The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
Steven P Armes - One of the best experts on this subject based on the ideXlab platform.
-
model anionic block copolymer vesicles provide important design rules for efficient nanoparticle occlusion within calcite
Journal of the American Chemical Society, 2019Co-Authors: Yin Ning, Lijuan Han, Matthew J Derry, Fiona C Meldrum, Steven P ArmesAbstract:Nanoparticle occlusion within growing crystals is of considerable interest because (i) it can enhance our understanding of biomineralization and (ii) it offers a straightforward route for the preparation of novel nanocomposites. However, robust design rules for efficient occlusion remain elusive. Herein, we report the rational synthesis of a series of silica-loaded poly(glycerol monoMethacrylate)-poly(2-Hydroxypropyl Methacrylate)-poly(ethylene glycol diMethacrylate)-poly(methacrylic acid) tetrablock copolymer vesicles using polymerization-induced self-assembly. The overall vesicle dimensions remain essentially constant for this series; hence systematic variation of the mean degree of polymerization (DP) of the anionic poly(methacrylic acid) steric stabilizer chains provides an unprecedented opportunity to investigate the design rules for efficient nanoparticle occlusion within host inorganic crystals such as calcite. Indeed, the stabilizer DP plays a decisive role in dictating both the extent of occlusion and the calcite crystal morphology: sufficiently long stabilizer chains are required to achieve extents of vesicle occlusion of up to 41 vol %, but overly long stabilizer chains merely lead to significant changes in the crystal morphology, rather than promoting further occlusion. Furthermore, steric stabilizer chains comprising anionic carboxylate groups lead to superior occlusion performance compared to those composed of phosphate, sulfate, or sulfonate groups. Moreover, occluded vesicles are subjected to substantial deformation forces, as shown by the significant change in shape after their occlusion. It is also demonstrated that such vesicles can act as "Trojan horses", enabling the occlusion of non-functional silica nanoparticles within calcite. In summary, this study provides important new physical insights regarding the efficient incorporation of guest nanoparticles within host inorganic crystals.
-
synthesis characterization and pickering emulsifier performance of anisotropic cross linked block copolymer worms effect of aspect ratio on emulsion stability in the presence of surfactant
Langmuir, 2019Co-Authors: Saul J Hunter, Matthew J Derry, Kate L Thompson, Joseph R Lovett, Fiona L Hatton, Chris Ian Lindsay, Philip Taylor, Steven P ArmesAbstract:Reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization is used to prepare epoxy-functional PGMA-P(HPMA- stat-GlyMA) diblock copolymer worms, where GMA, HPMA, and GlyMA denote glycerol monoMethacrylate, 2-Hydroxypropyl Methacrylate, and glycidyl Methacrylate, respectively. The epoxy groups on the GlyMA residues were ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to cross-link the worm cores via a series of hydrolysis-condensation reactions. Importantly, the worm aspect ratio can be adjusted depending on the precise conditions selected for covalent stabilization. Relatively long cross-linked worms are obtained by reaction with APTES at 20 °C, whereas much shorter worms with essentially the same copolymer composition are formed by cooling the linear worms from 20 to 4 °C prior to APTES addition. Small-angle X-ray scattering (SAXS) studies confirmed that the mean aspect ratio for the long worms is approximately eight times greater than that for the short worms. Aqueous electrophoresis studies indicated that both types of cross-linked worms acquired weak cationic surface charge at low pH as a result of protonation of APTES-derived secondary amine groups within the nanoparticle cores. These cross-linked worms were evaluated as emulsifiers for the stabilization of n-dodecane-in-water emulsions via high-shear homogenization at 20 °C and pH 8. Increasing the copolymer concentration led to a reduction in mean droplet diameter, indicating that APTES cross-linking was sufficient to allow the nanoparticles to adsorb intact at the oil/water interface and hence produce genuine Pickering emulsions, rather than undergo in situ dissociation to form surface-active diblock copolymer chains. In surfactant challenge studies, the relatively long worms required a thirty-fold higher concentration of a nonionic surfactant (Tween 80) to be displaced from the n-dodecane-water interface compared to the short worms. This suggests that the former nanoparticles are much more strongly adsorbed than the latter, indicating that significantly greater Pickering emulsion stability can be achieved by using highly anisotropic worms. In contrast, colloidosomes prepared by reacting the hydroxyl-functional adsorbed worms with an oil-soluble polymeric diisocyanate remained intact when exposed to high concentrations of Tween 80.
-
Synthesis, Characterization, and Pickering Emulsifier Performance of Anisotropic Cross-Linked Block Copolymer Worms: Effect of Aspect Ratio on Emulsion Stability in the Presence of Surfactant
2018Co-Authors: Saul J Hunter, Matthew J Derry, Kate L Thompson, Joseph R Lovett, Fiona L Hatton, Philip Taylor, Christopher Lindsay, Steven P ArmesAbstract:Reversible addition–fragmentation chain transfer (RAFT) aqueous dispersion polymerization is used to prepare epoxy-functional PGMA–P(HPMA-stat-GlyMA) diblock copolymer worms, where GMA, HPMA, and GlyMA denote glycerol monoMethacrylate, 2-Hydroxypropyl Methacrylate, and glycidyl Methacrylate, respectively. The epoxy groups on the GlyMA residues were ring-opened using 3-aminopropyltriethoxysilane (APTES) in order to cross-link the worm cores via a series of hydrolysis–condensation reactions. Importantly, the worm aspect ratio can be adjusted depending on the precise conditions selected for covalent stabilization. Relatively long cross-linked worms are obtained by reaction with APTES at 20 °C, whereas much shorter worms with essentially the same copolymer composition are formed by cooling the linear worms from 20 to 4 °C prior to APTES addition. Small-angle X-ray scattering (SAXS) studies confirmed that the mean aspect ratio for the long worms is approximately eight times greater than that for the short worms. Aqueous electrophoresis studies indicated that both types of cross-linked worms acquired weak cationic surface charge at low pH as a result of protonation of APTES-derived secondary amine groups within the nanoparticle cores. These cross-linked worms were evaluated as emulsifiers for the stabilization of n-dodecane-in-water emulsions via high-shear homogenization at 20 °C and pH 8. Increasing the copolymer concentration led to a reduction in mean droplet diameter, indicating that APTES cross-linking was sufficient to allow the nanoparticles to adsorb intact at the oil/water interface and hence produce genuine Pickering emulsions, rather than undergo in situ dissociation to form surface-active diblock copolymer chains. In surfactant challenge studies, the relatively long worms required a thirty-fold higher concentration of a nonionic surfactant (Tween 80) to be displaced from the n-dodecane–water interface compared to the short worms. This suggests that the former nanoparticles are much more strongly adsorbed than the latter, indicating that significantly greater Pickering emulsion stability can be achieved by using highly anisotropic worms. In contrast, colloidosomes prepared by reacting the hydroxyl-functional adsorbed worms with an oil-soluble polymeric diisocyanate remained intact when exposed to high concentrations of Tween 80
-
Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos
2016Co-Authors: Irene Canton, Nicholas J. Warren, Aman Chahal, Katherine Amps, Andrew Wood, Richard Weightman, Eugenia Wang, Harry Moore, Steven P ArmesAbstract:Human pluripotent stem cells (hPSCs; both embryonic and induced pluripotent) rapidly proliferate in adherent culture to maintain their undifferentiated state. However, for mammals exhibiting delayed gestation (diapause), mucin-coated embryos can remain dormant for days or months in utero, with their constituent PSCs remaining pluripotent under these conditions. Here we report cellular stasis for both hPSC colonies and preimplantation embryos immersed in a wholly synthetic thermoresponsive gel comprising poly(glycerol monoMethacrylate)-poly(2-Hydroxypropyl Methacrylate) [PGMA55-PHPMA135] diblock copolymer worms. This hydroxyl-rich mucin-mimicking nonadherent 3D gel maintained PSC viability and pluripotency in the quiescent G0 state without passaging for at least 14 days. Similarly, gel-coated human embryos remain in a state of suspended animation (diapause) for up to 8 days. The discovery of a cryptic cell arrest mechanism for both hPSCs and embryos suggests an important connection between the cellular mechanisms that evoke embryonic diapause and pluripotency. Moreover, such synthetic worm gels offer considerable utility for the short-term (weeks) storage of either pluripotent stem cells or human embryos without cryopreservation
-
synthesis and characterization of poly amino acid Methacrylate stabilized diblock copolymer nano objects
Polymer Chemistry, 2015Co-Authors: Vincent Ladmiral, Mona Semsarilar, Alexandre Charlot, Steven P ArmesAbstract: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.
Rongguo Wang - One of the best experts on this subject based on the ideXlab platform.
-
molecular dynamics simulations of the effect of sizing agent on the interface property in carbon fiber reinforced vinyl ester resin composite
Applied Surface Science, 2019Co-Authors: Weiwei Jiao, Weicheng Jiao, Tianlu Zheng, Wenbo Liu, Rongguo WangAbstract:Abstract The role of sizing agent in the formation of interphase and the effect on the interfacial properties of carbon fiber (CF) reinforced vinyl ester resin (VE) composite were studied by molecular dynamics (MD) simulations. A novel unsaturated sizing agent N-(4′4-diaminodiphenyl methane)-2-Hydroxypropyl Methacrylate (DMHM) was used in this study. Epoxy sizing agent (E44) and modified epoxy sizing agent (ME44) were used for comparison. Simulation results showed that DMHM exhibited the highest interfacial bonding strength with CF surface due to the strong polarity of the sizing agent molecule. This result was confirmed by the interfacial shear strength test. The swelling effect of sizing agent in liquid VE was evaluated by solubility in styrene and compatibility with VE component. All three sizing agents had good solubility in styrene according to the calculation of total solvation free energy, while E44 and DMHM exhibited good compatibility with VE molecule based on the mixing energy calculation. The swelling property of sizing agent was confirmed by nano-indentation test. The results of this study explain the higher interfacial shear strength (62.25 MPa) between VE and CF sized by DMHM.
-
preparation of carbon fiber unsaturated sizing agent for enhancing interfacial strength of carbon fiber vinyl ester resin composite
Applied Surface Science, 2018Co-Authors: Weiwei Jiao, Weicheng Jiao, Long Jiang, Fan Yang, Rongguo WangAbstract:Abstract The practical application of carbon fiber (CF) reinforced vinyl ester resin (VE) composite was hampered seriously by the poor interfacial adhesion property. In this work, a novel unsaturated sizing agent was designed and prepared to improve the interfacial strength by covalently bonding CF with VE matrix. The main component of the sizing agent, N-(4′4-diaminodiphenyl methane)-2-Hydroxypropyl Methacrylate (DMHM), was synthesized and confirmed by FTIR and NMR. XPS results of sized carbon fiber (SCF) showed that DMHM has adhered to desized fiber surface and reacted with some active functional groups on the surface. The SCF was characterized by high surface roughness and surface energy (especially the polar component), which means better wettability by VE. As a result, the interface shear strength and interlaminar shear strength of SCF/VE composite were enhanced by 96.56% and 66.07% respectively compared with CF/VE composite, benefited mainly from the strong and tough interphase.
S J Greaves - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of vinyl polymer silica colloidal nanocomposites prepared using commercial alcoholic silica sols
Langmuir, 2004Co-Authors: M J Percy, Steven P Armes, S J Greaves, J I Amalvy, David P Randall, John F WattsAbstract:The surfactant-free synthesis of vinyl polymer−silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl Methacrylate, methyl acrylate, n-butyl acrylate, and 2-Hydroxypropyl Methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1−2 h at 25 °C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more po...
-
synthesis of vinyl polymer silica colloidal nanocomposites via aqueous dispersion polymerization
Langmuir, 2003Co-Authors: M J Percy, V Michailidou, Steven P Armes, Christian Perruchot, John F Watts, S J GreavesAbstract:The surfactant-free synthesis of colloidal dispersions of vinyl polymer−silica nanocomposite particles in aqueous media using a batch emulsion polymerization protocol has been previously described [Percy, M. J.; et al. Langmuir 2000, 16, 6913]. In the present work 2-Hydroxypropyl Methacrylate [HPMA] was copolymerized with 4-vinylpyridine [4VP] using ammonium persulfate in the presence of an ultrafine silica sol. 4VP is used as an auxiliary in these syntheses; the strong interaction of this basic monomer with the acidic surface of the silica particles is essential for successful nanocomposite particle formation. HPMA monomer was selected since it has appreciable water solubility (up to 13% at 20 °C), but HPMA homopolymer is water-insoluble. This unusual solubility behavior ensured that these nanocomposite syntheses were conducted under true dispersion polymerization conditions. In view of the success of these syntheses, we conclude that emulsion monomer droplets and micelles are not a prerequisite for the ...
John F Watts - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of vinyl polymer silica colloidal nanocomposites prepared using commercial alcoholic silica sols
Langmuir, 2004Co-Authors: M J Percy, Steven P Armes, S J Greaves, J I Amalvy, David P Randall, John F WattsAbstract:The surfactant-free synthesis of vinyl polymer−silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl Methacrylate, methyl acrylate, n-butyl acrylate, and 2-Hydroxypropyl Methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1−2 h at 25 °C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more po...
-
synthesis of vinyl polymer silica colloidal nanocomposites via aqueous dispersion polymerization
Langmuir, 2003Co-Authors: M J Percy, V Michailidou, Steven P Armes, Christian Perruchot, John F Watts, S J GreavesAbstract:The surfactant-free synthesis of colloidal dispersions of vinyl polymer−silica nanocomposite particles in aqueous media using a batch emulsion polymerization protocol has been previously described [Percy, M. J.; et al. Langmuir 2000, 16, 6913]. In the present work 2-Hydroxypropyl Methacrylate [HPMA] was copolymerized with 4-vinylpyridine [4VP] using ammonium persulfate in the presence of an ultrafine silica sol. 4VP is used as an auxiliary in these syntheses; the strong interaction of this basic monomer with the acidic surface of the silica particles is essential for successful nanocomposite particle formation. HPMA monomer was selected since it has appreciable water solubility (up to 13% at 20 °C), but HPMA homopolymer is water-insoluble. This unusual solubility behavior ensured that these nanocomposite syntheses were conducted under true dispersion polymerization conditions. In view of the success of these syntheses, we conclude that emulsion monomer droplets and micelles are not a prerequisite for the ...
M J Percy - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of vinyl polymer silica colloidal nanocomposites prepared using commercial alcoholic silica sols
Langmuir, 2004Co-Authors: M J Percy, Steven P Armes, S J Greaves, J I Amalvy, David P Randall, John F WattsAbstract:The surfactant-free synthesis of vinyl polymer−silica nanocomposite particles has been achieved in aqueous alcoholic media at ambient temperature in the absence of auxiliary comonomers. Styrene, methyl Methacrylate, methyl acrylate, n-butyl acrylate, and 2-Hydroxypropyl Methacrylate were homopolymerized in turn in the presence of three commercially available ultrafine alcoholic silica sols. Stable colloidal dispersions with reasonably narrow size distributions were obtained, with silica contents of up to 58% by mass indicated by thermogravimetric analysis. Particle size distributions were assessed using both dynamic light scattering and disk centrifuge photosedimentometry. The former technique indicated that the particle size increased for the first 1−2 h at 25 °C and thereafter remained constant. Particle morphologies were studied using electron microscopy. Most of the colloidal nanocomposites comprised approximately spherical particles with relatively narrow size distributions, but in some cases more po...
-
synthesis of vinyl polymer silica colloidal nanocomposites via aqueous dispersion polymerization
Langmuir, 2003Co-Authors: M J Percy, V Michailidou, Steven P Armes, Christian Perruchot, John F Watts, S J GreavesAbstract:The surfactant-free synthesis of colloidal dispersions of vinyl polymer−silica nanocomposite particles in aqueous media using a batch emulsion polymerization protocol has been previously described [Percy, M. J.; et al. Langmuir 2000, 16, 6913]. In the present work 2-Hydroxypropyl Methacrylate [HPMA] was copolymerized with 4-vinylpyridine [4VP] using ammonium persulfate in the presence of an ultrafine silica sol. 4VP is used as an auxiliary in these syntheses; the strong interaction of this basic monomer with the acidic surface of the silica particles is essential for successful nanocomposite particle formation. HPMA monomer was selected since it has appreciable water solubility (up to 13% at 20 °C), but HPMA homopolymer is water-insoluble. This unusual solubility behavior ensured that these nanocomposite syntheses were conducted under true dispersion polymerization conditions. In view of the success of these syntheses, we conclude that emulsion monomer droplets and micelles are not a prerequisite for the ...
