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  • 1
    Digitale Medien
    Digitale Medien
    Generation of high pretilt angle and surface anchoring strength in nematic liquid crystal on a rubbed polymer surface (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 3594-3597 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The generation of high pretilt angles in nematic liquid crystal (LC), 4-n-pentyl-4-cyanobiphenyl (5CB), on the rubbed surface of polyimide (PI) containing trifluoromethyl moieties, was investigated. High pretilt angles of 5CB are strongly related to the low surface energy caused more by the existence of trifluoromethyl moieties at low rubbing strength (RS). It is considered that the high pretilt angles of 5CB are most likely due to the van der Waals (VDW) dispersion interactions between the LC molecules and polymer surface having low surface energy. The medium and low pretilt angles at high RS may be caused by the combination of the VDW polymer surface with that of the dispersion and the steric interactions between the LC molecules and the asymmetric triangular structure formed by unidirectional rubbing. Finally, it was found that the polar anchoring strength A of 5CB strongly depended on the surface ordering of the rubbed PI surface containing trifluoromethyl moieties; with A decreasing proportionately with increasing RS. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371264
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  • 2
    Digitale Medien
    Digitale Medien
    Effect of working on the aligning capability of liquid crystals on the rubbed polymer surfaces (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4046-4048 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The washing effects on the liquid crystal (LC) alignment capability on the rubbed polyimide PI surface were investigated. The induced optical retardation from the nonwashing process on the rubbed PI surface is larger when compared with the washing processes; it is attributed to the removal of dust in the washing process. The generated pretilt angles in 4-n-pentyl-4′-cyanobiphenyl (5CB) from the nonwashing process on the rubbed PI surface are almost the same as that of the rubbed PI surface after washing process. The polar anchoring energy of the weakly rubbed PI surfaces is increased by the washing process; the washing effects are clearly observed. The surface order parameter SS of 5CB for all washing processes is larger than that with the nonwashing process; it is attributed to the washing process. Consequently, we suggest that the LC aligning capability is largely attributed to the washing effects. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371327
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  • 3
    Digitale Medien
    Digitale Medien
    Odd–even effects of the polar anchoring strength in nematic liquid crystal on rubbed polyimide Langmuir–Blodgett films with alkyl chain lengths (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1334-1336 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The odd–even effect of the alkyl chain length of rubbed polyimide Langmuir–Blodgett (LB) films on the extrapolation length of 5CB has been successfully evaluated by measuring polar anchoring strength. The extrapolation length of 5CB for rubbed PI-LB films with even numbers is small compared with odd numbers for alkyl chain lengths of greater than 7 carbons. The extrapolation length of 5CB on rubbed PI-LB films with odd numbers increases gradually as the temperature increases but tends to diverge near the clearing temperature ( Tc=35.3 °C). The extrapolation length diverges because of rapidly decreasing surface order near Tc. It is suggested that the polar anchoring strength on rubbed PI-LB films with an even number is strong because of relatively high surface ordering caused by more crystalline surfaces. Finally, it is concluded that the odd–even effects of the polar anchoring strength in NLCs are strongly related to the character of the polymer and observed clearly for long alkyl chain lengths. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113233
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  • 4
    Digitale Medien
    Digitale Medien
    Effect of high pretilt angle for anchoring strength in nematic liquid crystal on rubbed polyimide surface containing trifluoromethyl moieties (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1202-1204 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The effects of high pretilt angle are investigated on the polar anchoring energy of the nematic liquid crystal (NLC), 5CB, on rubbed polyimide (PI) films containing trifluoromethyl moieties. The pretilt angle of 5CB rapidly increases up to about 45° with the rubbing strength (RS). Also, the polar anchoring energy of 5CB initially increases with the RS for weak rubbing and then decreases. From these results, we determined the relationship between the pretilt angle and the anchoring energy on rubbed PI films. We suggest that the polar anchoring energy of 5CB with a high pretilt angle is very small because of the combination of the microsurface excluded volume effect and the van der Waals interaction between the LC molecules and the substrate surface on weakly rubbed PI films containing trifluoromethyl moeities. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113236
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  • 5
    Digitale Medien
    Digitale Medien
    Study of the pretilt angle for 5CB on rubbed polyimide films containing trifluoromethyl moiety and analysis of the surface atomic concentration of F/C(%) with an electron spectroscope for chemical analysis (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2392-2394 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the generation of the pretilt angles for nematic liquid crystal (5CB) aligned in the cells using rubbed polyimide (PI) films containing trifluoromethyl moieties as a function of rubbing strength (RS). In order to characterize the films, we have conducted an analysis of the surface atomic concentration of fluorine (F) relative to that of carbon (C), F/C(%) with an electron spectroscopy for chemical analysis (ESCA) in the shallow surface region at the depth of 3 and 12 nm. It is shown that the F/C ratio at a depth of 3 nm decreases with RS, and that the observed pretilt angle shows a high value approaching 45° in the weak RS region, and tends to decrease with increasing RS. The existence of the trifluoromethyl moiety in the special PI, and its appearance in the surface region are considered to be responsible for the generation of high pretilt angles at low RS region since a surface covered by fluorine atoms has a low surface energy and the van der Waals dispersion force is thought to be dominant and hence perpendicular LC alignment is expected. With increasing RS the surface concentration of fluorine atoms decreases and repeated triangles will be formed; a combination of the dispersion force and steric interaction between LC molecules and these structures may cause a medium or low pretilted LC conformation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.108174
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  • 6
    Digitale Medien
    Digitale Medien
    Generation of the pretilt angles in nematic liquid crystal (5CB) aligned on the rubbed polypyrrole films (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 1025-1026 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the pretilt angles generated in the nematic liquid crystal 5CB media, aligned on polypyrrole (PP) films through rubbing. It is shown that the PP films may be synthesized with two kinds of counter ionic atomic groups, i.e., rheonium oxide (ReO−4) which can generate about 5° pretilt angles and bromide (Br−) where no pretilt angle is observed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.106487
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