Naser Mohammadi - Academia.edu (original) (raw)

Papers by Naser Mohammadi

Journal of Polymer Science Part B-polymer Physics, 2010

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene-b... more Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene-butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix-particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to αsca ∼ (d/λ)0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 82–88, 2010

Journal of Applied Polymer Science, 2004

The surface tension of thin, uncured epoxy films spun-cast onto oxidized silica wafers was analyz... more The surface tension of thin, uncured epoxy films spun-cast onto oxidized silica wafers was analyzed as a function of their thickness in the range of 5 to 75 nm. Based on contact angle measurements with polar and apolar liquids, the surface free energies of various films were analyzed and compared using Lifshitz–van der Walls/acid–base (LW/AB), harmonic mean (of Wu), geometric mean, and Zisman approaches. Results of harmonic mean and Zisman surface tension analyses, in spite of significant changes in contact angle attributed to changes in thickness, did not show significant changes. However, geometric mean and LW/AB methods did reveal limited changes in free energy of epoxy surface attributed to variations in thickness. The surface tension components showed a similar trend to that of contact angle changes. It seems that it is better to use surface free energy analysis methods, which use several liquids with different polarities, to reveal the accumulative effect of different group free energy densities on total surface free energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1972–1980, 2004

Journal of Applied Polymer Science, 2007

Poly(butadiene-stat-styrene)/poly(methylmetacrylate), SBR/PMMA, structural latices were synthesiz... more 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/nonionic mixed surfactants along with azobisisobutyronitrile, AIBN, and KPS as first and second-stage initiators, respectively. The surface polarity and wettability of the seed particles and finally the tendency of the systems to gain the minimum surface free energy change are the basis for the observed morphologies. On the other hand, the stability of core/shell particles was investigated via incremental addition of an electrolyte, ammonium acetate, at temperature close to the glass transition of PMMA shell, 85°C. The particle size measurement on destabilized samples showed that the core/shell latex only stabilized by anionic surfactant was considerabely microagglomerated with increasing the electrolyte content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Journal of Applied Polymer Science, 2008

The area fraction of tie molecules at the crystal–amorphous interface, amorphous phase dynamics, ... more The area fraction of tie molecules at the crystal–amorphous interface, amorphous phase dynamics, average crystal strength against stem sliding, and crack growth tortuosity concepts have been used simultaneously, for the first time, to develop a model for predicting the environmental stress cracking resistance of semicrystalline polymers. The model is based on the analogy of crack growth through the amorphous phase of semicrystalline polymers in a harsh environment at adhesive polymer–substrate interfaces. The model variable consists of the practical work of crack growth (Gc) times the crack growth path tortuosity (Γ) and correlates very well with the time to failure in the full notch creep test (FNCT) through a sigmoidal-type equation: FNCT = a{1 + exp[(b − GcΓ)/c]}−1, where a (3386), b (0.16), and c (0.006) are constants (r2 = 0.999). Gc is calculated by multiplication of the area fraction of tie molecules at the crystal–amorphous interface, the amorphous phase loss factor value at −25°C, and the sample storage shear modulus at the test temperature, whereas Γ is estimated as the product of the sample molecular weight and its distribution. The application of the Kendall rank correlation coefficient test as a primitive gross criterion of comparison among the proposed correlations also shows reasonable values of the rank correlation coefficient (0.891) and probability (0.000) for the new model. In other words, a point-to-point increasing or descending trend among the experimentally found data is ignored in comparison with the sound physical basis of the correlation toward the development of a comprehensive model. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polymer International, 2008

BACKGROUND: In the electrospinning process, through subjecting a pendent drop of a polymer soluti... more BACKGROUND: In the electrospinning process, through subjecting a pendent drop of a polymer solution to a high electric field, a fluid jet is ejected from the drop. To have a stable process, the rate at which the fluid is forced into the drop and the rate at which the fluid is carried away by the jet must be equal. A method is reported to find the point at which the flow into the drop is equal to the flow out of the drop.RESULTS: In the electrospinning of polyacrylonitrile solutions, by applying different voltages at a constant solution feed rate, two jet regimes were observed: stable jet and fluctuating jet regimes. The stable jet regime occurred at low voltages where the jet flow rate was lower than the feed rate, and the fluctuating jet regime occurred at higher voltages where the jet flow rate exceeded the feed rate. The highest voltage in the stable jet regime was the point where the jet flow rate was equal to the feed rate. This point was determined for different feed rates.CONCLUSION: By applying various voltages at different feed rates, and investigating the jet current, a curve showing stable processing points can be obtained. Copyright © 2008 Society of Chemical Industry

Thermochimica Acta, 2005

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4 -diacetoxybiphenyl and... more The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4 -diacetoxybiphenyl and sebacic acid in presence of a mixture 75:25 of diglycidyl terephthalate and triglycidyl trimellitic acid ester (D&TGE), as a curing agent, was studied by non-isothermal differential scanning calorimetry (DSC). The analysis of non-isothermal data was carried out using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, have been calculated by the Friedman technique. It shows a constant value of 95.5 ± 2.5 kJ/mol, in the 0.27 < α < 0.68 range. The activation energy, out of the above-mentioned interval, is strongly dependent on the degree of extent of the curing reaction.

Composites Science and Technology, 2010

This novel research aims to develop, for the first time, microcellular polyethylene fiber-reinfor... more This novel research aims to develop, for the first time, microcellular polyethylene fiber-reinforced polyethylene (PE/PE) clay containing nano-composites during a solid-state microcellular foaming process using supercritical nitrogen (scN 2 ) as a foaming agent. Results show that by employing clay nanoparticles in the matrix, expansion ratio of the microcellular processed composites enhance, because of the nucleating effect of nanoparticles. Microcellular nano-homocomposite has an average cell size of 0.5 lm. Trans-crystalline layer of composites with a length of about 3 lm; remain intact during the foaming process but the bulk matrix crystalline structure alters to a more oriented ''quasi-fibrillar" structure after foaming. Microcell growth in the amorphous interlamellar regions exerts a tension on the neighboring lamellas which cause some orientation on them. The DSC studies show the emerging of new crystalline sectors with a lower melting point which affirms the creation of a less perfect crystalline morphology due to cell wall movements during cell growth step and subsequent stabilization period of the cells.

Colloid and Polymer Science, 2004

The morphology of a quaternary blend containing a diglycidyl ether of bisphenol-A (DGEBA), a ther... more The morphology of a quaternary blend containing a diglycidyl ether of bisphenol-A (DGEBA), a thermoplastic modifier (PMMA), a phase-separating curing agent (diaminodiphenylmethane, DDM), and a non-phase-separating curing agent (methylenebis(3-chloro-2,6-diethylaniline, MCDEA) was studied as a function of volume fraction of the thermoplastic modifier and fractional concentration of the curing agents in their mixture. It was found that using mixtures of curing agents a co-continuous morphology could be obtained at PMMA concentrations as low as 2.5 volume percent. Using FTIR spectroscopy it was proved that specific interactions are present between PMMA and individual amine curing agents. On the other hand, there was no detectable specific interaction between PMMA and DGEBA. By analyzing the micro-indentation hardness data of the cryo-fractured samples and putting forward the “intrinsic hardness” concept, it was proposed that the co-continuous morphology is inherently more effective than the other morphologies in changing the mechanical properties of the above-mentioned multi-component blends.

T he structure-property relationships in segmented-chain liquid crystalline polyesters based upon... more T he structure-property relationships in segmented-chain liquid crystalline polyesters based upon diphenols and aliphatic dibasic acid chloride was studied by differential scanning calorimetry and polarizing optical microscopy. Two mesogenic monomers were synthesized by direct esterification of hydroquinone with p-hydroxybenzoic acid in a convenient method. The well-characterized mesogenic monomers incorporated into segmented liquid crystalline polyesters with short linear chain and COOH-end groups. The structure of the monomers and the polymers was studied by FTIR, 1 H NMR, MS. The temperature of transition between the phases and, as a consequence, the range of mesomorphism is highly dependent upon the molecular weight of the polyesters and the length of the mesogenic monomers.

Progress in Organic Coatings, 2004

Marangoni-Benard convection of three evaporating solvents, which are conventionally used in paint... more Marangoni-Benard convection of three evaporating solvents, which are conventionally used in paint industry, was investigated. The effect of vaporization, surface tension, and temperature gradients through the film layer according to new modified Marangoni number is discussed. Their surface patterns and its differences were studied. In xylene and MEK completely different planforms were observed, but regular and spreaded patterns could not be obtained with MiBK. Surface patterns and their relationship with coating film defects, such as orange peel, Benard cells, floating, flooding, picture framing, craters and so on are discussed. Effects of three surface-active agents normally referred in the coating technology as flow modifier or antifloating agent on surface pattern formation, in the pure solvents were also investigated. All of the three surface-active agents stopped the convection flow in the xylene layer, but interestingly none of them could affect on the convection flow in MEK layer.

Polymer, 2003

A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell p... more A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell particles dispersed in a good solvent for the shell was wet spun into a coagulation bath at room temperature. The SEM micrographs of as spun fibers showed various surface topographies and fiber diameters, ranging from 4.2 up to 20 mm depend upon the draw ratio. The osmium tetroxide stained cross-section of fibers observed by transmission electron microscope (TEM), indicated a heterogeneous morphology consisting of dark cores and fairly light shells, which is a result of self-stratification to an overall core/shell morphology in fiber cross-section. The inner core consisted of higher concentration of copolymers with double bonds, while the outer shell is made mainly of ungrafted PMMA chains. The equilibrium thermodynamic analysis based on minimization of surface free energy predicts a predominant core/shell structure which the SBR chains are encapsulated mainly by ungrafted PMMA homopolymers and SBR-g-PMMA copolymers which agrees quite well with the observed morphology. q

Journal of Adhesion Science and Technology, 2007

Measured adhesion energies of low-density polyethylene (LDPE) to thermoplastic starch (TPS) joint... more Measured adhesion energies of low-density polyethylene (LDPE) to thermoplastic starch (TPS) joint and of joints in presence of poly(ethylene-co-vinyl acetate) (EVA), polyethylene grafted with maleic anhydride (PE-g-MAH) and styrene-ethylene-butadiene-styrene grafted with maleic anhydride (SEBS-g-MAH) compatibilizers were investigated. The compatibilizers were introduced to the interface via their pre-mixing with the adherend (PE) or adhesive (TPS). The results showed adhesion energy improvement from 41 J/m2 for PE/TPS to 118, 151 and 272 J/m2 by adding 3.3 wt% of EVA, SEBS-g-MAH and PE-g-MAH to the PE adherend, respectively. On the other hand, by raising the compatibilizers to 5.75 wt%, similar joint adhesion energies of about 250 J/m2 were found for all studied systems. The measured adhesion energy increments were attributed to the migration of the compatibilizers to the interface during high temperature joint preparation. In addition, the observed efficacies of various compatibilizers were ascribed to their interfacial stress transfer capabilities. Joint viscoelastic function, i.e., joint adhesion energy divided by its thermodynamic work of adhesion, showed similar dependence on adherend tan δ divided by the adhesive tan δ (A) divided by the compatibilizer tan δ as the measured adhesion energy. This interesting finding supports the hypothesis that the main viscoelastic loss effects in joints with stiff adherends are localized in the interphase adjacent to the crack tip.

Journal of Cellular Plastics, 2010

This article discusses the development of microcellular HDPE and HDPE-clay nanocomposites via a b... more This article discusses the development of microcellular HDPE and HDPE-clay nanocomposites via a batch high temperature process using supercritical N 2 . The study incorporates the effects of clay content and nanocomposite microstructure on the foaming process performance and cellular morphology under investigation. It was possible to produce much nucleated and more expanded microcellular foams with the nanocomposites than with the pure HDPE, as over 14 vol% void fraction could be reached at 6 wt% clay containing nanocomposite as a good result for foaming by N 2 gas via a batch foaming process. We found that the state of nanoparticle dispersion affects the microcellular morphology, so a better dispersed nanocomposite results in a more nucleated system in the microcellular foaming process. Moreover, the relationship between crystalline morphology and cell structure was investigated. Crystallinity and melting point were the important parameters for controlling the cell growth mechanism in this foaming method.

Progress in Organic Coatings, 2004

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and... more The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2004

The contact angle of thin-uncured epoxy films spin casted on oxidized silica wafers has been inve... more The contact angle of thin-uncured epoxy films spin casted on oxidized silica wafers has been investigated as a function of their thickness in the range of 5-75 nm. Based on the contact angle measurements with polar and apolar liquids, the surface free energy of various films were analyzed and compared using Lifshitz van der Walls/acid-base and harmonic mean (Wu's) approaches. The results show that the nature of the surface of epoxy films change to more hydrophobic state as its thickness increases. Furthermore, time monitoring of the contact angle of the surface of epoxy films reveals a more rapid conformational change or flip-flop of surface epoxy chains for thicker layers.

Journal of Applied Polymer Science, 2009

The work focused on the elucidation of several key parameters in toughening poly(vinyl chloride) ... more The work focused on the elucidation of several key parameters in toughening poly(vinyl chloride) (PVC) by the methyl methacrylate–butadiene–styrene (MBS) core-shell particles. Accordingly, blends containing various weight percent of the MBS particles were prepared and characterized by dilute solution viscometry, dynamic light scattering, dynamic mechanical thermal analysis, transmission electron microscopy, and temperature variable impact test. The results showed PVC/MBS solution miscibility in almost all compositions with their maximum thermodynamic affinities at about 17 and 67 wt % of MBS in tetrahydrofurane (THF). In addition, MBS weight percent increase in its blend with the PVC above 10 led to severe impact energy raise with eventual leveling at about 17 wt %. Furthermore, blend toughness and its components miscibility in solution increased in parallel up to 20 wt % of MBS particles. On the other hand, blend toughness declined with test temperature decrease toward impact modifier core Tg at about −30°C even for the sample with 20 wt % of the MBS particles. Finally, the brittle-ductile transition of the blend containing 20 wt % of the MBS particles comparison with its matrix tan δ-temperature correlation implied 2500 J/m impact energy equivalence with 90°C sample temperature rise in secondary relaxation activation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

T he effect of two important parameters of film blowing process, i.e., take-up ratio and blow-up ... more T he effect of two important parameters of film blowing process, i.e., take-up ratio and blow-up ratio, on the overall orientation of low-density blown films have been investigated using birefringence measurements. Furthermore, by combining X-ray diffraction pole figure analysis and birefringence, the White and Spruiell biaxial orientation functions have been determined for afformentioned sample. Within the range of processing condition studied, increasing take-up ratio, increases orientation in both machine and transverse direction. Upon increasing blow-up ratio, orientation in the transverse direction increases and the overall orientation state approaches to equal biaxial one. Characterization of the crystalline regions by pole figure analysis reveals that a and b crystallographic axes preferentially orientate in the film plane and the direction normal to it, respectively. The amorphous regions do not have any preferential orientation.

Polymer, 2005

The effect of styrene content on non-exponential and non-Arrhenius behavior of the a-relaxation o... more The effect of styrene content on non-exponential and non-Arrhenius behavior of the a-relaxation of cured unsaturated polyester resins (UPR) was investigated by dynamic mechanical analysis (DMA). To compare the temperature dependence of the relaxation times, the Angell fragility concept was applied to samples with different crosslink densities. Furthermore, the number of structural units per cooperatively rearranging region (CRR) was estimated using random walk model and the modified Adam-Gibbs theory. The results showed that rising styrene content enhanced the crosslink density of the networks, which altered the intensity and broadness of the a-relaxation. The fragility index, a measure of temperature dependence of relaxation time, and the average size of CRR at glass transition region was also increased by styrene content. Therefore, the segmental relaxation in networks with higher crosslink density could be associated with stronger intermolecular coupling. In addition, it was observed that the mean required energy for internal rearrangement of structural units within the CRR decreased as the fragility index increased, while the mean barrier height for repositioning of a CRR in cooperation to its local environment was nearly constant. q Polymer 46 9088-9096 www.elsevier.com/locate/polymer 0032-3861/$ -see front matter q

Progress in Organic Coatings, 2005

Tensile strength and scratch resistance of an acrylic-melamine clear coat were evaluated at room ... more Tensile strength and scratch resistance of an acrylic-melamine clear coat were evaluated at room temperature and various test speeds. The basic fracture property, tensile strength, was measured on free films while the applied property, scratch resistance, was characterized on glass-supported thin film by a homemade instrument under different applied loads. The results showed similar trends for the reciprocal of scratch

Journal of Polymer Science Part B-polymer Physics, 2010

Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene-b... more Glass transition characteristics and mechanical wave attenuation of the neat and filled styrene-butadiene rubber (SBR) containing 10 wt % of rigid monosize polystyrene particles of various diameters from several hundred microns down to several tens of nanometers were investigated by dynamic mechanical thermal analysis, impedance tube, and ultrasonic spectroscopy. The results showed the matrix damping capacity and the breadth of glass transition increase by reducing the size of rigid particles due to the matrix-particles interfacial area increase as the major governing parameter. Matrix glass transition broadening toward higher temperatures was attributed to the increased dynamic heterogeneity induced by fillers, whereas the damping capacity increase was assigned to contribution of interfacial friction loss mechanism. The proposed postulation was confirmed based on the calculated temperature distribution of the relaxing matrix volume fraction. Sound wave attenuation by the matrix and PS particles filled systems led to a broad absorption peak for the former and appearance of a secondary absorption peak at lower frequencies for the latter. Intensity of this secondary peak was highest for the system containing PS nanoparticles. Finally, ultrasonic attenuation enhanced by the PS particle size to wavelength ratio increase according to αsca ∼ (d/λ)0.38 scaling law and declined by replacing the dense particles with larger hollow PS particles. Comparison of the normalized attenuation of the PS particle filled SBR in various mechanical wave attenuation regimes implied low sensitivity to particle size in vibration, mild differentiation in the sound, and finally severe differentiation in the ultrasound regimes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 82–88, 2010

Journal of Applied Polymer Science, 2004

The surface tension of thin, uncured epoxy films spun-cast onto oxidized silica wafers was analyz... more The surface tension of thin, uncured epoxy films spun-cast onto oxidized silica wafers was analyzed as a function of their thickness in the range of 5 to 75 nm. Based on contact angle measurements with polar and apolar liquids, the surface free energies of various films were analyzed and compared using Lifshitz–van der Walls/acid–base (LW/AB), harmonic mean (of Wu), geometric mean, and Zisman approaches. Results of harmonic mean and Zisman surface tension analyses, in spite of significant changes in contact angle attributed to changes in thickness, did not show significant changes. However, geometric mean and LW/AB methods did reveal limited changes in free energy of epoxy surface attributed to variations in thickness. The surface tension components showed a similar trend to that of contact angle changes. It seems that it is better to use surface free energy analysis methods, which use several liquids with different polarities, to reveal the accumulative effect of different group free energy densities on total surface free energy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1972–1980, 2004

Journal of Applied Polymer Science, 2007

Poly(butadiene-stat-styrene)/poly(methylmetacrylate), SBR/PMMA, structural latices were synthesiz... more 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/nonionic mixed surfactants along with azobisisobutyronitrile, AIBN, and KPS as first and second-stage initiators, respectively. The surface polarity and wettability of the seed particles and finally the tendency of the systems to gain the minimum surface free energy change are the basis for the observed morphologies. On the other hand, the stability of core/shell particles was investigated via incremental addition of an electrolyte, ammonium acetate, at temperature close to the glass transition of PMMA shell, 85°C. The particle size measurement on destabilized samples showed that the core/shell latex only stabilized by anionic surfactant was considerabely microagglomerated with increasing the electrolyte content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Journal of Applied Polymer Science, 2008

The area fraction of tie molecules at the crystal–amorphous interface, amorphous phase dynamics, ... more The area fraction of tie molecules at the crystal–amorphous interface, amorphous phase dynamics, average crystal strength against stem sliding, and crack growth tortuosity concepts have been used simultaneously, for the first time, to develop a model for predicting the environmental stress cracking resistance of semicrystalline polymers. The model is based on the analogy of crack growth through the amorphous phase of semicrystalline polymers in a harsh environment at adhesive polymer–substrate interfaces. The model variable consists of the practical work of crack growth (Gc) times the crack growth path tortuosity (Γ) and correlates very well with the time to failure in the full notch creep test (FNCT) through a sigmoidal-type equation: FNCT = a{1 + exp[(b − GcΓ)/c]}−1, where a (3386), b (0.16), and c (0.006) are constants (r2 = 0.999). Gc is calculated by multiplication of the area fraction of tie molecules at the crystal–amorphous interface, the amorphous phase loss factor value at −25°C, and the sample storage shear modulus at the test temperature, whereas Γ is estimated as the product of the sample molecular weight and its distribution. The application of the Kendall rank correlation coefficient test as a primitive gross criterion of comparison among the proposed correlations also shows reasonable values of the rank correlation coefficient (0.891) and probability (0.000) for the new model. In other words, a point-to-point increasing or descending trend among the experimentally found data is ignored in comparison with the sound physical basis of the correlation toward the development of a comprehensive model. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polymer International, 2008

BACKGROUND: In the electrospinning process, through subjecting a pendent drop of a polymer soluti... more BACKGROUND: In the electrospinning process, through subjecting a pendent drop of a polymer solution to a high electric field, a fluid jet is ejected from the drop. To have a stable process, the rate at which the fluid is forced into the drop and the rate at which the fluid is carried away by the jet must be equal. A method is reported to find the point at which the flow into the drop is equal to the flow out of the drop.RESULTS: In the electrospinning of polyacrylonitrile solutions, by applying different voltages at a constant solution feed rate, two jet regimes were observed: stable jet and fluctuating jet regimes. The stable jet regime occurred at low voltages where the jet flow rate was lower than the feed rate, and the fluctuating jet regime occurred at higher voltages where the jet flow rate exceeded the feed rate. The highest voltage in the stable jet regime was the point where the jet flow rate was equal to the feed rate. This point was determined for different feed rates.CONCLUSION: By applying various voltages at different feed rates, and investigating the jet current, a curve showing stable processing points can be obtained. Copyright © 2008 Society of Chemical Industry

Thermochimica Acta, 2005

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4 -diacetoxybiphenyl and... more The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4 -diacetoxybiphenyl and sebacic acid in presence of a mixture 75:25 of diglycidyl terephthalate and triglycidyl trimellitic acid ester (D&TGE), as a curing agent, was studied by non-isothermal differential scanning calorimetry (DSC). The analysis of non-isothermal data was carried out using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, have been calculated by the Friedman technique. It shows a constant value of 95.5 ± 2.5 kJ/mol, in the 0.27 < α < 0.68 range. The activation energy, out of the above-mentioned interval, is strongly dependent on the degree of extent of the curing reaction.

Composites Science and Technology, 2010

This novel research aims to develop, for the first time, microcellular polyethylene fiber-reinfor... more This novel research aims to develop, for the first time, microcellular polyethylene fiber-reinforced polyethylene (PE/PE) clay containing nano-composites during a solid-state microcellular foaming process using supercritical nitrogen (scN 2 ) as a foaming agent. Results show that by employing clay nanoparticles in the matrix, expansion ratio of the microcellular processed composites enhance, because of the nucleating effect of nanoparticles. Microcellular nano-homocomposite has an average cell size of 0.5 lm. Trans-crystalline layer of composites with a length of about 3 lm; remain intact during the foaming process but the bulk matrix crystalline structure alters to a more oriented ''quasi-fibrillar" structure after foaming. Microcell growth in the amorphous interlamellar regions exerts a tension on the neighboring lamellas which cause some orientation on them. The DSC studies show the emerging of new crystalline sectors with a lower melting point which affirms the creation of a less perfect crystalline morphology due to cell wall movements during cell growth step and subsequent stabilization period of the cells.

Colloid and Polymer Science, 2004

The morphology of a quaternary blend containing a diglycidyl ether of bisphenol-A (DGEBA), a ther... more The morphology of a quaternary blend containing a diglycidyl ether of bisphenol-A (DGEBA), a thermoplastic modifier (PMMA), a phase-separating curing agent (diaminodiphenylmethane, DDM), and a non-phase-separating curing agent (methylenebis(3-chloro-2,6-diethylaniline, MCDEA) was studied as a function of volume fraction of the thermoplastic modifier and fractional concentration of the curing agents in their mixture. It was found that using mixtures of curing agents a co-continuous morphology could be obtained at PMMA concentrations as low as 2.5 volume percent. Using FTIR spectroscopy it was proved that specific interactions are present between PMMA and individual amine curing agents. On the other hand, there was no detectable specific interaction between PMMA and DGEBA. By analyzing the micro-indentation hardness data of the cryo-fractured samples and putting forward the “intrinsic hardness” concept, it was proposed that the co-continuous morphology is inherently more effective than the other morphologies in changing the mechanical properties of the above-mentioned multi-component blends.

T he structure-property relationships in segmented-chain liquid crystalline polyesters based upon... more T he structure-property relationships in segmented-chain liquid crystalline polyesters based upon diphenols and aliphatic dibasic acid chloride was studied by differential scanning calorimetry and polarizing optical microscopy. Two mesogenic monomers were synthesized by direct esterification of hydroquinone with p-hydroxybenzoic acid in a convenient method. The well-characterized mesogenic monomers incorporated into segmented liquid crystalline polyesters with short linear chain and COOH-end groups. The structure of the monomers and the polymers was studied by FTIR, 1 H NMR, MS. The temperature of transition between the phases and, as a consequence, the range of mesomorphism is highly dependent upon the molecular weight of the polyesters and the length of the mesogenic monomers.

Progress in Organic Coatings, 2004

Marangoni-Benard convection of three evaporating solvents, which are conventionally used in paint... more Marangoni-Benard convection of three evaporating solvents, which are conventionally used in paint industry, was investigated. The effect of vaporization, surface tension, and temperature gradients through the film layer according to new modified Marangoni number is discussed. Their surface patterns and its differences were studied. In xylene and MEK completely different planforms were observed, but regular and spreaded patterns could not be obtained with MiBK. Surface patterns and their relationship with coating film defects, such as orange peel, Benard cells, floating, flooding, picture framing, craters and so on are discussed. Effects of three surface-active agents normally referred in the coating technology as flow modifier or antifloating agent on surface pattern formation, in the pure solvents were also investigated. All of the three surface-active agents stopped the convection flow in the xylene layer, but interestingly none of them could affect on the convection flow in MEK layer.

Polymer, 2003

A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell p... more A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell particles dispersed in a good solvent for the shell was wet spun into a coagulation bath at room temperature. The SEM micrographs of as spun fibers showed various surface topographies and fiber diameters, ranging from 4.2 up to 20 mm depend upon the draw ratio. The osmium tetroxide stained cross-section of fibers observed by transmission electron microscope (TEM), indicated a heterogeneous morphology consisting of dark cores and fairly light shells, which is a result of self-stratification to an overall core/shell morphology in fiber cross-section. The inner core consisted of higher concentration of copolymers with double bonds, while the outer shell is made mainly of ungrafted PMMA chains. The equilibrium thermodynamic analysis based on minimization of surface free energy predicts a predominant core/shell structure which the SBR chains are encapsulated mainly by ungrafted PMMA homopolymers and SBR-g-PMMA copolymers which agrees quite well with the observed morphology. q

Journal of Adhesion Science and Technology, 2007

Measured adhesion energies of low-density polyethylene (LDPE) to thermoplastic starch (TPS) joint... more Measured adhesion energies of low-density polyethylene (LDPE) to thermoplastic starch (TPS) joint and of joints in presence of poly(ethylene-co-vinyl acetate) (EVA), polyethylene grafted with maleic anhydride (PE-g-MAH) and styrene-ethylene-butadiene-styrene grafted with maleic anhydride (SEBS-g-MAH) compatibilizers were investigated. The compatibilizers were introduced to the interface via their pre-mixing with the adherend (PE) or adhesive (TPS). The results showed adhesion energy improvement from 41 J/m2 for PE/TPS to 118, 151 and 272 J/m2 by adding 3.3 wt% of EVA, SEBS-g-MAH and PE-g-MAH to the PE adherend, respectively. On the other hand, by raising the compatibilizers to 5.75 wt%, similar joint adhesion energies of about 250 J/m2 were found for all studied systems. The measured adhesion energy increments were attributed to the migration of the compatibilizers to the interface during high temperature joint preparation. In addition, the observed efficacies of various compatibilizers were ascribed to their interfacial stress transfer capabilities. Joint viscoelastic function, i.e., joint adhesion energy divided by its thermodynamic work of adhesion, showed similar dependence on adherend tan δ divided by the adhesive tan δ (A) divided by the compatibilizer tan δ as the measured adhesion energy. This interesting finding supports the hypothesis that the main viscoelastic loss effects in joints with stiff adherends are localized in the interphase adjacent to the crack tip.

Journal of Cellular Plastics, 2010

This article discusses the development of microcellular HDPE and HDPE-clay nanocomposites via a b... more This article discusses the development of microcellular HDPE and HDPE-clay nanocomposites via a batch high temperature process using supercritical N 2 . The study incorporates the effects of clay content and nanocomposite microstructure on the foaming process performance and cellular morphology under investigation. It was possible to produce much nucleated and more expanded microcellular foams with the nanocomposites than with the pure HDPE, as over 14 vol% void fraction could be reached at 6 wt% clay containing nanocomposite as a good result for foaming by N 2 gas via a batch foaming process. We found that the state of nanoparticle dispersion affects the microcellular morphology, so a better dispersed nanocomposite results in a more nucleated system in the microcellular foaming process. Moreover, the relationship between crystalline morphology and cell structure was investigated. Crystallinity and melting point were the important parameters for controlling the cell growth mechanism in this foaming method.

Progress in Organic Coatings, 2004

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and... more The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and dodecanedioic acid, as a model resin for powder coatings, in presence of triglycidyl isocyanurate (TGIC), as a curing agent, was studied by isothermal differential scanning calorimetry (DSC). The analysis of isothermal data was performed using the model-free isoconversional method. Activation energy as a function of extent of

Colloids and Surfaces A-physicochemical and Engineering Aspects, 2004

The contact angle of thin-uncured epoxy films spin casted on oxidized silica wafers has been inve... more The contact angle of thin-uncured epoxy films spin casted on oxidized silica wafers has been investigated as a function of their thickness in the range of 5-75 nm. Based on the contact angle measurements with polar and apolar liquids, the surface free energy of various films were analyzed and compared using Lifshitz van der Walls/acid-base and harmonic mean (Wu's) approaches. The results show that the nature of the surface of epoxy films change to more hydrophobic state as its thickness increases. Furthermore, time monitoring of the contact angle of the surface of epoxy films reveals a more rapid conformational change or flip-flop of surface epoxy chains for thicker layers.

Journal of Applied Polymer Science, 2009

The work focused on the elucidation of several key parameters in toughening poly(vinyl chloride) ... more The work focused on the elucidation of several key parameters in toughening poly(vinyl chloride) (PVC) by the methyl methacrylate–butadiene–styrene (MBS) core-shell particles. Accordingly, blends containing various weight percent of the MBS particles were prepared and characterized by dilute solution viscometry, dynamic light scattering, dynamic mechanical thermal analysis, transmission electron microscopy, and temperature variable impact test. The results showed PVC/MBS solution miscibility in almost all compositions with their maximum thermodynamic affinities at about 17 and 67 wt % of MBS in tetrahydrofurane (THF). In addition, MBS weight percent increase in its blend with the PVC above 10 led to severe impact energy raise with eventual leveling at about 17 wt %. Furthermore, blend toughness and its components miscibility in solution increased in parallel up to 20 wt % of MBS particles. On the other hand, blend toughness declined with test temperature decrease toward impact modifier core Tg at about −30°C even for the sample with 20 wt % of the MBS particles. Finally, the brittle-ductile transition of the blend containing 20 wt % of the MBS particles comparison with its matrix tan δ-temperature correlation implied 2500 J/m impact energy equivalence with 90°C sample temperature rise in secondary relaxation activation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

T he effect of two important parameters of film blowing process, i.e., take-up ratio and blow-up ... more T he effect of two important parameters of film blowing process, i.e., take-up ratio and blow-up ratio, on the overall orientation of low-density blown films have been investigated using birefringence measurements. Furthermore, by combining X-ray diffraction pole figure analysis and birefringence, the White and Spruiell biaxial orientation functions have been determined for afformentioned sample. Within the range of processing condition studied, increasing take-up ratio, increases orientation in both machine and transverse direction. Upon increasing blow-up ratio, orientation in the transverse direction increases and the overall orientation state approaches to equal biaxial one. Characterization of the crystalline regions by pole figure analysis reveals that a and b crystallographic axes preferentially orientate in the film plane and the direction normal to it, respectively. The amorphous regions do not have any preferential orientation.

Polymer, 2005

The effect of styrene content on non-exponential and non-Arrhenius behavior of the a-relaxation o... more The effect of styrene content on non-exponential and non-Arrhenius behavior of the a-relaxation of cured unsaturated polyester resins (UPR) was investigated by dynamic mechanical analysis (DMA). To compare the temperature dependence of the relaxation times, the Angell fragility concept was applied to samples with different crosslink densities. Furthermore, the number of structural units per cooperatively rearranging region (CRR) was estimated using random walk model and the modified Adam-Gibbs theory. The results showed that rising styrene content enhanced the crosslink density of the networks, which altered the intensity and broadness of the a-relaxation. The fragility index, a measure of temperature dependence of relaxation time, and the average size of CRR at glass transition region was also increased by styrene content. Therefore, the segmental relaxation in networks with higher crosslink density could be associated with stronger intermolecular coupling. In addition, it was observed that the mean required energy for internal rearrangement of structural units within the CRR decreased as the fragility index increased, while the mean barrier height for repositioning of a CRR in cooperation to its local environment was nearly constant. q Polymer 46 9088-9096 www.elsevier.com/locate/polymer 0032-3861/$ -see front matter q

Progress in Organic Coatings, 2005

Tensile strength and scratch resistance of an acrylic-melamine clear coat were evaluated at room ... more Tensile strength and scratch resistance of an acrylic-melamine clear coat were evaluated at room temperature and various test speeds. The basic fracture property, tensile strength, was measured on free films while the applied property, scratch resistance, was characterized on glass-supported thin film by a homemade instrument under different applied loads. The results showed similar trends for the reciprocal of scratch