Miniemulsion Polymerization Research Articles

Controlling size, shape, and charge of nanoparticles via low-energy miniemulsion and heterogeneous RAFT polymerization

Size, shape, and charge are key parameters of nanoparticles, and variations in these parameters can significantly impact their properties and applications. Among various nanoparticle synthesis methods, the combination of low-energy miniemulsions with reversible addition-fragmentation chain-transfer (RAFT) polymerization allows for the facile, rapid, and environmentally friendly preparation of uniform nanoparticles. However, this method cannot, yet, simultaneously control the size, shape, and charge of nanoparticles, thereby limiting its potential applications. Here we report the synthesis of polymeric nanoparticles with concurrent control over particle size, shape, and charge via low-energy miniemulsion and heterogeneous RAFT polymerization. Key to our approach is the combination of (i) a macromolecular surface-active agent to facilitate the formation of nanodroplets, (ii) various small-molecule surfactants with different charges to control the size and charge of nanodroplets, and (iii) a molecular transformer to control the morphology of the final polymeric nanoparticles. In particular, negatively charged polystyrene nanoparticles of different sizes (from ∼100 to ∼500 nm) and shapes (sphere, worm, and vesicle) were obtained by simply tuning the amount of added sodium dodecyl sulfate (SDS) and toluene. The nanoparticle charge was then switched from negative to positive by replacing SDS with cetyltrimethylammonium bromide (CTAB), a positively charged surfactant. In addition, biocompatible and neutral surfactants (including Tweens and Span 80) were employed to tune the nanoparticle size yielding challenging-to-synthesize nanoworms. This work provides a simple but powerful approach to produce nanoparticles of different properties, thus expanding the scope of nanomaterials made by RAFT low-energy miniemulsion polymerization.

Siloxane-based high solid acrylic latex by mini-emulsion polymerization for coatings with improved water resistance

Water resistance of a coating is an important parameter in its protective nature. Therefore, developing a viable coating formulation for improved water resistance has significant research interest. In this study, we prepared an acrylic latex composed of poly (methyl methacrylate-co-butyl acrylate-co-acrylic acid) having high solid content (54–57 %) by mini-emulsion polymerization. Herein, we synthesized a methacrylate-terminated tetrafunctional siloxane monomer (MTS) and used it at 0.5–4.0 wt% as a crosslinking comonomer in the acrylic emulsion formulation. The structural elucidation of MTS was performed by FT-IR, 1H &13C NMR and ESI-MS analysis. The copolymer latexes were characterized in terms of their solid content, particle size and viscosity. All the high solid latexes were stable for months without any coagulum. The analysis of microscopic, optical, thermal and mechanical properties of the air-dried cast films exhibited that the copolymers with MTS had rough surface morphology, high optical transparency (~98 % transmittance), and improved thermal properties and poor mechanical properties. In addition, the films showed improved water resistance as observed from the increased water contact angle from 43.0° (0 % MTS) to 64.2° (1 % MTS) and reduced water absorption from 50 % (0 % MTS) to 18.2 % (1 % MTS). This work focusing on the incorporation of siloxane moieties for improving the water resistance and many other properties of acrylic coatings will make an advancement to develop fluorine-free protective coatings.

Encapsulation of gold nanoclusters by photo-initiated miniemulsion polymerization

Gold nanoclusters (AuNC) with a precise number of Au atoms feature unique properties for imaging applications, including size dependent photoluminescence, very high photostability, and large Stokes shift. However, their low colloidal stability often leads to aggregation and fusion into larger gold nanoparticles (AuNPs), hindering the wider use of AuNC. Here, we report the first successful encapsulation of NIR emitting AuNC in polymer nanoparticles (PNPs). The AuNC, with 25 gold atoms and stabilized by 6-mercaptohexanoic acid (MHA), were encapsulated in PNPs with ca. 50 nm in diameter, obtained by miniemulsion polymerization of butyl methacrylate (BMA) and varying amounts of methyl methacrylate (MMA). While thermo-initiation led to aggregation of AuNC into plasmonic (non-emissive) AuNPs, the use of photo-initiation effectively preserved the AuNC inside the PNPs. By encapsulating a large number of AuNC, we obtained PNPs with high brightness in the NIR, both by one- and two-photons excitation.

Synthesis of conductive polymeric nanoparticles with hyaluronic acid based bioactive stabilizers for biomedical applications

In recent years, the use of organic materials to infer conductivity in biomedical devices has received increasing attention. Typical inorganic semiconductors and conductors are rigid and expensive, usually require multiple processing steps and are unsuitable for biomedical applications. Electrochemically or chemically doped conjugated polymers help to overcome these problems due to their stability, low cost, light weight and excellent electrical and optical properties. The conducting polymer poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) is the material of choice for biomedical applications as it is water soluble, however, there are growing concerns around its stabilizer, PSS, due to its release of acidic products upon degradation in-vivo. Here, we report the successful synthesis of PEDOT nanoparticles using hyaluronic acid (HA) as a stabilizer via an oxidative miniemulsion polymerisation technique. This improves the bioactivity and hydrophilicity of nanoparticles. The effect of varying amounts of HA and different molar ratios of EDOT:TOS has been studied and their role in the conductive and morphological properties of final nanoparticles has been fully elucidated. Furthermore, bioactivity and biocompatibility of the nanoparticles are demonstrated for customizable in vivo applications. Nanoparticles were found to have a conductivity up to 10 times greater than pristine PEDOT:PSS with increased addition of oxidant. The proposed easy-to-manufacture approach, along with the highlighted superior properties, expands the potential of conductive polymers in future customizable biological applications such as tissue scaffolds, nerve conduits and cardiac patches and represents a real breakthrough from the current state of the art.

Ready-to-use optical H2O2 sensor based on stimuli-responsive polyacrylic film and nanofibers containing spiropyran

Nowadays, design of conventional and efficient optical H2O2 sensors would be of great importance due to their lower cost and ease of follow-up, compared to the other widely used techniques such as electrochemical or chromatographic methods. Here, stimuli-responsive sensors containing photochromic (R/S)-2-(3′,3′-dimethyl-6-nitro-3′H-spiro[chromene-2,2′-indole]-1′-yl) ethanol (SPOH) and acrylic terpolymer film or nanofibers were prepared for H2O2 detection through a reaction-induced and concentration-dependent process. The polymer phase acts as an efficient substrate for exploitation of such sensors in aqueous media. Poly(methyl methacrylate-butyl acrylate-hydroxyethyl methacrylate) (MBH) was prepared via miniemulsion polymerization and its chemical structure was characterized by FTIR and 1H NMR spectroscopies. Then, it was doped with SPOH and the corresponding film (MBH/SPOH@F) and nanofibers (MBH/SPOH@NF) were fabricated via spin-coating and electrospinning techniques, respectively, and their morphologies were investigated by SEM. Colorimetric analyses were employed to evaluate performance of the obtained samples toward H2O2 after sensitization by UV irradiation. Both samples demonstrated visual color changes together with decrement in maximum absorption wavelengths with the increase in H2O2 concentration. Limit of detection (LOD) for MBH/SPOH@F and MBH/SPOH@NF were calculated to be 11 and 2.3 mg/dL, respectively. Moreover, MBH/SPOH@NF showed faster response (50 min) with respect to MBH/SPOH@F (60 min). Enhanced sensitivity of MBH/SPOH@NF comes from higher specific surface area and porosity of the nanofibers compared to the corresponding film. This led to more accessibility of H2O2 to SPOH molecules in the detection process. Finally, practical application of the ready-to-used and solid sensor was validated with the recovery of 94–97% in water resources.

Facile Fabrication of Hollow Molecularly Imprinted Polymer Latex Particles for Dibutyl Phthalate via One-step Miniemulsion Polymerization

Facile Fabrication of Hollow Molecularly Imprinted Polymer Latex Particles for Dibutyl Phthalate via One-step Miniemulsion Polymerization

Herceptin-Conjugated DOX-Fe3O4/P(NIPAM-AA-MAPEG) Nanogel System for HER2-Targeted Breast Cancer Treatment and Magnetic Resonance Imaging

It is essential to synthesize a "diagnosis and therapy" integration nanocarrier for magnetic resonance imaging-guided breast cancer-targeted chemotherapy. Here, we report Fe3O4/P(NIPAM-AA-MAPEG) nanogels (MNLs) based on in situ loading of doxorubicin (DOX) by miniemulsion polymerization. Especially, propyl acrylic acid (AA) moieties were introduced to absorb DOX by electrostatic interactions and conjugated with the antibody herceptin (HER) through the amino-carboxyl coupling reaction. The size and morphology of MNLs could be adjusted by varying the polymerization parameters, such as the monomer feeding ratio, ferrofluid content, and cross-linker content. The MNLs showed superior stability in a physiological environment, but their structures were destroyed in an acidic environment to accelerate DOX release. The dissociation of the HER-DOX-MNLs accelerated the delivery of DOX and enhanced the therapeutic effects. The studies exhibited that the HER-DOX-MNLs could inhibit the tumor growth. In addition, the MNLs with a high magnetic content had the potential advantages in magnetic resonance imaging (MRI) of breast cancer diagnosis. The dual-targeted pH-responsive nanogels were successfully designed as a multifunctional nanocarrier for realizing HER2-positive breast cancer chemotherapy and diagnostics.

One step nanoencapsulation of corrosion inhibitors for gradual release application

The direct application of corrosion inhibitors on metal surfaces is potentially dangerous for the environment and the restoration operators, thus new conservation strategies are mandatory. In this study, two copper corrosion inhibitors, 1H-benzotriazole (BTA) and 5-phenyl-1H-tetrazole (PT), are encapsulated in a silica nanocontainer, for future application in smart coatings, with the aim to reduce the amount of chemicals used in treatments, their dispersion in the environment and the direct exposure of the operators to these chemicals. In particular, composite silica nanocapsules, containing the corrosion inhibitors, are prepared via one-step synthesis, based on mini-emulsion polymerisation processes.The morphology, structure, and texture of these loaded silica nanocontainers are characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 physisorption (BET/BJH). Micro-Raman spectroscopy (RS) is performed to characterise the composition. UV–visible spectroscopy and thermal analysis (TG/DSC) are performed for the loading and encapsulation efficiency (L%, EE%) study.Synthesised nanocapsules show a core-shell structure and, when loaded with the inhibitors, have size ranging from about 130 to 170 nm and a BET surface area of the order of 800 m2/g. The EE% is maximum in the case of BTA and decreases to ∼52% in the case of PT.

Electrospinning of polymer nanofibers based on chiral polymeric nanoparticles

AbstractChiral polymeric nanoparticles (NPs) have emerged as a new and exciting field of research and in the last years due to their possible use for many applications in chiral chemistry however the efficiency of separating enantiomerically pure compounds has been always challenging. In this article, we focus on electrospun nanofibers formed by chiral functional NPs based on leucine or phenylalanine amino acids with polysulfone (PSF). Combining chiral functional NPs with PSF in electrospinning method provides us to get intertwined electrospun membranes with chiral property and used them for separation of racemic mixtures. We have also studied chiral functional conventional membranes formed by PSF and NPs. The NPs were prepared by miniemulsion polymerization and were characterized by DLS, SEM, MS, and NMR and display spherical structure with a narrow size distribution in the range of 200 to 250 nm. The characteristics of the membranes in terms of their morphology were analyzed. The permselective properties of the all membranes in the separation of racemic mixture were studied using aqueous solutions of leucine. Time‐resolved circular dichroism and chiral column high‐performance liquid chromatography (HPLC) were used to provide evidence for enantioselective separation. Our results show the membrane which is based on PSF and leucine NPs and formed by conventional method gives the best results for enantioselective separation by showing 18% enantiomeric excess (EE).

The role of 1-octyl-3-methylimidazolium hexafluorophosphate in anticorrosion coating formula development

A hydrophobic ionic liquid (1-octyl-3-methylimidazolium hexafluorophosphate, C8mimPF6) with a function of inhibiting corrosion was encapsulated at different concentrations in the copolymer of poly (methyl methacrylate) and poly (butyl acrylate) through miniemulsion polymerization. These latexes were coated on steel samples whose corrosion properties were evaluated by electrochemical techniques. It was found that increasing the C8mimPF6 concentration from 0 wt% to 30 wt%, the corrosion inhibition efficiency was remarkably improved from 41% to 89% based on the charge transfer resistance and from 64% to 87% based on the corrosion current density, respectively. The ionic liquid did not attend the reaction during latex preparation but behaved as corrosion inhibitors on the steel surface. Such an anticorrosion effect could be ascribed to the physical adsorption of the C8mim+ cation on the reaction sites and the hydrophobicity enhancement resulting from the hydrophobic PF6− anion.

Synthesis of Highly Stretchable and Electrically Conductive Multiwalled Carbon Nanotube/Polymer Nanocomposite Films

Emulsion-based methods offer a range of advantages for fabrication of polymer nanocomposite materials. Herein, we have explored the use of in situ miniemulsion polymerization as well as a variety of physical mixing methods for preparation of nanocomposite films comprising multiwalled carbon nanotubes (MWNTs) and statistical copolymers based on styrene and n-butyl acrylate. Nanocomposite films were prepared at room temperature via simple drop casting of the obtained nanocomposite latex. It is demonstrated that both the fabrication method and compositional details such as the nature of the surfactant greatly influence the latex stability and the physical properties of the resulting nanocomposite films. Films prepared via miniemulsion polymerization exhibited high stretchability, whereas films produced by physical mixing showed electrical conductivities of approximately 102 S m–1, which lies in the highest range reported to date for such materials via any preparation technique and is the highest ever for emulsion-based techniques within this concentration range of carbon nanotubes. The high electrical conductivity with tuneable mechanical properties shown in this study is envisaged to boost interest in polymer/CNT nanocomposites for different applications.

Investigation of the water barrier properties of graft copolymer latex films of acrylate and poly(dimethylsiloxane) macromonomers synthesized by RAFT miniemulsion polymerization

It is challenging to improve the water barrier performance for waterborne protective coating. We synthesized a series of acrylic-polydimethylsiloxane (PDMS) graft copolymer latexes p(MMA-co-BA)-g-PDMS) with high PDMS content of up to 50%, which were considered as bottle-brush polymers using reversible addition-fragmentation chain transfer mediated “macromonomer” miniemulsion copolymerization. We investigated the effect of PDMS side chains on the water barrier performance of graft copolymer latex film derived from these particles and their utilization in anti-corrosion coatings. The water contact angle reaches 117° for films cast from aqueous dispersions of graft copolymers with 50% PDMS, which indicates that their surface is significantly enriched with PDMS. The increase in PDMS content has a highly positive effect on the water barrier performance. Differential scanning calorimeter (DSC) on copolymer films after soaking in water indicates that the high PDMS content (50% PDMS) graft copolymer has only freezing bound water in films. Electrochemical impedance spectra tests showed that the graft copolymer exhibited a significant improvement in corrosion resistance over the control polyacrylate sample without PDMS. Furthermore, transmission electron microscopy observations reveal that the PDMS phase changes from a spherical domain texture to a bicontinuous gyroid texture in the bulk of latex films with the increasing PDMS content, which makes them suitable as waterborne anti-corrosion silicone coatings.

Gadolinium and Polythiophene Functionalized Polyurea Polymer Dots as Fluoro-Magnetic Nanoprobes.

A rapid and one-pot synthesis of poly 3-thiopheneacetic acid (PTAA) functionalized polyurea polymer dots (Pdots) using polyethyleneimine and isophorone diisocyanate is reported. The one-pot mini-emulsion polymerization technique yielded Pdots with an average diameter of ~20 nm. The size, shape, and concentration of the surface functional groups could be controlled by altering the synthesis parameters such as ultrasonication time, concentration of the surfactant, and crosslinking agent, and the types of isocyanates utilized for the synthesis. Colloidal properties of Pdots were characterized using dynamic light scattering and zeta potential measurements. The spherical geometry of Pdots was confirmed by scanning electron microscopy. The Pdots were post-functionalized by 1,4,7,10 tetraazacyclododecane-1,4,7,10-tetraacetic acid for chelating gadolinium nanoparticles (Gd3+) that provide magnetic properties to the Pdots. Thus, the synthesized Pdots possess fluorescent and magnetic properties, imparted by PTAA and Gd3+, respectively. Fluorescence spectroscopy and microscopy revealed that the synthesized dual-functional Gd3+-Pdots exhibited detectable fluorescent signals even at lower concentrations. Magnetic levitation experiments indicated that the Gd3+-Pdots could be easily manipulated via an external magnetic field. These findings illustrate that the dua- functional Gd3+-Pdots could be potentially utilized as fluorescent reporters that can be magnetically manipulated for bioimaging applications.

Exploring Various Techniques for the Chemical and Biological Synthesis of Polymeric Nanoparticles

Nanoparticles (NPs) have remarkable properties for delivering therapeutic drugs to the body’s targeted cells. NPs have shown to be significantly more efficient as drug delivery carriers than micron-sized particles, which are quickly eliminated by the immune system. Biopolymer-based polymeric nanoparticles (PNPs) are colloidal systems composed of either natural or synthetic polymers and can be synthesized by the direct polymerization of monomers (e.g., emulsion polymerization, surfactant-free emulsion polymerization, mini-emulsion polymerization, micro-emulsion polymerization, and microbial polymerization) or by the dispersion of preformed polymers (e.g., nanoprecipitation, emulsification solvent evaporation, emulsification solvent diffusion, and salting-out). The desired characteristics of NPs and their target applications are determining factors in the choice of method used for their production. This review article aims to shed light on the different methods employed for the production of PNPs and to discuss the effect of experimental parameters on the physicochemical properties of PNPs. Thus, this review highlights specific properties of PNPs that can be tailored to be employed as drug carriers, especially in hospitals for point-of-care diagnostics for targeted therapies.

Nonaqueous Emulsion Polycondensation Enabled by a Self-Assembled Cage-like Surfactant.

Nonaqueous emulsions are crucial for a range of applications based on water‐sensitive systems such as controlled polymerizations requiring anhydrous reaction conditions and the stabilization of readily hydrolyzable reagents or pharmacologically active components. However, defined molecular surfactants to stabilize such nonaqueous emulsions are scarce. We introduce a self‐assembled coordination cage, decorated with cholesterol functionalities, to serve as a molecular surfactant for various oil‐in‐oil emulsions of immiscible organic solvents. While the positively charged cage forms the amphiphile's polar moiety, the non‐polar cholesterol appendices can bend in a common direction to stabilize the emulsion. Templated by the droplets, polycondensation reactions were carried out to produce microstructured polyurethane and polyurea materials of different particle sizes and morphologies. Further, the amphiphilic cage can encapsulate a guest molecule and the resulting host‐guest assembly was also examined as a surfactant. In addition, the aggregation behavior of the amphiphilic cage in an aqueous medium was examined.

Cuprous oxide modified nanoencapsulated phase change materials fabricated by RAFT miniemulsion polymerization for thermal energy storage and photothermal conversion

Phase change materials (PCMs) have great promise in many fields related to energy utilization and thermal management. However, PCMs face great challenges in large-scale applications due to the intrinsic melting leakage, low thermal conductivity and poor photothermal conversion. Herein, nanoencapsulated phase change materials (NanoPCMs) were fabricated by RAFT miniemulsion polymerization using quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methyl methacrylate) (QPDMAEMA-b-PMMA) as emulsifier. N-octadecane and n-butyl stearate were used as binary cores, and Cu2O nanoparticles were doped into PMMA as hybrid shell. The resulting Cu2O/PMMA-NanoPCMs had an encapsulation efficiency of 86.68%, excellent thermal stability and thermal cycle durability. The thermal conductivity was enhanced by 67.25% compared with the original nanocapsules. Furthermore, the cotton fabrics finished with Cu2O/PMMA-NanoPCMs showed fast thermal response and superior photothermal conversion. Therefore, the synthesized nanocapsules are considered as potential candidates in the field of solar energy utilization and smart thermo-regulated textiles.

Encapsulation of Phase Change Materials via Interfacial Miniemulsion Polymerization for High Thermal Energy Storage Density

AbstractPhase change material (PCM) capsules have potential applications as a thermal management material in energy‐efficient buildings. It is desirable for PCM capsules to have high core‐loading and sub‐micrometer particle size. Herein, it is reported that interfacial reversible addition‐fragmentation chain transfer (RAFT) miniemulsion polymerization can be a convenient method to synthesize high PCM loading polymeric capsule latex. It is found that increasing particle size should be helpful to obtain well‐defined capsules of high PCM loading but post‐addition of surfactant should be carried out to remain the colloidal stability during polymerization. In the case of high PCM loading, a limiting conversion is observed. Increasing crosslinker (DVB) level up to 20 wt% based on monomers can increase the limiting conversion up to 94%. The well‐defined paraffin capsules of 365 nm in diameter is synthesized with 67 wt% PCM loading. The paraffin capsules have a crystallization/melting heat around 105 J g−1. Replacing paraffin with pure n‐octadecane, the crystallization/melting heat is increased up to 144 J g−1.

Effect of Fatty Acid Polyunsaturation on Synthesis and Properties of Emulsion Polymers Based on Plant Oil-Based Acrylic Monomers.

This study demonstrated that polymerization behavior of plant oil-based acrylic monomers (POBMs) synthesized in one-step transesterification reaction from naturally rich in oleic acid olive, canola, and high-oleic soybean oils is associated with a varying mass fraction of polyunsaturated fatty acid fragments (linoleic (C18:2) and linolenic (C18:3) acid esters) in plant oil. Using miniemulsion polymerization, a range of stable copolymer latexes was synthesized from 60 wt.% of each POBM and styrene to determine the impact of POBM chemical composition (polyunsaturation) on thermal and mechanical properties of the resulted polymeric materials. The unique composition of each plant oil serves as an experimental tool to determine the effect of polyunsaturated fatty acid fragments on POBM polymerization behavior and thermomechanical properties of crosslinked films made from POBM-based latexes. The obtained results show that increasing polyunsaturation in the copolymers results in an enhanced crosslink density of the latex polymer network which essentially impacts the mechanical properties of the films (both Young’s modulus and toughness). Maximum toughness was observed for crosslinked latex films made from 50 wt.% of each POBM in the monomer feed.

Sulfur-rich polymer nanoparticles prepared by miniemulsion polymerization.

The inclusion of sulfur in polymer materials is becoming an excellent strategy to exploit the large feedstock of elemental sulfur produced as waste by the oil industry. However, the resulting polymers have limited processability. Here we leverage the benefits of polymerization in dispersed media to produce suspensions of sulfur-rich polymer latexes that are water processable.

ω-Unsaturated methacrylate macromonomers as reactive polymeric stabilizers in mini-emulsion polymerization

Mini-emulsion polymerizations stabilized by ω-unsaturated methacrylate macromonomers showed dimpled particle morphologies and in addition bimodal particle size distributions when high concentrations were used.