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Balachandran R, Panov VP, Vij JK, Shanker G, Tschierske C, Merkel K, Kocot A. Dielectric and electro-optic studies of a bimesogenic liquid crystal composed of bent-core and calamitic units. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:032506. [PMID: 25314464 DOI: 10.1103/physreve.90.032506] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Indexed: 06/04/2023]
Abstract
A bimesogen, BR1, composed of a bent-core and calamitic unit, linked laterally via a flexible spacer is investigated by dielectric and electro-optic techniques. X-ray results show the presence of clusters in the nematic phase, and the cluster size is of the order of the thickness of a single layer. The splitting of the small-angle scattering Δχ/2 is about 50°, which indicates SmC like clusters with a significant tilt of the molecules in the quasilayers. The sign reversal of the dielectric anisotropy Δε' is observed as a function of frequency; the behavior is rather similar to that exhibited by the conventional dual frequency nematics, composed of a calamitic mesogen, with the exception that it occurs at much lower frequencies in this material. Interestingly, as the bimesogen enters its nematic phase, the average permittivity decreases as the temperature is lowered. This indicates the onset of antiparallel association of some of the dipoles in the system, and this type of association is much more prominent in BR1 in comparison to other bent-core liquid crystalline systems composed of the same bisbenzoate core unit. The analysis of the dielectric spectra using the Maier-Meier model confirms the onset of an antiparallel correlation of dipoles occurring at the isotropic to nematic phase transition temperature. Additionally these results support a model of the cluster where the transverse dipole moments in the neighboring layers are antiparalleled to each other.
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Affiliation(s)
- R Balachandran
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland and School of Physics and Astronomy, University of Manchester, M13 9PL Manchester, United Kingdom
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - G Shanker
- Institute of Chemistry, Organic Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Strasse 2, 06120 Halle, Germany and BMS R&D Centre, BMS College of Engineering, Bull Temple Road, Bangalore-560019, India
| | - C Tschierske
- Institute of Chemistry, Organic Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes-Strasse 2, 06120 Halle, Germany
| | - K Merkel
- Central Mining Institute, Katowice, Poland
| | - A Kocot
- Institute of Physics, Silesian University, Katowice, Poland
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Lehmann M. Star-Shaped Mesogens – Hekates: The Most Basic Star Structure with Three Branches. Top Curr Chem (Cham) 2011; 318:193-223. [DOI: 10.1007/128_2011_266] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
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Mamlouk-Chaouachi H, Heinrich B, Bourgogne C, Guillon D, Donnio B, Felder-Flesch D. Nematic self-organization of regioselectively polyfunctionalized [60]fullerene. ACTA ACUST UNITED AC 2011. [DOI: 10.1039/c1jm10982k] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Bonacucina G, Cespi M, Misici-Falzi M, Palmieri GF. Colloidal soft matter as drug delivery system. J Pharm Sci 2009; 98:1-42. [DOI: 10.1002/jps.21423] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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Newkome GR, Shreiner CD. Poly(amidoamine), polypropylenimine, and related dendrimers and dendrons possessing different 1→2 branching motifs: An overview of the divergent procedures. POLYMER 2008. [DOI: 10.1016/j.polymer.2007.10.021] [Citation(s) in RCA: 313] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Mamlouk H, Heinrich B, Bourgogne C, Donnio B, Guillon D, Felder-Flesch D. A nematic [60]fullerene supermolecule: when polyaddition leads to supramolecular self-organization at room temperature. ACTA ACUST UNITED AC 2007. [DOI: 10.1039/b700460e] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Merkel K, Kocot A, Vij JK, Mehl GH, Meyer T. Orientational order and dynamics of the dendritic liquid crystal organo-siloxane tetrapodes determined using dielectric spectroscopy. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:051702. [PMID: 16802949 DOI: 10.1103/physreve.73.051702] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Revised: 12/08/2005] [Indexed: 05/10/2023]
Abstract
The dielectric measurements have been carried out on the two zeroth generation dendrimers with four branched arms (called tetrapodes) based on the siloxane cores. The results are analyzed in the framework of the molecular theory of dielectric permittivity by Maier and Meier for nematogens. At least four molecular processes are resolved in the dielectric relaxation spectra in the nematic phase for each of the two tetrapodes. Three of them are assigned to the reorientation of the monomeric unit whereas the fourth is assigned to the rotation of the molecular segments in the individual arms of the monomeric unit around the long molecular axis. The dielectric relaxation strength of the low frequency process has been used to calculate the orientational order parameter. The dynamics of the resolved processes has been quantitatively analyzed using the results of the microscopic model of the rotational diffusion, given by Coffey and Kalmykov [W. T. Coffey and Yu. P. Kalmykov, Adv. Chem. Phys. 113, 487 (2000)] using the calculated order parameter. All molecular processes: the rotation around the short molecular axis (end-over-end rotation), precession around the director and the rotation around the long molecular axis (also called the spinning motion) are shown to have successfully been reproduced by the model. The anisotropy of the rotational diffusion coefficients gradually increases with a reduction in temperature, to a factor of 3 in the nematic phase relative to its isotropic phase.
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Affiliation(s)
- K Merkel
- Laboratory of Advanced Materials, Department of Electronic Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
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Chen Y, Shen Z, Gehringer L, Frey H, Stiriba SE. Supramolecular Thermotropic Liquid Crystalline Materials with Nematic Mesophase Based on Methylated Hyperbranched Polyethylenimine and Mesogenic Carboxylic Acid. Macromol Rapid Commun 2006. [DOI: 10.1002/marc.200500628] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Donnio B, Guillon D. Liquid Crystalline Dendrimers and Polypedes. SUPRAMOLECULAR POLYMERS POLYMERIC BETAINS OLIGOMERS 2006. [DOI: 10.1007/12_079] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Merkel K, Kocot A, Vij JK, Mehl GH, Meyer T. The orientational order parameters of a dendritic liquid crystal organo-siloxane tetrapode oligomer, determined using polarized infrared spectroscopy. J Chem Phys 2004; 121:5012-21. [PMID: 15332938 DOI: 10.1063/1.1769355] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The observed macroscopic anisotropic properties such as the components of infrared (IR) absorbances of liquid crystals are expressed in terms of the order parameters of the long molecular axis, molecular, and phase biaxiality. The order parameters of the organo-siloxane tetrapode liquid crystal of zero dendritic order (G0) in its nematic and smectic phases have been determined using results of the polarized IR spectroscopic measurements on a planar homogenously and hometropic aligned cells. The spatial components of the absorbances for the vibrational bands (in the mesogenic unit, terminal chains, and spacer) have been measured and analyzed. For the laboratory reference system, the apparent orientational order parameter S of the mesogen unit shows a significant drop in the transition from the nematic to the smectic phase while the phase biaxiality order parameter P increases to almost 0.4 in the smectic phase. This result shows that the director is tilted out of the sample plane in the smectic phase. The molecular biaxiality parameter D is found to be positive both for the nematic and smectic phases. This suggests that the carbonyl dipoles are oriented close to the tilt plane. For the vibrational bands in the chains, low values of S and D indicative of their low orientational order are obtained. As a result of the interaction among the molecules in the tilted smectic phases, the transition dipoles show positive correlations for the transversal and negative for the longitudinal dipoles.
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Affiliation(s)
- K Merkel
- Laboratory of Advanced Materials, Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
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