High-dielectric mouldable and printable wax reinforced with ceramic nanofillers and its suitability for capacitive sensing

Abstract

Functional polymer composites are being increasingly developed to improve performance and integration into devices. Paraffin wax, as a material suitable for paper-based microfluidics, can be combined with ceramic materials to adapt its dielectric constant, an essential property for many applications, such as printed electronics. Paraffin wax reinforced with high-dielectric ceramic nanofillers such as barium titanate (BT) has been developed with varying filler content up to 50 weight percentage (wt%) and processed by moulding and screen-printing techniques, without the use of solvents. BT shows homogenous dispersion in smaller agglomerates into paraffin wax composites, with agglomerates up to 20 μm of diameter for larger filler contents. The moulded composite wax shows a Young modulus of about 7.8 MPa in compression mode, similar to pristine wax and composites. Further, it supports forces up to 400 N under compression and strains up to 20%. Mechanical hysteresis decreases drastically for the 1st cycles, stabilizing at 30 kJ m−3 in the fifth cycle. Wax and respective composites were printed over a PET substrate and support bending deformation up to 4 mm of bending for 100 cycles. The dielectric constant of the pristine paraffin wax is about epsilon = 9, increasing up to epsilon = 18 for the composite with 50 wt% BT. Theoretical modelling of the dielectric response shows that models that consider the shape and orientation of the fillers predict in a more precise way the dielectric behaviour of the composites, being the Tinga model the one that presents a better prediction of the experimental dielectric behaviour for the BT/wax composites.