Liquid crystalline cellulosic elastomers: free standing anisotropic films under stretching

Abstract

The structure and local ordering of 1,6-hexamethylenediisocyanate-(acetoxypropy1) cellulose (HDI-APC) liquid crystalline elastomer thin films are investigated by using X-ray diffraction and scattering techniques. Optical microscopy and mechanical essays are performed to complement the investigation. The study is performed in films subjected or not to an uniaxial stress. Our results indicate that the film is constituted by a bundle of helicoidal fiber-like structure, where the cellobiose block spins around the axis of the fiber, like a string-structure in a smectic-like packing, with the pitch defined by a smectic-like layer. The fibers are in average perpendicular to the smectic-like planes. Without the stretch, these bundles are warped, only with a residual orientation along the casting direction. The stretch orients the bundles along it, increasing the smectic-like and the nematic-like ordering of the fibers. Under stress, the network of molecules which connects the cellobiose blocs and forms the cellulosic matrix tends to organize their links in a hexagonal-like structure with lattice parameter commensurate to the smectic-like structure.

From Cellulosic Based Liquid Crystalline Sheared Solutions to 1D and 2D Soft Materials

“…The former consisting of bands perpendicular to the shear direction while the latter has the bands slightly tilted from that direction. An out-of-plane angle variation of the sinusoidal molecular orientation was also reported [29,30]. The anisotropic nature of cellulosic solutions give them also unique characteristics that has impact, for example, in the way the viscosity changes with polymer concentration.…”

“…In order to characterize these type of networks, Wide Angle X-ray Scattering (WAXS) studies were performed [48] namely of crosslinked APC films produced from chiral nematic solutions [29]. The studies were carried on films subjected or not to a uniaxial stress.…”

“…X-rays results showed that the cholesteric order can be destroyed in sheared films and that a bundle of warped helicoidal fiber-like structures where the cellobiose block spins around the axis of the fiber can develop. The bundles should have fibers with both the levogyre and dextrogyre arrangements, with equal probabilities, and have a residual orientation along the shear direction [ 29 ].…”

Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt undergoing large shear flow and relaxation after flow cessation

“…Note here that stretched extrudates present little necking and nearly no strain recovery. This behavior can be attributed to the material liquid crystalline structure [32].…”

Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate network

“…The cellulose acetate used in the preparation of the CA/LC samples [ 29 – 33 ] was obtained from green and renewable sources. The used nematic LC is E7, a mixture of alkylcyanobiphenyls with a cyano head group [ 34 – 36 ].…”