Ordering and viscoelastic relaxation in multiarm star polymer melts

Vlassopoulos, D.; Pakuła, Tadeusz; Fytas, George; Roovers, Jacques; Karatasos, K.; Hadjichristidis, Nikos

doi:10.1209/epl/i1997-00403-3

Cited by 68 publications

(105 citation statements)

References 20 publications

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“…In earlier work, the "core-shell" morphology was observed in highly entangled, multiarm hyperstar polybutadienes and polyisoprenes, using rheology, solution viscometry, Monte Carlo simulations, SANS and SAXS measurements. 35,38 In fact, X-ray scattering confirmed that for the same number of arms of a symmetric star, the magnitude of scattering intensity was proportional to the concentration of star centers per unit volume and center-to-center correlation distance. This was also suggested by McLeish and Milner in highly dense stars.…”

Section: Discussionmentioning

confidence: 78%

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Kharchenko¹,

Kannan²,

Cernohous³

et al. 2002

Macromolecules

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In the preceding publication, we showed that the hyperbranched polystyrenes (HBPS) synthesized as part of this study may be viewed as starlike molecules with a high branch density, which are either unentangled or weakly entangled. In this paper, the role of architecture, especially the branch density, on the rheological and orientation behavior is investigated using simultaneous, quantitative stress and flow birefringence measurements in the melt state. Linear PS and eight-arm symmetric PS stars follow the stress-optical rule (SOR) over a wide dynamic range, with the stress-optical coefficient (C) governed by the arm molecular weight. When the branch density is "moderate" (greater than ∼20 arms), there is only a hint of nonterminal behavior in the viscoelastic moduli, while the C drops by 30% compared to a star with eight arms of comparable length. When the branch density is "high" (∼50 arms), and the arms are unentangled, the nonterminal behavior in G* is clearly apparent, and there is a dramatic breakdown in the stress-optical rule in these homopolymer melts. The quantitative birefringence measurements suggest that the "excess" birefringence may be due to the "form" contributions from the core-shell structure. Such a structure may be formed by the preferential radial stretching of the chain segments near the core, as suggested by other studies on hyperstars. For comparable chain density, the core would be bigger than the shell when the arm length is smaller. Therefore, the 5K-HBPS exhibits a more severe breakdown compared to the 10K-HBPS.

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Section: Discussionmentioning

confidence: 78%

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Kharchenko¹,

Kannan²,

Cernohous³

et al. 2002

Macromolecules

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“…It is essentially in the limit f ≫ 1 where a description of star polymers as sterically stabilized colloidal particles holds. This polymer-colloid hybrid character of star polymers has been explored in a number of publications dealing with the structural [4,6,11,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] and dynamical [4,27,28,[39][40][41][42][43][44][45][46][47][48] properties of the same.…”

Section: Introductionmentioning

confidence: 99%

Star Polymers: From Conformations to Interactions to Phase Diagrams

Likos¹,

Harreis²

2002

Condens. Matter Phys.

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We review recent progress achieved in the theoretical description of the interactions, correlations, and phase behavior of concentrated solutions of star polymers, sterically stabilized colloids, and micelles. We show that the theoretical prediction of an ultrasoft, logarithmically diverging effective interaction between the star centers, which has been confirmed by SANSexperiments and computer simulations, lies in the core of a host of unusual phenomena encountered in such systems. These include anomalous structure factors, reentrant melting behavior, as well as a variety of exotic crystal phases. Extensions to polydisperse stars and the role of many-body forces are also discussed. A particular 'mean-field' character of star polymer fluids is presented and it is shown that it manifests itself in the shape and structure of sedimentation profiles of these systems.

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“…This type of structure is related to the excluded volume interaction between compact but deformable macromolecular elements in a dense system. Evidence from experiments and simulations with regular multiarm stars (with f = 128) [9,10,11,14] indicates that the slow process can be attributed to translational cooperative rearrangements of stars (on macromolecular scale) within the ordered state. These rearrangements are of the same character as these suggested for the cooperative rearrangements in low molecular liquids [21].…”

Section: Resultsmentioning

confidence: 99%

“…The reason for their liquid-like structure formation is, in this case, the enhanced osmotic pressure that outbalances the elastic energy of the entropically stretched arms [10]. This type of weak order persists in the melt state as well [9,10], however, as a consequence of excluded volume effects on the macromolecular scale because of the intramolecular monomer density reaching the values of the bulk material [11]. The dynamics in non-dilute solutions revealed the presence of cooperative diffusion (poly- ) LS2 267 4460 -93 LS3 278 9300 -92 LS4 267 18300 -91 LS5 269 29300 -92 LS6 263 42300 -92 meric) and self diffusion and structural relaxation (colloidal) modes [4,12], whereas unusual thermal gelation behaviour was detected as a result of the strong excluded volume interactions [13].…”

Section: Introductionmentioning

confidence: 99%

“…The dynamics in non-dilute solutions revealed the presence of cooperative diffusion (poly- ) LS2 267 4460 -93 LS3 278 9300 -92 LS4 267 18300 -91 LS5 269 29300 -92 LS6 263 42300 -92 meric) and self diffusion and structural relaxation (colloidal) modes [4,12], whereas unusual thermal gelation behaviour was detected as a result of the strong excluded volume interactions [13]. In the melt state, the dynamics was characterized by a two-step terminal viscoelastic relaxation, consisting of a fast mode related to arm relaxation (independent of functionality f , but strongly dependent on arm molecular weight, M a ) and of a slow mode attributed to structural relaxation (cooperative rearrangements of stars, strongly dependent on both f and M a ) [9,10,14].…”

Section: Introductionmentioning

confidence: 99%

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Structure and Dynamics of Irregular Multiarm Star Polymers

Vlassopoulos¹,

Pakula²,

Roovers³

2002

Condens. Matter Phys.

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Melt properties of highly branched star polymers consisting of a 1,2-polybutadiene core and nearly 270 arms of 1,4-polybutadiene with varying sizes have been investigated using small angle X-ray scattering (SAXS) and dynamic rheological measurements in the linear viscoelastic limit. Despite their difference in internal structure compared to the regular stars with 128 arms and spherical dendritic core, these polymers exhibit the same features: a liquid-like ordering resulting from their specific intramolecular monomer density distribution. This leads to a dual terminal viscoelastic relaxation, consisting of a fast arm relaxation and a slow structural relaxation mechanisms. Both modes conform quantitatively to the generic behaviour of multiarm star polymers, suggesting a universality of the behaviour of highly branched macromolecular objects.

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Ordering and viscoelastic relaxation in multiarm star polymer melts

Cited by 68 publications

References 20 publications

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Role of Architecture on the Conformation, Rheology, and Orientation Behavior of Linear, Star, and Hyperbranched Polymer Melts. 1. Synthesis and Molecular Characterization

Star Polymers: From Conformations to Interactions to Phase Diagrams

Structure and Dynamics of Irregular Multiarm Star Polymers

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