Electrooptical Behavior of Liquid-Crystalline (Hydroxypropyl)cellulose/Inorganic Salt Aqueous Solutions

Abstract

The selective light reflection and turbidimetric property of concentrated aqueous solutions of (hydroxypropyl)cellulose (HPC), originating from their cholesteric mesophase structure and LCSTtype phase behavior, respectively, are much affected by coexistence of inorganic salts therein. This is ascribed to a strong dependence of both cholesteric helical pitch (P) and cloud point (T c) of the aqueous cellulosic solutions on the sort and concentration of the additive salts. By virtue of electrophoretic motility of the coexistent salt ions as P and/or T c shifter, the dynamic variation in cholesteric coloration and/or optical turbidity of the HPC solutions was realized under the action of a relatively weak electromotive force to electrodes in contact with their layered sample. It was reasonably taken that the electrical stimulation allowed the ion particles to migrate and localize in this lyotropic system, resulting in occurrence of a certain degree of gradient in magnitude of P and/or T c in response to the uneven ionic distribution. To make clearer the mechanism of the novel electrooptical function, discussion took into consideration a storage effect of electric charge in the solution samples, detectable as a remaining potential difference after cessation of the application of the electric field.

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

“…Figure 13 . This behavior is phenomenologically parallel to that found in previous experiments [61] using conventional alkali-metallic salts and was interpreted as being primarily a result of the generation of a disproportional dislocation of CnMim + and X À as P and/or T c shifters. In fact, the ionic fluctuation gives rise to an inner gradient of electric potential in the concentrated polymer medium.…”

“…A significant example of such functional development is the ion-mediated dynamic manipulation of cholesteric coloration and optical turbidity by using electrical stimulation of HPC lyotropics, including swollen gels [10,[61][62][63][64]. In the first demonstration [61], conventional metallic salts were employed as additive ions to shift P and/or T c . Such a dynamic concept is based on the possible electrophoretic migration of the dissociated ionic particles, as represented diagrammatically in Fig.…”

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

“…(In this study, the DS value of the HPC sample was determined on the basis of 1 H NMR data according to a method proposed by Ho et al 29 Some of the previous articles 13,17,18 reported DS¼1.8 for the same grade (Lot#5) of HPC from the same commercial origin; the value was determined by quantitative-mode solid-state 13 C NMR measurements.) 30 …”

“…17 However, there may be a certain difference between the two cases, in the process generating the disparity in cation/anion distribution. In the previous case, the electrical stimulation allows ion particles to directly migrate and localize in the lyotropic system, as the added salt would have already been completely ionized.…”

“…Furthermore, by using an electrophoretic motility of the coexistent ions as P and/or T c shifters, the dynamic variation in cholesteric coloration and/or optical turbidity of the HPC lyotropics, including solutions and gels, were realized under application of a relatively weak electric field. [15][16][17][18] Meanwhile, recently, low-temperature molten organosalts, that is, the so-called ionic liquids, have become a subject of great interest in various fields of chemistry, because of their possibilities as a green solvent, a new component of ion-conductive materials and so on. [19][20][21][22] Representative examples of the conventionally used ionic liquids are salts with N,N¢-dialkylimidazolium, N-alkylpyridinium, alkylammonium and alkylphosphonium as the cationic moiety.…”