Size Distribution Of Capsules Research Articles

Effect of variable capsule size distribution for unstructured packed bed encapsulated phase change material system

Packed bed encapsulated phase change material (PCM) energy storage systems have considerable potential for energy storage applications involved in renewable energy systems. In this paper, a 3D unstructured packed bed system consisting of spherical encapsulated phase change material with varying sizes of spheres is modelled. The main novelty of the work is that the geometry of the capsules and the flow between the capsules are resolved, even with unequal capsule sizes arranged in an irregular manner. The size of the spheres is varied by changing the radius of the spheres following specified normal distribution curves. Then, by changing the mean and standard deviation values, different size distributions of spheres are generated which are arranged in unstructured packed bed form. The model incorporates the flow of heat transfer fluid (HTF) through the gaps between the capsules, the heat transfer in both the HTF and the PCM capsules, the melting of PCM in each capsule, and the natural convection in the melted PCM. Based on the simulations, important parameters such as the melting time and energy storage rates are compared for different size distributions. It is found that for a normal distribution of capsule radius, increasing the mean radius by 2 times while keeping the standard deviation constant increases the melting rate considerably with an increase in melting time by 29.4%. The effect of standard deviation of radius was found to be significantly less as compared to that of the mean radius.

Development of a continuous reactor for emulsion-based microencapsulation of hexyl acetate with a polyuria shell

Microencapsulation is almost exclusively performed in batch processes. With today’s chemistry increasingly performed in flow reactors, this work aims to realise a continuous reactor setup for the encapsulation of an ester with a polyuria (PU) shell. The generation of an emulsion template is performed in a recirculation loop driven by a pump and equipped with static mixers, screen type and Kenics®. Calorimetric measurements are performed to characterise the energy dissipation rate inside the loop. The curing step is performed in a coiled tube reactor with two geometric configurations. Number based capsule size distributions are derived from micrograph analysis. Results indicate that the recycle pump is the main contributor to determine the capsule size distribution. A continuous setup is achieved for PU microcapsules containing hexyl acetate with a production rate of 198 g/h dry capsules, and a mean capsule diameter of 13.3 µm with a core content of 54 wt%.

Encapsulation of mesenchymal stem cells in glycosaminoglycans-chitosan polyelectrolyte microcapsules using electrospraying technique: Investigating capsule morphology and cell viability.

Polyelectrolyte microcapsules are modular constructs which facilitate cell handling and assembly of cell‐based tissue constructs. In this study, an electrospray (ES) encapsulation apparatus was developed for the encapsulation of mesenchymal stem cells (MSCs). Ionic complexation between glycosaminoglycans (GAGs) and chitosan formed a polyelectrolyte complex membrane at the interface. To optimize the capsules, the effect of voltage, needle size and GAG formulation on capsule size were investigated. It was observed that by increasing the voltage and decreasing the needle size, the capsule size would decrease but at voltages above 12 kV, capsule size distribution broadened significantly which yields lower circularity. Increase in GAG viscosity resulted in larger microcapsules and cell viability exhibited no significant changes during the encapsulation procedure. These results suggest that ES is a highly efficient, and scalable approach to the encapsulation of MSCs for subsequent use in bioprinting and other modular tissue engineering or regenerative medicine applications.

Synthesis and characterization of ethyl cellulose micro/nanocapsules using solvent evaporation method

In this study, oil-filled micro/nanocapsules were synthesized by the emulsion-solvent evaporation method using ethyl cellulose as a shell-forming material containing linseed oil. Shape and morphology of the prepared micro/nanocapsules were evaluated using scanning electron microscopy. The particle size distribution of nanocapsules was investigated using nanoparticle size analyzer. The micro/nanocapsules core and shell material were characterized by Fourier transform infrared spectra. Oil-filled micro/nanocapsules with a regular spherical shape were successfully synthesized in various diameters ranging from 33 nm to 400 μm. The size distribution of capsules was successfully controlled by controlling emulsion agitation rate in their synthesis process.

Multifactorial design of poly(d,l‐lactic‐co‐glycolic acid) capsules with various release properties for differently sized filling agents

ABSTRACTThe hydrolytic degradation and corresponding content release of capsules made of poly(d,l‐lactic‐co‐glycolic acid) (PLGA) strongly depends on the composition and material properties of the initially applied copolymer. Consecutive or simultaneous release from capsule batches of combinable material compositions, therefore, offers high control over the bioavailability of an encapsulated drug. The keynote of this study was the creation of a superordinated database that addressed the correlation between the release kinetics of filling agents with different molecular weights from PLGA capsules of alternating composition. Fluorescein isothiocyanate (FITC)–dextran (with molecular weights of 4, 40, and 2000 kDa) was chosen as a model analyte, whereas the copolymers were taken from various 50:50 PLGA, 75:25 PLGA, and polylactide blends. With reference to recent publications, the capsule properties, such as the size, morphology, and encapsulation efficiency, were further modified during production. Hence, uniform microdisperse and polydisperse submicrometer nanocapsules were prepared by two different water‐in‐oil‐in‐water emulsification techniques, and additional effects on the size and morphology were achieved by capsule solidification in two different sodium salt buffers. The qualitative and quantitative examination of the physical capsule properties was performed by confocal laser scanning microscopy, scanning electron microscopy, and Coulter counting techniques to evaluate the capsule size distribution and the morphological appearance of the different batches. The corresponding agent release was quantified by fluorescence measurement of the FITC–dextran in the incubation media and by the direct measurement of the capsule brightness via fluorescence microscopy. In summary, the observed agent release showed a highly controllable flexibility depending on the PLGA blends, preparation methods, and molecular weight of the used filling substances. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4219–4228, 2013

Facile preparation of highly monodisperse poly(NIPAAm)–AuNP composite hollow microcapsules by simple tubular microfluidics

We present an easy tubular microfluidic fabrication of highly monodisperse poly(NIPAAm)–AuNP composite hollow microcapsules with pickering effect assisted impregnation of AuNPs into the walls of microcapsules via UV-induced interfacial free-radical polymerization (IFRP). We maintained an excellent control over the monodispersity and capsule size distribution and the particles showed good thermosensitivity. The microfluidic device is simple and flexible in making; therefore, it permits a tunable UV curing chamber to control the polymerization time. Additionally, we present insight into the correlation between the polymerization time and the structural transformations (breathing, buckling and creasing) in the polymeric microcapsules. The structural transformations are independent of AuNPs embedded in the polymeric shell.

Formation and destruction of polyelectrolyte microcapsules modified by rhodamine 6G

Polyelectrolyte capsules with Rhodamine 6G molecules included into the shell are obtained in this work. The inclusion of dye molecules into the shell can provide the destruction of capsules by photosensitization. Measurements of the dye fluorescence intensity in the shell show that the energy of photoexcited molecules is effectively dissipated by the surrounding organic matrix. The capsule suspension is laser irradiated in the absorption band of Rhodamine 6G molecules. Measurements of the size distribution of capsules before and after laser irradiation reveal that the capsules are destroyed by laser illumination.

Production of oil-containing crosslinked poly(vinyl alcohol) microcapsules by phase separation: Effect of process parameters on the capsule size distribution

Oil-containing poly(vinyl alcohol) (PVA) microcapsules in the size range of 5–20 μm were prepared by the simple coacervation of PVA followed by chemical crosslinking of the coacervated PVA membrane with glutaraldehyde. Coacervation of the aqueous polymer solution was achieved by the addition of a phase separation inducer (e.g., sodium sulfate). PVA of different grades (e.g., molecular weight and degree of hydrolysis) was utilized both as stabilizer and wall-forming material. Dispersion of the oil phase in the aqueous PVA solution was effected by a homogenizer. The effects of the various process parameters, such as the agitation speed, the type and concentration of PVA, the volume ratio of the internal oil phase to the external aqueous phase, the viscosity of the oil phase as well as the electrolyte concentration in the aqueous solution, on the stability and the size distribution of the emulsion droplets and microcapsules were experimentally investigated. It was shown that high agitation rates and low interfacial tension (e.g., high PVA concentrations) resulted in a significant reduction of the size of the emulsion droplets and microcapsules. On the other hand, as the viscosity and the amount of the dispersed oil phase increased, the capsule size increased. Finally, it was found that the concentration of the electrolyte significantly affected the stability of the (o/w) emulsion, the size and concentration of coacervated PVA colloidal aggregates, as well as the morphology of the polymer wall membrane formed by the adsorption of the polymer-rich phase to the oil/water interface. © 1996 John Wiley & Sons, Inc.

Production of water-containing polymer microcapsules by the complex emulsion/solvent evaporation technique. Effect of process variables on the microcapsule size distribution.

The complex emulsion/solvent evaporation technique was employed for the production of water-containing polymer microcapsules. The inner phase of the microcapsules consisted of an aqueous solution of gelatin. Several polymers (e.g. poly(styrene), poly(methyl methacrylate), ethyl cellulose, poly(vinyl chloride)) were utilized as wall-forming materials and the effect of the polymer type on the size and the surface characteristics of the microcapsules was experimentally investigated. The size of the microcapsules was strongly affected by the conditions applied during the formation of both simple (w/o) and complex (w/o)/w emulsions. Poly(styrene) microcapsules with a mean Sauter diameter in the range of 4-12 microns were prepared by varying the rate of agitation (1500-4000 rpm) and the concentration of stabilizer (potassium oleate, 0.1-1.5% w/v) used in the formation of the (w/o)/w emulsion. High stabilizer concentrations and agitation rates resulted in a significant reduction of the mean size of the complex droplets and in a simultaneous increase of the breadth of the capsule size distribution.