with the experimental procedure of Sugden''s method only when in addition to the fixed frequency of bubble formation, also the dead time values for the two capillaries are kept constant. [Copyright &y& Elsevier]

Abstract: The analysis of the available bubble life times and dead times for the bubble pressure tensiometer BPA-1S shows that dynamic surface tensions can be measured also for surfactant solutions at concentrations many times higher than the corresponding CMC. For the three nonionic surfactants Triton X-100, Triton X-45, and C14EO8 experiments are performed for solutions with a concentration of up to 200 times the CMC (C14EO8). Comparison of the experimental data with micelle kinetics models yields rate constants for the fast micelle dissolution process, which are in a good agreement with values obtained by other experimental methodologies. [Copyright &y& Elsevier]

Abstract: The co-adsorption of hexane from the vapor phase and surfactants from an aqueous solution at the surface of drops are studied in dependence of surfactant concentration. For the anionic surfactant SDS as well as the cationic surfactant DoTAB a significant surfactant–hexane co-adsorption and a remarkable decrease in surface tension is observed. This hexane co-adsorption effect increases with surfactant concentration and reaches a maximum value at intermediate surfactant concentrations below the CMC values. Dynamic surface tension measurements by drop profile analysis tensiometry and calculation of the standard deviation from Laplacian shape fitting, demonstrate three different adsorption regions. The kinetics and equilibrium state of adsorption depend significantly on the surfactant concentration. For the initial effects (regular adsorption region) which appear quickly, a thermodynamic model is applied which is based on a mixed adsorption layer approach. [Copyright &y& Elsevier]

Abstract: The dilational rheology of liquid–air interfaces is very sensitive to the contents and composition of surface active molecules in the liquid. Therefore, these rheological quantities along with dynamic surface tension could prove suitable parameters for the diagnosis of certain deseases. The cerebrospinal fluid, expired air condensate and umbilical blood of newborns have been investigated for patients suffering from neurosyphilis and for a reference group for comparison. The visco-elasticity is measured by pendent drop analysis tensiometry with transient and harmonic surface area perturbations. It is shown that the dilational visco-elasticity parameters depend significantly on the disease, i.e. can be used as diagnostic tool. [Copyright &y& Elsevier]

Abstract: Maximum bubble pressure and pendent drop profile analysis tensiometry are used to study the dynamic surface tension and rheological characteristics of saliva samples taken from volunteers of various sexes and age, and children with caries. The tensiometric characteristics of the secretions released by parotid, submandibular and sublingual glands are studied, and age-related and sex-related changes of some tensiometric characteristics of saliva are found. The differences are most essential for the tensiometric characteristics of saliva samples taken from caries-free children as compared with those taken from children with caries. Thus, the dynamic interfacial tensiometry is very sensitive and capable of providing information additional to the biochemical data about the properties of saliva, and could be recommended for the development of new diagnostic methods in dentistry. [Copyright &y& Elsevier]

The influence of micellar dissolution processes on the dynamic surface tensions of micellar solutions of SDS and SDS–DTAB mixtures was investigated by bubble pressure tensiometry. Based on a kinetic model the micelle dissociation constants are determined from dynamic surface tension data. The calculated micelle dissociation constants of SDS were in the range between 260 and 1600 s-1, i.e., the slow relaxation time for the SDS micelle dissociation process was in the range between 0.004 and 0.0006 s. These results are in good agreement with the experimental data for SDS (slow relaxation process), obtained by others using different methods. The calculated micelle dissociation constants of the SDS–DTAB complex were in the range between 0.3 and 30 s-1. [Copyright &y& Elsevier]