Microcapsule size measurement

The particle size distribntion of microcapsules can also be measured using laser diffraction particle sizing, Mastersizer andZetasizer. For microcapsules prepared for inhalation, particle size measurement of the dry powders formnlated can be measured more accurately by the dry dispersion method. The Scirocco accessory of the Malvern Mastersizer allows particle size measurement of dry powders, with particle flow controlled by a variable feed-rate vibrating tray. 

Measurement of Size of Microcapsules. We measured the size of poly(L-lysine-a/r-terephthalic acid) microcapsules in various buffer solutions by the usage of a particle sizer (Malvern System 3601). About 15000 microcapsules are dispersed in 1 ml of suspension medium. 

One of the sessions of the Symposium was largely devoted to presentation and discussion on the use of various experimental calorimetric methods for use in assessing possible hazards in chemical processing operations. The methods described covered a wide range of sample sizes and degrees of complexity Grewer, T. Adiabatic small-scale reaction test in Dewar, simple to operate. Janin, R. Measurements of heat release by DSC and of pressure development in sealed microcapsules. 

The micromanipulation technique has been used to measure the mechanical strength of microcapsules of different size, shell thickness and shell composition (Sun and Zhang, 2001,2002 Xue and Zhang, 2008 Zhao and Zhang, 2004 Zhang et al., 1999). For example, the mechanical... 

The mechanical properties of single hydrated dextran microcapsules (< 10 pm in diameter) with an embedded model protein drug have also been measured by the micromanipulation technique, and the information obtained (such as the Young s modulus) was used to derive their average pore size based on a statistical rubber elasticity theory (Ward and Hadley, 1993) and furthermore to predict the protein release rate (Stenekes et al., 2000). 

Capsules smaller than 1 ixm are called nano-capsules because their size is measured in nanometers. When the core and the coating are not really separated, the microcapsule, or nanocapsule, is called microparticle, or nanoparticle. 

Nuyken, O. Dauth, J. Pekruhn, W. Thermosensitive microcapsules. II. New azomonomers, homo- and cocondensation, microencapsulation, release measurements, size distribution and thermo-printing. Angewandte Makromolekulare Chemie (1991), 190, 81-98. 

By this method, it was feasible to produce polyurea microcapsules continuously. Due to measuring problems concerning drop size and capsule size, it was not possible to show without doubt that the second micromixer does not change the dispersion. At present, it can only be stated that the impact is small. 

Coating thickness is sometimes difficult to measure conveniently due to the fine size of some powders and to the unevenness of the surface of some granular materials. A reasonably estimate of the coating thickness for spherical microcapsules can be calculated using the following expression (Dewettinck, 1977) ... 

Figure 11.31 Size distributions of one sample of microcapsules (a) determined by light microscopy (i) before and (ii) after in vitro release experiments (321 and 308 microcapsules, respectively were sized), (b) determined by measurement of the SEM photographs. Same sample as in (a) (i) before and (ii) after in vitro release experiments, for which were sized 187 and 114 microcapsules, respectively, du = mean volume diameter. From Jenkins and Florence [198].

The electrical charge of emulsion droplets was determined via zeta-potential measurement by electrophoretic light scattering. The oil droplet size of the emulsions was analysed by static light scattering after dilution of the emulsion to the required optical density or, in the case of spray-dried particles, after dissolution of an aliquot of the microcapsules. Microencapsulation efficiency was calculated from total oil content in the formulation and the gravimetric determination of the oil extracted from the microcapsules with petrol ether [62]. 

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