Colloids and Surfaces A: Physicochemical and Engineering Aspects
Dynamic surface tension of С10ЕО8 at the aqueous solution/hexane vapor interface as measured by bubble pressure tensiometry
Graphical abstract
Introduction
Several studies have shown that alkanes adsorb from the gas vapor phase at the water surface [1], [2], [3], [4], [5], [6], [7] and reduce the surface tension significantly. In these studies the drop profile analysis tensiometry turned out to be an excellent experimental tool and surface tension data were obtained for the adsorption of various alkanes (pentane, hexane, heptane, octane) at the water surface at room temperature [7]. In [8], [9], [10], [11], [12], [13], the co-adsorption of surfactants from an aqueous solution phase and alkane from a gas vapor phase was investigated. In [11], the surface tensions of water and aqueous solutions of the non-ionic surfactant C10EO8 (octaethylene glycol monodecyl ether) were measured at various concentrations in hexane saturated air by using the drop profile analysis tensiometry. For the analysis of the experimental data, an equation of state and a corresponding adsorption isotherm were derived. This theoretical model was based on the analysis of the chemical potentials of the solvent and of the surface active components in the solution bulk, in the gas phase and at the surface of the drop. The target of work presented in [12] was dedicated to the influence of the hexane partial vapor pressure on the surfactants and hexane co-adsorption. The study included cationic, anionic and non-ionic surfactants, each at different bulk concentrations and different hexane partial vapor pressures, respectively. On the basis of the model proposed in [11] the physics behind the co-adsorption was discussed.
An important field of application for the oil vapor co-adsorption from the gas phase is the simulation of the alveoli/air interface in the pulmonary system. In [13], [14], the adsorption of fluorocarbon gases (FCs) to dipalmitoylphosphatidylcholine (DPPC) monolayers, taken as a simplified model of lung surfactant, and its impact on the structure and behavior of these monolayers upon compression and expansion was investigated. Overviews of the role of FCs in medicine were published in [13], [14], [15], [16], [17], [18]. In particular, a discussion has been performed on the role of FCs in the treatment of acute respiratory distress syndrome, for alveolar environment of trauma patients and in pulmonary disease therapies [13], [19]. In [19], the adsorption dynamics of a series of phospholipids (PLs) at the interface between aqueous solutions or dispersions of a series of phospholipids and a gas phase saturated with perfluorohexane gas (PFH) was studied by bubble profile analysis tensiometry. It was found that the PFH gas has an unexpectedly strong effect on both the adsorption rate and the equilibrium interfacial tension of the phospholipids. First, the presence of PFH in the gas phase lowered the surface tension significantly, i.e., by up to 10 mN/m. Second, the adsorption rates of all the PLs at the liquid/vapor interface were significantly accelerated up to five times in the presence of PFH at low PLs concentrations. Both effects, the surface tension reduction and the increased adsorption rate, caused by PFH point to a strong interaction of the latter with the PLs monolayer, which acts as a co-surfactant at the interface. This behavior is similar to that observed at the interface between alkane vapor and aqueous solutions of various surfactants [7], [8], [9], [10], [11], [12]. PFH gas was also found to lower the kinetic barrier that opposes the displacement of albumin by dipalmitoylphosphatidylcholine at the air/water interface submitted to sinusoidal oscillations at frequencies in the range of those encountered in respiration [20].
In all studies on the adsorption of alkanes and fluorocarbons from the gas vapor phase at the surface of aqueous solutions, there is little work on the kinetics of lowering the surface tension at short adsorption times. This, however, would be especially important for investigations of respiratory systems, as in breathing the adsorption/desorption processes proceed at short times. The results in [19] indicate a high rate of the adsorption processes: for large phospholipids concentrations the results obtained by bubble profile analysis tensiometry are rather close to equilibrium at the shortest available time.
In the present work, studies were carried out by maximum bubble pressure tensiometry in the surface time range between 10 ms and several seconds. The bubble pressure experiments were performed with hexane saturated air, as it was done in [11]. It can be shown that the decrease in surface tension under dynamic conditions is larger at higher surfactant concentrations, and with increasing surfactant concentration the measured surface tension starts to decrease at shorter times. The results obtained are described theoretically by using a reorientation model and a diffusion mechanism for the adsorption of the surfactant C10EO8, and a non-diffusional mechanism for the adsorption of hexane. In addition a strong interaction between hexane and C10EO8 molecules in the adsorption layer is assumed.
Section snippets
Materials and methods
The dynamic surface tension was measured with the tensiometer BPA-1S (SINTERFACE Technologies, Germany). The instrument's design and measuring procedures were described in detail elsewhere [21], [22], [23], [24]. For the saturation of air by hexane vapor a special measuring cell and capillary were used. The cell includes an additional chamber with liquid hexane as shown in Fig. 1, through which the air has to pass before forming bubbles at the capillary tip. To reach bubble lifetimes down to 10
Results and discussion
Fig. 2 shows the dynamic surface tension of water at 25 °C for pure air and air saturated with hexane vapor, as measured with the BPA-1S. At this temperature the partial hexane vapor pressure is 20,000 Pa. For lifetimes in the range between 10 ms and 30 s, the surface tension of water decreases by about 1 mN/m due to the presence of hexane vapor. This figure also shows the results obtained with PAT using two different modes: the pendant drop (data [11], curve 1) and emerging bubble (line 2) modes.
Conclusions
The dynamic surface tension of water drops or drops of aqueous solutions of C10EO8 at the interfaces with air and saturated hexane vapor were measured by the maximum bubble pressure methods for times t ≥ 0.01 s. It can be shown that the dynamic surface pressure of C10EO8 solutions in a saturated hexane atmosphere increases at short adsorption times with increasing surfactant concentration. The obtained experimental results agree with a model based on a reorientation of the C10EO8 molecules and
Acknowledgements
The work was financially supported by the COST actions CM1101 and MP1106.
References (26)
Liquid–liquid interfaces: studied by X-ray and neutron scattering
Curr. Opin. Colloid Interface Sci.
(2002)- et al.
Alkane vapour and surfactants co-adsorption on aqueous solution interfaces
Colloids Surf. A
(2011) - et al.
Mixed adsorption layers at the aqueous CnTAB solution/hexane vapour interface
Colloid Surf. A
(2014) - et al.
Effect of partial vapor pressure on the co-adsorption of surfactants and hexane at the water/hexane vapor interface
Colloids Surf. A
(2015) - et al.
Fluidization of a dipalmitoyl phosphatidylcholine monolayer by fluorocarbon gases: potential use in lung surfactant therapy
Biophys. J.
(2006) - et al.
Adsorption layer characteristics of Triton surfactants. 2. Dynamic surface tensions and adsorption dynamics
Colloids Surf. A
(2009) Second virial coefficients for n-alkanes adsorbed at the vapor/water interface
Langmuir
(1996)Enthalpies of adsorption of n-alkanes adsorbed at the vapor/water interface
Langmuir
(2000)- et al.
Intermolecular forces between the n-alkanes methane to butane adsorbed at the water/vapor interface
Langmuir
(2003) - et al.
Lateral intermolecular forces in the physisorbed state: surface field polarization of benzene and n-hexane at the water/ and mercury/vapor interfaces
Langmuir
(2005)
Formation of n-alkane layers at the vapor/water interface
Langmuir
Adsorption of alkanes from the vapour phase on water drops measured by drop profile analysis tensiometry
Soft Matter
Adsorption of alkyltrimethylammonium bromides at water/alkane interfaces – competitive adsorption of alkanes and surfactants
Langmuir
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2017, Colloids and Surfaces A: Physicochemical and Engineering AspectsInfluence of alkane and perfluorocarbon vapors on adsorbed surface layers and spread insoluble monolayers of surfactants, proteins and lipids
2017, Advances in Colloid and Interface ScienceCitation Excerpt :In addition, Fig. 1 (curve 5) shows the dependence obtained by the emerging bubble method [18]. The surface tension values recorded in these experiments are higher as compared with those obtained in the drop profile experiments due to the losses of hexane caused by adsorption, which resulted in the decrease of hexane concentration in the bubble, see [10,18]. Fig. 3 illustrates the measurements of dynamic surface tension of the C10EO8 solution with a concentration of 2 × 10− 4 mol/l, obtained by three methods: pendant drop, emerging bubble (PAT) and maximum bubble pressure (BPA).
Adsorption of surfactants and proteins at the interface between their aqueous solution drop and air saturated by hexane vapour
2017, Colloids and Surfaces A: Physicochemical and Engineering AspectsCitation Excerpt :The adsorption of alkanes from the gas phase on drops of solutions of various surfactants was also studied by various authors. The experimental results and theoretical models for the concurrent adsorption of alkanes from the gas phase and surfactants (or proteins) from their solutions were presented in Refs. [1–15]. It was shown that the adsorption of alkanes or fluorocarbon gases from the gas phase at the surface of water and aqueous protein solutions results in an essential decrease of the surface tension; also the rate of the alkane adsorption at the surface of surfactant solutions is higher than that the pure water surface.
Surface tension of water and C<inf>10</inf>EO<inf>8</inf> solutions at the interface to hexane vapor saturated air
2016, Colloids and Surfaces A: Physicochemical and Engineering AspectsCitation Excerpt :The results of type 3 experiments are unstable. Therefore, in Refs. [19,21,24] the drop profile experiments were performed using a cell which contained a vessel filled with 1.5 ml of water, having an open free area of 2 cm2. This vessel was placed just underneath the capillary, to ensure that any water or solution drops fall into it.