Characterisation of ‘Hadley’ grains by confocal microscopy

This work forms part of an exploratory study to investigate the use of fluorescent laser scanning confocal microscopy (LSCM) for imaging pores and voids in hardened mortar and concrete. The study has revealed the suitability of the technique for the characterisation of hollow shell (Hadley) hydration grains (these are grains that contain a void within the original boundary of the cement grain). It was found that Hadley grains could be imaged using fluorescent light techniques, subsequent to their impregnation by epoxy resin doped with a fluorescent dye. Prior to this work, it was not clear whether hollow grains were impregnated due to connections with capillary pores, or if they had been impregnated due to connections with damage caused during surface preparation (i.e. micro-cracks or deep surface scratches). However using the 3D LSCM imaging technique it was observed that connections between Hadley grains and hardened cement paste (HCP) capillary pores did exist, in different forms, at depths well below the surface providing ‘conduits’ along which resin was able to flow and impregnate the hollow grains. Other aspects of imaging Hadley grains are also described, such as the sectioning of ‘tips’ of larger grains often taken as separate smaller pores or grains in 2D images.     

Study of the separation of yeast by microsieves: In situ 3D characterization of the cake using confocal laser scanning microscopy

In situ 3D characterization of Aquamarijn microsieves fouling was achieved using Confocal Laser Scanning Microscopy (CLSM). A filtration chamber allowing direct microscopic observation of microbial cell deposition and cake characterization, specially designed for in situ observations, was used. Fluorescent dyed Saccharomyces cerevisiae yeast suspensions were filtered through 0.8 μm and 2 μm pore diameters silicon nitride microsieves under constant flow rate. The on-line yeasts deposition was recorded and the cake construction was followed layer by layer. Based on the 3D image processing, cake properties (particle arrangement, homogeneity, thickness and porosity). The compressibility of the yeast cake was analyzed. Finally, cake removal efficiency was also studied during microsieve cleaning operation.     

Use of laser scanning confocal microscopy for characterizing changes in film thickness and local surface morphology of UV-exposed polymer coatings

Laser scanning confocal microscopy (LSCM) has been used to characterize the changes in film thickness and local surface morphology of polymer coatings during the UV degradation process. With the noninvasive feature of LSCM, one can obtain thickness information directly and nondestructively at various exposure times without destroying the specimens or deriving the thickness values from IR measurement by assuming uniform film ablation. Two acrylic polymer coatings were chosen for the study, and the physical and chemical changes of the two systems at various exposure times were measured and analyzed. Those measurable physical changes caused by UV exposure include film ablation, formation of pits and other surface defects, and increases in surface roughness. It was found in both coatings that changes in measured film thickness by LSCM were not correlated linearly to the predicted thickness loss using the changes in the CH band obtained by the Fourier Transform Infrared (FTIR) spectroscopy measurements in the later degradation stages. This result suggested it was not a uniform film ablation process during the UV degradation. At later stages, where surface deformation became severe, surface roughness and profile information using LSCM were also proven to be useful for analyzing the surface degradation process Presented at the 81st Annual Meeting of the Federation of Societies for Coatings Technology, November 13–14, 2004 in Philadelphia, PA.