ATTI DELLA “FONDAZIONE GIORGIO RONCHI” ANNO LXVI, 2011 - N. 1

Study of some electrical properties

for PMMA-TiO2 composites

BAHAA HUSSIEN (*), MARWA ABDUL-MUHSIEN (**),

AHMED HASHIM (***)

1. Introduction

Recently polymer matrix-ceramic fi ller composites are receiving increased

attention due to their interesting electrical and electronic properties. Integrated

decoupling capacitors, angular acceleration accelerometers, acoustic emission

sensors and electronic packaging are some potential applications. Ceramic materials

are typically brittle, possess low dielectric strength and in many cases are

diffi cult to be processed requiring high temperature. On the other hand, polymers

are fl exible, can be easily processed at low temperatures and exhibit high dielectric

break-down fi elds (Kontos et al., 2007).

Poly methyl methacrylate is one of the best organic optical materials, and

has been widely used to make a variety of optical devices, such as optical lenses.

It is known that its refractive index changes upon UV irradiation, either in the

pure or doped state, which provides a means to fabricate structures, such as gratings

or waveguides (Ahmed, 2008). Electrical conductivity measurement is one

of the most convenient tools in studying such structural changes of powder compacts,

and has the advantage that the conductivity can be measured continuously

(*) Babylon University

(**) Al-Mustansiriyah University, e-mail: marwa_alganaby@yahoo.com

(***) College of Science, Babylon University

MATERIALS

46 B. Hussien - M. Abdul-Muhsien - A. Hashim

throughout the whole densifi cation process (Kuno and Senna, 1977). Al-Ramadhan,

in 2008, studied the electrical properties of the composites poly-methyl

methacrylate-nickel as a function of temperature and concentration of the additive.

She explained that the electrical conductivity is increasing with the increase

of the concentration of the additive Ni and temperature. This paper deals with the

effect of TiO2 on the some electrical properties of poly-methyl methacrylate.

2. Experiment

The material used in the present paper is the poly-methyl methacrylate as

matrix and TiO2 as a fi ller.

Electronic balances of accuracy 10–4 have been used to obtain a weight

amount of TiO2 powder and polymer powder. These are mixed by hand lay up and

the microscopic examination is used to obtain homogenized mixture. The weight

percentages of TiO2 are 0, 10, 20, 30, 40 wt.% The Hot Press method is used to

press the powder mixture. The mixture of different TiO2 percentages have been

compacted at temperature 145oC under a pressure of 100 par for 10 minutes. It is

cooled to room temperature, the samples were disc shaped of a diameter of about

15 mm and thickness ranging between 2.4 and 3 mm. The resistivity was measured

over the range of temperature from 30°C to 90°C using Keithly electrometer

type 616C. The volume electrical conductivity ?? is defi ned as:

where:

3. Results and discussion

Figure 1 shows the electrical volume conductivity as a function of the concentration

of TiO2 at a temperature of 30°C, it appears that the conductivity increases

with the increase of the TiO2 additive concentration.

The increase of conductivity with increasing concentration of TiO2 is due

to the increase of the charge carriers, which increase with the increase of fi ller

contact, where the TiO2 particles at low concentrations are represented by small

darker regions. They become large when the TiO2 content increases and the networks

connect each other as illustrated in the microscopic photographs in Fig. 2,

? ? =

1

??

=

taken for samples of different concentrations (Bhattacharya et. al, 2008, He et. al,

2005, Srivastava and Mehra, 2003).

FIG. 1

Variation of D.C. electrical conductivity with TiO2 wt concentration

for PMMA-TiO2 composite

FIG. 2

Photomicrographs for PMMA-TiO2 composite

(a) for pure (×50), (b) for 10 wt.% TiO2 (×50), (c) for 30 wt.% TiO2 (×50)

(d) for 40 wt.% TiO2 (×50)

Figure 3 shows the behavior of electrical volume conductivity of the samples

with the temperature. Note that the electrical conductivity increases with the

increasing of temperature, and that any of these materials has a negative thermal

coeffi cient of resistance. The interpretation of this fact is that the polymeric chains

and TiO2 particles act as traps for the charge carriers which transited by hopping

48 B. Hussien - M. Abdul-Muhsien - A. Hashim

FIG. 4

Variation of D.C. electrical conductivity with reciprocal absolute temperature

for PMMA-TiO2 composite

FIG. 3

Variation of D.C. electrical conductivity with temperature

for PMMA-TiO2 composite

process: on increasing the temperature, segments of the polymer begin to move,

releasing the trapped charges.

The release of trapped charges is intimately associated with molecular motion.

The increase of current with temperature is attributed to two main parameters,

charge carriers and mobility of these charges. The increase of temperature

will increase the number of charge carriers exponentially. The mobility depends

on the structure and the temperature (Al-Ramadhan, 2008; Majdi and Fadhal,

1997).

Figure 4 shows the relationship between the natural logarithm of the conductivity

and the inverted absolute temperature of the PMMA-TiO2 composites.

By using the equation

? = ?0 exp(?Ea / kBT)

the activation energy was calculated. The high activation energy values for neat

sample and low TiO2 concentration sample can be attributed to the thermal

movement of ions and molecules, whereas the low activation energy values for

the samples of higher TiO2 content can be attributed to the electronic conduction

mechanism which is related to the decreasing of the distance among the TiO2

particles. (Hamzah et al., 2008)

The concentration increasing of TiO2 less the result of the activation energy

as shown in Fig. 5 of PMMA-TiO2 composites which is a reasonable support for

the above discussion (Ahmed and Zihilif, 1992).

4. Conclusions

1. The D.C electrical conductivity of the PMMA increases by increasing

TiO2 concentrations and temperature.

2. The activation energy of D.C electrical conductivity is decreases by increasing

TiO2 concentrations.

REFERENCES

AL-RAMADHAN Z., Effect of Nickel salt on electrical properties of polymethylmethacrylate, J.

of College of Education, Al-Mustansiriyah Univ., Baghdad, Iraq, No.3, 2008.

AHMED R.M., Optical study on polymethyl methacrylate/polyvinyl acetate, Zagazig Univ.,

Zagazig, Egypt, 2008 (e-mail: rania8_7@hotmail.com).

AHMED A.H., Doping effect on optical constant of polymethylmethacrlate, Eng. Technology,

25(4), 2007.

AHMED M.S., ZIHILIF A.M., The electrical conductivity of polypropylene and Nickel coated

carbon Fiber composite, J. Mater. Sci., 25 (706), (Univ. of Jordan, Amman, Jordan, 1992).

50 B. Hussien - M. Abdul-Muhsien - A. Hashim

HE X. J., DU J.H., YING Z., Positive temperature coeffi cient effect in multwalled carbon