Addition effects of imidazolium salts on mesophase structure and optical properties of concentrated hydroxypropyl cellulose aqueous solutions

Abstract

Addition effects of N-alkyl-substituted methylimidazolium salts ([CnMim][X]) on the mesophase structure and lower critical solution temperature (LCST)-type phase-separation behavior of concentrated hydroxypropyl cellulose (HPC) aqueous solutions were investigated mainly by spectrophotometry. In the cholesteric mesophase formation, at concentrations of more than 50 wt% HPC, helical pitch (P) was confirmed to shift upward according to the chaotropic strength of X -, for example, in a manner satisfying the order of Cl À oBr À oNO 3 À oI À . Organocations generally elevated P relative to the nonionic reference, the effectiveness being pronounced in the order ofWith regard to LCST behavior, imidazolium additives raised the cloud point (T c ) in the isotropic solutions of p40 wt% HPC, whereas the T c value of mesomorphic solutions was prone to be lowered by the addition. Discussion of these observations took into consideration the differences in the N-alkyl structure and amphiphilic nature between cationic imidazolium varieties, as well as the difference in the chaotropic strength between the counter anions. It was also exemplified preliminarily that this kind of salt-containing lyotropic system of HPC exercised an electro-optical function when coupled with an electric circuit.

Liquid Crystals of Cellulosics: Fascinating Ordered Structures for the Design of Functional Material Systems

“…6b) [31]. In the isotropic region, the surfactant-like action of the organo-cations on HPC molecules works as a T c -elevating factor, because of the gain in electrostatic stability of the solute polymer.…”

“…5a, b) are employed as additives in aqueous HPC lyotropics, particular attention should be paid to the amphiphilic structure and possible surfactant-like action of the organo-cation moiety CnMim + [31]. In mesophase formation at !50 wt% HPC, the helicoidal pitch P shifts upward according to the chaotropic strength of X À of the added IL (e.g., in a manner satisfying the order Cl À < Br À < NO 3 À < I À ) if the salt is well dissociated.…”

“…Fig. 3 Structural models and parameters for characterizing the chiral nematic arrangement of pitch P: (a) definition of the nematic layer spacing d and twist angle φ; these satisfy a relation φ/ d ¼ 360 /P; (b) pseudo-hexagonal packing of molecular chains of diameter a, tolerated as a shortrange order of the mesophase; (c) changing manner of P with variation in the angle φ between adjacent nematic directors, in terms of a threaded rod model [26] for a twisting molecule of cellulose derivative [27] The periodicity of the chiral mesophase and LCST-type phase boundary, and the ensuing optical properties of the HPC/water lyotropic system, are significantly affected by addition of a third component, such as a small amount of inorganic neutral salts [30] or ILs such as imidazolium salts [31]. For instance, when LiCl is dissolved in the lyotropic system, the wavelength of selective reflection (λ M ) shifts to the blue region and T c decreases.…”

Electrooptical Behavior of Aqueous (Hydroxypropyl)cellulose Liquid Crystals Containing Imidazolium Salts

“…As described in detail in previous studies, 9−12 the cholesteric periodicity and LCST-type phase boundary, and ensuing optical properties of the lyotropic system of HPC/water, are significantly affected by the addition of a small amount of inorganic salts 9 or organo-ionic liquids such as imidazolium salts 12 as the third component. As a universal rule, it was shown that both the cholesteric pitch (P) and the phase-separation temperature, and accordingly the wavelength of selective light reflection (λ M ) and the cloud point (T c ), varied systematically with a change in strength of a so-called "chaotropic" effect of the ions constituting the additive salts.…”

Effect of flexible spacer length on the mesophase structures of main-chain/side-chain liquid crystalline polymers based on ethyl cellulose

“…Since then, the LC behaviors of cellulose derivatives have aroused much interest in LC polymers within the scientific community. [35][36][37][38][39][40][41][42][43][44] During the past few years, rigid mesogens have been introduced into the backbone of cellulose to investigate the LC behavior of the resultant cellulose derivatives. [45][46][47][48][49] Although the chemical structure of these cellulose derivatives is similar to that of the combined MCSCLCPs, 16,26 rigid mesogenic side groups cannot form ordered structures themselves and merely function as substitutes of cellulose derivatives; therefore, these polymers exhibit the LC behavior only of the cellulose backbone.…”