Maximum Bubble Pressure Tensiometry Research Articles

Effect of Surfactants on the Splashing Dynamics of Drops Impacting Smooth Substrates.

We present the results of a systematic study elucidating the role that dynamic surface tension has on the spreading and splashing dynamics of surfactant-laden droplets during the impact on hydrophobic substrates. Using four different surfactants at various concentrations, we generated a range of solutions whose dynamic surface tension were characterized to submillisecond timescales using maximum bubble-pressure tensiometry. Impact dynamics of these solutions were observed by high-speed imaging with subsequent quantitative image processing to determine the impact parameters (droplet size and speed) and dynamic wetting properties (dynamic contact angle). Droplets were slowly formed by dripping to allow the surfactants to achieve equilibrium at the free surface prior to impact. Our results indicate that while only the fastest surfactants appreciably affect the maximum spreading diameter, the droplet morphology during the initial stages of spreading is different to water for all surfactant solutions studied. Moreover, we show that surfactant-laden droplets splash more easily than pure liquid (water). Based on the association of the splashing ratio to our tensiometry measurements, we are able to predict the effective surface tension acting during splashing. These results suggest that droplet splashing characteristics are primarily defined by the stretching of the equilibrated droplet free surface.

The influence of divalent cations on the dynamic surface tension of sodium dodecylbenzenesulfonate solutions

The kinetics of surfactant adsorption at interfaces is crucial in many industrial settings. Maximum bubble pressure tensiometry allows accessing the adsorption at time scales of tens of ms to uncover the initial stages of surfactant diffusion to the interface. This method was used to investigate electrolyte solutions of sodium dodecylbenzenesulfonate (SDBS), specifically targeting how the presence of small amounts of divalent cations (Mg2+, Ca2+, Sr2+ and Ba2+) influenced the adsorption kinetics and equilibrium. The dynamic surface tensions revealed that the adsorption of SDBS was strongly influenced by the presence of divalent cations due to strong interactions with the anionic surfactant. In addition, the type (i.e. size) of cations played a role. The strong divalent cation-surfactant interactions lead to distinct lowering of surfactant diffusion coefficients, calculated using the short-time approximation solution of the Ward-Tordai equation. The diffusion coefficients were slightly and similarly lowered for all types of divalent cations when the surfactant concentration was increased up to the critical micelle concentration (CMC). Above CMC, the diffusion coefficients increased steadily depending on the divalent cation. It was speculated that this could be due to differences in structure and aggregation numbers of micelles and slower disassembly of micelles to supply monomers for adsorption. Furthermore, CMC of SDBS was reduced according to the Hofmeister series in the presence of divalent cations.

Surface tension behavior of superspreading and non-superspreading trisiloxane surfactants

One parameter frequently considered to be relevant for superspreading of trisiloxane surfactants is surface tension kinetics. In the scientific literature, some experimental results reported for trisiloxane surfactants are in contradiction with fundamental concepts of surfactant monomer diffusion. Therefore, maximum bubble pressure tensiometry has been used to determine dynamic surface tension (DST) of two types of trisiloxane surfactants: superspreader and non-superspreader. Results show that both surfactants behave similarly at concentrations below critical micelle concentration (CMC), as expected. The CMC curves, as determined by drop shape analysis, confirmed that the more hydrophilic non-superspreader has a higher CMC as compared to the more hydrophobic superspreader. Accordingly, the lower surfactant monomer concentration of the superspreader results in a higher DST than the non-superspreader at the same surface age. So, in contrary to claims in the literature, there is nothing mysterious or unexpected concerning the surface tension behavior of trisiloxane surfactants.Graphical

Tensiometry as a Simple Analytical Method for Quantification of Solubility and Release of Aroma Molecules in Aqueous Media.

Dynamic tensiometry is shown to be a high-potential analytical tool in assessing physico-chemical characteristics of fragrance molecules, such as solubility limit, volatility as well as much rarely assessed interfacial activity of these amphiphilic molecules. Surface tension of aqueous solutions of selected essential oils has been measured as a function of time and fragrance concentration using maximum bubble pressure method. The effect of the temperature and saline solution on the rate of dissolution in water was assessed. Dynamic surface tension turned to be sensitive to the composition of fragrances, as demonstrated on examples of natural and synthetic mixtures. Furthermore, presented work reveals the possibility of maximum bubble pressure tensiometry method to quantify the amount of fragrance compositions in flavored salts, including the artificially aged carrier samples. Suggested here analytical approach can be used for the detection of the purity of essential oils, for the optimization of compositions and of the manufacturing processes of fragrances-containing products, as well as for the assessment of the release/evaporation of fragrances from carrier systems.

Thermodynamics, Kinetics and Dilational Visco-Elasticity of Adsorbed CnEOm Layers at the Aqueous Solution/Air Interface

The adsorption behaviour of linear poly(oxyethylene) alkyl ether (CnEOm) is best described by a reorientation model. Based on a complete set of experimental data, including the adsorption kinetics, the equilibrium surface tension isotherm and the surface dilational visco-elasticity, the thermodynamic and kinetic adsorption parameters for some CnEOm at the water/air interface were determined. For the study, six CnEOm surfactants were selected (n = 10, 12 and 14 and m = 4, 5 and 8) and were studied by bubble profile analysis and maximum bubble pressure tensiometry. A refined theoretical model based on a reorientation-adsorption model combined with a diffusion-controlled adsorption kinetics and exchange of matter allowed us to calculate the surface layer composition by adsorbing molecules in different orientations. It turns out that at larger surface coverage, the adsorption rate decreases, i.e., the apparent diffusion coefficients are smaller. This deceleration can be explained by the transition of molecules adsorbed in a state of larger molar surface area into a state with smaller molar surface area.

Adsorption behavior of non-conventional eco-friendly tyrosine glycerol ether surfactants

Due to the increasing demand for environmentally friendly surfactants, a novel non-conventional glycerol ether surfactant with 12 carbon atoms in the hydrophobic alkyl chain and the amino acid tyrosine in the hydrophilic head (TyrGE12) is synthesized. Measurements of dynamic surface tension by maximum bubble pressure tensiometry and drop profile tensiometry are carried out for alkali aqueous solutions over a wide concentration range and for surface ages spanning from milliseconds to hours. Critical Micelle Concentration (CMC) value, standard free energy of adsorption and other physicochemical properties are calculated based on static (equilibrium) surface tension measurements. Dynamic surface tension data are analyzed using approximate solutions of the Ward and Tordai model to estimate diffusion coefficients for short and long adsorption times. For concentrations above the CMC, the effective diffusion coefficient (D*) of monomers is also estimated. Diffusion coefficients for short adsorption times lie in a physically reasonable range whereas for long adsorption times the computed very low values indicate the presence of an adsorption barrier. Interfacial dilatational storage modulus and loss modulus measurements indicate a dominant elastic character of the adsorption layer for all the examined concentrations and oscillation frequencies. Local peaks in the values of both moduli, below and above CMC, imply that structural changes in the adsorption layer might be partially affected by the presence of micelles.

Dynamic surface properties of eco-friendly phenylalanine glycerol ether surfactants at the W/A interface

Dynamic surface tension and dilatational viscoelasticity data are presented for aqueous solutions of novel nonconventional eco-friendly phenylalanine glycerol ether surfactants, with 12 carbon atoms in the hydrophobic alkyl chain, PhGE12. Adsorption kinetics is studied in a broad range of concentrations and for time scales spanning from several milliseconds to several hours employing maximum bubble pressure tensiometry and drop profile tensiometry. Standard free energy of adsorption and diffusion coefficients for both short and long adsorption times are calculated and discussed. For short adsorption times diffusion coefficients lie in a physically reasonable range but for long adsorption times extremely low values are computed indicating the presence of an adsorption barrier. This barrier appears to mask any micellar kinetics effect for long adsorption times. Measurements of interfacial dilatational storage modulus and loss modulus indicate a visco-elastic character of the adsorption layer for all the examined concentrations and oscillation frequencies. Local peaks in the values of both moduli imply that structural changes occur with increasing concentration. However, these changes seem to be unrelated to the presence of micelles since they are observed at concentrations below the CMC.

Influence of solubilised dodecane on the dynamic surface tension and dilational rheology of micellar Triton X-45 and SDS solutions

Maximum bubble pressure tensiometry is used to measure the dynamic surface tensions of micellar solutions of TX45 and mixtures of SDS/TX45 at the solution/air interface. For measurements of the dilational visco-elasticity of the micellar solutions the buoyant bubble profile tensiometry with harmonic bubble surface area oscillations is applied. The influence of dodecane solubilised in TX45 and mixed SDS/TX45 micelles, respectively, on the dynamic surface tension and dilational characteristics of these micellar solutions is determined. It is shown that the solubilisation of dodecane by micelles leads to a slowdown in the dynamic surface tension change and an increase in the visco-elasticity of the micellar solutions. Theoretical models proposed earlier are used for the description of the influence of solubilised dodecane on the dynamic surface tension and visco-elasticity of micellar TX45 solutions. It is shown that the presence of solubilised dodecane leads to a decrease of the CMC value, and to a decrease of the micelles diffusion coefficient.

Effect of water hardness on surface tension and dilational visco-elasticity of sodium dodecyl sulphate solutions

The complementary drop and bubble profile analysis and maximum bubble pressure tensiometry are used to measure the dynamic surface tension of aqueous SDS solutions in the presence of hardness salts (CaCl2 and MgCl2 in the ratio of 2:1 at concentrations of 6 and 40FH). The presence of hardness salts results in an essential increase of the SDS adsorption activity, which indicates the formation of Ca(DS)2 and Mg(DS)2 in the SDS solutions. The surface tension isotherms of SDS in presence of Ca(DS)2 and Mg(DS)2 are described using the generalised Frumkin model.The presence of hardness salts accelerates the ageing of SDS solutions as compared with the addition of 0.01M NaCl due to a faster hydrolysis and hence formation of dodecanol. These results are used to estimate the possible concentration of dodecanol in the studied SDS solutions.The buoyant bubble profile method with harmonic surface oscillations is used to measure the dilational rheology of SDS solutions in presence of hardness salts in the frequency range between 0.005Hz and 0.2Hz. The visco-elasticity modulus in the presence of hardness salts is higher as compared with its values in the presence of 0.01M NaCl additions. The ageing of SDS solutions leads to an essential increase of the visco-elastic modulus.

In honour of the 65th birthday of Valentin B. Fainerman

This Honorary Note is dedicated to the 65th birthday of Valentin Fainerman and summarizes some of his contributions to the field of interfacial dynamics. First of all, he made the maximum bubble pressure tensiometry the most frequently used methodology in the short time range of surfactant adsorption at liquid surfaces. This work allows us now to use experimental data down to the time range of sub-milliseconds for analyzing adsorption mechanisms of surfactants and polymers and their mixtures. The contributions of V.B. Fainerman to the quantitative understanding of the thermodynamics of adsorption represent a significant step ahead and describe adsorption layers even of rather complex nature, such as mixed protein–surfactant layers. These models consider molecular interfacial reorientation and aggregation. His thermodynamic approach is able to explain various interfacial systems which includes for example also phase transitions in insoluble monolayers. Based on diffusional transport and the proposed thermodynamic models, the adsorption kinetics and dilational rheology of liquid interfacial layers have reached a new level of understanding.

Short time dynamic interfacial tension as studied by the growing drop capillary pressure technique

For the characterisation of interfaces between two immiscible liquids, capillary pressure tensiometry is the most versatile method. To measure short time interfacial tensions it has to be applied under very dynamic conditions for which the following protocols have been developed: 1—continuously growing drop (CGD); 2—pre-aged growing drop (PGD); 3—stopped growing drop (SGD). The CGD is a procedure analogous to the well-known maximum bubble pressure tensiometry for liquid–gas interfaces, however, the processes of drop detachment and formation of the subsequent drop require a rather complex data analysis. For the PGD protocol based on a growing drop with an initially pre-established equilibrium adsorption layer, the complexities are less, but for higher surfactant concentrations it is not optimum. The SGD protocol provides a drop with a fresh surface and the dynamic interfacial tension can be monitored in the absence of hydrodynamic effects. All three protocols complement each other and provide a good set of data for dynamic interfacial tensions at short adsorption times.

Adsorption layer characteristics of Triton surfactants: 4. Dynamic surface tension and dilational visco-elasticity of micellar solutions

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 0.1 ms up to 50 s 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 (0.005–0.2 Hz) 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.

Adsorption layer characteristics of Triton surfactants: Part 2. Dynamic surface tension and adsorption

The adsorption kinetics of four Tritons (TX45, TX100, TX165 and TX405) was studied by using the complementary drop and bubble profile and maximum bubble pressure tensiometry methods. While TX45 and TX100 can be quantitatively described by a diffusion controlled adsorption mechanism, based on the reorientation model for describing the equilibrium state of adsorption, the results for TX165 and TX405 deviate significantly from this adsorption mechanism. With additional assumptions, such as a finite rate constant for the transition of adsorbed molecules between states of different molar area, and effects of the composition of the Triton samples by many compounds of different ethylene oxide chains, a much better description of the experimental data is possible.

Correction for the Aerodynamic Resistance and Viscosity in Maximum Bubble Pressure Tensiometry

The application of the maximum bubble pressure tensiometry at short adsorption times (below 0.5 s) is complicated by the two effects aerodynamic resistance of the capillary and viscosity of the studied liquid. A procedureis shown that demonstrates how the two effects can be taken into consideration to obtain correct dynamic surface tensions. The parameters are determined for a commercial steel capillary of 0.25-mm diameter and 60-mm length. The correction procedure, in turn, can even be used to estimate the viscosity of the liquid under investigation in case it is unknown.

Maximum bubble pressure tensiometry—an analysis of experimental constraints

The maximum bubble pressure tensiometry is the only technique that allows measurements of dynamic surface tensions of surfactant solutions in the short time range down to milliseconds and even below. To reach such extremely short adsorption times, many hydrodynamic and aerodynamic effects have to be taken into consideration in order to measure physical values or to correct for the respective influences. In particular, the design of the instruments, and essentially the geometry of the measuring cell and capillary, are of key importance for accurate experiments. Another important issue is the way of determination of the characteristic bubble times, such as bubble dead time and lifetime. Examples demonstrate that the bubble pressure technique provides a powerful tool for studies of adsorption dynamics even for solutions of higher viscosities.

Accurate analysis of the bubble formation process in maximum bubble pressure tensiometry

A method has been developed to determine the characteristic times of bubble formation in maximum bubble pressure experiments. It consists in the analysis of gas flow from a continuous reservoir or pump through a capillary into the system volume attached to the measuring capillary. This method works more reliably than the analysis of the direct pressure signal in the gas volume. A discussion on the optimum choice of the internal gas volume is made with the aim of maximum accuracy of determination of the surface tension and bubble deadtime and lifetime. The findings are compared with conditions given in various commercial instruments.

An investigation of dynamic surface tension, critical micelle concentration, and aggregation number of three nonionic surfactants using NMR, time-resolved fluorescence quenching, and maximum bubble pressure tensiometry

Several physicochemical properties have been determined for N-dodecyllactobionamide (LABA), maltose 6′- O-dodecanoate (C 12-maltose ester), and tetra(ethylene oxide) dodecyl amide (TEDAd). The increase in the flexibility of the sugar headgroup, enabling more possible molecular conformations, reduces the minimum area/molecule at the liquid–vapor interface obtained at the critical micelle concentration (cmc). The obtained cmc's were 0.35 mM (LABA), 0.3 mM (C 12-maltose ester), and 0.5 mM (TEDAd). The monomer diffusion coefficient decreased with the molecular weight and increasing headgroup flexibility of the sugar headgroup, and values were in the range from 3.1×10 −10 to 3.6×10 −10 m 2/s. The micelle diffusion coefficients (0.46×10 −10 to 0.68×10 −10 m 2/s) indicated that the TEDAd micelles deviated most from spherical shape. The micelle aggregation numbers determined by time-resolved fluorescence quenching (TRFQ) were estimated to be 120±10 (LABA), 90±10 (C 12-maltose ester), and 130±10 (TEDAd). The dynamic surface tension measurements show that the adsorption of TEDAd onto the liquid–vapor interface at short surface lifetimes is diffusion-limited, whereas an adsorption barrier is present for the sugar surfactants. The analysis of the dynamic surface tension data above the cmc shows that the rate of demicellization is faster for TEDAd than for the two sugar-based surfactants.

Adsorption Properties of Novel Gemini Surfactants with Nonidentical Head Groups

Novel environmentally friendly gemini surfactants, each with two hydrophilic and two hydrophobic groups, have been synthesized and their physicochemical properties investigated. One of the hydrophilic groups is a methyl-capped polyoxyethylene chain with mol wt 350, 550, and 750 g/mol, respectively, and the other is a sulfate group; the hydrophobic part of the surfactant is made from oleylnitrile. This nitrile derivative of the fatty acid is used to achieve good hydrolytic stability. Du Nouy ring and maximum bubble pressure tensiometry were used for equilibrium and dynamic surface tensions, γe and γt, respectively. The aqueous-phase critical micelle concentrations of the heterogeminis (HGs) have been investigated. The results have been compared with those for mixtures of standard surfactants sodium decylsulfate and octaoxyethyleneglycol mono n-decyl ether under equivalent conditions. The HGs are shown to exhibit improved performance over the mixed system both in terms of micellization and surface tension lowering. Dynamic surface tension (DST) studies were performed to investigate air–water adsorption mechanisms. A diffusion-limited mechanism was confirmed in the initial stages of adsorption. However, closer to the equilibrium the DST data are inconsistent with a diffusion-only mechanism. In particular, the HGs show a larger deviation from diffusion control as compared to the model mixture, which is a signature of slower adsorption kinetics. In addition to air–water interfaces, properties of these HGs have also been investigated at solid silica–solution surfaces by optical reflectometry. These surfaces were either naturally hydrophilic or rendered hydrophobic by chemical modification. On either surface the maximum amount of adsorbed surfactant was found to increase when the polyoxyethylene chain length decreases.