Sol/gel transition and liquid crystal transition of HPC in ionic liquid

Abstract

This work uses an ionic liquid (IL), 1-butyl-3-methylimidazolium acetate, as a solvent to study the sol/gel transition (SGT) and liquid crystal transition (LCT) of hydroxypropylcellulose (HPC) solution. The LCT concentration of HPC at room temperature is 7 wt%, which is slightly higher than its SGT concentration of 6 wt%. For HPC concentrations of over 7 wt%, three rheological approaches were utilized, and the parameters relaxation time, hysteresis ratio and loss modulus (G 00 ) are measured to determine the LCT temperature. The relaxation study concludes that the LC-critical concentration of HPC is 7 wt%. When HPC exceeds 7 wt%, the LC transition temperatures, ranging from 45 to 51°C, can be measured and are proportional to the HPC concentration. The rheological results are then confirmed by making observations under a polarized optical microscope. All results are highly mutually consistent. Most significantly, the rheological parameters adopted herein can be used as good indicators of the LC transition. Of those indicators, G 00 changes distinctly at the LCT point, and can thus be suggested to be the most helpful indicator in determining the LCT temperature.

Hydrogels based on cellulose and chitin: fabrication, properties, and applications

“…Usually, physical associations are reversible, leading to a thermo-reversible and "green" (without cross-linkers) sol-gel transition process. 75,76 However, if (a) the reversible gel is coagulated in an anti-solvent, or (b) the NaOH/urea (or thiourea) solvent denatures at high curing temperatures (>60 °C, resulting in a yellow color) via reaction and thermal decomposition of the solvent molecules, 54,77 the solvents are washed out (in "a") or destroyed (in "b"), resulting in formation of socalled irreversible gels. Such irreversible physical gels, when vacuum-or supercritically-dried, exhibit lower degrees of crystallinity (reduced by 9-22%) than native cellulose or chitin.…”

Concentration Scaling on Linear Viscoelastic Properties of Cellular Suspensions and Effects of Equilibrium Phase Behavior

“…It predicts a transition from an equilibrium isotropic phase to an anisotropic liquid crystal phase as the volume fraction of rod-like molecules with a certain aspect ratio is increased. Onsager’s theory is also applicable in studies of phase transition from nanocrystalline cellulose (CNC [ 19 ], cellulose/AmimCl [ 20 ] and hydroxypropylcellulose (HPC) [ 21 ]) to micron scale cellulose and bio-particle (Cellulose Whiskers [ 22 ], fd virus [ 23 ] and Sacran solutions [ 24 ]). Phase transitions of structural fluids could affect their rheological properties.…”

3-D phase diagram of HPC/H2O/H3PO4 tertiary system

“…Hydroxypropyl cellulose (HPC), one of the most important cellulose derivatives, has various applications, such as thickening agents, fillers, dietary fiber, anti clumping agents and emulsifiers. Interestingly, many cellulose derivatives, including HPC, have been found to exhibit a liquid crystalline (LC) phase in variety of a range of solvents (Werbowyj and Gray 1976;Chang and Gray 1978;Aharoni 1980;Werbowyj and Gray 1980;Aharoni 1981Aharoni , 1982Conio et al 1983;Marsano and Fossati 2000;Rwei et al 2009). These LC polymers are of great interest because they exhibit a mesophase structure under certain thermal or solvent conditions.…”