Entrapped materials, multiple

The products can have a variety of shapes, such as spherical, oblong or irregular, can be monolithic or aggregates, and can have single or multiple walls. In Fig. 20.1 some typical morphologies of capsules are shown. The capsules consist of the coated or entrapped materials referred to as active, core material, fill, internal phase or payload (such as aroma chemicals). The coating or matrix material is called wall, membrane, carrier, shell or capsule. 

The nature of entrapped materials may have a bearing on the stability of the system. Due to the nature of the multiple emulsion, the middle phase may act as an osmotic reservoir, thus virtually all additions to this phase will set up osmotic gradients. This might include high concentrations of surfactant. To this end polymeric microspheres have been used as the internal reservoir when osmotic transfer of water will not compromise stability. 

The ability of multiple emulsions to entrap materials is one of their most useful assets and so the passage of materials from the... 

Industrial, centrifugal elevators usually operate at speeds of about 75 m /min, and handle free-flowing, fine and loose materials having lump sizes of <50 mm. Sticky material can be a problem. Fine fluidizing materials often require perforations in the bottom of the buckets to vent entrapped air. Centrifugal elevator capacities range up to 370 m /h for a single row of buckets, and up to 1400 m /h for multiple rows of buckets. The buckets can be mounted on a belt or chain. 

This sol-gel procedure is an elaboration on well established entrapment methods [29], but with the added advantage of stability and better flow properties. Interestingly, none of the examples presented thus far demonstrate competitive behavior between multiple ligands (i.e. displacement) in the FAC analysis of trimethoprim and pyrimethamine a reversed order of elution based on is described, but this could simply be due to the shift towards an on-rate limited situation for higher affinity compounds, as described earlier. Erosion of dynamic competition between ligands could occur if the sol-gel allows convective mixing of the entrapped protein however the bimodal pore structure of these materials would... 

It is desirable to know when the foam head has broken, so the vacuum tank should be provided with two sight windows one for illumination and one for observation. It is best to repeatedly break the vacuum during the degassing operation so that multiple foam heads rise and break. Care should be taken to avoid a rolling boil effect. Once all the air is removed from the adhesives, it will become very difficult to cause a foam head to rise. It is best to try to minimize the vacuum time, to reduce the loss of any volatile materials from the mixture. Applied vacuum along with agitation and vibration will effectively remove all entrapped air. 

A more typical situation is obtained with an ionic conductor which can be electrochemically reduced or oxidized. When it is inserted between two electrodes, both reactions can occur simultaneously oxidation at the anode and reduction at the cathode. According to our model the material can then be regarded as a double reservoir in which electrons can be stored at a certain level and holes at another, in two different parts of the material. The voltage of the corresponding cell simply equals the distance between the two levels to within the multiplication factor F 1 93, its electrical capacity is determined by the number of electrons and electron holes which can be entrapped. The electrode reactions occurring at che phase boundary of such a cell simply imply an injection or extraction of electronic carrier and no transfer of matter. This would certainly obviate many difficulties encountered in more traditional batteries. The validity of the principle was demonstrated in our laboratory with KI. The voltage obtained was approximately 1.3 V. For practical purposes the KI cell is obviously not of interest since its electrical capacity is too small. 

In most cases multiple emulsions are aimed for slow and sustained release of active matter from an internal liquid reservoir into the continuous phase. In some applications the multiple emulsions can serve also as an internal reservoir to entrap matter from the outer diluted continuous phase into the inner confined space. These applications are aimed to remove toxic matter. In other applications multiple emulsions are reservoirs for improved dissolution or solubilization of insoluble materials. The materials will dissolve in part in the inner phase, in part at the internal interface, and occasionally at the external interface. Applications related to protection of sensitive and active molecules... 

Multiple emulsions are usually not empty. Soluble active materials are entrapped during the emulsification in the inner oily phase. Because of the osmotic pressure gradient, the active matter tends to diffuse and migrate from the internal phase to the external interface mostly through a controlled reverse micellar transport mechanism (Figure 7.10a) (Garti and Bisperink, 1998 Garti and Benichou, 2001). The dilemma that researchers were faced with was how to control the diffusion of oil molecules, as well as the emulsifier molecules... 

Most of release studies are done in W/OAV multiple-emulsion systems where an active water soluble molecule is present in the inner aqueous phase. Several attempts have been made to explain the transport phenomena of entrapped addenda from the inner to the outer phase of multiple-emulsion droplets. It has been demonstrated that for lipid soluble material dissolved in the oil phase, the release obeys first-order kinetics and is diffusion controlled with excellent accordance to Pick s law. Two mechanisms for the permeation through the oil intermediate phase are well accepted, the first being via the reverse micellar transport (Figure 7.10 ) and the second via diffusion across a very thin lamellae of surfactant phase formed in areas where the oil layer is very thin (Figure 10b). 

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