ISSN:0193-2691    

DOI:10.1080/01932699808913239

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The apolar (Lifshitz van der Waals) component (γLWS) and the polar [electron-acceptor (γ+S) and electron-donor (γ−S)] parameters of the surface tension of biominerals and surfaces of dental hard tissues have been measured, as well as their ζpotentials. The interfacial tensions between their surfaces and aqueous solutions, determined using van Oss-Chaudhury-Good equations, are comparable with the interfacial free energy values obtained from the kinetics of crystallization and dissolution using a constant composition technique. The electron-donor (γ−S) parameters indicate that most of these minerals have a moderate to high hydrophobicity. The interfacial tension values are consistent with the order of the solubilities of these minerals.

ISSN:0193-2691    

DOI:10.1080/01932699808913211

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Ar and N2high resolution adsorption volumetry coupled to the Derivative Isotherm Simulation method was applied on nine homoionic illite samples (Li −, Na − K − Rb − Cs − Mg − Ca − Sr − and Ba − illites). By comparing the adsorption isotherms it appears that the nature of the surface cation strongly influences the adsorption mechanisms.

ISSN:0193-2691    

DOI:10.1080/01932699808913212

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Titanium oxide aqueous suspensions have been destabilized by a novel mechanism; the nucleation of octacalcium phosphate on the particle surfaces, using the constant composition technique. The results suggest that the potential energies resulting from the electric double layers around the titania particles play only secondary roles in the flocculation, in that a decrease inζ-potential of titania colloids from −47 mV to −13 mV does not in itself cause the titania suipension to flocculate, in contrast to the predictions of the classical DLVO theory. However, in the process of hucleation of the moderately hydrophobic octacalcium phosphate phase (γ-sequals;19.7 mJ m-2) onto titania particle surfaces, the latter become more hydrophobic with values ranging from 52 to 23.4 mJ m-2, This change is sufficient to cause the particles to flocculate since the energies of attraction result from hydrophobic interactions (90%) and van der Waals forces (10%).

ISSN:0193-2691    

DOI:10.1080/01932699808913213

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The surface tension values for a series of 2:1 phyllosilicate minerals with different structural characteristics and layer charges ranging from 0 to 2 per O10group have been examined. The average Lifshitz-van der Waals component (ΓLW)value is 40.3 ± 1.9 mJ/m2, and the average Lewis acid (®) parameter is 1.2 ± 0.6 mJ/2for those minerals with a layer charge greater than zero. In contrast, the Lewis base parameter (γe) varied greatly from a maximum of 59.7 mJ/m to a minimum of 23.7 mJ/m2. Those minerals with a layer charge of zero (three samples) had smaller γLWvalues of 32.0 ± 1.6 mJ/m2, slightly larger γ® values of 2.0 ± 0.4 mj/m2and significantly smaller values of γ® of 4.5 ± 1.6 mJ/m2. The hydrophobic versus hydrophilic character of these materials is largely governed by the value of γ° which is strongly related to the value of the layer charge.

ISSN:0193-2691    

DOI:10.1080/01932699808913214

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Poly[(vinyl alcohol)-co-(vinyl amine)] was prepared by copolymerization of vinyl acetate and N-vinyl forma-mide, followed by a two-step alkaline hydrolysis in which the vinyl acetate groups were hydrolyzed to vinyl alcohol groups, and the N-vinyl formamide groups, to amino groups. This copolymer was used as the stabilizer for the emulsion polymerization of styrene using persul-fate-ion initiator. The latexes were cationic; the particles were relatively uniform and of 100–500 nm diameter. The presence of amino groups was shown by electro-phoresis and Kjeldahl analysis. Comparison with sodium lauryl sulfate showed that the mechanism of particle nucleation was apparently entry of radicals into fine emulsion droplets rather than the conventional entry of radicals into emulsifier micelles.

ISSN:0193-2691    

DOI:10.1080/01932699808913215

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this study, a copolymer of N,N-dimethylacrylamide and hydroxyethyl-methacrylate was synthesized and hydrophobically modified with about 2 mole % of adamantyl groups. The mixing of this modified copolymer with water-soluble β-cyclodextrin polymers reveals thickening properties. Inclusion complexes formation between adamantyl groups and β-cyclodextrin cavities are responsible of intermolecular associations. Above a given total polymer concentration a phase separation occurs, giving a gel phase topped by a liquid phase. We have stated the phase diagram by analysis of the two phases in equilibrium. It has been observed that the two polymers are present in both phases and that the gel phase is more concentrated than the other one. This phase behavior is an original complex coacervation phenomenom which is due to the specific attractive interactions of the two different macromolecules: inclusion complexes formed between the two neutral polymers.

ISSN:0193-2691    

DOI:10.1080/01932699808913216

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Drug release is to a large extent influenced by penetration of a dissolution liquid into a polymer matrix. If an aqueous medium does not wet a matrix, its penetration into the polymer bulk and the resulting drug extraction would be considerably hindered. It is therefore of extreme importance to study not only the physical state of drug loaded matrices but also their wettability and their penetration by an aqueous medium.

ISSN:0193-2691    

DOI:10.1080/01932699808913217

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Zeolite has high internal and external surface areas and high internal and external cation exchange capacities suitable for surface modification by cationic surfactants. When the initial surfactant concentration is less than the critical micelle concentration, the sorted surfactant molecules primarily form a monolayer. Limited chromate sorption indicates that patchy bilayer may also form. When the initial surfactant concentration is greater than the critical micelle concentration and enough surfactant exists in the system, the sorbed surfactant molecules form bilayers, producing maximum chromate sorption. On a meq/kg basis, planar nitrate sorbs more on surfactant-modified zeolite surfaces than tetrahedral chromate. In the presence of sulfate or nitrate, chromate sorption is hindered due to competition for sorption sites. Quantitative sorption of nitrate and chromate and desorption of bromide indicate that the sorption of oxyanions is primarily due to surface anion exchange.

ISSN:0193-2691    

DOI:10.1080/01932699808913218

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Different components of granulated plastic mixtures can be separated by froth flotation. This technique involves selective adherence of gas bubbles onto the particles to be separated. This requires a sufficient difference in the wettability of the particles. Since the overwhelming majority of plastics are hydrophobic by nature, separation by flotation necessitates selective wetting of the components. However, a comprehensive understanding of wetting phenomena involved has not been established thus far, so that the wetting action of surfactants during flotation cannot be predicted. As a consequence, selection of suitable wetting agents is essentially based on trial-error test work. However, the test work needed can largely be reduced by more insight into the wetting mechanisms involved which is the subject of the present work.

ISSN:0193-2691    

DOI:10.1080/01932699808913219

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor