G. Marrucci

Bio: G. Marrucci is an academic researcher from University of Palermo. The author has contributed to research in topics: Constitutive equation & Viscoelasticity. The author has an hindex of 9, co-authored 15 publications receiving 522 citations.

A non-linear viscoelastic model with structure-dependent relaxation times: I. Basic formulation

Abstract: A non-linear constitutive equation for polymer melts and concentrated solutions is presented. Based on known results of network theories, the model contains a distinctive feature: that of letting the relaxation times depend upon the existing structure. The model extends the constitutive equation of linear viscoelasticity to the non-linear region in a well-defined way, with the uncertainty of just a single adjustable parameter. Predictions of the model for common cases of non-linear response are derived and discussed.

Testing of a constitutive equation for entangled networks by elongational and shear data of polymer melts

Abstract: An entangled network such as a polymer melt or a concentrated solution is here described by a set of two simultaneous equations. One of them is a balance of entanglements, the other gives the stress in the classical form of aMaxwell equation.

A non-linear viscoelastic model with structure-dependent relaxation times: II. Comparison with l.d. polyethylene transient stress results

Abstract: A model of non-linear viscoelasticity with relaxation times which depend on the structure is compared with experimental results reported in the literature for a L.D. polyethylene. The single parameter of the model is determined by comparison with steadystate shear results. The model is then used to interpret various transient data. These are: tangential and normal stress growth in shear, stress growth in elongation, normal stresses in shear creep. The comparison shows a good general agreement, thus supporting the suggestion of relating the change in time of the relaxation spectrum to structural variables.

Capillary experiments of flow induced crystallization of HDPE

Abstract: Flow-induced crystallization experiments are made in a capillary apparatus modified with a downstream reservoir under pressure. Capillary length, diameter, and entrance angle are changed, as well as flow rate. The results show that the crystallization temperature is influenced both by the elongational flow at the capillary entrance and by the shear flow along the capillary. The independent effect of the pressure equals that obtained under static conditions. The effect of shear is correlated in terms of shearing work.

Thixotropy—a review

Abstract: The ensuing mechanical response to stressing or straining a structured liquid results in various viscoelastic phenomena, either in the linear region where the microstructure responds linearly with respect to the stress and strain but does not itself change, or in the nonlinear region where the microstructure does change in response to the imposed stresses and strains, but does so reversibly. The complication of thixotropy arises because this reversible, microstructural change itself takes time to come about due to local spatial rearrangement of the components. This frequently found time-response of a microstructure that is itself changing with time makes thixotropic, viscoelastic behaviour one of the greatest challenges facing rheologists today, in terms of its accurate experimental characterisation and its adequate theoretical description. Here a history of thixotropy is given, together with a description of how it is understood today in various parts of the scientific community. Then a mechanistic description of thixotropy is presented, together with a series of applications where thixotropy is important. A list of different examples of thixotropic systems is then given. Finally the various kinds of theories that have been put forward to describe the phenomenon mathematically are listed.

A new constitutive equation derived from network theory

Abstract: A constitutive equation is derived from a Lodge—Yamamoto type of network theory for polymeric fluids. The network junctions are not assumed to move strictly as points of the continuum but allowed a certain “effective slip”. The rates of creation and destruction of junctions are assumed to depend on the instantaneous elastic energy of the network, or equivalently, the average extension of the network strand, in a simple manner. Agreement between model predictions and the I.U.P.A.C. data on L.D.P.E. is good.

Dynamics and thermodynamics of complex fluids. II. Illustrations of a general formalism

Abstract: For a number of well-known time-evolution equations for nonequilibrium systems we extract a common structure from these equations, referred to as a general equation for the nonequilibrium reversible-irreversible coupling (GENERIC). This fundamental structure is determined by four building blocks, two ``potentials'' (total energy and entropy) and two ``matrices.'' We illustrate for various examples how three of the four building blocks can be determined in a rather straightforward manner so that, within our GENERIC approach to nonequilibrium dynamics, understanding of a given nonequilibrium system is reduced to determining a single ``metric matrix,'' or friction matrix, either empirically or by more microscopic considerations. In formulating nonisothermal polymer kinetic theories, we show how the general structure provides a clear distinction between spring potentials of energetic and entropic origins in the various time-evolution equations.

Thixotropy - a general review

Abstract: The time-dependent behaviour associated with thixotropy rather than with viscoelasticity is discussed. The evolution of the concept is traced back and a generalized definition is accepted. Subsequently, the various experimental methods are considered with which meaningful measurements of thixotropy can be performed. The specific experimental difficulties encountered with the systems under consideration are treated separately. It is impossible to enumerate all materials that show thixotropy or anti-thixotropy. Instead, they are classified in groups according to their origin or application. The resulting table is used to deduce the characteristics which accompany thixotropic phenomena. This leads to a discussion of the time effects in terms of the molecular or microscopic structure. An attempt is made to provide a systematic outline of the published models and possible constitutive equations for thixotropic materials. Both inelastic and viscoelastic descriptions are included.

The rheology of dilute solutions of flexible polymers: Progress and problems

Abstract: Recent progress toward understanding the rheology of dilute solutions of flexible polymers is reviewed, emphasizing experimental results from flows imaging single deoxyribonucleic acid (DNA) molecules and filament-stretching rheometry of dilute polystyrene Boger fluids, as well as Brownian dynamics (BD) simulations of these flows. The bead-spring and bead-rod models are presented, the range of their applicability discussed, and methods presented for inclusion of hydrodynamics interactions, excluded volume, and other physical effects within BD simulations. After reviewing and updating work in the linear viscoelastic regime, the primary focus shifts to the more complex nonlinear regime. While BD predictions of the conformations of 20 to 100 micron long DNA molecules in strong shear and extensional flows has been in good to excellent agreement with the corresponding experiments, predictions of the polystyrene dilute solution rheometry data have been hit or miss, with poorer results obtained for the higher mo...