Giovanni Ianniruberto

• University of Naples Federico II

We propose a simple, robust method to measure both the first and second normal stress differences of polymers, hence obtaining the full set of viscometric material functions in nonlinear shear flow. The method is based on the use of a modular cone-partitioned plate (CPP) setup with two different diameters of the inner plate, mounted on a rotational...

Rheological properties of polymers for elastomer applications are strongly dependent on their molecular structure. Most commercially available elastomers are entangled polydisperse, branched polymers with an unknown molecular structure. From the experimental point of view, rheological measurements can be carried out in the linear and nonlinear visc...

We investigate the nonlinear shear and uniaxial extensional rheology of entangled polystyrene (PS) melts and solutions having the same number Z of entanglements, hence identical linear viscoelasticity. While experiments in extensional flows confirm that PS melts and solutions with the same Z behave differently, respective transient and steady data...

(Graph Presented) Shear thickening of telechelic associating polymers, particularly of hydrophobically modified ethoxylated urethanes (HEURs), is classically attributed to either non-Gaussian behavior of the chains, also called finite extensible nonlinear elasticity (FENE), or to flow-enhanced formation of network strands; however, in a recent pape...

Using the integral equation of the Doi–Edwards theory that only accounts for tube orientation of entangled linear polymers, we explore the behavior of the stress maximum typically observed in shear startup as a function of the waiting time tw between repeated startup runs. Depending on whether the first run is interrupted before the maximum, or suf...

It is widely accepted that the nonlinear viscoelasticity of polymers with long chain branching can be described by the pom-pom theory [ J. Rheol. 1998, 42, 81] that accounts for branchpoint withdrawal (BPW) as a nonlinear relaxation mechanism of the backbone. In spite of the remarkable success attained by refined theories derived from the original...

Recent experiments by Li and Wang (Macromolecules 43:5904-5908, 2010) on parallel superposition flows of nearly monodisperse entangled polymer solutions revealing a flow-induced acceleration of the relaxation dynamics are here analyzed by using a simple differential constitutive equation based on the tube model to examine the role of convective con...

The molecular mechanism known as convective constraint release (CCR) is here revisited to account for the fact that in fast flows topological entanglements decrease in number, as recently shown by the molecular dynamics simulations of Baig et al. [Macromolecules 43, 6886-6902 (2010)] and even before by the Brownian simulations of Yaoita et al. [J....

We report on the unusual response of a well-characterized entangled comb polymer in simple shear flow. The polymer with highly entangled backbone (about 16 entanglements) and on average 29 long branches (about 3 entanglements each) has been extensively characterized by interaction chromatography and its rheology carefully studied under controlled c...

The classical Doi–Edwards theory for the steady-state stress of entangled linear polymers in uniaxial elongational flow is here extended to entangled branched polymers, specifically to stars and pompoms, both symmetric and asymmetric. The arm withdrawal idea advanced long ago by McLeish and Larson is also fully exploited. Non-Gaussian corrections a...

It is known that polystyrene melts behave anomalously in fast elongational flows insofar as the steady-state elongational viscosity keeps decreasing with increasing stretching rate ε, without showing the typical upturn at ετ R ≈ 1, with τ R the Rouse time. The authors have recently suggested that such an anomalous behavior might be due to a decreas...

Well-entangled monodisperse linear polystyrene melts exhibit monotonic thinning of the steady state elongational viscosity with increasing the strain rate ε̇ even beyond the Rouse relaxation frequency, τR-1. This behavior is quite different from the thinning followed by hardening at ε̇ > τR-1 observed for entangled semidilute solutions. We attempt...

For entangled linear monodisperse polymers, uniaxial elongational flow behavior was examined with the primitive chain network (PCN) simulation, which was originally formulated for a network of Gaussian chains bound by sliplinks but was modified in this study to properly take into account the finite extensibility of actual chains. On an increase of...

The primitive chain network (PCN) model successfully employed to simulate the rheology of entangled polymers is here tested versus less coarse-grained (lattice or atomistic) models for what concerns the structure of the network at equilibrium (i.e., in the absence of flow). By network structure, we mean the distributions of some relevant quantities...

Molecular theories for polymer rheology are based on conformational dynamics of the polymeric chain. Hence, measurements directly related to molecular conformations appear more appealing than indirect ones obtained from rheology. In this study, primitive chain network simulations are compared to experimental data of entangled DNA solutions [Teixeir...

Although some experiments have addressed individual chain dynamics in the entangled state, the behavior of the quantity measured in the experiments, and its relation to chain conformation, deserves further study. In our previous work using primitive chain network simulations at equilibrium (Masubuchi et al, Nihon Reoroji Gakkaisi (J. Soc. Rheol. Jp...

Conformational relaxation of individual chain molecules in the entangled state has already been investigated by direct observation in fluorescent DNA experiments. Yet, possible connections between the quantity accessible in those experiments and well defined conformational measures have not been established so far. In this study, the relaxation beh...

Recent simulations of entangled polymer dynamics are based on slip-link models pioneered by Hua and Schieber (J. Chem. Phys. 1998, 109, 10018). In this study, we compare different slip-link models in their prediction of the linear viscoelasticity of bidisperse linear polymers to examine how effectively such models account for constraint release. We...

We discuss the maxima in stress which were recently observed in the start up of shearing flows of entangled polymer melts with a complex branched structure. More than one maximum has been observed, and maxima can be found at extremely large values of deformation, of the order of several hundred units of shear. Furthermore, such maxima may disappear...

Polymeric materials with dispersed solid particles are often used as functional materials. Hence their dynamics is worth being investigated. However, effective simulation methods of particle suspensions in polymeric matrices do not seem available. In this study a novel simulation method is proposed, which extends the primitive chain network model f...

We here report on some modifications of the Primitive Chain Network (PCN) model, originally proposed in [Y. Masubuchi et al., J. Chem. Phys. 115, 4387 (2001)], which both refine the model and make it suitable for predicting nonlinear rheological response in fast flows. Simulation results are compared with some existing viscoelastic data on monodisp...

Orientation and stretch of entangled polymers under large step shear deformations were investigated through primitive chain network simulations. In the simulations, entangled polymer dynamics is described by 3D motion of entanglements, 1D sliding of monomers along the chain, and creation/destruction of entanglements described by hooking/unhooking w...

Simulation results of the primitive chain network (PCN) model for entangled polymers are compared here to existing data of diffusion coefficient, linear and nonlinear shear and elongational rheology of monodisperse polystyrene melts. Since the plateau modulus of polystyrene is well known from the literature, the quantitative comparison between the...

The primitive chain network model of entangled polymers, where primitive chains and entanglements are assigned in real 3-D space, is a possible step in the multi-scale path from atomistic simulations to macroscopic constitutive equations. In any coarse-grained model of a polymeric system, however, determination of the basic parameters is a crucial...

Parallel superposition experiments are used here for the linear and nonlinear rheological characterization of a commercial polydisperse polymer melt in the entangled state. In the limit of small amplitude of the oscillations, we focus (to our knowledge for the first time) on the time-temperature superposition principle. With increasing oscillation...

We present a new multi-chain Brownian dynamics simulation of a polymeric network containing both crosslinks and slip-links (entanglements). We coarse-grain at the level of chain segments connecting consecutive nodes (cross- or slip-links). Affine displacement of nodes is not imposed; rather, their displacement as well as sliding of monomers through...

Damping functions of entangled polymers for shear, uniaxial, biaxial, and planar deformations, as well as normal stress ratios for shear deformations, were obtained from Brownian simulations making use of the primitive chain network model. To investigate the effect of the force balance over the entanglements and of the convective constraint release...

Bidisperse linear polymers are mixtures of long and short chains that have been widely investigated as ideal systems to explore the effects of constraint release, which is one of the key mechanisms of entangled polymer dynamics and hence involved in recent theories and models. In this study, simulations of bidisperse mixtures were performed to chec...

We present simulations of branched polymer dynamics based on a sliplink network model, which also accounts for topological change around branch points, i.e., for branch-point diffusion. It is well-known that, with the exception of stars, branched polymers may show a peculiar rheological behavior due to the exceptionally slow relaxation of the backb...

A coarse-grained molecular simulation for block copolymers in the entangled state is proposed as an extension of the primitive chain network model. Polymers are represented as a sequence of segments between consecutive entanglements, the latter being modeled as sliplinks with other chains. Each sliplink connects two chains only, i.e., entanglements...

The mechanical properties of a polymeric network containing both crosslinks and sliplinks (entanglements) are studied using a multichain Brownian dynamics simulation. We coarse-grain at the level of chain segments connecting consecutive nodes (cross- or sliplinks), with particular attention on the Gaussian statistics of the network. Affine displace...

Primitive chain network model for block copolymers is used here to simulate molecular dynamics in the entangled state with acceptable computational cost. It was found that i) the hooking procedure rearranging the topology of the entangled network is critical for the equilibrium structure of the system, and ii) simulations accounting for the differe...

The new tube model with variable diameter (Marrucci and Ianniruberto, 2004), recently introduced to inter-pret new elongational data of polymer melts, is here extended to encompass arbitrary flows, specifically shear flows. The predicted results compare well with existing data of entangled polymer melts. Challenges still remain when the comparison...

Motivated by recent data of Hassager and coworkers [A. Bach, K. Almdal, H.K. Rasmussen, O. Hassager, Elongational viscosity of narrow molar mass distribution polystyrene, Macromolecules, 36 (2003) 5174–5179], we develop a new tube model describing the non-linear behaviour of entangled monodisperse linear polymers. Within the context of well establi...

Abstract unavailable.

The concept of dynamic tube dilation (DTD) is here used to formulate a new simulation scheme to obtain the linear viscoelastic response of long chains with a large number of entanglements. The new scheme is based on the primitive chain network model previously proposed by some of the authors, and successfully employed to simulate linear and nonline...

A novel simulation method that can calculate the long-time response of polymeric liquids in the entangled state is described. The polymer chain is replaced by a sequence of subchains connecting consecutive entanglements, called the 'primitive' chain. Collectively, the primitive chains form a rubberlike network, the nodes of which are the entangleme...

Recent data by Hassager and co-workers [Bach et al. Macromolecules 2003, 36, 5174] of elongational viscosity of nearly monodisperse polystyrene melts are interpreted by including in the classical tube theories for entangled polymer dynamics an interchain repulsive contribution. The proposed theory predicts the observed power law of ηel vs ε in a st...

The primitive-chain network model for Brownian simulation of entangled polymers is extended so as to include the case of polymer blends. Predictions for the phase diagram and for the linear viscoelastic response appear consistent with earlier works.

Molecular Simulations of entangled linear polymers under fast shear flows, based on the primitive chain network model, are performed to investigate relaxation mechanisms of polymers. It is found that the original primitive chain network model incorporating all known molecular mechanisms (i.e., reptation, tube length fluctuation, thermal and convect...

Brownian dynamics simulations of the linear viscoelastic response of entangled polymers have been performed, and compared quantitatively with some existing solution data at a fixed concentration and variable molecular weight. The model is a three-dimensional network where the nodes are sliplinks connecting chains in pair. The simulations make use o...

A single-mode constitutive equation is proposed which accounts, in a very simple way, for the most important feature of the molecular theory for entangled polymers based on the 'tube' concept, i.e. that the orientation of the tubes and the stretching of the chain within them relax over different time-scales. The much faster relaxation of stretch is...

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Significant progress made in recent times on the basic molecular theory of Doi and Edwards for entangled polymers is briefly reviewed. In particular we present a recent version of the theory that is entirely described by a set of differential equations, and is therefore especially useful for simulations of complex flows as encountered in polymer pr...

The model recently proposed by the authors [J. Rheol., 45 (2001) 1305–1318] to account for convective constraint release (CCR) and chain stretch in entangled polymers is here extended to a multiple mode situation. Such an extension, indispensable for the polydisperse case, is believed to be important also for monodisperse polymers, especially in vi...

We propose a simple way of including chain stretch effects in convective constraint release theories for entangled polymers. The main idea is that the characteristic time of orientational relaxation depends in a series-parallel way on all three relevant mechanisms, i.e., reptation, constraint release (thermal and convective), and Rouse relaxation....

The classical dumbbell and Rouse models for dilute polymer solutions are here modified by introducing an anisotropic diffusivity which mimics the effect of topological interactions arising in polymeric solutions in the vicinity of the overlap concentration c∗. Closed-form constitutive equations are derived by making use of typical pre-averaging app...

A new model for Brownian dynamics simulations of entangled polymeric liquids is proposed here. Chains are coarse grained at the level of segments between consecutive entanglements; hence, the system is in fact a network of primitive chains. The model incorporates not only the ``individual'' mechanisms of reptation and tube length fluctuation, but a...

The theory of Doi and Edwards for entangled polymers has been recently modified for the case of fast flows to account for convective contributions to molecular dynamics. The flow-induced relative motion between neighboring chains removes constraints and speeds up relaxation. Convective constraint release (CCR) may thus explain why the shear stress...

The predictions of tube models in fast flows have recently been improved by incorporating convective constraint release (CCR). In this paper, we revisit CCR showing that, whenever chains are not stretched, an additional effect named convective conformation renewal (CCR2 to distinguish it from CCR) should also be considered. CCR2 consists in the los...

The usual assumption of affine deformation of the strands of a polymeric network appears not to fulfil force balance over the nodes of the network in case such nodes are entanglements. In an effort to improve over the classical theory of Doi and Edwards for entangled polymers, a simple model is here proposed which is so constructed as to obey force...

In the classical theory of Doi and Edwards for entangled polymers the strain measure Q arises from the assumption of affine deformation of the tube segments. On the other hand, we have recently argued [G. Marrucci, F. Greco, and G. Ianniruberto, "Possible role of force balance on entanglements," Macromol. Symp. (in press)] that force balance on the...

The viscosity of polymeric liquids crucially depends on polymer concentration c and molar mass M. These dependencies can generally be predicted from relatively simple theories, because what really matters is the chain-like structure of the polymer molecule rather than its detailed chemistry. In this chapter we summarize the main concepts leading to...

The basic concepts of entangled polymer dynamics, like that of ‘tube’ of constraints and of ‘reptation’, have not yet exhausted their momentum. Further progress has taken place recently with detailed calculations of tube length fluctuations and constraint release, not only for branched polymers but also for linear ones. Progress in the non-linear r...

In this work we examine the Doi–Edwards (D–E) theory corrected with convective constraint release (CCR) to show that open problems still remain. One of them is incomplete fulfilment of the Cox–Merz rule. Another problem is underprediction of the normal stress ratio in shear in the limit of low stresses. The latter problem is directly linked with de...

The molecular origin of the stress in entangled polymers is reconsidered here, in order to ascertain whether or not the pressure that the confined chain exerts on its `tube of constraints' should be accounted for. Indeed, the classical expression for the stress includes only traction along the chain. The analysis shows that the pressure terms signi...

The flow-induced concentration changes in polymers are analysed using the two-fluid theory of Doi and Milner, which predicts migration in flows with either curvilinear trajectories or non-uniform shear rates. Here we show that, even in simple shear flows, migration can be relevant since it can make the stationary solution with uniform concentration...

Two-dimensional simulations of the Brownian dynamics of polymers in a grid of topological obstacles were carried out in this study. A first model made use of the exact expression for the free energy of a chain with fixed ends interacting with an obstacle and can be used to derive the elastic force acting on the subchains of a Rouse-like model. With...

Two-dimensional simulations of the Brownian dynamics of polymers in a grid of topological obstacles were carried out in this study. A first model made use of the exact expression for the free energy of a chain with fixed ends interacting with an obstacle and can be used to derive the elastic force acting on the subchains of a Rouse-like model. With...

The molecular origin of the stress in entangled polymers is reconsidered here, in order to ascertain whether or not the pressure that the confined chain exerts on its `tube of constraints' should be accounted for. Indeed, the classical expression for the stress includes only traction along the chain. The analysis shows that the pressure terms signi...

To understand the flow behaviour of polymeric liquids, it is important to analyse the microscopic origin of the stress. The classical molecular theories relate the stress to the tensile force of entropic origin acting along the chains. The momentum transfer due to collisions between different molecules is not explicitly considered. Though certainly...

The dynamics of concentrated polymers of high molecular mass is dominated by topological interactions (or entanglements). The nonlinear effects shown by these systems in fast flows are still poorly understood, however. We have recently noted that a mechanism of convective constraint release should play a significant role in the nonlinear range, and...

A recently suggested relaxation mechanism which is expected to be dominant in fast flows of polymer melts is combined here with the tube model of Doi and Edwards, and the corresponding constitutive equation is derived. The mechanism consists of the renewal of topology by convective displacement of entanglements. Detailed predictions for the flow cu...

The migration phenomenon in polymeric solutions undergoing flow in straight channels is analyzed by using the recent two-fluid theory of Doi and Milner, so far applied to shear flows in rotating devices. Migration is predicted to take place along the transversal direction of the Poiseuille flow (from the walls of the channel toward the center) if a...

In this paper we derive a few analytical results for the case of polymeric solutions flowing past a spherical obstacle. The calculations are meant to ascertain the possible importance of flow-induced migration (i.e., of changes in concentration), making use of the recent two-fluid theory of Doi and Milner. In order to obtain solutions in closed for...

Slit devolatilization of polymers has been considered in a recent work by Maffettone et al. (1991), who have presented a successful model for single slit devolatilization. In this article, the stability of operation of a realistic multislit process is considered. It is shown that the flow rate per slit which can be stably operated may be significan...

We present a new multi-chain Brownian dynamics simulation of a polymeric network containing both crosslinks and sliplinks (entanglements). We coarse-grain at the level of chain segments connecting consecutive nodes (cross- or slip-links). Affine displacement of nodes is not imposed; rather, their displacement as well as sliding of monomers through...

We study the rheometrical and complex flow response of the double- convection-reptation (DCR) model with chain stretch proposed recently by Ianniruberto and Marrucci (2002) for entangled linear polymers. The single- and two-mode dierential versions of the model are used, with parameter values identied by Ianniruberto and Marrucci (2002) for a nearl...

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Synopsis We study the rheometrical and complex flow response of the double-convection-reptation DCR model with chain stretch proposed recently by Ianniruberto and Marrucci 2002 for entangled linear polymers. The single-and two-mode differential versions of the model are used, with the parameter values identified by Ianniruberto and Marrucci 2002 fo...