ZnSe Nanoparticles were synthesized by solvothermal method and the particle was characterized by Transmission Electron Microscopy. The polymer nanocomposite of 2% and 4% ZnSe/EVA was fabricated by direct sonicator method. The nanocomposites were characterized by UV-Vis-NIR and FT-IR spectroscopy. The thermal behaviour of the samples was also investigated and we found that the thermal stability of the composites increased with increasing the filler concentrations. The mechanical properties such as tensile strength, peel strength and refractive index of the samples were also studied and reported for the first.
Thermoplastics and thermosetting plastics have been found useful for various applications in the field of electronic and electrical technology. Fabrication of nanostructures in polymer matrices has attracted researchers due to the advantages of readily tunable bandgaps, electroactivity, excellent flexibility and good processability compared with conventional materials [
Poly Ethylene-co-Vinyl Acetate (EVA) is a commercial plastic with good low temperature flexibility and toughness. EVA exhibits rubbery property of enhanced elongation along with ease of processability of thermoplastics. Due to its surface gloss and impact strength, EVA copolymers find market in film manufacturing. The presence of vinyl acetate molecules in the polymer chain reduces the polymer regularity and crystallinity. EVA- clay nanocomposites are widely used in the manufacture of wires, cables and also in food packaging industry [
The II-VI semiconducting materials show significant properties from the optoelectronic point of view [
The present work mainly focused on the preparation of nanocomposite film based on EVA with varying ratio of ZnSe particles and studied the effect of ZnSe on the electrical, thermal and mechanical properties of EVA.
The materials such as zinc acetate and sodium selenite used for the preparation of ZnSe nanopowder are Merck GR grade of purity ≥ 98% purity. Zinc acetate of 4.388 g was dissolved in 100 ml of direct Millipore water and 0.519 g of sodium selenite (Na2SeO3) was dissolved in 30 ml of hydrazine hydrate (N2H4∙H2O). Both the prepared solutions were mixed up under vigourous stirring with external heat energy. Then these solutions were transferred into teflon lined sealed stainless steel autoclave and heated at 240˚C for 5 hrs in a muffle furnace. It was washed two times using Millipore water for removing impurities. In essence, stringent symmetry of nanoparticles can be controlled by chemical concentration, reaction temperature and kinetic control.
Ethylene Vinyl Acetate (EVA), copolymer used for the experiment was obtained from Exxon Mobil Chemicals, Singapore. The vinyl acetate content of the copolymer used was 9.4 wt% (Density- 0.931 g/cm3, Melt Flow Index- 2.1 g/10 min @190˚C, 2.16 kg). The copolymer was first dissolved in toluene. Then synthesized ZnSe nanoparticles were dispersed in a sonication bath for 2 hours on the basis of the desired weight fraction (2% and 4%) of ZnSe nanoparticle at room temperature. In order to make the resultant neat nanoparticles filled polymer samples, it was transfered to a teflon coated glass mould and spread with uniform thickness. Afterward, the mixture was heated at 40˚C for 18 hours in an air oven to evaporate the solvent completely and finally, a thin film of pure and ZnSe/EVA nanocomposites formed.
ZnSe nanoparticles were analyzed using Hitachi H7500 TEM where the sample is irradiated with an electron beam of uniform current density with the electron energy of 100 keV. The Fourier transform infrared (FT-IR) spectra of the samples have been carried out in the wave number range 400 - 4000 cm−1 using a Thermo Nicolet Make Avatar 370 FTIR Spectrometer and for signal detection, DTGS detector is used. The refractive indices of the samples were determined using HIOKI 3532 - 50 LCR IMPEDANCE ANALYZER and program version 4.03E was used to record the refractive indices of the samples by varying the frequencies from 100 Hz to 5 MHz. VARIAN CARY 5000 spectrophotometer is used to determine the optical absorption spectrum of the samples and recorded in the region of 200 to 2000 nm. The TGA and DTA analyses of ZnSe/EVA were carried out between 28 and 1300˚C at a heating rate of 20 K/min using the instrument NETSZCH STA 409C. The tensile properties of the virgin EVA and EVA nanocomposites were measured by an Instron 3366 universal testing machine according to ASTM D882. Peel strength was performed using an Instron tensile testing machine at a peel speed of 50 mm/min. Peel test with 180˚ stripping was carried out as per ASTM D 1876. Peel test involves stripping away of substrate joined by the adhesive. The substrates (glass paper, cotton and polyester) were flexible enough to permit a 180˚ turn near the point of loading. Peel strength values are recorded in Newton per millimeter (N/mm) of width of the bonded specimen.
Transmission Electron Microscopy (TEM) is a vital characterization tool for directly imaging nanomaterials to obtain quantitative measures of grain size, size distribution, and morphology. TEM of ZnSe nanoparticles are shown in
The FTIR spectra of the ZnSe/EVA nanocomposites are shown in
The refractive index of EVA/ZnSe has been determined using the measurement of dielectric constant with the help of LCR Impedance analyzer, by Maxwell’s rule [
where εr is the relative permittivity and µr is the relative permeability. µr is 1 for non-magnetic materials. The dielectric constant of the sample is calculated using the relation
?sub>r = Cd/?sub>0A; where the nanocomposite acts as a dielectric with ?sub>0 the absolute permittivity, C is the capacitance, d is the thickness and A is the area (mm2) of the ZnSe/EVA composite. It is reported that EVA posses almost unchangeable index of refraction in entire electromagnetic region. In this study, we investigated the
variation refractive index by varying frequency from 100 Hz to 1 MHz. The results of the variation of refractive index as a function of frequency for samples of different ZnSe nanoparticle concentration dispersed in EVA polymer matrix are shown in
In short, the average index profiles samples could be controlled from 1.52 to 2.28 by homogeneous dispersion of ZnSe nanoparticle in threshold concentration. The index difference of about 0.8 could be achieved easily from pristine matrix. By the inclusion of composites with different refractive indices, multi-layer anti-reflective coating and photovoltaic modules can be effectively modeled.
The UV-Vis-NIR spectra of the ZnSe/EVA nanocomposites are recorded in the region 200 to 2000 nm are sho- wn in
where hν is the photon energy, α is the absorption co-efficient, Eg is the band gap, A is a constant and n = 1 for the direct band gap [
EVA undergoes both physical and chemical changes while heating so that a clear distinctive thermal analysis is
needed. The Thermogravimetric (TG) and Differential Thermal Analysis (DTA) on pure and composite EVA polymer are carried out between room temperature to 500˚C. The TG-DTA traces of pure and doped samples are shown in Figures 7(a)-(c). It seemed nearly same behaviour for three samples with two steps decomposition between 290˚C to 500˚C. It is clear that the Pure EVA is thermally stable up to 298˚C whereas 2% ZnSe and 4% ZnSe doped EVA is stable upto 309˚C and 315˚C respectively. Thus the thermal stability of the EVA nanocomposite increased with increasing the filler concentrations. 28.5% of weight lost in the first stage decomposition of Pure EVA, but once can easily found from the thermogram that the weight loss in the first stage decomposition decreases as filler concentration increases and found to be 17.3% and 14.2% for 2% and 4% ZnSe/EVA respectively.
The virgin EVA samples showed tensile strength in the range of 29 - 31 MPa, with 430% elongation. The effect of nano ZnSe on tensile strength and elongation at break is shown in
The peel strength increases for EVA-ZnSe composites on all substrates on 2% incorporation. The adhesion properties differs, based on the molecular interactions of the adhesive with the adherent.
A facile approach towards the synthesis of ZnSe nanoparticles and ZnSe/EVA nanocomposites was established. The synthesized particle’s size was estimated as 80 nm. FT-IR analysis confirmed the presence of polymetric group of EVA, compared with its composites and corroborated the presence of ZnSe particles. The value of index of refraction of the composite could be easily controlled by varying the amounts of dispersed ZnSe nanoparticles. The band gaps of the pure, 2% and 4% ZnSe/EVA were found to be 4.74 eV, 4.44 eV and 4.08 eV respectively, thereby increasing the conductivity of the EVA with increasing the filler concentrations. The thermal stability of the samples increases with increasing the filler concentrations. The mechanical properties of the samples were also studied. The tensile strength and peel strength of the nanocomposites increase initially and drop down with ZnSe filler loading.
One of the authors is thankful to Department of Science and Technology, New Delhi, India for granting the fund to carry out the research.