Civil Engineering Reference
In-Depth Information
A history of these polymer blends concerning their thermodynamic and phase behav-
ior is presented by Dutta
et al
. [124]. Following are presented references from his work
[9-25] :
•
Flory
et al
. considered only the shape anisotropy of the rod-like mol-
ecules, they derived expressions for the phase equilibrium in mixtures of
low molar mass mesogens with rod-like polymers, semi-rigid polymers,
and l exible coil polymers;
•
Brochard extended Flory's theory to networks made of l exible chains,
swollen in a nematogenic solvent;
•
Ballauf extended the lattice theory of mixtures for blends of nematic liq-
uid crystals and l exible polymers to include the ef ect of isotropic inter-
actions between the components;
•
George
et al
. constructed phase diagrams for blends of linear ther-
motropic liquid crystalline polyesters with liquid crystals of similar
structure;
•
Ringsdorf
et al
. studied the miscibility of mixtures of low and high molar
mass nematic liquid crystals, as dependent on the chemical structure of
the component mesogens. Mixtures with unlike structures phase sepa-
rated in the nematic state, while miscibility occurred when the meso-
genic side group of the polymer was similar to the liquid crystals;
•
Achard
et al
. observed a biphasic region for mixtures of low molar mass
nematic solvents and some liquid crystalline polymers;
•
Sigaud
et al.
studied the ef ect of chemical structure of liquid crystals on
their miscibility with side chain liquid crystalline polymers;
•
Dubault
et al
. studied the phase diagrams of l exible polymers in low
molar mass nematic solvents, evidencing a biphasic region—isotro-
pic and nematic phases—which increased as the polymer molar mass
increased;
•
Lipatov
et al
. used a cobalt gun to irradiate phase-separated mixtures
of cholesteric liquid crystal microdomains dispersed in a polyurethane
matrix, etc.
In this context, some works investigated a series of blends obtained from hydroxy-
propyl cellulose in lyotropic phase, and a new partial aliphatic polyimide (PI) or its
poly(amic acid) precursor (PAA) [104]. h e l ow behavior of their mixed solutions in
N,N-dimethylacetamide shows the ef ect of composition, temperature and shear rate
on the orientation or mobility of the chain segments in the shear i eld. Specii c interac-
tions, such as the hydrogen bonds between PAA and the liquid crystalline component,
stabilized the resulted morphology. h e band texture, typical for lyotropic HPC solu-
tions, evidencing dif erent intensities and dimensions is observed from atomic force
microscopy images in PAA/HPC and PI/HPC blends (Figure 14.7) [104].
In another study, the liquid crystalline order in cellulose derivative solutions
observed in rheological investigations is preserved in solid i lms by slow evaporation of
the solvent and is evidenced in optical microscopy images [125]. h us, Figures 14.8 a, b,
and c of cellulose acetate phthalate (CAP) and hydroxypropyl cellulose i lms, show the
