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  • 1
    Electronic Resource
    Electronic Resource
    Self-diffusion of small molecules in colloidal systems (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 77-88 
    Details
    ISSN: 1435-1536
    Keywords: Self-diffusion ; obstruction factor irreversible processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The self-diffusion of small molecules in colloidal systems is calculated using the cell model to describe the effect of varying concentration of colloidal particles. The relevant boundary conditions are found using arguments from the thermodynamics of irreversible processes. From a general description of the self-diffusion in systems with spherically symmetrical particles we derive expressions for the concentration dependence of the effective self-diffusion coefficientD eff for several cases of practical importance. It is shown that when the molecule studied is strongly attracted to the particle a minimum inD eff is expected around volume fractionΦ=0.35. It is also shown that the often made distinction between free and bound molecules is often problematic and a more general description is proposed. The obstruction effect generated by the excluded volume is discussed both for spherical and spheroidal systems. It is pointed out that the often used formula due to Wang ((1954) J Amer Chem Soc 76:4755) is incorrect for self-diffusion and for the obstruction factor for spheres we obtain (1+0.5Φ)−1. This expresion is tested both by experiments on water diffusion in systems containing latex particles and through computer simulations and it is found valid over a wide concentration range. For prolate ellipsoids the obstruction factor is not greatly different from that for spheres, while for oblate aggregates the limiting obstruction factor of 2/3 can be obtained at low concentrations. It is demonstrated that this effect can be used to distinguish between different aggregate shapes. It is also shown that the disorder present in a solution of colloidal particles leads to a decrease in the obstruction effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410310
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  • 2
    Electronic Resource
    Electronic Resource
    Colloidal stability of PVC primary particles in vinyl chloride (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 439-444 
    Details
    ISSN: 1435-1536
    Keywords: Vinyl chloride ; PVC ; primary particles ; colloidal stability ; competeting growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The electrostatic contribution to the colloidal stability of PVC primary particles (R=0.15 μm) dispersed in vinyl chloride, was calculated using models based on the Coulombic interactions and the DLVO theory. The calculations were based on: a) the particle charge as obtained from literature data on the electrophoretic mobility of PVC primary particles in VCM and b) on estimates of the Debye length as obtained from measurements of the electrical conductivity of VCM and of solutions of Bu4NBF4 in VCM. The calculations showed that particle stability would decrease with particle size (experimentally-observed behaviour), only if the particle charge increased with size at a lower rate than in proportion to particle radius. The calculations also suggest that particle growth may be governed by a competitive growth mechanism of electrostatic origin. Particle growth is assumed to occur by absorption of many small, weakly charged basic particles from the monomer phase. According to the calculations, the electrostatic interaction between primary and basic particles may be such that the growth of the smaller primary particles is favoured over that of the larger ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01419548
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Surface and colloid chemistry of peat and peat dewatering. Electrostatic effects (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 164-172 
    Details
    ISSN: 1435-1536
    Keywords: Peat ; humic acid ; polyelectrolytes ; titration ; Poisson-Boltzmann equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A study of the potentiometric titration and metal ion binding properties of peat is reported. Peat is found to behave as a typical polyelectrolyte system which, especially at high pH's, can be very highly charged. One difference between peat and commonly investigated polyelectrolyte systems (like poly(acrylate)) is that a very broad spectrum of pKa values is required for the description of the titration characteristics of peat. The prime reason for this is assigned to the presence of humic acids, formed during decomposition of plant parts. The humic acids constitute a rather badly defined group of polyelectrolytes built up inter alia of carboxylic, phenolic and sugar groups. The presence of different length segments of conjugated double bonds provides conditions for light absorption at a broad range of wave-lengths, hence the black or brown colour of these compounds, as well as the stabilisation of resonance structures including carboxylate and phenolate groups. Because of large differences in double-bond segment lengths, a broad range ofpK a values results. For the analysis of potentiometric titrations, a theoretical model is developed which has the following characteristics: 1. The titratable groups are assumed to be evenly distributed on the peat surfaces. 2. The surfaces are assumed to be planar and no consideration of curvature effects is made. 3. Only monovalent and divalent counterions and monovalent coions are assumed to be present in the aqueous medium. 4. Counterions can bind to peat electrostatically in the counterion layer as well as specifically to different groups on the peat surface. 5. The electrostatic potential on the surface is calculated using the Poisson-Boltzmann equation. By means of this theoretical model, a very good description of the titration characteristics of peat is obtained if peat is assumed to contain titratable surfaces with a continuous spectrum of pKa values in the interval 1–11.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01452814
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    Paper (German National Licenses)
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