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Small-angle neutron scattering (SANS) has been used to investigate the conformation of linear and cyclic poly(dimethylsiloxane)s (PDMS) in chemically identical, undiluted blends. SANS measurements have been carried out on (1) linear hydrogenous (H) mixed with linear deuterated (D) PDMS and (2) cyclic H mixed with cyclic D PDMS. The conformational behavior of the cyclic and linear polymers is studied over a wide range of molar mass and composition. Isotopic blends of linear PDMS are shown to adopt conformations that agree well with theoretical predictions for Gaussian random-coil polymers and confirm previous SANS studies. As expected for chains obeying Gaussian statistics, the mean radii of gyration, R g, scale with the weight-average molar mass as Rg ∝ Mw 0.5 . A detailed study of H/D cyclic PDMS mixtures is presented, and we demonstrate that, since Rg ∝ Mw 0.4 , highly flexible cyclic polymers in the melt adopt an even more compact conformation than that of unperturbed rings. This behavior confirms previous predictions based on computer simulations and theoretical studies. The results are in excellent agreement with computer simulations and theoretical predictions reported in the literature.

The first example of QENS data from a room temperature ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate, over the temperature rnage 250 to 320 K was reported using a medium resolution spectrometer. These data were used to derive the intermediate incoherent dynamic structure factor. The data indicate that the existence of two different relaxation processes occurring in the sample over the probed time/temperature ranges

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