Guillermo Carbajal-Franco, M. S.

Dr. M. P. Eastman

Dr. C. V. Ramana

Dr. Eric Hagedorn

Wednesday, April 19, 2023

Colleges of Science and Engineering

Consultants: Dr. R. C. Hughes, Dr. T.L. Porter

PVDF- Basics

Polyvinylidene difluoride (PVDF),is also known under various trade names including _KYNAR (Trade Mark: Elf Atochem North American) SOEF (Trade Mark: Solvay S. A.)

PVDF is prepared by the polymerization of 1,1-vinylidene difluoride

The structure of the monomer is:

The structure of the polymer is:

F

H

H

F

Representations of the molecular structure of the vinylidene difluoride (VD) monomer and of the and forms of the PVDF polymer.

F

H

H

F

                

PVDF- form

PVDF- form

VD-wire

VD-space filling

With piezoelectric materials have a separation of charge which generates a net dipole in the case the dipoles are aligned (2),(3) below- stressing the material generates a voltage. Materials with unaligned dipoles (1) are not piezoelectric. Examples: Inorganic: barium titanate (BiTiO3) and lithium niobate (LiNbO3); Biological materials:  bone, tendons, sugar, dentin. Polymers: PVDF.

Piezoelectric Materials

http://en.wikipedia.org/wiki/Piezoelectricityhttp://www.physikinstrumente.com/tutorial/4_15.html

Important Properties of PVDF

Property Units Reported Value

Melting C 174

Glass Transition C ~ -30

Density g/ cm3 1.8

Heat Capacity Joule/(g K) 1.9

Tensile Strength psi 78000

Serving Temperature Long Term

C 140

Dielectric Constant (60 Hz)

- 9

Dielectric Strength KV/mm 160

Volume Resistivity Ohm/cm 1 x 1014

Refractive Index 1.42

PVDF Sensors PVDF is piezoelectric and the voltage induced by

bending PVDF films can be measured. The surface of the PVDF is coated with metal to allow electrical measurements.

PVDF is pyroelectric and readily absorbs thermal radiation in the range 1000-1200 cm-1. The voltage induced by exposing metalized PVDF films to thermal radiation can be measured.

By virtue of its piezoelectric properties PVDF possibly could be fabricated into a surface acoustic wave based sensing system.

Commercially available metal coated piezoelectric PVDF sensor elements

Smart Sensors

We use the term “Smart Sensor” to refer to systems that employ a sensor interfaced to microelectronics. Here we will use piezoelectric/pyroelectric PVDF films as our sensors and a computer will take the place of the microelectronics. The systems described are not engineered to minimize size and power consumption but clearly those would be goals in any widely deployed practical device.

A USB data acquisition port will allow measured voltage changes to be easily converted to computerized information for data storage and analysis.

Circuits

Voltage Follower TL082. Dual OpAmp Dual voltage source:

± 15V

Electronics

Circuits

1: TL082. Dual OpAmp 1: R 10 MΩ. 10 mega-

ohms resistors 1: 0.001 uF. 0.001 micro-

farads capacitor. 1 nF or 1 nano-farad

Dual voltage source:

± 15V

ElectronicsElectric Charge Measurement

Circuits

Differential Amplifier Electronics TL082. Dual OpAmp 3: R 10 MΩ. 10 mega-

ohms resistors Dual voltage source:

± 15V

Deflection Sensor

Two PVDF metal coated films mounted on both sides of a flexible material.

The response of these films capable of quantifying the magnitude, speed and direction of the flexion movement.

Circuit (A) used to follow voltage changes

PVDF sensor elements, detection circuit and USB data port

PVDF sensors mounted on a solid substrate and interfaced to a detection circuit

USB data port interfaced to laptop computer gives system properties of a “smart sensor”.

Output PVDF sensors on a ruler undergoing oscillator flexing-Note polarity (green/yellow). Blue represents the combined output signal.

Output PVDF sensors on flexed ruler-Note polarity (green/yellow) and combined signal.

Plot of ln(Displacement) vs time showing that the motion of the flexible material is described by the equation D=D0 exp (-t); this equation characterizes an under damped oscillator.

Pyroelectric Matrix Array

PVDF is pyroelectric and readily absorbs radiation around cm-1 .

Four sensors in matrix array. Array capable of quantifying the heat

intensity and the location of the heat source.

Four Panel Thermal Detection

Infrared Spectrum of PVDF taken on a Bruker IFS 66v spectrometer, equipped with a DTGS detector and a KBr beamsplitter.Note that the strong absorption around 1000 cm-1

Voltage output 4 panel Pyroelectric Sensor when exposed to an asymmetrically located heat source

Future Work

Mechanical and Thermal stabilization of sensor platform.

Detailed analysis of experimental results and development of effective learning strategies based on PVDF sensors

Develop and understand mathematical – electrical models

Use PVDF SAW devices in a chemical sensor system.

Personal Acknowledgements

Dr. Tim Porter of the Physics and Astronomy Department at Northern Arizona University helped design a number of our detection circuits.

Dr. Robert C. Hughes, Sandia National Laboratories, provided important advice during the early stages of this work.

Support Acknowledgement

This material is based upon work supported in part by the U. S.  Army Research Laboratory and the U.S. Army research Office under Contract

W911NF0410052.

Thank You for Your Attention