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Volumn 301, Issue 5637, 2003, Pages 1204-1211

Polarization-modulated smectic liquid crystal phases

Author keywords

[No Author keywords available]

Indexed keywords

FERROELECTRIC MATERIALS; LIGHT MODULATION; LIGHT POLARIZATION; MOLECULAR STRUCTURE; THERMODYNAMIC STABILITY;

EID: 0042823831     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1084956     Document Type: Article
Times cited : (290)

References (75)
  • 2
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    • D. R. Link et al., Science 278, 1924 (1997).
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    • D. M. Walba et al., Science 288, 2181 (2000).
    • (2000) Science , vol.288 , pp. 2181
    • Walba, D.M.1
  • 7
    • 0042706940 scopus 로고    scopus 로고
    • note
    • MHOBOW is a chiral molecule and is studied, unless explicitly indicated, as the racemate [(R)/(S)-MHOBOW], which behaves as if it were achiral.
  • 10
    • 0042706939 scopus 로고    scopus 로고
    • unpublished data
    • M. Nakata, unpublished data.
    • Nakata, M.1
  • 11
    • 0042205810 scopus 로고    scopus 로고
    • note
    • These materials exhibit the following B7 phase-transition temperatures (in °) upon cooling: MHOBOW [I 139 B7 90 B4], PBCOB [I 130 B7 80 X], H87 [I 160 B7 B2], CITRO [I 110 B7 85 X], and 10OAM5AMO10 [I 121 B7 99 X].
  • 12
  • 20
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    • H. S. Kitzerow, C. Bahr, Eds. (Springer-Verlag, New York)
    • P. P. Crooker, in Chirality in Liquid Crystals, H. S. Kitzerow, C. Bahr, Eds. (Springer-Verlag, New York, 2001).
    • (2001) Chirality in Liquid Crystals
    • Crooker, P.P.1
  • 30
    • 0041705300 scopus 로고
    • thesis, University of Colorado; Dissertation Abstracts no. 9620652
    • J. Pang, thesis, University of Colorado (1995); Dissertation Abstracts no. 9620652.
    • (1995)
    • Pang, J.1
  • 38
    • 0041705299 scopus 로고    scopus 로고
    • note
    • -1 full width at half maximum. Powder samples were in 1-mm-diameter glass capillaries in a temperature-controlled chamber. Sing[e-domain x-ray microbeam experiments were carried out on Microprobe Beamline BL-4A of the Photon Factory, Tsukuba, Japan, with 5-μm-thick LC samples contained between 80-μm-thick indium-tin oxide-coated glass plates. The microbeam x-ray experiment is detailed in (39).
  • 43
    • 0043208068 scopus 로고    scopus 로고
    • thesis, University of Colorado
    • D. Coleman, thesis, University of Colorado (2003).
    • (2003)
    • Coleman, D.1
  • 44
    • 0041705295 scopus 로고    scopus 로고
    • note
    • Note that in the Fourier transform of p(r) used to obtain the scattered intensity I(q), the displacement u(r) appears in the argument of an exponential and thus enters I(q) in a nonlinear way. Thus, with sinusoidal undulation, even though u(r) has only the single (fundamental) harmonic, multiple diffraction orders appear versus m for s = 1, 2.
  • 45
    • 0042706935 scopus 로고    scopus 로고
    • note
    • m ∼ 600 Å in MHOBOW). This effect was particularly noticeable in freely suspended film and freeze fracture experiments, where there is more exposure to air during observation and preparation, respectively.
  • 48
    • 0041705294 scopus 로고    scopus 로고
    • note
    • Several recent papers use evidence for polarization along the layer normal in B7 phases to argue that they are simply lamellar with triclinic local layer symmetry (9, 49). However, the phases in question are shown here to be undulated and polarization modulated so that the claim of triclinic behavior in a lamellar smectic may not be justified. In fact, a PM phase is triclinic essentially everywhere (wherever there is nonzero layer curvature). It may be that local triclinic symmetry actually drives the PM, but there is no evidence for this at present.
  • 50
    • 0042205807 scopus 로고    scopus 로고
    • note
    • m is larger in films than in bulk, but this may be due either to surface tension, which provides an additional elastic resistance to undulation, or due to the high surface-to-volume ratio of the films, which enhances hydrolysis and impurity buildup.
  • 54
    • 0043208069 scopus 로고    scopus 로고
    • note
    • The B7 materials strongly favor formation of freely suspended filaments (12, 16) rather than films, a consequence of their 2D lattice structure, but it was possible to obtain 1- to 10-layer-thick MHOBOW and 10OAM5AMO10 films at high T in the B7 phase by either pulling the film very slowly (∼20 μm/s) or by applying an ac field (∼5 V/mm) parallel to the film plane during the pulling. An initially thin spot will expand in area over a large fraction of the film after several hours.
  • 57
    • 0042205804 scopus 로고    scopus 로고
    • note
    • F and that the antiferroelectricity is that of the PM stripe pattern.
  • 59
    • 0042706934 scopus 로고    scopus 로고
    • note
    • Because the field-induced PM/UL-to-SmCP transition is an equilibrium energetic effect, the modulation should in principle return once the field is removed. However, it did not do so spontaneously in any of the experiments reported here or in (6). This is likely due to the fact that in order to reach the threshold field, the LC was only 1 to 5 μm thick, and because the layer structure shrinkage upon PM expulsion was locked in by the surfaces, an effect similar to the irreversible elimination of the chevron structure in SmCs by field application. The PM/UL-to-SmCP transition in CITRO could be reversed by waveform selection (square wave: PM/UL-to-SmCP; triangle wave: SmCP -to- PM/UL) (10).
  • 60
    • 0041705297 scopus 로고    scopus 로고
    • note
    • If p is the pitch of a helical winding of m(x) along a filament, then at radius ρ from the filament core we have α(ρ) = ρ(2π/p). Thus, if the pitch is independent of ρ, then the orientation of m also winds helically versus p at a given x and the PM lattice must have TGBs.
  • 63
    • 0041705296 scopus 로고    scopus 로고
    • note
    • th), about four orders of magnitude smaller than typical smectic layer compression moduli. Thus, the typical fluid smectic focal conic organization of layers is maintained.
  • 64
    • 0042205805 scopus 로고    scopus 로고
    • note
    • The winding of the 2D PM lattice on a filament of fixed cross-sectional layer structure is maintained topologically by the number of undulation periods around the filament. However, the PM lattice must have dislocations because of the curvature of the smectic layers (Fig. 7, B and C).
  • 66
    • 0041705293 scopus 로고    scopus 로고
    • note
    • The B1 lattice structure shown in Fig. 1H is one of many possibilities for alternation of polarization and tilt orientation, which also include PM in the absence of tilt. Thus, the homochiral, synpolar case (e.g., all stripe polarizations toward the reader and in magenta) would necessarity have an oblique 2D lattice, which has been found in some B1s, e.g., W1044.
  • 67
    • 0041705225 scopus 로고    scopus 로고
    • note
    • The polarization is sketched as uniform in the B1 phase in (53) and the B1rev phase in (69), but in fact must be splayed, e.g., as in Fig. 1H.
  • 69
    • 0043208067 scopus 로고    scopus 로고
    • note
    • W1044 has an oblique 2D reciprocal lattice characterized by strong [s, m] = [1, 1] and [1, -1] reflections, with complete absence of the s = 1, m even reflections, indicative of an interdigitated real lattice. The real lattice is as in Fig. 1H but oblique, possibly due to a uniform rather than alternating molecular tilt orientation (43).
  • 75
    • 0041705291 scopus 로고    scopus 로고
    • note
    • This work was supported by NSF grant DMR-0072989, NSF Materials Research Science and Engineering Centers grants 0213918 (University of Colorado) and 0080034 (University of California, Santa Barbara), and NASA grant NAG3-2457. Research was carried out in part at the National Synchrotron Light Source, supported by U.S. Department of Energy, Divisions of Materials and Chemical Sciences.


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.