Rheology of side-group liquid-crystalline polymers: effect of isotropic-nematic transition and evidence of flow alignment

Kannan, Rangaramanujam M.; Kornfield, Julia A.; Schwenk, Norbert; Boeffel, Christine

doi:10.1021/ma00060a038

Cited by 61 publications

(58 citation statements)

References 11 publications

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“…These results are in agreement with the results of Kannan et al [29] and Dan et al [30] which suggested that the large amplitude oscillatory shear orientated the SCLCPs.…”

Section: Rheological Propertiessupporting

confidence: 93%

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

et al. 2013

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A new polymerizable macromer containing naphthalene ring in the mesogen, 4-butoxyphenyl 6-(6-(methacryloyloxy)hexyl)-2-naphthoate, has been synthesized. The chemical structure of the macromer was confirmed by FTIR, 1 H NMR, 13 C NMR and liquid crystal behavior was confirmed by polarized optical microscope (POM) and small angle X-ray (SAXS). Results from the POM showed nematic phase appearing at 101.9°C and smectic phase at 83.8°C while differential scanning calorimetry (DSC) suggested presence of a wide mesophase range between 50 and 104°C. This macromer was used to synthesize a series of side-chain liquid crystal polymers (SCLCPs) with different molecular weights having narrow polydispersity (PDI) values via living atom transfer radical polymerization (ATRP). The mesomorphic properties of the liquid crystal macromer and polymers were characterized by POM, DSC and SAXS. In addition, the frequency behavior of the polymers in a smectic phase is characterized by the storage modulus, G', leveling off, at low frequencies. Complex viscosities, |η*| of the smectic phase exhibited a shear thinning behavior over the shear rates investigated.

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“…These results are in agreement with the results of Kannan et al [29] and Dan et al [30] which suggested that the large amplitude oscillatory shear orientated the SCLCPs.…”

Section: Rheological Propertiessupporting

confidence: 93%

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

et al. 2013

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“…We could be tempted to apply it to CL polymers since their chain conformation at rest is Gaussian [17], with as much flexibility as polystyrene. Actually, oscillatory shear experiments in the isotropic phase show that most of the comb-like polymethacrylate chains studied were not entangled [9], at least with the classical vision of entanglements [5]. A different picture is given at the macroscopic scale (a few microns) by rheology experiments: the existence of temporary clusters of chains [15] created by reversible bonds between side chains.…”

Section: The Cluster Questionmentioning

confidence: 98%

“…By drawing a fiber from the surface of a melt [6] or applying a simple extension to the melt [7,8], the mesogenic moieties usually tend to align along the stretching direction in the nematic phase or perpendicular to the stretching direction in the smectic phase. In the case of samples aligned with high amplitude shear, the complex modulus is affected [9]: it presents smaller values than in the non-aligned state (the mesogenic moieties are aligned in the vorticity direction [9], i.e. perpendicular to the flow).…”

Section: Introductionmentioning

confidence: 96%

Influence of the nematic order on the rheology and conformation of stretched comb-like liquid crystalline polymers

et al. 2000

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We have studied the rheology and the conformation of stretched comb-like liquid-crystalline polymers. Both the influence of the comb-like structure and the specific effect of the nematic interaction on the dynamics are investigated. For this purpose, two isomers of a comb-like polymetacrylate polymer, of well-defined molecular weights, were synthesized: one displays a nematic phase over a wide range of temperature, the other one has only an isotropic phase. Even with high degrees of polymerization N , between 40 and 1000, the polymer chains studied were not entangled. The stress-strain curves during the stretching and relaxation processes show differences between the isotropic and nematic comb-like polymers. They suggest that, in the nematic phase, the chain dynamics is more cooperative than for a usual linear polymer. Small-angle neutron scattering has been used in order to determine the evolution of the chain conformation after stretching, as a function of the duration of relaxation t r. The conformation can be described with two parameters only: λp, the global deformation of the polymer chain, and p, the number of statistical units of locally relaxed sub-chains. For the comb-like polymer, the chain deformation is pseudo-affine: λp is always smaller than λ (the deformation ratio of the whole sample). In the isotropic phase, λp has a constant value, while p increases as tr. This latter behavior is not that expected for non-entangled chains, in which p varies as tr 1/2 (Rouse model). In the nematic phase, λp decreases as a stretched exponential function of tr, while p remains constant. The dynamics of the comb-like polymers is discussed in terms of living clusters from which junctions are produced by interactions between side chains. The nematic interaction increases the lifetime of these junctions and, strikingly, the relaxation is the same at all scales of the whole polymer chain.

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“…The zero shear viscosity and terminal time scale with the molecular weight as M 1.3 and M 2.6 , respectively, instead of the Rouse values M 1 and M 2 [15]. The terminal time separates a viscous regime from a wide range (decades) of frequencies in which the storage and loss moduli are similar in magnitude and scale as the same power of frequency G ′ ,G ′′ ∼ ω 0.6 , rather than the Rouse behavior ω 0.5 [14][15][16]. The simultaneous scaling of the viscoelastic moduli is also characteristic of a system near its gel point [17], and has been observed in branched flexible polymers [18].…”

mentioning

confidence: 99%

“…In SCLCPs the orientation fluctuations are of order τ n ≈ 10 −3 s [13]. However, the mesogen is coupled to the polymer backbone, and the terminal times τ d for stress relaxation of these systems is of order τ d ≈ 1 s [14,15]. Moreover, SCLCP rheology is very different from flexible polymers and poorly understood.…”

mentioning

confidence: 99%

Transient and stationary flow behaviour of side chain liquid-crystalline polymers: Evidence of a shear-induced isotropic-to-nematic phase transition

2002

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Abstract. -This letter describes the non-linear rheology of the isotropic phase of a thermotropic side chain liquid-crystal polymer (SCLCP), from which we infer a flow-induced isotropic-to-nematic (IN) phase transition above a critical shear stress and construct non-equilibrium phase diagrams. In contrast to the well-studied wormlike-micellar solutions and predictions for simple liquid-crystalline systems, the critical stress does not vanish as the equilibrium transition temperature is approached from the above. We postulate that this is due to: i) the coupling between mesogens and the polymer backbone, whose equilibrium oblate nematic backbone conformation contrasts with the prolate non-equilibrium conformation; and ii) the peculiar topological constraints in SCLCP melts, which have been previously postulated as leading to long-lived clusters.Introduction. -Shear flow dramatically influences the microstructural order in complex fluids, and can sometimes induce phase transitions. Examples include the shear-induced isotropic-to-nematic (IN) phase transition in liquid-crystalline systems [1, 2] and in colloidal suspensions [3]. The possibility of inducing an isotropic-to-nematic (IN) transition by shear flow is appealing, and has been reported experimentally in semiflexible wormlike micelles [2]. Although this system is well studied, polymeric-like entanglements, the annealed length distribution, and solvent greatly complicate the physics. Mather et al. [4] have recently studied a linear thermotropic polymer and shown that it can undergo a flow-induced IN transition. A similar transition was then discovered in side chain liquid-crystalline polymers (SCLCPs) [5], based on birefringence measurements. In one SCLCP system, Small-Angle Neutron Scattering (SANS) demonstrated that, while the mesogenic side group is perpendicular to the polymeric backbone in the equilibrium nematic phase, flow induces paral lel alignment, with backbone and mesogen distribution functions prolate and oriented generally in the flow direction [5]. The aim of this paper is to continue this work with a study of the non-linear rheology of this system.The constitutive behaviour of a typical flow-induced shear-thinning phase transition is shown in fig. 1. For imposed strain rates in the unstable region, in which the stress decreases

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Rheology of side-group liquid-crystalline polymers: effect of isotropic-nematic transition and evidence of flow alignment

Cited by 61 publications

References 11 publications

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

Naphthalene group containing side chain liquid crystalline polymers and their rheological behavior

Influence of the nematic order on the rheology and conformation of stretched comb-like liquid crystalline polymers

Transient and stationary flow behaviour of side chain liquid-crystalline polymers: Evidence of a shear-induced isotropic-to-nematic phase transition

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