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

Ana R. Brás, Olga García Ballesteros, Maria Teresa Viciosa Plaza, Sónia P. Martins, Roberto L. Sastre, Carlos Jorge Mariano Miranda Dias, João Luís Maia Figueirinhas, Maria Madalena Alves Campos de Sousa Dionísio Andrade

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

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 d-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 d-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.
Original languageEnglish
Pages (from-to)429-441
Number of pages13
JournalLiquid Crystals
Volume35
Issue number4
DOIs
Publication statusPublished - Apr 2008

Keywords

  • Electro-optical response
  • PDLC
  • Anchoring transition
  • Dielectric relaxation

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