Particles, transmission electron viscosity

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). 

All measurements are performed using the refractive index of CdS. In the case of cadmium sulfide nanoparticles produced in the w/o microemulsion the viscosity rj and the refractive index no of the continuous oil phase, namely the xylene-pentanol (1 1) mixture ( = 1.454 cP, D = 1165) are used. Consequently rj and no for water are used when the CdS nanoparticles are redispersed in the aqueous phase. Morphology and size of the redispersed CdS particles are also determined by transmission electron microscopy. Therefore, a small amount of the aqueous solutions is dropped on copper grids, dried and examined in the EM 902 transmission electron microscope (Zeiss) (acceleration voltage 90 kV). The high amount of surfactant brings also difficulties for the preparation of the samples for TEM measurements and consequently samples have to be washed with water to reduce the amount of surfactant. 

Figure 1 compares experimental data for G and with the predictions of the emulsion model for a 90/10 (mass %) PMMA/PS at 200 C. For this blend, the viscosity of the minor component is considerably smaller than that of the major component, q(ps)I q pmma) 0-035. The morphology was characterized by transmission electronic microscopy (TEM) and the average particle radius was estimated by digital image analysis to be around 0.22 im. The interfacial tension has been taken as 1.5 mN/m [4]. It should be mentioned that the morphology of the blend was found to be the same before and after the rheological experiments carried out at 200 C for about 2 h. 

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