The investigation of the nuclear spin-lattice relaxation in the crystalline phases of mesogenic substances i s of interest for the elucidation of their molecular dynamics and for finding relations between the stability of solid phases and the occurrence of various mesophases.
Sektion Ph ysik der I ( a r l -l r~a r~-U n i v c r i~t LeipzigInlial t s u b e r s i c h t . Es werclen 1SrgeLiiissc einer vergleichendcn Nessung der Teinperatur-, Frequenz-und Winkelabhiingiglreit der S1)in-Qitter-Relnsationszciteii im Zeeman-nnd Dipolsystem, T, uncl TI,, an langkettigen Homologen drs mcistuntersuchten Fliissigkristalls P.44 vorgeutellt.Diskutiert wird insbesondere die Temperaturebhangigkcit dieser Zeitkonstanten in der nematischen im Veqleich ziir smektischen Phme.10 Ann. Physili. 7. I:ol~n, Ild. 33
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Recently the solid state of some p-alkoxybenzylidene-p-n-alkylanilines O-!&CH=N-Q)-C H has been studied by various.methods /1 to 5/ to 'mH2rn+1 n 2n+l find connections between the molecular dynamics in the crystalline phase and the liquid crystal properties of this homologous series. As yet the main interest has focused on the well-known nematogenes MBBA (m = 1, n = 4) and EBBA ( m = 2 , n = 4) where different solid modifications have been found /1, 6/ (cf. references i n / 3 / , too). Dielectric /1, 4 , 71 and NMR investigations /3, 8/ indicate differences in the internal mobility of the molecules for these phases.We recently reported T measurements in the series /8/ and present the cor- We observe three characteristically different types of T temperature dependence 1D ("a", "b", and "c") for different members of the series.In dependence on distinct cooling or heating procedures (cf. /1, 6, 7/) some of the substances (for instance MBBA , EBBA, and 40-4) reveal either one or another behaviour . 1) Fig. 1 shows a very characteristic type 'tarr behaviour, Fig. 2 represents a type "b" temperature dependence, and Fig. 3 an example for type "c" behaviour. (Type "aff was also found in 70-4, type "b" in metastable /1/ MBBA, 50-6, and EBBA under 1) Note that due t o very slow transitions between different solid phases "mixtures" of the three types may be observed, too.
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