**4. Gamma ray (-ray) interaction and attenuation coefficients**

In general the characteristic of radiation interaction with matter represented in photoelectric (*Predominates for photons in the low energy range between 10 keV and 200 keV*), Compton (*Predominated at energies of 100 keV - 10 MeV*. (McGervey, 1983)), Pair production (*Predominated at energies greater than twice the rest mass of an electron*, i.e. 2*m*0*c*2 = 1.022 MeV, *where m refers to mass of electron and c refers to speed of light* (Johns and Cunningham 1983)), Triplet production process (*occurs when the incident photon have an energy of* <sup>2</sup> <sup>0</sup> 4*m c* , i.e. *it implies both the pair production at the nucleus level plus triplet production*) and Raleigh scattering (*predominant for photons at low energy range from 1 keV to 100 keV*) table (3), is that each individual photon is absorbed or scattered from the incident beam in a single event. The photon number removed Δ*I* is proportional to the thickness traveled through x and the initial photon number *I*0, i.e. *<sup>o</sup> I Ix* , where, is a constant proportionality called the attenuation coefficient. In this case, upon integrating, we have the following equation (1)

$$I = I\_o e^{-\mu x} \tag{1}$$

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 119

The essence of -radiation interaction with molecules and the induction of physical and chemical characteristics that leading to form new compound is ascribed to the amount of energy being transferred, which will create ion, free radicals and excited molecule. Such interaction process is termed ionization and excitation of the molecules, which can cause chemical changes to the irradiated molecule. This is due to the fact that all binding energy for organic compound in the range of 10 – 15 eV. In case of low transferred energy by photon, the molecule undergoes excitation state before returning to the rest state by emitting X-ray photons or break down to release free radicals which in turn undergoes

The ejected electron from the irradiated molecule (A+) is subjected to the strong electric field of the formed positive charge. Therefore the recombination is a frequently occur, either during irradiation or after the end of irradiation to create energetic molecule (A\*\*). Such highly energetic excited molecule will break down into free radicals and new molecule (Denaro, 1972). The fundamental of this reaction can be shown in the following scheme Figure (1).

Fig. 1. The expected irradiation results of the organic molecules, where R. and S. are free

Radiation polymerization is a process in which the free radicals interact with the unsaturated molecules of a low molecular unit known as monomer to form high molecular mass polymer or even with different monomers to produce crosslink polymer. The formed polymer can be in different forms called homopolymer and copolymer depending on the monomer compositions link together. Radiation-induced polymerization process can be achieved in different media whether it is liquid or solid unlike the chemical polymerization which can only accomplished in aqueous media. It is also temperature independent. Radiation polymerization often continues even after removing away from the radiation source. Such condition is known as post-polymerization (Lokhovitsky and Polikarpov, 1980). Since radiation initiation is temperature independent, polymer can be polymerized in the frozen state around aqueous crystals. The mechanism of the radiation induced polymerization is concerning the kinetics of diffusion-controlled reactions and consists of several stages: addition of hydroxyl radicals and hydrogen atoms to carbon-carbon double bond of monomer with subsequent formation of monomer radicals; addition of hydrated

radicals and M and N are molecular products.

**5. Radiation polymerization** 

polymerization.

The attenuation coefficient is related to the probability of interaction per atom, i.e. the atomic cross section σa is given by equation (2)

$$
\mu = \frac{\sigma\_d N\_A \rho}{A} \tag{2}
$$

where *A* is the mass number and *N*A the Avogadro's number (6.022 x 1023 mol/1).

Table 3 briefly summarized the entire γ-radiation photon interactions with their possible energies required to initiate the reactions (Smith, 2000; Siegbahn, 1965).


Table 3.

The essence of -radiation interaction with molecules and the induction of physical and chemical characteristics that leading to form new compound is ascribed to the amount of energy being transferred, which will create ion, free radicals and excited molecule. Such interaction process is termed ionization and excitation of the molecules, which can cause chemical changes to the irradiated molecule. This is due to the fact that all binding energy for organic compound in the range of 10 – 15 eV. In case of low transferred energy by photon, the molecule undergoes excitation state before returning to the rest state by emitting X-ray photons or break down to release free radicals which in turn undergoes polymerization.

The ejected electron from the irradiated molecule (A+) is subjected to the strong electric field of the formed positive charge. Therefore the recombination is a frequently occur, either during irradiation or after the end of irradiation to create energetic molecule (A\*\*). Such highly energetic excited molecule will break down into free radicals and new molecule (Denaro, 1972). The fundamental of this reaction can be shown in the following scheme Figure (1).

Fig. 1. The expected irradiation results of the organic molecules, where R. and S. are free radicals and M and N are molecular products.

#### **5. Radiation polymerization**

118 Gamma Radiation

The attenuation coefficient is related to the probability of interaction per atom, i.e. the

*a A N A* 

Table 3 briefly summarized the entire γ-radiation photon interactions with their possible

Rayleigh electron,

resonance scattering, Thomson scattering

Compton scattering

Elastic Pair production

Triplet production inelastic pair production. Nuclear potential

scattering

where *A* is the mass number and *N*A the Avogadro's number (6.022 x 1023 mol/1).

energies required to initiate the reactions (Smith, 2000; Siegbahn, 1965).

Other names Approximate *E* of

Maximum importance.

<1MeV and greatest at small

Independent of

<1MeV least at small angle. Dominate in region of 1 MeV, decreases as *E* increase

Threshold ~1MeV, *E* > 5MeV. Increase as *E* increase.

Threshold at 2 MeV increases as *E* increases. Real Max > imaginary, below 3 MeV(both increase as *E* increases)

angles.

energy

Dominant at low *E* (1-500) KeV, cross section decrease as *E* increase

(2)

Z

Z3

Z2, Z3

Z

Z

Z

Z2

Z

Z4

dependence

atomic cross section σa is given by equation (2)

interaction

With bond atomic electron, with free electrons

With bond atomic electron, with free electrons

In Coulomb field of Nucleus

In coulomb field of electron & nucleus

With bonded electrons, all *E* given to electron

Process Type of

Photoelectric

Scattering from electrons coherent

Incoherent

Pair Production

Pair production Delbruk scattering

Table 3.

Radiation polymerization is a process in which the free radicals interact with the unsaturated molecules of a low molecular unit known as monomer to form high molecular mass polymer or even with different monomers to produce crosslink polymer. The formed polymer can be in different forms called homopolymer and copolymer depending on the monomer compositions link together. Radiation-induced polymerization process can be achieved in different media whether it is liquid or solid unlike the chemical polymerization which can only accomplished in aqueous media. It is also temperature independent. Radiation polymerization often continues even after removing away from the radiation source. Such condition is known as post-polymerization (Lokhovitsky and Polikarpov, 1980). Since radiation initiation is temperature independent, polymer can be polymerized in the frozen state around aqueous crystals. The mechanism of the radiation induced polymerization is concerning the kinetics of diffusion-controlled reactions and consists of several stages: addition of hydroxyl radicals and hydrogen atoms to carbon-carbon double bond of monomer with subsequent formation of monomer radicals; addition of hydrated

Synthesis of Polyaniline HCl Pallets and Films Nanocomposites by Radiation Polymerization 121

is fully achieved by ionizing radiation (Mohammed, 2007). The prime advantage of radiation processing in this work is that no oxidizing agent is used to polymerize the

PANI has high electrical conductivity that can be controlled by oxidation or protonic doping mechanism during synthesis. PANI is known for its excellent thermal and environmental stability but poor processibility due to insolubility in most common solvents and brittleness that limits its commercial applications. In the composites form with another water soluble polymers such as PVA, poly(vinyl pyrrolidone), poly(acrylic acid) and poly(styrene sulfonic acid) (PSSA) which used as stabilizers, the processibility of PANI could be improve and a functionalized protonic acid can be added into the composites to chemically polymerize PANI. The PANI dispersion can then be cast to form composite film containing PANI nanoparticles. To improve the conductivity further, chemically and electrochemically PANI/ polymer composites have been irradiated with x-rays, gamma radiation, and electron beams (Bodugoz *et al*., 1998; Sevil *et al*., 2003; Wolszczak *et al*., 1996 a and b; Angelopous *et al*. 1990). When ionizing radiation interacts with polymer materials active species such as ions and free radicals

Conducting PANI has been synthesized by chemical and electrochemical methods, which the later is considered the common one because of better purity. Chemically and electrochemically synthesized polyaniline are subjected to many shortcomings such as impurities, solvent toxicity, long tedious process, poor compatibility, insoluble, expensive, low production and difficult in their preparation, etc. However, report on synthesis of PANI nanoparticles using only -irradiation has not been reported until the date of 2007. The advantages of radiation processing is that no metallic catalyst, no oxidizing or reducing agent is needed, synthesis in a solid-state condition, fast and inexpensive, and controllable acquisitions. The synthesis of PVA/PANI nanoparticles by -irradiation doping is proposed

The materials used for preparing the samples in this study, namely as polyvinyl alcohol PVA, aniline hydrochloride AniHCl, -radiation as an effective tool for polymerization process and reducing agent, Petri-dishes, micrometer, UV-spectroscopy, Raman

The Aniline hydrochloride AniHCl monomer as 2.5, g (28.6 W/V) has been dissolved in distill deionized water of 100 ml under nitrogen atmosphere and bubbling in the solution with continuous stirring using magnetic stirrer for 3 hour. Then the solution has been irradiated with -radiation receiving 10, 20, 30, 40 and 50 kGy. The polymerized AniHCl i.e. polyaniline PANI-HCl has been precipitated filtered and collected in a form of powder. The

conducting PANI i.e. giving pure product.

**8. Conducting polyaniline nanoparticles** 

are produced and thus, improved the PANI conductivity.

in this work.

**9.2 Method** 

**9. Methodology** 

**9.1 Materials and equipments** 

spectroscopy and LCR-meter.

powder (2.5g) pressed by 10 tons to form pallets.

electrons to carbonyl groups and formation of radical anion of a very high rate constant and the decay of radicals with parallel addition of monomer to the growing chain.
