Forces between a rigid probe particle and a liquid interface. III. Extraction of the planar half-space interaction energy E(D)

The deformation of a liquid drop (radius R0) under the probe particle (radius a) greatly complicates the interpretation by atomic force microscopy. For rigid interfaces, F(DeltaX) can be directly related to the interaction energy E(D) per unit area between planar half-spaces of probe material and drop material across a thickness D of the liquid medium by the Derjaguin approximation, [formula in text], where D(0) is the intersurface separation distance on the line of the centers of the bodies and DeltaX0 is a constant set by the somewhat arbitrary choice of origin for the separation distance DeltaX between the stage on which the drop rests and the lowest point on the probe particle. The problem of absolute intersurface separation distance is common to all surface force measurement techniques. For rigid interfaces, DeltaX0 may be established by bringing the surfaces into close (essentially hard) contact and making measurements in the constant compliance regime. For deformable interfaces, this is not possible and a general method of extracting the absolute separation distance has yet to be devised. In this paper we discuss a general algorithm for extracting E(D+DeltaX0) from F(DeltaX) data. We apply the method to constructed data to investigate the effect of data noise and to a set of real data for a sessile tetradecane droplet in water with an anionic surfactant and a bare silica probe.     

Forces between cylindrical nanoparticles in a liquid crystal

Using classical density functional theory, the forces between two cylindrical nanoparticles in a liquid crystal solvent are calculated. Both the nematic and isotropic phases of the solvent are considered. In the nematic phase, the interaction is highly anisotropic. At short range, changes in the defect structure around the cylinders leads to a complex interaction between them. In the isotropic phase, an attractive interaction arises due to overlap between halos of ordered fluid adsorbed on the surfaces of the cylinders.     

Interaction between an ion-penetrable particle and a solid particle. II. Criteria for heterocoagulation

The potential energy of the total interaction between two spherical colloidal particles of different nature is calculated, i. e., of an ion-penetrable particle and an ion-impenetrable solid particle having a constant surface potential or constant surface charge density. The criteria for heterocoagulation are derived. The obtained results suggest a possibility of selective coagulation in the mixed system.     

Forces between two polymer layers adsorbed at a solid-liquid interface in a poor solvent

The forces between mica surfaces a distance D apart immersed in cyclohexane, bearing adsorbed layers of polystyrene, have been measured at temperatures lower than the corresponding critical temperatures. Polymers of two different molecular weights were used. The results show that these forces are attractive for 3R_g > D >. R_g (where R_g is the polymer radius of gyration) and repulsive at lower D, and may be understood in terms of the phase equilibrium of the polystyrene-cyclohexane system. The adsorption of the polymer under these conditions appears to be effectively irreversible over the time of our experiments. The adsorbance of polymer and the thickness of the adsorbed layers are comparable with values measured in other studies using entirely different techniques.     

Intramolecular energy transfer between chromophores separated by a rigid steroid bridge: II. Energy transfer as a probe to determine the ratio of two epimers

The singlet-singlet intramolecular energy transfer between naphthalene moiety and dansy! group held apart by a rigid steroid bridge was investigated for two molecules: β-(1-naphthyl) acetoxy-17α-dansyl-Δ⁵androstene (3a) and 3β-(1-naphthyl)acetoxy-17 β-dansyl-Δ⁵androstene (3b). The rates of energy transfer for 3a and 3b in cyclohexane are 6.9 × 10⁶ and 1.1 × 10⁸ s^?1 respectively. The difference in energy transfer rate between 3a and 3b is attributed to the different donor-acceptor separation and orientation. The ratio of the two epimers in the synthesized product mixture was obtained from the fluorescence decay measurements.     

Analysis of coumarins by micro high-performance liquid chromatography-mass spectrometry with a particle beam interface

Coumarins are a large group of compounds that are naturally present in plant tissues and that exhibit a wide range of pharmacological properties. Analytical methods based on chromatographic techniques and conventional detectors are inadequate to accurately analyze coumarins in complex matrices such as plant extracts. In this article a new method based on a modified particle beam liquid chromatography-mass spectrometry interface is described. The method allows specific and accurate determination of several coumarins in biological matrices. An application regarding the analysis of 18 coumarins in the extract of Smyrnium perfoliatum L. is also reported.     

The effect of gravity on the drainage of a thin liquid film between a solid sphere and a liquid/fluid interface

A study has been made of the influence of gravitational forces on the thinning of the liquid film which forms as a solid sphere comes to rest on a liquid/fluid interface. It is found that rates of drainage can be dramatically affected by the ratio of gravity to surface tension forces within the film. At long times a secondary film can possibly be formed which spreads out radially from the apex of the sphere.     

Interaction between a disclination and a uniaxial-isotropic phase interface in a nematic liquid crystal

We consider the interaction between a disclination line of strength +/-1/2 and an interface between the uniaxial and isotropic phases of a nematic liquid crystal. We apply a recently developed set of interface conditions including a configurational force balance which generalizes the Gibbs-Thomson equation to account for the curvature elasticity of the uniaxial phase and the orientation dependence of the interfacial free-energy density. We consider a rectangular vessel containing both phases and a disclination. We formulate a relevant free-boundary problem and use numerical methods to determine equilibrium shapes of the interface. When the interfacial free-energy is constant, the shape of the interface is insensitive to whether the strength of the defect is +1/2 or -1/2 and to rotations of the director field consistent with the boundary conditions. Accounting for the dependence of the interfacial free-energy density on the angle between the interfacial unit normal field and the director field eliminates these degeneracies. In particular, when such dependence is taken into account, different solution branches are found, indicating the presence of a bifurcation. We find also that, depending on the magnitude of the anisotropic contribution to the interfacial free-energy density, the interaction between the disclination and the interface may be repulsive or attractive. When the interaction is repulsive, the disclination line positions itself at an energetically optimal distance adjacent to the interface. Otherwise, the uniaxial phase expels the disclination to the interface where a cusp forms.     

Prediction of multicomponent liquid adsorption using excess quantities. II. Calculations for the liquid/solid interface

The utilization of excess quantities as the basis for a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. A new method for predicting liquid adsorption on solids is suggested, which is different from the existing equations with respect to the theoretical background and formulation. The applicability of the new model is tested with three ternary adsorption systems. The predicted surface excesses are discussed and compared with experimental ones and with those of other prediction models in the literature. The accordance between measured and predicted ternary data is convincing.     

Relationship between interfacial transfer and adsorption-desorption of surface-active bis-ammonium ions at a liquid/liquid interface

Cyclic voltammograms and interfacial tension-applied potential curves were recorded at the interface between water containing surface-active bis-quaternary ammonium ions, bis-A(2+), and an organic solvent such as 1,2-dichloroethane or nitrobenzene. An ordinary diffusion-controlled voltammetric wave for the transfer of bis-A(2+) from aqueous phase to organic phase, the first wave, was followed by a typical adsorption-related wave, the second wave. It was found from the potential dependence of the interfacial tension of bis-A(2+) that the second wave was due to the desorption of bis-A(2+) toward the organic phase. The influence of the structure of bis-A(2+) on voltammograms was investigated, and the potential for the first wave was found to depend on both the length of the side chain and that of the spacer chain, whereas the potential for the second wave depended on the latter only. The thermodynamic relations among three processes of the ion transfer, adsorption, and desorption were discussed based on the experimental results.     

Mobility of a particle immersed in a liquid film between two fluids

The mobility of a particle immersed in a liquid film between two viscous fluids is calculated in point approximation. The mobility in the direction parallel to the film diverges logarithmically as the ratio of the sum of outside viscosities to the film viscosity tends to zero, as in the [Saffman-Delbruck, Proc. Natl. Acad. Sci. U.S.A. 72, 3111 (1975)] expression for the mobility of a particle embedded in a membrane. A simple expression for the limiting behavior is derived. For any values of the parameters the mobility tensor can be evaluated by numerical quadrature of two one-dimensional integrals.     

An improved interface for liquid chromatography/electron-capture detector coupling. Part II

Summary An improved interface for the coupling of a liquid chromatograph (LC) and an electron-capture detector (ECD) allows the use of the LC-ECD combination for the determination of various types of chlorinated aromatic compounds. The addition of up to 6% of dioxan to the hexane used as mobile phase can be tolerated without serious deterioration of detector performance. Derivatization of polar compounds such as anilines, phenylurea herbicides, chlorophenols and hydroxylated polychlorobiphenyls with fluorine-and non-fluorine-containing acid anhydrides is a useful tool to extend the application range of LC-ECD. As an example, the analysis of a spiked soil sample is discussed.Presented at the 14th International Symposium on Chromatography London, September, 1982     

The interface between water and a hydrophobic gas

Classical molecular dynamics simulations have been performed to investigate the interface between liquid water and methane gas under methane hydrate forming conditions. The local environments of the water molecules were studied using order parameters which distinguish between liquid water, ice and methane hydrate phases. Bulk water and water/air interfaces were also studied to allow comparisons to be made between water molecules in the different environments and to determine the effects of the different methane densities studied. Good agreement between experimental and calculated surface tensions is obtained if long range corrections are included. The water surface is found to have a structure which is very similar to that of bulk water, but more tetrahedral, and more clathrate-like than ice-like. In these simulations the concentration of methane in water at the interface is shown to be appropriate for clathrates at higher gas densities (pressures). The orientation of water molecules around methane molecules in the interfacial region appears to depend only weakly on pressure and one of the difficulties in forming hydrate is the availability of water molecules tangential to the hydrate cage. At the interface, the water structure is more disordered than in the bulk water region with increased occurrence compared with the bulk of those angles and orientations found in the clathrate structure.     

Ultraviolet laser photo-modulation voltammetry of tetraphenylborate at a liquid/liquid interface.

Photo-modulation voltammetry was applied to detecting the photolysis of tetraphenylborate (TPhB) at a water/1,2-dichloroethane (DCE) interface by using a He-Cd laser emitting a beam with a major 325-nm line and minor lines of shorter wavelengths. When the interface was irradiated from the water-phase side, a new wave appeared in the photomodulation voltammogram, suggesting that TPhB was photolyzed and the anionic product was transferred across the interface. The concentration dependence of the photocurrents was successfully explained by a theory based on the photolytic process at the interface.     

Electron transfer across the polarized interface between water and a hydrophobic redox-active ionic liquid

Here we report the synthesis of a new redox-active ionic liquid (IL), (ferrocenylmethyl)dodecyldimethylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate that can be used to form the polarizable water│IL interface at an elevated temperature (43 °C). Experimental approach is based on the cyclic voltammetry of the charge transfer processes occurring at the IL membrane supported on a thin microporous filter. Evidence is provided of the interfacial electron transfer between the ferrocenated cation of IL and an electron acceptor, IrCl₆^2?, in the adjacent aqueous phase.     

Determination of chloramphenicol in muscle using a particle beam interface for combining liquid chromatography with negative-ion chemical ionization mass spectrometry.

A simple and rapid liquid chromatographic-mass spectrometric analysis of chloramphenicol in calf muscle is presented. A particle beam interface was used, with negative-ion chemical ionization mass spectrometry using methane as the reagent gas. The method specificity was tested for three related compounds, dehydrochloramphenicol, nitrosochloramphenicol and nitrophenylaminopropanediol. The extraction procedures require 5 g of muscle, and the quantification limit is 2 micrograms/kg for chloramphenicol. Residues were detected in calf muscle 48 h after intravenous administration of chloramphenicol (25 mg/kg body weight).     

Quantum rigid dipole in a permanent electric field. II. Model of librational motion in liquid water and ice Ih: Preliminary results

A theoretical one-body model of librational motion in liquid water and ice Ih is proposed within the quantum mechanical treatment of a rigid and pointlike dipole in a permanent electric field and the concept of the internal electric field justified for V-structure of liquid water.