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

ABSTRACT

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.

Graphical abstract

KEYWORDS:

• Dielectric properties
• phase transitions
• surface properties
• infrared spectroscopy
• thermogravimetric analysis (TGA)

Acknowledgments

The authors thank Degussa-Hüls for supplying the aerosil A380. LF, IZ and CPG are indebted to the Romanian Agency UEFISCDI for the funding by the PN19-03 Core Program (under the Project 21 N/08.02.2019).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Romanian National Authority UEFISCDI (Executive Agency for Higher Education, Research, Development and Innovation Funding) [the Project 21 N/08.02.2019 under PN19-03 Core Pro].