Microbeam resonant x-ray scattering from bromine-substituted bent-core liquid crystals

We studied the local layer structure in the B2 phase of bromine-substituted bent-core liquid crystals in the cell geometry using microbeam resonant x-ray scattering. In the homochiral state of B2 phase, the 3/2 order satellite peak was observed only when the incident x-ray energy is at the K absorption edge of bromine. This result clearly indicates that the B2 homochiral domain forms two-layer superlattice in adjacent layers, the same as in the rodlike Sm-$C_{\text{A}}$ phase. The work reports on microbeam resonant x-ray scattering experiment from the local layer of the bent-core liquid crystal in the device geometry. Moreover, we can say that bromine is also useful for the analysis of the superstructure of soft materials using resonant x-ray scattering.

Figure 1

Chemical structure and phase sequence of the used bent-core liquid crystal with a bromine atom (4-Br-14-O-PIMB).

Figure 2

(Color online) Optical geometry of x-ray microbeam measurement.

Figure 3

(Color online) X-ray fluorescence intensity as a function of the incident x-ray energy around the $\text{Br}K$ absorption edge from 4-Br-14-O-PIMB. The first peak above the absorption edge was set to resonant edge $E_0\left(=13.48\text{keV}\right)$.

Figure 4

(Color online) (a) A polarized optical microphotograph of the B2 phase $\left(129.5°\text{C}\right)$. An arrow shows the analyzed position. The scale mark shows $100\mu \text{m}$. (b) The two dimensional x-ray scattering profile obtained at the resonant energy. The darker part corresponds to the higher intensity. Thin blue arrows indicate the first and second layer diffraction and a thick red arrow shows the resonant x-ray scattering. The broken lines indicate the angular range to obtain the radial $Q$ scattering intensity profile. (c) The x-ray intensity profile of the first layer diffraction as a function of the $\omega$ angle. (d) The radial $Q$ scan profile obtained by integration of 2D x-ray profiles.

Figure 5

(Color online) 2D x-ray profile in the homochiral B2 phase when the incident energy is at $E_0$ (a) and at $E_0-20\text{eV}$ (a). A red arrow indicates the resonant x-ray scattering. (c) A series of radial $Q$ scan profiles as a function of the incident energy around Eo for 3/2- and second order reflections. Arrows indicate 3/2-order reflections.

Figure 6

(Color online) (a) A polarized optical microphotograph of the B2 phase $\left(129.5°\text{C}\right)$. An arrow shows the analyzed position. The scale mark shows $100\mu \text{m}$. (b) The two dimensional x-ray scattering profile obtained at the resonant energy. A red arrow indicates the resonant x-ray scattering.

Figure 7

(Color online) (a) A polarized optical microphotograph of the B2 phase $\left(129.5°\text{C}\right)$ under the high field application (square wave of $\pm 60\text{V}$ at 2.1 kHz). An arrow shows the irradiated position. The scale mark shows $100\mu \text{m}$. (b) The two-dimensional x-ray scattering profile obtained at the resonant energy.