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Volumn 301, Issue 5633, 2003, Pages 623-626

Surface-driven switching of liquid crystals using redox-active groups on electrodes

Author keywords

[No Author keywords available]

Indexed keywords

CRYSTAL ORIENTATION; DIELECTRIC PROPERTIES OF LIQUIDS; ELECTROCHEMICAL ELECTRODES; ELECTROOPTICAL DEVICES; MONOLAYERS; OXIDATION; REDOX REACTIONS; SURFACE REACTIONS;

EID: 0041766312     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1084527     Document Type: Article
Times cited : (130)

References (44)
  • 3
    • 0042988238 scopus 로고    scopus 로고
    • note
    • For a conventional 10-μm-thick optical cell with strong anchoring (parallel to surface) that is filled with the liquid crystal PEBAB, the onset of the electric field-induced transition in the orientation of the bulk liquid crystal [Freedericksz transition (36); Fig. 1A, 1] occurs at ∼3 V. The change in optical appearance is 90% complete at ∼6 V (38). The threshold voltage required for the onset of an electric field-induced change in the orientation of a liquid crystal can be reduced by use of hybrid aligned cells (39) or large pretilts (40) in the orientation of the liquid crystal. Saturation voltages in these systems are typically greater than a few volts. Hybrid aligned cells and pretilts can likely reduce further the switching voltages reported in this paper.
  • 4
    • 0042988241 scopus 로고    scopus 로고
    • note
    • Photoisomerization of surfaces decorated with azobenzene by using ultraviolet (UV) light can also lead to surface-driven orientational transitions in liquid crystals (41).
  • 10
    • 0042988237 scopus 로고    scopus 로고
    • note
    • Water-soluble ferrocene-based surfactants have been used to generate gradients in surface tension and control contact angles of isotropic aqueous solutions (42).
  • 14
    • 0041485552 scopus 로고    scopus 로고
    • note
    • We used BP because it is soluble in both 5CB and MBBA. The oxidation was initiated by heating the sample to ∼37°C. We used UV spectrophotometry and cyclic voltammetry to confirm oxidation of ferrocene to ferrocenium in the presence of BP.
  • 16
    • 0042988234 scopus 로고    scopus 로고
    • note
    • When BP was used to oxidize the ferrocene-terminated monolayer, the liquid crystal was deaerated to remove oxygen (43).
  • 18
    • 0041986618 scopus 로고    scopus 로고
    • note
    • The addition of 20 mM BP to 5CB and MBBA does not measurably change the birefringence of these liquid crystals and thus their interference colors (fig. S1).
  • 20
    • 0042988235 scopus 로고    scopus 로고
    • note
    • The anchoring of MBBA and MBBA with BP was indistinguishable when measured on a methylterminated monolayer.
  • 22
    • 0042487432 scopus 로고    scopus 로고
    • note
    • The addition of 20 to 35 mM TBAF to either 5CB or MBBA does measurably change the birefringence of these liquid crystals and thus their interference colors (figs. S2 and S3).
  • 24
    • 0042487431 scopus 로고    scopus 로고
    • note
    • We determined the orientation of 5CB in Fig. 3, D and E, by observing the interference colors of liquid crystals in optical cells prepared using surfaces that cause known orientations of the liquid crystal. The interference colors in Fig. 3, D and E, were also obtained by chemical oxidation (BP) of ferrocenyl monolayers with an optical cell identical to that shown in Fig. 3A (figs. S4 and S5).
  • 28
    • 0041485553 scopus 로고    scopus 로고
    • note
    • At potentials between 0 and 0.3 V, the luminosity increased with potential under crossed polars but decreased under parallel polars (Fig. 4, A and B), indicating the formation of a twisted distortion of liquid crystal within the optical cell.
  • 29
    • 0041986614 scopus 로고    scopus 로고
    • note
    • We measured the response time by analyzing frames of a video captured at a resolution of 1/30 of a second during a step change in potential from 0 to 0.2 V.
  • 30
    • 0041986615 scopus 로고    scopus 로고
    • note
    • When the sample was oriented at 45° with respect to one of the crossed polars, application of the overvoltage resulted in a change in color from green to pale yellow (Fig. 4C). This change in the interference color matches the change in color that was observed to accompany the out-of-plane transition of 5CB on the ferrocenium-terminated monolayers.
  • 44
    • 0041986613 scopus 로고    scopus 로고
    • note
    • Supported in part by the Biophotonics Partnership Initiative of the National Science Foundation (ECS-0086902), the Center for Nanostructured Interface (NSF 0079983), and the Army Research Office (DAAD19-02-1-0299).


* 이 정보는 Elsevier사의 SCOPUS DB에서 KISTI가 분석하여 추출한 것입니다.