Engineering Achiral Liquid Crystalline Polymers for Chiral Self-Recovery

Flexible construction of permanently stored supramolecular chirality with stimulus-responsiveness remains a big challenge. Herein, we describe an efficient method to realize the transfer and storage of chirality in intrinsically achiral films of a side-chain polymeric liquid crystal system by combining chiral doping and cross-linking strategy. Even the helical structure was destroyed by UV light irradiation, the memorized chiral information in the covalent network enabled complete self-recovery of the original chiral superstructure. These results allowed the building of a novel chiroptical switch without any additional chiral source in multiple types of liquid crystal polymers, which may be one of the competitive candidates for use in stimulus-responsive chiro-optical devices.

Activation Energy and Thermal Radiation Aspects in Bioconvection Flow of Rate-Type Nanoparticles Configured by a Stretching/Shrinking Disk

Recent trends in advanced nanotechnology developed thermal consequences of nanoparticles due to increasing significance in various engineering and thermal extrusion systems. The current continuation analyzes the axisymmetric stagnation point flow of magnetized rate-type nanoparticles configured by a porous stretching/shrinking rotating disk in the presence of motile microorganisms. A famous rate-type polymeric liquid namely Maxwell fluid has been used to examine the rheological consequences. Constitutive expressions based on the Buongiorno nanofluid model are used to examine the thermophoresis and Brownian motion features. With imposing similarity variables proposed by von Karman, the formulated problem is composed into dimensionless form. With the implementation of famous numerical technique bvp4c, the solution of governing flow equations is simulated. Graphical significance for each physical parameter is interpolated with relevant physical aspects. The variation in local Nusselt number, local Sherwood number, and motile density number corresponding to engineering parameters is numerically iterated and expressed in a tabular form. The study revealed that radial direction velocity component decreases by increasing the Deborah number and buoyancy ratio parameter. An enhanced temperature distribution for both stretching and shrinking cases has been noted by increasing the Biot number and thermophoresis parameter. A lower motile microorganisms distributed is noted due to the involvement of motile diffusivity.

Thermocapillary Marangoni Flows in Azopolymers

It is well known that light-induced multiple trans-cis-trans photoisomerizations of azobenzene derivatives attached to various matrices (polymeric, liquid crystalline polymers) result in polymer mass movement leading to generation of surface reliefs. The reliefs can be produced at small as well as at large light intensities. When linearly polarized light is used in the process, directional photo-induced molecular orientation of the azo molecules occurs, which leads to the generation of optical anisotropy in the system, providing that thermal effects are negligible. On the other hand, large reliefs are observed at relatively strong laser intensities when the optofluidization process is particularly effective. In this article, we describe the competitive thermocapillary Marangoni effect of polymer mass motion. We experimentally prove that the Marangoni effect occurs simultaneously with the optofluidization process. It destroys the orientation of the azopolymer molecules and results in cancelation of the photo-induced birefringence. Our experimental observations of polymer surface topography with atomic force microscopy are supported by suitable modelings.

Modeling of Polymeric Liquid Material Properties Effect on Pressure Transients in the Elastic Pipe

Material properties of polymeric liquids are of great importance for different technological processes. Particularly, such liquids demonstrate viscoelastic behavior in non-stationary transportation regimes, widely used in polymer processing, which influence the operation of the equipment. The paper is devoted to the modeling of pressure transient in a long thin-walled elastic tube with polymeric liquid. As distinct to previous results of the authors, material properties of the liquid are described by generalized Maxwell rheological equation accounting for a spectrum of relaxation times. It is supposed that the pressure pulse is generated at the tube end and propagates along the waveguide with the speed influenced by the tube geometry and wall elasticity, and the liquid compressibility and viscoelasticity. The problem is formulated in a quasi-one-dimensional approximation and solved by the operational method. The resulting relation for the pressure in the wave is inverted numerically. Effect of liquid relaxation time distribution on the pressure pulse propagation is studied. The results are relevant for the dynamic operation of equipment for polymer processing; they can be useful also for material characterization of high-molecular liquids.

Influence of Oxidation Degree of Graphene Oxide on the Shear Rheology of Poly(ethylene glycol) Suspensions

This work studies the influence of the concentration and oxidation degree on the rheological behavior of graphene oxide (GO) nanosheets dispersed on polyethylene glycol (PEG). The rheological characterization was fulfilled in shear flow through rotational rheometry measurements, in steady, transient and oscillatory regimes. Graphene oxide was prepared by chemical exfoliation of graphite using the modified Hummers method. The morphological and structural characteristics originating from the synthesis were analyzed by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and atomic force microscopy. It is shown that higher oxidation times increase the functional groups, which leads to a higher dispersion and exfoliation of GO sheets in the PEG. Moreover, the addition of GO in a PEG solution results in significant growth of the suspension viscosity, and a change of the fluid behavior from Newtonian to pseudoplastic. This effect is related to the concentration and oxidation level of the obtained GO particles. The results obtained aim to contribute towards the understanding of the interactions between the GO and the polymeric liquid matrix, and their influence on the suspension rheological behavior.