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    Characterization of reinforcing effect of alumina nanoparticles on the novolac phenolic resin

    , Article Polymer Composites ; Vol. 35, Issue 7 , July , 2014 , pp. 1285-1293 ; ISSN: 02728397 Etemadi, H ; Shojaei, A ; Sharif University of Technology
    Very fine alumina nanoparticles were loaded in novolac type phenolic resin (PF) using solution mixing method. The concentration of nanoalumina in PF was varied between 2.5 to 20 wt%. All the compounds were compression molded and then subjected to scanning electron microscopy (SEM), tensile, flexural, and dynamic mechanical analysis (DMA) tests. SEM analysis showed that the nanoalumina were dispersed uniformly at low concentrations, however, at high concentrations, dispersion was suppressed leading to agglomerates in the composites. Mechanical testing revealed that the nanoalumina had a great influence on the strength and stiffness of PF resin particularly at concentrations below 5 wt%.... 

    Cure kinetic and network structure of NR/SBR composites reinforced by multiwalled carbon nanotube and carbon blacks

    , Article Thermochimica Acta ; Volume 566 , 2013 , Pages 238-248 ; 00406031 (ISSN) Ahmadi, M ; Shojaei, A ; Sharif University of Technology
    Low structure carbon black (CBN330), conductive high structure carbon black (CBXE2B) and carboxylated multiwalled carbon nanotube (MWCNT) were loaded into the blend of natural rubber (NR) and styrene butadiene rubber (SBR) at different contents up to 10 phr. Kraus plots showed that all the reinforcements interact with NR/SBR blend appropriately. However, the CBXE2B whose interfacial area is the highest showed greatest value of Kraus interaction parameter. Flory-Rhener model and effective torque value revealed that all of the reinforcements enhanced the crosslink density, among them CBXE2B showed the highest impact and MWCNT placed in the second rank. It was also shown that the cure kinetic... 

    Experimental and theoretical study on the mechanical properties of novolac phenolic resin nanocomposites: Effects of nanoclay and multiwallwed carbon nanotube

    , Article ECCM 2012 - Composites at Venice, Italy, Proceedings of the 15th European Conference on Composite Materials, 24 June 2012 through 28 June 2012 ; 2012 ; 9788888785332 (ISBN) Jahanmard, P ; Shojaei, A ; Faghihi, M ; Sharif University of Technology
    European Conference on Composite Materials, ECCM  2012
    The present work focused on the characterization of mechanical properties of novolac phenolic resin (PF) filled with two types of clays, including modified and unmodified ones, and multiwalled carbon nanotube (MWCNT). It was found that the solution mixing method is able to disperse the nanoparticles within the PF resin appropriately. It was also shown that the unmodified clay (Closite Na+) has the highest influence on the mechanical properties possibly due to the good level of dispersion as well as the good interfacial interaction. Theoretical analysis based on the rubber elasticity theory showed that the nanoparticles influence the evolution of crosslinking density and network structure  

    Network structure and mechanical properties of polydimethylsiloxane filled with nanodiamond – Effect of degree of silanization of nanodiamond

    , Article Composites Science and Technology ; Volume 142 , 2017 , Pages 227-234 ; 02663538 (ISSN) Hajiali, F ; Shojaei, A ; Sharif University of Technology
    Reinforcement of polydimethylsiloxane (PDMS) was investigated using untreated nanodiamond (uND) and silane functionalized ND (sND) at various degrees of silanization. Scanning electron microscopy revealed an improved dispersion of ND in PDMS by silanization. The incorporation of uND and sNDs enhanced tensile strength up to 45% and 70%, respectively; however, greater improvement was observed for sNDs at very low concentrations, e.g. 0.2 wt%. The much improvement in crosslinking density, analyzed by Flory-Rehner model and Mooney-Rivlin plot, and interfacial interaction, characterized by Kraus and Cunneen-Russell plots, was also observed for sNDs. Interestingly, it was found that the extent of... 

    Kinetics of swelling of cylindrical temperature-responsive hydrogel: a semi-analytical study

    , Article International Journal of Applied Mechanics ; Volume 12, Issue 8 , 2020 Namdar, A. H ; Mazaheri, H ; Sharif University of Technology
    World Scientific  2020
    Cylindrical hydrogels have a wide variety of applications, especially in microfluidics as micro-valves, micro-mixers, and micro-lenses. Main advantages of them can be mentioned as their simple geometry and autonomous functionality due to their responses to the environmental stimuli. In current research, kinetics of swelling, shrinking and force generation of cylindrical temperature-responsive hydrogels have been investigated analytically. According to this, models of fluid permeation and large deformation of the hydrogels were considered and an analytical solution was performed. In order to study the behavior of the cylindrical hydrogels, the temperature is changed between higher and lower... 

    Effect of carbon-based nanoparticles on the cure characteristics and network structure of styrene-butadiene rubber vulcanizate

    , Article Polymer International ; Volume 61, Issue 4 , 2012 , Pages 664-672 ; 09598103 (ISSN) Saatchi, M. M ; Shojaei, A ; Sharif University of Technology
    The network structure of styrene-butadiene rubber (SBR) in the presence of carbon black (CB) with two different structures and multi-walled carbon nanotubes (MWCNTs) was investigated. Swelling behaviour, tensile properties at various strain rates and cure kinetics were characterized. Experimental data were analysed using the Flory-Rehner model as well as the tube model theory. It is found that the network structure of CB-filled SBR follows a three-phase composite model including rigid particles, semi-rigid bound rubber and matrix rubber. This bound rubber is postulated to be critical for the mechanical and deformational properties, development of crosslinking density in matrix rubber and... 

    Preparation of acrylated agarose-based hydrogels and investigation of their application as fertilizing systems

    , Article Journal of Applied Polymer Science ; Volume 122, Issue 4 , November , 2011 , Pages 2424-2432 ; 00218995 (ISSN) Pourjavadi, A ; Sadat Afjeh, S ; Seidi, F ; Salimi, H ; Sharif University of Technology
    In this study, we attempt to synthesize novel acrylated agarose (ACAG)-based hydrogels with three different crosslinking densities. Acrylate groups were inserted onto agarose (AG) backbone through homogeneous reaction of acrylic monomers with AG backbone. Hydrogels were synthesized through radical copolymerization of a mixture of acrylic acid and 2-hydroxyethyl acrylate with ACAG in aqueous solution using ammonium persulfate as an initiator. Infrared spectroscopy (FTIR) was carried out to confirm the chemical structure of the hydrogel. Moreover, morphology of the samples was assessed by scanning electron microscopy. The equilibrium swelling capacities of synthesized hydrogels were evaluated... 

    Vulcanization kinetics and reversion behavior of natural rubber/styrene-butadiene rubber blend filled with nanodiamond - The role of sulfur curing system

    , Article European Polymer Journal ; Volume 81 , 2016 , Pages 98-113 ; 00143057 (ISSN) Rabiei, S ; Shojaei, A ; Sharif University of Technology
    Elsevier Ltd  2016
    The effect of nanodiamond (ND) particles on the network structure and vulcanization kinetics of natural rubber (NR)/styrene-butadiene rubber (SBR) blend vulcanized by three different curing systems, namely conventional (CV), semi-efficient (SEV) and efficient (EV), was investigated. The filler dispersion, crosslink density, curing kinetics and reversion behavior were fully studied. The state of ND dispersion in the rubber matrix was investigated by the field emission scanning electron microscope (FESEM). Swelling experiments and tensile tests exhibited that upon incorporation of ND crosslink density of NR/SBR blend was enhanced significantly due to the large surface area of nano filler... 

    Design, fabrication and characterization of oxidized alginate-gelatin hydrogels for muscle tissue engineering applications

    , Article Journal of Biomaterials Applications ; Volume 31, Issue 1 , 2016 , Pages 152-161 ; 08853282 (ISSN) Baniasadi, H ; Mashayekhan, S ; Fadaoddini, S ; Haghirsharifzamini, Y ; Sharif University of Technology
    SAGE Publications Ltd  2016
    In this study, we reported the preparation of self cross-linked oxidized alginate-gelatin hydrogels for muscle tissue engineering. The effect of oxidation degree (OD) and oxidized alginate/gelatin (OA/GEL) weight ratio were examined and the results showed that in the constant OA/GEL weight ratio, both cross-linking density and Young's modulus enhanced by increasing OD due to increment of aldehyde groups. Furthermore, the degradation rate was increased with increasing OD probably due to decrement in alginate molecular weight during oxidation reaction facilitated degradation of alginate chains. MTT cytotoxicity assays performed on Wharton's Jelly-derived umbilical cord mesenchymal stem cells... 

    Effect of short carbon fiber on thermal, mechanical and tribological behavior of phenolic-based brake friction materials

    , Article Composites Part B: Engineering ; Volume 168 , 2019 , Pages 98-105 ; 13598368 (ISSN) Ahmadijokani, F ; Shojaei, A ; Arjmand, M ; Alaei, Y ; Yan, N ; Sharif University of Technology
    Elsevier Ltd  2019
    The phenolic-based brake friction composites containing 0, 1, 2 and 4 vol% carbon fiber were fabricated in this study. Thermogravimetric analysis (TGA) revealed the adverse impact of carbon fiber on the thermal stability of the composites under air atmosphere. Differential scanning calorimetry (DSC) of the uncured samples indicated the positive impact of carbon fiber on the crosslink density of the phenolic resin. Viscoelastic results drawn from the dynamic-mechanical analysis (DMA) suggested that inclusion of carbon fiber increased the storage modulus and decreased the damping factor of the frictional composites. The tribological behavior of the specimens was assessed with a chase type... 

    Enzymatic outside-in cross-linking enables single-step microcapsule production for high-throughput three-dimensional cell microaggregate formation

    , Article Materials Today Bio ; Volume 6 , 2020 Van Loo, B ; Salehi, S. S ; Henke, S ; Shamloo, A ; Kamperman, T ; Karperien, M ; Leijten, J ; Sharif University of Technology
    Elsevier B.V  2020
    Cell-laden hydrogel microcapsules enable the high-throughput production of cell aggregates, which are relevant for three-dimensional tissue engineering and drug screening applications. However, current microcapsule production strategies are limited by their throughput, multistep protocols, and limited amount of compatible biomaterials. We here present a single-step process for the controlled microfluidic production of single-core microcapsules using enzymatic outside-in cross-linking of tyramine-conjugated polymers. It was hypothesized that a physically, instead of the conventionally explored biochemically, controlled enzymatic cross-linking process would improve the reproducibility,... 

    Physico-mechanical properties and thermal stability of thermoset nanocomposites based on styrene-butadiene rubber/phenolic resin blend

    , Article Materials Science and Engineering A ; Volume 527, Issue 4-5 , 2010 , Pages 917-926 ; 09215093 (ISSN) Shojaei, A ; Faghihi, M ; Sharif University of Technology
    Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30 phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed...