Measuring the Equilibrium Spreading Pressure-A Tale of Three Amphiphiles.

A surfactant's equilibrium spreading pressure (ESP) is the maximum decrease in surface tension achievable at equilibrium below the Krafft point. Difficulties in measuring the ESP have been noted previously but no well-established experimental protocols to overcome them exist. We present a case study of three solid amphiphiles with different propensities to spread on the air-water interface.

Electrolytes at Uncharged Liquid Interfaces: Adsorption, Potentials, Surface Tension, and the Role of the Surfactant Monolayer.

The article summarizes the results of our research on the behavior of ions at uncharged fluid interfaces, with a focus on moderately to highly concentrated aqueous electrolytes. The ion-specific properties of such interfaces have been analyzed. The ion-specificity series are different for water|air and water|oil; different for surface tension , surface Δ potential and electrolyte adsorption, and they change with concentration.

Quantifying the Hydrophobic Effect per CF Moiety from Adsorption of Fluorinated Alcohols at the Water/Oil Interface.

Amphiphilic fluorocarbon substances are a trending topic of research due to their wide range of applications accompanied by an alarming environmental and health impact. In order to predict their fate in the environment, use them more economically, develop new water treatment methods, etc., a better understanding of their physicochemical behavior is required.

Phase transitions of fluorotelomer alcohols at the water|alkane interface studied molecular dynamics simulation.

Fluorosurfactants are long-lasting environmental pollutants that accumulate at interfaces ranging from aerosol droplet surfaces to cell membranes. Modeling of adsorption-based removal technologies for fluorosurfactants requires accurate simulation methods which can predict their adsorption isotherm and monolayer structure. Fluorotelomer alcohols with one or two methylene groups adjacent to the alcohol (7 : 1 FTOH and 6 : 2 FTOH, respectively) are investigated using the OPLS-AA force field at the water|hexane interface, varying the interfacial area per surfactant.

Theory of adsorption of ethoxylates at the water | oil and water | air interfaces. 1. Monolayers of single-component and Poisson distributed alkylphenol ethoxylates.

Currently, the bulk thermodynamic properties of an arbitrary liquid mixture of oligomers are accessible with reasonable accuracy through popular 3D statistical models (SAFT, Flory-Huggins) under a wide range of conditions. These models are implemented in widely available software suites used for process design. The hypothesis investigated here is that the same is, in principle, achievable with monolayers of mixed surfactants on liquid surfaces.

Effect of the solvent quadrupolarizability on the strength of the hydrogen bond: Theory vs data for the Gibbs energy and enthalpy of homo- and heteroassociation between carboxylic acids and water.

A cavity model of the effect of a solvent on thermodynamic parameters of dimerization of polar species in non-polar liquids has been developed and compared to experimental data. Bulk solution data have been collected for stearic acid in cyclohexane and in toluene to quantify the extent of self-association of the acid in terms of the dimer self-dissociation constant, Kd. Composition and temperature-dependent experimental data have been collected to determine Kd, the enthalpy of dissociation, and temperature-dependent infrared molar absorption coefficients.

Measuring the Adsorption of Electrolytes on Lipid Monolayers.

The interactions between ions and lipid monolayers have captivated the attention of biologists and chemists alike for almost a century. In the absence of experimentally accessible concentration profiles, the electrolyte adsorption remains the most informative quantitative characteristic of the ion-lipid interactions. However, there is no established procedure to obtain the electrolyte adsorption on spread lipid monolayers.

Interactions between Small Inorganic Ions and Uncharged Monolayers on the Water/Air Interface.

The interaction of several simple electrolytes with uncharged insoluble monolayers is studied on the basis of tensiometric and potentiometric data for the surface electrolyte solution|air. The induced adsorption of electrolyte on the monolayer is determined via a combination of data for equilibrium spreading pressure and surface pressure versus area isotherms. We show that the monolayer-induced adsorption of electrolyte is not only strongly ion-specific but also surfactant-specific.

Adsorption model and phase transitions of diblock perfluoroalkylated surfactants at the water∣alkane interface.

We present a theory of the adsorption behaviour and phase transitions in monolayers of perfluoroalkylated alcohols, n-CFCHOH, at the water∣oil interface, and validate it for a range of temperatures and surfactant structures. The reason for the observed cohesive behaviour is identified as dispersion attraction between the fluorocarbon blocks. The London constant is determined from the increment of the lateral attraction parameter with the size of the fluorocarbon chain.

Quadrupolarizability of Liquid Mixtures.

Theoretical expressions for the macroscopic polarizability and quadrupolarizability of a quadrupolar mixture are derived. The theory is demonstrated on the example of a liquid mixture of methane and nitrogen (nonquadrupolar plus quadrupolar component). It turns out that the dielectric permittivity (the "dipole strength" of the liquid) of this mixture changes little with the composition, while the quadrupolar length ("quadrupolar strength") almost triples as the fraction of nitrogen approaches one.

Improved methodology for performing the inverse Abel transform of flame images for color ratio pyrometry.

A new method is presented for performing the Abel inversion by fitting the line-of-sight projection of a predefined intensity distribution (FLiPPID) to the recorded 2D projections. The aim is to develop a methodology that is less prone to experimental noise when analyzing the projection of axisymmetric objects-in this case, co-flow diffusion flame images for color ratio pyrometry. A regression model is chosen for the light emission intensity distribution of the flame cross section as a function of radial distance from the flame center line.

Correction: Barrier kinetics of adsorption-desorption of alcohol monolayers on water under constant surface tension.

Correction for 'Barrier kinetics of adsorption-desorption of alcohol monolayers on water under constant surface tension' by Ivan L. Minkov et al., Soft Matter, 2019, DOI: 10.

Barrier kinetics of adsorption-desorption of alcohol monolayers on water under constant surface tension.

The desorption of spread decanol and dodecanol monolayers at controlled constant surface tension is shown to proceed under mixed barrier-diffusion control; the role of the convective diffusion is also discussed. The desorption rate is measured as a function of the density of the monolayer and the temperature. The rate of barrier desorption increases as the monolayer approaches the collapse point, reaching an infinite value.

Effective osmotic cohesion due to the solvent molecules in a delocalized adsorbed monolayer.

A molecular thermodynamic model is derived for an uncharged delocalized surfactant monolayer adsorbed at a liquid interface, taking explicit account for the solvent molecules present in the monolayer. The model is based on the scaled particle theory of hard-disc mixtures, and is also extended to sticky discs (i.e.

Adsorption parameters and phase behaviour of non-ionic surfactants at liquid interfaces.

A reasonable adsorption model is one that allows all adsorption parameters (adsorption constant, hard-disc area α, attraction parameter β) of a surfactant at a liquid interface to be predicted accurately as a function of the molecular structure and medium conditions. However, the established adsorption models of van der Waals and Frumkin lead to inconsistencies, such as negative β at water|oil, α significantly larger than the crystallographic area of the molecule, and phase behaviour that contradicts the experimental observations. Several less popular models that are better suited for liquid interfaces are investigated.

Energy of Liposome Patch Adhesion to the Pipet Glass Determined by Confocal Fluorescence Microscopy.

The formation of the gigaseal in the patch clamp technique is dependent on the adhesion between the cell or liposome membrane and the glass pipet. The adhesion results in a capillary force causing creep of the patch membrane up the pipet. The membrane can be immobilized by counteracting the capillary force by positive pressure applied to the patch pipet.

Adsorption of Ions at Uncharged Insoluble Monolayers.

A method is proposed for the experimental determination of the adsorption of inorganic electrolytes at a surface covered with insoluble surfactant monolayer. This task is complicated by the fact that the change of the salt concentration alters both chemical potentials of the electrolyte and the surfactant. Our method resolves the question by combining data for the surface pressure versus area of the monolayer at several salt concentrations with data for the equilibrium spreading pressure of crystals of the surfactant (used to fix a standard state).

A spherical cavity model for quadrupolar dielectrics.

The dielectric properties of a fluid composed of molecules possessing both dipole and quadrupole moments are studied based on a model of the Onsager type (molecule in the centre of a spherical cavity). The dielectric permittivity ε and the macroscopic quadrupole polarizability αQ of the fluid are related to the basic molecular characteristics (molecular dipole, polarizability, quadrupole, quadrupolarizability). The effect of αQ is to increase the reaction field, to bring forth reaction field gradient, to decrease the cavity field, and to bring forth cavity field gradient.

The polarized interface between quadrupolar insulators: Maxwell stress tensor, surface tension, and potential.

The quadrupolar Maxwell electrostatic equations predict several qualitatively different results compared to Poisson's classical equation in their description of the properties of a dielectric interface. All interfaces between dielectrics possess surface dipole moment which results in a measurable surface potential jump. The surface dipole moment is conjugated to the bulk quadrupole moment density (the quadrupolarization) similarly to Gauss's relation between surface charge and bulk polarization.

Gigaseal mechanics: creep of the gigaseal under the action of pressure, adhesion, and voltage.

Patch clamping depends on a tight seal between the cell membrane and the glass of the pipet. Why does the seal have such high electric resistance? Why does the patch adhere so strongly to the glass? Even under the action of strong hydrostatic, adhesion, and electrical forces, it creeps at a very low velocity. To explore possible explanations, we examined two physical models for the structure of the seal zone and the adhesion forces and two respective mechanisms of patch creep and electric conductivity.

Adsorption of ions at the interface oil|aqueous electrolyte and at interfaces with adsorbed alcohol.

We investigate the applicability of the Schmutzer's model for three types of interfaces: aqueous electrolyte|alkane, aqueous electrolyte|long chained alcohol phase, and aqueous electrolyte|alkane with adsorbed alcohol. The model predicts a strong decrease of the electrolyte desorption at water|alcohol interface in comparison with water|alkane, in quantitative agreement with the tensiometric data. The effect is related to the penetration of the alcohol -OH group into the surface layer of the aqueous solution.

Quadrupole terms in the Maxwell equations: Debye-Hückel theory in quadrupolarizable solvent and self-salting-out of electrolytes.

If the molecules of a given solvent possess significant quadrupolar moment, the macroscopic Maxwell equations must involve the contribution of the density of the quadrupolar moment to the electric displacement field. This modifies the Poisson-Boltzmann equation and all consequences from it. In this work, the structure of the diffuse atmosphere around an ion dissolved in quadrupolarizable medium is analyzed by solving the quadrupolar variant of the Coulomb-Ampere's law of electrostatics.

Quadrupole terms in the Maxwell equations: Born energy, partial molar volume, and entropy of ions.

A new equation of state relating the macroscopic quadrupole moment density Q to the gradient of the field ∇E in an isotropic fluid is derived: Q = αQ(∇E - U∇·E/3), where the quadrupolarizability αQ is proportional to the squared molecular quadrupole moment. Using this equation of state, a generalized expression for the Born energy of an ion dissolved in quadrupolar solvent is obtained. It turns out that the potential and the energy of a point charge in a quadrupolar medium are finite.

Fully atomistic molecular-mechanical model of liquid alkane oils: Computational validation.

Fully atomistic molecular dynamics simulations were performed on liquid n-pentane, n-hexane, and n-heptane to derive an atomistic model for middle-chain-length alkanes. All simulations were based on existing molecular-mechanical parameters for alkanes. The computational protocol was optimized, for example, in terms of thermo- and barostat, to reproduce properly the properties of the liquids.