Structural and phase separation characterization of poly(lactic acid)/poly(ethylene oxide)/carbon nanotube nanocomposites by rheological examinations

Zare, Yasser,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Composites Part B, Engineering Vol.144 No.-

<P><B>Abstract</B></P> <P>The morphology and phase separation have significant impacts on the properties and applications of polymer blends and nanocomposites. In this study, poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) blends and PLA/PEO/carbon nanotube (CNT) nanocomposites are prepared by solution mixing and the rheological approach is applied to study the morphology and phase separation of the prepared samples. Scanning electron microscopy (SEM) is also used to study the morphology and structure of samples. Additionally, the miscibility or immiscibility between polymer blends was analyzed through Han plots. The results display the lower critical solution temperature (LCST) phase diagram for the prepared samples demonstrating that the enhancement of temperature promotes phase separation. Moreover, the addition of nanoparticles transfers the LCST diagram to high temperatures. The deformation relaxation of PEO droplets commonly diminishes the modulus at very low frequencies, while the formation of big CNT networks in nanocomposites containing high CNT content results in a constant modulus. Han plots also represent the immiscibility in the samples containing 60 and 75 wt% PLA and the nanocomposites including 90 wt% PLA show homogenous structures. The SEM images verify the outputs of rheological tests conducted for the morphology of samples.</P>

Prediction of complex modulus in phase-separated poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites

Zare, Yasser,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Polymer testing Vol.66 No.-

<P><B>Abstract</B></P> <P>This study focuses on the modeling of complex modulus in phase-separated poly (lactic acid) (PLA)/poly (ethylene oxide) (PEO)/carbon nanotubes (CNT) nanocomposites. Palierne model for complex modulus of immiscible blends is developed assuming the significances of CNT and interphase regions. The predictions of developed model are compared to the experimental data from rheological experiment and the predictability of the developed model is studied. Furthermore, the roles of main parameters in the complex modulus of nanocomposites are explained to validate the developed model. The calculations show proper agreements with the experimental data confirming the predictability of the developed model. A higher concentration of continuous matrix and a smaller content of PEO droplets cause thicker and stronger interphase in nanocomposites. High CNT concentration and thin CNT mainly improve the complex modulus. Additionally, both thickness and complex modulus of interphase regions directly control the complex modulus of nanocomposites. This study can afford an insight for researchers to control and optimize the complex modulus in immiscible nanocomposites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Palierne model for complex modulus of immiscible blends is developed for nanocomposites. </LI> <LI> The complex modulus in phase-separated PLA/PEO/CNT nanocomposites is predicted. </LI> <LI> The developed model assumes the significances of CNT and interphase regions. </LI> <LI> The calculations show proper agreements with the experimental data. </LI> <LI> Thickness and stiffness of interphase directly control the complex modulus of samples. </LI> </UL> </P>

Roles of filler dimensions, interphase thickness, waviness, network fraction, and tunneling distance in tunneling conductivity of polymer CNT nanocomposites

Zare, Yasser,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Materials chemistry and physics Vol.206 No.-

<P><B>Abstract</B></P> <P>We present a simple model to express the tunneling conductivity of polymer CNT nanocomposites as a function of the filler dimensions, filler conductivity, interphase thickness, waviness, fraction of networked CNTs, and tunneling distance. This model expresses the percolation threshold and the fraction of networked CNTs in terms of filler dimensions, waviness, and interphase thickness. The model was tested using experimental results from the literature. The predictions show good agreement with the experimental results in all samples, demonstrating the model's robustness for estimating tunneling conductivity. Moreover, the tunneling distance decreases as the filler concentration increases in all samples. The model parameters have a reasonable effect on the tunneling conductivity. The waviness and tunneling distance inversely affect the tunneling conductivity. Further, the waviness weakens the effective length of the nanotubes, and large tunneling distances cannot effectively transfer electrons between two adjacent nanotubes. The interphase thickness directly controls the tunneling conductivity, because a thick interphase reduces the percolation threshold. Poor percolation also creates large and dense conductive networks in nanocomposites, which is desirable for conductivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A simple model for tunneling conductivity of polymer-CNT nanocomposites is suggested. </LI> <LI> Interphase thickness, fraction of networked CNTs, and tunneling distance are assumed. </LI> <LI> The model expresses the percolation threshold and the fraction of networked CNTs. </LI> <LI> The model is tested using experimental results from the literature and parametric analyses. </LI> <LI> The predictions show good agreement with the experimental results in all samples. </LI> </UL> </P>

Association of Sleep Duration and Quality With Health-Related Quality of Life in Fresher University Students

Sharifnezhad Ahmad,Garmabi Maryam,Naderi Fatemeh,Darrudi Fateme,Andishmand Zahra,Gholami Ali 대한수면학회 2023 sleep medicine research Vol.14 No.1

Background and Objective Sleep duration and quality are important factors for health-related quality of life (HRQoL). This study aimed at investigating the association of sleep duration and quality with HRQoL in fresher students of Neyshabur University of Medical Sciences.Methods The study included 471 fresher students. The sleep duration and sleep quality were measured with the Persian version of Pittsburgh Sleep Quality Index (PSQI) and the HRQoL was evaluated with the Persian version of the 12-Item Short Form Survey (SF-12). The data were collected from late September to early October in 2019 and 2020. The multiple linear regression model was used to determine the independent association of sleep duration and quality with HRQoL. A p-value ≤ 0.05 was considered statistically significant.Results The mean age of the participants was 21.8 ± 6.0 years and the majority of them (62.4%) were female. The total HRQoL score and the prevalence of poor sleep quality were 81.6% and 28.0%, respectively. Among the students, 51.8% and 6.4% reported a sleep duration shorter than 7 hours and equal or more than 9 hours, respectively. The multiple linear regression model showed that excessive sleep duration (≥ 9 h) and sleep quality were associated with Mental Component Summary (MCS) and total HRQoL, respectively (p = 0.036, p = 0.018).Conclusions Referring to the results, enough and quality sleep has beneficial effects on HRQoL in students. Therefore, future strategies should be developed to improve sleep and consequently HRQoL among university students.

Variations of tunneling properties in poly (lactic acid) (PLA)/poly (ethylene oxide) (PEO)/carbon nanotubes (CNT) nanocomposites during hydrolytic degradation

Kim, Sanghoon,Zare, Yasser,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Sensors and actuators. A, Physical Vol.274 No.-

<P><B>Abstract</B></P> <P>The combination of poly (lactic acid) (PLA) with water-soluble poly (ethylene oxide) (PEO) and carbon nanotubes (CNT) presents interesting results during hydrolytic degradation. This paper investigates the conductivity of PLA/PEO/CNT nanocomposites during degradation in phosphate-buffered saline (PBS) solution. A simple model is suggested to express the conductivity of samples during degradation by CNT properties, degradation fraction, interphase thickness and tunneling properties. The calculations of developed model are compared to the experimental data and the variations of tunneling resistivity and tunneling distance are explained. Moreover, the parametric examinations are applied to confirm the developed model. The predictions of conductivity acceptably agree with the experimental data during degradation. The degradation reduces the tunneling resistivity and tunneling distance between neighboring CNT, due to the exclusion of polymer matrix. The results demonstrate the positive effects of high degradation fraction, thick interphase, large tunneling diameter, slight tunneling resistivity and short tunneling distance between adjacent CNT on the conductivity of degraded nanocomposites. The current study can provide useful guidelines for analysis of conductivity in nanocomposites during degradation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> This paper studies the conductivity of PLA/PEO/CNT nanocomposites during degradation. </LI> <LI> A simple model is suggested for conductivity of nanocomposites during degradation. </LI> <LI> The degradation fraction, interphase and tunneling properties are considered for modeling. </LI> <LI> The degradation reduces the tunneling resistivity and tunneling distance between CNT. </LI> <LI> The tunneling properties largely manipulate the conductivity of degraded nanocomposites. </LI> </UL> </P>

Effect of Miscibility State on Crystallization Behavior and Polymorphism in Crystalline/ Crystalline Blends of Poly(vinylidene fluoride)/Poly(ethylene oxide)

Mahboube Mohamadi,Hamid Garmabi,Melih Papila 한국고분자학회 2016 Macromolecular Research Vol.24 No.8

Overall crystallization behavior and polymorphism of partially miscible blends of poly(vinylidene fluoride)/ poly(ethylene oxide) (PVDF/PEO) were systematically investigated. The PVDF/PEO blends were prepared from solution in the whole composition range. Isothermal and non-isothermal experiments were carried out using differential scanning calorimetry (DSC). Since the components of the blend crystallize separately due to high difference of the melting points, the changes in melting, crystallization, and equilibrium melting temperatures of PVDF and PEO as well as the degree of crystallization were evaluated. As the binary blends display an asymmetric lower critical solution temperature (LCST)-type phase diagram, the crystallization behavior and kinetics were strongly affected by the miscibility state of the blends in the melt. Particularly, the overall crystallization of PEO was accelerated in the blends with high level of PEO (>50 wt%) by two different mechanisms. The formation of phase separated domains at this composition range enhanced the nucleation ability due to the “spinodal decomposition/ interface assisted crystallization”. Moreover, presence of preexisting crystals of PVDF could act as a substrate for PEO crystallization and increased the crystallization growth rate. Wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) were also utilized to study the crystalline polymorphism of PVDF and PEO in the blends.

A simple model for constant storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes nanocomposites at low frequencies assuming the properties of interphase regions and networks

Zare, Yasser,Rhim, Sungsoo,Garmabi, Hamid,Rhee, Kyong Yop Elsevier 2018 Journal of the mechanical behavior of biomedical m Vol.80 No.-

<P><B>Abstract</B></P> <P>The networks of nanoparticles in nanocomposites cause solid-like behavior demonstrating a constant storage modulus at low frequencies. This study examines the storage modulus of poly (lactic acid)/poly (ethylene oxide)/carbon nanotubes (CNT) nanocomposites. The experimental data of the storage modulus in the plateau regions are obtained by a frequency sweep test. In addition, a simple model is developed to predict the constant storage modulus assuming the properties of the interphase regions and the CNT networks. The model calculations are compared with the experimental results, and the parametric analyses are applied to validate the predictability of the developed model. The calculations properly agree with the experimental data at all polymer and CNT concentrations. Moreover, all parameters acceptably modulate the constant storage modulus. The percentage of the networked CNT, the modulus of networks, and the thickness and modulus of the interphase regions directly govern the storage modulus of nanocomposites. The outputs reveal the important roles of the interphase properties in the storage modulus.</P>

Optimal placement of piezoelectric actuators and sensors on a smart beam and a smart plate using multi-objective genetic algorithm

Nestorovic, Tamara,Trajkov, Miroslav,Garmabi, Seyedmehdi Techno-Press 2015 Smart Structures and Systems, An International Jou Vol.15 No.4

In this paper a method of finding optimal positions for piezoelectric actuators and sensors on different structures is presented. The genetic algorithm and multi-objective genetic algorithm are selected for optimization and $H_{\infty}$ norm is defined as a cost function for the optimization process. To optimize the placement concerning the selected modes simultaneously, the multi-objective genetic algorithm is used. The optimization is investigated for two different structures: a cantilever beam and a simply supported plate. Vibrating structures are controlled in a closed loop with feedback gains, which are obtained using optimal LQ control strategy. Finally, output of a structure with optimized placement is compared with the output of the structure with an arbitrary, non-optimal placement of piezoelectric patches.

Optimal placement of piezoelectric actuators and sensors on a smart beam and a smart plate using multi-objective genetic algorithm

Tamara Nestorović,Miroslav Trajkov,Seyedmehdi Garmabi 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.4

In this paper a method of finding optimal positions for piezoelectric actuators and sensors ondifferent structures is presented. The genetic algorithm and multi-objective genetic algorithm are selected foroptimization and H∞ norm is defined as a cost function for the optimization process. To optimize theplacement concerning the selected modes simultaneously, the multi-objective genetic algorithm is used. Theoptimization is investigated for two different structures: a cantilever beam and a simply supported plate. Vibrating structures are controlled in a closed loop with feedback gains, which are obtained using optimalLQ control strategy. Finally, output of a structure with optimized placement is compared with the output ofthe structure with an arbitrary, non-optimal placement of piezoelectric patches.

Hybrid Layered Silicate/Calcium Carbonate Reinforced Highdensity Polyethylene Nanocomposites: Systematic Morphological Evaluation through Rheological Properties and Response Surface Method

Seyedemad Alavitabari,Mahboube Mohamadi,Hamid Garmabi,Azizeh Javadi 한국섬유공학회 2021 Fibers and polymers Vol.22 No.3

High-density polyethylene (HDPE) based hybrid nanocomposites comprising varying concentrations of layerednanoclay (NC) and spherical nano calcium carbonate (nCaCO3) were prepared by a two-step melt compounding process inthe presence of polyethylene grafted maleic anhydride (PE-g-MA) as the compatibilizer. Regarding multiple materialvariables (the NC, nCaCO3 and compatibilizer contents) participated in fabrication of the nanocomposites, response surfacemethodology (RSM) was utilized to find the correlation between the material variables, morphology and viscoelasticresponses in the melt state. Intercalation of the layered silicates was investigated by X-ray diffraction (XRD) technique, andmorphological characterization of the nanosized calcium carbonates was carried out by scanning electron microscope (SEM). The findings indicated that higher contents of the PE-g-MA facilitated the intercalation process and increased the interlayerdistance. Interestingly, incorporation of the second nanoparticle, nano calcium carbonate, resulted in viscosity incrementwhich is an influential factor on applied stresses during the melt mixing and subsequently, dispersion state of the nanoclaylayers. The interplay between the designated material parameters was also discussed by means of interaction plots.