Polymer dimensions in good solvents: crossover from semidilute to concentrated solutions.
Using small-angle neutron scattering, we studied the variation of the polymer radius of gyration (R_{g}) as a function of polymer concentration (varphi) for solutions of a flexible-chain poly(methyl methacrylate) in chloroform. We observed for the first time a distinct crossover between swollen coils in the semidilute regime, where R_{g};{2} proportional, variantvarphi;{-0.26+/-0.03}, and unperturbed coils in the concentrated regime, where R_{g} is independent on concentration. The crossover occurs at varphi;{double dagger} approximately 0.15, a value that agrees reasonably well with varphi;{double dagger} approximately 0.21 +/- 0.035, estimated with a scaling relationship between varphi;{double dagger} and the coil overlap concentration varphi;{*}.
Cheng
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Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Graessley
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Melnichenko
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