Orientation of Discotic Mesophases

Vauchier, C.; Zann, A.; Barny, P. Le; Dubois, Jean; Billard, J.

doi:10.1080/00268948108072663

Cited by 74 publications

(30 citation statements)

References 15 publications

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“…From an extensive work carried out on nematics and smectics [5][6][7], certain factors (the type of the orienting layer, the mechanical rubbing or its grooving) are known to control the surface alignment. The mechanisms for the surface-induced bulk alignment are based on a) the short-range surface-molecule and then molecule-molecule interactions [8] and b) the minimization of the long-range interactions between the surface and the bulk [9].The alignment techniques for discotic liquid crystals have so far included rotating magnetic field [10][11][12] and different surface treatments [13]. A strong rotating magnetic field (∼ 2 T) c EDP Sciences…”

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Observation of an anchoring transition in a discotic liquid crystal

1998

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PACS. 61.30Eb -Experimental determinations of smectic, nematic, cholesteric, and other structures. PACS. 61.30Gd -Orientational order of liquid crystals; electric and magnetic field effects on order. PACS. 64.70Md -Transitions in liquid crystals.Abstract. -We report the anchoring transition in a discotic liquid crystal, hexapentyloxytriphenylene (HPT), from edge-on to side-on alignment in a discotic phase. The topology, easy direction of orientation and the coating of the substrate with a polymer are the determining factors for the alignment and the anchoring transition in a discotic liquid crystal.Discotic liquid crystals are perfect examples of 2-dimensional self-organizing systems with a long-range order in the 3rd dimension. Finding reasons as to why and how such large molecules organize themselves interests physicists involved in exploring condensed matter [1]. Another reason for the continued interest in discotics lies in the potential applications of such systems. The type of orientation of the molecules inside a LC cell governs the characteristics of devices [1][2][3][4]. It has recently been shown [1,2] that the columnar phase structure of discotic liquid crystals is suitable for the fast transport of photogenerated charge carriers. These results demonstrate that molecular organization in discotics plays an essential role in improving the response time of organic photoconductors; the charge mobility of hexahexylthiotriphenylene (HHTT) [1] approximates to that of an organic crystal anthracene. Consequently, it is therefore of paramount importance that causes of the surface and the surface-induced bulk alignment in discotics be explored to advance their potential for use in devices. From an extensive work carried out on nematics and smectics [5][6][7], certain factors (the type of the orienting layer, the mechanical rubbing or its grooving) are known to control the surface alignment. The mechanisms for the surface-induced bulk alignment are based on a) the short-range surface-molecule and then molecule-molecule interactions [8] and b) the minimization of the long-range interactions between the surface and the bulk [9].The alignment techniques for discotic liquid crystals have so far included rotating magnetic field [10][11][12] and different surface treatments [13]. A strong rotating magnetic field (∼ 2 T) c EDP Sciences

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confidence: 99%

“…The alignment techniques for discotic liquid crystals have so far included rotating magnetic field [10][11][12] and different surface treatments [13]. A strong rotating magnetic field (∼ 2 T) c EDP Sciences…”

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confidence: 99%

Observation of an anchoring transition in a discotic liquid crystal

1998

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“…[23] has been observed. Contact preparations with aqueous D( -) mandelic or D( -) tartaric acid solutions, did not exhibit the fluid mesophase between 21 and 30°C.…”

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confidence: 84%

Optical microscopy and deuterium N.M.R. of non-ionic amphiphiles which exhibit thermotropic and aqueous lyotropic mesophases

Zimmermann¹,

Poupko²,

Luz³

et al. 1989

Liquid Crystals

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Tetrabenzocyclododecatetraene (I) substituted with eight methoxy-mono-, di-, and triethyleneoxide side chains exhibit the same highly ordered thermotropic mesophase, M . In the methoxydiethyleneoxide (I-2), and methoxytriethyleneoxide (1-3) derivatives this mesophase is also lyotropic and can sustain (at room temperature) up to 40 wt per cent water. The homologue (1-2) exhibits at higher water content another lyomesophase, MF, which is more fluid and nematic-like. Optical microscopy, differential scanning calorimetry and deuterium N.M.R. of both labelled (1-2) and water as well as of the water I7O were used to construct the (1-2)-water phase diagram and to characterize the various mesophases. It is found that both M and Mt. are uniaxial with negative birefringence and negative anisotropic magnetic susceptibility. The MF phase readily aligns in a magnetic field and is characterized by fast (-lo7 s-' ) reorientation of the mesogen molecules about the director. The M phase is apparently columnar, highly ordered and is not readily aligned by a magnetic field. The rate of molecular reorientation in this mesophase is much slower (-lo3 s -' ) compared with M F .

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“…Highly oriented fibres of copper laurate obtained by meltspinning of its columnar mesophase Anne-Marie Giroud-Godquin(1), Pascale Maldivi(1), Jean-Claude Marchon(1), Pierre Aldebert(2), Alain Péguy(3), Daniel Guillon (4,5) and Antoine Skoulios (4,5) (1)Laboratoires de [3]. Several alignment techniques including use of a magnetic field [4], various surface treatments [5], slow flow through a capillary [6], or stretching of the mesophase [7] have resulted in limited degrees of alignment.…”

Section: Short Communicationmentioning

confidence: 99%

“…Several alignment techniques including use of a magnetic field [4], various surface treatments [5], slow flow through a capillary [6], or stretching of the mesophase [7] have resulted in limited degrees of alignment. A process employing a mechanically operated pin which draws a strand from a reservoir cup of the mesogen at a desired temperature in the columnar phase has recently been shown to give highly oriented fibres [8].…”

Section: Short Communicationmentioning

confidence: 99%