Nano-sized Capsules Research Articles

Synthesis and application of paraffin/silica phase change nanocapsules: Experimental and numerical approach

The present study has been focused on the synthesis of silica encapsulated paraffin phase change materials and its application in cement-based systems. One-pot in-situ hydrolysis of tetraethyl orthosilicate as silica precursor and subsequent polycondensation have successfully encapsulated the paraffin droplets into nano-sized capsules of phase change materials (PCMs). The fabricated nanoencapsulated PCMs (NEPCMs) possess distinct core-shell structures with spherical geometry. Encapsulation ratio and encapsulation efficiency have been accomplished up to 92.9 and 90.24% with the latent heats of melting and solidification of 173.79 and 158.93 J/g, respectively. Calorimetry studies of the fabricated NEPCMs with ordinary Portland cement (OPC) have demonstrated 11% temperature reduction during the evolution of the heats of hydration, with the addition of only 3% NEPCMs. The synthesized PCMs are found to perform as high thermal energy storage materials with the capability of congruent heat storage and release without affecting their structure and geometry, therefore, can be considered as reliable and durable PCMs for concrete and building materials. The use of these NEPCMs can control the maximum temperature rise due to heat of hydration and therefore reducing the defects and cracks formation inside the mass concrete structures.

Micro- and Nanocapsules Based on Artificial Peptides.

The encapsulation of active ingredients into solid capsules from biodegradable materials has received significant attention over the last decades. In this short review, we focus on the formation of micro- and nano-sized capsules and emulsions based on artificial peptides as a fully degradable material. It deals with various approaches for the preparation of peptide-based capsules as well as with their crucial properties such as size and stability. We categorize all preparation procedures into three basic approaches: self-assembly, polymerization and crosslinking, and layer-by-layer technology. This article is meant to offer a short overview over all successful methods suitable for obtaining access to these very promising carrier systems.

Nanoencapsulation of binary nitrate molten salts for thermal energy storage: Synthesis, thermal performance, and thermal reliability

Molten salts have favorable features to serve as thermal energy storage (TES) media, and their nano-sized capsules are advantageous for efficient TES. However, their high water solubility hinders encapsulation by conventional methods, such as the sol–gel process. In this study, a binary nitrate molten salt mixture (NaNO3 and KNO3 in 60:40 mass ratio) was nanoencapsulated by a silica (SiO2) shell using emulsification and sol–gel techniques. The diameters of the molten salt capsules were controlled from a few micrometers to several hundred nanometers by regulating the stirring intensity and surfactant dosage during the synthesis process. Based on differential scanning calorimetry measurements, the encapsulation ratio and encapsulation efficiency were calculated 50.6% and 50.0%, respectively. Thermogravimetric analysis confirmed that the thermally stable SiO2 shell enhances the decomposition temperature of the binary nitrate salt mixture. Finally, the proposed nanoencapsulation protocol was also utilized to encapsulate a different nitrate salt mixture (NaNO3 and KNO3 in 80:20 mass ratio) and two single nitrate salts (NaNO3 and KNO3). This was done to validate both its applicability to all nitrate salt mixtures and the consistency of the chemical composition in each nanocapsule. The achievement for these nitrates suggests the possibility of comprehensive nanoencapsulation of water-soluble materials.

Encapsulation of an Anionic Surfactant into Hollow Spherical Nanosized Capsules: Size Control, Slow Release, and Potential Use for Enhanced Oil Recovery Applications and Environmental Remediation.

A new platform that allows encapsulation of anionic surfactants into nanosized capsules and subsequent release upon deployment is described. The system is based on DOWFAX surfactant molecules incorporated into sub-100 nm hollow silica nanoparticles composed of a mesoporous shell. The particles released 40 wt % of the encapsulated surfactant at 70 °C compared to 24 wt % at 25 °C after 21 and 18 days, respectively. The use of the particles for subsurface applications is assessed by studying the effectiveness of the particles to alter the wettability of hydrophobic surfaces and reduction of the interfacial tension. The release of the surfactant molecules in the suspension reduces the contact angle of a substrate from 105 to 25° over 55 min. A sustained release profile is demonstrated by a continuous reduction of the interfacial tension of an oil suspension, where the interfacial tension is reduced from 62 to 2 mN m–1 over a period of 3 days.

Irreversibility analysis of thermally driven flow of a water-based suspension with dispersed nano-sized capsules of phase change material

A precise understanding of the thermal behaviour and entropy generation of a suspension comprising nano-encapsulated phase change materials (NEPCM) is important for the thermal energy storage and heat transfer enhancement in various engineering applications. Studies to date, have improved the knowledge of the heat transfer of NCPCM. However, a suspension comprising NEPCM in the porous medium could enhance the overall heat transfer performance. Therefore, this study aims to investigate the thermal, hydrodynamic and entropy generation behaviour of the NEPCM-suspensions in a porous medium. Conjugate natural convection heat transfer and entropy generation in a square cavity composed of a porous matrix (glass balls), occupied by a suspension comprising nano-encapsulated phase change materials, and two solid blocks is numerically investigated. Galerkin Finite Element Method is employed to solve the nonlinear coupled equations for the porous flow and heat transfer. The phase transition and the released/absorbed latent heat of the nano-capsules are attributed in a temperature-dependent heat capacity field. The thermal conductivity ratio (1 ≤ Rk ≤ 100), the Darcy number (10−5 ≤ Da ≤ 10−1), the Stefan number (0.2 ≤ Ste ≤ 1), the porosity of porous medium (0.2 ≤ ε ≤ 0.9), the dimensionless fusion temperature (0.05 ≤ Tfu ≤ 0.95), the solid walls thickness (ds = 0.1 and 0.3), and the volume fraction of the nano-capsules (0.0 ≤ φ ≤ 5%) are considered for the numerical calculations. The numerical results illustrate that the rates of heat transfer and the average Bejan number are maximum and the generated entropy is minimum when the fusion temperature of the nano-capsules is Tfu = 0.5. Besides, adding the nano-sized particles of encapsulated phase change materials to the host fluid increases the heat transfer rate up to 45% (for the studied set of parameters) and also augments the average Bejan number. The total entropy generation elevates with the increment of the volume fraction of the nanoparticles, for low values of the Darcy number; however, a downward trend can be found for higher values of the Da. The combination of NEPCM-suspensions (with latent heat thermal energy storage) and a porous medium (with the extended surface area) provides an extensive capability for thermal enhancement and energy storage applications. In this regard, the findings of the current work demonstrate that the selection of the fusion temperature and Darcy number are two essential key parameters, which could change the trend of the results.

Pesticide Encapsulation at the Nanoscale Drives Changes to the Hydrophobic Partitioning and Toxicity of an Active Ingredient.

Given the costs associated with designing novel active ingredients, new formulations focus on the use of other ingredients to modify existing formulations. Nanosized encapsulated pesticides offer a variety of enhanced features including controlled release and improved efficacy. Despite the presence of nanosized capsules in current-use pesticide formulations, the analytical and toxicological implications of encapsulation are uncertain. To explore this issue quantitatively, we fractionated the capsules of a commercially available encapsulated insecticide formulation (γ-cyhalothrin active ingredient) into two size ranges: a large fraction (LF), with an average hydrodynamic diameter (HDD) of 758 nm, and a small fraction (SF), with an average HDD of 449 nm. We developed a novel extraction method demonstrating a time-dependent inhibition of γ-cyhalothrin from capsules for up to 48 h. An acute immobilization test with a freshwater macroinvertebrate (Ceriodaphnia dubia) revealed that the SF was significantly more toxic than both the LF and the free γ-cyhalothrin treatment (EC50 = 0.18 µg/L, 0.57 µg/L, and 0.65 µg/L, respectively). These findings highlight that encapsulation of γ-cyhalothrin mitigates hydrophobic partitioning in a time-dependent manner and influences toxicity in a size-dependent manner. Recognizing the analytical and toxicological nuances of various nanosized capsules can contribute to innovation in pesticide formulations and may lead to more comprehensive pesticide regulation.

Validating the early corrosion sensing functionality in poly (ether imide) coatings for enhanced protection of magnesium alloy AZ31

This work reports on the validation studies of early corrosion sensing poly ether imide (PEI) coatings with incorporated pH-sensing phenolphthalein loaded silica nano-sized capsules (SiNCs-PhPh) on AZ31 magnesium alloys. Immersion and drop tests validated the high sensing accuracy and PhPh color-signaling reproducibility of the coatings upon onset of corrosion. This behavior is correlated to the homogeneous dispersion of SiNC particle agglomerates confirmed by 3D Raman mapping and SEM analysis. Complementary differential video imaging technique (DVIT) assisted by electrochemical impedance spectroscopy (EIS) investigations provided clues for a good correlation between the kinetics of color signaling and the corrosion activity. Mechanistic insights into the pH-sensing/color-signaling functionality in PEI coatings are suggested.

Essential oils as solvents and core materials for the preparation of photo-responsive polymer nanocapsules

Light-triggered release of active ingredients from polymeric nanosized capsules can be employed in a wide range of applications, such as biomedicine, active packaging, and cosmetics. However, the preparation of core-shell polymeric nanocarriers typically involves the use of toxic organic solvents. To improve the sustainability and safety of nanocapsule applications, we demonstrate that natural essential oils can be used both as solvent and active material in light-responsive nanocapsules synthesized via miniemulsion polycondensation. The documented antimicrobial, anti-inflammatory, and antioxidant activity of essential oils enables the design of multipurpose light-responsive delivery platforms. The photo-responsive behavior of the capsules, achieved by means of photochromic azobenzene segments embedded in the capsule shell, is triggered by UV light irradiation (λ max = 360 nm). Light-induced release kinetics of the essential oils and a fluorescent probe molecule, coumarin-6, is evaluated via UV-vis spectroscopy and spectrofluorimetry, respectively, demonstrating the efficiency and reliability of the release mechanism. Biological tests prove that the capsules are non-cytotoxic and readily internalized by cells, indicating the suitability of these smart nanocarriers for biological applications.

Preparation and investigation of hybrid self-healing coatings containing linseed oil loaded nanocapsules, potassium ethyl xanthate and benzotriazole on copper surface

The effectiveness of self-healing epoxy and polyurethane hybrid coatings filled with linseed oil (LO) containing nano-sized capsules, potassium ethyl xanthate and benzotriazole was investigated for self-healing and anti-corrosion performance on the copper metal films. The characteristics of synthesized nanocapsules were studied by fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), field emission scanning electron microscopy (FESEM) for chemical structure, thermal stability and surface morphology investigations. Furthermore, size distribution of the prepared nanocapsules was investigated using dynamic light scattering (DLS). The anti-corrosion effect of coatings was studied by electrochemical impedance spectroscopy (EIS) and optical microscopy imaging. Taguchi method was used to reduce the number of experiments and anti-corrosion efficiency evaluations. The synthesized nanocapsules have 459–712 nm diameters. LO loading efficiency was almost 60%. Hybrid self-healing coatings which contain self-healing and anti-corrosion agents together showed synergistic effect at optimum levels (3 wt% LO and 5 wt% anti-corrosion agent). Adhesion pull-off test shows that higher amounts of nanocapsules, potassium ethyl xanthate and benzotriazole resulted in weaker adhesion for coatings.

Regular sleep and cytotoxic nanomedicine targeting tumor-associated macrophages for synergistic immunotherapy of breast cancer

Silica nanocapsules with various degrees of surface hydrophobicity were produced by using the inverse miniemulsion technique. Tetraethylorthosilicate was added concurrently with organosilanes containing a variety of hydrophobic ligands (e.g., cyclohexyl and octadecyl). The method is simple and yields nanosized capsules capable of containing hydrophilic components, while using relatively low amounts of surfactants. Commercially used hydrophobic chlorosilanes were demonstrated to be poor additives for the formation of silica nanocapsules. 29Si solid-state NMR was performed on selected silica nanocapsules to show that hydrophobic alkoxysilanes were incorporated within the silica nanocapsule network. Dynamic light scattering measurements of hydrophobized nanocapsules in a caustic medium indicated a relative increase in size with regard to pure silica nanocapsules. Contact angles of water on the nanocapsules generally increased with the length of hydrophobic ligand suggesting less interaction of the surface with water. The hydrophobicity of the nanocapsules was related to their ability to repulse a caustic water environment, thus delaying silica network degradation, which would cause nanocapsule breakage.

Controlling hydrophobicity of silica nanocapsules prepared from organosilanes

Silica nanocapsules with various degrees of surface hydrophobicity were produced by using the inverse miniemulsion technique. Tetraethylorthosilicate was added concurrently with organosilanes containing a variety of hydrophobic ligands (e.g., cyclohexyl and octadecyl). The method is simple and yields nanosized capsules capable of containing hydrophilic components, while using relatively low amounts of surfactants. Commercially used hydrophobic chlorosilanes were demonstrated to be poor additives for the formation of silica nanocapsules. 29Si solid-state NMR was performed on selected silica nanocapsules to show that hydrophobic alkoxysilanes were incorporated within the silica nanocapsule network. Dynamic light scattering measurements of hydrophobized nanocapsules in a caustic medium indicated a relative increase in size with regard to pure silica nanocapsules. Contact angles of water on the nanocapsules generally increased with the length of hydrophobic ligand suggesting less interaction of the surface with water. The hydrophobicity of the nanocapsules was related to their ability to repulse a caustic water environment, thus delaying silica network degradation, which would cause nanocapsule breakage.

Preparation of stimuli-responsive nano-sized capsules based on cyclodextrin polymers with redox or light switching properties

We report the preparation and encapsulation properties of stimuli-responsive nanocapsules, self-assembled by the noncovalent interactions of cyclodextrinappended polymers (host) and complementary ferrocene or azobenzene carriers (guest). The encapsulation process was significantly accelerated by applying (electro) chemical or light stimulus, enabling the easier and faster diffusion of guest molecules through the polymer layers. The nanocapsules were characterized by dynamic light scattering, confocal microscopy, ESEM, AFM, UV–visible and fluorescence spectroscopy, and electrochemical techniques. The encapsulation and release properties of the nanocapsules were reversible and could be repeated several times, indicating that the prepared nanoassemblies are very stable.

Fabrication of polyelectrolyte multilayered nano-capsules using a continuous layer-by-layer approach

The layer-by-layer approach is a highly versatile method for the fabrication of multilayered polymeric films and capsules. It has been widely investigated in research for various polyelectrolyte pairs and core template particles. However, the fabrication of nano-sized capsules at the larger scale is difficult and time consuming, due to the necessity of washing and centrifugation steps before the deposition of each polyelectrolyte layer. This results not only in a very long fabrication time, but also in the partial loss of particles during those intermediate steps. In this study, we introduced a continuous approach for the fabrication of multilayer polyelectrolyte based nano-capsules using calcium phosphate core nanoparticles and a tubular flow type reactor with the potential for synthesizing tens of milligrams of capsules per hour. Adsorption of the polyelectrolyte layer occurred in the tubing where particles and polyelectrolyte solution of choice were mixed, creating a layer of polyelectrolyte on the particles. After this, these newly surfaced-modified particles passed into the next segment of tubing, where they were mixed with a second polyelectrolyte of opposite charge. This process can be continuously repeated until the desired number of layers is achieved. One potential problem with this method concerned the presence of any excess polyelectrolyte in the tubing, so careful control of the amount of polymer added was crucial. It was found that slightly under dosing the amount of added polyelectrolyte ensured that negligible unadsorbed polyelectrolyte remained in solution. The particles created at each deposition step were stable, as they all had a zeta potential of greater than ±25mV. Furthermore the zeta potential measurements showed that charge reversal occurred at each stage. Having achieved the necessary number of polyelectrolyte layers, the calcium phosphate cores were easily removed via dissolution in either hydrochloric or acetic acid.

The influence of size on the toxicity of an encapsulated pesticide: a comparison of micron- and nano-sized capsules

Encapsulation technology involves entrapping a chemical active ingredient (a.i.) inside a hollow polymeric shell and has been applied to commercial pesticide manufacturing for years to produce capsule suspension (CS) formulations with average particle sizes in the micron-scale. The few literature sources that investigate the environmental fate and toxicity to non-target organisms of encapsulated commercially available pesticide products with regard to capsule size report on average sizes between 20 and 50μm. Here, we have identified a CS formulation with an average capsule size of approximately 2μm with some capsules extending into the nanometer scale (~200nm). Determining how carrier size influences toxicity is important to understanding if current pesticide risk assessments are sufficient to protect against products that incorporate encapsulation technology. Here, a commercial pyrethroid CS pesticide with lambda-cyhalothrin (λ-Cy) as the a.i. was separated into two suspensions, a fraction consisting of nano-sized capsules (~250nm) and a fraction of micron-sized capsules (~2200nm) in order to investigate the influence of capsule size on toxicity to embryonic zebrafish, Danio rerio. Toxicity was evaluated 24h after exposure to equivalent amounts of a.i. by the presence and severity of pyrethroid-specific tremors, 14 sublethal developmental impacts and mortality. Fish exposed to greater than 20μg a.i. L−1 technical λ-Cy or formulated product experienced curvature of the body axis, pericardial edema, craniofacial malformations, and mortality. Exposure to the unfractionated formulation, micro fraction, nano fraction and technical a.i. resulted in no significant differences in the occurrence of sublethal impacts or mortality; however, the technical a.i. exposure resulted in significantly less fish experiencing tremors and shorter tremors compared to any of the formulated product exposures. This suggests that the capsule size does not influence the toxic response of the entrapped λ-Cy, but the presence or absence of the capsules does. Testing across other encapsulated products is needed to determine if size does not have influence on toxicity regardless of encapsulation technology.

One-step radiation-induced construction of multi-responsive self-assemblies using simple cyclic ethers

A general and one-step method was developed as a versatile route to fabricate ‘smart’ self-assemblies via γ-irradiation of simple cyclic ethers under air atmosphere. Only by one-step irradiation in water, a series of amphiphilic oligomers containing oligo(ethylene glycol) (oligo-EG) side chains and their supramolecular assemblies with plentiful morphologies could be prepared, including flower-shaped aggregates, microsphere aggregates, well-defined core–shell micelles and nano-sized capsules. The morphology of the supramolecular assemblies could be facilely adjusted based on the different structures of the cyclic ethers. Moreover, the core–shell micelles prepared by irradiating dicyclohexano-18-crown-6 (DCH18C6) aqueous solutions could be easily controlled by simple external stimulations, such as varying temperature, pH and adding metal ions. Based on the results of a series of cyclic ethers, it is expected that this work can provide a novel and general approach to design and construct ‘smart’ supramolecular assemblies for biomedical and industrial applications.

Soft Capsules, Hard Capsules, and Hybrid Capsules

Capsule structures are often regarded as mimics of living cells and have attracted attention within bio-related fields. In addition, their use in other practical applications has become important. The demands of practical applications have stimulated recent developments in capsule science and technologies. In this review, we focus on recent developments on the preparation and functionalization of capsule objects. In particular, we will summarize research on micro and nano-sized capsules prepared using supramolecular concepts and related strategies. The examples are classified into three categories. Molecular capsules such as calixarene, cavitands, and dendrimers are introduced together with dynamic molecular capsules at the air-water interface in the first part. In the second category, soft polymer capsules prepared by interfacial condensation, template synthesis, and emulsion synthesis are described and the unique contribution of layer-by-layer assemblies is emphasized. In the final part, various hard capsules composed of gold, carbon, silica, and other inorganic substances are described together with hybrid capsules made from inorganic components and organic moieties. In this section, construction of hierarchic structures of mesoporous capsules is highlighted.

スフィンゴミエリンを含有したリポソーム製剤の安定化とその応用

近年, レシチン等の脂質を用いたリポソームやナノサイズレベルのカプセル化技術等を応用し, 肌への親和性に優れた皮膚化粧料が検討されている。その脂質の一種であるスフィンゴシンを構成成分とするスフィンゴリピッドは, その特性ならびに応用といった観点から検討され始めてきた新しい生体脂質の一つである。中でも, スプィンゴミエリンは, スフィンゴリン脂質の代表的なものとして多岐に知られている成分である。本研究では, このスフィンゴミエリンを化粧品原料として用いることを試み, 特に皮膚化粧料への配合を踏まえたスフィンゴミエリンからなるリボソーム製剤への応用につき, 検討を行った。その結果, 代表的なグリセロリン脂質の一つであるレシチンに比ベバリヤー能が高く, またリポソームの二分子膜構造が強固であることから, スキンケア製剤へ応用した場合には, 角層細胞間脂質構造の補完が期待され, 肌の保湿・エモリエント効果を促し, シワの改善効果をもたらすことが認められた。