Microscopy water content

Scanning electron microscopy shows the cement to consist of zinc oxide particles embedded in an amorphous matrix (Smith, 1982a). As with the zinc phosphate cement, a separate globular water phase exists since the cement becomes uniformly porous on dehydration. Porosity diminishes as the water content is decreased. Wilson, Paddon Crisp (1979) distinguish between two types of water in dental cements non-evaporable (tightly bound) and evaporable (loosely bound). They found, in the example they examined, that the ratio of tightly bound to loosely bound water was 0-22 1-0, the lowest for all dental cements. They considered that loosely bound water acted as a plasticizer and weakened the cement. 

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

At the same time investigations using light scattering, electron microscopy, positron annihilation, dielectricity and transport properties 30,- ) indicated the surfactant molecules not to be Involved in associations to colloidal size aggregates at these low water contents. The low light scattering intensity rather points to the surfactant molecules not to be inter-associated (Fig. 7). 

The stability and suitability of the formulations also needs to be determined, for example, whether the viscosity of the formulation is suitable for the administration route and is stable over time. The water content is a parameter that often has a direct influence on the stability of solid formulations and may influence the appearance of freeze-dried products immensely. Karl-Fisher titration, thermogravitometric analysis (TGA), or DSC is normally used to determine the water content. Various microscopic techniques, where both macroscopic and microscopic appearance of formulation can be determined, such as particle appearance by scanning electron microscopy (SEM) or transmission electron microscopy (TEM), are usually only needed for special formulation. There are several other methods, but which one to choose depends entirely on the formulation and the critical parameters (149,150). 

Transparent exopoly-meric particles (TEP) [8,19] 3-100 pm off California coast microscopy after Aldan blue staining 3 X 10 -5 X 10 polysaccharide matrix with high water content flexible, deformable, filmy , gel-hke... 

Many water-management advances have been made (Figure 2). However, fundamental properties associated with two-phase flow in porous media, including capillary pressure, liquid water content and, intrinsic and relative permeabilities, are still lacking and are needed for predictive models. This situation is due to the absence of measurement methods for thin materials. Contact porosimetry [57] does not presently allow measurement of the permeabilities or during wetting (to evaluate the presence of hysteresis). Fluorescence microscopy [58] can provide additional information about liquid water flow through porous media. 

---