Polymeric Stabilizer Research Articles

The Impact of Process and Formulation Parameters on the Fabrication of Efavirenz Nanosuspension to Improve Drug Solubility and Dissolution.

Efavirenz nanosuspensions (EZ-NSs) were developed by the wet milling method as the most promising top-down nanosizing technique. Different process and formulation parameters were studied and optimized to produce appropriate EZ-NS in suitable conditions to enhance drug dissolution. In the preliminary studies, various polymeric stabilizers, including Pluronic F68, sodium carboxymethylcellulose (CMC), hydroxypropyl methylcellulose (HPMC), and polyvinyl alcohol (PVA), as well as different sizes and weight of milling beads were used to prepare NSs. The effect of sodium lauryl sulfate (SLS) concentration on the NS properties was also evaluated. The influence of other formulation and process parameters, including polymer concentration, milling speed, and milling time, on the particle size and distribution of NSs were investigated using Box-Behnken design. The optimized freeze-dried nanosuspension was characterized by redispersibility, physicochemical properties, and stability. A combination of PVA and SLS was selected as steric and electrostatic stabilizers. The optimum EZ-NS displayed a uniform size distribution with a mean particle size and zeta potential of 254.4 nm and 21.1 mV, respectively. The solidified nanosuspension was well redispersed to the original nanoparticles. Significantly enhanced aqueous solubility (about 11-fold) and accelerated dissolution rate were observed for the optimized formulation. This could be attributed to the reduced particle size and partial amorphization of EZ during the preparation process, studied by X-ray diffraction. Accelerated studies confirmed the stability of the optimum freeze-dried formulation over the examined period of three months. Optimization of different variables led to the formation of EZ-NSs with desired properties through wet milling in a very short time compared to the previous study and therefore reduced production costs. This formulation seems to be a suitable approach for solubility and dissolution enhancement of EZ and may have a great potential to improve the drug's oral bioavailability.

Compressibility and cracking properties of soft soils treated with a polymeric stabiliser

The influence of polyacrylamide (PAM) on the mechanical and physical characteristics of two kinds of soft soils was investigated laboratory tests including consistency, standard Proctor compaction, incremental loading consolidation and desiccation tests were conducted on the untreated and treated soils. Based on results, addition of PAM caused a reduction in the soils' plasticity indices. Although adding PAM slightly increased the maximum dry density, it had a negligible impact on the optimum moisture content. An increase in PAM content reduced compressibility, initial void ratio, compression and swelling indices, coefficient of consolidation and permeability. Adding PAM caused the cracking potential of soils to decrease. Moreover, to have a better interpretation of the stabilisation mechanism as well as the microstructural changes induced by PAM, the field emission scanning electron microscopy and X-ray diffraction analyses were conducted on the soils. The results demonstrated that the PAM additive enables physical bonding between soil particles rather than chemical reactions. In other words, PAM does not change the soil in terms of the atomic structure of clay particles, rather it alters the whole structure of the clay mass by accumulating particles and creating a strong connection network between them by flocculating the aggregates.

Poly(acrylic acid) block copolymers as stabilizers for dispersion polymerization

Dispersion polymerization stabilized with poly(acrylic acid) has been performed for decades to produce polymer particles whose surfaces are modified with pH-responsive poly(acrylic acid) moieties. To improve stabilizer efficiency, poly(acrylic acid) block copolymers, in which a poly(acrylic acid) chain is attached to the terminus of a polystyrene or PMMA chain, were used as stabilizers for the dispersion polymerization of styrene or MMA. Compared with the poly(acrylic acid) homopolymer, polystyrene-block-poly(acrylic acid) was found to improve the controllable ranges of particle size and the carboxylic-acid-group surface density of the resulting polystyrene particles. Furthermore, we also investigated the effect of heterogeneity between the polymer species of the particle core and the attached polystyrene or PMMA chains in the poly(acrylic acid) block copolymers. Finally, we also examined the applicability of polystyrene-block-poly(acrylic acid) as a stabilizer and surface modifier for the dispersion polymerization of various monomers.

Molecular dynamics study of polymeric stabilizers as soil improvement materials

Environmentally friendly polymer materials have shown good potential and great development space in improving structural stability, reducing runoff erosion and promoting plant growth. Therefore, the adsorption behavior of five layered silicate clay minerals and six common polymer stabilizers under dry conditions was studied by Molecular dynamics method. The results show that PMMA has good balance and is suitable for the improvement of various clay types; CMC and PVA are suitable for improving clay with more montmorillonite; PASP, PU and PVAc are suitable for the improvement of clay with more muscovite mica, among which PASP has the best improvement effect.

Dissolution Behavior of Weakly Basic Pharmaceuticals from Amorphous Dispersions Stabilized by a Poly(dimethylaminoethyl Methacrylate) Copolymer.

Amorphous solid dispersions (ASDs) are a well-documented formulation approach to improve the rate and extent of dissolution for hydrophobic pharmaceuticals. However, weakly basic compounds can complicate standard approaches to ASDs due to pH-dependent solubility, resulting in uncontrolled drug release in gastric conditions and unstabilized supersaturated solutions prone to precipitation at neutral pH. This work examines the release mechanisms of amorphous dispersions containing model weakly basic pharmaceuticals posaconazole and lumefantrine from a basic poly(dimethylaminoethyl methacrylate) copolymer (Eudragit EPO) and compares their dissolution behavior with ASDs stabilized by acidic and neutral polymers to understand potential benefits to release from a basic polymeric stabilizer. It was found that dissolution of Eudragit EPO ASDs resulted in supersaturation under gastric conditions, which could be sustained upon adjustment to neutral pH. However, the dissolution behavior of Eudragit EPO ASDs was sensitive to the initial pH of the gastric media. For lumefantrine, elevated initial gastric pH resulted in precipitation of amorphous nanoparticles; for posaconazole, elevated gastric pH led to crystallization of the pharmaceutical from solution. This sensitivity to gastric pH was found to originate from the impact of Eudragit EPO on gastric pH and the solubility of each pharmaceutical in the first stage of dissolution. In total, these data illustrate benefits and liabilities for the use of Eudragit EPO for ASDs containing weak pharmaceutical bases to guide the design of robust pharmaceutical formulations.

30 Years of Vicente Rives’ Contribution to Hydrotalcites, Synthesis, Characterization, Applications, and Innovation

Hydrotalcite is the name of a mineral discovered in Sweden in 1842 whose formula is Mg6Al2(OH)16CO3·4H2O and presents a layered crystal structure that consists of positively charged hydroxide layers neutralized by interlayer anions as carbonate, also containing water molecules. The ease of their synthesis and the possibility of incorporating other layer cations and interlayer anions have made this type of layered double hydroxides (LDH) a group of very interesting materials for industry. In addition to LDH and due to the name of the most representative mineral, this group of compounds is commonly called hydrotalcite-like materials, or simply hydrotalcites. Another way of referring to them is as anionic clays because of their layered structure but, unlike classical clays, their layers are positive and their interlayers are anionic. The main fields of application of these solids comprise catalysis, catalyst support, anion scavengers, polymer stabilizers, drug carriers, or adsorbents. This paper briefly summarizes some of the work carried out by Professor Rives over more than thirty years, focused, among other topics, on the study of the synthesis, characterization, and applications of hydrotalcites. This research has led him to train many researchers, to collaborate with research groups around the world and to publish reference papers and books in this field. This contribution, written to be included in the Special Issue “A Themed Issue in Honor of Prof. Dr. Vicente Rives”, edited on the occasion of his retirement, only shows a small part of his scientific research and intends to value and recognize his cleverness and his enormous scientific and human quality.

Enzyme-Catalyzed Polymerization Process: A Novel Approach to the Preparation of Polyaniline Colloidal Dispersions with an Immunomodulatory Effect.

A green, nature-friendly synthesis of polyaniline colloidal particles based on enzyme-assisted oxidation of aniline with horseradish peroxidase and chitosan or poly(vinyl alcohol) as steric stabilizers was successfully employed. Physicochemical characterization revealed formation of particles containing the polyaniline emeraldine salt and demonstrated only a minor effect of polymer stabilizers on particle morphology. All tested colloidal particles showed in vitro antioxidation activity determined via scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals. In vitro, they were able to reduce oxidative stress and inhibit the production of reactive oxygen species by neutrophils and inflammatory cytokines by macrophages. The anti-inflammatory effect observed was related to their antioxidant activity, especially in the case of neutrophils. The particles can thus be especially advantageous as active components of biomaterials modulating the early stages of inflammation. In addition to the immunomodulatory effect, the presence of intrinsically conducting polyaniline can impart cell-instructive properties to the particles. The approach to particle synthesis that we employed─an original one using environmentally friendly and biocompatible horseradish peroxidase─represents a smart way of preparing conducting particles with unique properties, which can be further modified by the stabilizers used.

Mobility of Sub-50 nm Iron Oxide Nanoparticles with Ultrahigh Initial Magnetic Susceptibility in Intact Berea Sandstone at High Salinity

Superparamagnetic iron oxide nanoparticles (IONPs), which have been investigated extensively as contrast-enhancing agents in biology, are being explored for subsurface applications such as electromagnetic tomography, fracture mapping, and enhanced oil recovery. However, two key challenges must be addressed: (a) high magnetic susceptibility and (b) colloidal stability and mobility under harsh reservoir conditions of high salinity and temperature. Herein, we synthesize IONPs grafted with poly(2-acrylamido-3-propanesulfonate-co-acrylic acid) poly(AMPS-co-AA) to achieve a high surface grafting density of polymer (49%) with minimal aggregation to yield sub-50 nm IONPs. The IONPs were found to be colloidally stable at 120 °C for a period of one month at pH 8. In crushed Berea sandstone, polymer-grafted IONPs exhibited significantly high mass breakthrough (84%) and low retention (149 μg/g) when used with a sacrificial polymer preflood (0.1% v/v). Intact Berea core experiments showed an 8-fold improvement in mass breakthrough (65%) and a two-thirds reduction in retention (from 433 μg/g to 160 μg/g) when compared to previous studies with IONPs synthesized via coprecipitation. The high grafting density of polymeric stabilizer and small nanoparticle size contribute to the improved mobility in consolidated porous media at high salinity.

Chemical bath synthesis of Ag2S, CuS, and CdS nanoparticle-polymer nanocomposites: structural, linear, and nonlinear optical characteristics

In this study, CdS, CuS, and Ag2S nanoparticles (NPs) were synthesized by a chemical bath procedure in the presence of polyvinyl alcohol (PVA) as a polymer stabilizer. Morphological studies followed by X-ray diffraction (XRD) and atomic force microscopy (AFM) revealed monolithic and small size NPs. The average crystalline size of CdS, Ag2S, and CuS nanocomposites was 18.1, 26.7, and 21.7 nm, respectively. UV-Vis absorption and photoluminescence (PL) spectra of samples showed a near-infrared region (NIR) emission peak for CuS. The bandgap of samples measured using absorption data was 3.48, 2.75, and 2.30 eV for CdS, Ag2S, and CuS NPs, respectively. Nonlinear optical properties, including nonlinear refractive index and nonlinear absorption of the NPs, were measured by the Z-scan technique under a 632.8 nm wavelength He-Ne CW laser. PVA/Ag2S nanocomposite displayed reverse saturable absorbance (RSA) and self-focusing, while PVA/CdS and PVA/CuS displayed saturable absorbance and self-defocusing behavior under the chemical bath procedure synthesis.

Facile Synthesis of Urchin-like Hollow Au Crystals for In Situ SERS Monitoring of Photocatalytic Reaction

Hollow urchin-like Au nanocrystals have been widely studied due to their excellent surface plasmon resonance properties and large specific surface area, but the controllable preparation of hollow urchin-like Au nanocrystals is still a challenge. In this article, we successfully prepared hollow urchin-like Au nanocrystals using HAuCl4·3H2O and AgNO3 as precursors and ascorbic acid as the reducing agent. No surface ligands or polymer stabilizers are required in the preparation process. HAuCl4·3H2O and AgNO3 will first form AgCl cubes, then the reducing agent, ascorbic acid, will reduce the Au3+ in the solution to Au0, and Au0 will be deposited on the pre-formed AgCl cubes to form AgCl@Au nanocrystals. We characterized the morphology of the prepared Au nanocrystals by scanning electron microscopy and found that by increasing the amount of HAuCl4·3H2O in the reaction, the surface morphology of the Au nanocrystals would change from a rough spherical shape to an urchin-like shape. By further increasing the amount of the precursor HAuCl4·3H2O, urchin-like Au will convert into flake-like morphology. The AgCl in the interior was removed with ammonia water, and finally, hollow urchin-like Au crystals were formed. In addition, we used R6G molecule to explore the surface-enhanced Raman spectroscopy (SERS) enhancement effect of prepared Au crystals. The results show that the minimum detectable concentration of R6G reaches 10−8 M. Moreover, we applied hollow urchin-like Au nanocrystals as catalysts and SERS enhancing materials to detect the photocatalytic reaction of 4-NTP. We used a 785 nm laser as both the SERS light source and the catalytic light source to monitor the photocatalytic effect of the laser on 4-NTP in situ by adjusting the laser power.

Permeability and heterogeneity adaptability of surfactant-alternating-gas foam for recovering oil from low-permeability reservoirs

As the traditional polymer stabilizer is eliminated to improve the injectability of foam in low-permeability reservoirs, the stability, plugging capacity, conformance control and oil recovery performance of the surfactant-alternating-gas (SAG) foam become significantly important for determining its adaptability to permeability and heterogeneity, which were focused and experimentally researched in this paper. Results show that the SAG bubbles are highly stable in micron-sized channels and porous media (than in the conventional unconstrained graduated cylinder), making it possible to use in enhanced oil recovery (EOR). Such bubbles formed in porous media could be passively adjusted to match their diameter with the size of the pore. This endows the SAG foam with underlying excellent injectability and deep migration capacity. Permeability adaptability results indicate a reduced plugging capacity, but, increased incremental oil recovery by the SAG foam with decreased permeability. This makes it a good candidate for EOR over a wide range of permeability, however, parallel core floods demonstrate that there is a limiting heterogeneity for SAG application, which is determined to be a permeability contrast of 12.0 (for a reservoir containing oil of 9.9 mPa s). Beyond this limit, the foam would become ineffective.

Surfactin-stabilized poly(D,L-lactide) nanoparticles for potential skin application

In recent years polymeric nanoparticles stabilized by biocompatible polyesters of poly(D,L-lactide) origin have been under investigation due to their favorable properties as drug nanocarriers useful for cosmetics and pharmaceutical applications. However, their design and fabrication are still limited to nonionic or polymeric stabilizers whose surface activity, toxicity, and biocompatibility may be insufficient for biological issues including transdermal applications. Therefore, there is still an ample room to look for more modern ionic biosurfactants that, apart from favorable surface properties, can ensure high biocompatibility of the system, increase the skin penetration of the active substance, and, in the future, possibly also the antimicrobial and antitumor activity of the produced nanocarrier. Accordingly, herein, we present poly(DL-lactide) nanoparticles stabilized by surfactin - a biocompatible anionic biosurfactant, for potential transdermal administration. The nanoparticles were obtained via a nanoprecipitation approach, and their physicochemical evaluation including size, surface charge, morphology, and colloidal stability was assessed. DLS measurements TEM and AFM confirmed, respectively, the obtained nanoparticles’ diameter below 200 nm as well as their morphology and shape. Electrophoretic light scattering provided negative ζ-potential of the studied nanoobjects while backscattering profiles made it possible to prove their long-term kinetic stability. In order to test the optimized nanoparticles under the surfactin concentration, cytotoxicity of the obtained systems was evaluated in vitro upon two normal human skin cell lines, i.e., HaCaT (human epidermal keratinocytes) and NHDF cells (normal human dermal fibroblasts). These studies indicated the safest concentration of the biosurfactant for nanoparticle stabilization. The skin permeability tests provided on pig ear skin proved the enhanced ability of the nanoparticles to deeper penetrate the epidermis after 5 h of the permeation test. The presented results prove that these surfactin-stabilized poly(D,L-lactide) nanoparticles are good biocompatible candidates for transdermal applications.

Impact of polymeric stabilisers on the reaction kinetics of SrBr2

Thermochemical heat storage (TCHS) in salt hydrates attracts increasing interest due to the high energy density combined with loss-free storage. Strontium bromide hexahydrate (SBH), and composites thereof, are often suggested as suitable materials for this application. Although many aspects of SBH composites have been thoroughly investigated, very little has been done on the fundamental aspects of the hydration reaction and interactions between composite components on a molecular level. In this paper, we examine the interaction between SBH and polymeric additives polydiallyldimethylammonium chloride (PDAC), sodium carboxymethyl cellulose (CMC), and polyacrylic acid (PAA) in previously developed TCHS composites. The primary function of the polymeric additives is enhanced mechanical integrity however this study investigates potential implications on reaction temperature and speed the addition of such components might have. Focus is given to the interaction between SrBr2 and PDAC since such composites showed (de)hydration behaviour deviating from pure SrBr2. The reaction kinetics are investigated at several points in the phase diagram through thermogravimetric analysis (TGA), supplemented by powder x-ray diffraction (XRD) studies. Our findings show that there exists an interaction between SrBr2 and PDAC which manifests itself through shrinkage of crystallite size and increased lattice strain induced by preferential binding of PDAC to SrBr2. Depending on the PDAC content in the composite we have found out that 1) at excessive amounts PDAC inhibits hydration due to its sequestering properties 2) at low amounts it an enhances reaction kinetics due its hydrophilic nature.

Novel multifunctional antioxidants for polymers using eugenol as biogenic building block

Novel molecular and polymeric antioxidants (AO) were successfully synthesized using eugenol (4-allyl-2-methoxyphenol) as biogenic starting material. The structure of the novel stabilizers was confirmed by 1H-, 13C NMR spectra and Fourier Transform Infrared Spectrometry (FTIR). Furthermore, the polymeric stabilizers are characterized by Size-Exclusion Chromatography (SEC). Thermal gravimetric analysis (TGA) showed high temperature stability above 250 °C proving potential suitability as stabilizers for polyolefins. The impact of the molecular and polymeric antioxidants on the processing behavior and degradation of polypropylene (PP) was examined by prolonged extrusion experiments and oxidation induction time (OIT) measurements. Moreover, the long-term oxidative stability of the PP compounds during accelerated aging was investigated. The novel antioxidants provide excellent processing stability of PP.

Development of low-strength stabilization method for fouled ballasted tracks

In ballasted tracks on railways, fine fraction content (hereinafter referred to as “Fc”) mixed in ballast increases due to repeated train loads or track repair work using ballast tampers. When the Fc increases and becomes “fouled ballast”, settlement of ballasted track tends to increase even after track repair, which results in a rise in maintenance frequency. In such cases, ballast replacement is the standard measure applied to reduce frequency of maintenance. However, ballast replacement is costly, and railway operators therefore need countermeasures to prevent large settlement which are both low cost and quick enough to implement during periods of track work carried out at night. This study describes the development of a new repair method which reduces sleeper settlement by mixing super-quick hardening cement and polymeric stabilizer (hereinafter referred to as “stabilizing materials”) with fouled ballast. This method uses a ballast tamper and weakly stabilizes fouled ballast to allow tamping even after stabilization, hereinafter referred to as the “low-strength stabilization method”. This study investigates the relationship between sleeper settlement and amount of stabilizing materials needed for this low-strength stabilization method, and examines the settlement reduction mechanism through cyclic loading triaxial compression tests. Confirmation of settlement reduction was conducted through full-scale cyclic loading tests.

Hyperbranched ionic surfactants with polyether skeleton: Synthesis, properties and used as stabilizer for emulsion polymerization

A versatile strategy involves anionic ring-opening polymerization (AROP) and thiol-ene reaction was contributed for the construction of hyperbranched ionic surfactants. A series of hyperbranched surfactants composed of polyether skeleton and various ionic side groups such as anion, cation and zwitterion were synthesized and labeled as HPEanionic, HPEcationic and HPEzwitterionic, respectively. The chemical structures of all the intermediate and final products were verified by means of fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. The surface and interfacial tension reduction performances of three obtained ionic surfactants were systematically investigated. And the results confirmed all the resultant surfactants could effectively reduce the surface and interfacial tension of the solution, and the CMC values were all determined approximately to 0.1 mg/mL. Meanwhile, three surfactants exhibit relatively low Krafft temperatures (below 6 ℃) and good wettability to oil-wetted surface. To further explore their promising applications, HPEanionic was proposed for use as a stabilizer in emulsion polymerization. Dynamic light scattering (DLS) measurements as well as transmission electron microscope (TEM) observation confirmed well-defined latex was obtained indeed. Moreover, as compared to latex synthesized by using the traditional small molecule compound surfactants, latex synthesized using HPEanionic as stabilizer exhibit improved tolerance to salinity. This beneficial result is probably caused by the special hyperbranched structure of HPEanionic, which contributes both electrostatic repulsion and steric hindrance drive force for the stabilization of latex particles.

Temperature-Dependent Activity of Gold Nanocatalysts Supported on Activated Carbon in Redox Catalytic Reactions: 5-Hydroxymethylfurfural Oxidation and 4-Nitrophenol Reduction Comparison

In this study, the temperature-dependent activity of Au/AC nanocatalysts in redox catalytic reactions was investigated. To this end, a series of colloidal gold catalysts supported on activated carbon and titania were prepared by the sol immobilization method employing polyvinyl alcohol as a polymeric stabilizer at different hydrolysis degrees. The as-synthesized materials were widely characterized by spectroscopic analysis (XPS, XRD, and ATR-IR) as well as TEM microscopy and DLS/ELS measurements. Furthermore, 5-hydroxymethylfurfural (HMF) oxidation and 4-nitrophenol (4-NP) reduction were chosen to investigate the catalytic activity as a model reaction for biomass valorization and wastewater remediation. In particular, by fitting the hydrolysis degree with the kinetic data, volcano plots were obtained for both reactions, in which the maximum of the curves was represented relative to hydrolysis intermediate values. However, a comparison of the catalytic performance of the sample Au/AC_PVA-99 (hydrolysis degree of the polymer is 99%) in the two reactions showed a different catalytic behavior, probably due to the detachment of polymer derived from the different reaction temperature chosen between the two reactions. For this reason, several tests were carried out to investigate deeper the observed catalytic trend, focusing on studying the effect of the reaction temperature as well as the effect of support (metal–support interaction) by immobilizing Au colloidal nanoparticles on commercial titania. The kinetic data, combined with the characterization carried out on the catalysts, confirmed that changing the reaction conditions, the PVA behavior on the surface of the catalysts, and, therefore, the reaction outcome, is modified.

Hispolon-Loaded Liquid Crystalline Nanoparticles: Development, Stability, In Vitro Delivery Profile, and Assessment of Hepatoprotective Activity in Hepatocellular Carcinoma.

The present work describes the development and characterization of liquid crystalline nanoparticles of hispolon (HP-LCNPs) for treating hepatocellular carcinoma. HP-LCNPs were prepared by a top-down method utilizing GMO as the lipid and Pluronic F-127 as the polymeric stabilizer. The prepared formulations (HP1–HP8) were tested for long-term stability, where HP5 showed good stability with a particle size of 172.5 ± 0.3 nm, a polydispersity index (PDI) of 0.38 ± 0.31 nm, a zeta potential of −10.12 mV ± 0.05, an entrapment efficiency of 86.81 ± 2.5%, and a drug loading capacity of 12.51 ± 1.12%. Optical photomicrography and transmission electron microscopy images demonstrated a consistent, low degree of aggregation and a spherical shape of LCNPs. The effect of temperature and pH on the optimized formulation (HP5) indicated good stability at 45 °C and at pH between 2 and 5. In vitro gastrointestinal stability indicated no significant change in the particle size, PDI, and entrapment efficiency of the drug. The drug release study exhibited a biphasic pattern in simulated gastric fluid (pH 1.2) for 2 h and simulated intestinal fluid (pH 7.4) for up to 24 h, while the best fitting of the profile was observed with the Higuchi model, indicating the Fickian diffusion mechanism. The in vivo pharmacokinetic study demonstrated nearly 4.8-fold higher bioavailability from HP5 (AUC: 1774.3 ± 0.41 μg* h/mL) than from the HP suspension (AUC: 369.11 ± 0.11 μg* h/mL). The anticancer activity evaluation revealed a significant improvement in antioxidant parameters and serum hepatic biomarkers (SGOT, SGPT, ALP, total bilirubin, and GGT) in the diethyl nitrosamine-treated group of rats with the optimized LCNP formulation (HP5) vis-à-vis HP suspension.

Laboratory Studies for Design of a Foam Pilot for Reducing Gas Channeling from Gas Cap in Production Well in Messoyakhskoye Field

Summary This paper highlights the difference between foam injection for gas blocking in production well and injection well and emphasizes the use of polymer enhanced foam. Moreover, this paper shows systematic experimental methods for choosing suitable foam systems for gas blocking in production well considering different factors, which provides a guide regarding what kinds of foaming agents and polymer stabilizers should be used and how to evaluate them for designing a pilot application. The target in this work is the Vostochno-Messoyakhskoye field, operated by Gazpromneft, which is currently experiencing gas channeling from the gas cap in production wells because of strong heterogeneity. Foam has long been considered as a good candidate for gas blocking. However, foam injection for gas blocking in production wells is different from that in injection wells, which requires a long-term impact on gas-saturated highly permeable areas without significantly affecting the phase permeability of oil in the reservoir. Therefore, for gas blocking in production well, a long half-life time of foam is required to sustain stable foam because a continuous shear of surfactant solution/gas cannot be achieved as in injection wells. Thus, reinforced foam by polymer (polymer-foam) is chosen. Four polyacrylamide polymer stabilizers and five anionic surfactants were evaluated using bulk test to determine foaming ability, foam stability, and effect of oil by comparing foam rate and half-life time to determine the suitable foam system with optimal concentrations of reagents. Furthermore, filtration experiments were conducted at reservoir conditions to determine the optimal injection mode by evaluating apparent viscosity, breakthrough pressure gradient, resistance factor, and residual resistance factor. Polymer can significantly improve half-life time (increase foam stability), and the higher the polymer concentration, the longer the half-life time. But simultaneously, a high polymer concentration will increase the initial viscosity of the solution, which not only decreases the foam rate but also increases difficulties in injection. Therefore, an optimal polymer concentration of about 0.15–0.2 wt% is determined considering all these influences. Filtration experiments showed that the apparent viscosity in the core first increased and then decreased with foam quality (the volumetric ratio of gas to total liquid/gas flow). The optimal injection mode is coinjection of surfactant/polymer solution and gas to in-situ generate foam at the optimal foam quality of about 0.65. Filtration experiments on the different permeability cores showed that the gas-blocking ability of polymer-foam is better in high-permeability cores, which is beneficial for blocking high-permeability zone. It should also be noted that under a certain ratio of oil-to-foam solution (about lower than 1 to 1), the presence of high-viscosity crude oil slowly decreased the foam rate with increasing oil volume, but significantly increased the half-life time (i.e., foam stability which is favorable for foam treatment in production well).

Modeling the shear-dependent viscosity of nonionically stabilized waterborne dispersions

The performance of a rheological model that accounts for the effect of the volume fraction, the particle size distribution, and shear rate on the viscosity of water-borne dispersions stabilized with conventional nonionic surfactants and polymeric stabilizers is assessed. The model that contains three parameters fitted well the experimental data. The parameters were independent of the volume fraction, the particle size distribution, and the shear rate. Furthermore, two of them were not affected by the surfactant type and concentration, and temperature. The other parameter increased with the surfactant molecular weight and surface covering, but decreased with increasing temperature.Graphical