Influence of temperature on surface tension of three liquid crystal polymers and polyethylene terephtalate

In this work Pressure Volume Temperature (PVT) data for three different liquid crystal polymers (LCPs), namely Vectra A950^® and two LCPs based on 4,4′-dihydroxybiphenyl (PB-n) (where n is the number of methylene units present in the polymer) and polyethylene terephtalate (PET), were obtained for temperatures ranging from 50 to 300°C and pressures ranging from 0.1 to 200?MPa. The experimental data were fitted to the Flory–Orwoll–Vrij equation of state and used to predict the influence of temperature on the surface tension of the four materials studied.

The surface tension of PET was shown to decrease linearly with increasing temperature. The surface tension of both PB-11 (γ _PB-11) and Vectra A950^® (γ _Vectra) decreased linearly with increasing temperature for temperatures corresponding to the nematic phases of the materials. Abnormal behaviour was observed for the surface tension of PB-8 (γ _PB-8): at temperatures just above T _b (the temperature at which the material became birefringent), γ levelled off and then decreased. A clear discontinuity was observed for both γ _PB-8 and γ _PB-11 near the mesophase to isotropic transition. For both PB-8 and PB-11, γ decreased linearly with increasing temperature for temperatures corresponding to the isotropic phases of the materials.     

Effect of surface-active additives on the temperature behavior of interfacial tension in water-<Emphasis Type="Italic">n</Emphasis>-hexane systems

The temperature dependence of interface tension in a water-n-hexane system without additives and after addition of stearic acid was experimentally studied at four different concentrations. A method for determining the excess surface chemical potential from experimental data on the temperature dependence of interfacial or surface tension is proposed for a diluted solution of surface-active impurity. The excess surface chemical potential of stearic acid at the interface of a water-n-hexane binary mixture is determined.     

Some Physical Properties of Binary Liquid Systems: (2-Butanone + n-Propionic Acid or n-Butyric Acid)

Abstract

Density, viscosity and surface tension of two binary liquid systems: 2-butanone + n-propionic acid, 2-butanone + n-butyric acid have been determined at 20, 30 and 40°C, over the whole compositional range. The excess values of molar volume, viscosity, Gibbs free energy for the activation of flow and surface tension were evaluated. These excess values were fitted to a Redlich-Kister type of equation. The Grunberg-Nissan parameter, d, was also calculated. The binary viscosity data were fitted to the models of McAllister, Heric, Auslander and Teja and Rice. Surface tension data were fitted to the models of Zihao and Jufu, Rice and Teja, and an empirical two-constant model proposed in this study.     

Applications of the MBPT in the localized representation

Diagrammatic formulation of the MBPT is applied when the occupied and the virtual canonical orbitals are separately localized by unitary transformations. In this localized representation, due to the off-diagonal Fock matrix elements, the perturbation operator contains extra terms generating the so-called localization corrections. These corrections enter the perturbation energy in third and higher orders. Their magnitude depends on the type of localization, but they represent only a small fraction of the canonical corrections. The calculation of the localization corrections, however, does not need a significant amount of extra computer time. It is shown that by introducing an “order of neighborhood” local and nonlocal effects of the electron correlation can be separated and the contribution of the nonlocal effects can be neglected to a good approximation. Ab initio calculations have been carried out for the normal saturated hydrocarbons: C_2n+1H_4n+4 and for the all-trans conjugated polyenes C_2n+2H_2n+4. As to the ratio of the local and nonlocal corrections, it is shown that there is only a quantitative difference for these two kinds of systems (strongly or weakly localizable). Neglecting nonlocal effects, considerable amount of computer time can be saved.     

ESR Studies on the Micellization Behaviors of a Series of Novel Asymmetric Gemini Surfactants

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｒｅｃｅｎｔｙｅａｒｓ ,ｂｉｓ(ｑｕａｔｅｒｎａｒｙａｍｍｏｎｉｕｍ)ｓｕｒｆａｃ ｔａｎｔｓｏｒｇｅｍｉｎｉｓｕｒｆａｃｔａｎｔｓ ,ｉｎｗｈｉｃｈｔｗｏｃａｔｉｏｎｉｃｓｕｒｆａｃ ｔａｎｔｍｏｉｅｔｉｅｓａｒｅｃｏｎｎｅｃｔｅｄｗｉｔｈｔｈｅａｍｍｏｎｉｕｍｈｅａｄｇｒｏｕｐｂｙａｐｌｏｙｍｅｔｈｙｌｅｎｅｃｈａｉｎ ,ｎａｍｅｌｙ ,ａｓｐａｃｅｒｈａｖｅｂｅｃｏｍｅｏｆｉｎｔｅｒｅｓｔｄｕｅｔｏｔｈｅｉｒｅｘｃｅｐｔｉｏｎａｌｓｕｒｆａｃｅａｃｔｉｖｉｔｙａｎｄｒｅｍ…     

Low-rate dynamic contact angles on poly(n-butyl methacrylate) and the determination of solid surface tensions

 Low-rate dynamic contact angles of 22 liquids on a poly(n-butyl methacrylate) (PnBMA) polymer are measured by an automated axisymmetric drop shape analysis-profile (ADSA-P). It is found that 16 liquids yielded non-constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the remaining 6 liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension, i.e. γ_lv cos θ depends only on γ_lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces [34–37, 45–47]. The solid–vapor surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions [14] is found to be 28.8 mJ/m², with a 95% confidence limit of ±0.5 mJ/m², from the experimental contact angles of the 6 liquids. Received: 12 September 1997 Accepted: 22 January 1998     

Effect of lower alcohols on adsorption characteristics of sodium dodecyl sulfate solutions at liquid-gas interfaces

The dynamics of a decrease in the surface tension is studied for aqueous solutions of sodium dodecyl sulfate and its mixtures with lower alcohols (ethanol and n-propanol). Two approaches are analyzed as applied to the estimation of the adsorption of two surfactants from their mixed solutions at a liquid—gas interface, i.e., the Frumkin generalized model and the Fainerman—Miller model. It is shown that both approaches adequately describe the concentration dependences experimentally measured for the surface tension of sodium dodecyl sulfate—lower alcohol mixtures.     

Surface tension of polymer mixtures and copolymers

Contact angles θ of liquids of different polarity were measured on a series of mixtures of solid high polymers and a series of copolymers. The mixtures were composed of an alternating poly(ethylene-co-maleic anhydride) (EMA), and its addition product with n-octadecylamine, poly(ethylene-co-N-n-octadecylmaleamic acid) (EOM). The co-polymers were composed of the same monomeric units as the mixtures. The surface tension γ_s of EOM, calculated from θ by the Good-Fowkes-Owens-Wendt treatment, decreased slightly with increasing molecular weights and then reached a limiting value. Plots of γ_s against EOM concentration indicated large negative excess surface tension of the units with lower surface tension, EOM, in both series studied. For the mixture series, γ_a first sharply decreased with the EOM concentration; then it reached a limiting value, the γ_s of pure EOM, at a very low EOM concentration. This indicates phase separation of the two polymers, and the thickness of a monomolecular surface layer was calculated from these data. For the copolymers, γ_s varied logarithmically with the EOM concentration. Throughout the whole concentration range, the data fitted the equation developed by Belton and Evans for ideal mixtures.     

Correlation between glass transition temperature and chain structure for randomly crosslinked high polymers

The empirical form for the dependence, T_g(n) ≅ T_g(∞)·(1 + α/n), of the glass transition temperature T_g on the average number n of repeat units between crosslinks, is generalized for randomly crosslinked high polymers. The new form, T_g(n) ≅ T_g(∞) · [1 + c/(n·N_rot)], is based on a correlation study of data for 77 samples of 10 different sets of resins. The fitting parameter α is resolved into composition-dependent N_rot and composition-independent c terms. N_rot summarizes the average number of rotational degrees of freedom per repeat unit, and is estimated in a straightforward manner from the structure and mol fraction of each repeat unit. The value of c is found from data analysis to be 5 ± 2. The results of this work are consistent with expectations based on the entropy theory of glasses, and provide improved understanding and predictive ability for the properties of crosslinked polymers. © 1996 John Wiley & Sons, Inc.     

An examination of the basic postulates of surface chemistry: A variational calculus analysis of the classic rotating drop experiment

A demonstration, using the variational calculus, is given showing that it is impossible to describe the excess free energy in any liquid surface by the use of a single energy parameter, the surface tension, without violating the laws of motion. The addition of the required second parameter, the flexural rigidity, is shown to be adequate to explain published data on the systemn-hexadecane/glycerol, and to demonstrate that for small radii of curvature, the curvature parameter may contribute orders of magnitude more to the surface energy than the surface tension does.     

Effect of Oxyethylete Units on Adsorption and Micellization Properties of Novel Benzene Sulfonate Surfactants

The surface tension and fluorescence spectra of sodium octyl-[ω-octyloxy-poly(oxyethylene)]-yl-benzene sulfonates (APE_nBS) aqueous solutions have been investigated by Wilhelmy plate method and intrinsic probe methods, respectively to study the effect of EO units on their properties. It was discovered that the surface performance of these surfactants was greatly outstanding: the values of critical micelle concentration (CMC) reached to be of the order of magnitude of 10^?5 mol/L, the values of surface tension at CMC, γ_CMC, were between 25.79 to 31.02 mN/m, and the effectiveness and efficiency of surface tension reduction were excellent. The introduction of oxyethylene units to the surfactant molecule evidently improved the solubility of APE_nBS. With the increase in EO units, the CMC slightly changed after the first decreased. On the other hand, the surface excess concentration at saturation, Γ _max, decreased after the first increased and γ_CMC increased after the first decreased accordingly. The CMC determined by fluorescence spectra of intrinsic probe method were accorded with the CMC measured by surface tension method. The aggregation number N, characterized by quenching the fluorescence spectra with methyl viologen (MV²⁺) as the extrinsic quencher, gradually decreased first (from 0 to1) and then slightly changed (from 1 to 4) with increasing EO chain length. So we concluded that the appropriate number of EO units was the key factor to get the best physicochemical properties of APE_nBS.     

Mesomorphism of s-alkylthiopentono- lactones and their itol derivatives

Mesophasic properties of S-alkylthiopentonolactones (D-ribono, D-arabinono and D-xylono) and the corresponding itol derivatives with general formula Su-SR (R=n-C_nH_2n+1) are studied. It was shown that the thermotropic and lyotropic phase transition temperatures are influenced by the following structural parameters: alkyl chain length, free OH group number, cyclic or acyclic Su structure and itol conformation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of micelles of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in N-methyl acetamide—alcohol and N,N-dimethyl acetamide—alcohol mixtures

The critical micelle concentrations of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide in solutions of in N-methylacetami de and in N,N-dimethyl acetamide with added methanol, ethanol, n-propanol, n-butanol and n-pentanol were determined using electrical conductivity and surface tension measurements at various temperatures. Both methods show that micelles are formed in N-methyl acetamide and N, N-dimethyl acetamide solutions in a presence of n-alcohols. Critical micelle concentrations were also determined as functions of concentration of added alcohol. The data suggest that alcohol adding leads to an enhancement of penetration of alcohol into the micelle external shell that depends on the alcohol chain length. Thermodynamic parameters for micellar systems in a presence of n-alcohols were also calculated.     

Study on Foaming Properties and Dynamic Surface Tension of Sodium Branched-alkyl Benzene Sulfonates

Foaming properties and the dynamic surface tension (DST) were carried out with aqueous solutions of sodium branched-alkyl benzene sulfonates to elucidate the relationship between foaming properties and surfactant structures. The parameters of the DST (t*, n, R _1/2 ) are correlated with the foaming ability for alkyl benzene sulfonates with benzene ring substituting at positions 2, 4, and 8 of hexadecane. The parameters of the DST (t*, n, R _1/2 ) are correlated with the foaming ability of the same surfactant solutions. The results indicated that the molecular diffusion in the solution, adsorption, and arrangement at the air/water interface were changed with different molecular structures: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the value of t* and n decrease, and the value of R _1/2 increases, which lead to the high dynamic surface activity and high foam volume. The foam stability is correlated with the high surface dilational elasticity and the strength of surface monolayer: changing the substituted position of benzene ring from 2 to 8 of hexadecane, the branched-alkyl chain becomes more flexible, which is characterized by densely packed adsorbed molecules and high film elasticity of the adsorption film. Therefore, the foam stability increases.     

Speeds of sound and isentropic compressibil- ities of cyclohexane+1,3-dioxolane+2-butanol and n-hexane+1,3-dioxolane+2-butanol

Speeds of sound of the ternary mixtures cyclohexane+1,3-dioxolane+2-butanol and n-hexane+1,3-dioxolane+2-butanol have been measured at the temperatures of 298.15 and 313.15 K. Isentropic compressibilities and excess isentropic compressibilities have been calculated from experimental data. We have also compared the experimental isentropic compressibilities with calculated values from the free length theory and the collision factor theory. Experimental results show positive values of excess isentropic compressibilities in almost the whole composition range for the ternary mixture containing cyclohexane, meanwhile they are negative for the mixture containing n-hexane. Such different behaviour of these systems is related to the large free volume shown by n-hexane. This revised version was published online in July 2006 with corrections to the Cover Date.     

Interaction of Mo(CO)6 and its derivative fragments with the Cu(001) surface: Influence on the decomposition process

A theoretical study on the adsorption and decomposition of molybdenum carbonyl on the copper (001) surface is reported. The adsorption structures and energies of Mo(CO)_n molecules (n = 1 … 6) are computed systematically using density functional theory with Van der Waals corrections. By analyzing the energies of the various conformations, the main factors that determine the stable adsorption geometry are identified. Insight into the thermodynamics of decomposition is gained by calculating the reaction energy for dissociation of Mo(CO)_n into Mo(CO)_n?1 and CO. In the gas phase, this reaction is highly endothermic for all n. On the Cu surface, however, removal of the first CO group (n = 6) becomes strongly exothermic. The subsequent dissociation steps (n < 6), are endothermic even on the surface, but the reaction energies are much reduced. Dissociation is found energetically more favorable than desorption in all cases. The results clearly show that molybdenum carbonyl decomposition is strongly facilitated by the presence of the Cu surface. © 2014 Wiley Periodicals, Inc.     

Shape of the nematic-isotropic interface in conditions of partial wetting

A nematic liquid crystal in contact with a solid substrate is studied in the partial wetting regime. Both a mesoscopic Landau-de Gennes theory and a macroscopic effective interface Hamiltonian approach are considered. A generalized Young equation for the balance of forces at the three-phase contact line is derived, which takes into account corrections due to distortions of the nematic director field. It is also shown that the asymptotic form of the separation of the nematic-isotropic interface from the substrate has a logarithmic correction to the usual linear behaviour. The characteristic length scale of this correction is given by the ratio K/(2σ_NI), where K and σ_NI are the average elastic constant and the nematic-isotropic surface tension, respectively, and is of the order of a few hundred angstroms. Then, a simple form of an effective interface Hamiltonian is proposed, and results consistent with the predictions of the Landau-de Gennes theory are obtained. It is shown, in the framework of this macroscopic approach, that the line tension associated with the contact line remains finite, when the thermodynamic limit is taken, if the anchoring at both the nematic-substrate and the nematic-isotropic interfaces is homeotropic. However, in the case of different anchoring directions, the line tension diverges logarithmically with the system size.     

Distribution of chain ends at the surface of a polymer melt: Compensation effects and surface tension

We consider the surface of a nearly incompressible polymer melt, extending the usual ground-state analysis of self-consistent field theory to describe finite length polymers in the ground-state potential. To maintain self-consistency, further corrections to the potential are calculated within linear response theory. From this, we find an excess of ends near the surface, followed by a compensating depletion on the R_g length scale, which relies crucially on the finite compressibility of the melt. The attraction of ends to the surface can be described as resulting from a surface potential for ends with a strength on the order of k_BT. Our results address the long-standing controversies of the distribution of chain ends, the chain-length dependence of the surface tension, and the interaction between objects immersed in a melt. © 1995 John Wiley & Sons, Inc.     

Zwitterionic [(4‐n‐Alkyl‐1,4‐bisazoniacyclohex‐1‐yl)methyl]pentafluorosilicates: A New Class of Surface‐Active Compounds with a Hexacoordinate Silicon Atom

A series of [(4‐n‐alkyl‐1,4‐bisazoniacyclohex‐1‐yl)methyl]pentafluorosilicates (alkyl = hexyl, heptyl, octyl, nonyl, decyl; compounds 14 – 18 ) were synthesized and studied for their surface activity. The zwitterionic pentafluorosilicates with hexacoordinate Si atoms 14 – 18 were prepared by reaction of the respective [(4‐n‐alkylpiperazin‐1‐yl)methyl]trimethoxysilanes [obtained by treatment of (MeO)₃SiCH₂Cl with the respective n‐alkylpiperazine in the presence of NEt₃] with HF in water/ethanol. Surface tension measurements with solutions of 14 – 18 in 0.01 M hydrochloric acid proved that these compounds are surfactants, the increase of the n‐alkyl chain length resulting in an increase of surface activity ( 14 → 18 ). The equilibrium surface tension vs concentration isotherms for 14 – 17 (solutions of “surface‐chemically pure” samples in 0.01 M hydrochloric acid) were analyzed quantitatively.     

Adsorption and Thermodynamic Study of Pyrogenic Alumina Properties

Adsorption of n-pentane, triethylamine, diethyl ether, acetonitrile and chloroform has been investigated on pyrogenic alumina (S=140 m² g⁻¹). The results of our studies have shown the presence of active sites on the surface of pyrogenic alumina with irreversible adsorption of electron-donating molecules and CHCl₃ and the dependence of energetic surface properties on electronic structure of adsorbate, quantity of adsorbed substance and hydration degree of the surface. On the hydrated oxide surface the water molecules screen the active sites of the surface, which resulted in changing of interaction energy of adsorbent-adsorbate and decreasing the region of irreversible adsorption of organic bases and CH-acid. This revised version was published online in August 2006 with corrections to the Cover Date.