Determination of the symmetric invariant (σ2) of the order parameter near the biaxial nematic negative-positive transition point in lyotropic material

Autor(es)

dos Santos, Oscar Rodrigues ; Braga, Wladimir Sergio ; Simoes, Manuel ; Palangana, Antonio Jose

• Tipo de documento: Artigo Científico
• Fonte: PHASE TRANSITIONS; v. 97, n. 11-12, p. 8-pg., 2024-12-01.

Resumo

This paper explores the phase transitions between calamitic nematic ($N_{C}$NC), biaxial nematic ($N_{B}$NB) and discotic nematic ($N_{D}$ND) phases in a mixture containing potassium laurate (${\rm KL}$KL), decanol (${\rm DeOH}\rpar \comma\;$DeOH), potassium sulphate $\lpar {\rm K}_{2}{\rm SO}_{4}\rpar$(K2SO4) and water $\lpar {\rm H}_{2}{\rm O}\rpar$(H2O). These transitions are studied using refractive indices and conoscopic images. The $N_{C}$NC phase is uniaxial negative, while the $N_{D}$ND phase is uniaxial positive, as expected. The biaxial nematic phases, both negative ($N_{B}<^>{-}$NB- negative) and positive ($N_{B}<^>+$NB+ positive), are observed within the biaxial range and confirmed by conoscopic images. Temperature dependence of the symmetric invariant ($\sigma _{2}\rpar$sigma 2) of the order parameter is obtained from refractive index data in the biaxial nematic range. A transition from an $N_{B}<^>{-}$NB- to an $N_{B}<^>+$NB+ configuration is determined at this point where the corresponding $\sigma _{2}$sigma 2 reaches the maximum value. In this context, the micelle loses its predominant calamitic shape to acquire a predominant discotic shape. (AU)

• Processo FAPESP: 14/50983-3 - INCT 2014: fluidos complexos
• Beneficiário: Antonio Martins Figueiredo Neto
• Modalidade de apoio: Auxílio à Pesquisa - Temático