Thermotropic and Lyotropic Diacrylate Mixtures for the Fabrication of Cholesteric Pigments


Here a film of a cholesteric network is shown and the angular dependence of the reflected wavelength is evident. It was obtained by UV-photocrosslinking of a thermotropic mixture containing a cholesteric dopant and a nematic LC. The insert shows a SEM micrograph of the corresponding pigment particles ready for use in paint formulations.

 

Project description:                                

Cholesteric materials show selective reflection and an angular dependence of light which results in brilliant colors and a color effect called ‘color flop’ (picture left). Such systems can be produced by mixing nematic material with chiral dopants. However, the dilution of the mesogen with dopant and reactive solvent results in a less broad liquid crystalline temperature range. To solve this problem the synthesis of new nematic compounds with long, extended mesogenic units was realized. For applications such as cholesteric effect pigments, the cholesteric mesophase is permanently crosslinked by photopolymerization. From the binary (thermotropic) and ternary (lyotropic) cholesteric mixtures, films were fabricated by photocrosslinking. In this continuous process the mixture was spread into a thin film, photocrosslinked, and removed from the revolving stainless steel belt serving as substrate. To obtain pigment particles the films were subsequently ground in an air impact pulverizer (see insert left).

Equipment used in this project:                                                                                          

  • UV-Curing Fusion Systems F300/LC6 Conveyor Belt

  • Rheology, SEM Facilities

    • Publications and Patents:                                                                                                   

    G. Schmitt, R. Giesa, and H.-W. Schmidt, Chem. Phys. Chem. 4, 505-508 (2003)
    Cholesteric networks based on lyotropic mixtures

    G. Schmitt, R. Giesa, and H.-W. Schmidt, Liquid Crystals, 28, 1611-21 (2001)
    New liquid crystalline di- and tetra-acrylates for network formation

    Flüssigkristalline Stoffgemenge
    F. Prechtl, S. Haremza, F. Meyer, R. Parker, K. Kürschner, H.-W. Schmidt, G. Schmitt, R. Giesa; BASF AG,
    Patentanmeldung DE 100 257 82.2 (2001)

    Process for producing pigment particles
    Inventors: Schuhmacher, Peter; Faust, Tillmann; Siemensmeyer, Karl; Ostertag, Werner; Schmidt, Hans-Werner; Giesa, Reiner
    BASF A.-G., Germany, WO 09727251 (1997)

    Complete publication list
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