Disorder-order transitions in soft sphere polymer micelles

McConnell, Glen A.; Gast, Alice P.; Huang, John S.; Smith, Steven D.

doi:10.1103/physrevlett.71.2102

Cited by 236 publications

(313 citation statements)

References 18 publications

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“…These results may also be compared with the pioneering work of McConnell and Gast, who reported either fcc or bcc phases of SI diblocks of different composition in decane [8,9]. They found bcc packing for ''hairy'' micelles and fcc for ''crew-cut'' micelles, as the intermicelle potential varied from long range to more hard-spherelike.…”

Section: P H Y S I C a L R E V I E W L E T T E R S Week Ending 9 Aprimentioning

confidence: 66%

“…Consequently, analytical theory and computer simulations have been highly refined [2 -7]. This transition has recently been observed in block copolymer micelles [8][9][10][11][12][13], which are model soft colloids, analogous to highly branched star polymers. In contrast to star polymers, however, the micellar functionality can be tuned with temperature, providing direct access to the thermoreversible fcc/bcc transition.…”

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confidence: 99%

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Origin of the Thermoreversible fcc-bcc Transition in Block Copolymer Solutions

et al. 2004

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The thermoreversible fcc-bcc transition in concentrated block copolymer micellar solutions is shown to be driven by decreases in the aggregation number as the solvent penetrates the core, leading to a softer intermicelle potential. Small-angle neutron scattering measurements in a dilute solution are used to quantify the temperature-dependent micellar characteristics. The observed phase boundary is in excellent agreement with recent simulations of highly branched star polymers. DOI: 10.1103/PhysRevLett.92.145501 PACS numbers: 61.25.Hq, 64.70.Nd, 81.30.Hd, 83.80.Qr Block copolymers are self-assembling soft materials that display a rich variety of order-order and orderdisorder transitions (ODT) [1]. By tuning copolymer molecular weight and composition, solution concentration ( ), solvent selectivity, monomer incompatibility, and temperature (T), specific transitions can be placed for experimental convenience. Furthermore, the success of modern theory in computing free energies and structural details of the various equilibrium phases makes block copolymers a fertile ground for providing stringent tests of theory. The transition between face-centered (or close-packed) cubic (fcc) and body-centered cubic (bcc) lattices is particularly interesting. The fcc/bcc boundary is widespread in atomic systems, both one component and multicomponent, and is likewise well known in colloidal systems, both charged and uncharged. Consequently, analytical theory and computer simulations have been highly refined [2 -7]. This transition has recently been observed in block copolymer micelles [8][9][10][11][12][13], which are model soft colloids, analogous to highly branched star polymers. In contrast to star polymers, however, the micellar functionality can be tuned with temperature, providing direct access to the thermoreversible fcc/bcc transition.We have located the fcc/bcc boundary in several polystyrene-polyisoprene (SI) diblock copolymer solutions, in both styrene-and isoprene-selective solvents [12,13]. By shear aligning the close-packed phase in small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS) cells, we demonstrated that the transition is epitaxial and that the transformation pathway closely follows that seen in atomic systems [12,14]. However, beyond speculation about the possible role of changing solvent selectivity, we were not able to pinpoint the precise cause of the transition; why does bcc become favored over fcc upon heating? Here we demonstrate exactly how increasing T affects the micellar characteristics (i.e., aggregation number, core radius, overall radius, solvent concentration in the core, and number density), and compare the results with detailed simulations of the phase behavior of highly branched star polymers; the agreement between theory and experiment is gratifying.Two nearly symmetric SI copolymers were synthesized by anionic polymerization [13]. One incorporated perdeuterated styrene (dS), with block molecular weights of 15 800 (dS) and 15 400 (I), and the other used perdeute...

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Section: P H Y S I C a L R E V I E W L E T T E R S Week Ending 9 Aprimentioning

confidence: 66%

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confidence: 99%

Origin of the Thermoreversible fcc-bcc Transition in Block Copolymer Solutions

et al. 2004

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“…for the A15 and BCC lattices, respectively 54 -and could be masked by the form factor of the particles, which usually falls off quite rapidly with the wavevector. 36 These shortcomings could be overcome by complementing the X-ray studies by calorimetric measurements.…”

Section: B Phase Diagramsmentioning

confidence: 99%

“…36,37 These diblocks spontaneously form micelles with a polystyrene core and polyisoprene corona. Indeed, micelles based on diblocks with a core segment containing from 1.5 to 2 times as many monomers as the coronal segment crystallize into an FCC lattice.…”

Section: A New Paradigmmentioning

confidence: 99%

Maximizing Entropy by Minimizing Area: Towards a New Principle of Self-Organization

2001

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We propose a heuristic explanation for the numerous non-close-packed crystal structures observed in various colloidal systems. By developing an analogy between soap froths and the soft coronas of fuzzy colloids, we provide a geometrical interpretation of the free energy of soft spheres. Within this picture, we show that the close-packing rule associated with hard-core interaction and positional entropy of particles is frustrated by a minimum-area principle associated with the soft tail and internal entropy of the soft coronas. We also discuss these ideas in terms of crystal architecture and pair distribution functions and analyze the phase diagram of a model hard-sphere-square-shoulder system within the cellular theory. We find that the A15 lattice, known to be area minimizing, is favored for a reasonable range of model parameters and so it is among the possible equilibrium states for a variety of colloidal systems. We also show that in the case of short-range convex potentials the A15 and other non-close-packed lattices coexist over a broad ranges of densities, which could make their identification difficult.

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“…[37][38][39] Addition of selective low molecular weight solvent or homopolymer to the block copolymer gives rise to additional phase behaviors on the system. A stable FCC phase of spherical micelles has been reported in block copolymer solution systems [40][41][42][43][44][45][46][47] as well as in block copolymer/ homopolymer blends. 46 McConnell et al 40 studied poly(styrene-b-isoprene) (SI) in decane, a selective solvent to PI, and observed the FCC and BCC spheres phase.…”

Section: Ordered Structures and Phase Map In Solvent Selective For Thmentioning

confidence: 99%

Kinetics of hexagonal cylinders to face-centered cubic spheres transition of triblock copolymer in selective solvent: Brownian dynamics simulation

Liu

Bansil

2010

The Journal of Chemical Physics

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The kinetics of the transformation from the hexagonal packed cylinder (HEX) phase to the face-centered-cubic (FCC) phase was simulated using Brownian Dynamics for an ABA triblock copolymer in a selective solvent for the A block.The kinetics was obtained by instantaneously changing either the temperature of the system or the well-depth of the Lennard-Jones potential. Detailed analysis showed that the transformation occurred via a rippling mechanism. The simulation results indicated that the order-order transformation (OOT) was a nucleation and growth process when the temperature of the system instantly jumped from 0.8 to 0.5. The time evolution of the structure factor obtained by Fourier Transformation showed that the peak intensities of the HEX and FCC phases could be fit well by an Avrami equation.

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Disorder-order transitions in soft sphere polymer micelles

Cited by 236 publications

References 18 publications

Origin of the Thermoreversible fcc-bcc Transition in Block Copolymer Solutions

Origin of the Thermoreversible fcc-bcc Transition in Block Copolymer Solutions

Maximizing Entropy by Minimizing Area: Towards a New Principle of Self-Organization

Kinetics of hexagonal cylinders to face-centered cubic spheres transition of triblock copolymer in selective solvent: Brownian dynamics simulation

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