Adv Polym Sci (2013) 262: 109–122
DOI: 10.1007/12_2013_269
© Springer-Verlag Berlin Heidelberg 2013
Published online: 6 November 2013
Nematic Conformation of Chain Molecules
Predominating in the Ordered Mesophase
Akihiro Abe
Abstract The physical picture of the nematic conformation has been discussed
on the basis of the rotational isomeric state analysis for segmented liquid-crystal
(LC)-forming molecules, comprising mesogenic units on both sides of a flexible
spacer. The disorientation angles (θ) of the two terminal mesogenic units are calculated for given spatial configurations of the spacer. The observed odd-even character
of the thermodynamic quantities at the nematic (N)–isotropic (I) phase transition
T NI ¼ ΔH NI /ΔS NI has been interpreted in terms of the profiles of the calculated
distribution curves P(θ) À θ. Combined use of rotational isomeric state and
2
H NMR techniques has led to an estimate of the conformer fraction in the nematic
state. The transition entropies derived on this basis are favorably compared with the
constant–volume transition entropies obtained from the pressure–volume–temperature measurement. The observed V–T relation indicates that the expansivity of
the nematic LC phase is higher relative to that of the isotropic melt. It has been
pointed out that the nematic conformation might possibly gain extra stability from the
free volume effect in the LC state. These considerations offer an explanation why
amazingly long flexible chain segments can be accommodated in the nematic fluid.
Keywords Conformation of the spacer • Constant-volume transition entropy •
Nematic conformation • Odd-even effect • RIS/
2
H NMR analysis • Segmented LC
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
2 Dependence of Thermodynamic Properties on Degree of Polymerization . . . . . . . . . . . . . . . 111
3 Influence of Bond Angle Restrictions and Rotational Characteristics on the Odd-Even
Effect of Thermodynamic Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A. Abe (*)
Tokyo Institute of Technology, 6-27-12 Hiyoshi-Honcho, Kohoku-ku, Yokohama 223-0062,
Japan
e-mail: aabe34@xc4.so-net.ne.jp
DOI: 10.1007/12_2013_269
© Springer-Verlag Berlin Heidelberg 2013
Published online: 6 November 2013
Nematic Conformation of Chain Molecules
Predominating in the Ordered Mesophase
Akihiro Abe
Abstract The physical picture of the nematic conformation has been discussed
on the basis of the rotational isomeric state analysis for segmented liquid-crystal
(LC)-forming molecules, comprising mesogenic units on both sides of a flexible
spacer. The disorientation angles (θ) of the two terminal mesogenic units are calculated for given spatial configurations of the spacer. The observed odd-even character
of the thermodynamic quantities at the nematic (N)–isotropic (I) phase transition
T NI ¼ ΔH NI /ΔS NI has been interpreted in terms of the profiles of the calculated
distribution curves P(θ) À θ. Combined use of rotational isomeric state and
2
H NMR techniques has led to an estimate of the conformer fraction in the nematic
state. The transition entropies derived on this basis are favorably compared with the
constant–volume transition entropies obtained from the pressure–volume–temperature measurement. The observed V–T relation indicates that the expansivity of
the nematic LC phase is higher relative to that of the isotropic melt. It has been
pointed out that the nematic conformation might possibly gain extra stability from the
free volume effect in the LC state. These considerations offer an explanation why
amazingly long flexible chain segments can be accommodated in the nematic fluid.
Keywords Conformation of the spacer • Constant-volume transition entropy •
Nematic conformation • Odd-even effect • RIS/
2
H NMR analysis • Segmented LC
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
2 Dependence of Thermodynamic Properties on Degree of Polymerization . . . . . . . . . . . . . . . 111
3 Influence of Bond Angle Restrictions and Rotational Characteristics on the Odd-Even
Effect of Thermodynamic Quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A. Abe (*)
Tokyo Institute of Technology, 6-27-12 Hiyoshi-Honcho, Kohoku-ku, Yokohama 223-0062,
Japan
e-mail: aabe34@xc4.so-net.ne.jp