Lyotropic liquid crystalline solutions of hydroxypropyl cellulose in water: Effect of salts on the turbidity and viscometric behavior

Abstract

SynopsisEffect of addition of salt on the viscometric behavior of the dilute or concentrated aqueous solution of hydroxypropyl cellulose (HPC) was determined by means of an Ubbelohde or a cone-plate viscometer. That effect on the turbidity of the dilute system was also determined. As salts, NaC1, LiCl, and thiourea were chosen. The turbidity and viscometric behavior for the dilute system, and the viscometric behavior for the concentrated system were greatly affected by salt type and concentration. With increasing NaCl or LiCl concentration, the cloud point decreased,[el showed a maximum, Huggins' constant k' showed a minimum, and the shear viscosity for concentrated isotropic solutions showed a maximum. The 45 wt % solution with no salt showed a viscometric behavior which was characteristic of lyotropic liquid crystals; however, with increasing NaCl concentration, a critical temperature at which the shear viscosity showed a maximum with respect to temperature shifted to lower temperature. This behavior was due to an increase in the turbidity, not due to a phase transformation. On the other hand, an addition of thiourea did not affect so greatly the turbidity and viscometric behavior as an addition of NaCl or LiCl did. We speculated different actions of NaCl and thiourea.

Phase diagrams and rheological properties of cellulose ether solutions in magnetic field

“…4 displays the phase diagram measured for the HPC-water system. This diagram is largely consistent with the phase diagrams described for this system [27][28][29][30][31][32][33][34][35][36][37][38][39]. (1 -Refers to colorless solutions and 2 -refers to blue solutions, which is typical of cholesterol LC solutions.)…”

“…Molecules of cellulose and cellulose derivatives are characterized by a rigid helical conformation and, hence, they are capable of ordering and formation of cholesteric liquid crystals in concentrated solutions. Many studies were devoted to phase equilibrium in the HPC-water system, and the low critical solution temperature values were reported in a number of papers [27][28][29][30][31][32][33][34][35][36][37][38][39] a magnetic field on the liquid crystal structure was studied by Meuer [40], de Gennes [41]. The authors considered such a field distortion of the cholesteric structure and found out that the transition to complete nematic order occursed at the critical field strength.…”

Salt Addition Effects on Mesophase Structure and Optical Properties of Aqueous Hydroxypropyl Cellulose Solutions

“…In supplementary CD measurements for the saltcontaining systems, all the samples tested showed a negative signal of circular reflectivity, indicating that the cholesteric sense, i.e., the handedness of the supramolecular helical arrangement remained righthanded as it was in the absence of any salt. Thus the salt-addition was confirmed to affect simply the ampli- It is already known 6,7,14,19 that the HPC/water binary system phase-separates to give a lower critical solution temperature (LCST) and visually becomes turbid on heating. The addition of neutral salts also affects seriously this phase separation behavior.…”

“…5,6 There have been a number of studies concerned with mesomorphic characterization and structural and physical properties of this polymer for its individual solutions in many solvents. Among them, several reports have dealt with some effects of addition of neutral salts into concentrated HPC solutions in water 7,8 or in a few organic solvents 9 and demonstrated, for instance, that the mesomorphic behavior and rheological properties of the solutions are much affected by the coexistence of a small amount of the additives. The systematization and explanation of the effectiveness of the additive salts are still unsatisfactory, however.…”

Synthesis and swelling behaviour of hydrophobically modified responsive polymers in dilute aqueous solutions

“…In most cases, the decrease in viscosity with temperature leads to a loss of efficiency or a lack of control Polymer 46 (2005) of the process and there is a need for technological fluids which could enhance reversibly their viscosity upon heating. This property, which is opposed to gelation upon cooling described long ago with natural polymers like gelatine, has been reported initially with cellulosic derivatives (methyl, hydroxypropyl, ethyl(hydroxyethyl)) and their mixtures with ionic surfactants [25][26][27][28][29]. This specific property has been exemplified mainly during the last two decades with synthetic block copolymers, like poly(ethylene oxide)-b-poly(propylene oxide) [30][31][32], and then clearly rationalised with graft copolymers tailored with responsive side-chains [33][34][35][36][37][38].…”