Dielectric relaxation studies and electro-optical measurements in poly(triethylene glycol dimethacrylate)/nematic E7 composites exhibiting an anchoring breaking transition

• Published in: Liquid crystals 2008-04, Vol.35 (4), p.429-441
• Main Authors: Brás, A. R. E., García, O., Viciosa, M. T., Martins, S., Sastre, R., Dias, C. J., Figueirinhas, J. L., Dionísio, M.
• Format: Article
• Language: English
• Subjects: anchoring transition; dielectric relaxation; electro-optical response; PDLC
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678290801932850

Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was monitored through dielectric loss. Essential changes are felt mainly in the δ-peak, i.e. the dielectric response of the nematic when the director lies parallel to the applied electric field. An irreversible effect persists after the field had exceeded a critical value, which was manifest in a higher transmittance and a higher dielectric strength of the δ-peak in the OFF state. The initial scattering/opaque state of the sample can only be recovered by heating to the clearing temperature of the nematic LC. The effect referred, commonly called memory effect, is rationalized in terms of anchoring breakage of the LC at the polymer-LC interfaces. The electro-optical response was tested for different poly(triethylene glycol dimethacrylate)/nematic E7 composites in different composition ratios prepared by polymerisation-induced phase separation. The lowest threshold field was observed for the 30:70 composite.