[show abstract][hide abstract] ABSTRACT: This work deals with the rheological behavior and adherence properties of pressure sensitive adhesive formulations dedicated to medical applications. We have developed a specific viscoelastic substrate which mimics adhesion on human skin to measure the adherence properties of PSAs when they are stuck on the human skin. By comparing peeling results of PSAs, dedicated to medical applications, stuck on human skin and on this viscoelastic substrate we show that this substrate, based on a blend of natural proteins, presents a better representation of the interactions occurring at the skin/adhesive interface than conventional substrates used for peel test (i.e. glass and steel).
International journal of pharmaceutics 11/2008; 368(1-2):83-8. · 2.96 Impact Factor
[show abstract][hide abstract] ABSTRACT: The aim of this work is to use a recently developed statistical model of dispersions with non-hydrodynamic interactions (Dagréou et al., 2002) to describe the linear viscoelastic properties of suspensions of rigid hairy particles in a polymeric matrix. We first present numerical simulations of our model applied to this system; we demonstrate that taking physical interactions into account allows one to predict the complex relaxation behaviour of filled polymers. We then compare the statistical model to experimental results on suspensions of grafted silica particles in a polystyrene matrix and show that they are in reasonable agreement up to volume fractions close to percolation.L'objectif de ce travail est d'utiliser un modèle statistique (Dagréou et al., 2002) pour décrire les propriétés viscoélastiques linéaires de polymères chargés. Nous présentons d'abord des simulations numériques du modèle appliqué à ce système; nous montrons que la prise en compte des interactions non hydrodynamiques permet de prévoir un comportement complexe en élasticité. Nous comparons ensuite le modèle avec des résultats expérimentaux obtenus pour des suspensions de particules de silice greffée dans une matrice de polystyrène; il existe un assez bon accord entre théorie et expérience, jusqu'à des fractions volumiques proches de la percolation.
The Canadian Journal of Chemical Engineering 05/2008; 80(6):1126 - 1134. · 1.00 Impact Factor
[show abstract][hide abstract] ABSTRACT: This work deals with the study of the viscoelastic and adherence properties of pressure-sensitive adhesive (PSA) formulations dedicated to medical applications. We have developed a specific viscoelastic substrate to measure the adherence properties of PSAs that mimics adhesion on human skin. In the present article, we describe several experiments dedicated to a better understanding of adhesion on viscoelastic substrates without discussing specifically the case of human skin. In this way, we have studied different model adhesive formulations based on real medical formulations, and we have related the rheological behavior to the adherence properties obtained on different substrates to study the various specific effects due to the viscoelasticity of soft substrates. We propose from this study a failure criterion that allows one to derive a reasonable estimate of the peeling transition rate from cohesive to interfacial or stick–slip failure.
[show abstract][hide abstract] ABSTRACT: In this Note, we focused on the sharkskin defect, classically observed in linear polymer extrusion. The aim of this work is to link the sharkskin onset to the rheological properties of polymer melt and more particularly to the shape of the molecular weight distribution. Using the model of Brochard–de Gennes, we show that it is possible to eliminate the sharkskin if Mn≈10Me. To cite this article: A. Allal et al., C. R. Physique 8 (2007).
[show abstract][hide abstract] ABSTRACT: We have studied the relationship between rheological and peeling properties for hot-melt pressure-sensitive adhesives based on homopolymers or copolymers blended with tackifying resins. In this article, we particularly try to demonstrate that it is possible to define a quantitative link between rheology and adherence when the model formulations are deposited on substrates with strong (thermodynamic) adhesion. We describe the experimental results obtained on these model formulations and discuss the quantitative relationships obtained. In the case of “adhesion modulation” (derived from different treatments of the substrates), we show that the relationships become much more complicated, even with the same model adhesives. At the end, we discuss on the competition between adhesion and dissipation in the case of poor adhesion.
[show abstract][hide abstract] ABSTRACT: This work is focused on the sharkskin defect encountered during the extrusion of linear polymers. This defect is characterized by the development of surface cracks, perpendicular to the flow direction. Our purpose is to establish relationships between sharkskin onset and rheological and molecular properties of the extruded polymer. Starting from the elasticity theory of Griffith, we show that the period of the defect is proportional to its amplitude, and that the critical stress for the onset of sharkskin is a function of the plateau modulus, the weight average molecular weight and the molecular mass between entanglements. On the other hand, we show that the cracks propagation velocity is controlled by the extrudate velocity and the Rouse time. We explain that the critical shear rate for the onset of sharkskin depends on the longest time of the distribution of relaxation times, i.e. the tube renewal. Finally, the present approach allows to clarify the ambiguity of simultaneous apparition of sharkskin defect and wall slip, as reported in the literature.
[show abstract][hide abstract] ABSTRACT: The processing and application properties of hot-melt pressure-sensitive adhesives (HMPSA) are governed, to a large extent, by their rheological properties. Coating of the HMPSA is performed at high temperatures in the molten state. At room temperature, the adhesive satisfies the Dahlquist criterion and, consequently, has permanent tack. We have particularly studied the full formulations based on triblock and diblock copolymers, and also those based on newly designed molecules, such as tetrablock or radial copolymers. We have demonstrated in the previous articles of this series that, for these systems, the volume fraction of the free polyisoprene is the most important parameter that drives the tack performances by controlling the level of the secondary elastic plateau modulus observed in the low-frequency range. To improve the end-user properties, we have increased the diblock content in the blends. We describe here the dynamic mechanical properties, at room temperature, of the pure copolymer blends (i.e., without addition of a tackifying resin) and the full HMPSA formulations. We focus particularly in this article on blends that contain a high diblock content. The effect of the morphology of the diblock copolymer on the rheological behavior of the adhesive is discussed in detail. Finally, we propose a model, based on molecular dynamics concepts, which describes the rheological behavior in a very wide range of frequencies for all copolymers and full formulations of the study.
[show abstract][hide abstract] ABSTRACT: The aim of this work is to use a recently developed statistical model of dispersions with nonhydrodynamic interactions to describe the linear viscoelastic properties of emulsions of Newtonian liquids. None of the existing models can describe the rheological behavior of such systems, particularly the elastic properties, in the linear regime. We first present the results of numerical simulations of our model applied to emulsions. We show that taking nonhydrodynamic interactions into account allows to predict that emulsions of two purely viscous liquids have a complex viscoelastic behavior. We then compare the model to experimental results on oil/water emulsions, stabilized with ionic and nonionic surfactants. We find out that our statistical mechanical approach gives a much better description of the viscoelastic behavior of these samples than purely hydrodynamic models do. However, the elasticity observed is underestimated by our model. We indicate further theoretical developments which could improve the description of the viscoelastic properties of emulsions.
Journal of Colloid and Interface Science 03/2005; 282(1):202-11. · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: “Molecular rheology” is the missing link between the macromolecular structure of polymeric materials and their viscoelastic properties in the melt state. It complements the engineering or continuum mechanics aspects of rheology, which generally ignores the molecular details of the objects under study. The pioneering vision of the diffusion and relaxation processes of flexible macromolecular chains initiated by P.-G. de Gennes has lead to very effective and predictive models of viscoelasticity of polymer melts, which go far beyond academic interest.We present, in this paper, two very different examples of application of molecular rheology: molecular design of block copolymers corresponding to expected end-user properties (which are directly linked to linear viscoelastic properties) and formulation of blends of linear polymers in order to get strain-hardening effects in non-linear viscoelasticity usually obtained with long-chain branched (LCB) materials.
Journal of Non-Newtonian Fluid Mechanics 01/2005; · 1.57 Impact Factor
[show abstract][hide abstract] ABSTRACT: The viscoelastic properties of hot melt pressure-sensitive adhesives (HMPSA) based on formulations of block copolymers and tackifying resins have been studied in detail, through the variation of the complex shear modulus, G*, as a function of frequency, y . In this first article, we analyze the individual behavior of the components of HMPSA blends: (1) the two copolymers, styrene-isoprene (SI) diblock copolymer and styrene-isoprene-styrene (SIS) triblock copolymer and (2) two tackifying resins. The viscoelastic behavior of the overall formulation is also presented. We have mainly studied the effects of (1) the molecular characteristics of the SI and SIS copolymers and (2) the composition of the blends (mainly the effect of SI content, S content in SIS and SI, resin content) on the viscoelastic properties. A theoretical approach based on concepts of molecular dynamics leads to a model which describes reasonably well the linear viscoelastic properties of individual components and their formulations. Our systematic study can be used to design new copolymer molecules which can mimic the rheological behavior and end-user properties of regular formulations at room temperature.
Journal of Adhesion - J ADHES. 01/2003; 79:825-852.
[show abstract][hide abstract] ABSTRACT: The viscoelastic properties of hot melt pressure-sensitive adhesives (HMPSA) based on formulations of block copolymers and tackifying resins have been studied in detail, through the variation of the complex shear modulus, G*, as a function of frequency, omega. In this first article, we analyze the individual behavior of the components of HMPSA blends: (1) the two copolymers, styrene-isoprene (SI) diblock copolymer and styrene-isoprene-styrene (SIS) triblock copolymer and (2) two tackifying resins. The viscoelastic behavior of the overall formulation is also presented. We have mainly studied the effects of (1) the molecular characteristics of the SI and SIS copolymers and (2) the composition of the blends (mainly the effect of SI content, S content in SIS and SI, resin content) on the viscoelastic properties. A theoretical approach based on concepts of molecular dynamics leads to a model which describes reasonably well the linear viscoelastic properties of individual components and their formulations. Our systematic study can be used to design new copolymer molecules which can mimic the rheological behavior and end-user properties of regular formulations at room temperature.
[show abstract][hide abstract] ABSTRACT: We extend the previous work by Benallal et al. on the relationship between structure and rheological properties of linear polymer melts. The aim of this paper is to quantify the effect of the chemical structure on the viscoelastic properties. We show that these properties are governed by the monomer dimensions and the interaction energy. To cite this article: A. Allal et al., C. R. Physique 3 (2002) 1451–1458.
Comptes Rendus Physique - C R PHYS. 01/2002; 3(10):1451-1458.
[show abstract][hide abstract] ABSTRACT: We present a new approach to describe the rheological properties of dispersions with non-hydrodynamic interactions (steric, electrostatic and Van der Waals interactions) in the linear viscoelastic domain. Our model is based on the calculation of additional stresses resulting from interaction potentials between spheres and Brownian motion. We start from the statistical mechanical approaches which have been developed by Batchelor and Green and later Lionberger and Russel, to model the viscoelastic properties of emulsions and suspensions. We have extended their calculations to the more general case of viscoelastic deformable inclusions in a viscoelastic matrix. Our contribution lies in the computation of the hydrodynamic functions involved in the term describing interaction stresses. This computation is based on Palierne's results on the deformation field around a viscoelastic inclusion embedded in a viscoelastic matrix. We have also rewritten the conservation equation in the case of interest, over the whole frequency domain. We finally express the complex shear modulus of the dispersion as the sum of two terms : Palierne's complex shear modulus gives the purely hydrodynamic contribution; the interaction contribution depends on both the hydrodynamic properties and the interaction potential.
[show abstract][hide abstract] ABSTRACT: Three factors govern the adhesion properties of hot-melt and pressure-sensitive adhesives: (1) thermodynamic interfacial properties (Dupre adhesion energy); (2) interfacial losses due to specific interactions; and (3) viscoelastic losses in the bulk related to the rheological properties of the adhesive. In the present paper, we focus on the main factor in the adhesion properties, which is the viscoelastic factor. We extend in this paper the results obtained on a series of model adhesives to the case of industrial formulations: one SIS triblock copolymer-based PSA formulation and one EVA copolymer-based hot-melt formulation. After studying the rheologcal properties of these adhesives over a wide frequency range using time-temperature equivalence, we present data obtained on peel tests at various temperatures. As with model adhesives, the peel rate- temperature equivalence leads to the same shift factors as rheology. The experiments demonstrate that there is a one-to-one relationship between the cohesive fracture domain and the terminal region of relaxation exhibited in rheological testing. The first interfacial fracture mode is related to the rubbery plateau, and the brittle interfacial fracture mode observed at high peel rates to the glassy behavior exhibited at very high frequencies in rheological measurements.
[show abstract][hide abstract] ABSTRACT: The viscoelasticity of unentangled polystyrene melts has been investigated in terms of terminals parameters: zero-shear viscosity,
steady-state compliance and relaxation spectrum. The Rouse model applies well for molecular weights lower than the average molecular weight between entanglements, providing that one takes into account the proper variations of the radius
of gyration. Moreover, local motions at the scale of Kuhn segments have to be considered in order to describe correctly the
relaxation modes intermediate between the terminal zone and the glassy plateau.
On the other hand, reptation models are commonly used for describing the entangled regime. We propose an expression of the
shear modulus which accounts not only for the terminal modes (reptation, tube length fluctuations and tube renewal), but also for the relaxation
modes responsible for the plateau zone and the transition of the glassy plateau. A crossover region between the unentangled
and untangled regimes is located around . When the molecular weight increases, a shift transfer of Rouse modes towards reptation modes occurs. That leads to a continuity
of the expression of the shear modulus over the entire range of molecular weights.
[show abstract][hide abstract] ABSTRACT: The viscoelastic and peeling properties of polybutadiene/tackifying resin compatible blends have been studied in detail. Viscoelastic properties have been described through the variations of the complex shear modulus, G*(w), as a function of frequency, W, and peeling properties through the variations of peeling force (F) as a function of peeling rate (V).The first paper of this series presented the cohesive fracture domain and the present paper explores the interfacial fracture domain: (i) rubbery interfacial (interfacial 1); (ii) stick-slip; (iii) glassy interfacial (interfacial 2). After a general survey of the properties in the three domains we present a quantitative relationship between the peeling and linear viscoelastic properties as a function of the adhesive formulation, discussing the use of time-temperature equivalence for adhesive properties. The third part of the paper presents the trumpet model of de Gennes describing the crack shape and propagation: starting from a mechanical analysis of the peeling test, it is shown how one may calculate the variations of the peeling force as a function of peeling rate in the various interfacial fracture domains: this model defines a single interfacial fracture criterion which coexists with the cohesive fracture criterion defined earlier, whatever the fracture location.We present as a conclusion a critical discussion of the relevance and physical meaning of such a criterion and present a new outlook for the modeling and improvement of adhesive formulations.
The Journal of Adhesion. 08/1998; 68(3-4):203-228.