Shell Thickness Of Microcapsules Research Articles

Biomass‐Based, Interface Tunable, and Dual‐Responsive Pickering Emulsions for Smart Release of Pesticides

AbstractThe extremely low utilization efficiency of pesticides has driven people to develop low‐cost, sustainable, and smart delivery systems. Pickering emulsion (PE) derived from biomass is an attractive candidate. However, the stability of PE is insufficient, and pesticide release from PE can be hardly tuned. Herein, a facile in situ PE modification strategy to construct a stable and high‐performance pesticide delivery system from biomass resources is reported. In this process, PE stabilized by alkali lignin nanoparticles is initially prepared, and subsequently, opposite‐charged chitosan (CH), and sodium lignosulfonate (SL) are alternatively deposited onto the PE interface through layer‐by‐layer assembly to form a microcapsule system (CH+SL)n@PE. The resulting biomass‐based microcapsules show improved stability, high encapsulation efficiency, and super UV protection to avermectin (AVM), a hydrophobic and photo‐sensitive pesticide. Furthermore, the shell thickness of microcapsules can be finely tuned by controlling the deposited CH+SL layers, which enable (CH+SL)n@PE to have adjustable release behaviors. (CH+SL)20@PE prolongs the half‐life of AVM under UV irradiation by 5.0‐fold. Moreover, (CH+SL)n@PE exhibits pH and laccase dual responsiveness, which is beneficial to the targeted release of AVM in vivo. Therefore, the current PE modification strategy can provide an eco‐friendly, low‐cost, and smart system for precise delivery of pesticides.

Characterization of hydrophilic and hydrophobic core-shell microcapsules prepared using a range of antisolvent approaches

This study describes three straightforward approaches to leveraging gel network-restricted antisolvent precipitation techniques as a means of preparing hydrophilic hydrophobic core-shell microparticles. Briefly, hydrophilic polysaccharides (sodium alginate (ALG), κ-carrageenan (CAR), and agar (AG)) were utilized to prepare microgel beads that were then immersed in zein solutions (70% ethanol aqueous solution, 70% urea aqueous solution, and zein in 70% acetic acid, respectively), thereby facilitating the controlled, slow antisolvent precipitation of the protein layer on the microbead surfaces and inducing hydrophilic hydrophobic core-shell structure formation. This technique can be readily applied to a range of gelling systems and can be tailored to target particle sizes and shell thicknesses. The resultant core-shell particles offer great promise for controlled delivery of fragrances, drugs, or other bioactive compounds in an application-specific fashion, and can be individually tailored based upon the selected input concentrations and preparation methods. Importantly, this technique is generalizable and can be extended to prepare diverse particles with a range of core-shell structures produced from a wide assortment of hydrophobic materials. • Core-shell microcapsules were prepared using a range of antisolvent approaches. • Size and shell thickness of microcapsules can be regulated. • Core-shell particles offer great promise for controlled delivery in an application-specific fashion.

Characterization of polyurea microcapsules synthesized with an isocyanate of low toxicity and eco-friendly esters via microfluidics: Shape, shell thickness, morphology and encapsulation efficiency

There are some studies on the synthesis of polyurea microcapsules. However, there is hardly a case where both green solvents and non-toxic isocyanates are used, especially in microfluidics. In this work, an environmentally friendly chemical system of interfacial polymerization (isocyanate: HDB-LV; solvent: octyl salicylate or dibutyl adipate) is tested for the first time to produce polyurea microcapsules. The size of microcapsules is calibrated at 78 μm by microfluidics to quantitatively analyze the relationships among shell thickness, encapsulation efficiency and isocyanate concentrations. The influences of solvent types and reactant concentrations on the shape, morphology and shell thickness of microcapsules are studied. Esters with low water miscibility and low amine concentrations (lower reaction rate) are crucial for the formation of spherical microcapsules. An ester with high water miscibility can diffuse into the continuous phase during encapsulation, which results in broken microcapsules. A high concentration of amine can probably cause cross-linking not only at the interface but also inside the droplet template, which leads to microcapsule deformation. A linear relationship is observed between the shell thickness of microcapsules and the isocyanate concentration. Overall, a high encapsulation efficiency (more than 90%) for octyl salicylate is achieved with polyurea microcapsules.

Preparation and property optimization of bistable electrochromic microcapsules

In the improvement of stability and lifetime of bistable electrochromic (EC) materials, the microcapsule technique was used to protect the EC materials in a polymer shell, which was named bistable EC microcapsules (BEC-Ms). However, the particle size and shell thickness of microcapsules will affect their properties, such as response time, coloration efficiency, and bistable property. In this study, BEC-Ms was prepared via solvent evaporation method filled with PMMA as the shell and the mixture of crystal violet lactone (CVL), tetrabutylammonium perchlorate (TBAP), and phase change material (PCM) as the core. The particle size and shell thickness of microcapsules were adjusted and systematically investigated by controlling the emulsification rate and mass ratio of polymer shell to core. The optimized BEC-Ms with 2 μm size and 22.94 nm thickness showed excellent performance including fast response time (about 1 s), far lower than the safety of human body drive voltage (2 V), coloration efficiency (932 cm2 C−1), and good bistability (216 h). This approach provides a viable and alternative to flexible energy-efficient wearable display-related devices and smart textiles.

Preparation and performance of microcapsules for asphalt pavements using interfacial polymerization

Microcapsules for asphalt pavement containing asphalt rejuvenator as the core material were prepared via interfacial polymerization using high-speed shearing. Isophorone di-isocyanate (IPDI) and distilled water were used as the reaction monomers of the oil and water phases, respectively. Polyvinyl alcohol (PVA) was used as an emulsifier. The preparation process was optimized based on the type and concentration of the emulsifier, shearing speed, shell-core ratio, and reaction temperature. The technical properties of the asphalt pavement microcapsules prepared via the optimal preparation process were evaluated by Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM), laser particle size analyzer, and Thermogravimetric analysis (TGA) from the aspects of micromorphology, particle size, shell thickness, and thermal stability. Results showed that PVA possesses satisfactory emulsifying and shell-forming properties, which made it a suitable emulsifier in the oil phase. The optimized conditions of the microcapsule preparation are as follows: the concentration of the emulsifier solution was 0.4%, the shearing speed was 5000 RPM, the shell-core ratio was 0.6, and the range of reaction temperature was 60–70 °C. The diameter of the optimal microcapsules was primarily distributed between 10 and 17 µm. Furthermore, the average particle size was 14.26 µm; the microcapsule shell thickness was relatively uniform (2–3 µm). The results of FT-IR and TGA demonstrated that the asphalt pavement microcapsules maintain good chemical and quality stability at high temperature, indicating that the microcapsules can withstand the high temperature during the asphalt-mixture production process. The results of salt tolerance test showed that microcapsules have certain salt tolerance. The mean elastic modulus and hardness of microcapsules were 466.86 MPa and 56.27 MPa, respectively obtained by nano indentation test.

Microencapsulation of pendimethalin with polyurethane-urea and determination of its stability

In this study, pendimethalin (PM) used as an herbicide was encapsulated using interfacial polymerization method. The size, shell thickness, microencapsulation efficiency, the effect of mixing speed on capsule size and active substance release times of the produced microcapsules were investigated. Polyurethane-urea resin, which is the main component of the capsule shell, was synthesized using isocyanate / glycol / amine at different molar ratio at 55°C for 180 min. It was measured that the microencapsulation efficiency was 53.2–89.1% and the microcapsule shell thickness was 399.7–1479.0 nm. The lowest and highest release percentages of microcapsules under alcohol-water and ultraviolet (UV) light for 4 h at 20°C were found to be 30.79% and 40.12%, respectively. It has been found that the microcapsules containing ethyl glycol in the capsule wall composition had the highest stability, and the capsules containing PEG-400 in the capsule wall structure had the highest capsulation efficiency.

Experimental characterisation and modelling of mechanical behaviour of microcapsules

Results of experimental characterisation and modelling of mechanical behaviour of microcapsules for self-sensing polymer composites are presented. Melamine–formaldehyde microcapsules were selected for this purpose. The average diameter, size distribution, and shell thickness of microcapsules were evaluated from scanning electron microscopy images. Compressive properties of the shell material were evaluated in several ways. AFM measurements allowed estimating stiffness and strength of a single microcapsule. In parallel, modelling of the mechanical behaviour of a single microcapsule was performed. Buckling of a thin-walled spherical shell under external pressure was considered and closed-form solution in a linear statement was obtained. The results of analytical calculations were compared with FEM modelling. Two demonstrator thin-shells with the radius of centimetre scale, hollow and filled with water, were tested in compression between two rigid plates. The results of their numerical analysis obtained by FEM models developed are in good agreement with experimental results.

Synthesis and characterization of amine hardener filled microcapsules for self-healing composite applications

Materials experience microcracks during service conditions and thus might not fulfil their functionality. Hence there is a necessity to develop a method which enhances the functionality of the material without affecting its inherent properties. Self-healing of materials through microencapsulation repairs microcracks and extends the service life of material. In this work, amine hardener encapsulated polymethyl methacrylate (PMMA) microcapsules were synthesized using oil-in -water solvent evaporation technique. Various process parameters such as surfactant concentration, operating temperature, agitation speed and core to shell ratio were investigated to get the desired morphology and healing agent content. The challenges faced during the synthesis of microcapsules were reported. It was observed that solvent evaporation rate, stirring duration, surfactant type and concentration have an impact on the agglomeration of capsules. The molecular architecture, thermal stability and surface morphology of the microcapsules were characterized by Fourier-transform Infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA) and Scanning Electron Microscope (SEM) respectively. Core content of the capsules was evaluated by solvent extraction method and the capsules average size and size distribution were reported. The effect of different surfactants and their combinations such as Polyvinyl Alcohol (PVA), Tween 80 and (Tween 80 + PVA) on the microcapsules synthesis were reported. This study also reported the influence of surfactant concentration on the microcapsule shell thickness, which is a critical parameter in evaluating structural healing efficiency. Developed microcapsules ability to release core content and repair micro cracks was verified qualitatively with 3D optical microscope.

The photoelectric properties characteristics of dye-doped nematic liquid crystal microcapsules with different structural composition

In this study, we promote a new dye-doped nematic liquid crystal (DDNLC) microcapsules system sandwiched between two ITO substrates for making an electrochromic fabric coating with both low driving voltage and wide versatility. The effects of the dye dosage, particle size and shell thickness of microcapsules on the electro-optical properties of DDNLC microcapsules were systematically investigated. Results show that optical appearance of the optimized DDNLC microcapsules can be reversibly changed between transparent and colored states by switching on and off the direct-current power. Driving voltage, response time and delay time were close related to the particle size of DDNLC core in microcapsules, and an alignment model was used to calculate the geometric construction of the microcapsules. The proposed experimental results provide reliable simulations of the electro-optical properties of DDNLC microcapsules which showing great potential applications in a wide range of uses, such as electronic paper, military camouflage coating or intelligent flexible display fabric.

Hollow Microcapsules with Controlled Mechanical Properties Templated from Pickering Emulsion Droplets

AbstractHollow microcapsules with controlled mechanical strength are obtained from Pickering emulsion templates. The shell of the hollow microcapsules comprising UV‐curable resin and reactive silica nanoparticles enables tuning of the mechanical properties in a controlled manner. The results show that the particle stabilizer can be packed regularly on the oil–water interface and the shell thickness of microcapsules can be increased to 1–2 µm compared with traditional preparation methods. Hollow particles with thicker walls can prevent collapse and breakage. In this work, a nanoindentation device is used to measure the mechanical properties of hollow particles, and the results show a clear trend of reduced modulus and hardness decreases with increasing ratio of prepolymers in the reaction mixture. When the mass of PUA varies from 10% to 30%, the hardness decreases from 0.09 to 0.04 GPa, while the reduced modulus decreases from 0.17 to 0.06 GPa. The control of mechanical properties of the microcapsule can enhance its uses in conventional areas as well as in new fields such as precise micro force sensors etc.

Preparation of raspberry-like silica microcapsules via sulfonated polystyrene template and aniline medium assembly method

Raspberry-like composite particles and microcapsules were prepared with anionic sulfonated polystyrene (PSS) particles as templates and cationic aniline monomer as assembly medium. With the help of the sulfonated microgel shells, aniline and silica particles could not only adsorbed onto template surfaces but also go inward shells and finally form microcapsules with varied silica shell thickness. The sulfonation extent of PSS particles first climbed up and then decreased with sulfonation time due to the competition of sulfonation reaction and PSS chain detachment. The silica content in composite particles and shell thickness of microcapsules followed similar trend with sulfonation extent. The choice of aniline as assembly medium was checked by comparing with methyl methacrylate and [2-(methacryloyloxy) ethyl] trimethylammonium chloride, and it was found that the cationic and water-insoluble properties of aniline are both important for the composite efficiency.

Structure and Mechanical Properties of Consumer-Friendly PMMA Microcapsules

Environmentally and consumer-friendly poly(methyl methacrylate) (PMMA) microcapsules were prepared on the basis of an in situ polymerization reaction to encapsulate perfume oil, which aims to be delivered to fabric surfaces via liquid detergents. Microcapsules with a narrow size distribution were produced using a membrane emulsification system; results were compared with a standard homogenization procedure. The shell thickness of microcapsules was found to increase with the polymerization reaction time, which was measured using a lipophilic fluorescent dye dissolved in the perfume oil and confocal laser scanning microscopy. Microcapsules with a wide range of shell thicknesses could be produced by modifying the reaction time. The force versus displacement profiles obtained from compression of single such microcapsules between two parallel surfaces based on micromanipulation were very different: thin-shell microcapsules burst under compression, whereas thick-shell microcapsules did not. However, the intrins...

Microencapsulated Phase Change Materials and its Application in Thermal-Regulated Fibers

The phase change materials (PCMs) can absorb, store or release large latent heat over a defined temperature range while the materials change phase or state, so they can be potentially used in thermal energy storage. In this paper, a series of microencapsulated phase change materials (MicroPCMs) with n-octadecane and n-dodecanol as core were successfully fabricated respectively, where the styrene-based copolymer, acrylic based copolymer, melamine-formaldehyde resin and polyurea were selected as shell materials. The morphology of these MicroPCMs was observed by scanning electron microscopy (SEM), and the core-shell structure and the shell thickness of microcapsules were also characterized by SEM. In addition, the phase change properties of MicroPCMs were investigated using differential scanning calorimetry (DSC) analysis. Furthermore, thermal-regulated calcium alginate fiber was produced by adding MicroPCMs in wet-spinning process; and the effects of various types of MicroPCMs on fiber was discussed.

Synthesis and characterization of chitosan/urea‐formaldehyde shell microcapsules containing dicyclopentadiene

AbstractMicrocapsules containing healing agent have been used to develop the self‐healing composites. These microcapsules must possess special properties during the use of composites such as stability in surrounding, appropriate mechanical strength, and lower permeability. A new series of microcapsules containing dicyclopentadiene with chitosan/urea‐formaldehyde copolymer as shell materials were synthesized by in situ copolymerization technology. The microencapsulating mechanism was discussed and the process was explained. Also, the factors influencing the preparation of microcapsules were analyzed. The morphology and shell wall thickness of microcapsules were observed by using scanning electron microscopy. The size of microcapsules was measured using optical microscope and the size distribution was investigated based on data sets of at least 200 measurements. The chemical structure and thermal properties of microcapsules were characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis, respectively. The storage stability and isothermal aging experiment of microcapsules were also investigated. Results indicted that the chitosan/urea‐formaldehyde microcapsules containing dicyclopentadiene were synthesized successfully; the copolymerization occurred between chitosan and urea‐formaldehyde prepolymer. The microcapsule size is in the range of 10–160 μm with an average of 45 μm. The shell thickness of microcapsules is in the range of 1–7 μm and the core content of microcapsules is 67%. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Morphology, structure and thermal stability of microencapsulated phase change material with copolymer shell

A series of microencapsulated phase change materials (MicroPCMs) with n-octadecane as core were successfully fabricated by suspension-like polymerization. The influence of initiator type and polymerization temperature on MicroPCMs were investigated systemically. The morphology of these microcapsules with different copolymer shells and various phase changing material (PCM) contents were observed by scanning electron microscopy (SEM). In addition, the core-shell structure and the shell thickness of microcapsules were also characterized by SEM. Thermal gravimetric analysis (TGA) curves indicate that the effects of different copolymer shell and various PCM contents on thermal stability of MicroPCMs were insignificant. Besides, SEM micrographs show that all of the MicroPCMs with various PCM contents remained intact after heat treatment at 200 °C for 30 min, however, all of the heat-treated MicroPCMs had no enthalpy as demonstrated by differential scanning calorimetry (DSC) curves. From above results, the weight loss of MicroPCMs may be caused by the penetration of decomposed gas of n-octadecane through the intact shells.

Preparation and Characterization of Biocompatible Microcapsules of Sodium Cellulose Sulfate/Chitosan by Means of Layer-by-Layer Self-Assembly

A novel microcapsule system composed of sodium cellulose sulfate (NaCS) and chitosan was prepared by layer-by-layer (LbL) self-assembly technique. As a potential drug delivery system, it had several advantages in biocompatibility and biodegradation due to its use of natural polysaccharides. Some parameters in the preparation of the microcapsule, such as layers in the LbL process (up to 20 layers), chitosan viscosities (50, 100, and 200 mPas), outmost layer materials (NaCS or chitosan), and NaCl concentrations (0 M, 0.5 M, 1 M), were investigated to better understand their effects on the LbL process. A novel method for removing the core templates PLA and CaCO3 from the formed core-shell structure was proposed by addition of N-methyl pyrrolidone or EDTA-Na. This preparation process was well observed by a microscope-camera system. The hollow microcapsules were tested by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and scanning probe microscopy (SPM) to characterize their size, morphology, and surface. The results showed that the shell thickness of microcapsules was about 6 nm, and the average thickness of one layer of NaCS/chitosan polyelectrolyte complex was 1.5 nm. The molecular weight cutoff in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed about 70 kDa by using of diffusion test with the cell lysate of Escherichia coli.

A Novel Method to Control UV Curable Microcapsule Release Behavior

A new family of core/shell microcapsules containing photopolymerizable tripropylene glycol diacrylate (TPGDA) was synthesized by using interfacial polymerization. The chemical structure and properties of microcapsule was characterized by using Fourier Transform Infrared spectroscopy. The particles size and morphology of the microcapsules were studied by using scanning electron microscope. The thermal properties of microcapsules with various UV curing time were investigated by using differential scanning calorimetry. The controlled releasing behavior of the microcapsules with various UV curing time in organic solvent was studied. Effects of core/shell ratio and agitation rate on average particle size, size distribution and shell thickness of microcapsules were investigated. The higher agitation rate results a smaller particle size with a narrow size distribution. The rate of polymerization of TPGDA in core of microcapsules increases with decreasing particle size and the shell thickness. A higher photoinitiator concentration also increases the photopolymerization rate of the core material. The experiments of controlled releasing behavior showed that the release rate of functional components such as dye in the core can be controlled by changing the crosslink density of network formed from TPGDA.