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J Crassous

Publications and source records attributed to J Crassous.

5 recordsLinked to original sources
PubMed2002

Adhesion between weakly rough beads.

Cohesion effects are of prime importance in powders and granular media, and they are strongly affected by the roughness of the grain surface. We report measurements of the adhesion force between surfaces of Pyrex having a nanometric roughness, with a surface force apparatus. The two surfaces are immersed in liquid n-dodecane. The adhesion force measured is much smaller than expected in the case of smooth surfaces. We find that the adhesion force depends on the maximal load that has been applied on the surfaces, but does not depend on the time during which they have been in contact. We propose a model of plastic deformation of the small asperities in a macroscopic Hertz contact which is in good agreement with the experimental data.

Journal Article↗
PubMed2002

Nanorheology: An investigation of the boundary condition at hydrophobic and hydrophilic interfaces.

It has been shown that the flow of a simple liquid over a solid surface can violate the so-called no-slip boundary condition. We investigate the flow of polar liquids, water and glycerol, on a hydrophilic Pyrex surface and a hydrophobic surface made of a Self-Assembled Monolayer of OTS (octadecyltrichlorosilane) on Pyrex. We use a Dynamic Surface Force Apparatus (DSFA) which allows one to study the flow of a liquid film confined between two surfaces with a nanometer resolution. No-slip boundary conditions are found for both fluids on hydrophilic surfaces only. Significant slip is found on the hydrophobic surfaces, with a typical length of one hundred nanometers.

Journal Article↗
PubMed2000

The bromochlorofluoromethane saga.

Synthesis of optically active samples of bromochlorofluoromethane (CHFClBr) was performed via fractional crystallisation of the strychnine salts of bromochlorofluoroacetic acid (FClBrCCO2H). The S-(+) (R-(-)) absolute configuration of the acid was established by X-ray crystallography and the S-(+) (R-(-)) absolute configuration of the haloform was determined using Raman Optical Activity (ROA) and molecular modelling of the enantioselective molecular recognition process of CHFClBr by the chiral cryptophane-C. From these stereochemical assignments it was observed that the decarboxylation used to obtain S-(+)- and R-(-)-CHFClBr from respectively S-(+)- and R-(-)-FClBrCCO2H occurred with retention of configuration. Finally, the first parity violation (PV) test on CHFClBr was performed and yielded an upper bound for this small stereophysical effect.

Journal Article↗