| Summary: | 碩士 === 淡江大學 === 化學學系 === 82 === Hydrogn-bonded dimers of trans-4-alkoxy-4''-stilbazole
homologues(CnOSP,proton acceptors)and (1)3-alkoxybenzoic acid
homologues(3-CmObA,proton donor),(2)1,3,5-trihydroxy- benzene(3
OH,proton donor)exhibited mesophases. Hydrogen bonds were
confirmed by IR sepectroscopy. The enthalpies of phase
transsitions and texture of mesophases were studied by
Differential Scanning Calorimetry and Polarizing Optical
Microscopy, espectively. For the mixtures with 3-CmOBA as
proton donor(mole ratio1:1),enantiotropic SmA and SmC phase
were observed, and monotropic SmX phase (two-brush Schlieren
textures) was observe upon cooling the SmC phase when the
alkoxy chain consisted of even carbon numbers. The values of
transition enthalpy of SmA-SmC were smaller than 0.06KJ/mole
and those of SmC-SmX were smaller than 0.006KJ/mole. It was
suggested that the SmX could be the antiferrorlrctric phase on
the bases of optical textures and the transition enthapy. The
SmC-SmX transitions were attributed to be driven by the change
of straight-bend conformation of the hydrogen bonded complexes.
For the mixtures of 3OH and CnOSP with mole ratio 1:3 (3OH :
CnOSP),enantiotropic nematic phase were observed for n<=7, N-
SmA-reentrant N (Nr) were observed for n=8,and SmA and SmC were
observed for n=9,10,12. N-SmA-Nr transitions were alse observed
for mixture with C7OSP fraction less than 73%. The values of
transition enthalpy of N-SmA and SmA-Nr were smaller than
0.04KJ/mole. The occurrence of Nr phase was attributed to the
dimerization of the hydrogen bonded complexes.
|
|---|
