Molecular dynamics in bulk and surface species of cyanophenyl alkyl benzoates with 2, 3 and 7 carbon atoms in the alkyl chain: comparison in the whole homologous series

• Published in: Liquid crystals Vol. 47; no. 6; pp. 908 - 917
• Main Authors: Frunza, Stefan, Ganea, Constantin Paul, Zgura, Irina, Frunza, Ligia, Schönhals, Andreas
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 02.05.2020; Taylor & Francis Ltd
• Subjects: Atomic properties; Benzoates; Broadband; Chains; Composite materials; Dielectric properties; Dielectric strength; Homology; Hydrogen bonding; Infrared analysis; Infrared spectroscopy; Low temperature; Molecular dynamics; phase transitions; Spectrum analysis; Surface layers; surface properties; Temperature dependence; Thermal analysis; thermogravimetric analysis (TGA)
• ISSN: 0267-8292; 1366-5855
• DOI: 10.1080/02678292.2019.1687768

Molecular mobility of cyanophenyl alkylbenzoates (CPnBs) (n = 2, 3, 7 - number of carbon atoms in the alkyl chain) in the bulk and in composites with aerosil A380 is investigated by broadband dielectric spectroscopy, while thermal analysis and infrared spectroscopy were applied to characterise the molecular species. The work completes preliminary results obtained for the members with n = 4 ... 6. An interaction by hydrogen bonding, between aerosil surface - OH groups and - CN or ester groups of the CPnB molecules takes place. It slows down the relaxation process as observed for related composites in comparison to the pure materials. The existence of two types of bonding might be the reason that Vogel temperature for the relaxation process in the surface layer does not show the odd-even effect. Temperature dependence of the relaxation rates for composites shows a crossover behaviour from a high to a low temperature regime. Moreover, the temperature dependence of the dielectric strength is unusual. As the loading degree is similar, comparison of the dielectric, spectroscopic and thermal data obtained here and with the results obtained for the composites with n = 4 ... 6 can be directly done. Increasing the number of the members of the homologous series confirms and hardens the preliminary conclusions.