Summary
The absolute determination of the three Frank elastic constants of nematic liquid crystals (MBBA) has been performed by light scattering differential-cross-section measurements. The use of an optimized oblique-incidence geometry allows us to reduce several causes of error, like multiple scattering and spurious scattering due to crystal defects. All the three elastic constants have been obtained on the same specimen homeotropically aligned without changing the alignment of the director, thus reducing boundary distortion effects. It will be shown that the new technique has several advantages with respect to previously used ones. A full description of the experimental arrangement and a discussion of the obtained results is given in the text.
Riassunto
Sono stati determinati i valori assoluti delle costanti elastiche di Frank del cristallo liquido nematico MBBA, mediante misure della sezione d’urto differenziale della luce diffusa. L’uso di una geometria ottimizzata ad incidenza obliqua permette di ridurre parecchie cause di errore, come la diffusione multipla e la diffusione spuria dovuta ai difetti del cristallo. Tutte e tre le costanti sono state determinate usando sempre lo stesso campione allineato omeotropicamente senza variare l’allineamento del direttore, riducendo di conseguenza gli effetti di distorsione ai bordi. Nel testo si descrive il dispositivo sperimentale e si analizzano i risultati ottenuti, facendo vedere come tale nuova tecnica presenti parecchi vantaggi rispetto a quelle precedentemente usate.
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Miraldi, E., Trossi, L., Valabrega, P.T. et al. Absolute measurements of the elastic constants of nematic liquid crystals by light scattering. Nuovo Cimento B 66, 179–186 (1981). https://doi.org/10.1007/BF02721185
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DOI: https://doi.org/10.1007/BF02721185