Search for: glass-transition
Total 39 records
Article Physical Properties and Applications of Polymer Nanocomposites ; 2010 , Pages 743-772 ; 9781845696726 (ISBN) ; Bagheri, R ; Sharif University of Technology
The physical properties including glass transition temperature and permeability behavior of clay-filled epoxies are reviewed in this chapter. There is no consensus in the literature on how nanoclay affects the α-relaxation temperature in epoxy systems. This perhaps rises from the complexity of nanoclay morphology in polymeric resins and the interphase properties since morphology of nanoclay and interphase characteristics are two key parameters to control the glass transition process in epoxy nanocomposites. In addition, the possible existence of several α-transitions in montmorillonite-filled epoxies due to the existence of several relaxation domains may account for the controversial...
Article Construction and Building Materials ; Volume 249 , July , 2020 ; Najafabadi, E. P ; Bazli, M ; Vatani Oskouei, A ; Zhao, X. L ; Sharif University of Technology
Elsevier Ltd 2020
The compressive performance of glass fiber reinforced polymer (GFRP) profiles subjected to elevated temperature was investigated through a large number of (3 0 0) tests. The effects of profile cross-sectional area, slenderness, and temperature on the behavior of the GFRP profiles at temperatures ranging from 25 to 400 °C were determined. It was observed that the compressive strength of the GFRP profiles has been decreased by half as the temperature exceeded 90 °C, i.e., close to the glass transition temperature of the matrix. The temperature and ratio of cross-sectional area to external perimeter were determined as two major parameters affecting section capacity. © 2020 Elsevier Ltd
Article European Polymer Journal ; Volume 43, Issue 3 , 2007 , Pages 782-788 ; 00143057 (ISSN) ; Bagheri, R ; Sharif University of Technology
Polymer-layered silicate nanocomposites have been noticed recently due to their outstanding properties. The mechanical properties and deformation mechanism of epoxy/montmorillonite nanocomposites under compressive and flexural loadings were investigated. A reduction in compressive and flexural yield stress and also glass transition temperature with increasing the amount of organoclay was observed. This change in mechanical behavior of epoxy can be explained with observation of plastic deformation mechanism. The study of deformation mechanism revealed that presence of organoclay accelerates shear yielding in epoxy. Microscopic evaluation illustrated that nanoparticles in this system act as...
Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 81, Issue 6 , Jun , 2010 ; 15393755 (ISSN) ; Jabbari Farouji, S ; Movahed, M. S ; Jafari, G. R ; Rahimi Tabar, M. R ; Sharif University of Technology
The existence of the important similarities between gelation and glass transition makes it hard to distinguish between the two types of nonergodic states experimentally. Here, we report on a stochastic analysis of the scattered light intensity through a colloidal particles suspension during the gel and glass formation. In this analysis, we exploit the methods developed for complex hierarchical systems, such as turbulence. Using the multiplicative log-normal cascade models, we provide a criterion to distinguish gels from glasses
Discovery of novel quaternary bulk metallic glasses using a developed correlation-based neural network approach, Article Computational Materials Science ; Volume 186 , 2021 ; 09270256 (ISSN) ; Gholamipour, R ; Samavatian, V ; Sharif University of Technology
Elsevier B.V 2021
The immense space of composition-processing parameters leads to numerous trial-and-error experimental works for engineering of novel bulk metallic glasses (BMGs). To tackle this challenging problem, it is required to consider specific guidelines which are able to restrict the productive alloying compositions. In this work, a correlation-based neural network (CBNN) approach was developed, based on a dataset of 7950 alloying compositions, to design potential new MGs through prediction of casting ability, reduced glass transition (Trg) and critical thickness (Dmax). This approach involves individual and mutual characteristics of contributory factors to improve the prediction accuracy. To...
Article Journal of Applied Polymer Science ; Volume 119, Issue 4 , August , 2011 , Pages 2039-2047 ; 00218995 (ISSN) ; Farzi, G ; Kalaee, M. R ; Zabihpoor, M ; Sharif University of Technology
Processing conditions and final mechanical properties of polymer nanocomposites are affected by their interfacial layers behavior. However, it is impossible to determine directly the properties of these layers by dynamic rheometry tests. In this work, the interfacial layers properties are evaluated for polystyrene containing silica nanoparticles by the concept of glass-transition temperature shift. The samples were prepared via solution-mixing method and dynamic rheometry was used to determine the viscoelastic behavior of filled polymers in the melt state. This initial step showed that addition of silica particles increased the glass-transition temperature. By preference, decrease in the...
Article Journal of Applied Polymer Science ; Volume 114, Issue 6 , 2009 , Pages 3542-3547 ; 00218995 (ISSN) ; Kheirabadi, M ; Zohuriaan Mehr, M. J ; Kabiri, K ; Sharif University of Technology
Novel polyampholytic superabsorbing nanocomposites based on the zwitterionic sulfobetaine monomer [3-(methacrylamido)propyl)]dimethyl(3- sulfopropyl)ammonium hydroxide were synthesized through in situ polymerization in aqueous solution with different contents of an organo-modified clay (OMMT, Cloisite 30B). Structural and thermomechanical properties of hydrogels were characterized by FT-IR, XRD, and DMTA, respectively. Swollen gel strength of hydrogels was determined by a rheological method. Storage modulus of the hydrogels was considerably improved in comparison with its the clay-free counterpart. The nanocomposite hydrogel containing 15% OMMT possessed the highest gel strength. The glass...
Chemical corrosion and gamma-ray attenuation properties of Zr and Ti containing lead silicate glasses, Article Journal of Nuclear Materials ; Volume 385, Issue 3 , 2009 , Pages 527-532 ; 00223115 (ISSN) ; Raisali, G ; Sadrnezhaad, K ; Alipour, A ; Sharif University of Technology
Lead silicate glasses (LSGs) have high gamma-ray attenuation but low chemical durability properties. In this work, LSGs with (55.5-68.5 wt%) PbO content containing ZrO2 and TiO2 additions were produced. The chemical corrosion of various produced LSGs in 0.5 N HNO3 aqueous solution and determination of their gamma-ray attenuation coefficients for 60Co and 137Cs sources were investigated. The weight loss measurements, the SEM micrographs, the EDS analysis of the sample surfaces and the ICP analysis of solution were used to characterize the dissolution process. The effects of PbO content, ZrO2 and TiO2 additives on chemical corrosion, and also the effect of PbO on gamma-ray attenuation...
Article Materials and Design ; Volume 30, Issue 6 , 2009 , Pages 1976-1984 ; 02641275 (ISSN) ; Khademi, V ; Bagheri, R ; Haddadpour, H ; Kouchakzadeh, M. A ; Farsadi, M ; Sharif University of Technology
Toughness improvement of an epoxy resin and respective hoop wound composite were investigated systematically using amine-terminated butadiene acrylonitrile (ATBN) liquid rubber. Rubber modification improves fracture toughness of epoxy resin with slight reduction in the glass transition temperature (Tg), flexural and compressive properties of resin. Impact resistance of composite is improved by rubber modification similar to modified resin. Interlaminar shear strength (ILSS), compressive modulus and strength, and flexural strength of composite decreased slightly with rubber modification. To interpret the data, the void content of composite samples was determined and the damaged surfaces of...
Article Solar Energy ; Volume 189 , 2019 , Pages 404-411 ; 0038092X (ISSN) ; Heydari, M ; Ahangar, H ; Mohammadi, H ; Taherian Fard, H ; Taghavinia, N ; Samadpour, M ; Tajabadi, F ; Sharif University of Technology
Elsevier Ltd 2019
Carbazole compounds are p-type hole-transporting materials (HTMs) useful for perovskite solar cells (PSCs). In this work, we developed a new class of carbazol based HTMs; non-fused 3-D asymmetric structures (S14 and S12) as HTM of PSCs. To the best of our knowledge, there is no report on non-fused HTMs with a high glass transition temperature (Tg = 165 °C), which reduces crystallization and suppresses grain boundaries in glassy film, resulting in long-term durability. Experimental results show that tuning the carbazole moiety in S14 structure has a constructive influence on geometrical alignment, hole mobility, hydrophobicity, stability as well as efficiency. The resultant power conversion...
Article Industrial and Engineering Chemistry Research ; Volume 54, Issue 36 , August , 2015 , Pages 8954-8962 ; 08885885 (ISSN) ; Shojaei, A ; Bagheri, R ; Sharif University of Technology
American Chemical Society 2015
Thermally oxidized nanodiamond (OND), amine-functionalized ND (AND) and untreated ND (UND) were added to epoxy/TETA at 1 wt % loading. The ND enhanced the dynamic storage modulus of epoxy while decreasing the glass transition temperature because of the increment of free volume in the vicinity of the ND surfaces. The ND induced an acceleration effect on the curing reaction which could be due to functional groups of the ND and lack of any steric hindrance on molecules by the ND particles themselves. The Vyazovkin model-free isoconversional method indicated that all NDs decreased the activation energy; among them, AND showed the lowest value because of the significant promotion of the epoxide...
Article Journal of Non-Crystalline Solids ; 2015 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
In this work, the evolution of the local structure in Cu50-Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the...
Article Polymer - Plastics Technology and Engineering ; Volume 54, Issue 8 , 2015 , Pages 806-813 ; 03602559 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
Taylor and Francis Inc 2015
Nafion membrane encounters many different thermal conditions and mechanical loadings because of its wide range of applications as a proton exchange membrane (PEM). Molecular dynamics simulation of hydrated Nafion at different temperatures is carried out to investigate the alteration of the physical properties of Nafion under uniaxial loading over a wide range of temperatures. According to the simulation results, increase of the temperature reduces the yield stress. The results also show that the polymer chains ordering increases the glass transition temperature and enhances the self-diffusion coefficient of water in hydrated Nafion. Comparisons show that the elastic modulus and viscosity...
Article Journal of Non-Crystalline Solids ; Volume 432 , 2016 , Pages 334-341 ; 00223093 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Elsevier B. V 2016
In this work, the evolution of the local structure in Cu50–Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the...
Effect of temperature on the fracture surface morphology of Ti- and Zr-based bulk metallic glasses: exploring correlation between morphology and plasticity, Article Journal of Materials Science ; Volume 53, Issue 14 , July , 2018 , Pages 10372-10382 ; 00222461 (ISSN) ; Tavakoli, R ; Aashuri, H ; Sharif University of Technology
Springer New York LLC 2018
According to previous studies on the fracture surface morphologies of bulk metallic glasses, the stable crack growth region width and vein pattern size increase with the plasticity at room temperature. In the present work, the fracture surface morphologies of Ti- and Zr-based bulk metallic glasses bent over a wide temperature range (0.1–0.8 glass transition temperature) are systematically analyzed. According to our finding, the stable crack growth region width increases while the vein pattern size decreases as the ductility improves by varying temperature. This observation is in contrast to the common thought that the ductility is proportional to the stable crack growth region width and vein...
Effect of alumina on the performance and characterization of cross-linked PVA/PEG 600 blended membranes for CO2/N2 separation, Article Separation and Purification Technology ; Volume 210 , 2019 , Pages 627-635 ; 13835866 (ISSN) ; Islam, A ; Hamidullah, U ; Jamshaid, F ; Ahmad, A ; Zahid Butt, M. T ; Ijaz, A ; Sharif University of Technology
Elsevier B.V 2019
In this work, poly(vinyl) alcohol (PVA)/poly(ethylene) glycol (PEG) 600 g/mol cross-linked membranes with different alumina (Al2O3) content were synthesized. The membranes were then characterized by FTIR, TGA, DSC, SEM, mechanical strength and permeation properties for carbon dioxide and nitrogen gases at different operating temperatures. The FTIR results confirmed the acetal linkages of cross-linking at 1083 cm−1 and the presence of stretching and bending peaks of Al-O bond at 598 and 444 cm−1, respectively. TGA results showed that the thermal stabilities of the membranes improved with the addition of alumina particles. DSC analysis proved that the glass transition temperature of the...
Synthesis of SBR/PMMA core/shell latices: the role of initiator and surfactant on particle morphology and instability performance, Article Journal of Applied Polymer Science ; Volume 105, Issue 3 , 2007 , Pages 1412-1419 ; 00218995 (ISSN) ; Mohammadi, N ; Bagheri, R ; Sharif University of Technology
Poly(butadiene-stat-styrene)/poly(methylmetacrylate), SBR/PMMA, structural latices were synthesized by using equal moles of different kinds of surfactants: anionic, nonionic, and anionic/nonionic mixture in a two-stage emulsion polymerization. The results indicate that the application of anionic surfactants for the first stage, accompanying sodium persulfate initiator, KPS, for both stages led to core/shell and raspberry morphologies depended upon the hydrophilic lipophilic balance (HLB) of the surfactant. On the other hand, a core/shell structure was observed for structural latices which were synthesized via application of nonionic or anionic/non-ionic mixed surfactants along with...
Preparation of poly (acrylic acid) microgels by alcohol type cross-linkers and a comparison with other cross-linking methods, Article Polymer Bulletin ; 2021 ; 01700839 (ISSN) ; Bouhendi, H ; Keshavarzi, N ; Mahmoudi, M ; Pourjavadi, A ; Ghiass, M ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH 2021
Herein, poly (acrylic acid) (PAA) microgels were synthesized via alcohol type cross-linked by a free radical precipitation polymerization approach. At the first time, 1,6-hexanediol (1–6 diol), trimethylolpropane (TMP), and pentaerythritol (PEN) were selected as multifunctional cross- linking agent to synthesize cross-linked poly(acrylic acid) microgels. Alcohol type cross-linking agents can connect the PAA chains. The cross-linking reaction takes place due to reaction between hydroxyl groups of various cross-linkers and carboxyl groups of PAA chains. All of the hydroxyl groups do not participate in the reaction with acid groups of polymer chains through the polymerization stage; therefore,...
Effect of gamma ray on poly(lactic acid)/poly(vinyl acetate-co-vinyl alcohol) blends as biodegradable food packaging films, Article Radiation Physics and Chemistry ; Vol. 96 , 2014 , pp. 12-18 ; ISSN: 0969806X ; Dadbin, S ; Frounchi, M ; Sharif University of Technology
Poly(lactic acid) (PLA)/poly(vinyl acetate-. co-vinyl alcohol) [P(VAc-. co-VA)] blends as new transparent film packaging materials were prepared at various blend compositions and different vinyl alcohol contents. The blends and pure PLA were irradiated by gamma rays to investigate the extent of changes in the packaging material during gamma ray sterilization process. The miscibility of the blends was dependent on the blend composition and vinyl alcohol content; gamma irradiation had little effect on the extent of miscibility. The glass transition temperature of pure PLA and PLA/P(VAc-. co-VA) miscible blends reduced after irradiation. On the other hand in PLA/P(VAc-. co-VA) immiscible...
Article Tribology Letters ; Volume 41, Issue 2 , October , 2011 , Pages 325-336 ; 10238883 (ISSN) ; Shojaei, A ; Sharif University of Technology
This article deals with the rubber-based friction materials (RBFMs) which can be used in brake system. The physico-mechanical and tribological properties of a series of fiber filled RBFMs containing steel wool and aramid pulp at different concentrations along with a fiber-free reference material were characterized. Rubber-glass transition induced at higher sliding velocities was identified based on the friction fade behavior of the RBFMs. The rubber-glass transition which is inherently originated by viscoelastic response of polymeric binder was found to be influential on the tribological properties of the RBFMs. It was revealed that steel wool increased coefficient of friction (COF) and...