353 research outputs found
Adhesion and non-linear rheology of adhesives with supramolecular crosslinking points
Soft supramolecular materials are promising for the design of innovative and
highly tunable adhesives. These materials are composed of polymer chains
functionalized by strongly interacting moieties, sometimes called "stickers".
In order to systematically investigate the effect of the presence of
associative groups on the debonding properties of a supramolecular adhesive, a
series of supramolecular model systems has been characterized by probe-tack
tests. These model materials, composed of linear and low dispersity
poly(butylacrylate) chains functionalized in the middle by a single tri-urea
sticker, are able to self-associate by six hydrogen bonds and range in
molecular weight (M n) between 5 and 85 kg/mol. The linear rheology and the
nanostructure of the same materials (called "PnBA3U") was the object of a
previous study 1,2. At room temperature, the association of polymers via
hydrogen bonds induces the formation of rod-like aggregates structured into
bundles for M n \textless{} 40kg/mol and the behavior of a soft elastic
material was observed (G'\textgreater{}\textgreater{}G "and G'~ 0). For
higher M n , the filaments were randomly oriented and polymers displayed a
crossover towards viscous behavior although terminal relaxation was not reached
in the experimental frequency window. All these materials show however similar
adhesive properties characterized by a cohesive mode of failure and low
debonding energies (W adh \textless{}40J/m 2 for a debonding speed of
100m/s). The debonding mechanisms observed during the adhesion tests have
been investigated in detail with an Image tools analysis developed by our group
3. The measure of the projected area covered by cavities growing in the
adhesive layer during debonding can be used to estimate the true stress in the
walls of the cavities and thus, to characterize the in-situ large strain
deformation of the thin layer during the adhesion test itself. This analysis
revealed in particular that the PnBA3U materials with M n \textless{} 40 kg/mol
soften very markedly at large deformation like yield stress fluids, explaining
the low adhesion energies measured for these viscoelastic gels.
Pattern Formation During Deformation of a Confined Viscoelastic Layer: From a Viscous Liquid to a Soft Elastic Solid
We study pattern formation during tensile deformation of confined
viscoelastic layers. The use of a model system (PDMS with different degrees of
crosslinking) allows us to go continuously from a viscous liquid to an elastic
solid. We observe two distinct regimes of fingering instabilities: a regime
called "elastic" with interfacial crack propagation where the fingering
wavelength only scales with the film thickness, and a bulk regime called
"viscoelastic" where the fingering instability shows a Saffman-Taylor-like
behavior. We find good quantitative agreement with theory in both cases and
present a reduced parameter describing the transition between the two regimes
and allowing to predict the observed patterns over the whole range of
viscoelastic properties.Comment: 4 pages, 7 figures, typos corrected, figure 5 replace
A new sighting study for the fixed concentration procedure to allow for gender differences
The fixed concentration procedure (FCP) has been proposed as an alternative to the median lethal
concentration (LC50) test (organisation for economic co-operation and development (OECD) test guideline
[TG] 403) for the assessment of acute inhalation toxicity. The FCP tests animals of a single gender (usually
females) at a number of fixed concentration levels in a sequential fashion. It begins with a sighting study that precedes
the main FCP study and is used to determine the main study starting concentration. In this paper, we propose
a modification to the sighting study and suggest that it should be conducted using both male and female
animals, rather than just animals of a single gender. Statistical analysis demonstrates that, when females are more
sensitive, the new procedure is likely to give the same classification as the original FCP, whereas, if males are more
sensitive, the new procedure is much less likely to lead to incorrect classification into a less toxic category. If
there is no difference in the LC50 for females and males, the new procedure is slightly more likely to classify into
a more stringent class than the original FCP. Overall, these results show that the revised sighting study ensures
gender differences in sensitivity do not significantly impact on the performance of the FCP, supporting its use as
an alternative test method for assessing acute inhalation toxicity
Cavitation-induced force transition in confined viscous liquids under traction
We perform traction experiments on simple liquids highly confined between
parallel plates. At small separation rates, we observe a simple response
corresponding to a convergent Poiseuille flow. Dramatic changes in the force
response occur at high separation rates, with the appearance of a force plateau
followed by an abrupt drop. By direct observation in the course of the
experiment, we show that cavitation accounts for these features which are
reminiscent of the utmost complex behavior of adhesive films under traction.
Surprisingly enough, this is observed here in purely viscous fluids.Comment: Submitted to Physical Review Letters on May 31, 2002. Related
informations on http://www.crpp.u-bordeaux.fr/tack.htm
Interdigitation between surface-anchored polymer chains and an elastomer : consequences for adhesion promotion
We study the adhesion between a cross-linked elastomer and a flat solid
surface where polymer chains have been end-grafted. To understand the adhesive
feature of such a system, one has to study both the origin of the grafted layer
interdigitation with the network, and the end-grafted chains extraction out of
the elastomer when it comes unstuck from the solid surface. We shall tackle
here the first aspect for which we develop a partial interdigitation model that
lets us analytically predict a critical surface grafting density beyond which the layer no longer interdigitates
with the elastomer. We then relate this result with recent adhesion
measurements
Recommended from our members
Quantifying Rate-and Temperature-Dependent Molecular Damage in Elastomer Fracture
Elastomers are highly valued soft materials finding many applications in the engineering and biomedical fields for their ability to stretch reversibly to large deformations. Yet their maximum extensibility is limited by the occurrence of fracture, which is currently still poorly understood. Because of a lack of experimental evidence, current physical models of elastomer fracture describe the rate and temperature dependence of the fracture energy as being solely due to viscoelastic friction, with chemical bond scission at the crack tip assumed to remain constant. Here, by coupling new fluorogenic mechanochemistry with quantitative confocal microscopy mapping, we are able to quantitatively detect, with high spatial resolution and sensitivity, the scission of covalent bonds as ordinary elastomers fracture at different strain rates and temperatures. Our measurements reveal that, in simple networks, bond scission, far from being restricted to a constant level near the crack plane, can both be delocalized over up to hundreds of micrometers and increase by a factor of 100, depending on the temperature and stretch rate. These observations, permitted by the high fluorescence and stability of the mechanophore, point to an intricate coupling between strain-rate-dependent viscous dissipation and strain-dependent irreversible network scission. These findings paint an entirely novel picture of fracture in soft materials, where energy dissipated by covalent bond scission accounts for a much larger fraction of the total fracture energy than previously believed. Our results pioneer the sensitive, quantitative, and spatially resolved detection of bond scission to assess material damage in a variety of soft materials and their applications. © 2020 authors. Published by the American Physical Society
Quantifying and mapping covalent bond scission during elastomer fracture
Many new soft but tough rubbery materials have been recently discovered and
new applications such as flexible prosthetics, stretchable electrodes or soft
robotics continuously emerge. Yet, a credible multi-scale quantitative picture
of damage and fracture of these materials has still not emerged, due to our
fundamental inability to disentangle the irreversible scission of chemical
bonds along the fracture path from dissipation by internal molecular friction.
Here, by coupling new fluorogenic mechanochemistry with quantitative confocal
microscopy mapping, we uncover how many and where covalent bonds are broken as
an elastomer fractures. Our measurements reveal that bond scission near the
crack plane can be delocalized over up to hundreds of micrometers and increase
by a factor of 100 depending on temperature and stretch rate, pointing to an
intricated coupling between strain rate dependent viscous dissipation and
strain dependent irreversible network scission. These findings paint an
entirely novel picture of fracture in soft materials, where energy dissipated
by covalent bond scission accounts for a much larger fraction of the total
fracture energy than previously believed. Our results pioneer the sensitive,
quantitative and spatially-resolved detection of bond scission to assess
material damage in a variety of soft materials and their applications
The Slowly Formed Guiselin Brush
We study polymer layers formed by irreversible adsorption from a polymer
melt. Our theory describes an experiment which is a ``slow'' version of that
proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered
instantaneously irreversibly adsorbing chains and predicted a universal density
profile of the layer after swelling with solvent to produce the ``Guiselin
brush.'' Here we ask what happens when adsorption is not instantaneous. The
classic example is chemisorption. In this case the brush is formed slowly and
the final structure depends on the experiment's duration, . We find
the swollen layer consists of an inner region of thickness with approximately constant density and an outer region
extending up to height which has the same density decay as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter
Molecular weight effects on chain pull-out fracture of reinforced polymeric interfaces
Using Brownian dynamics, we simulate the fracture of polymer interfaces
reinforced by diblock connector chains. We find that for short chains the
interface fracture toughness depends linearly on the degree of polymerization
of the connector chains, while for longer chains the dependence becomes
. Based on the geometry of initial chain configuration, we propose a
scaling argument that accounts for both short and long chain limits and
crossover between them.Comment: 5 pages, 3 figure
- …