Preparation and Characterizations of Iron Oxide Nano Particles Reinforced Polymeric Thin Films

Recently, chemically cross-linked poly (vinyl alcohol) and poly (2-acrylamido-2-methyl-1-propanesulfonic acid) (PVA-PAMPS) films are effectively used in the mechanical devices, attributable to their biocompatibility and cost-effectiveness [12,13]. Notably, the PVA has been widely utilized in the fabrication of tablet coating, artificial tears, drug delivery and tissue replacement, owing to their specific characteristics of toxicologically safe, high oxygen permeability and biodegradability [14], conversely they possess very less mechanical stability. To overcome this major drawback, it should be chemically cross-linked / blended with other hydrophilic materials to acquire mechanically stable materials. Specifically, the PAMPS, a sulfonic acid acrylic monomer has high proton conductivity and well hydrated due to presence of sulfonic acid groups in its backbone, and they are effectively applied infuel cells, medical devices and actuators [7,15]. In order to improve their mechanical and thermal stabilities of these PVA and PAMPS polymers, they could be blended / chemically crosslinked for obtaining flexible, mechanically and thermally stable material [12,13]. Generally, the reinforcement of nano-particles into the polymer matrix enhances the mechanical, dimensional and thermal stabilities of the host polymer matrix. Very recently, Guo et al. [16] fabricated IONPs reinforced PVA composites with superior thermal stability, and the IONPs have robust interaction with the PVA matrices by hydrogen bonding between their hydroxyl groups.


Introduction
Magnetic nano-particles, which can be stimulated under magnetic field gradients, consist mainly iron, cobalt, nickel and their compounds [1][2][3][4].The magnetic nano-particles have been attracted due to the thermal, magnetic and optical properties [5].Thus, the particles are being potentially used in photonics, electronics, biomedical, magnetically tunable materials, micro and nanofluidics, magnetic particle imaging, data storage and sensors [6,7].In particular, iron oxide (Fe 2 O 3 ) nano-particles (IONPs) are widely used such applications due to their biocompatible and biodegradable nature and they can be easily controllable by magnetic field [8,9].Further, the IONPs have very large surfaceto-volume ratio, thus they possess high surface energies [5].However, they are in powdery form and possess less mechanical stability, protects their practical applications.In order to utilize this precious material practically, it could be blended with by thermo gravimetric analysis (TGA) and water-uptake ratio.The reinforcing effect of the IONPs on the micro structural property of the PVA/PAMPS matrix was extensively investigated by High Resolution-Scanning Electron Microscopy (HR-SEM).

Synthesis and characterizations of IONPs
The IONPs(α-Fe 2 0 3 , hematite) were synthesized using sodium borohydride as reducing agent [17].Figure 1 shows the schematic representation of synthesis of the IONPs.Firstly, FeCl 3 .6H 2 O (7.5 g) was dissolved in 100 mL distilled water and stirred for 4 hrs, andNaBH 4 (1 g / 100 mL) solution was added to the ferric chloride solution drop wise for an hour at room temperature.The color of solution changed from yellowish to black color, and the nano-particles dispersion were stirred for additional 10mins, and centrifuged, finally.The IONPs were dried in an oven at 100°C for 24 hrs, and stored ina desiccator until used, and they were characterized by FT-IR and TGA.

Preparation of PVA/PAMPS/IONP films
The PVA/PAMPS/IONP nano-composite films were prepared by Thermally Induced Phase Separation technique [12].Figure 2 shows the schematic representation of the fabrication of PVA/PAMPS/IONP films.Firstly, the PVA solution(solventdistilled water)was heated to 80°C with stirring until to obtain a homogeneous and transparent solution.Additionally, the PAMPS aqueous solution was poured into the PVA solution and stirred for additional 3 hour to attain homogeneity.Furthermore, the IONPs were dispersed in distilled water by ultrasonication for 10 min, and the IONPs dispersion was added to the PVA/ PAMPS mixture, and stirred in a mechanical stirrer for 5 hours to acquirea homogeneous mixture.Then, the solution was poured in a Teflon coated mold and dried in anoven at 90 °C for 24 hours to evaporate the solvent, utterly.The PVA/PAMPS/IONP films were prepared with various weight ratios, which are shown in the table 1.Furthermore, the PVA/PAMPS film was prepared at the weight ratio of 10:2 in distilled water to compare the influence of the IONPs on the PVA/PAMPS matrix.

Characterizations
Structural analysis of the PVA, PAMPS, IONPs and PVA/PAMPS/ IONP composite was carried out by Fourier Transform Infrared Spectroscopy (FT-IR,SHIMADZU, IR Prestige-21), and thermal stability of the samples was also analyzed by thermogravimetric analysis (TGA/SDTA851e, Mettler Toledo) under nitrogen atmosphere at heating rate of 10°C / min.Further, the hydrophilic nature of the as-prepared films was measured by water uptake measurement by gravimetric method [18,19].The cross-sectional and surface morphologies of the PVA / PAMPS and PVA/PAMPS/ IONP 1-4 thin films were observed by HR-SEM (FEI Quanta, FEG 200).For the analysis, the dried films were fractured, mounted on a stub and sputter-coated with gold.
1556 and 1650 cm-1 were showed the vibrational mode of amide groups, the two sharp peaks at 1039 and 1221 cm-1 were observed for the S-O stretching of sulfonate groups, and the band around 3400 -3000 cm-1owing to the O-H stretching vibration [12,13].In the IONPs spectrum, the broad band at 3700-3000 cm−1 indicated the stretching vibration mode of surface hydroxyl groups of the pristine IONPs [20].In the PVA/PAMPS/IONP spectrum, the stretching absorption band attributed to the C-N of PAMPS decreases with more cross-linking, followed by an increased sharp peak due to the C=O from PAMPS.The broad peak observed around 3500-3000 cm-1 due to the O-H stretching vibration of the PVA, PAMPS and IONPs in the nano-composite films.Hence, the incorporation of IONPs in the polymer matrix was concluded by the FT-IR.The mass loss of the PVA occurred in two stages: The first mass loss around100-150°C was attributable to the loss of water molecules and the second mass loss around 250-350°C owing to the thermal degradation of the PVA backbone [12,13].In the PAMPS, the decomposition temperature occurred at 100°C due to moisture loss, and around 300°C was the decomposition of sulfonate and propenyl groups.Finally, ~380 -430°C was the degradation of the PAMPS backbone [12].In the IONPs, two major mass losses at about 100°C and 200-250°C were observed.At 100°C, it could be attributed to the evaporation of moisture, and the mass of the IONPs becomes gradually decreased until the temperature reaches 380°C.The mass loss around 200 -300°C correspond to the thermal decomposition of oxygen-containing functional groups from the IONPs [21,22].In the degradation curve of PVA/PAMPS/IONP composite, minute mass loss at 100°C due to moisture content, and the mass of the sample gradually decreased to 600°C.The mass loss around 170-200°C,could be attributed to the removal of labile oxygen functional groups from the PVA/PAMPS/IONP nano-composite.The mass loss between 240-400°C, owing to the decomposition of sulfonic acid groups from the PAMPS, and the mass loss after 400°C belongs to the breaking of the polymer backbone.
The addition of IONPs changed the water uptake property of the as prepared nano-composite films, significantly (Table 1)

Figure 4
Figure4shows the Thermo Gravimetric Analysis (TGA) curves of PVA, PAMPS, IONPs and PVA/PAMPS/IONP composite.The mass loss of the PVA occurred in two stages: The first mass loss around100-150°C was attributable to the loss of water molecules and the second mass loss around 250-350°C owing to the thermal degradation of the PVA backbone[12,13].In the PAMPS, the decomposition temperature occurred at 100°C due to moisture loss, and around 300°C was the decomposition of sulfonate and propenyl groups.Finally, ~380 -430°C was the degradation of the PAMPS backbone[12].In the IONPs, two major mass losses at about 100°C and 200-250°C were observed.At 100°C, it could be attributed to the evaporation of moisture, and the mass of the IONPs becomes gradually decreased until the