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  • Wiley-Blackwell  (4)
  • 1990-1994  (4)
  • 1
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the present investigation, the sedimentation behavior, over an extended concentration range, in solutions of polystyrenes under good, marginal, and theta solvent conditions, is analyzed in the framework of a recent theoretical model, which takes into account the gradual screening of both hydrodynamic and excluded-volume interactions in the semidilute regime. The model inspires the construction of universal plots of the form S/S0 versus ksc, where S is the sedimentation coefficient at polymer concentration c, S0 is that at infinite dilution, and ks is the concentration dependence coefficient. The resulting analytical expressions, without adjustable parameters, are consistent with experimental sedimentation data over the whole concentration range studied.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Isotactic polystyrene samples crystallized from concentrated solutions (〉 10% by weight) in the thermodynamically good solvent toluene display a lamellar thickness L = (170 ± 15) Å at room temperature, as determined by neutron scattering investigation. This thickness is about twice the value reported for samples crystallized in poor solvents. The results may be interpreted in terms of a substantially smaller melting enthalpy of the polymer in toluene, producing a proportionally inverse increase of the thickness L̄c of the central, crystalline portion of the lamellae. In turn, we suggest that the overall thickness L of the lamellae increases more than proportionally with L̄c, due to the need of accomodating in the amorphous zone increasing amounts of polymer containing steric defects. The decrease of the melting enthalpy is also qualitatively consistent with growth rate results. The half-peak width of the Bragg diffraction peaks suggests that the crystalline fraction of the lamellar thickness is about 50%, in approximate agreement with results obtained by Overbergh, Berghmans and Reynaers (J. Polym. Sci., Polym. Phys. Ed. 14, 1177 (1976)) from bulk-crystallized samples showing about the same values of L and L̄c as observed by us.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fuzziness is quite a different notion from probability. Probability describes the objective uncertainty obtained on the basis of a large number of observations. Fuzziness describes the uncertainity that has a subjective meaning. Fuzzy notions describe the degrees of possession of a given property. The popularity of fuzzy set theory in solving control problems results from its ability to treat some situations which are difficult to deal with by the classical control theory. Fuzzy sets are used to control ill-defined, complex, non-linear systems. There are two aspects of this phenomenon. The first aspect concerns the descriptive ability of fuzzy sets. The second important feature is the applicability of fuzzy sets to work with incomplete, contradictory and subjective information. Fuzzy set theory is becoming increasingly important tool in the new fast developing disciplines of artificial intelligence: expert systems and neural networks. It creates completely new opportunities for the application of fuzzy sets in chemical engineering.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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