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  1. Article ; Online: Elasticity and yielding of mesophases of block copolymers in water-oil mixtures.

    Qavi, Sahar / Firestone, Millicent A / Foudazi, Reza

    Soft matter

    2019  Volume 15, Issue 28, Page(s) 5626–5637

    Abstract: Amphiphilic block copolymers self-assemble at the water/oil interface to form different mesomorphic structures, such as lamellar, micellar cubic, normal hexagonal, and reverse hexagonal structures. Usually, these structures are polycrystalline and the ... ...

    Abstract Amphiphilic block copolymers self-assemble at the water/oil interface to form different mesomorphic structures, such as lamellar, micellar cubic, normal hexagonal, and reverse hexagonal structures. Usually, these structures are polycrystalline and the value of their elastic modulus depends on the average orientation of their constituent's single crystals. We provide a model to predict the elastic modulus and yielding of mesophases from their characteristic length and intermicellar interactions. Shear modulus of each structure is calculated as a function of deformation (strain). Zero-shear modulus, G0, depends on the inverse of the intermicellar distance with a power law model. The power law index for each structure is approximately n + 2 where n is the degree of confinement in the mesophase: 1 for lamellar, 2 for both normal and reverse hexagonal, and 3 for micellar cubic structures. Rheological properties of different mesophases of Pluronic P84 in the presence of water and p-xylene are used as a case study. The model is found to be in good agreement with experimental data in the linear viscoelastic region. When compared to experimental data, the yield strain value obtained from the model is one order of magnitude higher than the limit of the linear viscoelastic regime and close to the strain at the cross-over point of storage and loss moduli. Frequency sweep measurements are done to characterize the relaxation and cooperative model behaviors of each mesophase structure.
    Language English
    Publishing date 2019-06-26
    Publishing country England
    Document type Journal Article
    ZDB-ID 2191476-X
    ISSN 1744-6848 ; 1744-683X
    ISSN (online) 1744-6848
    ISSN 1744-683X
    DOI 10.1039/c8sm02336k
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Polymerization in soft nanoconfinement of lamellar and reverse hexagonal mesophases.

    Qavi, Sahar / Bandegi, Alireza / Firestone, Millicent / Foudazi, Reza

    Soft matter

    2019  Volume 15, Issue 41, Page(s) 8238–8250

    Abstract: This work describes the kinetics of thermal polymerization in nanoconfined domains of lyotropic liquid crystal (LLC) templates by using chemorheological studies at different temperatures. We investigate lamellar and reverse hexagonal LLC phases with the ... ...

    Abstract This work describes the kinetics of thermal polymerization in nanoconfined domains of lyotropic liquid crystal (LLC) templates by using chemorheological studies at different temperatures. We investigate lamellar and reverse hexagonal LLC phases with the same concentration of the monomeric phase. Results show that the mesophase structures remain intact during thermal polymerization with very slight changes in the domain size. The polymerization rate decreases in the nanoconfined structure compared to the bulk state due to the segregation effect, which increases the local monomer concentration and enhances the termination rate. Additionally, the polymerization rate is faster in the studied reverse hexagonal systems compared to the lamellar ones due to their lower degree of confinement. A higher degree of confinement also induces a lower monomer conversion. Differential scanning calorimetry confirms the obtained results from chemorheology.
    Language English
    Publishing date 2019-10-02
    Publishing country England
    Document type Journal Article
    ZDB-ID 2191476-X
    ISSN 1744-6848 ; 1744-683X
    ISSN (online) 1744-6848
    ISSN 1744-683X
    DOI 10.1039/c9sm01565e
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article: Ultrafiltration membranes from polymerization of self-assembled Pluronic block copolymer mesophases

    Qavi, Sahar / Aaron P. Lindsay / Millicent A. Firestone / Reza Foudazi

    Elsevier B.V. Journal of membrane science. 2019 June 15, v. 580

    2019  

    Abstract: Industrially, ultrafiltration (UF) membranes are produced through non-solvent induced phase separation (NIPS), but due to environmental hazards inherent to the NIPS process as well as the low surface porosity and fouling resistance of membranes produced ... ...

    Abstract Industrially, ultrafiltration (UF) membranes are produced through non-solvent induced phase separation (NIPS), but due to environmental hazards inherent to the NIPS process as well as the low surface porosity and fouling resistance of membranes produced via this method, an alternative route to UF membranes is desirable. This work presents the self-assembly of Pluronic block copolymers in the presence of water and a monomeric phase as a new technique for the preparation of UF membranes without the need for organic solvent or post-modification. Different compositions of block copolymer, water, and monomer were polymerized to obtain both hexagonal and lamellar mesostructures, as indicated by small angle X-ray scattering (SAXS) and cross-polarized light microscopy. As-synthesized membranes were found to have pore sizes in the range of 3–4 nm with a molecular weight cutoff of 1500 g/mol and displayed both excellent fouling resistance and high permeance of water, vastly outperforming a conventional NIPS UF membrane. Further, in contrast to NIPS, the proposed method provides flexibility in terms of both the final membrane chemistry and pore size. As such, it is a versatile approach that can be easily tailored to produce membranes for a wide range of applications including wastewater treatment and food processing.
    Keywords artificial membranes ; composite polymers ; environmental hazards ; food processing ; fouling ; light microscopy ; molecular weight ; polymerization ; porosity ; separation ; small-angle X-ray scattering ; solvents ; ultrafiltration ; wastewater treatment
    Language English
    Dates of publication 2019-0615
    Size p. 125-133.
    Publishing place Elsevier B.V.
    Document type Article
    ZDB-ID 194516-6
    ISSN 0376-7388
    ISSN 0376-7388
    DOI 10.1016/j.memsci.2019.02.060
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    In stock of ZB MED Bonn / Germany

    Z 78/706: Show issues

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  4. Article: Double-stage phase separation in dynamically asymmetric ternary polymer blends

    Kuang, Chen / Qavi, Sahar / Foudazi, Reza

    RSC advances. 2016 Sept. 26, v. 6, no. 94

    2016  

    Abstract: In this work, the phase separation behavior of ternary blends of polystyrene/poly(vinyl methyl ether)/polyisoprene, PS/PVME/PI, and polystyrene/poly(vinyl methyl ether)/poly(ethyl methacrylate), PS/PVME/PEMA are investigated. Ternary blends of PS/PVME/PI ...

    Abstract In this work, the phase separation behavior of ternary blends of polystyrene/poly(vinyl methyl ether)/polyisoprene, PS/PVME/PI, and polystyrene/poly(vinyl methyl ether)/poly(ethyl methacrylate), PS/PVME/PEMA are investigated. Ternary blends of PS/PVME/PI and PS/PVME/PEMA are expected to exhibit complex phase separation behavior since PS and PVME have a lower critical solution temperature (LCST) with viscoelastic phase separation (VPS) behavior, while PI/PS, PI/PVME, PEMA/PS, and PEMA/PVME have an upper critical solution temperature (UCST) behavior. 2D and 3D phase diagrams for these two ternary systems are obtained by a compressible regular solution model. Casting the solutions of PS/PVME/PI and PS/PVME/PEMA blends forms two phase-separated domains in most compositions: (1) PI-rich or PEMA rich, and (2) PS/PVME-rich. Post-annealing of such samples at 110 °C leads to a second-stage phase separation due to unfavorable interaction of PS and PVME. Such behavior, which is observed for the first time, provides a new potential method for making different morphologies with the same system by changing annealing parameters and composition. The kinetics and morphology of ternary blends during phase separation are studied by optical microscopy and scanning electron microscopy.
    Keywords annealing ; light microscopy ; methyl ethers ; models ; physical phases ; polystyrenes ; scanning electron microscopy ; separation ; temperature ; viscoelasticity
    Language English
    Dates of publication 2016-0926
    Size p. 92104-92114.
    Publishing place The Royal Society of Chemistry
    Document type Article
    ISSN 2046-2069
    DOI 10.1039/c6ra17274a
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  5. Article: Getting control of hydrogel networks with cross-linkable monomers

    Cohn, Pamela G. / Qavi, Sahar / Cubuk, Jasmine / Jani, Mihir / Megdad, Mohamed Lamine / Shah, Dhvani / Cattafi, Cara / Baul, Panchatapa / Rajaraman, Shanthi / Foudazi, Reza

    Journal of materials chemistry B. 2021 Dec. 1, v. 9, no. 46

    2021  

    Abstract: The structure of a hydrogel network determines its ability to dissipate stress upon deformation, as well as its ability to swell in water. By designing systems with cross-linkable thiol groups in the monomers, radical thiol–ene chemistry was used to form ...

    Abstract The structure of a hydrogel network determines its ability to dissipate stress upon deformation, as well as its ability to swell in water. By designing systems with cross-linkable thiol groups in the monomers, radical thiol–ene chemistry was used to form controlled networks for acrylamide monomers. The use of radical thiol–ene chemistry effectively suppressed homo-polymerization of the bis(acrylamide) monomer and resulted in networks of alternating thiol and acrylamide monomers. Additionally, if the stoichiometry between the monomers is controlled, the network should approach that of ideality. In the case of bis(acrylamide) monomers, the incorporation of hydrogen-bond donors into the network creates a single network hydrogel with the benefits of high strength and ductility from the simultaneous incorporation of chemical and physical cross-links. Additionally, this strategy suppresses the formation of homo-polymerization in the acrylamide monomer to achieve an alternating network, which is supported with NMR characterization of base-digested fragments. For three different monomer compositions, the resulting gels had high compressive strength (up to 40 MPa) and tunable mechanical properties. The high mechanical strength of the 1 : 1, thiol : ene gel composition is due to the uniform distribution of cross-links, which creates defect-free networks for efficient stress transfer. The present one-pot synthetic strategy toward controlled gel networks affords monomer versatility and synthetic ease, as well as the potential for mechanically robust materials.
    Keywords acrylamides ; compression strength ; crosslinking ; deformation ; hydrogels ; hydrogen bonding ; stoichiometry ; strength (mechanics) ; thiols
    Language English
    Dates of publication 2021-1201
    Size p. 9497-9504.
    Publishing place The Royal Society of Chemistry
    Document type Article
    ZDB-ID 2702241-9
    ISSN 2050-7518 ; 2050-750X
    ISSN (online) 2050-7518
    ISSN 2050-750X
    DOI 10.1039/d1tb00482d
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  6. Article ; Online: Getting control of hydrogel networks with cross-linkable monomers.

    Cohn, Pamela G / Qavi, Sahar / Cubuk, Jasmine / Jani, Mihir / Megdad, Mohamed Lamine / Shah, Dhvani / Cattafi, Cara / Baul, Panchatapa / Rajaraman, Shanthi / Foudazi, Reza

    Journal of materials chemistry. B

    2021  Volume 9, Issue 46, Page(s) 9497–9504

    Abstract: The structure of a hydrogel network determines its ability to dissipate stress upon deformation, as well as its ability to swell in water. By designing systems with cross-linkable thiol groups in the monomers, radical thiol-ene chemistry was used to form ...

    Abstract The structure of a hydrogel network determines its ability to dissipate stress upon deformation, as well as its ability to swell in water. By designing systems with cross-linkable thiol groups in the monomers, radical thiol-ene chemistry was used to form controlled networks for acrylamide monomers. The use of radical thiol-ene chemistry effectively suppressed homo-polymerization of the bis(acrylamide) monomer and resulted in networks of alternating thiol and acrylamide monomers. Additionally, if the stoichiometry between the monomers is controlled, the network should approach that of ideality. In the case of bis(acrylamide) monomers, the incorporation of hydrogen-bond donors into the network creates a single network hydrogel with the benefits of high strength and ductility from the simultaneous incorporation of chemical and physical cross-links. Additionally, this strategy suppresses the formation of homo-polymerization in the acrylamide monomer to achieve an alternating network, which is supported with NMR characterization of base-digested fragments. For three different monomer compositions, the resulting gels had high compressive strength (up to 40 MPa) and tunable mechanical properties. The high mechanical strength of the 1 : 1, thiol : ene gel composition is due to the uniform distribution of cross-links, which creates defect-free networks for efficient stress transfer. The present one-pot synthetic strategy toward controlled gel networks affords monomer versatility and synthetic ease, as well as the potential for mechanically robust materials.
    MeSH term(s) Biocompatible Materials ; Hydrogels/chemistry ; Materials Testing ; Mechanical Phenomena ; Molecular Structure ; Rheology
    Chemical Substances Biocompatible Materials ; Hydrogels
    Language English
    Publishing date 2021-12-01
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2702241-9
    ISSN 2050-7518 ; 2050-750X
    ISSN (online) 2050-7518
    ISSN 2050-750X
    DOI 10.1039/d1tb00482d
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article ; Online: Physical chemistry of highly concentrated emulsions.

    Foudazi, Reza / Qavi, Sahar / Masalova, Irina / Malkin, Alexander Ya

    Advances in colloid and interface science

    2015  Volume 220, Page(s) 78–91

    Abstract: This review explores the physics underlying the rheology of highly concentrated emulsions (HCEs) to determine the relationship between elasticity and HCE stability, and to consider whether it is possible to describe all physicochemical properties of HCEs ...

    Abstract This review explores the physics underlying the rheology of highly concentrated emulsions (HCEs) to determine the relationship between elasticity and HCE stability, and to consider whether it is possible to describe all physicochemical properties of HCEs on the basis of a unique physical approach. We define HCEs as emulsions with a volume fraction above the maximum closest packing fraction of monodisperse spheres, φm=0.74, even if droplets are not of polyhedron shape. The solid-like rheological behavior of HCEs is characterized by yield stress and elasticity, properties which depend on droplet polydispersity and which are affected by caging at volume fractions about the jamming concentration, φj. A bimodal size distribution in HCEs diminishes caging and facilitates droplet movement, resulting in HCEs with negligible yield stress and no plateau in storage modulus. Thermodynamic forces automatically move HCEs toward the lowest free energy state, but since interdroplet forces create local minimums - points beyond which free energy temporarily increases before it reaches the global minimum of the system - the free energy of HCEs will settle at a local minimum unless additional energy is added. Several attempts have been undertaken to predict the elasticity of HCEs. In many cases, the elastic modulus of HCEs is higher than the one predicted from classical models, which only take into account spatial repulsion (or simply interfacial energy). Improved models based on free energy calculation should be developed to consider the disjoining pressure and interfacial rheology in addition to spatial repulsion. The disjoining pressure and interfacial viscoelasticity, which result in the deviation of elasticity from the classical model, can be regarded as parameters for quantifying the stability of HCEs.
    Language English
    Publishing date 2015-06
    Publishing country Netherlands
    Document type Journal Article ; Review
    ZDB-ID 210507-x
    ISSN 1873-3727 ; 0001-8686
    ISSN (online) 1873-3727
    ISSN 0001-8686
    DOI 10.1016/j.cis.2015.03.002
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    In stock of ZB MED Cologne/Königswinter

    Zs.A 2716: Show issues Location:
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