Miselli kiral nematik sıvı kristal fazlarda heliks adım uzunluğunun sıcaklığa bağımlılığının incelenmesi

ABSTRACT INVESTIGATION OF THE TEMPERATURE DEPENDENCE OF THE PITCH IN MICELLAR CHIRAL NEMATIC LIQUID CRYSTAL PHASES Karaman, Elif Bema MSc, Department of Chemistry Supervisor: Prof. Dr. Mahmut ACIMIŞ July 2004, 83 pages It is proposed that the micellar nematic or micellar chiral nematic liquid crystalline state owes its existence to intra- and inter-micellar interactions. For clarity, the intramicellar interactions are separated qualitatively into "hydrophobic effect" that dominates the interior of the micelle and "external effect" that describes repulsion and hydration of the head groups at the micelle interface. The intermicellar interactions are directed in space (spatial) and are of Coulombic nature, thus they describe the interactions between the micelles in three dimensions. inRemaining in the nematic range, the intra- and inter-micellar interactions can be minimized or maximized by adjusting the concentration of water. Nematic or chiral nematic liquid crystals with high water concentration have a low nematic-isotropic phase transition temperature (TNi), and thus a minimum intermicellar interactions, and vice versa. The question is whether the phase chirality, i.e. the pitch of chiral nematic phases, can be expressed in terms of the intra- and inter-micellar interactions. For this purpose a series of chiral nematic phases of the amphiphile, (DAC1), with positively charged head group (e.g. DAC1/MA, DAC1/HHMA, DAC1/APFDE), chiral nematic phases of the amphiphile, NaDDS, with negatively charged head group (e.g. NaDDS/CEEC, NaDDS/ADDE, NaDDS/ADDE/MA, NaDDS/ADDE /HHMA), chiral nematic phases with serine and alanine head groups (SDE, SDDE, ADDE), and finally esters of alanine and serine with perfluorinated carbon chains have been investigated. The pitch length of the chiral nematic phases of the DAC1, SDE, SDDE and ADDE amphiphiles with low T^.^s did not change with temperature, but the pitch length of those phases with high T^s decreased with increased temperature, indicating that the intermicellar forces are dominant in these systems. However, the pitch of NaDDS phases with low and high T^.^s is lengthened with increased temperature. This was interpreted in terms of weakening of intramicellar forces so that the chiral guest can not convey its chiral potential to the micelle, and as a result the pitch is lengthened. The phases of serine and alanine esters with perfluorinated carbon chains exhibited very short pitches indicating that the hydrophobicity has a significant effect on the pitch length. The pitch of these systems also gets short with ivincreased temperature, implying again the importance of intermicellar interactions in these systems. In short, our results offer clear evidences that the pitch of a micellar chiral nematic phase is a function of intra- or inter-micellar interactions and hydrophobicity. Keywords: Intra- and inter-micellar interactions, pitch length, temperature dependence, chiral nematic phases with perfluorinated carbon chains, chiral nematic phases