Morphology Of Microcapsules Research Articles

Design and fabrication of bifunctional microcapsules for solar thermal energy storage and solar photocatalysis by encapsulating paraffin phase change material into cuprous oxide

This article reported the design and fabrication of bifunctional microcapsules for solar photocatalysis and solar thermal energy storage by using cuprous oxide (Cu2O) as an inorganic shell to encapsulate a paraffin-type phase change material (PCM), n-eicosane. Such a new type of microcapsules was synthesized successfully by using an emulsion templating self-assembly method along with in-situ precipitation. The chemical structures of the resultant microcapsules were determined by Fourier-transform infrared spectroscopy, and the elemental distributions of microcapsule shell were confirmed by X–ray photoelectron spectroscopy and energy-dispersive X–ray spectroscopy. The scanning and transmission electronic microscopic observations demonstrated that the microstructures and morphologies of microcapsules were influenced significantly by the surfactant and alkali concentrations as well as the portion of cupper source for the synthesis. After the synthetic condition was optimized, the obtained microcapsules exhibited an interesting octahedral morphology and a typical core-shell structure. The thermal analysis results suggested that the microcapsules synthesized at the optimum condition not only obtained high encapsulation and energy-storage efficiencies but also presented a high thermal stability and phase-change reliability. Most of all, the microcapsules obtained a solar thermal energy-storage capability through solar photothermal conversion and also exhibited a high solar photocatalytic activity to organic dyes under the sunlight illumination. In addition, the microcapsules showed a gas-sensitive feature to some harmful organic gases in the presence of Cu2O shell. The microcapsules developed by this work indeed reveal a bifunctional feature derived from both the core and the shell materials and thus show a great potential for industrial and domestic applications due to their extended functions.

Encapsulation of grape seed extract in polylactide microcapsules for sustained bioactivity and time-dependent release in dental material applications

ObjectiveTo sustain the bioactivity of proanthocyanidins-rich plant-derived extracts via encapsulation within biodegradable polymer microcapsules. MethodsPolylactide microcapsules containing grape seed extract (GSE) were manufactured using a combination of double emulsion and solvent evaporation techniques. Microcapsule morphology, size distribution, and cross-section were examined via scanning electron microscopy. UV–vis measurements were carried out to evaluate the core loading and encapsulation efficiency of microcapsules. The bioactivity of extracts was evaluated after extraction from capsules via solvent partitioning one week or one year post-encapsulation process. Fifteen human molars were cut into 7mm×1.7mm×0.5mm thick mid-coronal dentin beams, demineralized, and treated with either encapsulated GSE, pristine GSE, or left untreated. The elastic modulus of dentin specimens was measured based on three-point bending experiments as an indirect assessment of the bioactivity of grape seed extracts. The effects of the encapsulation process and storage time on the bioactivity of extracts were analyzed. ResultsPolynuclear microcapsules with average diameter of 1.38μm and core loading of up to 38wt% were successfully manufactured. There were no statistically significant differences in the mean fold increase of elastic modulus values among the samples treated with encapsulated or pristine GSE (p=0.333), or the storage time (one week versus one year storage at room temperature, p=0.967). SignificancePolynuclear microcapsules containing proanthocyanidins-rich plant-derived extracts were prepared. The bioactivity of extracts was preserved after microencapsulation.

Coumarin-modified fluorescent microcapsules and their photo-switchable release property

In this study, we propose one kind of photo-responsive microcapsule based on the coumarin-modified shell. The coumarin group firstly reacts with pentaerythritol on a stoichiometric basis and then etherifies with the polymerizable isocyanate group to obtain the shell material. To stabilize the shell structure, we fabricate coumarin-modified microcapsules (CMMs) via interfacial polymerization and 365nm ultraviolet light irradiation. The particle size and surface morphology of microcapsules are measured by scanning electron microscopy and optical microscopy. After ultraviolet irradiation, the shell of CMMs exhibits variable fluorescence as well as reversible crosslinking and cleavage due to the [2+2] cyclization reaction. By introducing the fluorescent dye 2-anilino-6-dibutylamino-3-methylfluoran (ODB-2) into microcapsules, the controlled release behavior of CMMs can be measured by fluorescence microscope and fluorescence spectrophotometer. The CMMs exhibit distinct “on” state and “off” state separately under different ultraviolet light, achieving ODB-2 release and trapping. This result leads to precise characterization of controlled release property, which will be of interest in switchable microcapsules for drug delivery system and information recording device.

Processing conditions for the production of polystyrene microcapsules containing demineralized water

Microencapsulation has been important for engineering, biology, medicine, and several other fields of science. Microencapsulation is an effective way to protect the encapsulated material (e.g. an aqueous solution or pharmaceutical drug) and control its release to the external environment. Microcapsules are also used for producing anticorrosion systems and, in this case, studies about polymeric microcapsules containing acid solutions are relevant. In this paper, polystyrene microcapsules containing demineralized water were produced. The influence of the core-to-shell ratio, evaporation temperature, and the presence of sodium chloride and a surfactant on the yield of the microencapsulation process was evaluated. Microcapsules were characterized by scanning electron microscopy (SEM), and thermogravimetry that revealed the morphology and thermal behavior of microcapsules in response to changing core-to-shell ratios. SEM images showed mononuclear microcapsules with smooth surfaces. The results indicated that a core-to-shell ratio of 2:1 showed the best encapsulation performance under the conditions of this study. An increase in yield of about 38% was achieved by reducing the evaporation temperature. In addition, the yields obtained in this research are considerably higher than those found in literature.

Study on self-healing microcapsule containing rejuvenator for asphalt

Asphalt materials inevitably suffer crack problem caused by age, temperature and load, but recently self-healing microcapsules containing rejuvenator have offered a promising way to solve this problem. In this paper, the microcapsules were prepared by in-situ polymerization method and optimum preparation conditions were carefully explored, and then the morphology, particle size, coating rate, thermal stability and molecular structure of microcapsules were comprehensively investigated. Moreover, the healing ability of asphalt containing microcapsules under conditions of low-temperature and fatigue load was fully studied. Results indicated that the microcapsules could survive during the asphalt melting process and showed good healing performance under conditions of low-temperature and fatigue load, but the healing efficiency increased first and then decreased with the additive amount of microcapsules, and the optimal additive amount of microcapsules was 0.3–0.5wt% of the asphalt.

Morphological study of polymethyl methacrylate microcapsules filled with self-healing agents

Polymethyl methacrylate (PMMA) microcapsules filled with epoxy prepolymer, 3-aminomethyl-3,5,5-trimethylcyclohexylamine, and pentaerythritol tetrakis (3-mercaptopropionate) as healing agents have been prepared separately through internal phase separation method for self-healing purposes. PMMA with two different molecular weights (M¯1=36,000g/mol and M¯2=550,000g/mol) were used with two types of different emulsifiers (ionic and polymeric) to prepare microcapsules. The morphology of healing agent microcapsules was investigated using field emission scanning electron microscopy (FESEM). It was found that PMMA microcapsules separately filled with epoxy and amine had core-shell morphologies with smooth surfaces. The mercaptan/PMMA particles exhibited core-shell and acorn-shape morphologies. The surface morphology of mercaptan microcapsules changed from holed to plain in different emulsion systems. The spreading coefficient (S) of phases in the prepared emulsion systems were calculated from interfacial tension (σ) and contact angle (θ) measurements. The theoretical equilibrium morphology of PMMA microcapsules was predicted according to spreading coefficient values of phases in emulsion systems. It was also found that the surface morphology of PMMA microcapsules depended strongly on the nature of the core, molecular weight of PMMA, type and concentration of emulsifier.

The Effects of Ionic Gelation- Vibrational Jet Flow Technique in Fabrication of Microcapsules Incorporating β-cell: Applications in Diabetes.

In recent studies, we have incorporated bile acid and polyelectrolytes into pancreatic β-cell microcapsules and examined their cell viability and microcapsule morphology using various encapsulating methods. This study aimed to incorporate 3 colloids; ultrasonic gel (USG; 1%), polystyrenic sulphate (PSS; 0.1%) and polyallylamine (PAA; 3%) and ursodeoxycholic acid (UDCA; 4%) with the polymer sodium alginate (SA; 1.2%) and the copolymer poly-L-ornithine (PLO; 1%), and using a refined vibrational jet-flow microencapsulating method, test the microcapsule properties, and cell viability without or with UDCA. The pancreatic β-cells NIT-1 were encapsulated using concentric nozzles and a refined method using voltage > 600 mv and frequency of 1750 Hz with syringe flow of 1.5 ml/min (core) and formulation solution of 2.1 ml/min, with a mixture of SA, PLO, USG, PSS and PAA without UDCA (control) or with UDCA (test). Both formulations and microcapsules were examined for surface composition and thermal and chemical biocompatibilities. The microencapsulated cells were examined for bioenergetics and production of inflammatory biomarkers. UDCA distribution within the microcapsules was also examined. Using our method, viability remained low after the addition of PSS, PAA and USG, while the incorporation of UDCA enhanced cell viability, and thermal stability was maintained. Our refined microencapsulating method, when incorporating polystyrenic sulphate, polyallylamine, the gel and UDCA at 0.1:3:1:4 ratio respectively, produced stable microcapsules suggesting potential applications in cell microencapsulation and diabetes treatment.

Melamine-Formaldehyde Microcapsules: Micro- and Nanostructural Characterization with Electron Microscopy.

A systematic study has been carried out to compare the surface morphology, shell thickness, mechanical properties, and binding behavior of melamine-formaldehyde microcapsules of 5-30 μm diameter size with various amounts of core content by using scanning and transmission electron microscopy including electron tomography, in situ nanomechanical tensile testing, and electron energy-loss spectroscopy. It is found that porosities are present on the outside surface of the capsule shell, but not on the inner surface of the shell. Nanomechanical tensile tests on the capsule shells reveal that Young's modulus of the shell material is higher than that of bulk melamine-formaldehyde and that the shells exhibit a larger fracture strain compared with the bulk. Core-loss elemental analysis of microcapsules embedded in epoxy indicates that during the curing process, the microcapsule-matrix interface remains uniform and the epoxy matrix penetrates into the surface micro-porosities of the capsule shells.

Heat storage/release characteristics and mechanical properties of combat uniform fabrics treated with microcapsules containing octadecane as phase change materials

Combat uniform fabric was treated with octadecane-containing microcapsules to impart thermostatic function in this study. Size and morphology of microcapsules, and quantity of octadecane in the microcapsules were investigated. Heat release and storage properties with respect to a variety of treatment conditions was also investigated. Fourier transform infrared spectrometer (FT-IR), scanning electron microscope (SEM), thermogravimetric analysis-differential thermal analysis (TGA-DTA), and differential scanning calorimeter (DSC) were used to measure the properties of treated fabrics. Tensile properties, including tensile strength and elongation at break, and toughness, were measured by universal tensile testing machine in a conditioned environment (20±1 °C, 50±5 % RH). Microcapsules were round-shaped and sized between 4.22 and 4.92 µm with thermal stability under 110 °C of treatment temperature. Heat of fusion (ΔHf) and heat of crystallization (ΔHc) of the specimens increased along with the increase of microcapsule concentration. However, they decreased as the treatment temperature increased, at 12 % and 18 % of microcapsule concentrations. In case of specimens treated by 24 % of microcapsule concentration, ΔHf and ΔHc increased when specimens were cured at higher temperatures. Tensile strength of specimens decreased as treatment temperature increased. Elongation at break of all specimens decreased after treatment, but no specific tendency was observed. Toughness of all specimens exhibited a tendency of increase as concentration of microcapsules increased. Among the 9 treated specimens, specimen treated with 24 % of microcapsules and 110 °C of curing temperature had the best heat storage/release and mechanical properties for combat uniform.

Chitosan-coated hemoglobin microcapsules for use in an electrochemical sensor and as a carrier for oxygen

The article describes the preparation of chitosan-coated hemoglobin (Hb-CS) microcapsules by (a) preparing a CaCO3 precipitate containing Hb, (b) crosslinking Hb with glutaraldehye, (c) coating the particles with chitosan, and (d) preparing Hb-CS microcapsules by removing the CaCO3 template with a solution of disodium EDTA. The morphology and electrochemical properties of the Hb-CS microcapsules were investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An oxygen sensor was obtained by immobilizing the Hb-CS microcapsules on the surface of a glassy carbon electrode (GCE) first modified with gold nanoparticles. The application of Hb-CS microcapsules facilitates electron transfer on the surface of GCE and warrants the integrity and biological activity of Hb. The oxygen sensor, operated best at a working voltage of −0.335 V (vs. SCE), displays a low limit of detection (30 nM). The Hb-CS microcapsules also are shown to release loaded oxygen to an anaerobic aqueous environment within 300 min.

Influence of dual-component microcapsules on self-healing efficiency and performance of metal-epoxy composite-lap joints

ABSTRACTDual-component microcapsules were synthesized by solvent evaporation technique using epoxy resin and hardener as core materials and polymethyl methacrylate (PMMA) as shell wall materials. Morphology, core content, and size distribution of microcapsules were monitored by controlling the various processing parameters such as agitation speed, core–shell weight ratio, and concentration of emulsifiers. The molecular structure, morphologies, and thermal characteristics of the microcapsules were examined under Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and thermogravimetric analysis (TGA), respectively. Synthesized dual-component microcapsules were entrenched into the epoxy polymer to introduce the healing features in single lap shear epoxy adhesive joints. Healing efficiency as high as 89% was achieved when 10 wt% dual-component microcapsules were introduced in adhesives. Investigation of the fractured surfaces of the healing enabled adhesives reveals the presence of crack pinning and crack blunting sites represented by characteristic tails at the wake of microcapsules in cohesive zone. Such failure mechanisms responsibly influence the healing efficiency.

Physico-chemical characteristics of microencapsulated propolis co-product extract and its effect on storage stability of burger meat during storage at −15 °C

The objective of this study was to evaluate the antioxidant activity, physico-chemical characteristics of the microencapsulated propolis co-product extract (MPC) in a spray dryer and their effects on oxidative stability and sensory acceptability of burger meat during storage. The Capsul® was used as wall material and morphology of microcapsules was determined by scanning electron microscope, generating smooth and spherical microcapsules of different sizes, without cracks. The microencapsulation process efficiency (76.86%), in terms of phenolic compounds content, was high. Coumaric acid and epicatechin were present in high amounts. The oxidative stability of the burgers was assessed by the increase in malonaldeyde (MDA Kg−1 meat) on the processing day and weekly during 28 days of frozen storage. After 14 storage days, the lipid oxidation was inhibited due to the MPC addition. The MPC (0.95 mg MDA Kg−1 meat) provided greater lipid stability than the sodium erythorbate (1.20 mg MDA Kg−1 meat). Burger meat containing MPC showed lower grades than the ideal scale in the smell and flavor and close to the ideal grades for color, appearance, and texture. The global assessment of this burger was 63.80%. The MPC has interesting characteristics and brings prospects for its use as a natural ingredient in burger meat.

Preparation and property of epoxy resins-penetrated aligned carbon nanotube bundle hybrid microcapsules for self-healing polymers

The epoxy resins-penetrated aligned carbon nanotube bundle (ACNTsB) hybrid system (epoxy@ACNTsB) was prepared by soaking ACNTsB in the acetone solution of epoxy resins. Epoxy@ACNTsB was encapsulated in aqueous solution containing an amine curing agent to prepare hybrid microcapsules (MCs). The structure and morphology of MCs were characterized by Fourier transform infrared spectroscopy, scanning electronic microscopy, transmission electron microscopy, and laser scanning confocal microscopy. The thermal properties of MCs were carried out by differential scanning calorimetry and thermogravimetric analysis. The solvent resistance of MCs in acetone was also investigated. The results show that MCs exhibit high initial decomposition of temperatures (266°C). The content of epoxy resin in MCs is about 74% and the polymer film thickness of MCs is from 1 to 2 μm. MCs show high thermal and chemical stability below 200°C and excellent solvent resistance. MCs embedded in cyanate ester (CE) resins can significantly toughen the matrix. The fracture MCs can release the epoxy resins under heating condition, and the released epoxy resins can react with the reactive –OCN group/triazine rings in the CE matrix to rebond the crack surfaces. When the temperature schedule of 100°C/1 h + 200°C/2 h is applied, 10–15 wt% MCs can recover from 82.7% to 99.8% of the original fracture toughness of CE matrix.

Preparation of polyurea/melamine formaldehyde double-layered self-healing microcapsules and investigation on core fraction

Moisture curing type self-healing microcapsules become more attractive, while instability of active core material crippled the efficiency of self-healing behaviour. Polyurea (PU)/melamine formaldehyde (MF) double-layered self-healing microcapsules containing isophorone diisocyanate (IPDI) core with high and stable core fraction were prepared. The structure, morphology, particle size and distribution were studied with Fourier transform infra-red spectroscopy, optical microscopy, scanning electron microscopy and Mastersizer 3000. The influences of process conditions were investigated to uncover the principle of core fraction and morphology of microcapsules. The core fraction of microcapsules was reduced with the increase of ageing time, and microcapsules prepared with ice-bath, polyetheramine (PEA) and prepolymer of melamine formaldehyde (P-MF) had higher core fraction and better morphology. PEA D230 and 1500 rpm agitation rate were chosen according to optimised trade-offs in the core fraction and morphology of the microcapsules.

Properties of n-eicosane-filled microcapsules with different morphology. Phase Change Materials studied by positron spectroscopy and complementary methods

The Positron Annihilation Lifetime Spectroscopy (PALS) was used to investigate properties of selected Phase Change Materials (PCMs) as a function of temperature from 123 K to 333 K. Three different PCM microcapsules investigated in this work were built of n-eicosane filling and a siloxane polymer as a shell material. It has been found that the properties of ortho-positronium (o-Ps) annihilating in n-eicosane filler depend on the microcapsule morphology. In the samples where the whole interior is composed of n-eicosane and the polymer forms the outer shell only, the n-eicosane behaves like a neat macroscopic sample. In the microcapsules containing the network of polymer threads inside the globule, n-eicosane shows no rise of o-Ps intensity with time which is typical for all pure alkanes. For this morphology, the melting point of n-eicosane is preceded by the 4 K wide temperature range, where the structure resembling the rotator phase is observed (rotator phase appears in neat even-numbered alkanes with carbon chain over 20 atoms). Supplementary data were obtained by the DSC method. SEM images confirmed the morphological differentiation of microcapsules. Low temperature (close to liquid nitrogen) destroys the structure of microcapsules, particularly their outer shell.

An experimental application on denim garment to give thermal regulation property

In this context, the influence of ‘phase change material (PCM) finishing on denim jeans’ on thermal regulation and other selected properties was investigated. Denim garments were treated with microcapsulated PCM in various concentrations given in bath and by dipping, followed by the curing process. Differential scanning calorimeter tests were applied to denim fabrics. Morphology of microcapsules was characterized by scanning electron microscopy analyses and color analyses of the garments were done and evaluated.

Preparation of polystyrene/sodium monofluorophosphate microcapsules by W/O/W solvent evaporation method

Polystyrene (PS)/sodium monofluorophosphate (MFP) microcapsules were prepared by solvent evaporation method for direct addition into concrete and the effects of wall material content, MFP content, emulsifier and protective colloid on the morphology of microcapsules were discussed. The results showed that the average diameter of microcapsule particles slightly increased with the increase of PS content and MFP contents. Span 60 was the best emulsifier comparing with sodium lauryl sulfate and Tween 80. Increasing Span 60 content could decrease the size of microcapsules and the appropriate concentration of Span 60 was 0.5%. Lower concentration of polyvinyl alcohol (PVA), as a protective colloid in the external water phase, resulted in larger particles and higher encapsulation efficiency. The optimal PVA content was approximately 2%. PS/MFP microcapsules exhibited a good sustained release in a simulated concrete solution.

Fabrication of uniform alginate-agarose microcapsules loading FeSO4 using water-oil-water-oil multiple emulsions system combined with premix membrane emulsification technique

Abstract In this study, the uniform alginate-agarose microcapsules entrapping FeSO4 were successfully fabricated by premix membrane emulsification technique combined with ionic crosslinking solidification method. It was the first time to employ four phase emulsions system of W1/O1/W2/O2 for encapsulating FeSO4 into alginate-agarose microcapsules. We systematically investigated how the preparation parameters including type of oil phase and emulsifier, concentrations of alginate and agarose and volume ratios between oil and water phase influenced the stability of emulsions, the morphology and size distributions of microcapsules and loading efficiency of FeSO4. We found that the stability of emulsion was improved with the increase of viscosity and density of outer oil phase (O2), the concentration of emulsifier as well as the volume ratio between inner water phase and inner oil phase (W1/O1) within a certain range. Besides, loading capacity of Fe2+ in alginate/agarose microcapsules presented an increase tendency with the decrease of the volume ratio between external water phase (W2) and primary emulsion [W2/(O1/W1) (v/v)], and also decreased with the concentration of W2. Furthermore, Young’s modulus grew significantly with the increase of agarose/alginate (w/w). According to the above investigation, the optimal preparation parameters were obtained, and the microcapsules prepared with these parameters showed spherical and smooth morphology, average size of 2 μm in diameter, narrow size distributions and higher FeSO4 loading efficiency of 13.7 mg/g. The microcapsules could be applied for the human body iron supplement, and the encapsulation could well shield bad taste of FeSO4.

Microencapsulation: A potential and promising approach in drug delivery system

Novel drug delivery system is a method by which drug delivered can have significant effect on its efficacy. There are several advantages of novel drug delivery system over conventional multi dose therapy, which include improved efficacy, reduced toxicity, improved patient compliance and convenience. Many efforts have been made in developing novel drug delivery system, which emphasizes on controlled and sustained release dosage forms to obtain optimum benefits. There are various approaches in delivering a therapeutic substance to the target site in a sustained controlled release fashion. One such approach is using microspheres or microcapsules. Microencapsulation is a process by which solids, liquids or gases can be enclosed in microscopic particles by forming a thin coating of wall material around substances, which protects it from external environment and control the drug release yielding capsules ranging for one micron to several hundred microns in size (1µ- 800µ). There are different microencapsulation techniques, which are used to obtain microcapsules for controlled release of drug. The morphology of microcapsules depends on the core material and deposition of coating material. Substances may be microencapsulated for the purpose of confining core material within capsule wall for specific period of time. Core materials are also encapsulated so that the core material can be gradually released (controlled release or diffusion) or when external conditions trigger the capsule walls to rupture, melt, or dissolve. Microencapsulation has found many applications in science and technology.

Preparation and Properties of Melamine Urea-Formaldehyde Microcapsules for Self-Healing of Cementitious Materials.

Self-healing microcapsules were synthesized by in situ polymerization with a melamine urea-formaldehyde resin shell and an epoxy resin adhesive. The effects of the key factors, i.e., core–wall ratio, reaction temperature, pH and stirring rate, were investigated by characterizing microcapsule morphology, shell thickness, particle size distribution, mechanical properties and chemical nature. Microcapsule healing mechanisms in cement paste were evaluated based on recovery strength and healing microstructure. The results showed that the encapsulation ability, the elasticity modulus and hardness of the capsule increased with an increase of the proportion of shell material. Increased polymerization temperatures were beneficial to the higher degree of shell condensation polymerization, higher resin particles deposition on microcapsule surfaces and enhanced mechanical properties. For relatively low pH values, the less porous three-dimensional structure led to the increased elastic modulus of shell and the more stable chemical structure. Optimized microcapsules were produced at a temperature of 60 °C, a core-wall ratio of 1:1, at pH 2~3 and at a stirring rate of 300~400 r/min. The best strength restoration was observed in the cement paste pre-damaged by 30% fmax and incorporating 4 wt % of capsules.