A transient network of telechelic polymers and microspheres: structure and rheology

Molino, François; Appell, J.; Filali, M.; Michel, Eric; Porte, G.; Mora, Serge; Sunyer, Emmanuel

doi:10.1088/0953-8984/12/8a/368

Cited by 25 publications

(42 citation statements)

References 17 publications

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“…5). Such a Bingham behavior is suggested from the analogy with other related viscoelastic systems, whose similar nonlinear behavior has been interpreted in terms of a steady-state system of bulk fractures [4]. Here, the range ofγ on the high shear branch is limited to 26-37 s −1 so that we cannot discriminate between the two above behaviors and only further studies will help to select the correct nonNewtonian relation for the high shear branch.…”

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confidence: 87%

“…Such bands correspond to a new shearinduced structure (SIS), whose low viscosity is in general supposed to be responsible for the shear-thinning. This so-called shear-banding behavior has been observed in both ordered mesophases (lamellar, hexagonal, cubic) [3] and transient gels [4].A particularly well-documented example is the group of wormlike micellar systems of self-assembled surfactant molecules [5,6]. They consist of very long cylindrical aggregates whose configurations mimic polymer solutions.…”

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Velocity Profiles in Shear-Banding Wormlike Micelles

et al. 2003

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Using Dynamic Light Scattering in heterodyne mode, we measure velocity profiles in a much studied system of wormlike micelles (CPCl/NaSal) known to exhibit both shear-banding and stress plateau behavior. Our data provide evidence for the simplest shear-banding scenario, according to which the effective viscosity drop in the system is due to the nucleation and growth of a highly sheared band in the gap, whose thickness linearly increases with the imposed shear rate. We discuss various details of the velocity profiles in all the regions of the flow curve and emphasize on the complex, non-Newtonian nature of the flow in the highly sheared band.PACS numbers: 83.80.Qr, 47.50.+d, 83.85.Ei Understanding the correlation between mechanical and structural response in non-Newtonian fluids submitted to high deformation rates is crucial on both fondamental and technological grounds [1]. Among the variety of complex fluids investigated in recent years, a wide class exhibits flow-structure coupling that leads to a strong shear-thinning behavior: along the steady-state flow curve (shear stress σ vs. shear rateγ), a drop of up to three orders of magnitude in the effective viscosity η = σ/γ is observed in a very narrow stress range leading to a stress plateau (for a review, see for instance Refs. [1,2]). In correlation with this stress plateau, bands of different micro-structures and normal to the velocity gradient appear. Such bands correspond to a new shearinduced structure (SIS), whose low viscosity is in general supposed to be responsible for the shear-thinning. This so-called shear-banding behavior has been observed in both ordered mesophases (lamellar, hexagonal, cubic) [3] and transient gels [4].A particularly well-documented example is the group of wormlike micellar systems of self-assembled surfactant molecules [5,6]. They consist of very long cylindrical aggregates whose configurations mimic polymer solutions. However their dynamics is strongly modified by the equilibrium character of the chains, which enables them to break and recombine [7]. Generically, one starts from an isotropic viscoelastic solution of these micelles above the semidilute regime, which behaves like a Maxwell fluid at low shear rates. Upon increasingγ and entering the nonlinear regime, the onset of the stress plateau for a critical shear rateγ 1 is associated with the nucleation and growth of highly birefringent bands, suggesting strong alignment of the micelles along the velocity direction [5,6]. As the shear rate is further increased aboveγ 1 , the new organization progressively fills the gap at almost constant stress, up to a second critical shear rateγ 2 . Aboveγ 2 , the system enters a second regime of apparently homogeneous structure, with a second branch of increasing stress. The flow curve of Fig. 1 is typical of micellar systems like that investigated in the present work. Such a stress plateau has been reported for concentrations close to the equilibrium isotropic-nematic (I-N) transition, where coupling between the order parameter an...

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Velocity Profiles in Shear-Banding Wormlike Micelles

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“…Hydrogels may have this property, if the particles are hydrophilic and stable, which is why work on silica-filled oilin-water microemulsion networks has been undertaken [15]. Such networks are made of microemulsion droplets stabilized by a surfactant and bridged by a triblock copolymer with hydrophobic end-groups called telechelic polymer, which some- * julian.oberdisse@lcvn.univ-montp2.fr times micellizes also in absence of surfactant [16][17][18][19][20][21][22][23][24][25][26][27][28][29] . Very recently, networks of connected wormlike micelles have also attracted interest [29,30].…”

Section: Introductionmentioning

confidence: 99%

Silica nanoparticles dispersed in a self-assembled viscoelastic matrix: structure, rheology, and comparison to reinforced elastomers

Puech¹,

Mora²,

Porte³

et al. 2009

Braz. J. Phys.

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Model self-assembled networks of telechelic polymer C 18 − PEO(35k) − C 18 in water have been studied. The rheology of such transient networks has been investigated as a function of polymer concentration, and a typical percolation law has been observed. The network structure has been characterised by Small Angle Neutron Scattering in D 2 O, where the interactions between micelles formed by the hydrophobic C 18 -stickers of the polymer give rise to a peak in the scattered intensity. These model networks have then been used as a matrix for the incorporation of silica nanoparticles (R = 10 nm), and we have checked individual dispersion by scattering using contrast variation. The rheological response of the networks is considerably modified by the presence of the silica nanoparticles, and in particular an interesting dependence of the relaxation time on silica concentration has been found. The analogy in reinforcement behaviour of such a self-assembled, viscoelastic, and aqueous system with model experiments of elastomers filled with nanoparticles is discussed by comparison to a silica-latex system.

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“…The term "fluid fracture" [18] has been proposed to describe these individual events, which have been observed in different systems with similar rheological properties but different internal structures (connected microemulsions [19], copolymer cubic-phase [10,11]). …”

Section: A Brief History Of Flow Localizationmentioning

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An elasto-visco-plastic model for immortal foams or emulsions

et al. 2008

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A variety of complex fluids consist in soft, round objects (foams, emulsions, assemblies of copolymer micelles or of multilamellar vesicles -also known as onions). Their dense packing induces a slight deviation from their prefered circular or spherical shape. As a frustrated assembly of interacting bodies, such a material evolves from one conformation to another through a succession of discrete, topological events driven by finite external forces. As a result, the material exhibits a finite yield threshold. The individual objects usually evolve spontaneously (colloidal diffusion, object coalescence, molecular diffusion), and the material properties under low or vanishing stress may alter with time, a phenomenon known as aging. We neglect such effects to address the simpler behaviour of (uncommon) immortal fluids: we construct a minimal, fully tensorial, rheological model, equivalent to the (scalar) Bingham model. Importantly, the model consistently describes the ability of such soft materials to deform substantially in the elastic regime (be it compressible or not) before they undergo (incompressible) plastic creep -or viscous flow under even higher stresses.

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A transient network of telechelic polymers and microspheres: structure and rheology

Cited by 25 publications

References 17 publications

Velocity Profiles in Shear-Banding Wormlike Micelles

Velocity Profiles in Shear-Banding Wormlike Micelles

Silica nanoparticles dispersed in a self-assembled viscoelastic matrix: structure, rheology, and comparison to reinforced elastomers

An elasto-visco-plastic model for immortal foams or emulsions

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