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  • 1995-1999  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 274 (1996), S. 809-818 
    ISSN: 1435-1536
    Keywords: Living polymers gels ; reverse micelles ; SANS
    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 We report new results from small-angle neutron scattering ond 12-cyclohexane/lecithin/water micellar solutions performed as a function of the water content (w 0), temperature (T) and dispersed phase volume fraction (ϕ). The data from dilute samples are interpretable in terms of the existence of giant cylindrical reverse micelles and are well fit with a core-shell model (that provides the micelle structure and dimensions) with values of 28 and 45 Å for the inner core and the outer shell radii, almost independent on temperature and concentration. Such a result could appear consistent with the current idea that worm-like micelles are living polymers. On the contrary, the appearance of a sharp interference maximum at high concentrations (ϕ〉0.15) suggests arguments against the current hypothesis of an entangled network of giant flexible cylinders. Further arguments against the current hypothesis are given by the close similarity between the above described results and those from free of water micelles (for sure not cylinders). All the data are well fitted in terms of a unique model taking into account the micellar form factor plus a hard sphere structure factor. The data analysis suggests a micellar size distribution determined by the competition between concentration and interaction effects on which temperature plays not a minor role. Following our results, the current hypothesis of a gel structure in terms of an entangled network can be assumed as wrong and some caution has to be taken in assuming wormlike micelles as living polymers.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Colloid & polymer science 275 (1997), S. 910-921 
    ISSN: 1435-1536
    Keywords: Key words Living polymers ; gels ; reverse micelles
    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  Experimental results from colloidal suspensions of worm-like micelles are currently interpreted in terms of close analogies between this kind of systems and polymeric solutions. In particular, it was hypothesized that the viscoelastic properties of dense systems of giant flexible cylindrical micelles can be rationalized in terms of an entangled network of worm-like aggregates, very similar to a neutral random polymeric network. Such an idea is strongly supported by theoretical results that, in a mean-field appro ximation, suggests for an unlimited growth process of the micellar contour length with concentration. The mean-field theory indicates for an exponentially shaped length distribution function, with mean 〈L〉 depending on concentration, φ, in agreement with a scaling law 〈L〉∝φα (α=0.5 in the simpler approach). A number of experimental results seem to be successfully interpretable within this framework. Aim of this work is to show that the agreement between theory and experiment is just an accident, being the mean-field approach, in principle, inadequate in describing systems dense enough to show a concen tration dependence of the mean micellar size. It will be unambiguously shown that there is no way to describe semi-diluted micellar solutions through a mean-field approximation and that there does not exist any scaling law of the kind 〈L〉∝φα. Furthermore, it will be shown that the shape of the size distribution function is markedly different from the exponential one. The basis for a more realistic approach for the growth process of micellar aggregates is also presented and some pre liminary indications are success fully compared with experimental results.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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