Effects of Added Polysaccharides on the Isotropic/Nematic Phase Equilibrium of κ-Carrageenan

Abstract

The effects of added ι-carrageenan (IC), guar gum (GG), locust bean gum (LBG), or dextran (Dx) on the isotropic−nematic phase equilibrium of κ-carrageenan (KC) in solutions of 0.1 M NaI were studied. The concentrations of the polysaccharides in the separating phases were determined by NMR, and the phase volumes were observed, at different mixing ratios. All added polysaccharides were enriched in the isotropic phase, but to very different extents. GG partitioned relatively evenly between the two phases, and its effect on the relative phase volumes was very small. Dx was moderately enriched in the isotropic phase. LBG was different from the other added polysaccharides in that already relatively small amounts prevented a macroscopic phase separation, probably due to the increased viscosity. IC was exceptional in that it showed a very strong preference for the isotropic phase. As a consequence, the relative phase volumes were affected on addition of IC, and the nematic phase appeared at a much lower KC concentration than for KC alone. The reason for the exclusion of IC from the nematic phase is not clear, but it is speculated that it could depend on a tendency to form aggregates.

Isotropic−Nematic Phase Equilibrium and Phase Separation of κ-Carrageenan in Aqueous Salt Solution: Experimental and Theoretical Approaches

“…The helix-coil transitions were in accordance with the transitions observed from previous oscillatory and calorimetric measurements. 34,48,49 K-Carrageenan Sample B. To characterize further the lyotropic behavior of KC polysaccharide and confirm the above results, we have prepared a new sample B (that contains both phases which are not macroscopically phase separated, B biph ) and also two other samples B iso and B nem after centrifugation and separation of isotropic and anisotropic phases (see Experimental Section).…”

Enhanced Alignment of Water-Soluble Polythiophene Using Cellulose Nanocrystals as a Liquid Crystal Template

“…An example of the CNC and PPBT ordering in the biphasic region (5 wt % CNCs + 3 mg/mL PPBT) is shown in Figure ; spherulites are apparent under POM (Figure c) and at high magnification the fingerprint texture of the chiral nematic phase can be visualized within the spherulites (Figure d). The anionic nature of PPBT in water may be the cause for its biphasic stability; charged polymers tend to partition more evenly due to the entropy of mixing of the counterions . Another possibility is that in the aqueous CNC environment, which is acidic due to the sulfate half ester groups, the PPBT side chain is protonated to form a carboxylic acid that hydrogen bonds with the surface hydroxyl groups of the CNCs.…”

“…The liquid crystal ordering of CNCs has been exploited previously as a guide for a variety of materials to yield functional structures such as mesoporous silica, , nanocomposite hydrogels, and photonic polymer composite films . In these systems, the CNCs retain and impart their helicoidal chiral nematic order, which can act as a one-dimensional (1D) photonic structure for applications in sensing, lasing, and optoelectronic devices. − However, compatibility issues between the CNC LC host and guest materials have also been reported. − Namely, the addition of coils into rod suspensions generally results in demixing and the formation of new phases, − which is undesirable from an application standpoint. In work by Edgar and Gray, when blue dextran, a glucose polymer, was added to suspensions of CNCs it caused phase separation and defects in the sample and the polymer preferentially partitioned into the isotropic phase.…”

“…The anionic nature of PPBT in water may be the cause for its biphasic stability; charged polymers tend to partition more evenly due to the entropy of mixing of the counterions. 26 Another possibility is that in the aqueous CNC environment, which is acidic due to the sulfate half ester groups, 40 the PPBT side chain is protonated to form a carboxylic acid that hydrogen bonds with the surface hydroxyl groups of the CNCs. Evidence for depletion attraction caused by the PPBT was also found in the measured p, which is a function of the rod packing.…”

Structure and functionality of chitin nanocrystal dispersions

“…This phenomenon has been shown to occur for several mixed colloidal systems (Adams, Digic, Keller & Fraden, 1998;Beck-Candanedo, Viet & Gray, 2007;Dogic, Purdy, Grelet, Adams & Fraden, 2004;Ramzi, Borgstrom & Piculell, 1999). In the present system, increased ChN concentration means gel strengthening and sometimes the enhancement is such that may hinder the macroscopic phase separation; nonetheless, it may occur locally, at a microscopic scale .…”