Size-Controlled Synthesis of Polymer Nanoparticles with Tandem Acoustic Emulsification Followed by Soap-Free Emulsion Polymerization

Review of High-Frequency Ultrasounds Emulsification Methods and Oil/Water Interfacial Organization in Absence of any Kind of Stabilizer

Emulsions are multiphasic systems composed of at least two immiscible phases. Emulsion formulation can be made by numerous processes such as low-frequency ultrasounds, high-pressure homogenization, microfluidization, as well as membrane emulsification. These processes often need emulsifiers' presence to help formulate emulsions and to stabilize them over time. However, certain emulsifiers, especially chemical stabilizers, are less and less desired in products because of their negative environment and health impacts. Thus, to avoid them, promising processes using high-frequency ultrasounds were developed to formulate and stabilize emulsifier-free emulsions. High-frequency ultrasounds are ultrasounds having frequency greater than 100 kHz. Until now, emulsifier-free emulsions' stability is not fully understood. Some authors suppose that stability is obtained through hydroxide ions' organization at the hydrophobic/water interfaces, which have been mainly demonstrated by macroscopic studies. Whereas other authors, using microscopic studies, or simulation studies, suppose that the hydrophobic/water interfaces would be rather stabilized thanks to hydronium ions. These theories are discussed in this review.

Colloidal Stability of Emulsifier-free Triolein-in-Water Emulsions: Effects of Temperature

Herein, we report the colloidal stability of emulsifier-free (EF-) triolein-in-water (TO/W) emulsions prepared by mixing TO and water using a high-powered bath-type ultrasonicator (HPBath-US; 28 kHz, 300 W) in the absence of emulsifiers such as surfactants. In particular, the effect of the temperature (15-60℃) on the colloidal stability of EF-TO/W emulsions was examined because this is important for the practical application of EF-TO/W emulsions, for example, in foods, pharmaceuticals, and cosmetics. We found that the colloidal stability of the EF-TO/W emulsions decreased with increase in the temperature from 15 to 25°C, whereas it increased with increase in temperature from 25 to 40°C, and the high colloidal stability of the EF-TO/W emulsions was maintained above 40°C. The reduction in the colloidal stability of EF-TO/W emulsions between 15 and 25°C is likely a result of the TO droplets formed by thermal motion, as well as enhanced Ostwald ripening at higher temperatures. On the other hand, the increase in the colloidal stability of the EF-TO/W emulsions from 25 to 40°C and their high colloidal stability above 40℃ is attributed to the reduction in the interfacial tension between TO and water at higher temperatures. This decrease in the interfacial tension between TO and water with temperature increase is related to the transformation of short-range ordered domains (clusters) of TO molecules in the liquid state, which increases the colloidal stability of the EF-TO/W emulsions.

Peter L, Chan C, Mikhailova T, Bexheti V, Kapadia A, Carbery WP, Ng K, Maity P. Microfluidic-Supported Synthesis of Anisotropic Polyvinyl Methacrylate Nanoparticles via Interfacial Agents

For polymer particles, recent studies emphasized that the particle shape—not size—plays the dominant role in novel applications in fields ranging from nanotechnology, biomedicine, to photonics, which has intensified the quest...

Unimodal sized silica nanocapsules produced through water-in-oil emulsions prepared by sequential irradiation of kilo- and submega-hertz ultrasounds

This study investigates the regulation of the size of 100 nm hollow-sphere silica particles using surfactant-free water-in-oil (W/O) emulsion. First, water droplets were dispersed in soybean oil via sequential ultrasound irradiation (28 kHz → 200 kHz → 950 kHz). A precursor of hollow silica particles was prepared using hydrolysis and polymerization of methylsilyl trichloride into a stable W/O emulsion. The final structure/morphology of the silica particles was influenced by the volume ratio of water/soybean oil, the cycle number of the sequential ultrasound irradiation, and the amount of organosilane added to the emulsion. The emulsion was stabilized by Ostwald ripening, as the size distribution at 5/10³ (water/oil = v/v) was a bimodal split between a water droplet size of a few μm and some with a size of a few tens of nm. The most appropriate cycle number was 3 in this system. Further cycling to 5 resulted in a broad and bimodal size distribution of the final particles due to rapid coalescence of water droplets. Subsequent hydrolysis of methylsilyl trichloride consumed water with diminishing large droplets, forming fine and unimodal (0.12 ± 0.02 μm) hollow silica particles. Very fine and uniform-sized hollow particles (0.08 ± 0.01 μm) were successfully produced by decreasing the volume ratio to 1/10³ (water/oil) because of a transparent stable emulsion as a homogeneous template of the hollow structures.

Silica nanocapsules were prepared using water droplets dispersed in soybean oil via sequential ultrasound irradiation (28 kHz → 200 kHz → 950 kHz).

Anodic substitution reaction of carbamates in a flow microreactor using a stable emulsion solution

An anodic substitution reaction in a flow microreactor using a stable emulsion solution prepared by tandem acoustic emulsification is demonstrated.

Ultrasmall Polymer Nanoparticles Formed by Instantaneous Nanosplitting of Surfactant-Free Emulsion

Application of polymer nanoparticles has progressively broadened. There is now increasing interest in smaller polymer nanoparticles for use in organic solar cells and drug delivery systems. Unfortunately, it is difficult to control the particle size below 50 nm with conventional synthesis methods. Our previously proposed "two-step nanoprecipitation method" overcomes this problem. An oil-in-water emulsion is first formed from polymer solution and deionized water without using surfactant; it is then injected into ethanol to form particles. The particle formation mechanism in this method has now been investigated, and an interesting phenomenon was discovered: the injected droplets instantaneously split into nanosize droplets with a size of 100-150 nm. The splitting was very effective, and the formed nanosize droplets were virtually monodisperse. This occurred only for a mixture composition in which the surface tension of the poor solvent mixture (water and ethanol) equaled that of the good solvent. This composition also resulted in formation of the smallest particles. By adjusting the conditions, we were able to synthesize extremely small nanoparticles (∼5 nm) of poly(3-hexylthiophene). This method has the potential to synthesize nanoparticles composed of other types of materials, such as nonconductive polymers and small molecules.

Size-controlled synthesis of polymer hollow nanoparticles using emulsion templates prepared by tandem acoustic emulsification

We have developed a new emulsion template method for the synthesis of poly(methylmethacrylate) (PMMA) hollow nanoparticles with different sizes. This synthetic method involves sequential ultrasonic irradiation (20 kHz → 500 kHz → 1.6 MHz → 2.4 MHz → 5.0 MHz) for acoustic emulsification of a water-insoluble fluorous solvent such as perfluoromethylcyclohexane (PFMCH) in an aqueous medium, followed by monomer (methylmethacrylate (MMA)) adsorption on the surface of the PFMCH emulsion droplets and photopolymerization of the adsorbed MMA in the obtained emulsion solution. Since the size of the PFMCH droplet templates can be tuned according to the number of steps of tandem acoustic emulsification, the obtained PMMA particle size can also be controlled. The subsequent removal of the core fluorous solvent by the heat treatment yielded size-controlled PMMA hollow nanoparticles and monodisperse PMMA hollow nanoparticles of different sizes. Furthermore, we confirmed that the substances could go in or go out of the hollow particles through the shells. Such a nice permeability is important for applications such as nanoreactors and drug delivery systems.

Ultrasonic nano-emulsification - A review

The emulsions with nano-sized dispersed phase is called nanoemulsions having a wide variety of applications ranging from food, dairy, pharmaceutics to paint and oil industries. As one of the high energy consumer methods, ultrasonic emulsification (UE) are being utilized in many processes providing unique benefits and advantages. In the present review, ultrasonic nano-emulsification is critically reviewed and assessed by focusing on the main parameters such pre-emulsion processes, multi-frequency or multi-step irradiations and also surfactant-free parameters. Furthermore, categorizing aposematic data of experimental researches such as frequency, irradiation power and time, oil phase and surfactant concentration and also droplet size and stability duration are analyzed and conceded in tables being beneficial to indicate uncovered fields. It is believed that the UE with optimized parameters and stimulated conditions is a developing method with various advantages.

Atom Transfer Radical Polymerization Enabled by Sonochemically Labile Cu-carbonate Species

Atom transfer radical polymerization (ATRP) has been previously mediated by ultrasound using a low concentration of copper complex in water (sono-ATRP) or by addition of piezoelectric materials in organic solvents (mechano-ATRP). However, these procedures proceeded slowly and yielded polymers contaminated by new chains initiated by hydroxyl radicals or by residual piezoelectrics. Unexpectedly, in the presence of sodium carbonate, rapid sono-ATRP of methyl acrylate in DMSO was achieved (80% conversion in <2 h) with excellent control of molecular weights and low dispersities (M_w/M_n < 1.2). The in situ formed Cu^II/L-CO₃ complex in the the presence of ultrasound generated Cu^I/L species as activators for ATRP and carbonate radical anions. The latter were scavenged by DMSO that was oxidized to dimethyl sulfone. This simple and robust process employs low-intensity ultrasound, air-stable Cu^II/L catalysts, and carbonate or bicarbonate salts (washing soda or baking soda) to prepare well-defined polyacrylates.

Combined ultrasonic and gamma-irradiation to prepare TiO2@PET-g-PAAc fabric composite for self-cleaning application

The grafting of polyacrylic acid (PAAc) onto the fabric of Poly(ethyleneterephthalate) (PET) was loaded with TiO₂ by a mixture sonication of TiO₂ dispersed in AAc dissolved in acetone solvent. Ultrasonic irradiation was utilized as a tool for a good dispersion of TiO₂ onto the PET fabric. The grafted PET fabrics with acrylic acid AAc monomer were successfully obtained using gamma-ray induced graft polymerization, the degree of grafting PET-g-PAAc fiber was 105%. The chemical compositions and crystal structure of grafted TiO₂@PET-g-PAAc fabrics were characterized by ATR-FTIR and XRD. It was found that loading of PET fiber with in TiO₂ particles showing the formation of anatase and rutile as performed by XRD. The thermal property of TiO₂@PET-g-PAAc was investigated by differential thermal analysis (DTA). The obtained result indicated the thermal property of the grafted TiO₂@PET-g-PAAc was increased. Image of scanning electron microscope (SEM) indicated the good adherent and good distribution of PAAc and TiO₂ with PET fabric. The self-cleaning property of TiO₂@PET-g-PAAc has been evaluated by using three kinds of dyes as models.

Surfactant-free synthesis of sub-100 nm poly(styrene-co-divinylbenzene) nanoparticles by one-step ultrasonic assisted emulsification/polymerization

The preparation of sub-100 nm surfactant-free polymeric nanoparticles was achieved via a new protocol that involves acoustic oil-in-water emulsification and concomitant free-radical polymerization of apolar monomers such as St and DVB.

Regulating the size and molecular weight of polymeric particles by 1,1-diphenylethene controlled soap-free emulsion polymerization

Nanoparticles with various sizes and molecular weights were produced via altering the amount of the monomer and DPE in the SFEP.

One-step synthesis of dual clickable nanospheres via ultrasonic-assisted click polymerization for biological applications

Dual clickable nanospheres (DCNSs) were synthesized in one step using an efficient approach of ultrasonic-assisted azide-alkyne click polymerization, avoiding the need of surfactants. This novel approach presents a direct clickable monomer-to-nanosphere synthesis. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and dynamic laser scattering (DLS) were used to characterize the synthesized DCNSs. Numerous terminal alkynyl and azide groups on the surface of DCNSs facilitate effective conjugation of multiple molecules or ligands onto a single nanocarrier platform under mild conditions. To exemplify the potential of DCNSs in biological applications, (1) multivalent glyconanoparticles (GNPs) were prepared by clicking DCNSs with azide-functionalized and alkyne-functionalized lactose sequentially for the determination of carbohydrate-galectin interactions with quartz crystal microbalance (QCM) biosensor. Using protein chip (purified galectin-3 coated on chip) and cell chip (Jurkat cells immobilized on chip), the QCM sensorgrams showed excellent binding activity of GNPs for galectins; (2) fluorescent GNPs were prepared by clicking DCNSs with azide-functionalized Rhodamine B and alkyne-functionalized lactose sequentially in order to target galectin, which is overexpressed on the surface of Jurkat cells. The fluorescent images obtained clearly showed the cellular internalization of fluorescent GNPs. This fluorescent probe could be easily adapted to drugs to construct lectin-targeted drug delivery systems. Thus, DCNSs prepared with our method may provide a wide range of potential applications in glycobiology and biomedicine.

Sonication-induced formation of size-controlled self-assemblies of amphiphilic Janus-type polymers as optical tumor-imaging agents

In this study, amphiphilic Janus-type polymers were synthesized via ring-opening metathesis polymerization (ROMP), multiple vicinal diol formation, and grafting of poly(ethylene glycol) monomethyl ether (mPEG). These amphiphilic polymers formed self-assemblies, which were a mixture of micelles and multimicellar aggregates, in water. By choosing suitable Janus-type polymers and irradiating an aqueous solution of polymers using a sonicator, either small micelles or large multimicellar aggregates were obtained selectively. Hydrophobic substituents controlled the aggregation-disaggregation behavior, leading to the formation of metastable self-assemblies by sonication. The formation of self-assemblies with a uniform size was affected by ultrasonic frequency, rather than power. In vivo optical tumor imaging revealed that the large-size multimicellar aggregates persisting for a long time in blood circulation slowly accumulated in tumor tissues. In contrast, the tumor site was rapidly, clearly visualized using the small-size micelles.

Preparation of W/O nanoemulsion using tandem acoustic emulsification and its novel utilization as a medium for phase-transfer catalytic reaction

We have successfully demonstrated that W/O nanoemulsion prepared by the tandem acoustic emulsification is extremely useful medium for enhancing the rate of phase-transfer catalytic reactions.