The research activities of our group focus on polymer mechanical properties
and interfaces and often contain both a deformation and fracture component and
an interface and adhesion component. We are particularly interested in the processes
where deformation of the material is in the large strain regime and in the understanding
of macroscopic fracture or adhesion processes.
For all the specific topics that we have investigated, we try to establish
a connection between the molecular structure or the material organization at
the nano and micro level, and the macroscopic mechanical properties. Often in
fracture processes, complex and inhomogeneous deformations occur before an actula
macroscopic fracture takes place. The undersanding of these large deformation
processes which modify the structure of the material are essential to understand
the fracture process itself. In essence for deformable materials, it is not
the undeformed material which fractures but it is often a highly deformed and
modifed structure, which needs specific chaacterization methods.
We have developed specific techniques adapted to the investigation of the fracture
of highly deformable materials, which generally use in-situ observation of deformation
mechanisms and confined polymer layers. In addition of course we use standard
tools of polymer science such as DSC, rheology in the linear regime, NMR and
FTIR for the characterization of the chemical structure.
A second key aspect of our work is the behavior of materials at interfaces.
Because interfaces impose a boundary condition to the deforamtion, understanding
their structure and how this structure influences the boundary conditions is
essential to understand the deformation behavior. Often interfaces are also
weak mechanical points and improving, or more generally controlling the level
of adhesion at an interface, is an importat practical and scientific goal.
We present now some examples of applications where interfaces are important
which will be followed by some examples of research projects.
 |
In coextruded polymer multilayers, several polymers are put in contact in the melt state
in a specially designed die within the extruder. Once the multilayer has exited the die and cools down, it is
essential for the integrity of the assembly that a good adhesion was achieved between the layers
during this relatively short contact time in the melt state.
In the typical food packaging application, a polar central layer acts as a barrier to oxygen and water,
while the two outside layers (typically a polyolefin) impart their ductility to the assembly. Two
additional tie-layers are necessary to obtain a good adhesion between the polar layer and the polyolefin.
th tie-layer contains typically some modified polyolefin chains which are miscible with the
polyolefin layer and can react chemically with a polar function on the center layer |
More info:
Laurens, C., Ober,R., Creton, C. and Léger, L.
(2004) "Crystalline Orientation and Adhesion at polypropylene/polyamide
6 interfaces compatibilized with syndiotactic polypropylene-polyamide-6
diblock copolymers". Macromolecules, 37, 6806-6813.
abstract
Laurens, C., Creton, C., Léger, L. (2004) " Adhesion
promotion mechanisms at isotactic polypropylene/polyamide 6 interfaces
: role of the copolymer architecture ", Macromolecules, 37, 6814-6822.
abstract
|
Topic
|
Research Projects
|
Mechanisms of adhesion of soft adhesives:
In this area, we investigate the effect of systematic changes in the molecular
structure or architecture of polymers typically used as pressure-sensitive-adhesives, on the micromechanisms
of deformation during debonding of the adhesive layer.
The main tool used in these investigations is the probe tack tester,
which has been designed to test the adhesive properties of confined deformable layers in a reproducible way while observing the
deformation mechanisms in real time.
The rheological properties of the materials used are also of course characterized and whenever
possible, tensile tests are carried out to determine the large strain deformation properties
of the material.
|
Mechanics of the probe tack test
Mechanics of the probe tack
Adhesives based on acrylic statistical copolymers
Adhesives based on styrene-isoprene block copolymers
|
More info
Shull, K.R. and Creton, C. (2004) "Deformation Behavior of Thin,
Compliant Layers Under Tensile Loading Conditions". J. Polym. Sci. Polym.
Ed. 42, 4023-4043.
abstract
Lindner A, Lestriez B, Mariot S, Creton C, Maevis T, Luhmann B, Brummer
R (2006) "Adhesive and rheological properties of lightly crosslinked
model acrylic networks" J. Adh. 82 (3), 267-310. abstract
Creton, C., A. Roos, and A. Chiche (2005) "Effect of the
diblock content on the adhesive and deformation properties of PSAs based
on styrenic block copolymers" in Adhesion: Current Research and Applications,
W.G. Possart, Editor. Wiley-VCH: Weinheim. p. 337-364. abstract
B. Lestriez, H. Lakrout, A. Chiche, A. Roos and C. Creton. "Probe
tack tests as a characterization tool in pressure-sensitive-adhesives"
Proceedings of the PSTC Technical Seminar TECH XXIV, Orlando, USA, 2-4
May 2001. pdf file
|
Effects of a surface modification on the failure mechanisms of soft adhesives
The interfacial debonding of very deformable materials such as soft adhesives
depends of course on the mechanical properties of the adhesive itself but depends also
on the chemical composition and surface roughness of the adherent which provides a boundary
condition to the deformation of the material imposed by the applied load.
The surface of the adherent can be modified either chemically (by modifying the surface with
functional groups or with polymers capable of entanglements with the adhesive material, or
topographically through a modification of the surface roughness.
In both cases the debonding mechanism will be modified and a relatively complex
coupling between the deformation properties of the adhesive and the interactions at the
interface will determine the observed debonding pattern.
|
Effect of surface roughness on the debonding mechanisms of soft
adhesives
From adhesion to release with changes in rheological properties of the adhesives
or in chemical composition of the surface
Switchable adhesion with bicomponent polymer brushes.
|
More info
H. Retsos, A. Kiriy, V. Senkovskyy, M. Stamm, M. M. Feldstein and
C. Creton (2006) "Controlling tack with Bicomponent Polymer Brushes",
Adv. Mat. 18 (19), 2624-2628.
abstract
Josse, G., Sergot, P., Dorget, M. and Creton, C. (2004).
"Measuring interfacial adhesion between a soft viscoelastic layer and
a rigid surface using a probe method." Journal of Adhesion, 80
(1-2), 87-118.
abstract
Chiche, A., P.Pareige and C. Creton (2000) "Role of surface roughess
in controlling the adhesion of a soft adhesive on a hard surface" Comptes
Rendus de L'Académie des Sciences, Série IV, 1: 1197-1204.
abstract
C. Creton, G. Josse, A. Chiche. "Mécanismes d 'adhésion et
contrôle de l 'adhérence pour les matériaux très déformables" Proceedings
of the 9èmes journées de la formulation, Lyon, France, 9-10 december 2002.pdf file
|
|
Fracture of interfaces between polymer melts
When two very entangled high molecular weight polymer melts
are put in contact, polymer chains interdiffuse and entanglements are formed across
the interface increasing its mechanical strength.
The conditions of this reinforcement depend on the nature of the polymers, on their
molecular weight and on their degree of miscibility.
In order to test reproducibly this mechanical strength of the interface
a specific test of fluid fracture was developed. This test confines the two fluid layers
between two parallel rigid plates and fractures then the interface by applying a tensile stress.
The confinement is essential to avoid excessive deformation unrelated to the interfacial strength.
|
Study of the Adhesion between polymer melts
|
More info
R. Schach, Y. Tran, A. Menelle, C. Creton "Adhesion at
Interfaces Between Immiscible Polymer Melts" World Polymer Congress,
41' International Symposium on Macromolecules, Rio de Janeiro, Brazil,
16-21th july 2006 pdf file
R. Schach and C. Creton "Adhesion between Polymeric Fluids
using a Probe Method" Proceedings of the 229th ACS National Meeting,
San Diego, USA, 13-17 March 2005. pdf
file
R.Schach, C.Creton "Polymer-polymer adhesion of uncrosslinked
elastomers at short contact times"
Proceedings of EURADH ' 04, Freiburg am Breisgau, Germany, 5-9 Sept. 2004.
pdf file
|
|
Mechanical properties of hydrogels
When a water-soluble polymer is chemically crosslinked, it forms a network which swells but
no longer dissolves in water. This water-swollen crosslinked polymer is then called a hydrogel.
Although the equilibrium swelling properties and the elastic properties of
hydrogels have been well studied, their large-strain and fracture properties remain poorly
understood.
More specifically, while most hydrogels are rather weak solids, certain types of
hydrogels can be quite strong, due to their specific network architecture. The reasons of
this exceptional toughness are poorly understood
|
Synthesis and rheological properties of hydrogels containing grafted hydrophobic
groups.
|
More info
G. Miquelard-Garnier, C. Creton, D. Hourdet "Synthesis
and rheological behaviour of new hydrophobically modified hydrogels"
World Polymer Congress, 41' International Symposium on Macromolecules,
Rio de Janeiro, Brazil, 16-21th july 2006 pdf
file
|
