Multilayer adsorption of alcohols from benzene/n-heptane mixtures on silica gel

An equation for multilayer adsorption from multicomponent liquid mixtures on solid surfaces¹ has been examined. For this purpose experimental adsorption data for four alcohols from benzene/n-heptane mixture on silica gel have been measured. Average number of the adsorbed layers, heterogeneity parameter and capacity of the surface phase have been evaluated by using the equation mentioned above.

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Mehrschichten-Adsorption von Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel

Zusammenfassung Eine Gleichung für Mehrschichten-Adsorption an festen Oberflächen¹ aus Mehrkomponentenlösungen wurde getestet. Zu diesem Zweck wurden experimentelle Daten für die Adsorption von vier Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel herangezogen. Der Mittelwert für die Anzahl der Adsorptionsschichten, der Heterogenitätsparameter und die Kapazität der Oberflächenphase wurde aus dieser Gleichung berechnet.

     

A new way for calculating the adsorption capacity from surface excess isotherms

 Adsorption of n-butanol and water from butanol–water mixtures is studied on adsorbents of different hydrophobicity (activated carbon and hydrophobized montmorillonites). The shape of the adsorption isotherms of the hydrophobized clay minerals does not indicate preferential adsorption of butanol. Therefore, the adsorption capacity cannot be determined on the basis of the Langmuir isotherm. A new equation for determining the adsorption capacity is derived by combining the free enthalpy of adsorption with the adsorption excess amount. Both collections of data are obtained from the surface excess isotherm. The reliability of the adsorption capacity is checked by X-ray diffraction measurements. Received: 1 November 1997 Accepted: 19 February 1998     

Surface mixed adsorption films of 2,4,6- trimethylphenol–2,4,6-trichlorophenol at aqueous solution/air interface

 The results of experimental studies of the adsorption at the solution/air interface from an aqueous mixture: 2,4,6-trimethylphenol–2,4,6-trichlorophenol are presented. The surface properties of the above-mentioned mixture were studied by surface potential and surface tension measurements. These measurements were carried out as a function of the concentration of 2,4,6-trimethylphenol aqueous solution at a constant concentration of 2,4,6-trichlorophenol. Using the results obtained and based on the Gibbs equation, Helmholtz formula and Motomura’s method the relative surface excesses of adsorbed substances, effective dipole moments, surface molar fractions of solutes and miscibility of adsorbed films were determined. Received: 7 November 1997 Accepted: 26 February 1998     

Experimental determination of the static permittivity of extremely thin liquid layers of water dependent on their thickness

 A new method for determining the static permittivity (dielectric constant) of extremely thin liquid interlayers is illustrated. A special condenser, which can be filled with a test liquid, is constructed. Both condenser plates – one planar, the other spherically curved – are made of vitreous carbon and are supplied with a high-grade politure. In order to adjust plate separation distances from 10 nm up to about some μm the planar plate can be easily shifted by a piezoelectric translation stage; the plate separation is monitored by an optical system supported by displacement transducers. The measuring frequency was kept constant at 1 MHz. Water was chosen as the test liquid. At 19.8 °C thin water layers having thickness smaller than 0.3 μm exhibit a decrease of the dielectric constant. The experimental data are consistent with a decay length α^-1 of the order of 1 nm which in view of the underlying crude model must be regarded as approximative. Received: 28 May 1996 Accepted: 30 September 1996     

Adsorption of TX100 and TX165 at the aqueous solution–air interface: free enthalpy of adsorption and equation of state

Surface tension measurements of aqueous solutions of TX100 and TX165 were made at different temperatures. The thermodynamic parameters of the adsorption calculated from the surface tension measurements, using several methods, have given slightly different values. The equation of state for the TX100 and TX165 monolayers at the solution–air interface was analysed. There is excellent agreement between the modified Volmer equation of state and the experimental π–A isotherms. Received: 13 July 1999/Accepted in revised form: 20 October 1999     

Adsorption of cationic polyelectrolyte onto a model carboxylic latex and the influence of adsorbed polycation on the charge regulation at the latex surface

 Adsorption of a well-characterized cationic polyacrylamide (CPAM) onto the surface of a model colloid (monodisperse polystyrene latex with carboxylic functional groups) was studied over a wide range of pH (4–9) and KCl concentration (c _s =10^-3–0.3 M). The surface charge density of the latex particles with and without adsorbed CPAM was also measured over the same range of electrolyte compositions. The adsorbed amount of CPAM increases with increase in c _s and pH. The polyelectrolyte adsorption alters substantially the surface charge density of the latex particles as compared to the polymer-free case. A large overcompensation of the surface charge by the adsorbed polyelectrolyte is established at high c _s and low pH. A qualitative explanation of the observed features is put forward. Received: 3 December 1996 Accepted: 20 January 1997     

Particle adsorption in evaporating droplets of polymer latex dispersions on hydrophilic and hydrophobic surfaces

Stain patterns formed by drying up of droplets of polymer latex dispersion on hydrophilic and hydrophobic surfaces were examined in light of the mechanism of particle adsorption in evaporating droplets. On hydrophilic surfaces, the volume of droplets decreased with time, keeping the initial outline of contact area, and circular stain patterns were formed after the dry-up of droplets. By the microscopic observation of particles in the droplets, it was found that a large portion of the particles were forced to adsorb on the outline of the contact area where a microscopic thin water layer was formed because of hydrophilicity of the surface. On hydrophobic surfaces, on the other hand, the contact area of droplets decreased as evaporation proceeded, while no particle was adsorbed on the surface at the early stages. The particles in the droplets started to aggregate when the concentration of particles reached a critical value, and the aggregates adsorbed on the surface forming tiny spots after the dry-up. Time evolutions of contact angle, contact area and volume of the droplets were analyzed in light of differences in the adsorption mechanisms between hydrophilic and hydrophobic surfaces. Received: 14 January 1998 Accepted: 1 May 1998     

Structure of adsorption layers of ionic surfactants at the solid/liquid interface

A large number of experimental results of different surfactant adsorption systems (mainly on the silicas) obtained from both equilibrium and kinetic studies under different conditions are interpreted by a model of small individual surface aggregates. The adsorption model is contrasted with the influences of various factors, including electrostatic interaction, hydrophobic interaction, concentrations, types of coions, types of counterions, surfactant structure, alkyl chain length, types of head groups, neutral electrolytes, pH, adsorbent structure, porosity, surface charge density, and surface polarity.Dedicated to Frau Professor Dr. Elsa Ullmann on the occasion of her 80th birthday     

Influence of temperature on the composition of mixed monolayer formed at the methyl alcohol/acetic acid aqueous solutio–air interface

The influence of temperature on the composition of mixed monolayer formed at the methyl alcohol/acetic acid aqueous solution was examined by surface tension measurements. Surface tension of various two-component solutions was obtained at 10, 20 and 28 °C temperatures in the 0–0.5 M range of bulk concentration of alcohol and acid, respectively. Three independent methods, i.e., the Gibbs adsorption equation (GAE), regular solution approximation (RSA) and Butler adsorption isotherm (BAI) were applied to calculate surface composition of the methyl alcohol/ acetic acid mixed monolayer. It was shown that in the temperature range of 10–28 °C the surface molar fraction of the solutes remained constant for the fixed bulk concentration of alcohol and acid. Additionally, based on the RSA and BAI methods, we showed there were no interactions between solute molecules in the mixed monolayer in the studied range of concentrations. Received: 18 December 1997 Accepted: 8 May 1998     

Kinematic Viscosities of Binary Liquid Mixtures of 2-Butanone with 1,2-Propanediol

Kinematic viscosities of the binary 2-butanone (1) + 1,2-propanediol (2) solvent system have been measured for mixtures covering the whole miscibility range expressed by 0 x _i 1, at 19 temperatures in the range –10 t/°C 80. The measured values have been used to test empirical equations that express the kinematic viscosities as functions of the composition and temperature. Excess kinematic viscosities (^E) have also been calculated. Sign and magnitude of these quantities are discussed in terms of type and nature of specific intermolecular interactions. Furthermore, derived quantities such as thermodynamic parameters of viscous flow (G, H and S), are analyzed on the basis of Eyring's model. All the investigated excess mixing properties indicate the probable existence of stable two-component adducts in this binary solvent system.     

An effective cross-linking of polymer layer on monodisperse, poly(maleic anhydride-styrene)-modified colloidal silica particles and properties of the composite

Summary  The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles with diluted HCl solution; 5–6 and 0.5–1.1 μmol g^-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and −102 to −107 mV in a neutral aqueous solution and ethanol, respectively. Received: 26 May 1997 Accepted: 4 August 1997     

Highly monodisperse crosslinked polystyrene microparticles by dispersion polymerization

 Highly monodisperse polystyrene microparticles cross-linked with urethane acrylates were produced by dispersion polymerization in ethanol solution in the presence of 2,2′-azobis (isobutyronitrile) initiator, polyvinylpyrrolidone stabilizer, and Aerosol–OT costabilizer. Different from conventional crosslinkers, the urethane acrylates employed as a crosslinker showed an excellent effect on maintaining the monodispersity of polystyrene microparticles even in the moderate crosslinker concentration. This was believed that the urethane acrylate helped forming the monomer-swellable surface of primary particles, because of its structurally long tetramethylene oxide groups in its molecule. However, at high concentration of the urethane acrylate, the rough surface and the coagulum of particles were observed, which was attributed to the seriously decreased solubility of the monomer mixtures in ethanol solution. The solubility of the mixtures of styrene monomer and urethane acrylate in the media had a serious effect on the average particle size and morphology of the final particles. This could be confirmed by the measurement of cloud points and fractional conversions. Received: 21 February 1997 Accepted: 25 May 1998     

Ammonia, cyclohexane, nitrogen and water adsorption capacities of an activated carbon impregnated with increasing amounts of ZnCl(2), and designed to chemisorb gaseous NH(3) from an air stream

The adsorption capacity of ZnCl(2)-impregnated activated carbon (AC) for NH(3) is reported in terms of stoichiometric ratio of reaction (NH(3) per ZnCl(2)). This ratio depends on the testing conditions used. Compared to the ratio obtained under dry conditions, the ratio is higher under humid conditions or increased NH(3) concentrations. The linear increase of the NH(3) capacity with increasing loading of ZnCl(2) breaks down at about 3.5 mmol ZnCl(2)/g AC. This behavior is explained in terms of preferential adsorption of a monolayer of salt followed by aggregation of the impregnant once a monolayer is completed. The effect of increasing the loading of ZnCl(2) on the capacity for gases for which the impregnants are not intended, namely cyclohexane, nitrogen, and water vapor, is also discussed. A break in the linear relationship between water capacity and impregnant loading at about 3.5 mmol ZnCl(2) seems to correspond to a full monolayer coverage of ZnCl(2) on AC. The monolayer of ZnCl(2) is shown to reduce the uptake of water into AC, while the ZnCl(2) aggregates are shown to be hydrophilic.