Yang Xiang, Research Engineer in Chemical EngineeringMICRO-PROBE FOR PHYSICAL AND CHEMICAL

Non-uniform porosity of paper and coated paper is important in printing and paper making industries. Current porosity measurements give results averaged over a large area. A new method is developed to determine local variations in porosity and surface chemistry. A measured volume of a probe liquid is applied to a hemispherical glass probe. The substrate of interest is brought into contact with the fluid drop. The resulting liquid bridge exerts a force on the probe due to surface tension forces. A video camera is used to visually correlate the physical phenomena with the force-time data. The force-time data is recorded for substrates in four main groups: 1) non-porous, 2) model porous, 3) swellable substrates, and 4) real substrates. The force is found to be a function of the minimum fluid column radius and the surface tension of the fluid for non-porous substrates. For porous samples, the force rapidly increases to a value and is followed by a decrease. For porous samples, this decrease is related to the radial spreading of the fluid into the porous substrate and is related to the local rate of fluid uptake. A theoretical model is proposed that describes the results on porous substrates

Static Sims Investigation of Metal-polymer Interfaces

The formation of the interface between thermally evaporated metals (aluminium, copper) and polymers [poly(ethylene terephthalate) (PET), poly(methyl methacrylate) (PMMA)] has been investigated by static SIMS. Two generations of instrument have been used. The first one, using a quadrupole mass spectrometer directly connected to the same ultrahigh vacuum environment as the metallization chamber, has allowed an in situ characterization of the interface formation after each metal deposition in the submonolayer regime. The second system, using a time-of-flight (ToF) mass spectrometer, has allowed ex situ analyses of Al/PET, Cu/PET, Al/PMMA and Cu/PMMA interfaces. The high mass resolution of the ToF spectrometer led to the unambiguous identification of the molecular fragments that are characteristic of polymer-metal interaction. The results show that Al atoms react with the oxygenated parts of PET and PMMA. This interaction limits the lateral diffusion of Al atoms on the polymer surface and, consequently, induces a two-dimensional growth of the Al film on these polymer substrates. In the Cu deposition case, a weaker metal-polymer interaction is observed. This leads to Cu clustering and a three-dimensional growth. Time-of-flight SIMS molecular imaging clearly reveals Cu clusters on the PMMA surface