Molten-State Dielectrophoretic Alignment of EVA/BaTiO3 Thermoplastic Composites: Enhancement of Piezo-Smart Sensor for Medical Application

Abstract

Dielectrophoresis has recently been used for developing high performance elastomer-based structured piezoelectric composites. However, no study has yet focused on the development of aligned thermoplastic-based piezocomposites. In this work, highly anisotropic thermoplastic composites, with high piezoelectric sensitivity, are created. Molten-state dielectrophoresis is introduced as an effective manufacturing pathway for the obtaining of an aligned filler structure within a thermoplastic matrix. For this study, Poly(Ethylene-co Vinyl Acetate) (EVA), revealed as a biocompatible polymeric matrix, was combined with barium titanate (BaTiO₃) filler, well-known as a lead-free piezoelectric material. The phase inversion method was used to obtain an optimal dispersion of the BaTiO₃ within the EVA thermoplastic matrix. The effect of the processing parameters, such as the poling electric field and the filler content, were analyzed via dielectric spectroscopy, piezoelectric characterization, and scanning electron microscopy (SEM). The thermal behavior of the matrix was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry analysis (DSC). Thermoplastic-based structured composites have numerous appealing advantages, such as recyclability, enhanced piezoelectric activity, encapsulation properties, low manufacturing time, and being light weight, which make the developed composites of great novelty, paving the way for new applications in the medical field, such as integrated sensors adaptable to 3D printing technology.

Keywords: molten-state dielectrophoresis; piezoelectric sensor performance; structured materials; thermoplastic composites.

Figure 1

TGA curves of: (A) pure EVA, (B) EVA/BaTiO₃ composites at different filler contents.

Figure 2

(A) DSC analysis of pure EVA-2 thermal cycles detailed in Figure 16, (B) the normalized heat flow derivative as a function of temperature.

Figure 3

DSC analysis of EVA-BaTiO₃ unstructured composites: 3 vol%, 16 vol% and 29 vol%.

Figure 4

The 0–3 unstructured EVA/BaTiO₃ composites with different volume fractions: (A) 3 vol%, (B) 16 vol%, (C) 29 vol%.

Figure 5

SEM micrographs of EVA/BaTiO₃ composites structured at 6 kV·mm⁻¹: (A) 3 vol% filler content, (B) 16 vol% filler content, (C) 29 vol% filler content.

Figure 6

XRD pattern of BaTiO₃ nanoparticles: (A) in the whole range of 20°–70°, (B) zoom-in on the $2\theta$ region of 44° and 46°.

Figure 7

Experimental permittivity values for both structured and unstructured composites compared with Yamada (0–3 connectivity) and Bowen’s (1–3 connectivity) models.

Figure 8

(A) Measured piezoelectric charge coefficient (d₃₃), (B) piezoelectric voltage coefficient, (C) transduction coefficient, as a function of the filler content for both structured and unstructured composites.

Figure 9

Fitting with Van den Ende’s model for (A) EVA/BaTiO₃ unstructured composites, (B) EVA/BaTiO₃ composites structured at E = 6 kV·mm⁻¹.

Figure 10

Inter-particle distance in the thickness direction as function of the volume fraction of BaTiO₃ for structured and unstructured composites, following Van den Ende’s model.

Figure 11

Piezoelectric charge coefficient versus poling electric field of 0–3 EVA/BaTiO₃ and 1–3 EVA/BaTiO₃ with a volume fraction of (A) 3 vol%, (B) 16 vol%, (C) 29 vol%.

Figure 12

Ashby graph of d₃₃·g₃₃ as a function of 1/(Y·ρ) for various piezoelectric materials.

Figure 13

SEM observation of the BaTiO₃ nanoparticles.

Figure 14

Illustration of the mold used to develop 0–3 and 1–3 composites.

Figure 15

Illustration of the poling setup.

Figure 16

Thermal cycle for DSC measurements of EVA and EVA/BaTiO₃ composites.