Order fluctuations in the mesophase of polydiethylsiloxane as studied by the dipolar-correlation effect on the stimulated echo

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Abstract
Order fluctuations in polydiethylsiloxane (PDES) mesophase are studied using the dipolar‐correlation effect on the stimulated echo. The attenuation of the stimulated echo is described on the basis of a two‐site slow exchange model. The conclusion is that collective chain fluctuations result in temporarily and locally ordered and temporarily and locally defect‐enriched states. The local order parameter is inhomogeneously distributed in the samples as indicated by the absence of any oscillatory modulation of the dipolar‐correlation effect. The mean exchange time between the two mobility states varies in the temperature range of the mesophase between 0.1 and 1 s. It turned out to be an exponential function of the reduced temperature relative to the isotropization temperature. Apart from this implicit function no explicit dependence on the molecular weight could be detected. This suggests that the exchange phenomenon and the type of the order fluctuations are features universal for the PDES mesophase.