Electrical and Photoelectrical Properties of Polyaniline Modified Poly(vinylidene fluoride)

Latex Films

Gururaj M. Neelgund, Valery N. Bliznyuk, Alexander A. Pud, Erika Hrehorova and Margaret K. Joyce

Department of Paper Engineering, Chemical Engineering and Imaging Western Michigan University, Kalamazoo, MI 49008

Introduction

Polyvinylidene fluoride (PVDF) is a non-reactive thermoplastic fluoropolymer

•Crystalline polymer•Low melting point (160 ~ 170 oC)

Key features

•Excellent chemical resistance

•Excellent mechanical properties

•High temperature capabilities (continuous use

temperature up to 150°C) and excellent ageing

resistance

Key features•Physiologically harmless •High dielectric constant •Ferroelectric and piezoelectric properties

Applications•Membranes: wastewater treatment, gas separation •Chemical Process Industry: pipes and fittings, pumps, valves•Anti-corrosion material in chemical industry: acids, organic solvents and halogens•Insulation material in electronic / electric industries •Lithium batteries•Computer industry•Air/space industry

Polyaniline modified poly(vinylidene fluoride) (PVDF-PANI) particles

PVDF-PANI core-shell nanoparticles

PVDF nanoparticles (200nm)PVDF-PANI core-shell nanoparticles

(220 nm)

TEM images

DSC thermograms

PVDF latex nanoparticles:melting transistion, Tm=164 oC

PVDF-PANI core-shell latex nanoparticles: melting transistion, Tm=168 oC

DSC revealed the crystalline nature of PVDF-PANI particles

Electrical Properties: I–V characteristics measurement

A pair of silver electrodes wasdeposited on the glass substrate by thermal evaporation technique

The Keithley 2400 multimeteroperated from PC was used to measure I–V characteristics

The thicknesses of the PVDF-PANI films were measured by atomic force microscope (AFM)

Annealing profile: Electrical Properties

I–V characteristics for PVDF-PANI film subjected to annealing at 180 °C

-10 -5 0 5 10-3x10-6

-2x10-6

-1x10-6

0

1x10-6

2x10-6

3x10-6

7

6543

2

1

I (A)

U (V)

(1) as prepared (2) 1 min of annealing(3) 3 min of annealing(4) 4 min of annealing(5) 5 min of annealing(6) 10 min of annealing(7) 20 min of annealing

An increase in conductivity has been observed after a short time (3 min) of annealing at 180 oC (i.e., above the melting transition of PVDF).

Morphological changes in PVDF-PANI film

Schematic representation

Compaction of the film, which facilitates increasein mobility of charge carriers

Thermal aging of PVDF-PANI particles, especially at high temperature like 180 °C andloss of dopant DBSA on PANI

Less contact between the surface of PVDF-PANInanoparticles

Morphological changes in PVDF-PANI film

AFM images

2.0X10-620 min of annealing4.2x10-63 min of annealing3.3x10-7As prepared film

ConductivityS/cm

Sample

As prepared film After 3 min of annealing After 20 min of annealing

260 280 300 320 340 360 380 400 420 440 460 480 500 520

-4x10-11

-2x10-11

0

2x10-11

4x10-11

OffOffOffOff OnOnOnOn

I (A)

Time (sec)

0 50 100 150 200 250 300 350 400 450 500-6x10-11

-4x10-11

-2x10-11

0

2x10-11

4x10-11

6x10-11

I (A)

Time (sec)

Effect of photo illumination on PVDF-PANI film

PVDF-PANI film is sensitive to photo illumination, increase in conductivity by photo illumination

Application: Sensor

-1.0 -0.5 0.0 0.5 1.0-3x10-5

-2x10-5

-1x10-5

0

1x10-5

2x10-5

3x10-5

16

1

I (A)

U (V)

Expose to ammonia gas

(1) measured in air (2) 1 min (3) 3 min (4) 5 min (5) 7 min (6) 9 min (7) 11 min (8) 13 min (9) 15 min (10) 20 min (11) 30 min (12) 40 min (13) 50 min (14) 60 min (15) 90 min (16) 120 min

PVDF-PANI film annealed at 180 oC for 3 min was exposed to 0.1 ppm NH3

Decrease in conductivity by absorption of NH3 molecules

Application: Sensor

Expose to HCl gas

(1) measured in air (2) 1 min (3) 3 min (4) 5 min (5) 7 min (6) 9 min (7) 11 min (8) 13 min (9) 15 min (10) 20 min (11) 30 min (12) 50 min (13) 70 min

PVDF-PANI film annealed at 180 oC for 3 min was exposed to 0.1 ppm HCl

Increase in conductivity by absorption of HCl molecules

-1.0 -0.5 0.0 0.5 1.0-1.5x10-5

-1.0x10-5

-5.0x10-6

0.0

5.0x10-6

1.0x10-5

1.5x10-5

13

1

I (A)

U (V)

Sensor response of PVDF-PANI film exposed to NH3 and HCl gases

HClNH3

Sensing response is more for NH3 gas compare to HCl gas

0 20 40 60 80 100 120

0

1

2

3

4

5

6

S (%

)

Time (min)

0.1 ppm HCl 0.5 ppm HCl 1.0 ppm HCl

0 20 40 60 80 100 120 140 160

0

20

40

60

80

100

S (%

)

Time (min)

0.1 ppm NH3 0.5 ppm NH3 1.0 ppm NH3

Conclusions

Homogeneous, spherical polyvinylidene fluoride (PVDF) nanoparticles have been prepared and are successfully modified by coating with polyaniline (PANI): PVDF-PANI core-shell nanoparticles.

Ideal time of annealing to achieve the highest conductivity from PVDF-PANI film is 3 min at 180 oC.

PVDF-PANI core-shell nanoparticles are sensitive to photo illumination.

PVDF-PANI nanoparticles are promising candidate for the development of ammonia sensors.