Polymeric Stabilizer Research Articles

Alizarin Yellow R (AYR) as compatible stabilizer for miniemulsion polymerization

HypothesisMany solid particles have been used in Pickering stabilized (mini)emulsions. Stabilizing “particles” can be also formed in situ e.g. by aggregation of dye molecules as reported recently. Among the dyes sodium 2-hydroxy-5-[(E)-(4-nitrophenyl)diazenyl]benzoate (Alizarin Yellow R, (AYR)) is one of the best stabilizers. It is assumed to act as sole stabilizer also in heterophase polymerizations and offers a great potential for applications. ExperimentsAqueous solutions of AYR in varying concentrations (0.3, 0.5, 1.0, 1.5, 2.0mg/mL (dye/water)) were employed as continuous phase in direct miniemulsions. The oil phase comprised ethenylbenzene (styrene) and hexadecane. The effects of AYR concentration and ultrasonication time on size and distribution of the droplets were investigated. The miniemulsions were polymerized with a water-soluble azo-initiator (2,2′-azobis[n-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, VA-057) and conversion and kinetics were determined. FindingsThe AYR is successfully employed as stabilizer in Pickering-like miniemulsion polymerizations of styrene. The higher the AYR concentrations the more stable the miniemulsions, the smaller the droplet sizes and the narrower the distributions are, ranging from ca. 450 to 180nm and 0.38 to 0.15, respectively. The nucleation mechanism of the polymer particles could be revealed by the number ratio of droplets and particles and follows droplet nucleation. This is confirmed by polymerization kinetics, which is in accordance with classical miniemulsion polymerization, too.

Assessment of strength development in stabilized soil with CBR PLUS and silica sand

Abstract This paper investigates the potential use of a nano polymer stabilizer, namely CBR PLUS for stabilization of soft clay and formulation of an optimal mix design of stabilized soil with CBR PLUS and silica sand. The highway settlements induced by the soft clay are problematic due to serious damages in the form of cracks and deformation. With respect to this, soil compaction and stabilization is regarded as a viable method to treat shallow soft clayey ground for supporting highway embankment. The objectives of this paper are: i) to stabilize the compacted soil with CBR PLUS and silica sand in the laboratory; and ii) to evaluate the permeability, strength and California bearing ratio (CBR) of the untreated and stabilized soil specimens. The suitability of stabilized soil was examined on the basis of standard Proctor compaction, CBR, unconfined compression, direct shear, and falling head permeability tests. Furthermore, the chemical composition of the materials was determined using X-ray Fluorescence (XRF) test. It was found that the optimal mix design of the stabilized soil is 90% clay, 1% CBR PLUS, 9% silica sand. It is further revealed that, stabilization increases the CBR and unconfined compressive strength of the combinations by almost 6-fold and 1.8-fold respectively. In summary, a notable discovery is that the optimum mix design can be sustainably applied to stabilize the shallow clay without failure.

Assembly of highly stable aqueous dispersions and flexible films of nitrogen-doped graphene for high-performance stretchable supercapacitors

Here, we propose a route for production of highly stable nitrogen-doped graphene (NG) aqueous dispersions and flexible NG films. The NG dispersions are formed through sonication of NG hydrogels in methyl orange solution and stabilized through electrostatic repulsion without using any polymeric or surfactant stabilizer. The flexible NG films are formed by vacuum filtration of as-prepared NG dispersions and transferred onto stretchable and adhesive polyacrylate for the fabrication of stretchable supercapacitors. The supercapacitor exhibits high gravimetric specific capacitances of 315 F g−1 under no strain and 300 F g−1 under 30% applied strain at a current density of 1 A g−1. The fabrication of aqueous dispersions and stretchable NG films makes NG materials attractive for a diversity of applications in stretchable electronics.

Room‐Temperature Processing of Printed Oxide FETs Using Ultraviolet Photonic Curing

Oxide semiconductors are highly suitable materials for solution‐processed/printed electronics (PE); the growing interest in them can be related to their excellent intrinsic properties, such as high mobility, optical transparency, thermal and environmental stability, and so on. However, high process temperatures remain as the foremost challenge that may limit the compatibility of printed oxide electronics to inexpensive flexible substrates. Here, the possibility of using photonic curing methods to lower the process temperature is investigated, even down to room temperature (RT). Two distinct ultraviolet (UV) curing techniques, involving UV–visible light pulses and continuous‐wave UV lasers are exercised and compared. Combining UV curing with oxide nanoparticulate channel layer and electrolytic gate insulators, it is demonstrated that high performance field‐effect transistors (FETs) with device mobility as high as 12 cm2 V−1 s−1 can be processed entirely at room temperature and realized on plastic substrates. The fabrication steps include printing of a heavily stabilized semiconducting nanoparticulate channel layer, followed by decomposition and removal of the semi‐insulating polymer ligands using UV‐photon energies. The curing process is found to be fast and high‐throughput manufacturing technique compatible. At the same time, the energy requirement to remove the polymer stabilizers is insignificant, thereby ensuring no temperature rise of the parent substrates.

Freezing Directed Construction of Bio/Nano Interfaces: Reagentless Conjugation, Denser Spherical Nucleic Acids, and Better Nanoflares

While nanoparticle solutions cannot freeze in general, they may remain stable in the presence of polymer stabilizers. We herein communicate that gold nanoparticles (AuNPs) are stable in the presence of thiolated DNA after a freeze-thaw cycle. The DNA is conjugated to AuNPs during freezing without additional reagents and the conjugation can be completed in a few minutes. More importantly, the DNA density is 20-30% higher than that prepared by the typical salt-aging method. By lowering temperature, DNA hybridization is also promoted, allowing the construction of better nanoflares with doubled probe density and signaling sensitivity. This freezing method works for AuNPs from 5 to 100 nm and all tested DNA sequences. The mechanism was studied by separating the effect of temperature, freezing and thawing, where the exclusion of salt and AuNPs by the growing ice crystals is deemed critical. In addition to developing a simple method, this study articulates unique physical processes during freezing with important fundamental surface science implications, and it could be extended to other systems.

Stable, Fluorescent Polymethylmethacrylate Particles for the Long-Term Observation of Slow Colloidal Dynamics.

Suspensions of solid micron-scale colloidal particles in liquid solvents are a foundational model system used to explore a wide range of phase transitions, including crystallization, gelation, spinodal decomposition, and the glass transition. One of the most commonly used systems for these investigations is the fluorescent spherical particles of polymethylmethacrylate (PMMA) suspended in a mixture of nonpolar solvents that match the density and the refractive index of the particles to minimize sedimentation and scattering. However, the particles can swell in these solvents, changing their size and density, and may leak the fluorescent dye over days to weeks; this constrains the exploration of slow and kinetically limited processes, such as near-boundary phase separation or the glass transition. In this paper, we produce PMMA colloidal particles that employ polymerizable and photostable cyanine-based fluorescent monomers spanning the range of visible wavelengths and a polymeric stabilizer prepared from polydimethylsiloxane, PDMS-graft-PMMA. Using microcalorimetry, we characterize the thermodynamics of an accelerated equilibration process for these dispersions in the buoyancy- and refractive-index-matching solvents. We use confocal differential dynamic microscopy to demonstrate that they behave as hard spheres. The suspended particles are stable for months to years, maintaining fixed particle size and density, and do not leak dye. Thus, these particles enable longer term experiments than may have been possible earlier; we demonstrate this by observing spinodal decomposition in a mixture of these particles with a depletant polymer in the microgravity environment of the International Space Station. Using fluorescence microscopy, we observe coarsening over several months and measure the growth of the characteristic length scale to be a fraction of a picometer per second; this rate is among the slowest observed in a phase-separating system. Our protocols should facilitate the synthesis of a variety of particles.

Highly Active Gold and Gold–Palladium Catalysts Prepared by Colloidal Methods in the Absence of Polymer Stabilizers

AbstractSupported gold and gold–palladium nanoparticles were found to be effective catalysts for the selective oxidation of glycerol and benzyl alcohol. The properties and stabilities of catalysts are often sensitive to factors such as the dimensions, shape, and composition of the metal nanoparticles. Although colloidal methods provide an easy and quick way to synthesize supported metal catalysts, they typically involve the use of polymers such as polyvinyl alcohol and polyvinylpyrrolidone as steric stabilizers, which can sometimes be detrimental in subsequent catalytic reactions. Herein, we report the synthesis of supported gold and gold–palladium nanoparticles without the addition of stabilizing polymers. The catalysts prepared with and without the addition of polymers performed very similarly in the selective oxidation of glycerol and benzyl alcohol, which suggests that polymers are not essential to make active catalysts for these reactions. Thus, this new stabilizer‐free method provides a facile and highly effective way of circumventing the inherent problems of polymer stabilizers in the preparation of gold and gold–palladium catalysts.

Evaluation of age retardation effect of antioxidants in dense-graded asphalt (DGA) mixture using large molecular size

This study evaluated the effectiveness of antioxidant (AO) on retarding aging of asphalt mixture using the large molecular size (LMS) of gel-permeation chromatogram (GPC) technique. A polymer stabilizer (designated as KL) and a hydrated lime (HL) were used for preparing dense-graded asphalt (DGA) mixes to examine the effect of the AOs on age retardation. The asphalt mixtures prepared with and without AO were aged artificially in two stages; the short-term aging (SA) for one hour at 160°C and the long-term aging (LA) for one week at 76°C. The LMS values were used in the statistical test for estimation of age retardation effect of the AOs and for predicting absolute viscosity. It was found that the KL and HL were effective for inducing reduction of aging significantly at α=0.05 after SA and LA. Therefore, it was found that the LMS, which was obtained by GPC test, was a dependable variable that can be used for evaluation of age retardation. It was also observed that the KL and HL did apparently have an effect of reducing the AV, predicted by LMS, after SA and LA.

Mixing Methods Evaluation of a Styrene-Acrylic Based Liquid Polymer for Sand and Clay Stabilization

In recent years, alternative soil stabilizers to supplement to cementitious soil stabilizers have been attempted for some applications and provided promising results. This study focuses on the application of a low viscosity liquid polymer for shallow soil improvement. The mixing method of soil specimens treated with the liquid polymer soil stabilizer, which belongs to Styrene Acrylic family, was studied through an experimental testing program. The tested soils included poorly graded sand and sulfate-rich clay. The water, liquid polymer and dry soil were mixed with different sequence to assess the effect on strength. The specimens were cured in controlled environment for up to 35 days before tested. It was found that the curing of the polymer stabilizer in sand and clay were time consuming and took to a month to reach their full strength. The mixing method did not show tangible difference for stabilized sandy specimens and demonstrated significant effect on stabilized clay specimen. Specifically, as to clay, when water was added after the dried soil and polymer were thoroughly, no improvement was observed.

Efavirenz Dissolution Enhancement IV-Antisolvent Nanocrystallization by Sonication, Physical Stability, and Dissolution.

Efavirenz is a fundamental drug in the HIV therapy; however, it has a low bioavailability due to low water solubility. Particle nanonization should enhance its dissolution and therefore its bioavailability. Nanocrystallization is a promising technique for preparing drug nanocrystals. A solution containing efavirenz (EFV) and methanol was added to an aqueous solution of particle stabilizers, under sonication. The adequate polymer stabilizer and its concentration and drug load were evaluated. Particle size and zeta potential of suspensions were measured. Nanosuspensions were freeze-dried and the resulting powder was characterized by some techniques, with special attention to dissolution. Particle size and zeta potential analysis showed that HMPC and PVP were the most suitable polymers. All samples prepared with these stabilizers had nanosized particles and proper zeta potential; however, sedimentation and particle growth were detected with Turbiscan™. Time-related destabilization occurred when the lowest polymer concentration of 20% was used. SEM analysis of the dried powder shows film formation for suspensions with 40% of polymer and particle aggregation in samples with less polymer. Dissolution profiles of samples were higher than EFV raw material, although the lower the polymer concentration, the higher the dissolution.

Urchin-like gold microstructures with tunable length of nanothorns

In this paper, we exploited a unique reaction of silver ions to create and design urchin-like gold microstructures (UL-AuMSs) with controllable length of nanothorns. The UL-AuMSs were synthesized via a simple one-pot synthetic protocol without using any surface capping agents or polymeric stabilizers. The reactants consisted of tetrachloroauric (III) acid, silver nitrate, and hydrogen peroxide (H2O2). H2O2 functioned as the sole reducing agent while trace silver ions played an important role as the shape controlling agent. Without trace silver ions, quasi-sphere gold microstructures (QS-AuMSs) were obtained. The time-dependent SEM investigations corroborated that UL-AuMSs and QS-AuMSs grew from flower-like gold microstructures (FL-AuMSs). The added trace silver ions reacted with physically adsorbed chloride ions on gold surfaces and formed into solid silver chloride capable of altering the dendritic growth of QS-AuMSs to the dominated trunk-growth of UL-AuMSs. The cleaned UL-AuMSs with average thorn lengths of 166 and 187nm expressed high SERS activity as 0.1nM of Rhodamine 6G could be detected with a short 15-min incubation. The easily visualized UL-AuMSs under a microscope assisting the SERS detection at selected spots was demonstrated.

Controlled cationic polymer particles prepared by dispersion polymerizations using poly(l-lysine) macromonomers as a stabilizer

A novel poly(l-lysine) macromonomer was successfully prepared via a click reaction between vinyl benzyl azide and propargyl-terminated poly(l-lysine), and it was used as a functional stabilizer for the dispersion polymerization of styrene; narrowly distributed polystyrene particles were produced as a result, onto which cationic poly(l-lysine) chains were grafted. The resulting particles exhibited a pH-responsive dispersion behavior in aqueous solutions due to the properties of the poly(l-lysine) chains at the particle surface. It was found that the particle size and the surface density of the resultant particles could be varied by tuning the concentrations of the macromonomer, styrene, and initiator used in the initial solution of the dispersion polymerization. The poly(l-lysine) macromonomer was also found to be effective when used as a stabilizer for the dispersion polymerization of both methyl methacrylate and a styrene/acrylonitrile mixture.

Technical improvement for producing porous polymer microspheres in foam phase

This study has developed a method to produce porous polymeric microspheres in a foam phase. And, the foam phase was a mixture of polymer, organic solvent, porogen and emulsion stabilizer. The process was comprised of a series of constant steps homogenization of the materials, growth of the foam phase and collection of the products. The growth of the foam phase was the key which combined mechanical agitation, solvent evaporation and oil droplets development under increasing temperature. The method has been seen time-saving, high yield and continuous process and it could be useful for industrial production of porous polymer microspheres in a continuous process.

On the possibility of preparing stable silver iodide nanosols in the presence of chitosan used as a polymer stabilizer

The effect of preparation conditions for positively and negatively charged silver iodide sols on the particle size and number concentration has been determined. It has been found that the preparation of a mixture of precursors with a concentration of 0.01 mol/L at a KI to AgNO3 volume ratio of 10: 7 or 7: 10 leads to the formation of a large number of small particles (on the order of 50–60 nm) corresponding to the range of true colloidal systems with a maximum interfacial area. The presence of a polymer stabilizer–chitosan–leads to a significant improvement of the stability of the sol particles, which makes it possible to use the resulting polymer-colloidal dispersions containing nanoparticles of silver iodide sols to design hybrid materials for biomedical applications.

(Invited) Processing and Applications of Monodisperse Two-Dimensional Nanomaterial Inks

Two-dimensional nanomaterials have emerged as promising candidates for next-generation electronics and optoelectronics [1], but advances in scalable nanomanufacturing are required to exploit this potential in real-world technology. This talk will explore methods for improving the uniformity of solution-processed two-dimensional nanomaterials with an eye toward realizing dispersions and inks that can be deposited into large-area thin-films [2]. In particular, density gradient ultracentrifugation allows the solution-based isolation of graphene [3], boron nitride [4], montmorillonite [5], and transition metal dichalcogenides (e.g., MoS2, WS2, ReS2, MoSe2, WSe2) [6,7] with homogeneous thickness down to the atomically thin limit. Similarly, two-dimensional black phosphorus is isolated in organic solvents [8] or deoxygenated aqueous surfactant solutions [9] with the resulting phosphorene nanosheets showing field-effect transistor mobilities and on/off ratios that are comparable to micromechanically exfoliated flakes. By adding cellulosic polymer stabilizers to these dispersions, the rheological properties can be tuned by orders of magnitude, thereby enabling two-dimensional nanomaterial inks that are compatible with a range of additive manufacturing methods including inkjet [10], gravure [11], screen [12], and 3D printing [13]. The resulting printed two-dimensional nanomaterial structures show promise in several applications including photodiodes [14], anti-ambipolar transistors [15], gate-tunable memristors [16], and heterojunction photovoltaics [17,18]. [1] D. Jariwala, et al., ACS Nano, 8, 1102 (2014). [2] E. B. Secor, et al., Journal of Physical Chemistry Letters, 6, 620 (2015). [3] A. A. Green, et al., Nano Letters, 9, 4031 (2009). [4] J. Zhu, et al., Nano Letters, 15, 7029 (2015). [5] J. Zhu, et al., Advanced Materials, 28, 63 (2016). [6] J. Kang, et al., Nature Communications, 5, 5478 (2014). [7] J. Kang, et al., Nano Letters, 16, 7216 (2016). [8] J. Kang, et al., ACS Nano, 9, 3596 (2015). [9] J. Kang, et al., Proc. Nat. Acad. Sci. USA, 113, 11688 (2016). [10] E. B. Secor, et al., Journal of Physical Chemistry Letters, 4, 1347 (2013). [11] E. B. Secor, et al., Advanced Materials, 26, 4533 (2014). [12] W. J. Hyun, et al., Advanced Materials, 27, 109 (2015). [13] A. E. Jakus, et al., ACS Nano, 9, 4636 (2015). [14] D. Jariwala, et al., Proc. Nat. Acad. Sci. USA, 110, 18076 (2013). [15] D. Jariwala, et al., Nano Letters, 15, 416 (2015). [16] V. K. Sangwan, et al., Nature Nanotechnology, 10, 403 (2015). [17] D. Jariwala, et al., Nano Letters, 16, 497 (2016). [18] T. A. Shastry, et al., ACS Nano, 10, 10573 (2016).

The impact of porous silicon nanoparticles on human cytochrome P450 metabolism in human liver microsomes in vitro

Engineered nanoparticles are increasingly used as drug carriers in pharmaceutical formulations. This study focuses on the hitherto unaddressed impact of porous silicon (PSi) nanoparticles on human cytochrome P450 (CYP) metabolism, which is the major detoxification route of most pharmaceuticals and other xenobiotics. Three different surface chemistries, including thermally carbonized PSi (TCPSi), aminopropylsilane-modified TCPSi (APTES-TCPSi) and alkyne-terminated thermally hydrocarbonized PSi (Alkyne-THCPSi), were compared for their effects on the enzyme kinetics of the major CYP isoforms (CYP1A2, CYP2A6, CYP2D6, and CYP3A4) in human liver microsomes (HLM) in vitro. The enzyme kinetic parameters, Km and Vmax, and the intrinsic clearance (CLint) were determined using FDA-recommended, isoenzyme-specific model reactions with and without PSi nanoparticles. Data revealed statistically significant alterations of most isoenzyme activities in HLM in the presence of nanoparticles at 1mg/ml concentration, and polymorphic CYP2D6 was the most vulnerable to enzyme inhibition. However, the observed CYP2D6 inhibition was shown to be dose-dependent in case of TCPSi and Alkyne-THCPSi nanoparticles and attenuated at the concentrations below 1μg/ml. Adsorption of the probe substrates onto the hydrophobic Alkyne-THCPSi particles was also observed and taken into account in the determination of the kinetic parameters. Three polymer additives commonly used in pharmaceutical nanoformulations (Pluronics F68 and F127, and polyvinylalcohol) were also separately screened for their effects on CYP isoenzyme activities. These polymers had less effect on the enzyme kinetic parameters, and resulted in increased activity rather than enzyme inhibition, in contrast to the PSi nanoparticles. Although the chosen subcellular model (HLM) is not able to predict the cellular disposition of PSi nanoparticles in hepatocytes and thus provides limited information of probability of CYP interactions in vivo, the present study suggests that mechanistic interactions by the PSi nanoparticles or the polymer stabilizers may appear if these are effectively uptaken by the hepatocytes.

Morphology and thermodynamics of selenium-containing nanosystems: The effect of polymer stabilizers

Nanosystems based on zero-valent selenium and biocompatible polymer stabilizers (polyvinylpyrrolidone with molecular weight (MW) М w = (10–55) × 103, poly-N,N,N,N-trimethylacryloyloxyethylammonium methylsulfate with М w = (30–250) × 103 and polyethylene glycol with М w = (1–40) × 103) are studied by means of static and dynamic light scattering, and the resulting data are compared. Dense spherical multimolecular nanosystems are found to be formed. Morphological and thermodynamic characteristics of selenium-containing nanosystems, depending on the nature and MW of the polymer stabilizer, are determined. It is shown that the properties of nanosystems can be adjusted by varying the molecular weight of the polymer stabilizer.

Effect of the Polymeric Stabilizer in the Aqueous Phase Fischer-Tropsch Synthesis Catalyzed by Colloidal Cobalt Nanocatalysts.

A series of small and well defined cobalt nanoparticles were synthesized by the chemical reduction of cobalt salts in water using NaBH4 as a reducing agent and using various polymeric stabilizers. The obtained nanocatalysts of similar mean diameters (ca. 2.6 nm) were fully characterized and tested in the aqueous phase Fischer-Tropsch Synthesis (AFTS). Interestingly, the nature and structure of the stabilizers used during the synthesis of the CoNPs affected the reduction degree of cobalt and the B-doping of these NPs and consequently, influenced the performance of these nanocatalysts in AFTS.

Polymorph formation in fenofibrate in the absence and presence of polymer stabilizers: a low wavenumber Raman and differential scanning calorimetry study

In situ, variable temperature low wavenumber Raman spectroscopy and differential scanning calorimetry together with scanning electron microscope imaging were used to investigate polymorph formation in the non‐hydrogen bonded, anti‐cholesterol drug fenofibrate (FNB), in the absence and presence of two non‐ionic polymeric stabilizers: triBlock copolymer pluronic‐F127 (PF/127) and hydroxypropyl methyl cellulose (HPMC/E3).Low wavenumber Raman spectra show that metastable phase II formation occurs on initial cooling to 25 °C following the first heat‐up to 100 °C for both pure FNB and FNB in the presence of PF/127, but not in the presence of HPMC/E3. Differential scanning calorimetry results on the other hand show that phase II of FNB crystallizes near 75 °C during the first heat‐up of the drug in the presence of PF/127 but was not observed in the pure drug or the drug in the presence of HPMC/E3. These results are discussed in terms of molecular simulations carried out to determine the non‐bonded interaction energies between the polymers and FNB. Copyright © 2017 John Wiley & Sons, Ltd.

Development of a Predictive Model for the Stabilizer Concentration Estimation in Microreservoir Transdermal Drug Delivery Systems Using Lipophilic Pressure-Sensitive Adhesives as Matrix/Carrier

Microreservoir-type transdermal drug delivery systems (MTDDS) can prevent drug crystallization; however, no current predictive model considers the impact of drug load and hydration on their physical stability. We investigated MTDDS films containing polyvinylpyrrolidone (PVP) as polymeric drug stabilizer in lipophilic pressure-sensitive adhesive (silicone). Medicated and unmedicated silicone films with different molar N-vinylpyrrolidone:drug ratios were prepared and characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, microscopy, dynamic vapor sorption (DVS), and stability testing for 4 months at different storage conditions. Homogeneously distributed drug-PVP associates were observed when nonaqueous emulsions, containing drug-PVP (inner phase) and silicone adhesive (outer phase), were dried to films. DVS data were essential to predict physical stability at different humidities. A predictive thermodynamic model was developed based on drug-polymer hydrogen-bonding interactions, using the Hoffman equation, to estimate the drug-PVP ratio needed to obtain stable MTDDS and to evaluate the impact of humidity on their physical stability. This new approach considers the impact of polymorphism on drug solubility by using easily accessible experimental data (Tm and DVS) and avoids uncertainties associated with the solubility parameter approach. In conclusion, a good fit of predicted and experimental data was observed.