摘要:

The concept of surface tension is usually introduced as a force per unit length originated from the “stress tensor” at the liquid surface (and vaguely extended to solids). This mechanical model of the surface tension, a paradigm for many workers in the field, is wrong. The inferences from the model, however, are correct in the more common uses. Some contradictions may appear but not sufficient to abandon such a simple and intuitive concept. The origin of the surface tension, of a liquid or solid surface, is in the molecular interactions, when some other phase is put in contact with such a surface. Recent developments using the surface tension components allow to predict interfacial surface tensions and to measure surface tension of solids. Although the power of this approach is evident, its use is only incipient because some results, particularly the presence of negative interfacial tensions, are difficult to interpret using the erroneous vision of surface tension as a consequence of a “stress tensor” at the liquid (or solid) surface. We present here some properties of liquids useful to fundament the concept of surface tension and briefly refer to Laplace's equation, Young's equation and capillarity, attempting to correct some misinterpretations.

ISSN:0193-2691    

DOI:10.1080/01932690008913313

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Polyvinylacetate-SiO2gels have been obtained by radical polymerization of vinyl acetate (VAc) in the presence of tetraethoxysilane (TEOS). The reaction system was: VAc:TEOS:EtOH:H2O:S (nonylphenol ethoxylated with 25 moles ethylene oxide) in different ratios. The reaction was performed at 65°C. The initiator of radical polymerization was benzoyl peroxide and a crosslinking agent of sol-gel process bis maleate of diethylene glycol. Traces of acetic acid, maleic acid or acrylic acid catalyze the polymerization of TEOS. The presence of the surfactant (S) ensures the homogeneity of the initial system. The conditions of obtaining homogeneous gels have been selected. Ternary diagrams containing TEOS:EtOH:H2O or (VAc+TEOS):EtOH:H2O:S were used in order to establish the domains of homogeneous compositions in the systems. Refractometric and conductometric measurements have shown that the mentioned systems are microemulsions. X-ray diffraction, surface area measurements, DTA/TGA method, as well as IR spectrometry have been used in the characterization of the gels obtained.

ISSN:0193-2691    

DOI:10.1080/01932690008913314

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The adsorption of polyoxyethylene mono soya bean fatty acid [Soy (EO)20,40and80] and polyoxyethylene (80) monolinoleate [Li(EO)80] onto Na-montmorillonite has been determined at 30°C. The adsorption isotherms of all the tested surfactants exhibit an L-shaped following the Langmuirian model. The experimental adsorption data are fitted to Langmuir adsorption equation, the maximum amount adsorbed, Γmax, and the minimum area occupied per molecule, Amaxat the pseudo-plateau have been calculated. Γmaxvalue increases with the increase in the number of ethylene oxide units following the order, Soy (EO)20< Soy (EO)40Soy (EO) ≃ Li (EO)80. Both Soy (EO)80and Li (EO)80nearly show the same adsorption behavior.

ISSN:0193-2691    

DOI:10.1080/01932690008913315

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The hydrolysis of p-nirrophenyl picolinate (PNPP) catalyzed by the Cu(II) and Zn(H) complexes of d-glucosamine schiff base was investigated kinetically by observing the rates of the release of p-nitrophenol in the buffered micellor solution at different pit and 25°C. The scheme for reaction acting mode involving a ternary complex contain ligand, metal ion and substrate in micelle was establish and the reaction mechanisms were discussed The experimental results indicated that the complexes catalyzed efficiently the hydrolysis of PNPP, especially Zn(II) complex. The rate constant kN, which shows the catalytic reactivity of complexes, WBI determined to be 0.4251 s−1far Cu(II) complex at pH 7 60 in micellar solution. The catalytic reactivity of Zn(II) complex were much larger than Cu(II) complex, the kNwas determined to be 3.1914 s−1at same pH value.

ISSN:0193-2691    

DOI:10.1080/01932690008913316

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The kinetics of dispersion polymerization of styrene in alcohol/methyl or butyl cellosolve was investigated with dried-weigh methods. The reaction parameters, such as concentration of initiator, polymerization temperature, and solvent, play an important role in determine polymerization rate. It was found that polymerization rate increases with the reaction temperature. The apparent activation energy is of 42.2kJ/mole and 52.6kJ/mole for the initial polymerization stage and the stationary polymerization interval. The polymerization rate increases with the concentration of the initiator with approximately 0.67 order dependence at conversion about 5%. It was described that the relation of conversion with the Hansen Parameters of media in detail by analysis of solvent dispersion, polarity and hydrogen bonding contributions. More significant was the result that polymerization rate versus conversion curve consisted of 3 intervals (2 non-stationary and 1 stationary one). The plateau of polymerization rate was observed in the curve of polymerization rate vs. monomer conversion.

ISSN:0193-2691    

DOI:10.1080/01932690008913317

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Micellar catalysis by nine cationic surfactants of the basic hydrolysis of 2,4-dinitrochlorobenzene(DNCB) was studied. The results obtained are as follows: (I) The second-order constants k2for the hydrolysis reaction of DNCB catalized by the cationic micelles increase by a factor of 11–100 than that in water. Plots of k2against the surfactant concentration show an S-type curve, and the catalytic effect is observed below the critical micelle concentration(CMC) of the surfactants. (2) For a series of surfactants, there is an optimal chain length for the alkyl of the surfactants to show the greatest catalytic effect. (3) The hydrolysis rate of DNCB decreases as the base concentration increases. (4) For the surfactants with the same hydrophilic and hydrophobic groups, chlorides have advantage over bromides in enhancing the reaction rate. These results can be interpreted in term of the changes in CMC, micelle size, solubilization capacity of the micelles, binding degree of counterion et al.

ISSN:0193-2691    

DOI:10.1080/01932690008913318

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The pyrogallic method for determining the activity of SOD is studied in the aqueous solution and in the CTAB/n-pentanol/n-octane/water microemulsion. The required generation ran of the substrate O2is obtained in he reverse microemulsion by increasing the apparent pH and dielectric constant. The activity of SOD is finally determined in such a system and a bell-shaped profile is recorded. But subactivity is found only due to the decrease of the substrate concentration and the high pH value

ISSN:0193-2691    

DOI:10.1080/01932690008913319

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Large unilamellar vesicles composed of a nonionic synthetic glycotipid, 1,3 - di- 0 - phylanyl -2-0-(β- maltotriosyl ) glycerol show pH-dependent aggregation - dissocialion process, that is, vesicle aggregation occurs in the lower pH region and vesicle dissociation occurs in the higher pH region. This process is almost reversible and the aggregation threshold pH is dependent on NaCl concentration. Fluorescence technique has been applied to study whether the vesicle fusion occurs or not during the aggregation-dissociation process. It is concluded pH can only induce the aggregation of this nonionic glycoltpid vesicle.

ISSN:0193-2691    

DOI:10.1080/01932690008913320

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Urea is found to show the hydrotrope action when the aqueous solubility of surfactant CTAB is enhanced while it will show the hydrotrope-solubilization action when the solubilized amount of n-C5H11OH in O/W microemulsion and that of water in W/O microemulsion are increased. The mechanism of the hydrotrope-sotubilization action of urea is in fact the increase of the stability of W/O and O/W microemulsion and structural transition from the lamellar liquid crystal phase to the bicontinuous structure.

ISSN:0193-2691    

DOI:10.1080/01932690008913321

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The diffusion coefficients of Triton X-100 micelles with different shape are determined by cyclic voltammetry without any probe. The first CMC (3.2 × 10−4mol-Lminus;1) and the second CMC (1.3 × 10minus;3mol-Lminus;1) of Triton X-100 micelles arc obtained, and the mechanism of electrochemical reaction for Triton X-100 is deduced, When n-hexanol is added, the diffusion coefficient of Triton X-100 micelles with different shape increases, but the solubilization fraction of n-hexanol decreases in spherical micelles and is almost constant in rodlike ones. However, the micropolarity of micelles decreases in both spherical and rodlike micelles. Furthermore, the diffusion coefficient of Triton X-100 micelles with different shape increases with temperature and the diffusion activation energy increases with n-hexanol content.

ISSN:0193-2691    

DOI:10.1080/01932690008913322

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor