Molecular Alignment of Bubble Domains in Cholesteric-Nematic Mixtures

Abstract

The emission spectrum of SiCl, produced in a tube discharge through a continuous flow of SiC1, vapour, has three systems of doublet bands degraded towards the further ultra-violet, the 0, o bands being at M 2942, 2924, M 2436, 2424, and M 2232, 2 2 2~. They are attributed to transitions B + X, C + X and D + X, where X is a double level with electronic separation 207'9 cm?, we= 531.0 and x,w,=2.2; B is a single level 34186.0 cm:l above X with wa =698*7; C is a close doublet 41234.8 and 41247.8 cm;l above X with U , = 674.2 and x,we = 2.2 ; and D is a single level 45005.9 cm;l above X, with w X = 663. These figures are from band-head measurements only. Datta's analysis of the-B + X system is confirmed, except in his identification of the 2,o and 3,o bands and his interpretation of observed isotope band-heads. With Datta's 2, o and 3, o bands are two groups of prominent bands between h 2830 and X 2770 not fitting into any of the three systems; their emitter may be a chloride of silicon other than SiC1. I. I N T R O D U C T I O NP A R T of the spectrum described in this paper was observed in 1913 in the glow produced by the interaction of SiCl, vapour and active nitrogen(').A The whole of it was observed in 1923 in the uncondensed induction-coil discharge in SiC1, vapour flowing continuously through a discharge tube('). Lowdispersion spectrograms of the discharge were taken with a small quartz-prism instrument (Hilger's E 6) and some of the stronger bands were also photographed in higher dispersion (about 7-5 A. /". ) with a 2-4-m. concave grating. The spectrum was seen to consist of two somewhat similar parts A and B, one on either side of the AlCl band-system that resulted from the use of aluminium electrodes. Each part consisted of bands degraded to the further ultra-violet, i.e. opposite in direction to the S i 0 bands, which were present if residual air had not been entirely displaced by the SiC1, vapour. Parts A and B were regarded as two related band-systems, each having progressions of bands with common separations of about 525 cm? and regular variations of intensity. A constant separation, amounting to about 205 cm? in A and 195 cm? in B, was also recognized, but this did not suffice for the make-up of the usual Deslandres' arrangement of the band-heads; it was, in fact, the interval between the heads of sub-bands such as had been observed in other doublet band-systems but were not understood. The observed numerical relations have now proved to be significant for the vibrational analysis, which was not apparent at that time.

Optically generated reconfigurable photonic structures of elastic quasiparticles in frustrated cholesteric liquid crystals

“…2) [14]. Such structures can spontaneously occur in CLCs confined into homeotropic cells, similar to the so-called cholesteric fingers and cholesteric bubbles [12,13,[27][28][29][30][31][32][33]. In the reconstructed director field configuration (Fig.…”

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes

“…11 The helical structure of cholesteric LCs (CLCs) does not readily accommodate many confinement geometries. When CLCs are confined in slit cells with the cell gap close to cholesteric pitch, bubble domain defects are often observed under thermal quenching, 12 external electric field, [13][14][15][16][17][18] or illuminations of focused laser beams. [19][20][21][22][23] By microscopically reconstructing the director fields, Smalyukh and coworkers showed that the bubble domain defects are made of either torons or baby Skyrmions (2D Skyrmions).…”

Two-dimensional skyrmions and other solitonic structures in confinement-frustrated chiral nematics

“…We have found that some of the studied laser-generated structures can also be obtained spontaneously when cooling the samples from the isotropic phase (although less reliably and without the control of spatial locations) and after applying low-frequency (10 Hz) electric fields to induce hydrodynamic instability. These localized structures, along with torons and hopfions, are several members of the large family of so-called cholesteric bubbles that were typically studied when occurring spontaneously, but not well understood in past experimental works [20,[34][35][36][37][38][39][40][41][42][43][44]. We note that the study of axially symmetric cholesteric configurations reported here is not exhaustive.…”

“…We note that the study of axially symmetric cholesteric configurations reported here is not exhaustive. In fact, several other configurations might have been already identified in prior literature [20,[23][24][25][26][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] that we have not explored so far using our 3D imaging experiments and different types of generation (laser realignment, low-frequency electric field, temperature quench with and without temperature gradients). In addition, in future work, studies of mutually linked multi-toron and multihopfion configurations that also belong to this family will be reported [51].…”