Tuning of the Temperature Window for Unit-Cell and Pore-Size Enlargement in Face-Centered-Cubic Large-Mesopore Silicas Templated by Swollen Block Copolymer Micelles

Close-packed structures of uniformly sized spheres are ubiquitous across diverse material systems including elements, micelles, and colloidal assemblies. However, the controlled access to a specific symmetry of self-assembled close-packed spherical particles has not been well established. We investigated the ordering of spherical block copolymer micelles in aqueous solutions that was induced by rapid temperature changes referred to as quenching. As a function of quench depth, the quenched self-assembled block copolymer micelles formed three different close-packed structures: face-centered cubic (fcc), random stacking of hexagonal-close-packed layers (rhcp), and hexagonal-close-packed (hcp). The induced hcp and rhcp structures were stable for at least a few weeks when maintained at their quench temperatures, but heating or cooling these hcp and rhcp structures transformed both structures to fcc crystallites with coarsening of the crystal grains, which suggests that these noncubic close-packed structures are intermediate states. Time-resolved scattering experiments prove that the micellar rhcp structures do not originate from the rapid growth of competing close-packed structures. We speculate that the long-lived metastable hcp and rhcp structures originate from the small size of crystal grains, which introduces a nonnegligible Laplace pressure to the crystal domains. The reported transitions from the less stable hcp to the more stable rhcp and fcc are experimental observations of Ostwald’s rule manifesting the transition order of the key close-packed structures in the crystallization of close-packed uniform spheres.

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β-lactam Functionalized Poly(isoprene-b-ethylene oxide) Amphiphilic Block Copolymer Micelles as a New Nanocarrier System for Curcumin

Current Nanoscience ◽

10.2174/157341310791171090 ◽

2010 ◽

Vol 6 (3) ◽

pp. 277-284 ◽

Cited By ~ 7

Author(s):

Konstantinos Gardikis ◽

Konstantinos Dimas ◽

Aristidis Georgopoulos ◽

Eleni Kaditi ◽

Stergios Pispas ◽

...

Keyword(s):

Block Copolymer ◽

Ethylene Oxide ◽

Amphiphilic Block Copolymer ◽

Block Copolymer Micelles ◽

Copolymer Micelles

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Donnan Equilibria in Polymeric Micellar Systems with Weak Polyelectrolyte Shells: The Lowering of the pH Value

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19971730 ◽

1997 ◽

Vol 62 (11) ◽

pp. 1730-1736 ◽

Cited By ~ 4

Author(s):

Petr Munk ◽

Zdeněk Tuzar ◽

Karel Procházka

Keyword(s):

Ionic Strength ◽

Block Copolymer ◽

Ph Value ◽

Electrolyte Solutions ◽

Hydrogen Ions ◽

Micellar Systems ◽

Weak Electrolytes ◽

Block Copolymer Micelles ◽

Copolymer Micelles ◽

Polyelectrolyte Solutions

When two electrolyte solutions are separated and only some of the ions can cross the boundary, the concentrations of these ions are different on both sides of the boundary. This is the well-known Donnan effect. When weak electrolytes are involved, the imbalance includes also hydrogen ions: there is a difference of pH across the boundary and the dissociation of nondiffusible weak electrolytes is suppressed. The effect is very pronounced when the concentration of the weak electrolyte is high and ionic strength is low. The significance of this phenomenon is discussed for polyelectrolyte solutions, and particularly for block copolymer micelles with weak polyelectrolyte shells. The effect is quite dramatic in the latter case.

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A Monte Carlo Study of Flexible Polymer Chain Conformations in Restricted Volumes. I. A Model for Insoluble Blocks Conformations in Swollen Cores of Multimolecular Spherical Block Copolymer Micelles

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19932290 ◽

1993 ◽

Vol 58 (10) ◽

pp. 2290-2304 ◽

Cited By ~ 2

Author(s):

Zuzana Limpouchová ◽

Karel Procházka

Keyword(s):

Monte Carlo ◽

Block Copolymer ◽

Monte Carlo Study ◽

Volume Effect ◽

Micellar Systems ◽

Flexible Polymer ◽

Block Copolymer Micelles ◽

Copolymer Micelles ◽

Chain Conformations ◽

Chain Lengths

Monte Carlo simulations of chain conformations in a restricted spherical volume at relatively high densities of segments were performed for various numbers of chains, N, and chain lengths (number of segments), L, on a tetrahedral lattice. All chains are randomly end-tethered to the surface of the sphere. A relatively uniform surface density of the tethered ends is guaranteed in our simulations. A simultaneous self-avoiding walk of all chains creates starting conformations for a subsequent equilibration. A modified algorithm similar to that of Siepmann and Frenkel is used for the equilibration of the chain conformations. In this paper, only a geometrical excluded volume effect of segments is considered. Various structural and conformational characteristics, e.g. segment densities gS(r), free end densities gF(r) as functions of the position in the sphere (a distance from the center), distributions of the tethered-to-free end distances, ρTF(rTF), etc. are calculated and their physical meaning is discussed. The model is suitable for studies of chain conformations is swollen cores of multimolecular block copolymer micelles and for interpretation of non-radiative excitation energy migration in polymeric micellar systems.

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Study of Sedimentation Velocity of Block Copolymer Micelles

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19930071 ◽

1993 ◽

Vol 58 (1) ◽

pp. 71-76 ◽

Cited By ~ 3

Author(s):

Minmin Tian ◽

C. Ramireddy ◽

Stephen E. Webber ◽

Petr Munk

Keyword(s):

Block Copolymer ◽

Methacrylic Acid ◽

Mixed Solvent ◽

Hard Spheres ◽

Sedimentation Velocity ◽

Hydrodynamic Coefficient ◽

Block Copolymer Micelles ◽

Copolymer Micelles ◽

Size Heterogeneity ◽

Good Agreement

No anomalies were observed during the measurement of sedimentation coefficients of block copolymer micelles formed by copolymers of styrene and methacrylic acid in a mixed solvent; 80 vol.% of dioxane and 20 vol.% of water. The shapes of the sedimenting boundaries suggest that the size heterogeneity of the micelles is small. Linear relations between 1/s and c were obtained. The value of the hydrodynamic coefficient κ was between 2 and 4 in a good agreement with the value 2.75 or 2.86 that was obtained by combining Burgers' or Fixman's values of the coefficient of the concentration dependence kvs for hard spheres with Einstein's value of [η] for spheres.

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