arXiv subjects

Philippe Fontaine

Publications and source records attributed to Philippe Fontaine.

4 recordsLinked to original sources

arXiv2023

Interface-templated crystal growth in sodium dodecyl sulfate solutions with NaCl

Many ionic surfactants, such as sodium dodecyl sulphate (SDS) crystallize out of solution if the temperature falls below the crystallization boundary. The crystallization temperature is impacted by solution properties, and can be decreased with the addition of salt. We have studied SDS crystallization a t the liquid/vapor interfaces from solutions at high ionic strength (sodium chloride). We show that the surfactant crystals at the surface grow from adsorbed SDS molecules, as evidenced by the preferential orientation of the crystals identified using grazing incidence X-ray diffraction. We find a unique timescale f or the crystal growth from the evolution of structure, surface tension, and visual inspection, which can be controlled through varying the SDS or NaCl concentrations.

cond-mat.soft↗

arXiv2019

Grazing incidence x-ray diffraction studies of lipid-peptide mixed monolayers during shear flow

Grazing Incidence X-ray Diffraction (GIXD) studies of monolayers of biomolecules at the air-water interface give quantitative information of in-plane packing, coherence lengths of the ordered diffracting crystalline domains and the orientation of hydrocarbon chains. Rheo-GIXD measurements revel quantitative changes in the monolayer under shear. Here we report GIXD studies of monolayers of Alamethicin peptide, DPPC lipid and their mixtures at the air-water interface under the application of steady shear stresses. The Alamethicin monolayer and the mixed monolayer show flow jamming transition. On the other hand, pure DPPC monolayer under the constant stress flows steadily with a notable enhancement of area/molecule, coherence length, and the tilt angle with increasing stress, suggesting fusion of nanocrystallites during flow. The DPPC-Alamethicin mixed monolayer shows no significant change in the area/DPPC molecule or in the DPPC chain tilt but the coherence length of both phases (DPPC and Alamethicin) increases suggesting that the crystallites of individual phases are merging to bigger size promoting more separation of phases in the system during flow. Our results show that Rheo-GIXD has the potential to explore in-situ molecular structural changes under rheological conditions for a diverse range of confined biomolecules at the interfaces.

cond-mat.soft↗

arXiv2004

A novel approach to the synthesis of nanostructured metal-organic films: X-ray radiolysis of silver ions using a Langmuir monolayer as a template

An application of the radiolysis method using X-ray synchrotron beam is developed as a novel approach to the synthesis of metal-organic films with controlled shapes and thickness. We demonstrate that a Langmuir monolayer deposited onto a silver ion-containing subphase, irradiated by an incident beam impinging below the critical angle for total reflection, induces the synthesis of a stable nanostructured silver-organic ultrathin film at the air-water interface. The X-ray scattering is also used to monitor in situ the structure of the silver layer during the synthesis process. The layer is observed by AFM after its transfer onto a silicon substrate. One observes a film thickness of 4.6 nm, in good agreement with the X-ray penetration depth, about 4.5 nm. The silver structure is oriented by the initial organic film phase. This experiment demonstrates the considerable potential of this approach to produce various controlled metal-organic films with a surfactant self-assembly as a template.

cond-mat.soft↗

arXiv2004

Fast and Adjustable Resolution Grazing Incidence x-ray Liquid Surfaces Diffraction achieved through 2D Detector

We developed a setup using a two dimensional camera for Grazing Incidence x-ray Diffraction (GIXD) on Langmuir monolayers and more generally for surface diffraction on two dimensional powders. Compared to the classical setup using a linear detector combined with Soller's slits, the acquisition time is reduced of a factor of at least 10 (from more than one hour to a few minutes) using the same x-ray source (synchrotron bending magnet) with a comparable signal to noise ratio. Moreover, using an horizontal gap slit, the experimental resolution can be adjusted and for small values of the gap, better resolution can be achieved compared to the one obtained with the linear detector.

cond-mat.soft↗