Chemistry Reference
In-Depth Information
Noel
et al.
, 1978; Fayolle
et al.
, 1979; Ringsdorf
et al.
, 1982; Finkelmann
et al.
, 1982; Benthack-Thoms and Finkelmann, 1985; Sigaud
et al.
, 1987).
The Kofler's contact method (Kofler and Kofler, 1954) was used in the
studies so that the phase diagram was composed in a relatively short time.
Thus, at temperatures of its isotropic phase a small amount of the poly-
mer is put between a glass slide and a cover slip. The model compound is
then introduced by capillary action such that the polymer and the model
compound are in contact. The preparation contains the complete possible
concentration range which begins at the model compound and ends with
the polymer. By changing the temperature one can determine the temper-
ature of each transition which occurs in the contact zone between the two
pure substances. The contact method is limited because the gradient in con-
centration in the contact zone is unknown. Consequently the preparations
of well-defined compositions are also examined to complete the phase dia-
gram and fix the concentration position of the transitions. As one example,
the phase diagram of terephthal-bis(4-n-butylaniline) and the polymer pre-
pared from di-n-propyl-p-terphenyl-4,4
-carboxylate and an aliphatic diol
was obtained by Fayolle
et al.
(1979) to confirm the smectic C phase of the
polymer.
Nevertheless, the rule of selective miscibility must be applied with
caution. The highly viscous nature of polymeric mesophases could possi-
bly prevent the mixing of the mesophase of polymers and certain model
compounds. Therefore, while the miscibility of model compounds with a
polymer may be used to identify the type of mesophase, the lack of com-
patibility does not necessarily suggest that the mesophases are not the same.
Some model compounds and polymers with the same mesophase may even
be inherently incompatible. As a result, some judgment is required in order
to make both the proper choice of the model compound and the correct
assignment of the mesophase when using this technique.
4.4.2.
Infrared dichroism
The detailed information about molecular orientation in oriented film spec-
imens can be obtained from IR dichroism measurements (Hu
et al.
, 1985;
Wu
et al.
, 1986). Light is absorbed when the direction of oscillation of its
electrical vector has a component along the direction of oscillation of the
absorbing group. The intensity of the absorption band of an oriented poly-
mer thus depends on the direction of the electrical vector of the incident ray
