A PRESSURE-CONTROLLED AND TEMPERATURE-CONTROLLED SAMPLE CELL FOR THE STRUCTURAL INVESTIGATION OF LYOTROPIC LIQUID-CRYSTALS USING A SMALL-ANGLE X-RAY-DIFFRACTION LINE SOURCE

We present the design and performance of a temperature- and pressure-c ontrolled sample cell for the small-angle x-ray diffraction analysis o f lyotropic liquid crystalline materials. The particular requirements for such a system of high resolution, high intensity, and control on s ample homogeneity can be particularly well fulfilled using line-source diffraction. We thus designed a sample cell that will allow the use o f a line source. Sample volume is kept small (20 mu l) to keep the con tained energy low. The hydrostatic system, based on beryllium x-ray wi ndows, Bridgman type seals with lead O rings and a stainless-steel bod y is rated to achieve pressure control within +/-3 bar between O and 3 000 bar at ramping rates of 30-100 bar/s. Temperature control is achie ved within +/-0.03 K between room temperature and 180 degrees C. Maxim um heating rates correspond to 0.8 K/s. Control algorithms are impleme nted on a Microrobotics K4 controller, using a modest amount of comput ing power. (C) 1996 American Institute of Physics.