The Experts below are selected from a list of 14643 Experts worldwide ranked by ideXlab platform

Steven P. Armes - One of the best experts on this subject based on the ideXlab platform.

  • Aqueous one-pot synthesis of epoxy-functional Diblock Copolymer worms from a single monomer: new anisotropic scaffolds for potential charge storage applications
    2018
    Co-Authors: Fiona Hatton, Albert M Park, Yiren Zhang, Gregory D Fuchs, Christopher K Ober, Steven P. Armes
    Abstract:

    Nitroxide-functional polymers have garnered considerable interest in recent years and appear to hold promise for energy storage applications. However, their synthesis can be both expensive and time-consuming. Here, we propose a highly convenient method for the preparation of TEMPO-functional Diblock Copolymer nanoparticles directly in water. Epoxy-functional Diblock Copolymer worms are synthesized from a single monomer, glycidyl methacrylate (GlyMA), using a three-step, one-pot protocol in aqueous solution via polymerization-induced self-assembly (PISA). First, an initial aqueous emulsion of GlyMA was heated at 85 °C for 9 h to afford an aqueous solution of glycerol monomethacrylate (GMA). Then reversible addition-fragmentation chain transfer (RAFT) polymerization of GMA was conducted in aqueous solution using a dicarboxylic acid-based RAFT agent to produce a water-soluble PGMA homopolymer. Finally, chain extension of this pre-cursor block via RAFT aqueous emulsion polymerization of GlyMA at 50 °C produced amphiphilic Diblock Copolymer chains that self-assembled in situ to form a 15% w/w aqueous dispersion of Diblock Copolymer worms. These worms can be derivatized directly using 4-amino-TEMPO in aqueous solution, affording novel crosslinked anisotropic nanoparticles that contain a relatively high density of stable nitroxide radicals for potential charge storage applications

  • order order morphological transitions for dual stimulus responsive Diblock Copolymer vesicles
    Macromolecules, 2016
    Co-Authors: Joseph R Lovett, Steven P. Armes, Nicholas J Warren, Mark J Smallridge, Robert B Cracknell
    Abstract:

    A series of non-ionic poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) Diblock Copolymer vesicles has been prepared by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. Based on our recent work describing the analogous PGMA-PHPMA Diblock Copolymer worms [Lovett J. R.; Angew. Chem.2015, 54, 1279-1283], such Diblock Copolymer vesicles were expected to undergo an order-order morphological transition via ionization of the carboxylic acid end-group on switching the solution pH. Indeed, irreversible vesicle-to-sphere and vesicle-to-worm transitions were observed for PHPMA DPs of 175 and 200, respectively, as judged by turbidimetry, transmission electron microscopy (TEM), and dynamic light scattering (DLS) studies. However, such morphological transitions are surprisingly slow, with relatively long time scales (hours) being required at 20 °C. Moreover, no order-order morphological transitions were observed for vesicles comprising longer membrane-forming blocks (e.g., PGMA43-PHPMA225-250) on raising the pH from pH 3.5 to pH 6.0. However, in such cases the application of a dual stimulus comprising the same pH switch immediately followed by cooling from 20 to 5 °C, induces an irreversible vesicle-to-sphere transition. Finally, TEM and DLS studies conducted in the presence of 100 mM KCl demonstrated that the pH-responsive behavior arising from end-group ionization could be suppressed in the presence of added electrolyte. This is because charge screening suppresses the subtle change in the packing parameter required to drive the morphological transition.

  • polydimethylsiloxane based Diblock Copolymer nano objects prepared in nonpolar media via raft mediated polymerization induced self assembly
    Macromolecules, 2015
    Co-Authors: Alejandra P Lopezoliva, Oleksand O Mykhaylyk, Nicholas J Warren, Arthi D Rajkumar, Matthew J Derry, Kay E B Doncom, Matthew J Rymaruk, Steven P. Armes
    Abstract:

    Monocarbinol-functionalized polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was converted via esterification into a chain transfer agent (CTA) for reversible addition–fragmentation chain transfer (RAFT) polymerization. The degree of esterification was determined to be 94 ± 1% by 1H NMR spectroscopy and 92 ± 1% by UV absorption spectroscopy. This PDMS CTA was then utilized for the dispersion polymerization of benzyl methacrylate (BzMA) in n-heptane at 70 °C. As the PBzMA block grows, it becomes insoluble in the reaction medium, which drives the in situ formation of PDMS–PBzMA Diblock Copolymer nanoparticles via polymerization-induced self-assembly (PISA). Depending on the precise reaction conditions, the final Diblock Copolymer chains can self-assemble to form spheres, worms, or vesicles. Systematic variation of the Copolymer concentration and the target degree of polymerization (DP) of the PBzMA block enables construction of a phase diagram that allows the reproducible targeting of pure co...

  • synthesis and characterization of poly amino acid methacrylate stabilized Diblock Copolymer nano objects
    Polymer Chemistry, 2015
    Co-Authors: Vincent Ladmiral, Mona Semsarilar, Alexandre Charlot, Steven P. Armes
    Abstract:

    Amino acids constitute one of Nature's most important building blocks. Their remarkably diverse properties (hydrophobic/hydrophilic character, charge density, chirality, reversible cross-linking etc.) dictate the structure and function of proteins. The synthesis of artificial peptides and proteins comprising main chain amino acids is of particular importance for nanomedicine. However, synthetic polymers bearing amino acid side-chains are more readily prepared and may offer desirable properties for various biomedical applications. Herein we describe an efficient route for the synthesis of poly(amino acid methacrylate)stabilized Diblock Copolymer nano-objects. First, either cysteine or glutathione is reacted with a commercially available methacrylate-acrylate adduct to produce the corresponding amino acid-based methacrylic monomer (CysMA or GSHMA). Well-defined water-soluble macromolecular chain transfer agents (PCysMA or PGSHMA macro-CTAs) are then prepared via RAFT polymerization, which are then chain-extended via aqueous RAFT dispersion polymerization of 2-hydroxypropyl methacrylate. In situ polymerization-induced self-assembly (PISA) occurs to produce sterically-stabilized Diblock Copolymer nano-objects. Although only spherical nanoparticles could be obtained when PGSHMA was used as the sole macro-CTA, either spheres, worms or vesicles can be prepared using either PCysMA macro-CTA alone or binary mixtures of poly(glycerol monomethacrylate) (PGMA) with either PCysMA or PGSHMA macro-CTAs. The worms formed soft free-standing thermo-responsive gels that undergo degelation on cooling as a result of a worm-to-sphere transition. Aqueous electrophoresis studies indicate that all three Copolymer morphologies exhibit cationic character below pH 3.5 and anionic character above pH 3.5. This pH sensitivity corresponds to the known behavior of the poly(amino acid methacrylate) steric stabilizer chains.

  • Mechanical properties of a waterborne pressure-sensitive adhesive with a percolating poly(acrylic acid)-based Diblock Copolymer network: Effect of pH
    Journal of Colloid and Interface Science, 2015
    Co-Authors: Robert S Gurney, Elodie Siband, Damien Dupin, Steven P. Armes, Andrew Morse, Joseph L Keddie
    Abstract:

    Copolymerizing an acrylic acid comonomer is often beneficial for the adhesive properties of waterborne pressure-sensitive adhesives (PSAs). Here, we demonstrate a new strategy in which poly(acrylic acid) (PAA) is distributed as a percolating network within a PSA film formed from a polymer colloid. A Diblock Copolymer composed of PAA and poly(. n-butyl acrylate) (PBA) blocks was synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization and adsorbed onto soft acrylic latex particles prior to their film formation. The thin adsorbed shells on the particles create a percolating network that raises the elastic modulus, creep resistance and tensile strength of the final film. When the film formation occurs at pH 10, ionomeric crosslinking occurs, and high tack adhesion is obtained in combination with high creep resistance. The results show that the addition of an amphiphilic PAA-. b-PBA Diblock Copolymer (2.0. wt.%) to a soft latex provides a simple yet effective means of adjusting the mechanical and adhesive properties of the resulting composite film.

Oleksand O Mykhaylyk - One of the best experts on this subject based on the ideXlab platform.

  • polydimethylsiloxane based Diblock Copolymer nano objects prepared in nonpolar media via raft mediated polymerization induced self assembly
    Macromolecules, 2015
    Co-Authors: Alejandra P Lopezoliva, Oleksand O Mykhaylyk, Nicholas J Warren, Arthi D Rajkumar, Matthew J Derry, Kay E B Doncom, Matthew J Rymaruk, Steven P. Armes
    Abstract:

    Monocarbinol-functionalized polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was converted via esterification into a chain transfer agent (CTA) for reversible addition–fragmentation chain transfer (RAFT) polymerization. The degree of esterification was determined to be 94 ± 1% by 1H NMR spectroscopy and 92 ± 1% by UV absorption spectroscopy. This PDMS CTA was then utilized for the dispersion polymerization of benzyl methacrylate (BzMA) in n-heptane at 70 °C. As the PBzMA block grows, it becomes insoluble in the reaction medium, which drives the in situ formation of PDMS–PBzMA Diblock Copolymer nanoparticles via polymerization-induced self-assembly (PISA). Depending on the precise reaction conditions, the final Diblock Copolymer chains can self-assemble to form spheres, worms, or vesicles. Systematic variation of the Copolymer concentration and the target degree of polymerization (DP) of the PBzMA block enables construction of a phase diagram that allows the reproducible targeting of pure co...

  • thermo responsive Diblock Copolymer worm gels in non polar solvents
    Journal of the American Chemical Society, 2014
    Co-Authors: Lee A Fielding, Matthew J Derry, Oleksand O Mykhaylyk, Jacob A Lane, Steven P. Armes
    Abstract:

    Benzyl methacrylate (BzMA) is polymerized using a poly(lauryl methacrylate) macromolecular chain transfer agent (PLMA macro-CTA) using reversible addition–fragmentation chain transfer (RAFT) polymerization at 70 °C in n-dodecane. This choice of solvent leads to an efficient dispersion polymerization, with polymerization-induced self-assembly (PISA) occurring via the growing PBzMA block to produce a range of PLMA–PBzMA Diblock Copolymer nano-objects, including spheres, worms, and vesicles. In the present study, particular attention is paid to the worm phase, which forms soft free-standing gels at 20 °C due to multiple inter-worm contacts. Such worm gels exhibit thermo-responsive behavior: heating above 50 °C causes degelation due to the onset of a worm-to-sphere transition. Degelation occurs because isotropic spheres interact with each other much less efficiently than the highly anisotropic worms. This worm-to-sphere thermal transition is essentially irreversible on heating a dilute solution (0.10% w/w) bu...

  • raft aqueous dispersion polymerization yields poly ethylene glycol based Diblock Copolymer nano objects with predictable single phase morphologies
    Journal of the American Chemical Society, 2014
    Co-Authors: Nicholas J Warre, Oleksand O Mykhaylyk, Daniel Mahmood, Anthony J Rya, Steven P. Armes
    Abstract:

    A poly(ethylene glycol) (PEG) macromolecular chain transfer agent (macro-CTA) is prepared in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). Polymerizations conducted under optimized conditions at 50 °C led to high conversions as judged by 1H NMR spectroscopy and relatively low Diblock Copolymer polydispersities (Mw/Mn < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean degree of polymerization of the core-forming PHPMA block allowed PEG113-PHPMAx Diblock Copolymer spheres, worms, or vesicles to be prepared at up to 17.5% w/w solids, as judged by dynamic light scattering and transmission electron microscopy studies. S...

  • raft aqueous dispersion polymerization yields poly ethylene glycol based Diblock Copolymer nano objects with predictable single phase morphologies
    Journal of the American Chemical Society, 2014
    Co-Authors: Nicholas J Warren, Daniel Mahmood, Oleksand O Mykhaylyk, Anthony J Ryan, Steven P. Armes
    Abstract:

    A poly(ethylene glycol) (PEG) macromolecular chain transfer agent (macro-CTA) is prepared in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). Polymerizations conducted under optimized conditions at 50 °C led to high conversions as judged by (1)H NMR spectroscopy and relatively low Diblock Copolymer polydispersities (M(w)/M(n) < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean degree of polymerization of the core-forming PHPMA block allowed PEG113-PHPMA(x) Diblock Copolymer spheres, worms, or vesicles to be prepared at up to 17.5% w/w solids, as judged by dynamic light scattering and transmission electron microscopy studies. Small-angle X-ray scattering (SAXS) analysis revealed that more exotic oligolamellar vesicles were observed at 20% w/w solids when targeting highly asymmetric Diblock compositions. Detailed analysis of SAXS curves indicated that the mean number of membranes per oligolamellar vesicle is approximately three. A PEG113-PHPMA(x) phase diagram was constructed to enable the reproducible targeting of pure phases, as opposed to mixed morphologies (e.g., spheres plus worms or worms plus vesicles). This new RAFT PISA formulation is expected to be important for the rational and efficient synthesis of a wide range of biocompatible, thermo-responsive PEGylated Diblock Copolymer nano-objects for various biomedical applications.

  • Micellization and Adsorption Behavior of a Near-Monodisperse Polystyrene-Based Diblock Copolymer in Nonpolar Media
    2014
    Co-Authors: David J. Growney, Oleksand O Mykhaylyk, Steven P. Armes
    Abstract:

    The micellar self-assembly behavior of a near-monodisperse polystyrene–hydrogenated polyisoprene (PS–PEP) Diblock Copolymer is examined in non-polar media (either n-heptane or n-dodecane). Direct dissolution of this Diblock Copolymer leads to the formation of relatively large polydisperse colloidal aggregates that are kinetically frozen artifacts of the solid-state Copolymer morphology. Dynamic light scattering (DLS) and transmission electron microscopy studies indicate that heating such Copolymer dispersions up to 90–110 °C leads to a structural rearrangement, with the generation of relatively small, well-defined spherical micelles that persist on cooling to 20 °C. Variable temperature 1H NMR studies using deuterated n-alkanes confirm that partial solvation (plasticization) of the polystyrene micelle cores occurs on heating. This increased mobility of the core-forming polystyrene chains is consistent with the evolution from a kinetically-trapped to a thermodynamically-favored Copolymer morphology via exchange of individual Copolymer chains, which are observed by DLS. These micellar self-assembly observations are also consistent with small-angle X-ray scattering (SAXS) studies, which indicate the formation of star-like micelles in n-heptane, with a mean polystyrene core diameter of about 20 nm and an overall diameter (core plus corona) of about 80 nm. Micelle dissociation occurs on addition of chloroform, which is a good solvent for both blocks. Finally, physical adsorption of this PS–PEP Diblock Copolymer onto a model colloidal substrate (carbon black) has been confirmed using X-ray photoelectron spectroscopy. A Langmuir-type adsorption isotherm has been constructed using a supernatant depletion assay based on UV spectroscopy analysis of the aromatic chromophore in the polystyrene block. Comparable results were obtained using thermogravimetric analysis to directly determine the amount of adsorbed Copolymer. Based on the maximum adsorbed amounts observed at 20 °C, these studies strongly suggest that individual PS–PEP Copolymer chains adsorb onto carbon black from chloroform, whereas micellar adsorption occurs from n-alkanes

Nicholas J Warren - One of the best experts on this subject based on the ideXlab platform.

  • order order morphological transitions for dual stimulus responsive Diblock Copolymer vesicles
    Macromolecules, 2016
    Co-Authors: Joseph R Lovett, Steven P. Armes, Nicholas J Warren, Mark J Smallridge, Robert B Cracknell
    Abstract:

    A series of non-ionic poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (PGMA-PHPMA) Diblock Copolymer vesicles has been prepared by reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA at 70 °C at low pH using a carboxylic acid-based chain transfer agent. The degree of polymerization (DP) of the PGMA block was fixed at 43, and the DP of the PHPMA block was systematically varied from 175 to 250 in order to target vesicle phase space. Based on our recent work describing the analogous PGMA-PHPMA Diblock Copolymer worms [Lovett J. R.; Angew. Chem.2015, 54, 1279-1283], such Diblock Copolymer vesicles were expected to undergo an order-order morphological transition via ionization of the carboxylic acid end-group on switching the solution pH. Indeed, irreversible vesicle-to-sphere and vesicle-to-worm transitions were observed for PHPMA DPs of 175 and 200, respectively, as judged by turbidimetry, transmission electron microscopy (TEM), and dynamic light scattering (DLS) studies. However, such morphological transitions are surprisingly slow, with relatively long time scales (hours) being required at 20 °C. Moreover, no order-order morphological transitions were observed for vesicles comprising longer membrane-forming blocks (e.g., PGMA43-PHPMA225-250) on raising the pH from pH 3.5 to pH 6.0. However, in such cases the application of a dual stimulus comprising the same pH switch immediately followed by cooling from 20 to 5 °C, induces an irreversible vesicle-to-sphere transition. Finally, TEM and DLS studies conducted in the presence of 100 mM KCl demonstrated that the pH-responsive behavior arising from end-group ionization could be suppressed in the presence of added electrolyte. This is because charge screening suppresses the subtle change in the packing parameter required to drive the morphological transition.

  • polydimethylsiloxane based Diblock Copolymer nano objects prepared in nonpolar media via raft mediated polymerization induced self assembly
    Macromolecules, 2015
    Co-Authors: Alejandra P Lopezoliva, Oleksand O Mykhaylyk, Nicholas J Warren, Arthi D Rajkumar, Matthew J Derry, Kay E B Doncom, Matthew J Rymaruk, Steven P. Armes
    Abstract:

    Monocarbinol-functionalized polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was converted via esterification into a chain transfer agent (CTA) for reversible addition–fragmentation chain transfer (RAFT) polymerization. The degree of esterification was determined to be 94 ± 1% by 1H NMR spectroscopy and 92 ± 1% by UV absorption spectroscopy. This PDMS CTA was then utilized for the dispersion polymerization of benzyl methacrylate (BzMA) in n-heptane at 70 °C. As the PBzMA block grows, it becomes insoluble in the reaction medium, which drives the in situ formation of PDMS–PBzMA Diblock Copolymer nanoparticles via polymerization-induced self-assembly (PISA). Depending on the precise reaction conditions, the final Diblock Copolymer chains can self-assemble to form spheres, worms, or vesicles. Systematic variation of the Copolymer concentration and the target degree of polymerization (DP) of the PBzMA block enables construction of a phase diagram that allows the reproducible targeting of pure co...

  • raft aqueous dispersion polymerization yields poly ethylene glycol based Diblock Copolymer nano objects with predictable single phase morphologies
    Journal of the American Chemical Society, 2014
    Co-Authors: Nicholas J Warren, Daniel Mahmood, Oleksand O Mykhaylyk, Anthony J Ryan, Steven P. Armes
    Abstract:

    A poly(ethylene glycol) (PEG) macromolecular chain transfer agent (macro-CTA) is prepared in high yield (>95%) with 97% dithiobenzoate chain-end functionality in a three-step synthesis starting from a monohydroxy PEG113 precursor. This PEG113-dithiobenzoate is then used for the reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). Polymerizations conducted under optimized conditions at 50 °C led to high conversions as judged by (1)H NMR spectroscopy and relatively low Diblock Copolymer polydispersities (M(w)/M(n) < 1.25) as judged by GPC. The latter technique also indicated good blocking efficiencies, since there was minimal PEG113 macro-CTA contamination. Systematic variation of the mean degree of polymerization of the core-forming PHPMA block allowed PEG113-PHPMA(x) Diblock Copolymer spheres, worms, or vesicles to be prepared at up to 17.5% w/w solids, as judged by dynamic light scattering and transmission electron microscopy studies. Small-angle X-ray scattering (SAXS) analysis revealed that more exotic oligolamellar vesicles were observed at 20% w/w solids when targeting highly asymmetric Diblock compositions. Detailed analysis of SAXS curves indicated that the mean number of membranes per oligolamellar vesicle is approximately three. A PEG113-PHPMA(x) phase diagram was constructed to enable the reproducible targeting of pure phases, as opposed to mixed morphologies (e.g., spheres plus worms or worms plus vesicles). This new RAFT PISA formulation is expected to be important for the rational and efficient synthesis of a wide range of biocompatible, thermo-responsive PEGylated Diblock Copolymer nano-objects for various biomedical applications.

Thomas P Russell - One of the best experts on this subject based on the ideXlab platform.

  • synthesis and photophysical property of well defined donor acceptor Diblock Copolymer based on regioregular poly 3 hexylthiophene and fullerene
    Journal of Materials Chemistry, 2009
    Co-Authors: Jea Uk Lee, Todd Emrick, Ali Cirpan, Thomas P Russell
    Abstract:

    A new, well-defined Diblock Copolymer (P3HT-b-C60) based on regioregular poly(3-hexylthiophene) (P3HT) and fullerene was synthesized. First, regioregular P3HT was synthesized through Grignard metathesis polymerization, and then methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) were Copolymerized by using an end-functionalized P3HT as a macroinitiator for the atom transfer radical polymerization to yield a Diblock Copolymer (P3HT-b-P(MMA-r-HEMA)). A fullerene derivative functionalized with carboxylic acid, [6,6]-phenyl-C61-butyric acid (PCBA), was then chemically linked to the HEMA unit in the second block (P(MMA-r-HEMA)) to produce a Diblock Copolymer with the second block containing fullerenes. Annealing thin films of the Copolymer revealed nanometer-scale phase separation, a more suitable morphology for enabling excitons generated in the P3HT domain to more efficiently reach the donor–acceptor interface, relative to simple blends of P3HT and C60. As a result, photoluminescence of the P3HT-b-C60Diblock Copolymer in the films showed a complete quenching of photoluminescence of P3HT, which is indicative of charge transfer between P3HT and fullerene.

  • surface functionalized cdse nanorods for assembly in Diblock Copolymer templates
    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 2006
    Co-Authors: Qingling Zhang, Suresh Gupta, Todd Emrick, Thomas P Russell
    Abstract:

    Poly(ethylene oxide)-covered CdSe nanorods were prepared and assembled in Diblock Copolymer templates by floating the block Copolymer templates onto aqueous nanorod solutions. The assembly was enabled by consideration of the surface ligand coverage of the nanorods. Alkane-covered CdSe nanorods prepared by state-of-the-art techniques are not compatible with this assembly process. However, poly(ethylene oxide) (PEO)-functionalized CdSe nanorods were successfully used to assemble the nanorods into the channels and pores of Diblock Copolymer templates. Other water-dispersible CdSe nanorods, such as those covered with 11-mercaptoundecanoic acid (MUA), did not give the desired assemblies. These results are understood by considering the surface energies of the PEO-covered CdSe nanorods in this interfacial assembly process.

  • electric field induced sphere to cylinder transition in Diblock Copolymer thin films
    Macromolecules, 2004
    Co-Authors: A V Zvelindovsky, G J A Sevink, Oleg Gang, B M Ocko, Yuqing Zhu, Samuel P Gido, Thomas P Russell
    Abstract:

    An electric field induced sphere-to-cylinder transition in thin films of asymmetric polystyrene-b-poly(methyl methacrylate) Diblock Copolymers was observed. In the absence of an applied electric field, thin films of the asymmetric Diblock Copolymer consisted of layers of spherical microdomains with poor in-plane long-range ordering. Under a ∼40V/μm applied electric field, hexagonally packed cylindrical microdomains normal to the surface were found. Cross-sectional transmission electron microscopy images of the intermediate stages of the alignment indicated that, under an electric field, the asymmetric Diblock Copolymer formed spherical microdomains that were deformed into ellipsoids and, with time, interconnected into cylindrical microdomains oriented in the direction of the applied electric field. Simulations suggest that improved long-range order of the cylindrical microdomains could be achieved by cycling the electrical field.

  • electric field alignment of asymmetric Diblock Copolymer thin films
    Macromolecules, 2004
    Co-Authors: A V Zvelindovsky, G J A Sevink, Hiroshi Jinnai, K S Lyakhova, Thomas P Russell
    Abstract:

    The electric field alignment of cylindrical microdomains in Diblock Copolymer thin films was studied using small-angle neutron scattering and transmission electron microscopy. The alignment process was followed with the block Copolymer films in different initial states. Starting from a poorly ordered state, the cylindrical microdomain orientation was biased by the surface field that initially drove the cylindrical microdomains to be oriented parallel to the film surface. With further annealing, the cylinders were disrupted locally and formed ellipsoid-shaped microdomains that, with time, connected into cylindrical microdomains oriented in the field direction. Starting from an ordered state with cylinders parallel to the surface, the applied electric field enhanced fluctuations at the interfaces of the microdomains. The growth of the fluctuations continued until the cylindrical microdomains broke up into spherical microdomains, similar to that seen in the thermoreversible cylinder-to-sphere order−order tra...

  • local control of microdomain orientation in Diblock Copolymer thin films with electric fields
    Science, 1996
    Co-Authors: T L Morkved, Heinrich M Jaeger, M Lu, A M Urbas, E E Ehrichs, P Mansky, Thomas P Russell
    Abstract:

    Local control of the domain orientation in Diblock Copolymer thin films can be obtained by the application of electric fields on micrometer-length scales. Thin films of an asymmetric polystyrene-polymethylmethacrylate Diblock Copolymer, with cylindrical polymethylmethacrylate microdomains, were spin-coated onto substrates previously patterned with planar electrodes. The substrates, 100-nanometer-thick silicon nitride membranes, allow direct observation of the electrodes and the Copolymer domain structure by transmission electron microscopy. The cylinders aligned parallel to the electric field lines for fields exceeding 30 kilovolts per centimeter, after annealing at 250°C in an inert atmosphere for 24 hours. This technique could find application in nanostructure fabrication.

Armes S.p. - One of the best experts on this subject based on the ideXlab platform.

  • Synthesis of Diblock Copolymer spheres, worms and vesicles via RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate
    'Royal Society of Chemistry (RSC)', 2021
    Co-Authors: Hunter S.j., Mykhaylyk O.o., Jones E.r., Armes S.p.
    Abstract:

    RAFT aqueous emulsion polymerization of hydroxybutyl methacrylate using a poly(glycerol monomethacrylate) precursor leads to Diblock Copolymer spheres, worms or vesicles. A pseudo-phase diagram is constructed and the vesicles are briefly evaluated as a Pickering emulsifier

  • Investigating the adsorption of anisotropic Diblock Copolymer worms onto planar silica and nanocellulose surfaces using a quartz crystal microbalance
    'Royal Society of Chemistry (RSC)', 2021
    Co-Authors: Engström J., Armes S.p., Reid M.s., Brotherton E.e., Malmström E., Hatton F.l.
    Abstract:

    Electrostatic adsorption of cationic polyelectrolytes onto anionic cellulosic substrates is an attractive route for facile surface modification of biorenewable materials. Recently, attention has focused on adsorbing cationic spherical Diblock Copolymer nanoparticles onto model cellulose and/or nanocellulosic substrates. Herein, we investigate physical adsorption of highly anisotropic Copolymer worms bearing either anionic or cationic charge onto planar silica, cellulose nanocrystal (CNC) or cellulose nanofibril (CNF) surfaces using quartz crystal microbalance with dissipation monitoring. Electrostatic interactions dominate in the case of anionic silica and CNC surfaces because the adsorbed mass of cationic worms was greater than that of anionic worms. However, either anionic or cationic worms could be adsorbed onto in situ generated CNF substrates, suggesting that additional interactions were involved: hydrogen bonding, van der Waals forces, and possibly covalent bond formation. Scanning electron and atomic force microscopy studies of the dried planar substrates after adsorption experiments confirmed the presence of adsorbed Copolymer worms. Finally, composite worm/CNF films exhibited restricted swelling behavior when immersed in water compared to reference CNF films, suggesting that the worms reinforce CNF films by acting as a physical crosslinker. This study is the first investigation of the physical adsorption of highly anisotropic Diblock Copolymer worms onto cellulosic surfaces

  • Oil-in-oil pickering emulsions stabilized by Diblock Copolymer nanoparticles
    'Elsevier BV', 2020
    Co-Authors: Rymaruk M.j., Cunningham V.j., Brown S.l., Williams C.n., Armes S.p.
    Abstract:

    Hypothesis Diblock Copolymer nanoparticles have been shown to be Pickering emulsifiers for both oil-in-water and water-in-oil emulsions. Recently, we reported the preparation of sterically-stabilized Diblock Copolymer spheres in a low-viscosity silicone oil (Macromolecules 53 (2020) 1785–1794). We hypothesized that such spheres could be used as a Pickering emulsifier for a range of oil-in-oil emulsions comprising droplets of a bio-sourced oil dispersed in silicone oil. Experiments Diblock Copolymer spheres were prepared via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in silicone oil and characterized by dynamic light scattering and transmission electron microscopy. These spheres were evaluated as Pickering emulsifiers for a series of oil-in-oil Pickering emulsions. The influence of both sphere size and core-forming block composition was investigated. Findings Optimization of the nanoparticle size and core-forming block composition enabled stable bio-sourced oil-in-silicone emulsions to be obtained for nine out of the ten bio-sourced oils investigated. These emulsions were characterized in terms of their mean droplet size by optical microscopy

  • RAFT dispersion polymerisation of lauryl methacrylate in ethanol–water binary mixtures: synthesis of Diblock Copolymer vesicles with deformable membranes
    'Royal Society of Chemistry (RSC)', 2020
    Co-Authors: Gibson R.r., Cornel E.j., Musa O.m., Fernyhough A., Armes S.p.
    Abstract:

    Polymerisation-induced self-assembly (PISA) is widely recognised to be a powerful platform technology for the rational synthesis of Diblock Copolymer nano-objects. RAFT alcoholic dispersion polymerisation is an important PISA formulation that has been used to prepare block Copolymer spheres, worms and vesicles. In this study, we have utilised the RAFT dispersion polymerisation of lauryl methacrylate (LMA) using a poly(N-(2-methacryloyloxy)ethyl pyrrolidone) (PNMEP) stabiliser in order to prepare vesicles with highly deformable membranes. More specifically, a PNMEP28 precursor was chain-extended with LMA in an 80 : 20 w/w ethanol–water mixture to produce a series of PNMEP28-PLMAx Diblock Copolymer nano-objects (Mw/Mn ≤ 1.40; LMA conversions ≥98% in all cases, as indicated by 1H NMR spectroscopy). Differential scanning calorimetry studies confirmed that the membrane-forming PLMA block had a relatively low glass transition temperature. Transmission electron microscopy and small angle X-ray scattering were used to identify Copolymer morphologies for these highly asymmetric Diblock Copolymers. A mixed sphere and vesicle morphology was observed when targeting x = 43, while polydisperse vesicles were obtained for x = 65–151. Slightly smaller vesicles with lower mean aggregation numbers and thicker membranes were obtained when targeting higher PLMA DPs. A minor population of sheet-like lamellae was observed for each target Copolymer composition, with lamellar stacking leading to a structure peak in the scattering patterns recorded for PNMEP28-PLMA129 and PNMEP28-PLMA151. Bearing in mind potential industrial applications, RAFT chain-end removal strategies were briefly explored for such PNMEP28-PLMAx vesicles. Thus, 96% of dithiobenzoate chain-ends could be removed within 3 h at 50 °C via LED irradiation of a 7.5% aqueous dispersion of PNMEP28-PLMA87 vesicles at a wavelength of 405 nm. This appears to be an attractive method for RAFT chain-end removal from Diblock Copolymer nano-objects, particularly those comprising highly hydrophobic cores

  • Rationally designed anionic Diblock Copolymer worm gels are useful model systems for calcite occlusion studies
    'Royal Society of Chemistry (RSC)', 2019
    Co-Authors: Fielding L.a., Hendley Iv C.t., Asenath-smith E., Estroff L.a., Armes S.p.
    Abstract:

    Binary mixtures of anionic and non-ionic macromolecular chain transfer agents (macro-CTAs) are utilized in order to rationally design Diblock Copolymer nanoparticles with tunable morphologies and anionic character via pseudo-living radical polymerization. More specifically, poly(methacrylic acid) (PMAA) and poly(glycerol monomethacrylate) (PGMA) macro-CTAs are pre-mixed prior to reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization of 2-hydroxypropyl methacrylate (HPMA). This strategy facilitates the formation of PHPMA-based Diblock Copolymer spheres, worm-like micelles and vesicles via polymerization-induced self-assembly (PISA). The presence of the anionic PMAA stabilizer block has a dramatic impact on the resulting Copolymer morphology, particularly if the degree of polymerization (DP) of the PMAA stabilizer chains is longer than that of the PGMA. Two phase diagrams have been constructed to investigate the effect of the relative proportion and molar mass of the two macro-CTAs. Such a systematic approach is essential for the reproducible synthesis of pure worm-like micelles, which occupy relatively narrow phase space. The rheological behavior of a series of soft, free-standing worm gels is investigated. Finally, such gels are examined as model matrices for the growth of biomimetic calcite crystals and the role of the anionic PMAA stabilizer chains in directing crystal growth is evaluated