Abstract
The macroscopic properties of novel liquid crystal (LC) systems—LCs with unconventional molecular structure as well as conventional LCs in unconventional geometries—directly descend from their mesoscopic structural organization. While X-ray diffraction (XRD) is an obvious choice to investigate their nanoscale structure, conventional diffractometry is often hampered by experimental difficulties: the low scattering power and short-range positional order of the materials, resulting in weak and diffuse diffraction features; the need to perform measurements in challenging conditions, e.g., under magnetic and/or electric fields, on thin films, or at high temperatures; and the necessity to probe micron-sized volumes to tell the local structural properties from their macroscopic average. Synchrotron XRD allows these problems to be circumvented thanks to the superior diffraction capabilities (brilliance, q-range, energy and space resolution) and advanced sample environment available at synchrotron beamlines. Here, we highlight the potentiality of synchrotron XRD in the field of LCs by reviewing a selection of experiments on three unconventional LC systems: the potentially biaxial and polar nematic phase of bent-core mesogens; the very high-temperature nematic phase of all-aromatic LCs; and polymer-dispersed liquid crystals. In all these cases, synchrotron XRD unveils subtle nanostructural features that are reflected into macroscopic properties of great interest from both fundamental and technological points of view.
Highlights
Soft matter [1] is central to a number of promising advanced technological applications spanning across physics, chemistry, biology, and medicine
LCmaterials, systems,exhibiting here we unique will focus on nanoscale structure of new unconventional and liquid crystal (LC)-based physical thermotropic nematics, the most studied class of
Bent-core mesogens (BCMs) are bent-shaped molecules typically consisting of a bent aromatic
Summary
PDLCs are composite materials consisting of droplets of low molar mass LC randomly dispersed. While the polymeric matrix acts as an isotropic solid binder, the the droplets exhibit a strong optical anisotropy that depends on the orientation of the LC therein. Beyond the scope of applications, in the last decades, the interest in PDLCs has considerably stimulated fundamental research concerning the polymerization-induced phase separation process stimulated fundamental research concerning the polymerization-induced phase separation process used for their preparation [71], their dielectric and optical properties [72,73], the reorientational used for their preparation [71], their dielectric and optical properties [72,73], the reorientational dynamics of the LC inside the droplets [74], the dependence of the measured macroscopic parameters dynamics of the LC inside the droplets [74], the dependence of the measured macroscopic parameters (e.g., switching time, driving voltage, etc.) on the shape and distribution of the droplets, and (e.g., switching time, driving voltage, etc.) on the shape and distribution of the droplets, and especially the unusual physical properties exhibited by the LC when confined to small cavities [75]. These transitions can in turn be used to obtain a measure of the surface anchoring strength [76]
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