Optical properties for prepared polyaniline / Ferro fluid nano composites

Pure nano Ferro fluid was synthesized by chemical co-precipitation method. The composite of polyaniline with nano sized Ferro fluid was prepared by In-situ–chemical oxidation polymerization method with ammonium per sulphate as an oxidant in aqueous hydrochloric acid under constant stirring at room temperature. The optical properties, absorption, transmission, optical energy gap (Eg) and optical constant refractive index (n) have been investigated. The value of the Eg decreased with increasing Ferro fluid concentration.


Introduction
In recent years the manufacture of devices using inorganic/organic hybrid materials has attracted much interest from both the scientific and the technological points of view, improvements in the electronic and the optical properties of these devices are closely related to surface effects.The grain boundaries (a double Schottky barrier could be formed at the grain boundaries) of polycrystalline materials play a significant role in their electrical properties and interfaces, which usually play important roles in device characteristics [1].Magnetic fluids are stable colloidal dispersions of nanosized magnetic, particles in a liquid carrier.Although.The particles used in most commercial applications are iron oxides (magnetite, maguemite) because of their resistance to oxidation, transition metals have the benefit of higher saturation magnetisation.Magnetic fluids can be used in rotating shaft seals, exclusion seals, loudspeakers, dampers, in clinometers shock absorbers of DVD and CD actuators, medical applications, etc. [2].Incorporation of a magnetic material, such as Fe 3 O 4 , into an organic material has attracted great attention due to the resulting electrical properties as well as the many different applications, such as: charge dissipation devices for computer hard disks, batteries, electrochemical display devices, molecular electronics, non-linear optics, sensors and microwave absorption materials [3].Polyaniline (PANI) as the organic material has attracted much attention due to its characteristics, such as air stability and good solubility in several solvents, besides it shows several changes in its electronic structure depending on its oxidation level.Also, mulifunctionality of the PANI micronanostructures combined with optical or magnetic function has also attracted interests in order to match the requirements of the technology applications [4].PANI is usually considered as a p-type semiconductor [5], presence of reactive -NH-groups in the polymer chain which in parts chemical flexibility to the system and improves the processcibility to a large extent [6].Electrical and optical properties can be changed by oxidation and/or by protonation.Several reports are dealing with the preparation of hybrid materials such as SnO 2 /polyaniline [7] TiO 2 /polyaniline [8], Fe 2 O 3 /polyaniline [9], and ZnO/Polyaniline [10].PANI is widely used in the area of electrochemical materials.

Experimental work
This part presents raw materials and preparation method used to prepare polyaniline /Ferro fluid nano composites.

Raw materials
The

Preparation of Ferro fluid
Measure 2gm of ferric chloride (FeCl 3 ) in to a Beaker, add 10ml of distilled water, stir the solution, measure 1gm of ferrous chloride (FeCl 2 ), add 10ml of distilled water, add drop wise HCL (1M) to melt the solution completely, add the solution to the beaker containing FeCl 3 and continue in stirring.Add a small piece of steel woo lcontinue in stirring until the solution has turned dark green.Filter with a coffee filter.While stirring, add 150 ml of house hold ammonia (NH 3 ), the solution color will change to Black.With the stirring, heat the solution to near boiling, add 5ml of olic acid, continue in stirring and heat near boiling until the smell of ammonia disappears, usually about an hour.Power of and collect the magnetic particles (the Black amount).The reaction for the prepared Ferro fluid is shown below:

Preparation of polyaniline\ ferro fluid nano composite
Polyaniline -Ferro fluid nanocomposites were prepared for different weight of (1, 1.5, and 2) g of Ferro fluid by in-situ oxidation polymerization method.Initially known weight of Ferro fluid (1g) was added to aniline prepared in aqueous hydrochloric acid (1M) and stirred for half an hour, then allow settling down for another half an hour.To this solution, ammonium persulphate as an oxidant prepared in aqueous hydrochloric acid (1M) was added drop-wise for half an hour under constant stirring at room temp.The monomer to oxidizing agent ratio was kept at 1: 2. Stirring was continue for two hours, the resulting dark green mixture was kept over night and then filter.The precipitated polymer was washed with300ml distilled water, then with 150 ml methanol to remove excess initiator, monomer and oligomer.Finally, the polymer was dried in air for about one hour and then in an oven at 80°C for 6 hours.Similarly nanocomposites for remaining weight of Ferro fluid were prepared.

sample preparation
Polyaniline /Ferro fluid nano composites powder of weight (0.05) g. was dissolved in 5 mL of Dimethyl sulfoxide (DMSO), then the solution was stirred by using electromagnetic stirrer for two hours to achieve a homogenous content.Because the Polyaniline was partially dissolved, the solution should be filtered, to remove any particles not solving.UV/160 Shimadzu spectrophotometer was used to measured transmission and absorption spectra of the prepared samples at wavelength range (200-800nm).The absorptions spectrum was used to determine the optical energy gap.Computer program is used and Tauc formula was employed in the program.

Result and discussion 1. Absorption
The absorption was determined for the PANI /Ferro fluid.The variation of the absorption versus the wavelength for different concentration of Ferro polyanyline is shown in Fig. 1.From the figures, in general the absorption is high at UV region and decreasing in the optical region.

Optical energy gap
Tauc [11] put the empirical equation between the optical energy gap and energy of incident photon which is where A is a constant, hυ is the energy of incident photon, which can be calculated using the equation ℎ = 1240 () � , and r is the order of the optical transition depending on the nature of electronic transition.The transition is called direct if the extremities of V.B. and C.B. lie at the same point in k -space, while the transition is called indirect if the transition is possible only with phonon assisted (∆k ≠ 0 ) [12].Thus the value of r may be 1/2, 2, 3/2 and 3 corresponding to the allowed direct, allowed indirect, forbidden direct and forbidden indirect transition respectively.The optical energy gap (E g ) for polyaniline has been determined.A plot of (αh) 2 versus hν with different concentration of Ferro fluid (1,1.5, and 2 wt%) as shown in Fig. 2 the plot is linear indicating the direct band gap nature of the polymer.Extrapolation of the line to the hν axis gives the band gap to pure and doped samples therefore the optical energy gap is determined from this figure.The additive of Ferro decreases the optical band gap from 3eV to 2.4eV.The reduction in the optical band gap is probably due to the modification of the polymer structure [13].are in close agreement with the results of Sayed [14].

Refractive index
For normal incident of plane electromagnetic wave the reflectance is given by the equation ( 15) which leads to The variation of the refractive index as a function of the wavelength for Polyaniline at different Ferro fluid wt.% doping is shown in Fig. 4 which shows a variation of n at room temperature.It is observed that in general the refractive index decreases with the increase of wavelength.The dispersion curve of n(λ) is presented in figure for pure and doped PANI.The refractive index decreases in pure PANI but it has higher values compared with doped samples because the addition of Ferro, in general, the reflective index which increases by increasing the C -H bonds [16].Fig. 5 shows the reflective index for pure PANI.

Conclusions
Polyaniline polymer was prepared via the oxidation of aniline hydrochloride with ammonium peroxy disulfate in aqueous medium.The Ferro/fluid was prepared by coprecipitation method.The composite of polyaniline with nano sized Ferro fluid was prepared by In-situ -chemical oxidation polymerization method.It was found the optical energy gap was decreasing when increasing the concentration of Ferro fluid wt% from (3-2.4eV).was noticed that all samples have allowed direct optical energy gap.

Fig. 1 :Fig. 2 :
Fig. 1: The variation of absorption as a function of wavelength for PANI/Ferro fluids samples.

Fig. 3
Fig.3 shows the relation between the energy gap and the concentration percentage of Ferro fluid.It can be seen from this figure that all samples have one direct optical energy gap.We have found energy gap decreases with increasing the concentration percentage of Ferro of 1%, 1.5% while for sample with 2% wt.The increasing is very fast and this increasing in the optical energy gap can be explained as fallow: The addition of Ferro to