Can polymersomes form colloidosomes?

Hydroxy-functionalized polymersomes (or block copolymer vesicles) were prepared via a facile one-pot RAFT aqueous dispersion polymerization protocol and evaluated as Pickering emulsifiers for the stabilization of emulsions of n-dodecane emulsion droplets in water. Linear polymersomes produced polydisperse oil droplets with diameters of ～50 μm regardless of the polymersome concentration in the aqueous phase. Introducing an oil-soluble polymeric diisocyanate cross-linker into the oil phase prior to homogenization led to block copolymer microcapsules, as expected. However, TEM inspection of these microcapsules after an alcohol challenge revealed no evidence for polymersomes, suggesting these delicate nanostructures do not survive the high-shear emulsification process. Thus the emulsion droplets are stabilized by individual diblock copolymer chains, rather than polymersomes. Cross-linked polymersomes (prepared by the addition of ethylene glycol dimethacrylate as a third comonomer) also formed stable n-dodecane-in-water Pickering emulsions, as judged by optical and fluorescence microscopy. However, in this case the droplet diameter varied from 50 to 250 μm depending on the aqueous polymersome concentration. Moreover, diisocyanate cross-linking at the oil/water interface led to the formation of well-defined colloidosomes, as judged by TEM studies. Thus polymersomes can indeed stabilize colloidosomes, provided that they are sufficiently cross-linked to survive emulsification.     

Monodisperse w/w/w Double Emulsion Induced by Phase Separation

We develop an approach to fabricate monodisperse water-in-water-in-water (w/w/w) double emulsion in microfluidic devices. A jet of aqueous solution containing two incompatible solutes, dextran and polyethylene glycol (PEG), is periodically perturbed into water-in-water (w/w) droplets. By extracting water out of the w/w droplet, the solute concentrations in the droplet phase increase; when the concentrations exceed the miscibility limit, the droplet phase separates into two immiscible phases. Consequently, PEG-rich droplets are formed within the single emulsion templates. These PEG-rich droplets subsequently coalesce with each other, resulting in transiently stable w/w/w double emulsions with a high degree of size uniformity. These double emulsions are free of organic solvents and thus are ideal for use as droplet-vessels in protein purification, as microreactors for biochemical reactions, and as templates for fabrication of biomaterials.     

Synthesis of single‐core and multiple‐core core‐shell nanoparticles by RAFT emulsion polymerization: Lead sulfide‐copolymer nanocomposites

We report here a simple and direct route for the preparation of lead sulfide (PbS) quantum dots (QDs) embedded into polymeric nanospheres by emulsion polymerization. In this process, QDs are first dispersed in an aqueous solution containing a statistical oligomer constituted of five butyl acrylate and ten acrylic acid units prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a trithiocarbonate as RAFT agent. Then, the dispersion of PbS QDs is engaged into an emulsion polymerization process to form core‐shell nanoparticles. Transmission electron microscopy reveals the presence of single‐core core‐shell particles at low concentration of PbS QD, whereas multiple‐core core‐shell particles containing either well separated or aggregated PbS QDs are formed at high concentration of PbS QDs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Interface composition of multiple emulsions: rheology as a probe

We have investigated the dynamic rheological properties of concentrated multiple emulsions to characterize their amphiphile composition at interfaces. Multiple emulsions (W1/O/W2) consist of water droplets (W1) dispersed into oil globules (O), which are redispersed in an external aqueous phase (W2). A small-molecule surfactant and an amphiphilic polymer were used to stabilize the inverse emulsion (W1 in oil globules) and the inverse emulsion (oil globules in W2), respectively. Rheological and interfacial tension measurements show that the polymeric surfactant adsorbed at the globule interface does not migrate to the droplet interfaces through the oil phase. This explains, at least partly, the stability improvement of multiple emulsions as polymeric surfactants are used instead of small-molecule surfactants.     

Highly magnetic latexes from submicrometer oil in water ferrofluid emulsions

The synthesis of functionalized submicrometer magnetic latex particles is described as obtained from a preformed magnetic emulsion composed of organic ferrofluid droplets dispersed in water. Composite (polystyrene/γ‐Fe₂O₃) particles were prepared according to a two‐step procedure including the swelling of ferrofluid droplets with styrene and a crosslinking agent (divinyl benzene) followed by seeded emulsion polymerization with either an oil‐soluble [2,2′‐azobis(2‐isobutyronitrile)] or water‐soluble (potassium persulfate) initiator. Depending on the polymerization conditions, various particle morphologies were obtained, ranging from asymmetric structures, for which the polymer phase was separated from the inorganic magnetic phase, to regular core–shell morphologies showing a homogeneous encapsulation of the magnetic pigment by a crosslinked polymeric shell. The magnetic latexes were extensively characterized to determine their colloidal and magnetic properties. The desired core–shell structure was efficiently achieved with a given styrene/divinyl benzene ratio, potassium persulfate as the initiator, and an amphiphilic functional copolymer as the ferrofluid droplet stabilizer. Under these conditions, ferrofluid droplets were successfully turned into superparamagnetic polystyrene latex particles, about 200 nm in size, containing a large amount of iron oxide (60 wt %) and bearing carboxylic surface charges. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2642–2656, 2006     

A review of: “Nineteenth Century Attitudes: Men of Science (Chemists and Chemistry Series,Vol. 13)”. Sydney Ross. Kluwer Academic Publishers; Dordrecht, 1991. pp. xi+235. $69.00.

Abstract

The potential of polytetrafluoroethylene (PTFE) membranes as water‐in‐oil (W/O) emulsification devices was investigated to obtain uniformly sized droplets and to convert them into microcapsules and polymer particles via subsequent treatments. Uniform W/O emulsion droplets have not been achieved using glass membranes unless the membrane was rendered hydrophobic by treatment with silanes. If a PTFE membrane is capable of providing uniform droplets for a W/O emulsion, a coordinated membrane emulsification system can be established since glass membranes have been so successful for O/W (oil‐in‐water) emulsification. In order to examine the feasibility of PTFE membrane emulsification, O/W and W/O emulsion characteristics prepared using PTFE membranes were compared with those prepared by the conventional SPG (Shirasu porous glass) membrane emulsification method. A 3 wt.% sodium chloride solution was dispersed in kerosene using a low HLB surfactant. Effects of the membrane pore size, permeation pressure, and the type of emulsifiers and concentration on the droplet size and on the size distribution (CV, coefficient of variation) were investigated. The CV of the droplets was fairly low, and the average droplet size was correlated with the critical permeation pressure of the dispersed phase, revealing that the PTFE membrane could be used as a one‐pass membrane emulsification device. Low CV values were maintained with a Span 85 (HLB = 1.8) concentration, 0.2–5.0 wt.% and a range of HLB from 1.8–5.0. For a brief demonstration of practical applications, nylon‐6,10 microcapsules prepared by interfacial polycondensation and poly(acrylamide) hydrogels from inverse suspension polymerization are illustrated.     

Surfactant‐free synthesis of amphiphilic diblock copolymer in aqueous phase by a self‐stability process

Amphiphilic polymeric particles with hydrophobic cores and hydrophilic shells were prepared via living radical emulsion polymerization of styrene using a water‐soluble poly(acrylamide)‐based macro‐RAFT agent in aqueous solution in the absence of any surfactants. Firstly, the homopolymerization of acrylamide (AM) was carried out in aqueous phase by reversible addition‐fragmentation chain transfer radical polymerization (RAFT) using a trithiocarbonate as a chain transfer agent. Then the PAM‐based macro‐RAFT agent has been used as a water‐soluble macromolecular chain transfer agent in the batch emulsion polymerization of Styrene (St) free of surfactants. The RAFT controlled growth of hydrophobic block led to the formation of well‐defined poly(acrylamide)‐copolystyrene amphiphilic copolymer, which was able to work as a polymeric stabilizer (self‐stability). Finally, very stable latex was prepared, having no visible phase separation for several months. FTIR and ¹H‐NMR measurements showed that the product was the block copolymer PAM‐co‐PS in the form of stable latex. Atomic force microscope (AFM), transmission electron microscope (TEM), and dynamic light scattering (DLS) studies indicated that the nanoparticles have a narrow particle size distribution and the average particle hydrodynamic radius was kept in the diameter of 58 nm. Core‐shell structure of the copolymer was also recorded by TEM. The mechanism of the self‐stability of polymer particles during the polymerization in the absence of surfactants was studied. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3098–3107, 2008     

Synthesis of polymer–inorganic patchy microcapsules with tunable patches

We introduce a facile and versatile approach for the formation of ball-like polymer–inorganic patchy microcapsules with a tunable shell by combining sol–gel chemistry of silica precursor and phase separation between the polymer and the precursor. Firstly, chloroform-in-water emulsion droplets containing poly(methyl methacrylate) (PMMA), silica precursor [tetraethyl orthosilicate (TEOS)] and co-surfactant sodium dioctyl sulfosuccinate (Aerosol OT or AOT) were prepared by shaking the mixture by hand. Due to the added AOT, water molecules diffuse into the chloroform droplets, and the tiny water droplets would coalesce gradually, triggering the formation of double emulsion droplets. Upon further solvent evaporation, the concentration of the polymer and the silica precursor in the oil shell of the double emulsions increases, leading to the phase separation between the polymer and the precursors (and partially formed silica through the hydrolysis and condensation of TEOS). Because of the confined geometry of the oil shell in the double emulsions, polymeric disc-like structures, stabilized by AOT, were dispersed in the silica precursors. Meanwhile, the silica precursor hydrolyzed and condensed when brought in contact with the aqueous solution, ultimately leading to the formation of a mineralized shell around the polymer domains and the hybrid patchy microcapsules. Effect of synthesis conditions, such as the amount of TEOS, AOT, and PMMA used, the pH value, and solvent evaporation rate on interfacial behavior of the solvent/water; and the morphology of the patchy microcapsules were investigated. Patchy microcapsules with tunable patch size and shape can be generated through tailoring the experimental parameters. Our study indicates that the hybrid patchy microcapsules can be formed by taking advantage of the sol–gel chemistry and the phase separation process, and the underlying generality of the synthesis procedure allows for a variety of applications, including drug storage, coatings, delivery, catalysis, and smart building blocks in self-assembling systems.     

Preparation of monodisperse crosslinked polymelamine microcapsules by phase separation method

Monodisperse polymelamine microcapsules were prepared by phase separation method. Control of microcapsule diameter was investigated using the uniform-sized oil-in-water emulsion droplets as the capsule core. The monodisperse emulsion droplets were prepared using the Shirasu porous glass (SPG) membrane emulsification technique. The effects of the diameter of the oil droplet and concentration of sodium dodecyl sulfate (SDS), which is a typical emulsifier in SPG membrane emulsification, on microencapsulation were investigated. The microcapsules were aggregated when oil droplets with small size were microencapsulated at high SDS concentration. To reduce the SDS concentration, the creamed emulsion was used. The monodisperse polymelamine microcapsules were successfully prepared by using the creamed emulsion. The microcapsule diameter was almost similar to the diameter of the encapsulated oil droplet. The coefficient of variation values was about 10% for all microcapsules prepared in this study. Control of microcapsule diameter was achieved in the range of 5–60 μm.     

Versatile Preparation of Nonspherical Multiple Hydrogel Core PAM/PEG Emulsions and Hierarchical Hydrogel Microarchitectures

The preparation of nonspherical materials composed of separated multicomponents by droplet‐based microfluidics remains a challenge. Based on polymerization‐induced phase separation and droplet coalescence in microfluidics, we prepared emulsions of variously shaped PAM/PEG core/shell droplets and hydrogels composed of two separated components, which show flexible and transformable hierarchical structures and microarchitectures. We find that AM/PEG aqueous droplets form a core/shell structure after polymerization resulting from phase separation. Thus multicore/shell droplets are easily produced by coalescence of core/shell structures. By changing the polymerization temperature and the flow rate, the morphology of the multicore droplets and the hydrogel can be easily adjusted. The hydrogels exhibit apparent anisotropy and different protein release rates depending on their structures. The preparation technique is simple and versatile and the resulting hydrogels have potential applications in many fields.     

Preparation of PEG-modified urethane acrylate emulsion and its emulsion polymerization

In order to improve stability and reduce droplet size, the PEG-modified urethane acrylates were synthesized by the reaction of polyethylene glycol (PEG) with residual isocyanate groups of urethane acrylate to incorporate hydrophilic groups into the molecular ends. The droplet sizes of the PEG-modified urethane acrylate emulsions were much smaller than those of unmodified urethane acrylate emulsions at the same surfactant composition, and the droplet sizes of these emulsions were significantly effected not by surfactant compositions and types, but by the reaction molar ratio of PEG, because the urethane acrylate containing polyoxyethylene groups as terminal groups aided the interfacial activity of surfactant molecules and acted as a polymeric surfactant. The actions of PEG-modified urethane acrylate were confirmed by the investigation of adsorption of urethane acrylate in a water/benzene interface.For polymerization of emulsions, the stability of emulsion in the process of emulsion polymerization was changed by the type of surfactant or initiator. In the case of emulsion polymerization with a water soluble initiator (K₂S₂O₈), the emulsions prepared using TWEEN 60 were broken in the process of polymerization. However, polymerization of these emulsions could be carried out using an oil soluble initiator (AIBN). The conversion of emulsion polymerization changed with the type of urethane acrylates, that is, the reaction molar ratio of PEG to 2-HEMA.     

Amphiphilic polysaccharides: useful tools for the preparation of nanoparticles with controlled surface characteristics

Polymeric surfactants obtained by hydrophobic modification of dextran are used as stabilizers for oil-in-water emulsions. The kinetics of interfacial tension decrease is studied as a function of polymer structural characteristics (degree of hydrophobic substitution) and at various polymer concentrations. Several hydrocarbon oils, either aliphatic (octane, decane, dodecane, and hexadecane) or aromatic (styrene), are tested. Kinetics exhibits the same general trends no matter which oil or polymer is considered. The emulsifying properties of the polymeric surfactants are illustrated by the preparation of oil-in-water emulsions. The droplet size at the preparation is correlated to the amount of oil and to the polymer concentration in the aqueous phase. For low polymer/oil ratios, it is shown that the droplet size is limited by the initial amount of polymer. On the contrary, for high polymer/oil ratios, the droplet size seems to level down, indicating that other parameters become predominant. Emulsion aging occurs by Ostwald ripening, and it is demonstrated that the theoretical equation of Lifshitz, Slyozov, and Wagner (LSW) correctly describes the experimental results. The nature of the oil has important effects on emulsion aging, as described by the LSW equation. The aging of emulsions containing oil mixtures is quantitatively described on the basis of the results with pure oils. The influence of polymer chemical structure can be conveniently correlated to interfacial tension results through the LSW equation. On the contrary, the influence of oil volume fraction seems to be overestimated by the usual correction factor, k(phi). The effect of temperature on emulsion aging is finally examined. Miniemulsions stabilized with dextran derivatives are used for the radical polymerization of styrene. Following this procedure, polysaccharide-covered polystyrene nanoparticles are prepared and characterized (size and surface coverage). The size of the particles is directly correlated to that of the initial droplets for styrene volume fractions around 10%. On the contrary, for initial styrene volume fractions around 20%, particles exhibit a larger size than the initial droplets, indicating that coalescence processes take place during polymerization. The amount of dextran at the surface of the particles is determined and compared to the adsorbed amounts resulting from emulsion preparation.     

Nano‐emulsion use for the synthesis of polyaniline nano‐grains or nano‐fibers

We report that nano‐emulsions can be creatively used as a morphology selective synthesis method to prepare not only nano‐grains but also nano‐fibers with high selectivity. Synthesis of the two different morphological materials was demonstrated using polyaniline synthesis as a model case. Polyaniline nano‐grains were synthesized from aniline molecules in nano‐size aqueous droplets as polymerization sites whose droplets were generated by inverse water‐in‐oil nano‐emulsion use, and polyaniline nano‐fibers were synthesized from aniline in aqueous nano‐dimensional channels as polymerization sites whose channels were generated by direct oil‐in‐water nano‐emulsion use containing high population of oil droplets. Using the approaches, we successfully synthesized nano‐fibers of 60 nm diameter with 0.5 µm length and also nano‐grains having diameter of 60–80 nm. The two different polymerization sites of nano‐scale dimension were made by changing the ratio among surfactant, aqueous aniline/HCl solution, and oil, i.e. organic solvent. We found the nano‐fibers synthesized from the channels formed by the direct oil‐in‐water nano‐emulsion have higher bulk electrical conductivity than the nano‐grains which were synthesized from the droplets formed by the inverse water‐in‐oil emulsion. We also found that the emulsion use allows us to use a room temperature synthesis unlike conventional synthesis methods which require to use ice bath temperature. Physical properties of both nano‐fibers and nano‐grains synthesized were characterized by Fourier transform infrared (FTIR), UV–Vis spectra, scanning electron microscopy (SEM), and four probes conductivity measurement. Copyright © 2009 John Wiley & Sons, Ltd.     

Fabrication of "hairy" colloidosomes with shells of polymeric microrods

Novel colloidosome microcapsules with aqueous gel cores and integral shells of rodlike polymeric particles have been prepared and characterized. The synthesis is based on templating water-in-oil emulsions stabilized by rodlike particles followed by gelling of the aqueous phase, dissolution of the oil phase in ethanol, and redispersion of the obtained colloidosome capsules in water. Such capsules may find applications as vehicles for delivery and controlled release of drugs, cosmetics, and food supplements.     

Effect of the presence of polymer in miniemulsion droplets on the kinetics of polymerization

Solution of polystyrene in styrene were dispersed in an aqueous gel phase comprising sodium lauryl sulfate, cetyl alcohol, and water using an emulsification process known to produce monomer droplet sizes inthe submicron size range (referred to as miniemulsion droplets). The shelf-life stabilities of these miniemulsions were studied to determine their relative droplet sizes, and the emulsions were concommitantly polymerized in an isothermal batch reaction calorimeter. The polymerization kinetics and final particle sizes produced were compared with miniemulsion and conventional emulsion polymerizations prepared using equivalent recipes without the addition of polystyrene. The results indicate that polymerization of miniemulsions prepared from polymer solutions produce significantly different kinetics than both miniemulsion and conventional emulsion polymerizations. In general, a small amount of polymer greatly increases the rate of polymerization and the final number of particles produced in the polymerization to the extent where even conventional polymerizations carried out above the critical micelle concentration of the surfactant polymerize more slowly. The results are explained by considering the system to be comprised of small, stable pre-formed monomer-swollen polymer particles which are able to efficiently capture aqueous phase radicals. This enables the system to produce a large final number of particles, similar to the initial number of pre-formed polymer particles, as opposed to miniemulsions and micelles in which only a relatively small fraction of the initial number of species (droplets or micelles) become polymer particles. © 1994 John Wiley & Sons, Inc.     

Fractional crystallization of oil droplets in O/W emulsions dispersed by Synperonic F127

The aim of this works is to study an oil-in-water emulsion stabilized with a triblock copolymer Synperonic F127 which presents a double size distribution of oil droplets. The emulsions were studied experimentally by means of differential scanning calorimetry (DSC) and dynamic light scattering (DLS). The DSC analysis was carried out focusing on the cooling behavior of the emulsion. The cooling thermograms of the oil-in-water emulsion revealed two crystallization peaks with Gaussian profile; the interesting characteristic is that both peaks are separated in temperature. In accordance to previous works for a single oil dispersed within an aqueous phase, the DSC technique must show a single Gaussian peak of crystallization attributable to a size distribution of droplets. In the present case of emulsions stabilized with 1 g/L of Synperonic F127, the aggregation behavior of triblock as a function of temperature allows to produce an emulsion with a double size droplet distribution. Comparison with emulsions stabilized with 2 and 4 wt% of non-ionic Tween 20 are also presented.     

Polymerization of electric field-centered double emulsion droplets to create polyacrylate shells

Porous and hollow particles are widely used in pharmaceuticals, as solid phases for chromatography, as catalyst supports, in bioanalytical assays and medical diagnostics, and in many other applications. By controlling size, shape, and chemistry, it is possible to tune the physical and chemical properties of the particles. In some applications of millimeter-scale hollow shells, such as in high energy density physics, controlling the shell thickness uniformity (concentricity) and roundness (sphericity) becomes particularly important. In this work, we demonstrate the feasibility of using electric field-driven droplet centering to form highly spherical and concentric polymerizable double emulsion (DE) droplets that can be subsequently photopolymerized into polymer shells. Specifically, when placed under the influence of an ～6 × 10(4) V(rms)/m field at 20 MHz, DE droplets, consisting of silicone oil as the inner droplet and tripropylene glycol diacrylate with a photoinitiator in N,N-dimethylacetamide as the outer droplet, suspended in ambient silicone oil, were found to undergo electric field-driven centering into droplets with ≥98% sphericity and ～98% concentricity. The centered DE droplets were photopolymerized in the presence of the electric field. The high degrees of sphericity and concentricity were maintained in the polymerized particles. The poly(propylene glycol diacrylate) capsules are just within the sphericity requirements needed for inertial confinement fusion experiments. They were slightly outside the concentricity requirement. These results suggest that electric field-driven centering and polymerization of double emulsions could be very useful for synthesizing hollow polymer particles for applications in high energy density physics experiments and other applications of concentric polymer shells.     

Highly concentrated emulsified microemulsions as solvent-free plant protection formulations

Effective plant protection agents are readily available and well implemented in industry. However, delivery to the plant and application on the leaf are processes that still need to be optimized. Up to now plant protection formulations represent either emulsion or suspension concentrates that often contain environmentally harmful organic solvents and/or adjuvants. Emulsified microemulsions are hierarchically organized systems comprising emulsion droplets that confine a water-in-oil microemulsion. In the present contribution we show that emulsified microemulsions prepared from environmentally friendly components can be loaded with the plant-protection agent Fenpropimorph® up to 48 wt.% without organic solvent. The emulsion itself is highly concentrated, containing 60 wt.% of dispersed phase, and can be readily diluted with water for spraying in farming applications. Small-angle X-ray measurements reveal the existence of a water-in-Fenpropimorph® microemulsion confined inside the emulsion droplets. Dynamic light scattering shows that the emulsions prepared are monomodal, comprising droplet radii in the hundred nanometer range.     

Designer polymer-based microcapsules made using microfluidics

Filled microcapsules made from double emulsion templates in microfluidic devices are attractive delivery systems for a variety of applications. The microfluidic approach allows facile tailoring of the microcapsules through a large number of variables, which in turn makes these systems more challenging to predict. To elucidate these dependencies, we start from earlier theoretical predictions for the size of double emulsions and present quantitative design maps that correlate parameters such as fluid flow rates and device geometry with the size and shell thickness of monodisperse polymer-based capsules produced in microcapillary devices. The microcapsules are obtained through in situ photopolymerization of the middle oil phase of water-in-oil-in-water double emulsions. Using polymers with selected glass transition temperatures as the shell material, we show through single capsule compression testing that hollow capsules can be prepared with tunable mechanical properties ranging from elastomeric to brittle. A quantitative statistical analysis of the load at rupture of brittle capsules is also provided to evaluate the variability of the microfluidic route and assist the design of capsules in applications involving mechanically triggered release. Finally, we demonstrate that the permeability and microstructure of the capsule shell can also be tailored through the addition of cross-linkers and silica nanoparticles in the middle phase of the double emulsion templates.     

Molecular Watchmaking: ab initio Emulsion Polymerization by RAFT-controlled Self-assembly

Controlled radical polymerization using RAFT has the potential to make polymers with virtually any desired molecular architecture. For this to be implemented on an industrial scale, it must be performed by polymerization in disperse media. However, simply adding a RAFT agent to a conventional emulsion polymerization recipe leads to a loss of molecular weight control and formation of coagulum, probably because of nucleation in droplets, which is normally an unlikely phenomenon in emulsion polymerizations. Recently, a method has been devised for implementing RAFT in ab initio emulsion polymerization that avoids droplets in the particle formation stage. The molecular weight distribution of the polymer thus formed shows that molecular weight control is maintained throughout the polymerization. A model is developed to predict the particle size formed in this new type of emulsion polymerization. The new methodology enables synthesis of novel dispersions where molecular architecture can be precisely controlled, such as structured core-shell particles.