Mechano‐Optical Response of Novel Polymer Composites Based on Elastic Polyurethane Matrix Filled with Low‐Molar‐Mass Cholesteric Droplets

Abstract

Among the various types of liquid crystalline (LC) structures, the cholesteric mesophase attracts special attention in view of helical supramolecular structure determining their specific optical properties. The helix pitch of cholesteric liquid crystals is very sensitive to mechanical stress, resulting in change of their optical properties and position of selective light reflection peak. Here, films of polymer‐dispersed cholesteric liquid crystals based on polyurethane elastomer are prepared and studied. Liquid crystal mixtures based on chiral cholesterol derivatives are uniformly dispersed in the form of micrometer‐sized droplets in an elastomeric matrix. A significant mechano‐optical response of the composites under the action of deformation is demonstrated, and the change in the position of the selective light reflection band during mechanical stress is studied in detail. A shift in the selective light reflection peak by 100 nm or more is found. This process is accompanied by color transformations of brightly colored films. Such materials can be promising for creating stress and deformation sensors, ripple and bending sensors, and other technical devices.

Polymer-Dispersed Cholesteric Liquid Crystal under Homeotropic Anchoring: Electrically Induced Structures with λ1/2-Disclination

“…The application multiplicity of CLC dispersions is due to the vast diversity of the formed orientational structures, which are determined by the boundary conditions, the droplet’s shape, the CLC elasticity constants, the ratio of the droplet’s size d and the cholesteric intrinsic helix pitch characterized by the relative chiral parameter [ 16 , 17 , 18 , 19 , 20 , 21 ]. For example, luminescence or Bragg reflection of light by cholesteric depends on both the CLC pitch [ 22 , 23 , 24 , 25 ] and the orientation of the cholesteric layers in the droplet [ 3 , 26 , 27 ].…”

Electrically Induced Optical and Structural Response of Cholesteric and Nematic Droplets with Conical Boundary Conditions

“…Применение капсулированных полимером жидких кристаллов (КПЖК) в электрооптических устройствах обусловлено способностью капель жидкого кристалла (ЖК) изменять ориентацию директора (единичного вектора, направленного вдоль преимущественной ориентации длинных осей молекул жидкого кристалла), под воздействием внешних факторов, например электрического поля [1]. КПЖК-материалы широко используются в: дисплеях [2], световых затворах [3], тепловых датчиках или датчиках давления [4,5], электрически управляемых линзах Френеля [6] и умных окнах с функцией управления рассеянием света [7,8].…”

Mechanochromic Responses of Cholesteric Liquid Crystal Droplets with Nanoscale Periodic Helical Structures Showing Reversible and Tunable Structural Color

“…Liquid crystals, which possess both ordering and fluidity, have shown a rich set of mesophases with unique properties and have demonstrated various applications beyond displays. − In cholesteric liquid crystal (CLC) phases, molecules spontaneously self-assemble into a periodic helical structure with a distinct helical pitch. − When the helical pitch is comparable to the wavelength of visible light, structural color appears due to selective Bragg reflection. − Since the wavelength of selective Bragg reflection depends on the helical pitch, the structural color of CLCs could be tuned in response to various external stimuli, such as mechanical stress, − temperature, electric field, , or light. − The performances of stimuli-triggered responses have intrigued the developments of CLCs for various applications, such as anti-fake materials, − intelligent sensors, − and smart actuators. − …”