Papers by Patrick Guenoun
Soft Matter
Layer by layer fabrication of lamellar perforated phases on top of substrates.
The European Physical Journal E
Stable stimuli-responsive emulsions between oil and water are formed with an amphiphilic block co... more Stable stimuli-responsive emulsions between oil and water are formed with an amphiphilic block copolymer bearing polystyrene (PS) and poly(dimethylaminoethyl methacrylate) (PDMAEMA) moieties. Different kinds of emulsions like direct, multiple or inverse ones are reproducibly formed as a function of chemical parameters such as pH and salt concentration. To test the correlation between the different nature of the emulsion and the conformation of the polymer chain at the interface, neutron reflectometry at the oil/water interface was carried out. An original sample cell was built and the procedure to get reliable results with it on the FIGARO reflectometer at the Institut Laue-Langevin is described. Results show that for direct emulsions, the copolymer is much more extended on the water side than on the oil side. In the case where multiple emulsions are stabilized, the conformation is strongly modified and is compatible with a more equilibrated extension of the chain on both sides. The inverse case shows that the extension in oil is stronger than in water. These results are discussed in term of polymer brushes (charged or neutral) extension with respect to salt addition and hydrophobic interactions.
Journal of Polymer Science Part B: Polymer Physics
We investigate the spontaneous rolling of polydimethylsiloxane(PDMS) thin films and demonstrate t... more We investigate the spontaneous rolling of polydimethylsiloxane(PDMS) thin films and demonstrate the fabrication of capillaries with topographical and chemical patterns on the inner wall. Thin films of polydimethylsiloxane(PDMS) are either coated by a layer of hard material or have their surface hardened by plasma oxidation. They are then driven out of equilibrium by selective solvent swelling in vapor phase resulting in a tubular rolled-up system. The inner diameter of those is measured as a function of layer thickness for different solvents and capping types. Those results are shown to be in good agreement with Timoshenko theory. Before rolling, the future inner surface can be characterized and functionnalized. We demonstrate topographical and chemical patterning, respectively by embossing and microcontact printing. These methods are very simple and can easily produce cylindrical capillaries with inner diameter between 20 and some hundreds of microns with fully functionnalized inner surface, overcoming many difficulties encountered in conventional soft lithography techniques.
Soft Matter
Phase separation of thermo-responsive polymers in solution is a complex process, whose understand... more Phase separation of thermo-responsive polymers in solution is a complex process, whose understanding is improved by following the dynamical modes as the transition is approached.
Langmuir, 2016
Multiple water-in-oil-in-water (W/O/W) emulsions are promising materials to design carriers of hy... more Multiple water-in-oil-in-water (W/O/W) emulsions are promising materials to design carriers of hydrophilic molecules or drug delivery systems, provided stability issues are solved and biocompatible chemicals can be used. In this work, we designed a biocompatible amphiphilic copolymer poly(dimethylsiloxane)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMS-b-PDMAEMA) that can stabilize emulsions made with various biocompatible oils. The hydrophilic/hydrophobic properties of the copolymer can be adjusted using both pH and ionic strength stimuli. Consequently, the making of O/W (oil in water), W/O (water in oil), and W/O/W emulsions can be achieved by sweeping pH and ionic strength. Of importance, W/O/W emulsions are formulated over a large pH and ionic strength domain in a one-step emulsification process via transitional phase inversion and are stable for several months. A Cryo-TEM and interfacial tension studies show that the formation of these W/O/W emulsions is likely to be correlated to the interfacial film curvature and microemulsion morphology.
Journal of Colloid and Interface Science, Jan 15, 2004
We report investigations of hair surface potential under wetting at the nanometric scale by atomi... more We report investigations of hair surface potential under wetting at the nanometric scale by atomic force microscopy (AFM). Surface potential imaging was used to characterize the electrostatic properties of the hair samples. We found that the surface potential noticeably increases along the edges of the cuticles. These results are correlated with wetting behavior of different liquids performed using AFM in noncontact mode.
Langmuir, Oct 19, 2010
We monitored single-layer Langmuir-Blodgett films of behenic acid deposited on silanized glass or... more We monitored single-layer Langmuir-Blodgett films of behenic acid deposited on silanized glass or silicon substrates by atomic force microscopy (AFM) in liquid. We observed the in situ transformation of the monolayer to a bilayer when the surrounding solution was NaOH or KOH with pH > 8.3. The final state is that of an inverted bilayer, in which both the hydrophobic OTS (octadecyltrichlorosilane) and the alkane chains are exposed to the surrounding solution, defying common intuition based on hydrophobic-hydrophilic energy considerations. Strong sodium-containing carboxylic dimers formed between the headgroups are shown to be responsible for the stabilization of this configuration; calcium ions slow down/inhibit the transformation.
Soft Matter, 2016
As the need of new methods for the investigation of thin films on various kinds of substrates bec... more As the need of new methods for the investigation of thin films on various kinds of substrates becomes greater, a novel approach based on AFM nanoindentation is explored. In particular, a successful method for the investigation of thin layers on soft substrates is demonstrated.
Langmuir, Aug 1, 2007
We present the 2D self-assembly properties of an amyloid-like peptide (LSFDNSGAITIG-NH2) (i.e., L... more We present the 2D self-assembly properties of an amyloid-like peptide (LSFDNSGAITIG-NH2) (i.e., LSFD) over a whole range of spatial scales. This peptide is known to adopt an amyloid-like behavior in water where it aggregates into fibrils. Monolayers of this 12 amino acid peptide were built by direct spreading and compression of an organic unstructured LSFD solution at the air/water interface. Investigation by infrared spectroscopy of the peptide secondary structure reveals beta-sheet formation at the water surface. As evidenced by Brewster angle microscopy, compression of the peptidic film results in the formation of large condensed domains. We used atomic force microscopy to show that these domains are made of rather monodisperse, elongated domains of monomolecular thickness, which are about 1 microm long and hundred of nanometers wide. These nanodomains can be compacted up to the formation of a homogeneous monolayer on the micrometer scale. These bidimensional structures appear as a surface-induced counterpart of the bulk amyloid fibrils that do not form at the air/water interface. These self-assembled peptide nanostructures are also very promising for building organized nanomaterials.
Physical review letters, 1994
ABSTRACT
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996
The process of adiabatic heating of compressible fluids ͓piston effect ͑PE͔͒ has been investigate... more The process of adiabatic heating of compressible fluids ͓piston effect ͑PE͔͒ has been investigated in SF 6 at off-critical density Ϸ1.27 c near the coexistence temperature in the absence of convection. The temperature response of the fluid to an internal heat pulse has been recorded at different distances from the heat source confirming a ͑spatially͒ homogeneous temperature rise outside an expanding boundary layer during heating. This process can be distinguished from the following conductive heat transfer when the energy contained in the boundary layer diffuses. This observation is confirmed by both experiment and calculations. During and after the heating process, (P,,T) data of the fluid behaves according to a given equation of state at equilibrium because hydrodynamic velocities remain small. The isentropic character of the PE was confirmed by both calculations from the pressure and density measurements. The presented experimental results were obtained on ESA's critical point facility ͑CPF͒ during the Spacelab IML-2 mission in July 1994. ͓S1063-651X͑96͒04507-2͔
Journal de Physique II, 1997
Physical Review E, 1994
Coalescence processes are investigated during phase separation in a density-matched liquid mixtur... more Coalescence processes are investigated during phase separation in a density-matched liquid mixture (partially deuterated cyclohexane and methanol) under near-critical conditions. As a result of the interplay between capillary and lubrication forces, ``nose'' coalescence appears to be always associated with the slow growth of isolated droplets (exponent ~=1/3), whereas ``dimple'' coalescence corresponds to the fast growth of interconnected droplets (exponent ~=1). At each stage of growth, the distribution of droplets trapped during dimple coalescence is reminiscent of all of the previous coalescence events.
Bulletin de la Société Française de Physique, 2006
matériaux biologiques pour appréhender les ingrédients minimaux conduisant à des propriétés voulu... more matériaux biologiques pour appréhender les ingrédients minimaux conduisant à des propriétés voulues (relation structure-propriétés) ? • enfin, ces matériaux sont obtenus dans des conditions environnementales modérées (température, pression, valeur de pH). À l'inverse, les techniques traditionnelles de fabrication humaine font souvent appel à des conditions extrêmes de température, de pression ou de pH, conditions coûteuses à réaliser et qui ne permettent pas d'obtenir les mêmes matériaux.
Physical Review Letters, 1992
We consider droplets on a substrate that grow according to a power law. When the droplets touch, ... more We consider droplets on a substrate that grow according to a power law. When the droplets touch, they coalesce with mass conservation. It is shown by both numerical study and analytical arguments that such a system exhibits a 1/f2 noise even at low frequencies in the fluctuations of the substrate coverage. This type of noise is expected to be independent
2 Volume Set, 2011
... The surface density of anchoring points is high enough such Functional Polymer Films, First E... more ... The surface density of anchoring points is high enough such Functional Polymer Films, First Edition. Edited by Wolfgang Knoll and Rigoberto C. Advincula. 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2011 by Wiley-VCH Verlag GmbH & Co. KGaA. Page 2. ...
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Papers by Patrick Guenoun