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| - An NMR Self-Diffusion Investigation of Aggregation Phenomena inSolutions of Ethyl(hydroxyethyl)cellulose
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| - Water solutions of ethyl(hydroxyethyl)cellulose have been investigated with the PFG NMRtechnique and by means of 1H NMR relaxation measurements. The echo decays in PFG experimentshave been recorded for EHEC with concentrations ranging from the dilute (c< c*) to the semidilute (c>c*). In addition, the temperature dependence of the echo decay was investigated. It is shown that theecho decays deviate substantially from Gaussian diffusion behavior. We discuss this in terms ofpolydispersity, aggregation, and scaling effects. It is argued that the observed deviations are too largeto be caused by polydispersity effects alone. We base this conclusion on the observation that the molarmass scaling of the polymer diffusion coefficient goes roughly as M-4. We focus on using a log-normaldistribution of diffusion coefficients in the evaluation procedure of the PFG data. It is found that bycomparing the diffusion coefficients extracted from this type of procedure with “Dmean” as extracted froma “stretched exponential” approach, there is a difference in the evaluated diffusion constant by up to 1order of magnitude. The difference depends on the degree of deviation from linear behavior in the echodecay when represented in a logarithmic plot vs the relevant experimental parameter.
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