Microencapsulation in polyurea shell: Kinetics and film structure

Abstract

Interjacial polycondensation is an important polymerization

An experimental study of polyurea membrane formation by interfacial polycondensation

“…This step was identically performed for all the experiments except for the concentration of HMDI in the organic phase, which was chosen according to the needs of the experiment. This was found to result in the same drop size distribution in all experiments [9] as determined by particle size analysis on the emulsion as well as on the microcapsules after the encapsulation experiment. In the second step, an appropriate volume of this emulsion, depending on the required phase volume ratio, was added to an aqueous solution of HMDA held in a beaker, under conditions of mild stirring.…”

“…In some experiments, sodium lignosulfonate (instead of Tween-85) was used as the surfactant since it was found that microcapsules thus formed were better able to maintain their shape under the sample preparation procedures used for electron microscopy. The experimental procedure followed for the preparation of polyurea microcapsules was in general similar to that reported earlier [8,9]. A two-step procedure was adopted to ensure that the drop size distribution was the same in all the experiments.…”

“…The reaction, since it employs highly reactive monomers, is extremely fast and this poses problems in measurement of rates. Yadav et al in their studies on microencapsulation in polyurea shells devised a simple on-line pH measurement technique for following the process kinetics [8,9]. Their work demonstrated the potential of the technique in following fast kinetics in a system of this kind, but the potential could not be fully realized because of the discrete nature of the measurement.…”

“…With polyurea microcapsules, a variation in permeability by an order of magnitude could be achieved by varying the crystallinity of the polyurea [15]. The reaction kinetics seems to be important in controlling the crystallinity-there being a rough inverse correlation between rate and crystallinity [5,9,16]. The role of surfactants and interfacial tension in controlling particle structure has been sought to be explained based on thermodynamics [17].…”

Quantitative Compositional Mapping of Core−Shell Polymer Microspheres by Soft X-ray Spectromicroscopy

“…8,9 Particular morphologies desired for different applications include internal porosity 10 and core-shell structures. 11,12 To optimize the internal or core-shell morphologies of such composite materials for particular applications, such as controlled release capsules [13][14][15] or chromatographic separations, 16 one needs, first, to visualize the internal structure at high spatial resolution and, second, to perform quantitative chemical analysis at the spatial scale of that structure. Traditional chemical spectroscopies used for polymer studies, such as infrared and nuclear magnetic resonance, can easily differentiate chemical species but do not have the necessary submicron spatial resolution.…”