55 research outputs found
Protocol to perform pressurized blister tests on thin elastic films
This work aims to identify common challenges in the preparation of the
blister test devices designed for measurement of energy release rate for
brittle thin films and to propose easy-to-implement solutions accordingly. To
this end, we provide a step-by-step guide for fabricating a blister test device
comprised of thin polystyrene films adhered to glass substrates. Thin films are
first transferred from donor substrates to an air-water interface, which is
then used as a platform to locate them on a receiver substrate. We embed a
microchannel at the back of the device to evacuate the air trapped in the
opening, through which the pressure is applied. We quantify the height and the
radius of the blister to estimate the adhesion energy using the available
expressions correlating the normal force and the moment with the shape of the
blister. The present blister test provided adhesion energy per unit area of \mbox{mJ}/{\mbox m}^2 for polystyrene on glass, which is in good
agreement with the measurement of \mbox{mJ}/{\mbox m}^2 found
in our independent cleavage test
Generation of silicone poly-HIPES with controlled pore sizes via reactive emulsion stabilization
Macrocellular silicone polymers are obtained after solidification of the
continuous phase of a PDMS (polydimethylsiloxane) emulsion, which contains PEG
(polyethylene glycol) drops of sub-millimetric dimensions. Coalescence of the
liquid template emulsion is prohibited by a reactive blending approach. We
investigate in detail the relationship between the interfacial properties and
the emulsion stability, and we use micro- and millifluidic techniques to
generation macro-cellular polymers with controlled structural properties over a
wider range of cell-sizes (0.2-2mm) and volume fractions of the continuous
phase (0.1-40%). This approach could easily be transferred to a wide range of
polymeric systems
Rescaling the dynamics of evaporating drops
The dynamics of evaporation of wetting droplets has been investigated
experimentally in an extended range of drop sizes, in order to provide trends
relevant for a theoretical analysis. A model is proposed, which generalises
Tanner's law, allowing us to smooth out the singularities both in dissipation
and in evaporative flux at the moving contact line. A qualitative agreement is
obtained, which represents a first step towards the solution of a very old,
complex problem
Water-based peeling of thin hydrophobic films
Inks of permanent markers and water-proof cosmetics create elastic thin films
upon application on a surface. Such adhesive materials are deliberately
designed to exhibit water-repellent behavior. Therefore, patterns made up of
these inks become resistant to moisture and cannot be cleaned by water after
drying. However, we show that sufficiently slow dipping of such elastic films,
which are adhered to a substrate, into a bath of pure water allows complete
removal of the hydrophobic coatings. Upon dipping, the air-water interface in
the bath forms a contact line on the substrate, which exerts a
capillary-induced peeling force at the edge of the hydrophobic thin film. We
highlight that this capillary peeling process is more effective at lower
velocities of the air-liquid interface and lower viscosities. Capillary peeling
not only removes such thin films from the substrate but also transfers them
flawlessly onto the air-water interface
Transition from Cassie to Wenzel state in patterned soft elastomer sliding contacts
In this paper, we presented an experimental and theoretical analysis of the
formation of the contact between a smooth elastomer lens and an elastomer
substrate micropatterned with hexagonal arrays of cylindrical pillars. We show
using a JKR model coupled with a full description of the deformation of the
substrate between the pillars that the transition between the top to the full
contact is obtain when the normal load is increased above a well predicted
threshold. We have also shown that above the onset of full contact, the
evolution of the area of full contact was obeying a simple scaling.Comment: 4 pages, 6 figures. Submitte
Chemical modification of PDMS surface without impacting the viscoelasticity: Model systems for a better understanding of elastomer/elastomer adhesion and friction
The influence of both viscoelastic and interfacial parameters on the surface properties of elastomers is difficult to study. Here, we describe a simple route to achieve surface modification of PDMS without impacting the viscoelastic properties of the bulk. PEG modified PDMS surfaces were synthesized by two step surface modification based on hydrosilylation. The covalent grafting of PEG on the surface has been evidenced by AFM and ATR-FTIR, and its effect on the hydrophilicity characterized by static and dynamic contact angle. The static water contact angle of the PEG-modified PDMS decreases from 110° (for unmodified PDMS) to 65°. Dynamic contact angles also show a significant decrease in both advancing and receding contact angles, along with a significant increase in the contact angle hysteresis, which can be related to an increase in the surface energy as estimated by JKR measurements. The viscoelastic properties of modified PDMS are found to be quantitatively comparable to those of the unmodified PDMS. This simple method is an efficient way to prepare model materials which can be used to get a better understanding of the exact contribution of the surface chemistry on surface properties of elastomers
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