Reverse micelles: inert nano-reactors or physico-chemically active guides of the capped reactions

Reverse micelles present self-assembled multi-molecular entities formed within specific compositional ranges of water-in-oil microemulsions. The structure of a reverse micelle is typically represented as nano-sized droplet of a polar liquid phase, capped by a monolayer of surfactant molecules, and uniformly distributed within a non-polar, oil phase. Although their role in serving as primitive membranes for encapsulation of primordial self-replicating chemical cycles that anticipated the very origins of life has been proposed, their first application for 'parent(hesis)ing' chemical reactions with an aim to produce 'templated' 2D arrays of nanoparticles dates back to only 25 years ago. Reverse micelles have since then been depicted as passive nano-reactors that via their shapes template the growing crystalline nuclei into narrowly dispersed or even perfectly uniform nano-sized particles. Despite this, numerous examples can be supported, where from deviations from the simple unilateral correlations between size and shape distribution of reverse micelles and the particles formed within may be reasonably implied. A rather richer, dynamical role of reverse micelles, with potential significance in the research and design of complex, self-assembly synthesis pathways, as well as possible adoption of their application as an aspect of biomimetic approach, is suggested herein.     

Surface-modified hemispherical polystyrene/polybutyl methacrylate composite particles

Micrometer-sized polystyrene/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73 degrees C within the template microspheres. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, XPS, advancing contact angle, light microscope, SEM, and cross-sectional TEM. Selective surface functionalization of the poly(n-butyl methacrylate) phase of the composite particles was performed by carrying out a similar swelling and polymerization process in the presence of a water-soluble vinylic monomer such as acrylamide.     

“EMULSION COPOLYMER THEORY: KINETICS AND SEQUENCE DISTRIBUTIONS”

Gelatin is well suited in the preparation of nanosize particles by precipitation of organic substances. Due to their amphiphilic structure, the gelatin molecules exhibit a pronounced surface activity. The surface activity was investigated by means of the Wilhelmy plate and the maximum bubble pressure technique within a time frame of more than five orders of magnitude. The influence of an emulsifier and the gelatin/emulsifier interaction are discussed. By means of laser Doppler electrophoresis, the electrophoretic mobility of A-type and B-type gelatin is measured. The molecular weight distribution of gelatin is measured by size exclusion chromatography. The size of dissolved and adsorbed gelatin molecules is determined by means of dynamic light scattering. It is shown that the surface activity of the gelatin/emulsifier complexes controls the size of the precipitated particles. Furthermore, we show that gelatin is adsorbed by hydrophobic interactions and provides excellent colloidal stability to nanosize particles.     

Polymer–TiO2 composite nanorattles via RAFT‐mediated emulsion polymerization

In this work, successful synthesis of polymer nanorattles containing titanium dioxide pigment particles in the centers of air voids is reported. The method used amphiphilic macro‐RAFT copolymers as stabilizers for pigment dispersion and the subsequent encapsulation of the pigment with polymer. The particles were first encapsulated by a water swellable hydrophilic layer, followed by a hard hydrophobic layer. Nanorattles were formed by swelling of hydrophilic polymer layers on the surface of the encapsulated pigment particles in a basic solution at elevated temperature. After swelling, the outer hard polymer shell was crosslinked to improve its strength. Air void sizes of the nanorattles were found to be controlled by swelling time, temperature, and the hydrophilic polymer layer thickness. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of micrometer‐sized homo and composite polyacrylonitrile particles of narrow size distribution on the basis of single‐step swelling of uniform polystyrene template microspheres

Polyacrylonitrile/polystyrene micrometer‐sized composite particles of narrow size distribution were prepared by a single‐step swelling of uniform polystyrene template microspheres with emulsion droplets of methylene chloride containing the monomer acrylonitrile and the initiator benzoyl peroxide. Methylene chloride was then evaporated carefully, followed by polymerization of acrylonitrile at 70 °C within the shrunken template particles. Polymerization of acrylonitrile also occurred at the particles' surface due to the interaction of surface polyacrylonitrile oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform polyacrylonitrile particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, TGA‐DSC, XRD, XPS, advancing contact angle, light microscope, SEM and cross‐sectional TEM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4847–4861, 2004     

Synthesis and characterization of micrometer‐sized particles of narrow size distribution with chloromethyl functionality on the basis of single‐step swelling of uniform polystyrene template microspheres

Polystyrene template microspheres of 1.4 ± 0.1 μm were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2‐methoxy ethanol. These template particles were then swelled at room temperature in a single step with emulsion that was prepared in sodium dodecyl sulfate aqueous solution from a swelling solvent (dibutyl phthalate) containing the initiator (benzoyl peroxide) and monomer(s) (chlormethylstyrene, divinylbenzene, or ethylene dimethacrylate). Composite uniform particles composed of the template polystyrene and noncrosslinked or crosslinked polychloromethylstyrene were prepared by polymerizing the monomer(s) within the swelled particles at 73 °C. Crosslinked uniform polychloromethylstyrene particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. The influence of various reaction parameters, such as dibuthyl phthalate concentration, chloromethylstyrene concentration, crosslinker type and concentration, and so forth on the molecular weight, size, size distribution, shape, morphology, surface area, and decomposition temperature of the particles was investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1342–1352, 2002     

Hydrophobic, organically dispersible gold nanoparticles of variable shape produced by the spontaneous reduction of aqueous chloroaurate ions by hexadecylaniline molecules

In addition to control over the size and monodispersity of nanoparticle, nanomaterial synthesis procedures are increasingly required to control their shape and assembly as well. We demonstrate in this paper synthesis of organically dispersible, hydrophobic gold nanoparticles of spherical shape and encased in triangular thin polyaniline shells by doing reaction under static conditions and assembly of these particles onto polymer nanorod/nanowire-like templates by varying the molar ratio of chloroaurate ions to hexadecylaniline and varying the solvent by the spontaneous reduction of aqueous chloroaurate ions by hexadecylaniline molecules in a biphasic reaction setup. Under stationary conditions (no stirring), a biphasic mixture of hexadecylaniline in toluene and chloroaurate ions in water leads to the electrostatic complexation of chloroaurate ions with hexadecylaniline at the liquid-liquid interface and their phase transfer into the organic phase, followed by their reduction by the hexadecylaniline molecules. By varying the conditions, the templating action of gold nanoparticles or the polyaniline nanodispersions can be tuned in the organic medium and resulting assembly.     

Fabrication of tailorable pH responsive cationic amphiphilic microgels on a microfluidic device for drug release

Cationic, amphiphilic microgels of differing compositions based on hydrophilic, pH, and thermoresponsive 2‐(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic, nonionic n‐butyl acrylate (BuA) are synthesized using a lab‐on‐a‐chip device. Hydrophobic oil‐in‐water (o/w) droplets are generated via a microfluidic platform, with the dispersed (droplet) phase containing the DMAEMA and BuA, alongside the hydrophobic cross‐linker, ethylene glycol dimethacrylate, and a free radical initiator in an organic solvent. Finally, the hydrophobic droplets are photopolymerized via a UV light source as they traverse the microfluidic channel to produce the cationic amphiphilic microgels. This platform enables the rapid, automated, and in situ production of amphiphilic microgels, which do not match the core‐shell structure of conventionally prepared microgels but are instead based on random amphiphilic copolymers of DMAEMA and BuA between the hydrophobic cross‐links. The microgels are characterized in terms of their swelling and encapsulation abilities, which are found to be influenced by both the pH response and the hydrophobic content of the microgels. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 59–66     

Synthesis and characterization of ferromagnetic Fe3C/C composite nanoparticles as a catalyst for carbon nanotube growth

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. These template particles dispersed in aqueous solution have been used for the entrapment of ferrocene by a swelling process of methylene chloride emulsion droplets containing ferrocene within these particles, followed by evaporation of methylene chloride. The effects of CH₂Cl₂ volume and the [CH₂Cl₂]/[FeC₁₀H₁₀] (w/w) ratio on the size and size distribution of the swollen template particles were elucidated. Air-stable Fe₃C nanoparticles embedded in amorphous carbon matrix (Fe₃C/C) have been prepared by thermal decomposition of the ferrocene-swollen template polystyrene particles at 500 °C for 2 h in a sealed cell. Decomposition of these swollen template particles for 2 h at higher temperatures led to the formation of carbon nanotubes (CNTs) in addition to the Fe₃C/C composite nanoparticles. The yield of the CNTs increased as the annealing temperature was raised. An opposite behavior was observed for the diameter of the formed CNTs. The size and size distribution, crystallinity, and magnetic properties of the different Fe₃C/C composite nanoparticles have also been controlled by the annealing temperature.     

Solidification of non-halogen fire-retardant liquids by encapsulation within porous uniform PDVB microspheres for preparation of fire-retardant polymeric blends

Polystyrene/polydivinyl benzene (PS/PDVB) composite microspheres of narrow size distribution were prepared by a single-step swelling process of uniform PS microspheres with DVB and benzoyl peroxide, followed by polymerization of DVB within the microspheres. Dissolution of the PS template resulted in porous uniformly sized PDVB microspheres. New, solid, non-halogenated, fire-retardant composite microspheres of narrow size distribution were prepared by encapsulation of resorcinol bis (diphenyl phosphate) (RDP) within the pores of the PDVB microspheres. The encapsulation was performed by two different methods as follows: (1) vacuum and (2) heat/cool cycles. The loading capacity of the RDP into the PDVB particles was elucidated. PS/PDVB-RDP blends were prepared by mixing PS with the PDVB-RDP microspheres. Thermogravimetric analysis (TGA) illustrated that the thermal stability of the PS increases as the content (10–40 %) of the PDVB-RDP increased. Polycarbonate/poly(acrylonitrile-butadiene-styrene)/PDVB-RDP (PC/ABS/PDVB-RDP) blends were prepared by melting PC/ABS together with the PDVB-RDP microspheres at 250 °C and then pelleting it in an injection molding machine at 250 °C and 40 t. The improved thermal stability of the PC/ABS by blending it with PDVB-RDP was demonstrated by a vertical burn test on PC/ABS/PDVB-RDP bones.     

Vapour-growth of Sn on stearic acid molecular layers

Tin metal was vacuum deposited at room temperature on to Langmuir–Blodgett (LB) films with surfaces of either hydrophilic head groups or hydrophobic tail groups. Different growth modes on different surfaces of the LB films were observed with an atomic force microscope. Fine Sn particles deposited on the hydrophobic surface were uniform in size and similar in shape, but on the hydrophilic surface large Sn particles were observed. Chemical interactions between organic functional groups and deposited metal seems critical for the manner of crystal growth. The possibility of control over the crystallization of metals using two-dimensionally assembled organic molecules is demonstrated.     

Synthesis of nonspherical colloidal particles with anisotropic properties

We describe a promising and flexible technique for fabricating uniform nonspherical particles with anisotropic phase and surface properties. Our approach is based on the seeded polymerization technique in which monomer-swollen particles are polymerized. The polymerization causes a phase separation to occur, giving rise to two-phase nonspherical particles. We show that the elastic contraction of the swollen polymer particles induced by elevated polymerization temperatures plays an important role in the phase separation. Moreover, chemical anisotropy of nonspherical particles can be obtained by using immiscible polymer pairs and by employing surface treatments. Furthermore, we are able to produce amphiphilic dumbbell particles consisting of two different bulbs: hydrophilic poly (ethylene imine)-coated polystyrene and hydrophobic polystyrene. Controlled geometries of these amphiphilic nonspherical particles will allow a wide range of potential applications, such as engineered colloid surfactants.     

Development of PEG-PLA/PLGA microparticles for pulmonary drug delivery prepared by a novel emulsification technique assisted with amphiphilic block copolymers

We developed a novel "spray dry-based" method for preparing surface-modified particle via "block copolymer-assisted" emulsification/evaporation for pulmonary drug delivery. The method included three steps: (1) o/w emulsion containing both hydrophobic polymers and amphiphilic block copolymers was obtained by emulsification of water and a polymer-containing organic solvent, (2) the o/w emulsion was misted with a nebulizer, and (3) the emulsion mists were dried by a heater. In this way, the hydrophobic polymers and the hydrophobic part of the amphiphilic block copolymers gradually tangled during the evaporation of organic solvents from the o/w emulsion. Consequently, the hydrophilic polymer chain was introduced on the particle surface. The particle surface can be easily modified although there are no reactive groups in the hydrophobic polymer molecules. We successfully obtained dry PEG-PLA/PLGA microparticles by controlling the weight ratio of the block copolymer and the hydrophobic polymer. The introduction of PEG to the particle surface involves an increase in the Zeta potential of the particles. Interestingly, the "dimpled" microparticles having a diameter of approximately 2 μm were obtained. The "dimpled" microparticles can serve as drug carriers for pulmonary drug delivery, because the particles have a large surface area. We expect that this novel surface-modification technique will enable efficient fabrication of particles in drug delivery systems.     

Effect of packing parameter on phase diagram of amphiphiles: an off-lattice Gibbs ensemble approach

We determine the phase diagram of several amphiphilic molecules as a function of the amphiphilic parameter alpha defined as the ratio of the volume of hydrophilic to hydrophobic segments using the Gibbs ensemble Monte Carlo method supplemented by configurational bias scheme. Specifically, we study amphiphilic molecules h(1)t(7), h(2)t(6), and h(3)t(5), for which alpha=0.14, 0.33, and 0.60 respectively, and demonstrate that the former two exhibit phase separation while h(3)t(5) forms micelles, supporting the contention that alpha=0.5 is the border line for phase separation and micellization, as observed in previous lattice Monte Carlo studies [Panagiotopoulos et al., Langmuir 18, 2940 (2002)]. Further, we study the phase separation in amphiphilic molecules as a function of the packing parameter by varying the size of the hydrophilic head for each molecule. We find that a larger hydrophilic head lowers the critical temperature T(c), and raises the critical density rho(c).     

Amphiphilic PEG/alkyl‐grafted comb polylactides

Amphiphilic polylactides (PLAs) with well‐defined architectures were synthesized by ring‐opening polymerization of AB monomers (glycolides) substituted with both a long chain alkyl group and a triethylene glycol segment terminated in either a methyl or benzyl group. The resulting amphiphilic PLAs had number average molecular weights >100,000 g/mol. DSC analysis revealed a first‐order phase transition at ～ 20 °C, reflecting the crystalline nature of the linear alkyl side chains. Polymeric micelles were prepared by the solvent displacement method in water. Dynamic light scattering measurements support formation of a mixture of 20‐nm‐diameter unimolecular micelles and 60‐nm particles comprised of an estimated 25 polymer molecules. UV–vis characterization of micelles formed from acetone–water solutions containing azobenzene confirmed encapsulation of the hydrophobic dye, suggesting their potential as new amphiphilic PLAs as drug delivery vehicles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5227–5236, 2007     

Amphiphilicity-driven organization of nanoparticles into discrete assemblies

We present a method for organizing metallic nanoparticles in solution that is based on the hydrophobic effect and does not require either hydrogen bonding or molecular recognition. When amphiphilic V-shaped molecules are attached to a gold cluster, an aggregation process ensues in aqueous solution and leads to the formation of well-defined cylindrical and vesicular nanoarrays of particles. The metallic clusters densely pack at the boundary separating the hydrophobic core from the hydrophilic corona of the hybrid micelle-like aggregates. This design allows one to assemble and disassemble the nanoparticles in a reversible manner and control the size and the morphology of the arrays by changing the conditions of the solution preparation. The versatility of this method is demonstrated by its applicability to different metals with covalently attached amphiphilic arms with various chemical compositions (PS-PEO and PB-PEO) and molecular weights.     

Oxidation-sensitive polymeric nanoparticles

We have recently demonstrated the possible use of organic polysulfides for the design of oxidation-sensitive colloidal carriers in the form of polymeric vesicles, which are particularly suitable for the encapsulation of hydrosoluble drugs. In the present research we extend our efforts to carriers specifically suitable for hydrophobic molecules. Exploiting the living emulsion polymerization of episulfides, we have produced new cross-linked polysulfide nanoparticles. Here we demonstrate how this process allows the production of stable nanoparticles with a good control over their size and functionality. The nanoparticles showed negligible cytotoxicity on a fibroblast model; furthermore, they exhibited sensitivity to oxidative conditions, which first produce swelling and then solubilize the material.     

Interfacial water on hydrophobic surfaces recognized by ions and molecules

Recent spectrophotometric and molecular dynamics simulation studies have shown that the physicochemical properties and structures of water in the vicinity of hydrophobic surfaces differ from those of the bulk water. However, the interfacial water acting as a separation medium on hydrophobic surfaces has never been detected and quantified experimentally. In this study, we show that small inorganic ions and organic molecules differentiate the interfacial water formed on the surfaces of octadecyl-bonded (C(18)) silica particles from the bulk water and the chemical separation of these solutes in aqueous media with hydrophobic materials can be interpreted with a consistent mechanism, partition between the bulk water phase and the interfacial water formed on the hydrophobic surface. Thermal transition behaviour of the interfacial water incorporated in the nanopores of the C(18) silica materials and the solubility parameter of the water calculated from the distribution coefficients of organic compounds have indicated that the interfacial water may have a structure of disrupted hydrogen bonding. The thickness of the interfacial water or the limit of distance from the hydrophobic surface at which molecules and ions can sense the surface was estimated to be 1.25 ± 0.13 nm from the volume of the interfacial water obtained by a liquid chromatographic method and the surface area, suggesting that the hydrophobic effect may extend beyond the first solvation shell of water molecules directly surrounding the surfaces.     

Stable polymethacrylate nanocapsules from ultraviolet light-induced template radical polymerization of unilamellar liposomes

We employed UV-induced template polymerization to create hollow nanometer-sized polymer capsules. Homogeneous, unilamellar liposomes served as a two-dimensional template for the cross-linking of either butyl methacrylate or hydroxyethyl methacrylate with the bifunctional ethyleneglycol dimethacrylate. Different molar ratios of lipid/hydrophobic monomer/bifunctional monomer/photoinitiator were tested and dynamic light scattering revealed negligible changes of size at a defined molar ratio of 2/1/10/20, respectively. Cryo-transmission electron microscopy provided clear evidence that incorporation of the methacrylate monomers into and polymerization in the hydrophobic bilayer phase does not disrupt vesicle integrity. Moreover, after solubilization of the lipids, the polymethacrylate nanocapsules were stable at conditions needed for negative staining and could be visualized by atomic force microscopy. In contrast to previous findings, the nanocapsule size and shape did not change considerably after removal of the template phase, and the size distribution remained strictly monomodal. The employed method is not only an advance to fortify liposomes, but the nanocapsules themselves can be functionalized.     

Charge and size selective molecular transport by amphiphilic organic nanotubes

Amphiphilic constructs with accessible, nanometer-size cavities can enable selective encapsulation, separation, and purification of nanomaterials and biomacromolecules on a similar length scale. We have developed a new method for the fabrication of amphiphilic organic nanotubes from multicomponent bottlebrush copolymers with triblock terpolymer side chains. The obtained nanotubes were demonstrated to be very effective and highly selective carriers for positively charged molecules and nanometer-size macromolecules by means of liquid-liquid extractions. Unprecedented discrimination between dendrimers with about 2 nm size differential was achieved.