UMIST، منچستر، انگلستان
UMIST، منچستر، انگلستان
دانشگاه صنعتی امیرکبیر، تهران، ايران
در سال 1335 در شيراز متولد شد. دوران دبستان و دبيرستان را در خراسان طی کرد و در سال 1353 وارد پلی تکنيک تهران ( دانشگاه صنعتی اميرکبير) شد و در سال 1361 در مهندسی پليمر فارغ التحصيل شد. طی مدت 8سال، به علت سال های اوج خيزش انقلابی مردم مسلمان ايران در مواجهه با رژيم مستبد محمد رضا در قبل از انقلاب و جريانات تسخير لانه جاسوسی و انقلاب فرهنگی پس از پيروزی انقلاب اسلامی، تنها 8 ترم تحصيلی دانشگاه فعاليت داشت. از سال 1363 تا 1369 دوره های کارشناسی ارشد و دکترا مهندسی پليمر را در UMIST انگلستان گذراند و از آن تاريخ تا کنون به عنوان عضو هيات علمی دانشگاه تربيت مدرس فعاليت دارد. هم اکنون به عنوان استاد مهندسی پليمر فعال در زمينه سامانه های نانو کامپوزيتی هوشمند شناخته می شود.
In this work, the effect of volume fraction, thermal, mechanical and interphase properties of nanoparticles on the shape memory behavior of amorphous polymeric nanocomposite was investigated. The proposed novel viscoelastic constitutive modeling with phase transition approach was utilized. A constitutive model for uniaxial tension under thermomechanical loading at small strain was developed. The model predicted 11.48 and 14.46% improvement in shape fixing ratio and 65 and 110.52% enhancement of strain recovery rate for nanocomposites containing 0.2 and 1.2 wt% of multiwalled carbon nanotubes, respectively. The theoretical results were in good accordance with the experimental data.
Smart nanocomposite hydrogels can undergo large deformation under external stimuli. Several coupled physical processes simultaneously affect the transient swelling behaviour of pH and temperature-sensitive hydrogels. Besides, the hydrogel properties change in response to the external stimuli in the presence of nanoparticles, which affect its transient deformation and swelling behaviour. This work focused on transient swelling modeling of pH and temperature-sensitive polymer/clay nanocomposite hydrogels. The time-dependent processes were considered simultaneously with material properties updating in each time-step during the finite element procedure. A set of experiments was designed to evaluate the numerical solving results in the free and
Fabrication and improvement of electromagnetic interference (EMI) shielding products have recently been the subject of intense research. In the present study, the NdFeB magnetic powder was used in prolonged high-energy wet ball milling to synthesize and enhance properties of the magnetic filler of EMI shielding composites. The physicochemical changes induced in particles prepared by the process confirmed that the applied oleic acid surfactant was simply converted into a thin amorphous carbon layer on NdFeB nanoparticles. Increasing the amount of surfactant in the ball milling procedure caused a thicker layer of the carbonaceous blend to be formed on magnetic nanoparticles. We found that the thicker layer of the amorphous carbon covering the
Nitrile-based nanocomposite heat insulators are very attractive materials, due to their higher deformation bearing in special applications such as high temperature and turbulent media, compared to their non-elastomeric counterparts. Ablation behavior of nitrile rubber-based insulators containing silica and silica-clay aerogels was investigated in comparison with those containing fumed silica. An oxyacetylene flame test under a standard condition with a heat flux of 2500 kW m− 2 for 15 s was used for observation of ablation behavior of the samples. The results showed that the incorporation of 15 phr (part per hundred parts of rubber) silica aerogel into the compound decreased the mass of insulator and its linear ablation rate by 15% and 29
To facilitate a single element with the promoted dual sensing and actuation functionality, compared to the conventional individual sensors and actuators, different kinds of piezoelectric structures should be evaluated. Here, finite element method (FEM) simulations together with some aspects of the nanotechnology afforded an opportunity to simplify structure tailoring of the high performance sensor/actuator single element. First, we prepared ultrathin-shell poly (vinylidene fluoride) (PVDF) aligned hollow nanofibers. This geometrically confined nanostructure with low dielectric constant of ∼3.6, efficiently increased strain, yielded to enlarge the piezoelectric voltage by ∼250%, bending actuation by ∼38%, and the β-phase content by ??
In this work, a small diameter tubular vascular graft (inner diameter< 5 mm) was prepared from electrospun polyvinyl alcohol (PVA) containing graphene. Nanofibrous nanocomposite scaffolds showed high porosity with an average pore size of 5–6 nm and exhibited exfoliated morphology. Measurement of the water contact angle of the fibrous nanocomposite scaffold indicated a significant change in hydrophilicity on the addition of hydrophobic additives. To examine further in vitro biocompatibility, endothelial cells were seeded on the flat and tubular nanocomposite scaffolds and cultured over 4 days. The results indicated that the cells could adhere and proliferate well on nanocomposite scaffolds than neat PVA. The 3-(-4, 5-dimethylthiazol)-2, 5-
In this study, we fabricated and characterized nanometric chitosan (Cs)/laponite (La) nanocomposite nanogels for controlled drug delivery applications. Cs and Cs/La nanocomposite nanogels were formed by ionic gelation method using tripolyphosphate. The release of honey as a model drug was monitored using a blood glucose meter. The results of dynamic light scattering and field emission scanning electron microscopy demonstrated that in the wet state, the mean particle size of nanogels were 133 nm and 118 nm for Cs nanogels and Cs/La nanocomposite nanogels, moderately reducing to 32 nm and 95 nm at dried state, respectively. X-ray diffraction analysis confirmed exfoliated morphology for nanocomposite nanogels. Although honey loading increased
Mathematical modeling has increasingly recognized as a powerful tool that could aid the understanding of shape memory behavior in semicrystalline shape memory polymer (SMP). Up to now, studies have not fully taken into account the viscous effect of the amorphous phase in the whole shape memory cycle, which causes a more realistic prediction of the SMP behavior. In this work, a constitutive thermoviscoelastic model was developed to predict the thermomechanical behavior of semicrystalline SMP. The simulated results of the proposed model for a typical uniaxial deformation were compared with the case having no dissipation effect, also with experimental data. The accuracy improvements in the results of the stress–strain trends together with f
Shape memory hydrogels are a class of smart materials with the ability of multiple shape forming. Their low stiffnesses are the main challenge. In this work, pure PAAm and PAAm nanocomposite shape memory hydrogels containing multiwalled carbon nanotubes (MWCNT) were prepared by in-situ radical polymerization. The presence of MWCNT guarantees an enhancement of stiffness and shape recovery of polyacrylamide (PAAm) hydrogel system as well as its recovery speed from temporary to permanent shape of nanocomposite hydrogel under indirect heat stimulation. By examining the electrical conductivity and rheological properties, the corresponding percolation threshold was obtained at 0.2 wt% of MWCNT. The results of dynamic mechanical analysis (DMA) sho
Shape memory nanocomposite hydrogels are intelligent soft materials in which, the nanoparticles can impart desirable mechanical properties to the polymeric matrix. The main challenge is the capability to program from permanent to temporary shapes and vice versa under the direct and indirect thermal stimuli. In this work, carbon nanotubes (CNT) with a high modulus of 1 TPa, was used to mechanically reinforce polyvinyl alcohol (PVA) and polyvinyl alcohol/chitosan (PVA/Cs) hydrogel networks. Adding appropriate amount of conductor component enables the system to be electrically activated, which leads to achieving the original permanent shape without applying mechanical external force. The PVA/Cs/CNT hydrogel containing 0.25 wt% of CNT, sho
High performance, low density and easy preparation are desirable attributes of electromagnetic wave absorption materials. In this study, we prepared graphene flakes containing ellipsoid like magnetic Ni, Fe and NiFe-nano-particles in a one-step electrochemical deposition process. The synthesized nanoparticles presenting a superparamagnetic-like response. The saturation magnetization of the Gr/Ni, Gr/Fe, and Gr/NiFe hybrid nanocomposites was 4.4, 371.7, and 546.8 kA/m, respectively, and a coercivity of 1454, 3500, and 2000 A/m, respectively. The total Electromagnetic shielding of these fabricated composites reached 25, 20, and 18.5 dB, in the X band. In the Gr/NiFe nano-composites, the improvement in microwave screening is due to high satura
The crucial effect of the morphology of nanocomposite aerogel on its effective thermal conductivity caused the presence of comprehensive theoretical investigation. Classic unit cell model provided an analytical relationship between microstructure and thermal conductivity of pristine silica aerogels, but the predicted results showed more than 250% deviation from the experimental results. In this work, the classic unit cell model was modified for nanocomposite aerogel by considering the effect of phonon scattering, secondary porosity, and clay mineral presence. The modified classic unit cell model (MCUM) acted as a powerful tool in the analysis of thermal conductivity mechanism of silica/clay mineral nanocomposite aerogels. Clay mineral was u
Shape memory polymers have promising applications in different fields. In this work, polyvinyl alcohol/multiwall carbon nanotube nanocomposite aerogels were fabricated through supercritical CO 2 drying of electrospun hydrogel counterparts. Mercury porosimetry measurements and scanning electron microscopy results indicated that the nanofibrous aerogel had a high porosity (more than 80%), low density (0.025–0.036 g cm− 3), high surface area (more than 1700 m 2 g− 1) and a pore size less than 100 nm. By incorporating multiwall carbon nanotubes, the density and Young’s modulus of the polyvinyl alcohol/multiwall carbon nanotube nanocomposite aerogel were increased up to 0.03 g cm− 3 and 38 MPa, respectively. A percolation threshold of
In this work, the network formation of reduced graphene oxide (rGO) in comparison with multiwall carbon nanotubes (MWCNTs) in the in-situ biosynthesized bacterial cellulose (BC) matrix-based nanocomposite aerogels was investigated. A modified model was proposedfor predicting the overall broadband dielectric properties (AC conductivity and dielectric permittivity) of BC-based nanocomposite aerogels that had a good agreement with experimental data. Broadband dielectric properties indicated higher percolation values for both BC/MWCNTs (0.7 wt%) and BC/rGO (0.9 wt%) nanocomposite aerogels in comparison to Dynamic mechanical thermal analysis (DMTA) findings. Fractal dimensions of 2.6 and 1.86 were obtained for rGO and MWCNTs networks, respec
Smart nanocomposite aerogels have promising applications. In this work, different percentages of multiwall carbon nanotube (MWCNT) added into synthesized polyurethane (PU) gel in the molten state, using a two‐roll mill. By soaking the PU/MWCNT nanocomposite gel into the water, PU/MWCNT hydrogels containing more than 90 wt % of water were prepared. The obtained hydrogels were freeze‐dried to produce aerogel counterparts. The aerogels were fully characterized using mercury porosimetry, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE‐SEM). The electrical percolation threshold of conductive aerogel system was measured. The shape‐memory behavi
In this work, SiC/C aerogels with a high specific surface area (>1000 m2*g−1) and high porosity (>90%) synthesized through carbothermal reduction of biphenylene-bridged polysilsesquioxane (BP)/clay mineral nanocomposite aerogels. BP/clay mineral nanocomposite aerogels first prepared via sol-gel method followed by supercritical CO2 (ScCO2) drying process, then used to form SiC/C aerogels by intermolecular carbothermal reduction. The exfoliated BP/clay mineral nanocomposite aerogel caused the growth of several millimeters long SiC nanowires (NWs) with a diameter in the range of 30–90 nm on the surface of SiC/C monolith aerogel and worm-like SiC nanostructures in the interior of SiC/C aerogel. Digital microscope, XRD, FE-SEM, FT-IR, TE
A series of high density polyethylene/Cloisite 20A/graphite nanocomposites were prepared via melt blending for production of polymeric pipes for natural gas transfer. The microstructural, mechanical, thermal, electrical and barrier properties of prepared nanocomposites were investigated. An intercalated morphology was observed for prepared nanocomposites. Improved mechanical properties eg over 148% increase in the Young’s modulus were observed by incorporating the nanoparticles to the polyethylene matrix. The thermal analysis showed that the melting point of polyethylene was slightly increased by incorporating both fillers, ie Cloisite 20A and graphite in it and the crystallinity was depended on the type of filler. The results showed that
Hypothesis: Sensitizing the nanocomposite hydrogel systems to multiple stimuli ensures increasing their efficiency from the viewpoint of the magnitude and rate of response of the system. Adding nanosilver to dual stimuli (pH and temperature) responsive chitosan/poly (vinyl alcohol)/nanoclay nanocomposite hydrogel system increases the sensitivity of the chosen system to the third stimulus, ie the electric field, and enhances the overall rate of response of the system. Methods: The reduction of a silver salt to silver nanoparticles was performed by a green synthesis method within the nanocomposite hydrogel system using chitosan as a reducing agent and poly (vinyl alcohol) as a stabilizer. Silver nanoparticle formation was investigated by UV-V
In this work, a thermodynamic‐based equilibrium‐swelling model was proposed to predict the swelling process of neutral/cationic polymers‐clay nanocomposite hydrogels sensitive to dual stimuli temperature and pH. Indeed, the new swelling model can estimate the effect of the rigid clay nanoparticles component on swelling behavior of blend nanocomposite hydrogels. The mixing term in model was developed based on lattice theory by considering the effects of solvent‐polymers, solvent‐clay, and polymer‐clay interaction parameters. The influence of the ionic groups of the clay layers and cationic polymer on the swelling was also taken into account in the proposed model. The model was verified by preparation of polyvinyl alcohol/chitosa
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