Banca de QUALIFICAÇÃO: JOSE MIGUEL ZUÑIGA PRADO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSE MIGUEL ZUÑIGA PRADO
DATE: 27/03/2025
TIME: 09:00
LOCAL: Sala 407 do Bloco B do Campus de Santo André da Universidade Federal do ABC
TITLE:

Synthesis and characterization of PVDF polymer films with graphene derivatives for potential applications in biomedicine

PAGES: 60
BIG AREA: Engenharias
AREA: Engenharia Biomédica
SUBÁREA: Bioengenharia
SUMMARY:

Polymeric materials such as poly(vinylidene fluoride) (PVDF) have been extensively studied for their piezoelectric properties, making them ideal for sensor and biomedical applications. This research focuses on the development of a flexible ultrasound transducer based on a PVDF/reduced graphene oxide (RGO) composite, aiming to enhance piezoelectric performance. Various RGO synthesis techniques were explored, including thermal treatment reduction (RGO_T), hydrazine reduction (RGO_Q), and microwave-assisted plasma reduction (RGO_P) using Ar/N₂ gas mixtures. Among these, the PVDF/RGO_T composite, reduced at 500°C, demonstrated superior piezoelectric properties reported in the literature, exhibiting a remanent polarization of 0.02 μC/cm² and a relative permittivity of 31 at 10 Hz.

The RGO_T concentrations were varied to 0.1%, 0.5%, 1%, and 1.5% to analyze their effect on the final composite. Using a mixture of dimethylformamide (DMF) and acetone in a 2:1 volume ratio. To enhance the 𝛽-phase of PVDF, annealing processes were employed, varying temperatures (60°C and 70°C) and times (2h, 17h, 20h, and 24h). This controlled heating process played a key role in increasing the 𝛽-phase content, directly impacting the material’s piezoelectric efficiency. X-ray diffraction (XRD) analysis revealed that the PVDF/RGO1%20H sample exhibited the highest contribution from the 𝛽-phase at 54.4%, which is the main phase for piezoelectricity, while the 𝛼-phase and 𝛾-phase contributed 10.8% and 34.8%, respectively.

In the composite film design, a 0-3 connectivity configuration was selected, where RGO particles (phase 0) are dispersed within a continuous PVDF matrix (phase 3). This arrangement offers multiple advantages, including high mechanical flexibility, ease of fabrication through mixing and molding, low cost, and suitability for complex geometries and thin films (11 μm thickness).

To enable efficient electrical signal collection, a transductor was fabricated, the PVDF film underwent gold sputtering, where a 30 nm layer of gold was deposited on both surfaces of the film, creating a conductive interface. Subsequently, during the layer assembly process, the piezoelectric composite film was sandwiched between two conductive layers, forming a structured capacitive configuration. The upper and lower conductive sheets were connected to copper electrodes, ensuring that they remained isolated from each other to effectively capture the electrical output generated by mechanical deformation of the piezoelectric material.

The work involves synthesizing piezoelectric materials, fabricating and integrating the transducer, and developing a strategy for experimental validation. The pressure sensor underwent testing under cyclic mechanical impacts with constant periodic deformation to evaluate its capacity to generate electrical signals. Key electrical parameters were recorded, revealing a peak-to-peak voltage of 1.039 V. Additionally, a second impact test was performed using steel balls that dropped from different heights, introducing variable deformation to the piezoelectric material. The recorded output voltage (V_out) increased with impact height, reaching a maximum of 1.3 V. Notably, in Test T1, the voltage rose from 390 mV at 50 mm to 1.3 V at 200 mm, while in Test T2, it ranged from 220 mV at 50 mm to 1.3 V at 200 mm. These results further confirm the sensor’s effectiveness in converting mechanical impacts into electrical signals.

The results emphasize the promise of the PVDF/RGO composite and the transducer for use in biomedical sensing applications, especially in portable medical devices and ultrasound biosensors. These findings lay strong groundwork for future advancements in flexible and high-performance ultrasound transducers.

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 1762438 - JEAN JACQUES BONVENT
Membro Titular - Examinador(a) Interno ao Programa - 1941387 - FERNANDA DIAS DA SILVA
Membro Titular - Examinador(a) Externo ao Programa - 2123676 - OLAVO LUPPI SILVA
Membro Suplente - Examinador(a) Interno ao Programa - 1831780 - DANILO DA CRUZ CENTENO
Membro Suplente - Examinador(a) Externo à Instituição - SILGIA APARECIDA DA COSTA - EACH USP