Effect of nonionic surfactants in release media on accelerated in-vitro release profile of sirolimus eluting stents with biodegradable polymeric coating

It is a well-known fact that sirolimus(SRL) undergoes degradation process via hydrolysis in aqueous media, leading to incorrect assessment of drug amount and thus release characteristics of formulations.The main objective of the present study was to evaluate the effect of nonionic surfactants in media on invitro release profiles for sirolimus eluting stents(SES) coated with biodegradable polymeric matrix.Phosphate buffer and acetate buffer incorporating nonionic surfactants with varying concentrations were examined for adequate solubility and stability(by RP-HPLC). Good sink condition was achieved in phosphate buffer(at pH 4.0) with 1.0% Tween 20, 1.0% Brij 35% and 0.5% Brij 58. Hydrodynamic size(by DLS) and the micelle-water partition coefficient(P) with standard free energy of solubilization(ΔGs°) of drug were evaluated to get some understanding about the solubilization phenomena. About 80% of drug release during the period of 48 h was achieved in optimized drug release media which was 1.0% Tween20 in phosphate buffer pH 4.0. The obtained accelerated SRL release profile in optimized medium correlated well with the real time in-vitro release in phosphate buffer(pH 7.4). Surface morphology changes(by SEM), changes in gravimetric weights and molecular weight change(by GPC) were examined before and after drug release to understand the drug release mechanism which explains that the polymer did not undergo degradation during the drug release.

Effects of pore structure on surfactant/polymer floodingbased enhanced oil recovery in conglomerate reservoirs

To understand the displacement characteristics and remaining oil displacement process by the surfactant/polymer(SP) flooding in cores with different pore structures, the effects of pore structure on the enhanced oil recovery of SP flooding was investigated at the pore, core and field scales through conducting experiments on natural core samples with three typical types of pore structures. First, the in-situ nuclear magnetic resonance core flooding test was carried out to capture the remaining oil variation features in the water flooding and SP flooding through these three types of cores. Subsequently, at the core scale, displacement characteristics and performances of water flooding and SP flooding in these three types of cores were evaluated based on the full-size core flooding tests. Finally, at the field scale, production characteristics of SP flooding in the bimodal sandstone reservoir and multimodal conglomerate reservoir were compared using the actual field production data. The results show: as the pore structure gets more and more complex, the water flooding performance gets poorer, but the incremental recovery factor by SP flooding gets higher;the SP flooding can enhance the producing degree of oil in 1-3 μm pores in the unimodal and bimodal core samples, while it produces largely oil in medium and large pores more than 3 μm in pore radius in the multimodal core sample. The core flooding test using full-size core sample demonstrates that the injection of SP solution can significantly raise up the displacement pressure of the multimodal core sample, and greatly enhance recovery factor by emulsifying the remaining oil and enlarging swept volume. Compared with the sandstone reservoir, the multimodal conglomerate reservoir is more prone to channeling. With proper profile control treatments to efficiently enlarge the microscopic and macroscopic swept volumes, SP flooding in the conglomerate reservoir can contribute to lower water cuts and longer effective durations.

An Experimental Study on Alkaline/Surfactant/Polymer Flooding Systems Using Natural Mixed Carboxylate

Orthogonal-test-design method has been used to determine the optimal formula by phase behavior and interfacial tension studies, respectively. The effect of each component of two alkaline/surfactant/polymer flooding systems on interfacial tension is discussed, in which a low-price natural mixed carboxylate (SDC) is used as the major surfactant. The results indicate that the optimal composition is SDC (0.5%), alkaline NaHCO3/Na2CO3 with mass ratio of 1 (1.0%), and hydrolyzed polyacrylamide(0.1%). In the coreflood experiment, their oil recovery is increased by about 25.2% and 26.8% original oil in place, respectively.

The effect of betaine surfactants on the association behavior of associating polymer

The interfacial properties and rheological behavior of surfactant/polymer complex systems were measured to investigate the association behavior of the associating polymer.Compared with the pure surfactant solution,there are two inflection points in the surface tension curve for the surfactant/polymer complex systems.The two inflection points are dependent on the surfactant type and polymer concentration.The effect of surfactant on the rheological behavior of polymer can be divided into two aspects.First,the addition of short-chain betaine surfactant is detrimental to the viscosity of polymer solution due to the electrostatic shielding effect.Second,long-chain betaine surfactant also reduces the viscosity of polymer solutions at low concentrations.However,when the concentration of the long-chain betaine surfactant is relatively high,the long-chain betaine surfactant could form worm-like micelles that promote the intermolecular association and thus increase the number of associating junctions,thereby resulting in the augmentation of viscosity.So it is necessary to apply the long-chain betaine surfactant to build the polymer/surfactant flooding system.The interaction model between surfactant and polymer is proposed,which is different from the traditional‘Three-Region Model’.

Stabilization of nickel nanoparticle suspensions with the aid of polymer and surfactant: static bottle tests and dynamic micromodel flow tests

Nickel nanoparticles can work as catalyst for the aquathermolysis reactions between water and heavy oil.A homogeneous and stable suspension is needed to carry the nickel nanoparticles into deeper reservoirs.This study conducts a detailed investigation on how to achieve stabilized nickel nanoparticle suspensions with the use of surfactant and polymer.To stabilize the nickel nanoparticle suspension,three surfactants including sodium dodecyl sulfate,cationic surfactant cetyltrimethylammonium bromide and polyoxyalkalene amine derivative(Hypermer) along with xanthan gum polymer were introduced into the nickel nanoparticle suspension.Static stability tests and zeta potential measurements were conducted to determine the polymer/surfactant recipes yielding the most stable nickel nanoparticle suspensions.Dynamic micromodel flow tests were also conducted on three suspensions to reveal how the nickel nanoparticles would travel and distribute in porous media.Test results showed that when the injection was initiated,most nickel nanoparticles were able to pass through the gaps between the sand grains and produced in the outlet of the micromodel;only a small number of the nickel nanoparticles were attached to the grain surface.A higher nickel concentration in the suspension may lead to agglomeration of nickel nanoparticles in porous media,while a lower concentration can mitigate this agglomeration.Moreover,clusters tended to form when the nickel nanoparticle suspension carried an electrical charge opposite to that of the porous media.Follow-up waterflood was initiated after the nanofluid injection.It was found that the waterflood could not flush away the nanoparticles that were remaining in the micromodel.

Influence of Surfactant-polymer Complexes on Crystallization and Aggregation of CaCO_3

Hollow calcium carbonate（CaCO3） microspheres with different morphologies were synthesized via the precipitation reaction of calcium chloride with sodium carbonate in the presence of different surfactant-polymer complexes.The selected anionic surfactants were sodium dodecyl sulfonate（SDS） and sodium dodecyl benzenesulfonate（SDBS）,respectively.The selected water-soluble polymers were polyacrylic acid（PAA） and polyvinyl pyrrolidone（PVP）.In this work,SDS-PVP ＂pearl-necklace model＂ micellar complex was formed via hydrophobic effectiveness between SDS and PVP and it served as the spherical template to generate spherical CaCO3 aggregates with hollow microspheres composed of about 500 nm irregular shaped particles.SDS-PAA complexes and SDBS-PAA complexes formed ＂core-shell model＂ aggregates with calcium ions serving as the medium to link the anionic surfactant and the polymer.SDS-PAA ＂core-shell model＂ aggregates would act as templates for hollow CaCO3 microspheres consisting of 30―50nm irregular shaped crystallites.SDBS-PAA ＂core-shell model＂ aggregates served as the spherical aggregate templates to generate spherical CaCO3 aggregates consisted of many small spherical particles which had grown together.All the obtained CaCO3 hollow microspheres are calcite particles.This research may provide new insight into the control of morphologies of hollow CaCO3 microspheres in the presence of surfactantpolymer complexes.

XPS Study on Water-Soluble Polymer Surfactant Film

By means of changing the detection angle, the molecular conformation of a new type of polymer surfactant, acrylamide-poly(oxyethykene alkyl ether)acrylate-anionic monomer random copolymer, was studied by x-ray photoelectron spectroscopy(XPS) in detail.

Rheological behavior of alkali-surfactant-polymer/oil emulsion in porous media

Based on deep analysis of ASP/oil emulsions flow behavior characteristic,a mathematical description of non-Newtonian emulsion was developed,and variation of rheological behaviors along the percolation flow direction was given.The effects of emulsions rheological behavior on oil recovery were quantity researched by a 2-D positive rhythm profile geological model.The result shows that the high viscosity and reduction of water phase permeability by emulsification can improve low-middle layer flow rate and enhance sweep efficiency,and the enhancement degree is related with emulsification degree.The study result can be used as reference for scheme design and production performance forecast during ASP flooding.

A SURFACTANT-ASSISTED APPROACH FOR PREPARING COLLOIDAL AZO POLYMER SPHERES WITH NARROW SIZE DISTRIBUTION

A surfactant-assisted method for preparing colloidal spheres with narrow size distribution from a polydispersed azo polymer has been developed in this work. The colloidal spheres were formed through gradual hydrophobic aggregation of the polymeric chains in THF-H2O dispersion media, which was induced by a steady increase in the water content. Results showed that the addition of a small amount of surfactant （SDBS） could significantly narrow the size distribution of the colloidal spheres. The size distribution of the colloidal spheres was determined by the concentrations of azo polymer and the amount of surfactant in the systems. When the concentrations of polymer and surfactant amount were in a proper range, colloidal spheres with narrow size distribution could be obtained. The colloidal spheres formed by this method could be elongated along the polarization direction of the laser beams to be a new type of the colloid-based functional materials. upon Ar^＋ laser irradiation. The colloidal spheres are considered

The Research of Complex System Property between Thermosensitive Polymer and Surfactant

In this paper, the rigid structural thermosensitive polymer （made in lab） of NBS （N-butyl styrene）, N, N-DEAM （diethyl acrylamide） and AM （acrylamide） was prepared. The influence of viscosity for copolymer solution under different reaction conditions such as temperatures and inorganic salt （monovalent salt and divalent salt） was analyzed. The experiment studies the combination of polymer situation and three different types of surfactants under certain conditions of the room temperature （25℃） and the formation temperature （76℃）. At last, the influence of the surfactant kinds and concentration on the viscosity of the polymer solution are studied. The results show that： The copolymer solution, the apparent viscosity of which decreases with the increasement of temperature, but its viscosity has suddenly increased and thereafter dropped in the transition temperature. So the temperature sensitive effect ofcopolymer is very significantly. When the concentration of inorganic salt and surfactant can be controlled in certain extent, the copolymer solution, the effect increases with the increasement of the concentration, but the viscosity of which decreases with the increasement of shear rate. Shear rate can be controlled in certain extent, shearing stability properties of the copolymer solution are proved.

Combination of binary active sites into heterogeneous porous polymer catalysts for efficient transformation of CO_(2) under mild conditions

The transformation of CO_(2)into cyclic carbonates via atom-economical cycloadditions with epoxides has recently attracted tremendous attention.On one hand,though many heterogeneous catalysts have been developed for this reaction,they typically suffer from disadvantages such as the need for severe reaction conditions,catalyst loss,and large amounts of soluble co-catalysts.On the other hand,the development of heterogeneous catalysts featuring multiple and cooperative active sites,remains challenging and desirable.In this study,we prepared a series of porous organic catalysts(POP-PBnCl-TPPMg-x)via the copolymerization metal-porphyrin compounds and phosphonium salt monomers in various ratios.The resulting materials contain both Lewis-acidic and Lewis-basic active sites.The molecular-level combination of these sites in the same polymer allows these active sites to work synergistically,giving rise to excellent performance in the cycloaddition reaction of CO_(2)with epoxides,under mild conditions(40℃ and 1 atm CO_(2))in the absence of soluble co-catalysts.POP-PBnCl-TPPMg-12 can also efficiently fixate CO_(2)under low-CO_(2)-concentration(15%v/v N2)conditions representative of typical CO_(2)compositions in industrial exhaust gases.More importantly,this catalyst shows excellent recyclability and can easily be separated and reused at least five times while maintaining its activity.In view of their heterogeneous nature and excellent catalytic performance,the obtained catalysts are promising candidates for the transformation of industrially generated CO_(2)into high value-added chemicals.

Study on Optimization of Polymer Enhanced Foam Formulation System

Taking the pilot test area of polymer enhanced foam flooding in Y oilfield as the prototype, a numerical core model was established, and the polymer enhanced foam formulation system was optimized by analyzing the resistance factor and the change rule of oil recovery of different formulation systems. Research shows that the higher the polymer concentration, the greater the resistance factor, and the more obvious the sealing effect formed in the formation. The concentration of surfactant has a greater impact on the resistance factor. With the increase of surfactant concentration, the resistance factor increases significantly, and the plugging effect of foam agent on core is significantly enhanced. With the increase of gas-liquid ratio, the resistance factor first increases and then decreases. When the gas-liquid ratio is 1:1, the resistance is the largest, and the foam agent has the strongest plugging effect on the core. The optimal formula system of polymer enhanced foam flooding in Y oilfield is: polymer concentration is 1200 mg/L, surfactant concentration is 0.25 wt%, gas-liquid ratio is 1:1.

Research on Influence Factors of Surfactivity of Polyester Polyether Block Copolymer

Polyester polyether block copolymer （PPBC） was synthesized by ester-exchange and polycondensation reactions using dimethyl terephthalate （DMT）, ethylene glycol （EG） and polyethylene glycol （PEG） as monomer. The effects of PEG molecular weight, mol ratio of DMT to PEG （nDMT/nPEG）, temperature and time of polycondensation reaction and vacuum degree in the reaction system on the surface tension and critical micelle concentration （CMC） of PPBC aqueous solution were studied. It was found that both the molecular weight and the concentration of PEG can affect PPBC＇s surface activity obviously, and the optimum synthesis condition of PPBC used as surfactant is as follows： PEG molecular weight is 1 500, tool ratio of DMT to PEG is 3, temperature and time of polycondensation reaction is 260℃ × 1 h, vacuum degree of condensation reaction is 0.03-0.05 MPa. It was proved by surface tension measurement of PPBC aqueous solution that the PPBC synthesized in this condition is a good surfactant with excellent surfactivity.

Interaction between Cationic Surfactants and Bromopyrogallol Red as well as Its Application for the Sensitive and Selective Determination of Mo in Mo/W Binary Mixtures

Prior to formation of the micelles of cationic surfactant (CSF), bromopyrogallol red (BPR) could exist in the forms of both monomer and oligomer After that, however, only BPR monomer existed. Nonionic surfactant OP-10 favoured the oligomerization of BPR monomer. The mixed micellar media prepared by mixing CSF and OP-10 in an appropriate ratio could be used for the sensitive and selective determination of Mo in Mo/W binary mixtures.

EFFECTS OF NH_4Cl ON THE INTERACTION BETWEEN POLY(ETHYLENE OXIDE) AND IONIC SURFACTANTS IN AQUEOUS SOLUTIONS

The interaction of poly(ethylene oxide)(PEO)with the ionic surfactants,sodium dodecylsulfate(SDS)and cetyltrimethylammonium chloride(CTAC)respectively,in aqueous solutions containing a certain concentration of NH_4Cl, is studied by the viscosity measurement.It has been found that the ion-dipole interaction between PEO and ionic surfactants is changed considerably by the organic salt.For anionic suffactant of SDS,the addition of NH_4Cl into solution strengthens the interaction between PEO and the headgroup o...

Photocatalytic degradation of 2,4-dichlorophenol with V_2O_5-TiO_2 catalysts: Effect of catalyst support and surfactant additives

Binary oxide catalysts with various weight percentage V2O5 loadings were prepared by solid‐state dispersion and the nanocomposites were modified with surfactants. The catalysts were analyzed using X‐ray diffraction, diffuse‐reflectance spectroscopy, Fourier‐transform infrared spectroscopy, scanning electron microscopy, and N2 adsorption‐desorption. The photocatalytic activities of the catalysts were evaluated in the degradation of 2,4‐dichlorophenol under ultraviolet irradiation. The photocatalytic activity of 50 wt%V2O5‐TiO2 （50V2O5‐TiO2） was higher than those of pure V2O5, TiO2, and P25. Interactions between V2O5 and TiO2 affected the photocatalytic efficiencies of the binary oxide catalysts. Cetyltrimethylammonium bromide （CTAB） and hexadecyltrimethylammonium bromide （HTAB） significantly enhanced the efficiency of the 50V2O5‐TiO2 catalyst. The highest per‐centage of 2,4‐dichlorophenol degradation （100%） and highest reaction rate （2.22 mg/（L·min）） were obtained in 30 min with the （50V2O5‐TiO2）‐CTAB catalyst. It is concluded that the addition of a surfactant to the binary oxide significantly enhanced the photocatalytic activity by modifying the optical and electronic properties of V2O5 and TiO2.

Enhancement of Formation of Polar Microenvironment in Polymer by Compressed CO_(2)

The copolymer (EO)22(PO)52(EO)22 in p-xylene can solubilize much more water in the presence of compressed CO2 than the case without CO2.

Lessons learned from coreflood experiments with surfactant-polymer and alkali-surfactant-polymer for enhanced oil recovery

A review of coreflood experiments for chemically enhanced oil recovery(EOR)is presented in this paper,particularly surfactant-polymer(SP)and alkali-surfactant-polymer(ASP)processes.The objective of this review is to gain a general outlook and insight from coreflood experiments injecting SP or ASP slug as tertiary recovery.The discussion is separated into sections based on relevant core and fluid properties as well as surfactant selection and SP/ASP slug design and their impact on incremental recovery.Most studies in this review have been published within the last twenty years but few older coreflood works have been included for benchmarking.Parameters in each reviewed study have been summarized in tables to help readers gain detailed observation.Lessons learned from these past experiments should help other chemical EOR practitioners or students of the field in benchmarking or improving the outcomes of their future SP/ASP experiments.

Effect of Surfactant Concentration on Aqueous LiBr Solution Absorption Rate

It is well known that small amounts of surfactants, such as 1-Octanol, in the aqueous solution can increase the absorption rate significantly. In this paper, experimental data were obtained for absorption of water vapour into an aqueous LiBr solution with different concentrations of 1-Octanol. An experimental rig was specifically designed and developed in this work in order to investigate the effect of surfactant (1-Octanol) on the enhancement of the heat and mass transfer in the absorption process, in addition to, the investigation of the impact of the use of magnetic stirrer inside the absorber. The experimental rig for this study was based on the refrigeration mode of the intermittent vapour absorption system. In order to study the heat and mass transfer in water-lithium bromide vapour absorption air conditioning systems, it was necessary to monitor the concentration of the solution continuously. As a consequence, two procedures for obtaining the LiBr solution concentration were used. The first method was based on the measurement of the density and temperature of the solution, while the second was based on its electrolyte conductivity and the temperature. The experimental results showed that the surfactant concentration has a significant effect on the absorption rate;this is called the Marangoni instability. It has been concluded that, in order to clarify the absorption enhancement phenomenon, it is necessary to understand the physicochemical aspects of the absorption process and the effect of surfactants on the enhancement of such process. Additionally, it has been concluded that new approaches are needed to explain the observed behaviour.

The ternary combination of polymer gel, microsphere and surfactant for conformance control and oil displacement to improve oil recovery in strong heterogeneous reservoir

The reservoir heterogeneity of Suizhong 36-1 oilfield is very obvious,the average permeability reaches 2000mD.Long-term water injection development leads to serious water channeling in high permeability layers,resulting in ineffective circulation of injected water and reduction of oil recovery.It is urgent to form an effective EOR method.In this paper,the oil displacement effect of different combination slugs including polymer gel,polymer microsphere and surfactant is evaluated by means of conformance control and chemical flooding.Three-layer heterogeneous 3-D plate model is used for oil displacement experiment.The experimental results show that the combination slug sequentially composed of polymer gel,polymer microspheres and surfactant have the best oil displacement effect with the oil recovery increment by 21.2% after the first water flooding.In addition,using the best slug combination for two rounds flooding,the recovery factor increased by 28.2% compared with the first water flooding.This paper provides some new insights for enhanced oil recovery in strong heterogeneity reservoir.