Civil Engineering Reference
In-Depth Information
Table 14. 1
(Continued)
(Acetyl)ethyl cellulose (substitution degree =
2.5) let → right
chloroform, dichloromethane, dichloroacetic
acid, aqueous phenol, acetic acid, m-cresol
(Acety1)ethyl cellulose (substitution degree
= 2.5) / right
dichloroacetic acid
2-Ethyloxypropyl cellulose / right
acetonitrile, dioxane, methanol
Acetoacetoxypropyl cellulose / let
acetic acid
Phenylacetoxy cellulose (substitution degree
= 1.9) /let
dichloromethane
4-methoxyphenylacetoxy cellulose (substitu-
tion degree = 1.8) / let
dichloromethane
Trimethylsilyl cellulose (substitution degree
= 1.55) / let
dichloromethane
p-Tolylacetoxy cellulose (substitution degree
= 0.5-1.8) / let
dichloromethane
6-
o
-Trityl-2,3-
o
-hexyl cellulose / let
acetic acid, tetrahydrofuran
6-
o
-Trityl-2,3-
o
-pentyl cellulose / right
tetrahydrofuran
for the initial hydrolysis (e.g., sulfuric or phosphoric acid), and also by the chloride
acid, respectively, for obtaining a birefringent glassy phase at er the treatment of post-
sulphation [76, 79-83].
Chiral nematic phases are able to self-assemble, thus obtaining the materials with
unique properties being thus obtained [1, 84-86]. Cellulose i lms with optical proper-
ties of chiral nematic liquid crystals are obtained by simple molding of this suspension
[79] . Such i lms are adapted to rel ect the dif erent light colors by changing the concen-
tration of the salt suspension for a particular cellulose and a set of hydrolysis condi-
tions. Moreover, above a critical concentration, the i bers of the aqueous suspension of
cellulose form a chiral nematic phase and are aligned using a magnetic i eld [82, 86].
Hydroxypropyl cellulose is a cellulose derivative which, in concentrated solutions,
presents the typical optical properties of liquid crystals with a helical arrangement. Its
structure depends on the nature of the solvent, and also on concentration. Studies on
the formation of a band structure on the surface of i lms prepared from solutions of
hydroxypropyl cellulose in lyotropic phase under shear are important because of the
numerous physical interactions involved [87]. In addition, the optical and mechanical
properties of anisotropy on the surface of the polymer i lm and the possibility of their
use as alignment layers for liquid crystals [88] give them special importance for new
applications. Otherwise, hydroxypropyl cellulose was i rst a cellulose derivative capable
of spontaneously forming anisotropic solutions when dissolved in aqueous solutions
and in organic solvents, which provides a good example for understanding the phe-
nomenological aspects of liquid crystals. h us, the uncommon rheological character-
istics of hydroxypropyl cellulose liquid crystal solutions in water at room temperature
show that the liquid mesophase occurs at a gravimetric concentration of about 40%.
h e solutions present iridescent colors characteristic of the cholesteric liquid crys-
tal phase [89, 90]. Also, HPC may form many mesophases of isotropic, anisotropic,
