The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform
Rolando Castillo - One of the best experts on this subject based on the ideXlab platform.
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Alignment of Worm-Like Micelles at intermediate and high shear rates.
Journal of Colloid and Interface Science, 2019Co-Authors: Brisa Arenas-gómez, Cristina Garza, Rolando CastilloAbstract:Abstract Hypothesis Rheology combined with Small-Angle Neutron Scattering (Rheo-SANS) can determine the local structural order in Worm-Like Micelle (WLM) solutions when the shear rate increases beyond the ending of the gradient shear banding. There, Micelles are supposedly aligned, but viscosity reveals a transition regime as the shear rate increases. Experiments The mixture of 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate (TDPS), sodium dodecylsulfate (SDS) (R = [SDS]/[TDPS] = 0.55), and a water solution of NaCl (0.2 mol/L), was studied with mechanical rheology and Small-Angle Neutron Scattering (SANS) in the quiescent fluid and under flow. Findings The system self-assembles in WLMs and presents gradient shear banding. SANS patterns of the bands formed during the shear banding were obtained in a Couette geometry along the 1–2 plane, as well as the orientation parameter along the gap. At very high shear rates, in the paranematic phase, we found an apparent transition on the flow curves with its corresponding change in the orientation parameter. The origin of this transition is unclear, but we present possible explanations of why we observe it.
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Structure, rheology, and microrheology of wormlike Micelles made of PB–PEO diblock copolymers
Soft Matter, 2018Co-Authors: Antonio Tavera-vázquez, Brisa Arenas-gómez, Cristina Garza, Rolando CastilloAbstract:A diblock copolymer made of poly(1,4-butadiene)-block-polyethylene oxide, with a degree of polymerization of the polybutadiene and polyethylene oxide blocks of 37 and 57, respectively, self-assembles in water as Worm-Like Micelles determined by small angle neutron scattering with an average diameter of ∼12.7 nm, a core radius of ∼2.7 nm, a shell radius of ∼3 nm, and an estimated persistence length of >225 nm. Worm-Like Micelles of almost the same diblock copolymer, but with a smaller polyethylene oxide block (degree of polymerization 45) were also measured. The Worm-Like Micelles were also observed with negative staining using low energy electron microscopy. The boundary between dilute and semidilute regimes was estimated to be ∼0.8 wt%. The viscoelastic spectra at low and intermediate frequencies do not follow the Maxwell model. These Micelles do not present the same rheological behavior of Worm-Like Micelle solutions of conventional surfactants. The slow dynamics of the self-assembly explains this uncommon behavior for the system. Any micellar rearrangement is impeded due to the extremely high hydrophobicity of the polybutadiene block; stress mainly relaxes by the reptation mechanism. Using diffusive wave spectroscopy, we measured the mean square displacement of particles in the micellar solution. From the mean square displacement, we obtained G′(ω) and G′′(ω) at high frequencies. |G*| exhibits a power law behavior showing the stress relaxation changes as frequency increases, first dominated by the Rouse–Zimm modes and then by the bending modes of the Kuhn segments. This allowed us to estimate the Worm-Like Micelle persistence lengths that depend on the copolymer concentration.
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Worm-Like Micelles in water solutions of 1, 4 poly (1, 3-butadiene)-polyethylene oxide diblock copolymer
The European Physical Journal E, 2014Co-Authors: Brisa Arenas-gómez, Cristina Garza, Marko Vinceković, Rolando CastilloAbstract:The main purpose of this study is to determine for the first time the structure of the self-assembled aggregates in the system made of 1,4 poly(1,3-butadiene)-polyethylene oxide diblock copolymer (IUPAC name: poly(but-2-ene-1,4-diyl)-block-polyoxyethylene) and water, and the rheological behavior of the solution. The degree of polymerization of the polybutadiene and polyethylene oxide blocks is 37 and 45, respectively. The diblock copolymer concentration was limited to be $ \le$ 2.5 wt% to avoid phase separation. Small X-ray scattering revealed that the diblock copolymer self-assembles in Worm-Like Micelles with a diameter of ∼ 12 nm. This system does not closely follow the rheological behavior of Worm-Like Micelle solutions made of typical surfactants. The system steadily shear thins reaching very low viscosity values at large shear rates, however there are not shear-thickening peaks. In thixotropic loops, the micellar solution does not present hysteresis. The viscoelastic spectra do not follow the Maxwell model at low and intermediate frequencies. This uncommon behavior for a Worm-Like micellar system is explained by the slow dynamics of the self-assembly. The extremely high hydrophobicity of the polybutadiene block does not allow any micellar rearrangement Graphical abstract
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Worm-Like Micelles in water solutions of 1, 4 poly (1, 3-butadiene)-polyethylene oxide diblock copolymer
European Physical Journal E, 2014Co-Authors: Brisa Arenas-g??mez, Marko Vincekovi??, Cecilia De La Garza, Rolando CastilloAbstract:The main purpose of this study is to determine for the first time the structure of the self-assembled aggregates in the system made of 1,4 poly(1,3-butadiene)-polyethylene oxide diblock copolymer (IUPAC name: poly(but-2-ene-1,4-diyl)-block-polyoxyethylene) and water, and the rheological behavior of the solution. The degree of polymerization of the polybutadiene and polyethylene oxide blocks is 37 and 45, respectively. The diblock copolymer concentration was limited to be ≤2.5 wt% to avoid phase separation. Small X-ray scattering revealed that the diblock copolymer self-assembles in Worm-Like Micelles with a diameter of ∼ 12 nm. This system does not closely follow the rheological behavior of Worm-Like Micelle solutions made of typical surfactants. The system steadily shear thins reaching very low viscosity values at large shear rates, however there are not shear-thickening peaks. In thixotropic loops, the micellar solution does not present hysteresis. The viscoelastic spectra do not follow the Maxwell model at low and intermediate frequencies. This uncommon behavior for a Worm-Like micellar system is explained by the slow dynamics of the self-assembly. The extremely high hydrophobicity of the polybutadiene block does not allow any micellar rearrangement.
Frank S. Bates - One of the best experts on this subject based on the ideXlab platform.
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Structure and properties of PBO–PEO diblock copolymer modified epoxy
Journal of Polymer Science Part B, 2020Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems.
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Structure and properties of PBO-PEO diblock copolymer modified epoxy
Journal of Polymer Science, Part B: Polymer Physics, 2005Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems. (c) 2005 Wiley Periodicals, Inc.
Junxian Wu - One of the best experts on this subject based on the ideXlab platform.
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Structure and properties of PBO–PEO diblock copolymer modified epoxy
Journal of Polymer Science Part B, 2020Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems.
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Structure and properties of PBO-PEO diblock copolymer modified epoxy
Journal of Polymer Science, Part B: Polymer Physics, 2005Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems. (c) 2005 Wiley Periodicals, Inc.
Yonathan S. Thio - One of the best experts on this subject based on the ideXlab platform.
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Structure and properties of PBO–PEO diblock copolymer modified epoxy
Journal of Polymer Science Part B, 2020Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems.
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Structure and properties of PBO-PEO diblock copolymer modified epoxy
Journal of Polymer Science, Part B: Polymer Physics, 2005Co-Authors: Junxian Wu, Yonathan S. Thio, Frank S. BatesAbstract:Amphiphilic poly(n-butylene oxide)-b-poly(ethylene oxide) (PBO-PEO) diblock copolymers of various compositions were synthesized and studied as modifiers for epoxy resins. In blends of PBO-PEO, epoxy resin, and curing agent, the copolymers formed well-defined microstructures that persisted upon curing of the epoxy. The resulting morphologies were vesicles, Worm-Like Micelles, and spherical Micelles (in order of increasing size of PEO block), as well as transitional morphologies. Addition of 5% by weight of these block copolymers improved the fracture toughness of the epoxy by as much as 19 times with relatively small reduction in the elastic modulus. The highest level of toughness was measured in a system containing branched Worm-Like Micelles. Close examination of the fracture surfaces of these compositions suggests that although all the dispersed morphologies played a similar role to inclusions in particle-toughened thermosets, crack deflection toughening contributed to the significantly higher levels of toughness in the Worm-Like Micelle systems. (c) 2005 Wiley Periodicals, Inc.
Brisa Arenas-gómez - One of the best experts on this subject based on the ideXlab platform.
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Alignment of Worm-Like Micelles at intermediate and high shear rates.
Journal of Colloid and Interface Science, 2019Co-Authors: Brisa Arenas-gómez, Cristina Garza, Rolando CastilloAbstract:Abstract Hypothesis Rheology combined with Small-Angle Neutron Scattering (Rheo-SANS) can determine the local structural order in Worm-Like Micelle (WLM) solutions when the shear rate increases beyond the ending of the gradient shear banding. There, Micelles are supposedly aligned, but viscosity reveals a transition regime as the shear rate increases. Experiments The mixture of 3-[dimethyl(tetradecyl)azaniumyl]propane-1-sulfonate (TDPS), sodium dodecylsulfate (SDS) (R = [SDS]/[TDPS] = 0.55), and a water solution of NaCl (0.2 mol/L), was studied with mechanical rheology and Small-Angle Neutron Scattering (SANS) in the quiescent fluid and under flow. Findings The system self-assembles in WLMs and presents gradient shear banding. SANS patterns of the bands formed during the shear banding were obtained in a Couette geometry along the 1–2 plane, as well as the orientation parameter along the gap. At very high shear rates, in the paranematic phase, we found an apparent transition on the flow curves with its corresponding change in the orientation parameter. The origin of this transition is unclear, but we present possible explanations of why we observe it.
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Structure, rheology, and microrheology of wormlike Micelles made of PB–PEO diblock copolymers
Soft Matter, 2018Co-Authors: Antonio Tavera-vázquez, Brisa Arenas-gómez, Cristina Garza, Rolando CastilloAbstract:A diblock copolymer made of poly(1,4-butadiene)-block-polyethylene oxide, with a degree of polymerization of the polybutadiene and polyethylene oxide blocks of 37 and 57, respectively, self-assembles in water as Worm-Like Micelles determined by small angle neutron scattering with an average diameter of ∼12.7 nm, a core radius of ∼2.7 nm, a shell radius of ∼3 nm, and an estimated persistence length of >225 nm. Worm-Like Micelles of almost the same diblock copolymer, but with a smaller polyethylene oxide block (degree of polymerization 45) were also measured. The Worm-Like Micelles were also observed with negative staining using low energy electron microscopy. The boundary between dilute and semidilute regimes was estimated to be ∼0.8 wt%. The viscoelastic spectra at low and intermediate frequencies do not follow the Maxwell model. These Micelles do not present the same rheological behavior of Worm-Like Micelle solutions of conventional surfactants. The slow dynamics of the self-assembly explains this uncommon behavior for the system. Any micellar rearrangement is impeded due to the extremely high hydrophobicity of the polybutadiene block; stress mainly relaxes by the reptation mechanism. Using diffusive wave spectroscopy, we measured the mean square displacement of particles in the micellar solution. From the mean square displacement, we obtained G′(ω) and G′′(ω) at high frequencies. |G*| exhibits a power law behavior showing the stress relaxation changes as frequency increases, first dominated by the Rouse–Zimm modes and then by the bending modes of the Kuhn segments. This allowed us to estimate the Worm-Like Micelle persistence lengths that depend on the copolymer concentration.
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Worm-Like Micelles in water solutions of 1, 4 poly (1, 3-butadiene)-polyethylene oxide diblock copolymer
The European Physical Journal E, 2014Co-Authors: Brisa Arenas-gómez, Cristina Garza, Marko Vinceković, Rolando CastilloAbstract:The main purpose of this study is to determine for the first time the structure of the self-assembled aggregates in the system made of 1,4 poly(1,3-butadiene)-polyethylene oxide diblock copolymer (IUPAC name: poly(but-2-ene-1,4-diyl)-block-polyoxyethylene) and water, and the rheological behavior of the solution. The degree of polymerization of the polybutadiene and polyethylene oxide blocks is 37 and 45, respectively. The diblock copolymer concentration was limited to be $ \le$ 2.5 wt% to avoid phase separation. Small X-ray scattering revealed that the diblock copolymer self-assembles in Worm-Like Micelles with a diameter of ∼ 12 nm. This system does not closely follow the rheological behavior of Worm-Like Micelle solutions made of typical surfactants. The system steadily shear thins reaching very low viscosity values at large shear rates, however there are not shear-thickening peaks. In thixotropic loops, the micellar solution does not present hysteresis. The viscoelastic spectra do not follow the Maxwell model at low and intermediate frequencies. This uncommon behavior for a Worm-Like micellar system is explained by the slow dynamics of the self-assembly. The extremely high hydrophobicity of the polybutadiene block does not allow any micellar rearrangement Graphical abstract
