Miniemulsion Droplets Research Articles

Polymeric Nanoreactors for Hydrophilic Reagents Synthesized by Interfacial Polycondensation on Miniemulsion Droplets

We describe a versatile method to obtain functional hollow nanoreactors with a hydrophilic liquid core. The synthesis of hollow polyurea, polythiourea, and polyurethane nanocapsules was performed by interfacial polycondensation or cross-linking reactions in inverse miniemulsion. The miniemulsions were built upon emulsification of a solution of amines or alcohols in a polar solvent with cyclohexane as the nonpolar continuous phase. The addition of suitable hydrophobic diisocyanate or diisothiocyanate monomers to the continuous phase allows the polycondensation or the cross-linking reactions to occur at the interface of the droplets. The wall thickness of the capsules can be directly tuned by the quantity of the reactants. The nature of the monomers and the continuous phase are the critical factors for the formation of the hollow capsules, which is explained by the interfacial properties of the system. The resulting polymer nanocapsules could be subsequently dispersed in water. The capsules were found to be...

Antiseptic Nanocapsule Formation via Controlling Polymer Deposition onto Water‐in‐Oil Miniemulsion Droplets

AbstractThe stable nanodroplet was prepared by inverse miniemulsion with an aqueous antiseptic solution dispersed in an organic medium of solvent/nonsolvent mixture containing an oil‐soluble surfactant and the polymer for shell formation. The change in gradient of the solvent/nonsolvent mixture, obtained by heating at 50 °C, led to the precipitation of the polymer in the organic phase and deposition onto the large interphase of the aqueous miniemulsion droplets. The monodisperse polymer nanocapsule, with the size range of 80–240 nm, dispersed in cyclohexane phase was achieved as a function of surfactant concentration. By variation of polymer content, molecular weight and type, an encapsulation efficiency of 20–100% was obtained as detected by proton‐nuclear magnetic resonance spectroscopy measurement. The nanocapsule could be easily transferred into water as continuous phase resulting in aqueous dispersion with nanocapsule containing the antiseptic agent as an aqueous core. The encapsulated amount of the antiseptic agent was evaluated to indicate the durability of the nanocapsule's wall. Additionally, the different types of polymer having glass transition temperature ranging from −60 to 100°C have been successfully used. Currently, the research work on the incorporation of nanocapsules onto natural rubber (NR) latex in order to prepare NR latex glove containing the antiseptic agent nanocapsules is carried out. By using the simple and versatile layer‐by‐layer (LbL) technique based mainly on an electrostatic interaction between oppositely charged species, the deposition of nanocapsules onto NR latex film has successfully been fulfilled.

Preparation of gradient copolymers via ATRP in miniemulsion. II. Forced gradient

AbstractA series of forced gradient copolymers with different controlled distribution of monomer units along the copolymer backbone were successfully prepared by atom transfer radical polymerization in miniemulsion. The newly developed initiation technique, known as activators generated by electron transfer, was beneficial for forced gradient copolymers preparation because all polymer chains were initiated within the miniemulsion droplets and the miniemulsion remained stable throughout the entire polymerization. Various monomer pairs with different reactivity ratios were examined in this study, including n‐butyl acrylate/t‐butyl acrylate, n‐butyl methacrylate/methyl methacrylate, and n‐butyl acrylate/styrene. In each case, the added monomer diffused across the aqueous suspending medium and gradient copolymers with different forced distributions of comonomer units along the polymer backbone were obtained. The shape of the gradient along the backbone of the copolymers was influenced by the molar ratio of the monomers, the reactivity ratio of the comonomers as well as the feeding rate. The shape of the gradient was also affected by the relative hydrophobicities of the comonomers. Copolymerizations exhibited good control for all feeding rates and comonomer feeding ratios, as evidenced by narrow molecular weight distribution (Mw/Mn = 1.20–1.40) and molecular weight increasing smoothly with polymer yield, indicating high initiation efficiency. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1413–1423, 2007

Polymeric Nanocapsules Containing Nematic LCs as Hydrophobes in Miniemulsion Polymerization

AbstractThe distinct polymeric nanocapsule hybrid‐structures consisting of LCs in the core and PMMA or polystyrene in the corona domain were prepared by one‐step miniemulsion polymerization. Nematic LCs (4′‐pentyl‐4‐biphenylcarbonitrile and 4′‐heptyloxy‐4‐biphenylcarbonitrile) were especially adopted as hydrophobes that can suppress Ostwald ripening and had an important role to stabilize the miniemulsion droplets and control the size distributions of the latexes. The polymeric nanocapsule structures with narrow size distributions were confirmed by TEM and DLS measurements.magnified image

標識化合物の分光測定による高分子・低分子溶液の物性研究

The conformation, interaction, and dynamics of target functional groups in polymer and surfactant solutions were studied by fluorescence or vibrational spectroscopy with labeling techniques. The rotational relaxation process of polystyrene chains was investigated by measuring the time-resolved fluorescence anisotropy decay curve of an anthryl group end-capped polystyrene. The decay curves observed for the dilute and concentrated polymer solutions are well reproduced by the modified intermittent motion model. The fluorescence of pyrene excimers was monitored in order to reveal the transfer of the internal phase among miniemulsion droplets. It was revealed that the internal phase of miniemulsion droplets is miscible without changing the droplet diameter. The blue shift of the isolated CD stretching band of 2-butoxyethanol observed for the aqueous solution during a dilution process was investigated by infrared spectroscopy with mono-deuterium labeling techniques. The result indicated that the large blue shift of the CD stretching band of the butoxy group mainly arises from the hydration of the ether oxygen atom.

Preparation of polyurethane nanocapsules by miniemulsion polyaddition

The encapsulation of organic liquids in polyurethane nanocapsules by interfacial miniemulsion polycondensation of isophorone diisocyanate and propanetriol has been performed. The influence of type and amount of encapsulated organic liquid has been studied and it was found that the encapsulation efficiency is dependent on the water solubility of the organic liquids, their interfacial tension against water and their compatibility with polyurethane. It was also shown how different types of surfactants and variations in pH and ionic strength of the continuous phase affected the stability during polymerization and the diameter of the miniemulsion droplets and the resulting nanocapsules. The long-chained anionic surfactant Disponil FES77 can be utilized over a larger pH range than SDS due to the contribution of steric stabilization. Relatively narrow size distributions were obtained.

Formation of Novel Layered Nanostructures from Lanthanide‐Complexes by Secondary Interactions with Ligating Monomers in Miniemulsion Droplets

AbstractSummary: The addition of neutral, inert inner shell lanthanide complexes such as Gd(III)‐(tmhd)3, Eu(III)‐(fod)3, or Ho(III)‐thmd3, broadly available as NMR shift reagents, towards ester‐containing monomers such as butyl acrylate and subsequent polymerization in miniemulsion droplets leads to the spontaneous formation of highly organized layered nanocomposite particles, as revealed by electron microscopy and small angle X‐ray scattering. The nanocomposite comprises a lanthanide complex phase and a polymer phase with a lamellar repeat period of about 3.5 nm, rather independent of the system composition.TEM micrograph of a PGd‐3 nanocomposite and corresponding chemical structure of the complex Gd(tmhd)3.magnified imageTEM micrograph of a PGd‐3 nanocomposite and corresponding chemical structure of the complex Gd(tmhd)3.

Polymeric Nanocapsules Containing an Antiseptic Agent Obtained by Controlled Nanoprecipitation onto Water‐in‐Oil Miniemulsion Droplets

The modified nanoprecipitation of polymers onto stable nanodroplets has been successfully applied to prepare well-defined nanocapsules whose core is composing of an antiseptic agent, i.e., chlorhexidine digluconate aqueous solution. The stable nanodroplets were obtained by inverse miniemulsions with an aqueous antiseptic solution dispersed in an organic medium of solvent/nonsolvent mixture containing an oil-soluble surfactant and the polymer for the shell formation. The change of gradient of the solvent/nonsolvent mixture of dichloromethane/cyclohexane, obtained by heating at 50 degrees C, led to the precipitation of the polymer in the organic continuous phase and deposition onto the large interface of the aqueous miniemulsion droplets. The monodisperse polymer nanocapsules with the size range of 240-80 nm were achieved as a function of the amount of surfactant. Using various polymer contents, molecular weights and types, an encapsulation efficiency of 20-100% was obtained as detected by proton-nuclear magnetic resonance spectroscopy ((1)H NMR) measurements. The nanocapsules could be easily transferred into water as continuous phase resulting in aqueous dispersions with nanocapsules containing an aqueous core with the antiseptic agent. The encapsulated amount of the antiseptic agent was evaluated to indicate the durability of the nanocapsule's wall. In addition, the use of different types of polymers having glass transition temperatures (T(g)) ranging from 10 to 100 degrees C in this process has been also successful.

Kinetics and mechanism of miniemulsion polymerization of a sparingly water-soluble fluoro monomer

AbstractIn order to clarify the kinetics and mechanism of miniemulsion polymerization of a sparingly water-soluble monomer, the miniemulsion polymerization of 1,1,2,2-tetrahydroperfluorodecyl acrylate was conducted at 50°C using potassium persulfate as initiator and sodium dodecyl sulfate as emulsifier, respectively. It was found that the rate of polymerization was proportional to the 0.65 power of the initial initiator concentration and to the 0.30 power of the number of miniemulsion droplets (latex particles). It is pointed out that the kinetics of this polymerization system may be subject to the modified case III kinetics of emulsion polymerization with predominant bimolecular termination in the aqueous phase.

Characterization of Miniemulsion Polymerization by Small-Angle Neutron Scattering

Emulsion polymerization is one of the major techniques for the manufacture of adhesives, coatings, thermoplastics and elastomers. In miniemulsion polymerization, relatively stable oil droplets within a size range of 500 to 5000 A are prepared by emulsifying a monomer in a medium, generally water, with the aid of a surfactant and a hydrophobic compound. Droplet size and size distribution are by far the most important parameters of miniemulsion because they affect directly both the miniemulsion stability and droplet nucleation. Therefore, the understanding of the mechanism ruling miniemulsion polymerization strongly depends on an accurate determination of the particle size.

Preparation of polyurethane dispersions by miniemulsion polymerization

AbstractWith a two‐step miniemulsion polymerization, hydrophobic polyurethane (PU) dispersions were prepared with a cosurfactant, the costabilizer hexadecane (HD) in the oil phase, and sodium dodecyl sulfate (SDS) in the water phase. The first step involved the formation of NCO‐terminated prepolymers between isophorone diisocyanate and poly(propylene glycol) oligomer in toluene. Next, PU dispersions were produced by a miniemulsion method in which an oil phase containing NCO‐terminated prepolymers, HD, the chain extender 1,4‐butanediol (BD), the crosslinking agent trimethylol propane (TMP), and the catalyst dibutyltin dilaurate was dispersed in the water phase containing SDS. The influence of experimental parameters, such as the ultrasonication time, concentrations of SDS and HD, and TMP/BD and NCO/OH equivalent ratios, on the sizes of the miniemulsion droplets and polymer particles, as well as the molecular weights and thermal properties of the PU polymer, was examined. The chemical structure of the produced PU polymer was identified with a Fourier transform infrared spectrometer. The molecular weight distribution and average particle size were measured through gel permeation chromatography and dynamic light scattering, respectively. The thermal stability of the PU polymer was characterized with thermogravimetric analysis. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4870–4881, 2005

Miniemulsion Droplets as Single Molecule Nanoreactors for Polymerase Chain Reaction

Polymerase chain reaction (PCR) was successfully carried out inside stable and narrowly distributed water-in-oil nanodroplets with a size of 100-300 nm in diameter. The droplets were obtained by the miniemulsion process. Each aqueous droplet serves as a single nanoreactor for the PCR. It was found that the size of the droplets highly depends on the sonication parameters (i.e., time and amplitude) and that these parameters have a great influence on the final concentration of the PCR product. The parameters were chosen that way that conditions for single molecule chemistry were obtained, since the 3D-space is compartimentalized in small nanoreactors in each of which the same reaction takes place in a highly parallel fashion on every single DNA molecule.

Novel Experimental Technique for the Determination of Monomer Droplet Size Distribution in Miniemulsion

AbstractSummary: The lack of accurate knowledge for measuring monomer droplet size and droplet size distribution has hampered the further progress of miniemulsion polymerization. Monomer droplet size is probably the most important characteristics of a miniemulsion, influencing the miniemulsion stability and the nucleation mechanism. To date, several experimental techniques have been tested to measure miniemulsion droplet size, but none are convenient and accurate. This work presents a novel experimental technique, using a powerful new scanning transmission electron microscopy (STEM) imaging system, which allows transmission observations of wet samples in an environmental scanning electron microscopy (ESEM). This new imaging technique is a useful technique to directly measure droplet size and droplet size distribution.Miniemulsion droplets in dark field wet STEM imaging conditions.magnified imageMiniemulsion droplets in dark field wet STEM imaging conditions.

Monte Carlo Simulation of Droplet Nucleation in RAFT Free Radical Miniemulsion Polymerization

The early stages of the reversible addition/fragmentation transfer (RAFT) miniemulsion polymerization were simulated, focusing on the effect of the RAFT agent on droplet nucleation. For highly reactive RAFT agents, a large number of free radicals (Nc) needed to be captured by a droplet in order to initiate polymerization in the droplet, which was totally different from the behavior of regular miniemulsion polymerization. More interestingly, it was found that droplet size had a significant influence on Nc value. It was shown that the RAFT agent has a significant influence on miniemulsion polymerization, leading to long induction periods and retardation of polymerization. In addition, miniemulsion droplets with different sizes are nucleated at different times, which could lead to very low nucleation efficiency. The results would be very helpful in understanding and designing a RAFT miniemulsion polymerization system.

Hybrid polymer latexes—acrylics‐polyurethane: II. mechanical properties

AbstractPolyurethanes were prepared from reaction of isophorone diisocyanate (IPDI) with polypropylene glycol (PPG), with chain extension with butanediol (BDO). Their end groups are either methoxy, or methacrylic groups. These polyurethanes (PUs) are dissolved in mixtures of acrylic monomers (methylmethacrylate, MMA, and butylacrylate, BA). The solutions are sonicated to produce miniemulsion droplets, using sodium dodecyl sulfate (SDS) as surfactant, the PU being the hydrophobe. These miniemulsions were polymerized, with an oil‐soluble peroxide initiator. Those latexes with methoxy end groups in the PU are fully soluble, while those containing the acrylic end groups are almost fully crosslinked, but can easily form smooth films. The mechanical properties of these films were studied from their stress–strain curves, and compared with those films formed from the uncrosslinked hybrid latexes. Copyright © 2005 John Wiley & Sons, Ltd.

Evolution of water-in-oil emulsion controlled by droplet-bulk ion exchange: acoustic, electroacoustic, conductivity and image analysis

Water-in-kerosene emulsion stabilized with SPAN surfactant exhibits a slow transition (on scale of hours) from an emulsion to a mini-emulsion state. We continuously monitor this transition in the relatively concentrated samples (5 vol.% water), without dilution, using acoustic, electroacoustic and conductivity measurements. Continuous stirring prevents sedimentation. We confirm our measurements with microscopic image analysis and by comparing with a stable water-in-car oil microemulsion stabilized with AOT. Acoustic measurements yield information about the droplet size evolution in time. The original droplets, having a size of about 0.4 μm, slowly coalesce into larger droplets. After 10 h the droplet size has increased to about 5 μm. At this point a mini-emulsion fraction appears with a droplet size of only 25 nm and the droplet size distribution becomes bimodal. It takes another 24 h for the emulsion droplets to completely transform into a mini-emulsion state. The conductivity exhibits a rapid change during the first 10 h of emulsion coalescence, but the rate becomes much slower as the mini-emulsion fraction begins to grow. Electroacoustic measurements shows that the original emulsion droplets carry a substantial surface charge, which we are able to calculate using Shilov's theory for overlapped DLs. The measured electroacoustic signal gradually decays with time. In the final state the mini-emulsion droplets generate practically no electroacoustic signal and appear uncharged. This fact, combined with conductivity measurements, indicates a strong role for electrostatic factors in emulsion stability and its transition to mini-emulsion state. We suggest that ion exchange between the exterior and interior diffuse layers leads to a gradual collapse of the exterior DL and explains all the experimental observations.

Anionic surfmers in mini-emulsion polymerisation

Mini-emulsion polymerisation of styrene or methylmethacrylate, initiated with ammonium persulphate, have been carried out, in the presence of hexadecane or of polymethylmethacrylate as hydrophobic costabilizer, and the simple hemiester of linear dodecyl alcohol and maleic anhydride, or polymerisable surfactants (surfmers) derived from the condensation of succinic anhydride and either hydroxy propylmethacrylate (MAES), or hydroxyethylmethacrylate (ABS). While the pure surfmers have not so good surface activity, from surface tension measurements, stable mini-emulsion droplets are obtained using a mixture with low amounts of SDS, which have diameters of about 100–200 nm, which remain stable upon polymerisation. Most of the surfmers remain grafted onto the particle surface, thus conferring to these particles strong stability in the various tests. However, due to the high water solubility of the surfmers, another part remains in the serum as unconverted monomer or water-soluble polymers. To cite this article: A. Guyot et al., C.R. Chimie 6 (2003).

Metastable and Stable Morphologies during Crystallization of Alkanes in Miniemulsion Droplets

Undercooling and crystallization of different alkanes in stable nanodroplets with narrow size distributions were analyzed by using DSC measurements. The crystal structure was determined by X-ray measurements. Alkane droplets with a defined size between 100 and 500 nm in water were prepared by using the miniemulsion process. The required undercooling to obtain crystallization in such droplets is significantly increased compared to that for the bulk material since the nucleation mechanism is shifted from heterogeneous to homogeneous nucleation. For the even alkanes (C18−C24), a structure change from the triclinic in the bulk to orthorhombic structure in small droplets (100 nm) was detected and attributed to confinement effects inside the droplets. An intermediate rotator phase is of less relevance for the nanosized droplets. For odd alkanes, a strong temperature shift of the crystallization point compared to the bulk system was detected, but no structure change was observed. Both in bulk and in miniemulsion...

Formation and Growth of Water-in-CO2 Miniemulsions

We report nonflocculated dilute water-in-CO2 (W/C) miniemulsions stable for 24 h in contrast with flocculated unstable macroemulsions reported previously. The surfactants, poly(1,1-dihydroperfluorooctyl methacrylate)-b-poly(ethylene oxide) (PFOMA-b-PEO), were synthesized by atom transfer radical polymerization to achieve the proper hydrophilic−CO2-philic balance (HCB) and a low interfacial tension (∼0.2−2 mN/m) between water and CO2. The average particle diameter, ranging from 70 to 140 nm, was measured with multiwavelength turbidimetry utilizing Mie theory, and the interfacial tension was measured with high pressure pendant drop tensiometry. Because flocculation and coalescence were suppressed nearly completely, it became feasible to investigate emulsion droplet formation and droplet growth by Ostwald ripening. Droplet formation was characterized as a function of the mechanical energy at various CO2 densities and temperatures and was correlated quantitatively to the interfacial tensions. The molar water/surfactant ratios reached 1170, in contrast with values of only about 5−60 for W/C microemulsions. The ability to stabilize nanometer-sized miniemulsion droplets with large water/surfactant ratios is of great practical interest in reactions, separations, and materials formation processes in CO2.

Crystallization in Miniemulsion Droplets

Undercooling and crystallization in stable nanodroplets with a narrow size distribution were analyzed using differential scanning calorimetry (DSC) measurements. Hexadecane droplets in water and NaCl solution droplets in petrolether were prepared using the miniemulsion process. It was found that the undercooling required to obtain crystallization in such droplets is significantly increased, compared to the bulk material: for the hexadecane droplets, a shift from 12 °C (bulk) to approximately −4 °C (droplets) is observed, and for the NaCl solution, a shift from −22 °C (bulk) to −46 °C (droplets) is observed. This is explained by the fact that, in miniemulsions, each droplet must be nucleated separately and the nucleation mechanism is shifted from heterogeneous to homogeneous nucleation. The undercooling additionally increases as the temperature decreases, which is explained with finite size effects for spinodal decompositions. The interfacial tension does not have any influence on the crystallization process. It was found that the crystallization rate in miniemulsion droplets is higher than that of the bulk and is proportional to the droplet size.