Miniemulsion Droplets Research Articles

Replacing organics with water: Macromolecular engineering of non-water miscible poly(meth)acrylates via interfacial and ion-pair catalysis SARA ATRP in miniemulsion

The paper presents the possibility to synthesize immiscible with water, well-defined poly(meth)acrylates via supplemental activation and reducing agent atom transfer radical polymerization (SARA ATRP) in a miniemulsion environment, using a copper wire (Cu0) as reducing agent and supplemental activator. This is the first example of interfacial and ion-pair catalysis presented for Cu0-mediated ATRP carried out in heterogeneous media. In addition, scanning electron microscopy (SEM) was used for further analysis of the occurring processes and miniemulsion droplets were characterized by dynamic light scattering (DLS). Particular attention was paid to the selection of optimum reaction conditions and the applicability of the developed system for a wide range of monomers. For the sake of the environment, the advantages of the presented polymerization technique in the context of sustainable development of the chemical industry were analyzed and highlighted by calculating the green metrics (environmental factors – E-factors) for the synthesized polymers.

Exploring the Role of Miniemulsion Nanodroplet Confinement on the Crystallization of MoO3: Morphology Control and Insight on Crystal Formation by In Situ Time-Resolved SAXS/WAXS

Enclosed nanoscale volumes, i.e., confined spaces, represent a fascinating playground for the controlled synthesis of inorganic materials, albeit their role in determining the synthetic outcome is currently not fully understood. Herein, we address the synthesis of MoO3 nano- and microrods with hexagonal section in inverse miniemulsion droplets and batch conditions, evaluating the effects of spatial confinement offered by miniemulsion droplets on their crystallization. Several synthetic parameters were systematically screened and their effect on the crystal structure of h-MoO3, as well as on its size, size distribution and morphology, were investigated. Moreover, a direct insight on the crystallization pathway of MoO3 in both synthetic conditions and as a function of synthetic parameters was provided by an in situ time-resolved SAXS/WAXS study, that confirmed the role of miniemulsion confined space in altering the stepwise process of the formation of h-MoO3.

Facile synthesis of chromium chloride/poly(methyl methacrylate) core/shell nanocapsules by inverse miniemulsion evaporation method and application as delayed crosslinker in secondary oil recovery

Cr(III)–hydrolyzed polyacrylamide (HPAM) gels have been extensively studied as a promising strategy controlling waste water production for mature oilfields. However, the gelation time of the current technologies is not long enough for in-depth placement. In this study, we report a novel synthesis method to obtain chromium chloride/poly(methyl methacrylate) (PMMA) nanocapsules which can significantly delay the gelation of HPAM through encapsulating the chromium chloride crosslinker. The chromium chloride-loaded nanocapsules (Cr–NC) are prepared via a facile inverse miniemulsion evaporation method during which the hydrophobic PMMA polymers, pre-dispersed in an organic solvent, were carefully controlled to precipitate onto stable aqueous miniemulsion droplets. The stable aqueous nanodroplets (W) containing Cr(III) are dispersed in a mixture of organic solvent (O 1 ) with PMMA and nonsolvent medium (O 2 ) to prepare an inverse miniemulsion. With the evaporation of the O 1 , PMMA forms Cr–NCs around the aqueous droplets. The Cr–NCs are readily transferred into water from the organic nonsolvent phase. The Cr–NCs exhibit the tunable size (358–983 nm), Cr loading (7.1–19.1%), and Cr entrapment efficiency (11.7%–80.2%), with tunable zeta potentials in different PVA solution. The Cr–NCs can delay release of Cr(III) and prolong the gelation time of HPAM up to 27 days.

Strategies to incorporate a fluorinated acrylate monomer into polymer particles: from particle morphology to film morphology and anticorrosion properties

Four strategies to incorporate a fluorinated monomer (perfluoro octyl acrylate, POA) into a waterborne polymeric dispersion are investigated. Due to the very low water solubility of the POA monomer, three of the strategies use miniemulsion droplets containing the whole POA monomer in the initial charge. The rest of the comonomers of the formulation (methyl methacrylate, MMA, and n-butyl acrylate, BA) are partially incorporated in the initial miniemulsion or fed to the reactor as a preemulsion. In the fourth strategy, a conventional seeded semibatch emulsion polymerization is carried out using cyclodextrin in the seed and feeding the POA/MMA/BA preemulsion to the reactor. Each process strategy led to a distinct particle morphology and hence a particular film morphology. We found that the strategy that produced core–shell particles with the core composed by pure polyPOA yielded the films that showed the best corrosion protection as measured in salt-spray test (1200 h standing without damage).

Lignin-based nanogels for the release of payloads in alkaline conditions

Bio-based nanoparticles are promising materials in agriculture because they enable a controlled release of agrochemicals to plants. The release can be more specific by engineering nanoparticles with stimuli-responsive properties. Herein, we reported lignin-based nanogels which can release payloads in alkaline conditions. Lignin methacrylate was emulsified in miniemulsion droplets and graft copolymerized with acrylic acid to form core-shell nanogels. The successful incorporation of acrylic acid and lignin units in the nanogels was confirmed by FT-IR, H-NMR and XPS spectroscopies. TEM and dynamic light scattering analysis demonstrated that the nanogels were spherical and uniformly dispersed in the aqueous phase. AFM nanoindentation and thermal analysis indicated that the nanogels were mechanically and thermally durable. Lignin-based nanogels exhibited a pH-responsive swelling at high amounts of acrylic acid. Various hydrophobic payloads were encapsulated in high yield and could be preferentially released in alkaline conditions. Lignin-based nanogels are therefore the potential nanocarrier for the controlled release of agrochemicals such as pesticides or fungicides.

Synthesis via miniemulsion polymerization of an acrylate copolymer/Algerian MMT nanocomposite

The synthesis of a new nanocomposite based on poly (methylmethacrylate-co-acrylic acid) (P(MMA-co-AA)) and an Algerian montmorillonite (AMMT), via miniemulsion polymerization involving a radicular reaction, was carried out. The modification of AMMT properties induced by the ion-exchange process was followed by FTIR and XRD analysis. The monomer miniemulsion droplets stability was investigated in presence of different surfactants by dynamic light scattering. The optimal experimental conditions for the polymerization were determined with regards to various parameters: surfactant nature and quantity, clay and co-stabilizer amounts and initiator nature. The hybrid copolymer/clay P(MMA-co-AA)/AMMT, characterized by H-NMR, FTIR and XRD, revealed a full exfoliation of the AMMT structure. Its thermal stability, investigated by differential scanning calorimeter (DSC), is improved in comparison with that of PMMA due to the organoclay fine-dispersion generated by the sonication process.

High pressure semibatch emulsion and miniemulsion copolymerization of vinyl acetate and ethylene

AbstractThis study presents the experimental study of semibatch emulsion and miniemulsion copolymerization of vinyl acetate (VAc) and ethylene to vinyl acetate‐ethylene (VAE) copolymer at 60°C and 80–300 psig. In the miniemulsion copolymerization, a water‐soluble initiator (K2S2O8) is used and VAc miniemulsion is prepared in presence of surfactant and cosurfactant using a sonicator or a high‐shear homogenizer. Then, ethylene gas is supplied to the reactor at constant partial pressure. In a miniemulsion process, the mass transfer limitations of VAc from monomer droplets to the aqueous phase, and to micelles or polymer latex particles that are present in conventional macro‐emulsion polymerization can be eliminated and the transfer of ethylene dissolved in the aqueous phase to the miniemulsion droplets is the major ethylene transport process for the polymerization. The experimental data show that the amount of ethylene incorporation into the copolymer is higher in miniemulsion polymerization than in emulsion polymerization. The ethylene pressure has been found to have a strong impact on the ethylene incorporation into the copolymer phase in both emulsion and miniemulsion copolymerizations but the increase is more pronounced in miniemulsion case. The VAE copolymer latex particles prepared by miniemulsion polymerization exhibited higher storage stability than those prepared by macro‐emulsion polymerization.

Styrene-Butadiene Rubber by Miniemulsion Polymerization Using In Situ Generated Surfactant.

An alternative approach for the synthesis of styrene butadiene rubber (SBR) copolymer latexes was explored in order to obtain low gel fractions and high solid contents. The ultra-turrax-assisted miniemulsion stabilized by in situ surfactant generation was adopted as the main strategy since this technique can inhibit the eventual presence of secondary nucleation producing polybutadiene particles and also control the cross-linking degree. Styrene monomer was first miniemulsified using an ultra-turrax and in situ generated surfactant using either hexadecane (HD) or octadecyl acrylate (ODA) as the hydrophobe. Dynamic light scattering (DLS) measurements of droplet size indicated faster stabilization and the production of smaller droplet diameters ca. 190 nm (PdI = 0.08) when employing in situ generated potassium oleate (K-Oleate) in comparison to SDS-based miniemulsions. High butadiene-level SBR latexes with ca. 50% solids content, a glass transition temperature (Tg) of −52 °C, and a butadiene to styrene weight ratio of 75:25, were then obtained using the miniemulsion droplets as seeds. Turbiscan and DLS measurements revealed a very stable resulting latex with SBR particle diameter of ca. 220 nm and a low polydispersity index (PdI). Secondary nucleation was prevented as indicated by the low Np/Nd value. Cryo-TEM images showed a narrow distribution of particle size as well as the absence of agglomeration. The gel content was below 10% when tert-dodecyl mercaptan (t-DM) was used as chain transfer agent (CTA).

Synthesis of high payload nanohydrogels for the ecapsulation of hydrophilic molecules via inverse miniemulsion polymerization: caffeine as a case study

The association of an active principle with a nanocarrier is known to improve its stability and protect it from external factors. Nevertheless, loading of nanoparticles with highly hydrophilic substances like caffeine remains a tricky issue. In the present study, inverse miniemulsion systems were successfully coupled to UV radiation to synthesize polymeric nanohydrogels for drug delivery. The proper choice of the continuous and dispersed phase chemical composition led to the entrapment of active principle into the miniemulsion droplets. Our confinement-based strategy enabled unprecedented caffeine encapsulation efficiency inside 100-nm particles. Dimensional, thermal, and spectroscopic characterizations were carried out to investigate both unloaded and loaded nanohydrogels. Furthermore, in vitro release studies evaluated caffeine release kinetics from nanohydrogels by means of dialysis tests. It was demonstrated that controlled and sustained release occurred within the first 50 hours. Experimental data were found to fit the Higuchi model suggesting that the active principle release is diffusion controlled.

Preparation and characterization of CdS/ZnS core-shell nanoparticles

Cadmium sulfide/zinc sulfide (CdS/ZnS) core-shell nanoparticles in polyacrylamide (PAM) colloid particle were prepared by the succession of inverse miniemulsion polymerization and absorption. The cadmium sulfate (CdSO4)-PAM colloid was firstly prepared by inverse miniemulsion polymerization, the CdS nanoparticles were formed by reaction between CdSO4 in PAM particles and excessive sodium sulfide in being-absorbed miniemulsion droplets; and then the ZnS nanoparticles were orientated-grew onto CdS nanoparticles by slowly absorbing zinc acetate in miniemulsion droplets. The effects of the Cd2+/Zn2+ molar ratios on CdS/ZnS-PAM particles preparation were investigated. When the Cd2+/Zn2+molar ratio was 1:1, the Z average diameter of the CdS/ZnS-PAM particles was 178 nm. The CdS/ZnS crystals showed a greater size with Zn2+ mole fraction increase. The core-shell structure of CdS/ZnS nanoparticles was confirmed successfully by transmission electron microscopy observation, X-ray diffraction analysis and so on. The ZnS shell layer played an important role in modification and reduced the surface defects of nanocrystals effectively. The succession method will provide a great advantage in core-shell structure CdS/ZnS preparation.

Preparation of Thermochromic Films from Latexes Made by Miniemulsion Polymerization

AbstractThermosensitive‐thermochromic pigments are classified as smart materials capable of detecting and/or responding to environmental stimuli, and specifically in this study, changes in temperature that induce a change in the color of the material. This study aims to obtain nanoparticles of poly(styrene‐co‐butyl acrylate) and poly(styrene‐co‐methyl methacrylate), containing thermosensitive‐thermochromic pigments that are incorporated into the monomer droplets in miniemulsion polymerization. Miniemulsion polymerization has the advantage that the pigment particles can be dispersed directly in the monomer droplets and are encapsulated when the miniemulsion droplets are polymerized. Using controlled/living radical polymerization (or Reversible Deactivation Radical Polymerization), it is possible to produce polymers with better control of microstructure and narrower molecular weight distributions. Nitroxide‐mediated polymerization (NMP) is conducted using the BlocBuilder initiator, as well as a conventional free radical polymerization (FRP) using potassium persulfate (KPS) and 2,2‐azobis(2‐methylpropionitrile) (AIBN). Stable latexes containing the thermosensitive‐thermochromic pigments are obtained by both NMP and FRP. Films are made from the latexes and shown to exhibit thermochromic behavior.

Confined Crystallization of Pigment Red 146 in Emulsion Droplets and Its Mechanism.

In this work, the effect of confined space on crystallization processes of pigments was investigated by using C.I. Pigment Red 146 (PR 146) as a model compound. The colloidal system (i.e., emulsion droplets) was used as a nanoreactor to prepare nanoscale PR 146 for the inkjet printer. The effects of the space confinement were investigated by comparing the products of PR 146 prepared from bulk solution, macroemulsion, and miniemulsion. The results showed that PR 146 crystallized in mini-emulsion had the narrowest particle size distribution and the average particle size can be as small as 172.5 nm, one order of magnitude smaller than the one obtained from the bulk solution. X-ray diffraction (XRD) data revealed that PR 146 crystallized in all three solutions where the crystalline state and had similar crystallite sizes. The process mechanism of crystallization confined in the miniemulsion droplets was proposed and explained. The function mechanism of the co-stabilizer during the crystallization of PR 146 in emulsion was also explained. It was found that sodium chloride could counteract the pressure difference as an osmotic pressure agent and prevent the migrating of water from small droplets into big droplets. The influences of dosages of emulsifiers and co-stabilizers on droplet size and the size of the obtained PR 146 particles were evaluated and the optimal conditions were determined. Furthermore, the disparity of PR 146 products prepared by different methods was investigated by UV–Vis spectra. The aqueous dispersion of PR 146 crystallized in miniemulsion had the highest absorbance and darkest color.

The building of molecularly imprinted single hole hollow particles: A miniemulsion polymerization approach

The structural design on the molecularly imprinted polymers (MIP) has been increasingly concerned because of advanced recognition efficiency. We here demonstrate a facile miniemulsion based polymerization to synthesize single hole hollow MIP particles for the recognition of bisphenol A (BPA). Uniform submicron products can be achieved through one-step polymerization in the aqueous dispersion, where the polymer seed has been swelled in the miniemulsion of the cross-linker and functional monomers together with the template molecules of BPA. After the removal of the seed and the template molecules by extraction, the electron microscopy characterization reveals bowl-like particles with a single hole on the concave surface. The unique single hole hollow structure is determined by the polymerization induced phase separation in the miniemulsion droplets and can be altered by monomer components. The characteristic of MIP is illustrated by the molecular recognition in the rebinding tests, where the particles prepared under the optimal formulation exhibit remarkable kinetics and desirable selectivity towards BPA in the mixed solution of methanol and water (20:80, v/v). The MIP particles with single hole hollow structure would be attractive in environmental and analytic fields for BPA decontamination.

One-pot synthesis of PDMAEMA nanocapsules for controlled release of hydrophobic cargo

ABSTRACTIn this work, poly((N,N-dimethyl amino)ethyl methacrylate) (PDMAEMA) homopolymers are synthesized using RAFT technique, which is then used as stabilizers to prepare miniemulsion droplets in a toluene/hexadecane(HD)/1,2-Bis-(2-iodoethyl)ethane(BIEE)/hydrophobic molecule/water mixture. Upon the reaction between BIEE and the stabilizers of miniemulsion droplets, the polymeric nanocapsules are formed and capable of encapsulating hydrophobic molecule in their oil core in one-step reaction. The release of hydrophobic cargo from the nanocapsules can be controlled by the variation of amount of surfactant (Tween®20) in the release medium and a long duration sustained release was achieved.

Synergy of Miniemulsion and Solvothermal Conditions for the Low-Temperature Crystallization of Magnetic Nanostructured Transition-Metal Ferrites

Crystalline first-row transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) ferrites were prepared by an unprecedented synergetic combination of miniemulsion synthesis and solvothermal route, pursuing unconventional conditions in terms of space confinement, temperature, and pressure. This synergy allowed for obtaining six different crystalline ferrites at much lower temperature (i.e., 80 °C) than usually required and without any postsynthesis thermal treatment. X-ray diffraction (XRD) revealed that analogous ferrites synthesized by miniemulsion at ambient pressure or in bulk (i.e., from an aqueous bulk solution and not in the confined space of the miniemulsion droplets) either at ambient pressure or under solvothermal conditions did not result in comparatively highly crystalline products. To follow the structural evolution at local level as a function of reaction time and depending on the synthesis conditions, X-ray absorption spectroscopy (XAS) was used to determine the cation distribution in these structures. W...

Dual Role of Zirconium Oxoclusters in Hybrid Nanoparticles: Cross-Linkers and Catalytic Sites.

Organic-inorganic hybrid nanoparticles are prepared by free-radical copolymerization of methyl methacrylate (MMA) with the structurally well-defined methacrylate-functionalized zirconium oxocluster Zr4O2(methacrylate)12. The polymerization process occurs in the confined space of miniemulsion droplets. The formation of covalent chemical bonds between the organic and the inorganic counterparts improves the distribution of the guest species (oxoclusters) in the polymer particles, overcoming problems related to migration, leaching, and stability. Because of the presence of a high number of double bonds (12 per oxocluster), the oxoclusters act as efficient cross-linking units for the resulting polymer matrix, thus ruling its swelling behavior in organic solvents. The synthesized hybrid nanostructures are applied as heterogeneous systems in the catalytic oxidation of an organic sulfide to the corresponding sulfoxide and sulfone by hydrogen peroxide, displaying quantitative sulfide conversion in 4-24 h, with overall turnover numbers (TON) up to 8000 after 4 cycles.

Synthesis of pH-Responsive Lignin-Based Nanocapsules for Controlled Release of Hydrophobic Molecules

Lignin-based pH-responsive nanocapsules were successfully fabricated via an interfacial miniemulsion polymerization. Lignin was first grafted with allyl groups through etherification and further dispersed in an oil-in-water (O/W) miniemulsion system via ultrasonication. Then allyl-functionalized lignin was reacted with a thiol-based cross-linking agent in the interfaces of miniemulsion droplets to form nanocapsules via a thiol–ene radical reaction. The FTIR and 1H NMR spectra indicated the successful grafting of allyl groups on lignin. TEM images showed that lignin nanocapsules had particle sizes ranging from 50 to 300 nm. These newly synthesized nanocapsules could be readily loaded with hydrophobic coumarin-6 during the preparation of a miniemulsion system with 0.713 mmol/g entrapment efficiency. Moreover, the release of encapsulated coumarin-6 could be controlled by varying pH in the solution due to the existence of acid-labile β-thiopropionate cross-linkages in the capsule shell. An approximately linear release profile was observed at pH 7.4, whereas the release followed a Korsmeyer–Peppas profile at pH 4. The syntheses of lignin-based nanocapsules not only provide a facile approach to utilize the waste biomaterials from biorefinery industries, but also have great potential for applications in a controllable delivery of hydrophobic molecules such as drugs, essential oils, antioxidants, etc.

Glutathione Responsive Hyaluronic Acid Nanocapsules Obtained by Bioorthogonal Interfacial "Click" Reaction.

Azide-functionalized hyaluronic acid and disulfide dialkyne have been used for "click" reaction polymerization at the miniemulsion droplets interface leading to glutathione responsive nanocapsules (NCs). Inverse miniemulsion polymerization was chosen, due to its excellent performance properties, for example, tuning of size and size distribution, shell thickness/density, and high pay loading efficiency. The obtained size, size distribution, and encapsulation efficiency were checked via fluorescent spectroscopy, and the tripeptide glutathione was used to release an encapsulated fluorescent dye after cleavage of the nanocapsules shell. To show the glutathione-mediated intracellular cleavage of disulfide-containing NC shells, CellTracker was encapsulated into the nanocapsules. The cellular uptake in dendritic cells and the cleavage of the nanocapsules in the cells were studied using confocal laser scanning microscopy. Because of the mild reaction conditions used during the interfacial polymerization and the excellent cleavage properties, we believe that the synthesis of glutathione responsive hyaluronic acid NCs reported herein are of high interest for the encapsulation and release of sensitive compounds at high yields.

RAFT inverse miniemulsion periphery polymerization in binary solvent mixtures for synthesis of nanocapsules

Herein we report the synthesis of polymeric nanocapsules with an aqueous core via inverse miniemulsion periphery RAFT polymerization (IMEPP) of styrene/divinyl benzene in binary solvent mixtures using an amphiphilic macroRAFT species comprising N-(2-hydroxypropyl) methacrylamide and styrene as dual steric stabilizer and RAFT agent. Inverse miniemulsions were prepared using various ratios of toluene and n-hexane as the continuous phase. For toluene:hexane volume ratios of 100:0–60:40, hollow polymeric nanocapsules were successfully obtained with average diameters generally well below 300nm. Issues with poor colloidal stability were encountered using toluene:hexane=50:50. Moreover, the particle size distributions exhibited the greatest uniformity in pure toluene. It is rationalized that the presence of (excessive) amounts of n-hexane in the continuous phase leads to poor steric stabilization of miniemulsion droplets as well as the formation of solid (non-hollow) particles in the continuous phase.

Response surface optimization of miniemulsion: application to UV synthesis of hexyl acrylate nanoparticles

This paper presents the UV synthesis in miniemulsion of nanoparticles from hexyl acrylate monomers using radical photoinitiator type I benzoin methyl ether. The optimization of such a miniemulsion composition is studied to produce monodisperse nanoparticles with a mean size d p inferior to 200 nm after photopolymerization of the droplets. The correlation between the size distributions of the droplets and the corresponding nanoparticles was verified. Therefore, a composite design was built as regards to the amount of the surfactant (sodium dodecyl sulfate), the co-stabilizer (pentadecane), and the monomer (hexyl acrylate) in order to model the mean size and the polydispersity of the miniemulsion droplets. A range of monodisperse droplets size between 150 and 175 nm was achieved. After UV irradiation, high monomer conversion yield (>90 %) was reached leading to nanoparticles with mean size ranging from 100 to 165 nm. These hexyl acrylate nanoparticles have been obtained after 10 min of irradiation, offering new opportunities for nanoparticles synthesis in enclosed and/or plastic vessels.