Search for: polyelectrolyte
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    Polyelectrolytes polarization in nonuniform electric fields

    , Article International Journal of Modern Physics C ; Volume 25, Issue 12 , 2014 ; ISSN: 17936586 Farahpour, F ; Ejtehadi, M. R ; Varnik, F ; Sharif University of Technology
    Stretching dynamics of polymers in microfluidics is of particular interest for polymer scientists. As a charged polymer, a polyelectrolyte (PE) can be deformed from its coiled equilibrium configuration to an extended chain by applying uniform or nonuniform electric fields. By means of hybrid lattice Boltzmann (LB)-molecular dynamics (MD) simulations, we investigate how the condensed counterions (CIs) around the PE contribute to the polymer stretching in inhomogeneous fields. As an application, we discuss the translocation phenomena and entropic traps, when the driving force is an applied external electric field  

    Translocation of Star Shaped Polyelectrolyte Through Nanopore

    , M.Sc. Thesis Sharif University of Technology Aghajani, Zeinab (Author) ; Ejtehadi, Mohammad Reza (Supervisor)
    Polymer translocation through the nanopores is one of the fundamental macromolecular processes in life. Some examples are , mRNA translocation through nuclear pores, injection of DNA from a virus head into a host cell, protein translocation across biological membranes through membrane channels. Also some applications are suggested for the process, e.g. DNA sequencing by probing the signals during the translocation, drug delivery and/or gene therapy. During the translocation the polymer should pass entropic barrier of the pore and it can be facilitated by changing the chemical potential, application of eclectic field, flow field, or chemical concentrations. In electrically driven... 

    Multiwalled carbon nanotube-polyelectrolyte gels: Preparation and swelling behavior for organic solvents

    , Article Solid State Ionics ; Vol. 257 , 2014 , pp. 32-37 ; ISSN: 01672738 Pourjavadi, A ; Doulabi, M ; Sharif University of Technology
    In this article, we report the first multiwalled carbon nanotube-polyelectrolyte gel containing vinylimidazolium-typed ionic liquid monomer as an absorbent of less-polar or nonpolar organic solvents. To prepare such MWCNT-polyelectrolyte gel, the modified MWCNTs with polymerizable vinyl groups on their surfaces were prepared and then underwent copolymerizations with dodecyl methacrylate and vinylimidazolium in the presence of AIBN as initiator, yielding a cross-linked polyelectrolyte. In order to estimate the compatibility between the solvents and the polymers, a series of vinylimidazolium-typed ionic liquid monomers ([Cnvim][X]) with different alkyl tail length (C6, C10 and C12) and counter... 

    Novel polyelectrolyte gels as absorbent polymers for nonpolar organic solvents based on polymerizable ionic liquids

    , Article Polymer (United Kingdom) ; Volume 53, Issue 25 , 2012 , Pages 5737-5742 ; 00323861 (ISSN) Pourjavadi, A ; Doulabi, M ; Hosseini, S. H ; Sharif University of Technology
    Novel class of polyelectrolyte gels based on the copolymer of vinylimidazolium-typed ionic liquid monomer and Dodecyl methacrylate was prepared by free radical polymerization. A small amount of 3-n-Dodecyl-1- vinylimidazolium tetrafluoroborate is incorporated into crosslinked polyacrylates to provide new lipophilic polyelectrolyte gels that evaluated for swelling in less-polar and nonpolar organic solvents. Their swelling degree becomes more than 50 times as much as their dried weights in some organic solvents. By varying the polarity of the neutral monomer in these polyelectrolyte gels, the design of gels that can absorb solvents of nearly any polarity is demonstrated. The present... 

    Study on Dynamics of Charged Study on Dynamics of Charged Polyelectrolytes in Inhomogeneous Electric Fields and Its Application in Translocation Phenomenon

    , Ph.D. Dissertation Sharif University of Technology Farahpour, Farnoush (Author) ; Ejtehadi, Mohammad Reza (Supervisor)
    Polymers not just because of their increasing applications in industry but according to their fundamental role in biological mechanisms, has been a topic of interest among different scientific groups. Chemical structure, acroscopic properties and dynamical behavior of these macromolecules are studied in different ways. An important sub-group of polymers are those which according to their chemical properties, after dissolving, release some ions in water and become charged and called polyelectrolytes. A polyelectrolyte with vital importance in our life is DNA which encodes the genetic instructions used in the development and functioning of all known living organisms. One of the main goals in... 

    Solute dispersion by electroosmotic flow through soft microchannels

    , Article Sensors and Actuators, B: Chemical ; Volume 255, Part 3 , February , 2018 , Pages 3585-3600 ; 09254005 (ISSN) Hoshyargar, V ; Khorami, A ; Ashrafizadeh, S. N ; Sadeghi, A ; Sharif University of Technology
    Elsevier B.V  2018
    We study the hydrodynamic dispersion (HD) by electroosmotic flow in soft microchannels. Considering a fully developed flow in a slit microchannel of low surface potential and adopting the Taylor dispersion theory, we derive analytical solutions for the solute concentration field and the effective dispersion coefficient. We also conduct numerical analyses to broaden the paper's scope to high surface potentials and to specify a criterion for the validity of the Debye-Hückel linearization in soft microconduits as well as to investigate the broadening of an analyte band from the time of injection. It is demonstrated that the effective dispersion coefficient of a neutral solute band is generally... 

    A thermodynamically consistent electro-chemo-mechanical theory for modeling axonal swelling

    , Article Journal of the Mechanics and Physics of Solids ; Volume 145 , 2020 Dehghany, M ; Naghdabadi, R ; Sohrabpour, S ; Li, Y ; Hu, Y ; Sharif University of Technology
    Elsevier Ltd  2020
    In the present study, for the first time, a thermodynamically consistent large deformation theory is developed to model the multi physics problem of axonal swelling which is the hallmark of most of the brain diseases. To this end, the relevant axonal compartments are first explained and the corresponding model parts are introduced. Next, the problem is formulated as an open thermodynamic system and the corresponding constitutive and evolution equations are extracted utilizing the balance laws. Here, a multiplicative decomposition of the deformation gradient is used to capture the active behavior of the axonal actin cortex. Specific free energy functions are given for the model parts to... 

    Tuning electrokinetic flow, ionic conductance, and selectivity in a solid-state nanopore modified with a pH-responsive polyelectrolyte brush: A molecular theory approach

    , Article Journal of Physical Chemistry C ; Volume 124, Issue 34 , 2020 , Pages 18513-18531 Sadeghi, M ; Saidi, M. H ; Moosavi, A ; Kröger, M ; Sharif University of Technology
    American Chemical Society  2020
    We use an efficient molecular theory approach to study electrokinetic flow within a pH-responsive nanopore grafted with a polyelectrolyte (PE) brush. The flow rate, migration and convective conductance, electric potential and velocity fields, species distributions and the degree of ionization of the weak PE functional groups and nanopore selectivity are obtained and interpreted while considering pH-induced surface charges. The theory is generally based on writing the overall free energy of the system including the entropies arising from the conformations of flexible, excluded volume chains, the mixing of mobile species, electrostatic contribution, and the free energy due to the chemical... 

    Electrokinetic mixing and displacement of charged droplets in hydrogels

    , Article Transport in Porous Media ; Vol. 104, Issue. 3 , Jun , 2014 , pp. 469-499 ; ISSN: 01693913 Mohammadi, A ; Sharif University of Technology
    Mixing in droplets is an essential task in a variety of microfluidic systems. Inspired by electrokinetic mixing, electric field-induced hydrodynamic flow inside a charged droplet embedded in an unbounded polyelectrolyte hydrogel is investigated theoretically. In this study, the polyelectrolyte hydrogel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which is located at the plane of shear, with the electrostatic potential ζ. The fluid inside the droplet attains a finite velocity owing to hydrodynamic coupling with the... 

    Polyelectrolyte nanocomposite membranes using imidazole-functionalized nanosilica for fuel cell applications

    , Article Journal of Macromolecular Science, Part B: Physics ; Volume 54, Issue 1 , Nov , 2015 , Pages 17-31 ; 00222348 (ISSN) Tohidian, M ; Ghaffarian, S. R ; Nouri, M ; Jaafarnia, E ; Haghighi, A. H ; Sharif University of Technology
    Taylor and Francis Inc  2015
    The preparation and characterization of a new type of nanocomposite polyelectrolyte membrane, based on DuPont Nafion/imidazole-modified nanosilica (Im-Si), for direct methanol fuel cell applications is described. Related to the interactions between the protonated imidazole groups, grafted on the surface of nanosilica, and negatively charged sulfonic acid groups of Nafion, new electrostatic interactions can be formed in the interface of Nafion and Im-Si which result in both lower methanol permeability and also higher proton conductivity. Physical characteristics of these manufactured nanocomposite membranes were investigated by scanning electron microscopy, thermogravimetry analysis,... 

    Electric-field-induced response of a droplet embedded in a polyelectrolyte gel

    , Article Physics of Fluids ; Volume 25, Issue 8 , 2013 ; 10706631 (ISSN) Mohammadi, A ; Sharif University of Technology
    The electric-field induced response of a droplet embedded in a quenched polyelectrolyte gel is calculated theoretically. The response comprises the droplet translation and the electric-field induced flow fields within the droplet. The gel is modeled as a soft, and electrically charged porous solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no free charge. An analytical solution, using the perturbation methodology and linear superposition, is obtained for the leading-order steady response to a DC electric-field. The fluid within the droplet is driven due to hydrodynamic coupling with the electroosmotic flow. The fluid velocity... 

    Oscillatory response of charged droplets in hydrogels

    , Article Journal of Non-Newtonian Fluid Mechanics ; Volume 234 , 2016 , Pages 215-235 ; 03770257 (ISSN) Mohammadi, A ; Sharif University of Technology
    Elsevier  2016
    Characterization of droplet-hydrogel interfaces is of crucial importance to engineer droplet-hydrogel composites for a variety of applications. In order to develop electrokinetic diagnostic tools for probing droplet-hydrogel interfaces, the displacement of a charged droplet embedded in a polyelectrolyte hydrogel exposed to an oscillating electric field is determined theoretically. The polyelectrolyte hydrogel is modeled as an incompressible, charged, porous, and elastic solid saturated with a salted Newtonian fluid. The droplet is considered an incompressible Newtonian fluid with no charges within the droplet. The droplet-hydrogel interface is modeled as a surface with the thickness of zero... 

    The role of ion partitioning in electrohydrodynamic characteristics of soft nanofluidics: Inclusion of EDL overlap and steric effects

    , Article Chemical Engineering Science ; Volume 190 , 2018 , Pages 443-458 ; 00092509 (ISSN) Reshadi, M ; Saidi, M. H ; Sharif University of Technology
    Elsevier Ltd  2018
    In this paper, we aim to account for the partitioning of finite sized ions and electric double layer (EDL) overlapping effects on the electrostatics and hydrodynamics of soft nanofluidics by stablishing a modified Poisson-Boltzmann (MPB) equation enjoying mean field approach. The application of the present MPB equation enables us to describe the interaction between the steric effect and electrostatic repulsion of EDL ions due to permittivity difference of polyelectrolyte layer (PEL) and electrolyte solution. Utilizing the Debye-Hückel approximation pertinent to low surface potentials, we analytically derive the solutions of electric potential and velocity profiles of mixed electroosmotic and... 

    Unsteady solute dispersion by electrokinetic flow in a polyelectrolyte layer-grafted rectangular microchannel with wall absorption

    , Article Journal of Fluid Mechanics ; Volume 887 , 2020 Sadeghi, M ; Saidi, M. H ; Moosavi, A ; Sadeghi, A ; Sharif University of Technology
    Cambridge University Press  2020
    The dispersion of a neutral solute band by electrokinetic flow in polyelectrolyte layer (PEL)-grafted rectangular/slit microchannels is theoretically studied. The flow is assumed to be both steady and fully developed and a first-order irreversible reaction is considered at the wall to account for probable surface adsorption of solutes. Considering low electric potentials, analytical solutions are obtained for electric potential, fluid velocity and solute concentration. Special solutions are also obtained for the case without wall adsorption. To track the dispersion properties of the solute band, the generalized dispersion model is adopted by considering the exchange, the convection and the... 

    Growth of Polymer/TiO2 Nanostructures by Layer-by-Layer Self Assembly Method as Electrodes of Photoelectrochemical Cells

    , Ph.D. Dissertation Sharif University of Technology Rahman, Masoud (Author) ; Taghavinia, Nima (Supervisor) ; Shahrokhian, Saeed (Co-Advisor)
    Dye sensitized solar cells (DSCs) are among the 3rd generation solar cells which their mechanism of light absorption is similar to chlorophyll in green leafs and is based on photo-excitation of dyes. The electron-hole pairs of photo-excited dye separate at the interface of mesoporous semiconductor-dye-electrolyte. One of the approaches to increase the light path length and therefore the light harvesting efficiency in DSC is the addition of light scatterers inside the mesoporous semiconductor (photoanode).In this research, nanoparticulated hollow TiO2 fibers are introduced as novel light scatterers in DSCs with simultaneous light scattering, light trapping and high surface area. Light... 

    Electrical Gating of Nanochannels of Polyelectrolyte Brushes

    , M.Sc. Thesis Sharif University of Technology Moghaddasi Fereidani, Roya (Author) ; Ejtehadi, Mohammad Reza (Supervisor)
    The nuclear pore complex mediates all transport between the cell cytoplasm and the nucleus. Being inspired by this biological system, in this project we intended to design an artificial gate by using polyelectrolyte brushes in a cylindrical nanochannel, which will be opened by applying a tangent electrical field and will close by eliminating the field. Grafted polyelecrolyte brushes have the potential to be useful for the design of advanced gating systems for many applications like functional and conrolleble MEMS devices. In order to design the desired gating system we have employed the ESPResSo software to conduct a coarse-grained molecular dynamics simulation in NVT ensemble to simulate... 

    The combination of KMnO4 oxidation and polymeric flocculation for the mitigation of membrane fouling in a membrane bioreactor

    , Article Separation and Purification Technology ; Volume 159 , 2016 , Pages 124-134 ; 13835866 (ISSN) Zarei baygi, A ; Moslemi, M ; Mirzaei, S. H ; Sharif University of Technology
    KMnO4 oxidation combined with polyelectrolyte (K530CF) flocculation was investigated to mitigate membrane fouling in a membrane bioreactor. The optimum dosages of chemical additives in order to enhance the removal of soluble microbial products (SMPs) were determined. This method was able to reduce the concentration of COD in the effluent to 57.1% and 51.1% lower than those in the experiments in the absence of chemical flocculants and in the presence of polyelectrolyte, respectively. NH3-N removal was improved by combining KMnO4 and K530CF. When KMnO4 was used along with polyelectrolyte, the zeta potential was neutralized to a greater extent which resulted in an improvement in the... 

    Transport in droplet-hydrogel composites: response to external stimuli

    , Article Colloid and Polymer Science ; Volume 293, Issue 3 , March , 2015 , Pages 941-962 ; 0303402X (ISSN) Mohammadi, A ; Sharif University of Technology
    Springer Verlag  2015
    Determination of effective transport properties of droplet-hydrogel composites is essential for various applications. The transport of ions through a droplet-hydrogel composite subjected to an electric field is theoretically studied as an initial step toward quantifying the effective transport properties of droplet-hydrogel composites. A three-phase electrokinetic model is used to derive the microscale characteristics of the polyelectrolyte hydrogel, and the droplet is considered an incompressible Newtonian fluid. The droplet-hydrogel interface is modeled as a surface, which encloses the interior fluid. The surface has the thickness of zero and the electrostatic potential ζ. Standard... 

    Biomimetic proteoglycan nanoparticles for growth factor immobilization and delivery

    , Article Biomaterials Science ; Volume 8, Issue 4 , 2020 , Pages 1127-1136 Zandi, N ; Mostafavi, E ; Shokrgozar, M. A ; Tamjid, E ; Webster, T. J ; Annabi, N ; Simchi, A ; Sharif University of Technology
    Royal Society of Chemistry  2020
    The delivery of growth factors is often challenging due to their short half-life, low stability, and rapid deactivation. In native tissues, the sulfated residual of glycosaminoglycan (GAG) polymer chains of proteoglycans immobilizes growth factors through the proteoglycans'/proteins' complexation with nanoscale organization. These biological assemblies can influence growth factor-cell surface receptor interactions, cell differentiation, cell-cell signaling, and mechanical properties of the tissues. Here, we introduce a facile procedure to prepare novel biomimetic proteoglycan nanocarriers, based on naturally derived polymers, for the immobilization and controlled release of growth factors.... 

    Bottom-up synthesis of nitrogen and oxygen co-decorated carbon quantum dots with enhanced DNA plasmid expression

    , Article Colloids and Surfaces B: Biointerfaces ; Volume 184 , 2019 ; 09277765 (ISSN) Yadegari, A ; Khezri, J ; Esfandiari, S ; Mahdavi, H ; Karkhane, A. A ; Rahighi, R ; Heidarimoghadam, R ; Tayebi, L ; Hashemi, E ; Farmany, A ; Sharif University of Technology
    Elsevier B.V  2019
    In this paper, a bottom-up hydrothermal route is reported for the synthesis of oxygen and nitrogen co-decorated carbon quantum dots (CQDs) using ammonium hydrogen citrate (AHC) as a single precursor. DLS data approved the formation of 4.0 nm (average size) CQDs. XRD pattern shows the interlayer spacing (002) of 3.5 Å for CQDs, which is exactly the same as that of crystalline graphite. XPS and FTIR spectra verified the formation of oxygen and nitrogen functional groups on the CQDs surface. Co-decorated carboxyl, hydroxyl and amine groups on the CQDs surfaces make them as promising polyelectrolyte for gene delivery. Toxicity assay showed a survival rate of 70% under different incubation times...