Figure 1

Rayleigh-Brillouin spectra obtained at $q=0.025{\mathrm{n}\mathrm{m}}^{-1}$ for 17% (b),(c) and 9% (a) SI solutions in toluene at $20°\mathrm{C}$. (a) The rich phonon spectrum for 17% is represented by the superposition of three Lorentzians (solid lines). (b) The phonon spectrum of the same solution at a different orientation relative to the laser beam that affects only the intensity of the lowest phonon (2). The diagram, (d), shows schematically the orientation of the lamellar axis, $z$, relative to the light scattering wave vector $q$ and the angle $\alpha$ between the lamellar plane and $q$. (c) Only the longitudinal phonon (1) is observed at low SI concentrations. The frequency region $\sim \pm 1\mathrm{G}\mathrm{H}\mathrm{z}$ about the central peak is provided by the reference beam used for the stabilization of the tandem-FP interferometer. The numbers identify the modes: (1) is longitudinal mode, (2) is the “Bragg” mode, and (3) is the $q$-independent mode.Reuse & Permissions

Figure 2

Rayleigh-Brillouin spectra recorded at $q=0.012{\mathrm{n}\mathrm{m}}^{-1}$ for (a) 17% and (b) 30% SI solutions in toluene at $20°\mathrm{C}$. The numbers identify the modes as in Fig. 1.Reuse & Permissions

Figure 3

The phonon dispersion relations for the ordered SI solutions. The open circles and squares are, respectively, for the 17% and 30% SI solutions and the lines represent linear fits to the acoustic phonons. The solid circles and squares are for the opticlike mode for the 17% and 30% SI solutions, respectively. The Bragg mode (see text) is denoted by solid triangles 17% and solid inverted triangles 30%. The solid lines are computed from the dispersion relation for the lamellar spacings 168 and 192 nm, and show the acoustic, Bragg [Eq. (1)], and opticlike [Eq. (2)] phonons. The arrows on the horizontal axis indicate the edges of the first Brillouin zone in the two ordered SI solutions. This inset is a photograph of the ordered 17% solution. The granular reflective texture of the sample can be seen, as well as the shift in color due to the viewing angle of the lamellar grains.Reuse & Permissions