Elongation of Discotic Liquid Crystal Strands and Lubricant Effects

Abstract

After a short review on the physics of pulled threads and their mechanical properties, the paper reports and discusses the strand elongation of disordered columnar phases, hexagonal or lamella-columnar, of small molecules or polymers. The mechanical properties appear to be relevant to the length of the columns of molecules compared to the thread length, instead of the usual correlation length. If, taking the entanglement effect into account, the column length is short, the strand exhibits rather fluid-like properties that may even look nematic-like at the macroscopic scale. The Plateau-Rayleigh instability breaks the thread shortly thereafter. However, because the hydrodynamic objects are the columns instead of the molecules, the viscosity is anomalously large. The observations show that the strands in the columnar phases are made of filaments, or fibrils, which are bundles of columns of molecules. This explains the grooves and rings, which are observed on the antenna or bamboo-like strand profiles. On pulling a strand, the elongation stress eventually exceeds the plasticity threshold, thus breaking the columns and the filaments. As a result, cracks, more exactly, giant dislocations are formed. These change the strand thickness by steps of different birefringence colors. Interestingly, the addition of a solute may drastically change the effective viscosity of the columnar phase and its mechanical properties. Some solutes, such as alkanes, exhibit lubricant and detangling properties, whereas others such as triphenylene, are antilubricant.

A fibre forming smectic twist–bent liquid crystalline phase

“…In case of Newtonian liquids, the Rayleigh-Plateau (RP) instability leads to breaking of a uid cylinder into droplets, when the length-todiameter ratio is larger than p. 2 Therefore, bres typically rupture when they are longer than a critical length. 3 Nematic or cholesteric liquid crystals do not form stable cylinders with an aspect ratio larger than p. However, several types of smectic or columnar liquid crystals have been demonstrated to form freelysuspended laments with very large slenderness ratios. [4][5][6] It appears that in these materials, a 2D transversal order is essential to achieve mechanical stability of the bre structure.…”

Effects of Particle Size Distribution on the Physicochemical, Functional, and Structural Properties of Alfalfa Leaf Powder

“…Based on the above analysis, G5 has a different crystal structure from the other samples. The alfalfa leaf was subjected to shear, friction, and other forces in the crushing process, and the unstable crystallization zone was activated, leading to a changed crystal structure [36]. Meanwhile, the CIs of G1, G2, G4, and G5 were significantly different, but there was no significant difference between G2 and G3 (p < 0.05) (Figure 8b).…”