فصلنامه مواد پیشرفته و پوشش های نوین
پیاپی 33 (تابستان 1399)

In this experimental study, silver colloidal solution was synthesized using Tollens method. Plasmonic kit was fabricated by drop-coating of silver colloidal solution on glass substrate and finally, detection of tryptophan amino acid was performed using plasmonic kit and surface enhanced Raman spectroscopy. The field emission scanning electron microscopy (FESEM) image shows the most of silver nanoparticles on plasmonic kit have the sizes between from 1400 to 1500 nm. Plasmon peak at around 410 and observation of FCC structure in XRD characterization confirmed the formation of silver nanoparticles. Surface plasmon resonance of silver nanoparticles as well as light scattering from larger agglomerated silver particles enhance the molecular vibrations of tryptophan amino acid. By calibrating the intensity of molecular vibrations in terms of tryptophan amino acid concentration, a quadratic relationship was obtained from which the concentration of the tryptophan amino acid could be determined by measuring SERS spectra. Raman spectroscopy improves the Raman signals of tryptophan amino acid due to the resonance of surface plasmons of silver nanoparticles and the light scattering from larger silver particles. As the tryptophan amino acid concentration decreases, the SERS signals are attenuated by the decrease in the number of molecular vibrations in which rapid and convenient detection of tryptophan amino acid could be performed up to a concentration of 10-7 M using the silver plasmonic substrates. In addition, by calibration, the concentration of the amino acid could be determined using silver plasmonic substrates and Raman spectroscopy, which could lead to the development of nano-sensors.

One of the materials used in the manufacture of sensors is nanocomposites. Nanocomposite components have better properties than other materials due to the surface interaction between the base material and the filler. The aim of this study was to synthesize nanocomposites including graphene and polytechnic as a conductive polymer for use in electrochemical sensors. Electropolymerization method was used to synthesize nanocomposite. Graphene was chosen as the phase and poly catechol phase as a reinforcing phase and this polymer material was distributed on a wide range of graphene. SEM images of synthesized nanocomposites showed that this composition has a very porous morphology consisting of a sheet-like structure. Sodium nitrite and barium sulfate were used for oxidation on the modified electrode surface. The results showed that the electrochemical sensor made in a wide range of concentrations of nitrite has a linear response and can be used for quantitative measurement of these two species. Using calibration curve slope for the two studied species, the detection limit of this electrochemical sensor for nitrite was calculated to be 0.741 μM for nitrite. The results showed that synthesized nano sensor could be used as an anesthetic due to high sensitivity, optimal linear response, acceptable stability and not interference with interference. The use of graphene nanoscopes, which has the most effective properties to reduce electron transfer resistance and increase conductivity at the electrode surface, has been able to provide a very suitable surface with a high surface area for use in nanosized composites.

In this research, a polymer of cellulose acetate butyrate (CAB) was synthesized, which is used as a primer in automotive coating system in order to improvement of drying rate and the ability of applying coating layer immediately. Esterification reaction on α-cellulose was performed using acetic acid, butyric acid, acetic anhydride and butyric anhydride and dichloromethane was used as an isotropic solvent. Results indicated that the efficiency of the final product on performance of primers in the presence of a solvent and useful catalysts depended on time and temperature reaction. The optimum sample obtained at 111 in 180 min by using catalysts (phosphoric acid, sulfuric acid, isopropanol). Results illustrated improvement of physical properties including (brightness, lightness, adherence) and mechanical properties including (impact resistance and bending) in coated film The absorption frequency changes in UV-VIS and IR spectra confirmed the existence of carbonyl functional group in comparison with the blank sample. 

In this research, poly(styrene-spiropyran) photo-responsive polymers were synthesized by free radical polymerization. For this purpose, an acrylate group was substituted on the spiropyran to allow the polymerization by the vinyl group. Different analyses such as nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), UV-vis spectroscopy, and water contact angle analysis were used to characterize and evaluate the properties of the synthesized polymers. The results of NMR and FTIR analyses indicated the successful copolymerization of styrene and spiropyran. The optical properties of the polymers were evaluated in a chloroform solvent. The color of all solutions was changed to purple by UVA irradiation, which subsequently was eliminated by visible light with a wavelength of 590 nm. Contact angle analysis showed that with increasing spiropyran content, the contact angle of coatings increased and the surfaces were more hydrophobic. UV irradiation made the surface hydrophilic. The water contact angle changes during UV irradiation increased with increasing the spiropyran content of the coatings. As a result, the hydrophobic surface became a hydrophilic one. Therefore, photo-responsive coatings were developed using poly(styrene-spiropyran) polymers.

In this work, the fabrication of a broadband MAC with a multilayer structure, prepared by carbon nanotube (CNT), silicon carbide (SiC) and carbonyl iron (CI) particles as fillers, was carried out, in which a hexagonal mesh sized knitted polyester fabric was sandwiched between two layers functioning as the frequency selective surface (FSS). The gradient and alternating multilayer structures were simultaneously employed so that a number of optimum main properties, e.g. cost-efficiency, low density along with high and broad band microwave absorbing properties, could be attained. The impact of a single layer sample possessing one type of filler, a single layer sample possessing various types of fillers and a multilayer sample on the above-mentioned main parameters was also studied. Network analyzer was utilized in 4-18 GHz in order to analyze not only the electromagnetic parameters but also the reflection loss (RL) versus frequency of samples by using the transmission/reflection approach. In comparison with other samples, a return loss value as high as 50.80 dB, absorption band width (RL-5 dB) as high as 14.23 GHz and density of 1.73 gr/cm3 could be achieved by using the multilayer MACs with three layers containing multi fillers (CNT, CI and SiC), with various concentrations, and two FSS film interlayers, possessing a 2mm total thickness. Furthermore, to verify the effect of FSS to improve mechanical properties of samples along its effect on microwave absorbing properties, the mechanical properties of samples containing FSS and without FSS analyzed by a standard tensile test instrument.

Reduced graphene oxide coated with zinc ferrite (ZnFe2O4@rGO) nanocomposite was successfully synthesized by the one-step hydrothermal (HT) and the two-step sol-gel/hydrothermal (SG/HT) methods. The results of SEM and TEM images showed that the graphene oxide sheets for HT and SG/HT syntheses had dimensions of 0.3-0.04 μm and 0.7-0.07 μm, respectively,. According to these images, the size of ZnFe2O4 nanoparticles coted on graphene oxide sheets for HT and SG/HT syntheses were observed at 10-40 nm and 25-70 nm, respectively. Comparison of the optical absorption spectrum of ZnFe2O4@rGO nanocomposites synthesized by HT and SG/HT methods revealed that the amount of band gap energy in SG/HT synthesis was about 7% less than from SG/HT synthesis. According to the results obtained from the Raman spectrum for the synthesized graphene oxide sample, the ID/IG ratio was 0.88,. The results of FTIR spectra demonstrated effective reduction of GO as well as composite formation between rGO plates and ZnFe2O4 nanoparticles for both SG/HT and HT synthesis methods. The results of the magnetic properties of ZnFe2O4@rGO nanocomposites synthesized by HT and SG/HT methods by VSM and magnet with 1 T intensity, states that both methods of synthesis produced superparamagnetic materials,. Based on the results of this study, it can be said that for photothermal therapeutic applications which particle size and uniformity of ZnFe2O4@rGO nanocomposites are important, single-step HT method, and for photocatalytic applications and contrast agent in MRI, which need more photocatalytic and magnetic properties, the two-step SG/HT method can be better choice.

The low strength of epoxy adhesives as well as their non-adhesion to aluminum surfaces have posed a serious challenge to the use of this resin in some special applications, including the aerospace industry. In order to improve tensile strength, two types of rubber acrylonitrile butadiene styrene (ABS) and methacrylate butadiene styrene (MBS) rubber modifiers were used. In order to better adherence of epoxy composites to the aluminum alloy AA2024-T3, the cerium conversion coating was used in optimal conditions. The results of electrochemical impedance spectroscopy and polarization curve showed that the obtained cerium conversion coating at 20 g / l cerium nitrate concentration, pH of 3.5, and 15 min of immersion time, has provided a uniform coating on the surface with the highest corrosion resistance and adhesion properties. Besides, the images of field emission scanning electron microscopy showed the formation of uniform cerium conversion coatings on the sample surface. The results of the stress-strain experiment showed that the addition of 4% of ABS and 1% of GO increased the tensile strength of up to 70% and 47%, respectively. Using conversion coatings resulted in a 60% increase of adhesion properties in the lap shear test. The pull-off test also proved a significant rise in adhesion strength due to the presence of conversion coatings.