The Experts below are selected from a list of 129 Experts worldwide ranked by ideXlab platform
Paschalis Alexandridis - One of the best experts on this subject based on the ideXlab platform.
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interaction of poloxamer block Copolymers with cosolvents and surfactants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Rouja Ivanova, Paschalis Alexandridis, Björn LindmanAbstract:Abstract The interactions of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block Copolymers (Poloxamers) with cosolvents and surfactants are addressed here. Ternary isothermal (25°C) systems of Pluronic F127 (Poloxamer 407) in the presence of water and polar water-miscible solvents (glycerol, propylene glycol or ethanol), a partially water-miscible solvent (glycerol triacetate), a non-ionic surfactant (tetraethylene glycol monooctyl ether, C8(EO)4), an anionic surfactant (sodium dodecyl sulfate, SDS), and a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) have been investigated by phase behavior studies and small angle x-ray scattering (SAXS). A number of regions with different lyotropic liquid crystalline structure have been identified in each ternary Poloxamer–water–cosolvent/surfactant system. For a given Poloxamer, the composition range over which a given self-assembled structure is stable varies according to the cosolvent/surfactant type (and properties). The effects that the different cosolvents or surfactants exhibit on the Poloxamer phase behavior are interpreted in terms of the preference of the cosolvent/surfactant Molecules to locate in different domains of the PEO–PPO–PEO block Copolymer self-assembly. Organic solvents, depending on their relative polarities, locate preferably in the PEO-rich or the PPO-rich domains of the microstructure. Some solvents (e.g. ethanol and glycerol triacetate) may show amphiphilic behavior and act as cosurfactants by preferably locating at the interface between the PEO-rich and the PPO-rich domains. The location of the solvents in the block Copolymer assemblies is established by an analysis of the trends in the structure lattice spacing (obtained from SAXS) and the interfacial area per block Copolymer Molecule.
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evolution in structural polymorphism of pluronic f127 poly ethylene oxide poly propylene oxide block Copolymer in ternary systems with water and pharmaceutically acceptable organic solvents from glycols to oils
Langmuir, 2000Co-Authors: Rouja Ivanova, And Bjo Lindma, Paschalis AlexandridisAbstract:The evolution in the self-assembly of an amphiphilic poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO-PPO-PEO) block Copolymer in ternary systems with water and organic solvents of varying relative polarity is examined. The phase behavior and microstructure of two ternary systems consisting of Pluronic F127 (Poloxamer 407), water, and the pharmaceutically acceptable solvents propylene carbonate (4-methyl-1,3-dioxolan-2-one) or triacetin (glycerol triacetate) are presented. The microstructure of the lyotropic liquid crystalline phases formed and their characteristic length scales are determined from small-angle X-ray scattering (SAXS). The trends in the SAXS lattice spacing and the interfacial area per block Copolymer Molecule help establish the location of the solvents in the microstructure. The phase behavior of the two systems studied here is discussed in the context of ternary systems of Pluronic F127 with water and polar solvents (“glycols”, e.g., propylene glycol) or apolar organi...
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13C-NMR Evidence on Amphiphile Lifetime in Reverse (Water-in-Oil) Micelles Formed by a Poloxamer Block Copolymer
Journal of colloid and interface science, 1998Co-Authors: Paula C. A. Barreleiro, Paschalis AlexandridisAbstract:Abstract The dynamics of exchange between amphiphile assembled in reverse (water-in-oil) micelles and unimer (free in solution) amphiphile were probed by13C-NMR spectroscopy in a ternary isothermal system consisting of a poly(ethylene oxide)-poly(propylene oxide) block Copolymer (poloxamer), water, and xylene. An upper bound was obtained for the lifetime of a block Copolymer Molecule within the reverse micelle, using the theoretical treatment of exchange phenomena in NMR which is based on extensions of the Bloch equations.
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Surface Activity of Poly(ethylene oxide)-block-Poly(propylene oxide)-block-Poly(ethylene oxide) Copolymers
Langmuir, 1994Co-Authors: Paschalis Alexandridis, V. Athanassiou, Shinya Fukuda, T. A. HattonAbstract:The surface tension of aqueous solutions of seven poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Pluronic Copolymers, covering a wide range of molecular weights (3400-14600) and PPO/PEO ratios (0.19-1.79), was determined over the 10[sup [minus]5]-10% w/v concentration range, at two temperatures (25 and 35[degree]C). Two breaks (changes in slope) were observed in the surface tension vs log concentration curve for most of the Copolymers. The low-concentration break, occurring at bulk Copolymer concentrations of approximately 10[sup [minus]3]%, is believed to originate from rearrangement of the Copolymer Molecules on the surface at complete coverage of the air/water interface. The breaks at the high-concentration part of the surface tension curve occurred at concentrations that correspond to the critical micellization concentration values as determined by a dye solubilization technique. The surface area per Copolymer Molecule, A, increased as a function of the number of EO segments, N[sub EO], obeying a scaling law (A [approx] N[sub EO][sup 1/2]) similar to that of lower molecular weight C[sub i]E[sub j] nonionic surfactants. 56 refs., 6 figs., 2 tabs.
G. Ten Brinke - One of the best experts on this subject based on the ideXlab platform.
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Comb Copolymer brush with chemically different side chains
Macromolecules, 2002Co-Authors: Roman Stepanyan, A.v. Subbotin, G. Ten BrinkeAbstract:An investigation of side chain microphase separation within a single comb Copolymer Molecule containing chemically different A and B side chains has been carried out. Expressions for the transition point chi(AB)* in a good (chi(AB)* similar to N-3/8), marginal (chi(AB)* similar to N-1/2), theta (chi(AB)(*) similar to N-2/3), and poor (chi(AB)* similar to N-1) solvent are derived both by a mean field calculation and by scaling arguments. Properties of the system below and above the transition point are described. Some unusual "bowlike" conformations are predicted for a single Molecule in the microphase separated state in a good solvent.
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Strongly adsorbed comb Copolymers with rigid side chains
Physical Review E, 2001Co-Authors: R Stepanyan, A.v. Subbotin, G. Ten BrinkeAbstract:We study the conformational behavior in a plane of a comb Copolymer Molecule, consisting of a semiflexible backbone and rigid side chains interacting via a van der Waals potential. Using a mean-field approach, two different regimes are distinguished depending on the strength of the attraction between the side chains. In the weak attraction limit the side chains are oriented preferably perpendicular to the backbone. The persistence length $\ensuremath{\lambda}$ of the comb Copolymer Molecule scales as the second power of the length of the side chain L: $\ensuremath{\lambda}\ensuremath{\propto}{L}^{2}.$ In the strong attraction limit all side chains become strongly tilted and the persistence length scales as $\ensuremath{\lambda}\ensuremath{\propto}{L}^{4}.$ The nonlinear bending regime is also studied and characterized by a change in structure and a decreasing moment of bending force as a function of curvature, i.e., bending becomes easier.
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Elasticity of Comb Copolymer Cylindrical Brushes
Macromolecules, 2000Co-Authors: A.v. Subbotin, M. Saariaho, Olli Ikkala, G. Ten BrinkeAbstract:An analysis of the cylindical brush of an isolated comb Copolymer Molecule consisting of a semiflexible backbone and flexible side chains is presented. Using the Alexander−de Gennes approximation, we calculate the free energy of both straight and bent cylindrical brush and the brush persistence length λ, and show that λ scales as a function of the side chain length M as λ ∝ M2. The discrepancy between the asymptotic scaling behavior and recent computer simulation results is also discussed.
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Cylindrical brushes of comb Copolymer Molecules containing rigid side chains
Macromolecules, 2000Co-Authors: A.v. Subbotin, M. Saariaho, Olli Ikkala, Roman Stepanyan, G. Ten BrinkeAbstract:An analysis of the cylindrical brush of an isolated comb Copolymer Molecule, consisting of a semiflexible backbone and rodlike side chains, is presented. Using a mean-field approach and a simplyfying assumption, which is tested by computer simulations, we find that the persistence length of the brush, λ, scales as λ ∝ L2/ln L for large values of the side chain length L. In the cylindrical brush regime the order parameter of the rods is negative, implying that the rods orient normal to the cylindrical axis.
A.v. Subbotin - One of the best experts on this subject based on the ideXlab platform.
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Comb Copolymer brush with chemically different side chains
Macromolecules, 2002Co-Authors: Roman Stepanyan, A.v. Subbotin, G. Ten BrinkeAbstract:An investigation of side chain microphase separation within a single comb Copolymer Molecule containing chemically different A and B side chains has been carried out. Expressions for the transition point chi(AB)* in a good (chi(AB)* similar to N-3/8), marginal (chi(AB)* similar to N-1/2), theta (chi(AB)(*) similar to N-2/3), and poor (chi(AB)* similar to N-1) solvent are derived both by a mean field calculation and by scaling arguments. Properties of the system below and above the transition point are described. Some unusual "bowlike" conformations are predicted for a single Molecule in the microphase separated state in a good solvent.
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Strongly adsorbed comb Copolymers with rigid side chains
Physical Review E, 2001Co-Authors: R Stepanyan, A.v. Subbotin, G. Ten BrinkeAbstract:We study the conformational behavior in a plane of a comb Copolymer Molecule, consisting of a semiflexible backbone and rigid side chains interacting via a van der Waals potential. Using a mean-field approach, two different regimes are distinguished depending on the strength of the attraction between the side chains. In the weak attraction limit the side chains are oriented preferably perpendicular to the backbone. The persistence length $\ensuremath{\lambda}$ of the comb Copolymer Molecule scales as the second power of the length of the side chain L: $\ensuremath{\lambda}\ensuremath{\propto}{L}^{2}.$ In the strong attraction limit all side chains become strongly tilted and the persistence length scales as $\ensuremath{\lambda}\ensuremath{\propto}{L}^{4}.$ The nonlinear bending regime is also studied and characterized by a change in structure and a decreasing moment of bending force as a function of curvature, i.e., bending becomes easier.
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Elasticity of Comb Copolymer Cylindrical Brushes
Macromolecules, 2000Co-Authors: A.v. Subbotin, M. Saariaho, Olli Ikkala, G. Ten BrinkeAbstract:An analysis of the cylindical brush of an isolated comb Copolymer Molecule consisting of a semiflexible backbone and flexible side chains is presented. Using the Alexander−de Gennes approximation, we calculate the free energy of both straight and bent cylindrical brush and the brush persistence length λ, and show that λ scales as a function of the side chain length M as λ ∝ M2. The discrepancy between the asymptotic scaling behavior and recent computer simulation results is also discussed.
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Cylindrical brushes of comb Copolymer Molecules containing rigid side chains
Macromolecules, 2000Co-Authors: A.v. Subbotin, M. Saariaho, Olli Ikkala, Roman Stepanyan, G. Ten BrinkeAbstract:An analysis of the cylindrical brush of an isolated comb Copolymer Molecule, consisting of a semiflexible backbone and rodlike side chains, is presented. Using a mean-field approach and a simplyfying assumption, which is tested by computer simulations, we find that the persistence length of the brush, λ, scales as λ ∝ L2/ln L for large values of the side chain length L. In the cylindrical brush regime the order parameter of the rods is negative, implying that the rods orient normal to the cylindrical axis.
T. A. Hatton - One of the best experts on this subject based on the ideXlab platform.
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Surface Activity of Poly(ethylene oxide)-block-Poly(propylene oxide)-block-Poly(ethylene oxide) Copolymers
Langmuir, 1994Co-Authors: Paschalis Alexandridis, V. Athanassiou, Shinya Fukuda, T. A. HattonAbstract:The surface tension of aqueous solutions of seven poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) Pluronic Copolymers, covering a wide range of molecular weights (3400-14600) and PPO/PEO ratios (0.19-1.79), was determined over the 10[sup [minus]5]-10% w/v concentration range, at two temperatures (25 and 35[degree]C). Two breaks (changes in slope) were observed in the surface tension vs log concentration curve for most of the Copolymers. The low-concentration break, occurring at bulk Copolymer concentrations of approximately 10[sup [minus]3]%, is believed to originate from rearrangement of the Copolymer Molecules on the surface at complete coverage of the air/water interface. The breaks at the high-concentration part of the surface tension curve occurred at concentrations that correspond to the critical micellization concentration values as determined by a dye solubilization technique. The surface area per Copolymer Molecule, A, increased as a function of the number of EO segments, N[sub EO], obeying a scaling law (A [approx] N[sub EO][sup 1/2]) similar to that of lower molecular weight C[sub i]E[sub j] nonionic surfactants. 56 refs., 6 figs., 2 tabs.
Rouja Ivanova - One of the best experts on this subject based on the ideXlab platform.
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interaction of poloxamer block Copolymers with cosolvents and surfactants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001Co-Authors: Rouja Ivanova, Paschalis Alexandridis, Björn LindmanAbstract:Abstract The interactions of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block Copolymers (Poloxamers) with cosolvents and surfactants are addressed here. Ternary isothermal (25°C) systems of Pluronic F127 (Poloxamer 407) in the presence of water and polar water-miscible solvents (glycerol, propylene glycol or ethanol), a partially water-miscible solvent (glycerol triacetate), a non-ionic surfactant (tetraethylene glycol monooctyl ether, C8(EO)4), an anionic surfactant (sodium dodecyl sulfate, SDS), and a cationic surfactant (cetyltrimethyl ammonium bromide, CTAB) have been investigated by phase behavior studies and small angle x-ray scattering (SAXS). A number of regions with different lyotropic liquid crystalline structure have been identified in each ternary Poloxamer–water–cosolvent/surfactant system. For a given Poloxamer, the composition range over which a given self-assembled structure is stable varies according to the cosolvent/surfactant type (and properties). The effects that the different cosolvents or surfactants exhibit on the Poloxamer phase behavior are interpreted in terms of the preference of the cosolvent/surfactant Molecules to locate in different domains of the PEO–PPO–PEO block Copolymer self-assembly. Organic solvents, depending on their relative polarities, locate preferably in the PEO-rich or the PPO-rich domains of the microstructure. Some solvents (e.g. ethanol and glycerol triacetate) may show amphiphilic behavior and act as cosurfactants by preferably locating at the interface between the PEO-rich and the PPO-rich domains. The location of the solvents in the block Copolymer assemblies is established by an analysis of the trends in the structure lattice spacing (obtained from SAXS) and the interfacial area per block Copolymer Molecule.
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evolution in structural polymorphism of pluronic f127 poly ethylene oxide poly propylene oxide block Copolymer in ternary systems with water and pharmaceutically acceptable organic solvents from glycols to oils
Langmuir, 2000Co-Authors: Rouja Ivanova, And Bjo Lindma, Paschalis AlexandridisAbstract:The evolution in the self-assembly of an amphiphilic poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO-PPO-PEO) block Copolymer in ternary systems with water and organic solvents of varying relative polarity is examined. The phase behavior and microstructure of two ternary systems consisting of Pluronic F127 (Poloxamer 407), water, and the pharmaceutically acceptable solvents propylene carbonate (4-methyl-1,3-dioxolan-2-one) or triacetin (glycerol triacetate) are presented. The microstructure of the lyotropic liquid crystalline phases formed and their characteristic length scales are determined from small-angle X-ray scattering (SAXS). The trends in the SAXS lattice spacing and the interfacial area per block Copolymer Molecule help establish the location of the solvents in the microstructure. The phase behavior of the two systems studied here is discussed in the context of ternary systems of Pluronic F127 with water and polar solvents (“glycols”, e.g., propylene glycol) or apolar organi...