Phase Separation and Morphology of PDLC Based on Poly(Ethyl 2-Cyanoacrylate)

The paper deals with polymer/liquid crystal composites prepared by polymerization induced phase separation of homogeneous mixtures of ethyl a-cyanoacrylate (ECA) and nematic E7. DSC analysis of the polymerization reaction indicates that the monomer conversion is unaffected by the presence of E7 which acts only as a diluent. Thermal characterization of the composite films PECA/E7 reveals a partial solubility of E7 in the polymer matrix (about 20%), a degradation of the LC purity, an anomalous variation of the specific heat increment of E7 at Tg and of the isotropization enthalpy with the E7 content in phase separated systems. SEM analysis offers adequate support to justify the DSC behavior; indeed, whereas the 20% E7 mixture has a fracture surface similar to that of the unblended matrix, the 40% E7 composite shows a LC separated droplet morphology with a low connection grade. The morphology changes considerably upon increasing the E7 concentration in the blend or lowering the curing temperature; heterogeneous LC-droplet and polymer-ball morphologies appear, arising from differences in the rate of polymerization of ECA between two early separated phases: a LC-poor one, rich in ECA/PECA and a LC-rich phase, still containing substantial amount of monomer.