We have performed small-angle Rayleigh light-scattering measurements in polymer solutions under various externally applied temperature gradients. Our experiments confirm the existence of an enhancement of the concentration fluctuations. The nonequilibrium concentration fluctuations are proportional to $(\nabla T{)}^2{/k}^4$, where $\nabla T$ is the applied temperature gradient, and $k$ is the wave number of the fluctuations. The measured strengths of the nonequilibrium fluctuations in the dilute and semidilute concentration regime agree with the strengths calculated from fluctuating hydrodynamics.

• Received 15 June 1998

DOI:https://doi.org/10.1103/PhysRevLett.81.5580