Liquid crystalline phase transition of a semiflexible polymer: acetoxypropyl cellulose

Abstract

Acetoxypropyl)cellulose (APC) fractions form thermotropic mesophases and also form lyotropic mesophases in dibutyl phthalate (DBP). The liquid crystal to isotropic transitions of these mesophases are examined. The critical concentration for mesophase formation, 0\ increases markedly with temperature. This increase is caused primarily by the reduced stiffness of the chain; as calculated in the preceding paper, the axial ratio of the Kuhn segment decreases from 10.8 to 5.6 ± 0.4 in the temperature range from 25 to 150 °C. At room temperature, the volume fraction of APC in DBP needed for anisotropic phase separation is 0.52 ± 0.02, for chains with contour lengths from 102 to 103 nm. The ordered phase coexists with a more dilute isotropic phase up to a polymer volume fraction of 0.69 ± 0.04. The concentrations of both phases increase with that of the solution. The molar mass of the APC in the mesophase exceeds that in the isotropic phase. The enthalpy of the transition to an isotropic solution, measured by differential scanning calorimetry, decreases with a reduction in the APC concentration. The experimental results are interpreted in the light of recent theories for liquid crystalline phase separation. Theories introducing orientational anisotropic interactions between chains are used to explain the extended temperature or concentration range of the thermotropic and lyotropic APC mesophases. However, the variation in critical concentration can be roughly predicted over a very wide temperature range from the freely jointed segment model without anisotropic interactions.

Mesophase formation in high molecular-weight xanthan solutions

“…Its polydispersity, Ip ~ 1.4, probably produces an increase in the width of the biphasic regime. However, different results for mesophase formation in cellulosic derivatives solutions have been recently published [12,[41][42][43][44] and the reported variations of e' with chain length show that polydispersity cannot be responsible for the very large decrease in c' which has been observed. On the other hand, variations in xanthan rigidity, as concentration increases due to chain confinement, can produce phase diagram modifications.…”

“…These mesophases have been observed, by using cross-polarized light microscopy and viscometry, in various macromolecular systems e.g. aromatic polyamides [1][2][3][4], polyisocyanates [5,6], cellulosic polymers [7][8][9][10][11][12] and, more especially, polysaccharides [13 151.…”

Tunable topographical cellulose matrices for electro-optical liquid crystal cells

“…The pitch of the cholesteric helix can also be locked by using different procedures among them by photoinitiated crosslinking of pendant acrylate groups [10]. One of the most studied thermotropic cellulose esters is acetoxypropylcellulose (APC), it is cholesteric from below room temperature up to 180°C [6] and can originate lyotropic phases in some common solvents [11,12]. Rheo-optical and rheological studies [13] were also performed in APC in order to better understand the relationship between the textures observed in optical microscopy and the light scattering patterns.…”

Rheo-optical characterization of liquid crystalline acetoxypropylcellulose melt undergoing large shear flow and relaxation after flow cessation

“…It presents a linear structure of β-d-glucopyranose monomers, in which free primary and secondary hydroxyl groups can be fully or partially substituted through esterification or etherification, among other chemical reactions, conferring different chemical configurations to the molecules of the cellulose derivatives [1][2][3]. The introduction of substituent's groups in the main chain can originate dramatic changes in the chemical and physical properties of cellulose.…”