RESEARCH GOAL

Design and produce electroactive composite films with hierarchically designed structures (on the nano- and micro-scales) to enhance piezoelectric efficiency and improve both actuation and sensing capabilities

ELECTROSPINNING POLYMERS

Inject polymer solution into electric field with syringe

Needle and collector plate electrically charged (oppositely) to generate electric field

Fibers form at end of needle, spin along electric field and collect on the plate, forming a film
-- Diameter and quality of fibers depend on process conditions

The polymer being investigated is PVDF (polyvinylidene difluoride)
-- PVDF has a piezoelectric crystalline phase which occurs under specific processing conditions – drawing and solution casting
-- Electrospinning is a combination of drawing and solution casting

ELECTROSPINNING PROCESS

PROCESSING FILMS

Two films are consolidated together with a thin layer of silicon in between them
-- First pressed without heat, then heat added for a short time
-- If the temperature is too high, the PVDF melts and loses its piezoelectric characteristics

After consolidation, the films are prepared for electroactive tests
-- Electrodes and wire leads attached to either side
---- Carbon grease, silver paint, and nanotube deposition are being investigated as electrodes
-- Samples poled through heating under strong electric fields

TEST METHODS

Method 1
-- Apply voltage to sample and use digital image correlation to observe strain in films
-- Able to detect anisotropic strains and correlate the strains to changes in voltage
-- This method can only test for actuation

Method 2 (Pictured)
-- Using a load transducer and a tensile fixture, it is possible to for actuation and sensing abilities
-- Actuation provides load feedback when voltage is applied
-- Sensing provides voltage feedback when strain is applied

ACTUATION

-- Prepared samples are tested with one of the two test methods
-- Any actuation detected and the voltage causing it is noted
-- Early tests only yielded a very small amount of actuation, and not on a consistent basis
--- This confirms that the samples must be poled prior to testing

SENSING

-- Prepared samples tested with method 2
-- The tests for sensing have shown more results than actuation tests thus far
--- Nanocomposite films containing carbon nanotubes have had the better performance

- Electroactive PVDF films could be used as sensors in various applications
-- Drop-in replacement for strain gauges.
-- Potentially cheaper and more reliable.

FUTURE WORK

- An environmental chamber that allows full control of environmental conditions will be used in the future to spin all samples, ensuring reliable results
- The effects of pressure on the electrospinning process will be studied.
- Standardize the attachment of electrodes (to sample) to improve accuracy

ACKNOWLEDGEMENTS

This material is based upon work supported by the National Science Foundation under Grant No. (1138182), Dr. Mary Poats, Program Director, as well as the Air Force Office of Scientific Research (AFOSR) Young Investigator Grant (FA9550-09-1-0218), Dr. Byung-Lip Lee, Program Director.