Increase In Copolymer Concentration Research Articles

Gelation of copolymers of acrylamide and sodium acrylate upon coordination with Cu2+ ions in concentrated solutions

The phase state of Cu2+ complexes with acrylamide and sodium acrylate copolymers at different copolymer concentrations and components molar ratios was studied. The change in complex stoichiometry from 2 to 3 carboxylate groups per Cu2+ ion was detected with an increase of copolymer concentration. In the concentrated solutions of copolymers, gelation is observed upon addition of Cu2+ ions, with the lowest concentration of copper required for gelation decreasing with the increase in copolymer concentration. These hydrogels are attributed to the formation of meta-stable inter-polymer metal complexes, which are able to persist due to a low segment mobility. The phase separation of complexes is shown to be associated with the bidentate coordination of carboxylate groups to Cu2+ ions, while the hydrogels formed in concentrated solutions mostly consist of bridging structures. Gelation threshold corresponds to the second critical concentration of poly(acrylamide-co-sodium acrylate) and is lower for copolymers with the higher molecular weight. Low acrylate content in the copolymers prevents collapse of the hydrogels caused by the salting-out effect. A higher gel content can be reached by increasing the copolymer concentration or the molar ratio of copper ions to carboxylate groups, with the latter reducing the swelling degree.

Adsorption of Mixed Dispersions of Silica Nanoparticles and an Amphiphilic Triblock Copolymer at the Water–Vapor Interface

This study investigates the surface modification of hydrophilic silica nanoparticles by non-chemical adsorption of an amphiphilic triblock copolymer, Pluronic F-127, and elucidates its influence on the interfacial dispersion properties. The interaction between Pluronic F-127 and silica nanoparticles drives the formation of copolymer-decorated particles with increased hydrodynamic diameter and reduced effective charge as the copolymer concentration increases, while the opposite effect occurs as the particle concentration increases at a fixed polymer concentration. This indicates that increasing the copolymer concentration leads to an increase in the coating density, whereas increasing the particle concentration leads to a decrease. This is of paramount importance for modulating the reorganization of the Pluronic F-127 shell upon adsorption at fluid–fluid interfaces and, thus, the adsorption of the decorated nanoparticles at the interface and the rheological properties of the obtained layers. In fact, the relationship between copolymer concentration and interfacial tension, as well as the mechanical response of the interface, mirrors the patterns observed in Pluronic F-127 solutions, and only a shift mediated by the Pluronic F-127 concentration is found. This suggests that the presence of particles limits the space available for Pluronic F-127 molecules to reorganize at the interface but does not significantly affect the interfacial behavior of the particle-laden interface.

Antifouling improvement of a polyacrylonitrile membrane blended with an amphiphilic copolymer

Abstract The amphiphilic copolymer polyacrylonitrile-co-poly(hydroxyethyl methacrylate) (PAN-co-PHEMA) was readily blended with polyacrylonitrile (PAN) to fabricate a flat-sheet blending membrane through non-solvent induced phase separation (NIPS). In the membrane-forming process, the hydrophilic PHEMA chains are uniformly distributed on the surface, as revealed by the energy-dispersive X-ray tests. The sponge-like sub-layer embedded with droplet-shaped structures is formed at the cross-sections of membranes, because of the high viscosity of the casting solution. With the increase of copolymer concentration, the mean pore size of the blending membranes increases from 26.9 to 99.8 nm, leading to the increase of membrane flux from 93.6 to 205.4 l/(m2h). The incorporation of PAN-co-PHEMA copolymer endows the blending membrane with a rough surface microstructure and enhanced hydrophilicity. The rejection ratio of membranes for emulsified pump oil reaches 99.9%, indicating a prominent separation performance. In the cycle permeation experiments, the flux recovery ratio of the blending membranes is as high as 99.6%, which is much higher than those of PAN membrane. The irreversible fouling of blending membranes induced by oil adsorption is alleviated, and converted into reversible fouling, owing to the reduction of the adhesion force between foulant and membrane surface. These results suggest that the anti-fouling property of PAN membranes has been dramatically strengthened via the addition of PAN-co-PHEMA copolymer.

Phase behavior and interfacial tension of ternary polymer mixtures with block copolymers.

The phase behavior and interfacial tension of ternary polymeric mixtures (polystyrene/polystyrene-b-poly(methyl methacrylate)/poly(methyl methacrylate), PS/PS-b-PMMA/PMMA) are investigated by dissipative particle dynamics (DPD) simulations. Our simulation results show that, as the PS-b-PMMA diblock copolymer concentration increases, the interfacial tension decreases due to the decayed correlations between homopolymers PS and PMMA. When the chain lengths of copolymers are fixed, with the increase of the chain lengths of PS and PMMA homopolymers the interfacial width becomes wider and the interfacial tension becomes smaller, due to the copolymers presenting more stretched and swollen structures in the mixtures with the short length of homopolymers. However, with simultaneously increasing chain lengths of both diblock copolymer and homopolymers with a fixed ratio, the interfacial tension increases because the copolymer chains with longer chain length penetrate more deeply into the homopolymer phase and the interactions between diblock copolymers become weaker. These results will provide a way to mix incompatible homopolymers to improve material performances.

Formulation variables influencing the properties and physical stability of green multiple emulsions stabilized with a copolymer

To obtain multiple emulsions containing Agnique™ AE 3-2H as oil phase and Atlas™ G-5000 as emulsifier, two formulation variables were studied: the effect of the Atlas™ G-5000 concentration in emulsions containing 15 wt% Agnique™ AE 3-2H and the study of the influence of the solvent concentration maintaining the Agnique™ AE 3-2H/Atlas™ G-5000 ratio equal to 10. To assess microstructure and physical stability of these emulsions different techniques were employed, namely laser diffraction, transmitted light optical microscopy, steady-state measurements, and multiple light scattering. An increase in copolymer concentration and solvent concentration provoked a decrease in Sauter diameter but an increase in volume mean diameter and polydispersion due to droplet coalescence. Regardless of polymer concentration, all emulsions showed Newtonian behavior which led to shear thinning with increasing oil concentration. The main destabilization processes are creaming, when the concentration of polymer or solvent is low, and coalescence, when both concentrations are high.

Improved fouling resistance of poly(vinylidene fluoride) membrane modified with poly(acryloyl morpholine)-based amphiphilic copolymer

An amphiphilic copolymer of poly(methyl methacrylate)-co-poly(N-acryloylmorpholine) (PMMA-co-PACMO) was synthesized via radical copolymerization. The copolymer was directly blended with poly(vinylidene fluoride) (PVDF) to prepare flat membranes using the phase inversion technology. During membrane formation, the hydrophilic PACMO chains were preferably segregated onto membrane surface, which endowed the PVDF/PMMA-co-PACMO membranes with the enhanced hydrophilicity. The prepared PVDF/PMMA-co-PACMO membranes showed lower protein adsorption than pristine PVDF membrane, due to the elimination of interaction force between membrane and protein. With the increase of copolymer concentration in the casting solution, the macrovoids were gradually formed at the cross section of the PVDF/PMMA-co-PACMO membranes. Filtration experiments indicated that the total and irreversible membrane fouling ratios were significantly suppressed via the incorporation of PMMA-co-PACMO. The flux recovery ratio of the PVDF/PMMA-co-PACMO membrane was as high as 98.4%. These results suggested that the hydrophilic modification by blending amphiphilic copolymer PMMA-co-PACMO was a feasible approach to improve anti-fouling property of PVDF membrane.

A new sight of water‐soluble polyacrylamide modified by β‐cyclodextrin as corrosion inhibitor for X70 steel

The application of water‐soluble polyacrylamide modified by β‐cyclodextrin (ACDPAM) as a corrosion inhibitor on X70 steel in 0.5 M H2SO4 solution has been evaluated using electrochemical measurements, weight loss, and scanning electron microscopy (SEM). The polarization curves results reveal that the copolymer acts as a mixed‐type inhibitor. The inhibition efficiency is found to increase by the increase in copolymer concentration and decreases by the rise in temperature, and it also exhibits effective inhibition even at a higher temperature. The adsorption of ACDPAM on X70 steel surface obeys the Langmuir adsorption isotherm and is governed by chemisorption. The SEM results demonstrate that X70 surface is protected by ACDPAM.

Effect of copolymer concentration on the structure and permeability of temperature-sensitive poly(vinylidene fluoride) hollow fiber membrane

Temperature-sensitive poly(vinylidene fluoride)-grafted-poly( N-isopropylacrylamide) (PVDF- g-PNIPAAm) copolymer hollow fiber membrane was fabricated by dry–wet spinning technique using N,N-dimethyl formamide as solvent and poly(ethylene glycol) as pore-making agent, respectively. The effect of PVDF- g-PNIPAAm copolymer concentration in the spinning solution on the structure and performance of resultant fiber membranes were investigated by field-emission scanning electronic microscopy, pore size measurements, mechanical tests, and filtration experiments. It was found that the microvoid in the inner cross-section of hollow fiber membrane changed to a finger-like structure with the increase of copolymer concentration from 16 to 20%. The increasing copolymer concentration also led to the increase of the inner diameter, outer diameter, and wall thickness and the decrease of mean pore size and porosity. When the permeation temperature was increased from 20 to 45°C, a remarkable reduction of pure water flux and a drastic increase of the retention of bovine serum albumin were observed around 32°C, indicating an obvious temperature-sensitive permeability.

Synthesis of novel thermoresponsive micelles by graft copolymerization of N-isopropylacrylamide on poly(ε-caprolactone-co-α-bromo-ε-caprolactone) as macroinitiator via ATRP

α-Bromo-e-caprolactone (α-BrCL) was synthesized from α-bromocyclohexanone by using 3-chloroperoxybenzoic acid. α-BrCL was then used as a comonomer in the ring-opening polymerization of e-caprolactone (CL) initiated with aluminum isopropoxide to synthesize poly(CL-co-α-BrCL) copolymer. This copolymer was used as the macroinitiator in the atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAAm) for the synthesis of stimuli-responsive and biodegradable PCL-g-PNIPAAm copolymer. A core-shell type nano-structure was formed with a hydrophilic outer shell and a hydrophobic inner core from these copolymers, which exhibited a phase transition temperature around 31 °C. The copolymers were characterized by 1H-NMR and FT-IR spectroscopies. Number-average molecular weight of the poly(CL-co-α-BrCL) and PCL-g-PNIPAAm copolymers was calculated from corresponding 1H-NMR spectra to be 5770 and 6810 gmol−1, respectively. Thermal stability of the copolymer was investigated by thermogravimetric analysis (TGA) and crystallization behavior was studied by differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) showed that the self-assemble micelle aggregates had well defined spherical shape. From the fluorescence spectra, fluorescence intensity of pyrene in the copolymer micelles increased and red-shifted as the copolymer concentration increases, indicating the formation of self-assemble polymeric micelles in water. The critical micelle concentration was found to be 3.2 × 10−3 mg/mL. TEM results showed that micelles have spherical shapes with a diameter of about 70 nm. The obtained micelles can be desirable for potential applications in biomedical fields, such as drug delivery systems.

Estudo da mistura do éter diglicidílico do bisfenol-A com poli(etileno-co-acetato de vinila)-g-poli(metacrilato de metila) por espectroscopia dielétrica e calorimetria exploratória diferencial

As curvas calorimétricas e os espectros de relaxação dielétrica correspondentes às misturas do éter diglicidílico do bisfenol-A com diferentes concentrações do copolímero poli(etileno-co-acetato de vinila)-g-poli(metacrilato de metila) (EVA-g-PMMA) foram obtidos utilizando a calorimetria exploratória diferencial (DSC), e a espectroscopia de relaxação dielétrica (DSR), respectivamente. A temperatura de transição vítrea (Tg) do segmento de PMMA aumenta com o conteúdo de copolímero na mistura. O comportamento da Tg foi descrito pela equação de Gordon-Taylor, utilizando a fração mássica de PMMA. Nos espectros dielétricos, aparecem as relaxações do tipo α características dos dois segmentos moleculares. Neste caso, o aumento da concentração de copolímero provocou o aumento da temperatura de relaxação α correspondente ao segmento de PMMA, e não foi observada mudança na relaxação α para a fração de EVA. Estes comportamentos revelam que os segmentos estruturais do copolímero apresentam interações bem diferenciadas com o monômetro epoxídico. O segmento de PMMA é miscível, portanto, provocou fortes interações com a resina quando comparado à fração de EVA, que não manifestou interação aparente e originou a heterogeneidade do sistema.

TUNING OF BLOCK COPOLYMER-MEDIATED SYNTHESIS OF GOLD NANOPARTICLES

The yield and stability of synthesis of gold nanoparticles has been examined using triblock copolymer Pluronic P85 (EO26PO39EO26) at varying concentrations as a function of hydrogen tetrachloroaureate (III) hydrate (HAuCl4.3H2O) in aqueous solution. The surface plasmon resonance in the time-dependent UV-Visible spectra reveals that increase in the block copolymer concentration increases the yield of the gold nanoparticles but decreases their stability. Small-angle neutron scattering (SANS) suggests that the number density of block copolymer micelles increase almost linearly with the concentration, which is related to result in higher numbers of nucleation centers and therefore increase in the yield of gold nanoparticles. The fact that increase in the number density of nanoparticles also increases the chances of aggregation and this tends to decrease the stability at higher block copolymer concentration. Transmission electron microscopy (TEM) images confirm the larger sizes of the nanoparticles formed in these systems at higher concentrations.

Swelling and Gelation Time Behavior of Sulfonated Polyacrylamide/Chromium Triacetate Hydrogels

A hydrogel was prepared by crosslinking of aqueous solutions of sulfonated polyacrylamide/chromium triacetate for use in water shut-off operations in oil reservoirs. The effects of pH, salinity, retarder and temperature, as well as co-polymer and crosslinker concentration, on the gelation time were investigated. The results indicated that as temperature increased, gelation occurred more rapidly. The activation energy was measured as about 86 kJ/mol. The effects of initial pH and retarder on the gelation time were also examined. The results showed that addition of retarder and increasing of pH increased and decreased the gelation time, respectively. The increase of co-polymer concentration in solution increased the gel swelling. However, the increase of crosslinker concentration decreased the gel swelling. In the presence of electrolytes, the gel swelling decreased by about 80%. Finally, some usable practical recommendations are offered for the gelling systems in reservoirs.

Concentration Effect on Tuning of Block Copolymer-Mediated Synthesis of Gold Nanoparticles

Synthesis of gold nanoparticles has been examined using triblock copolymer Pluronic P85 (EO26PO39EO26) at different concentrations as a function of hydrogen tetrachloroaureate (III) hydrate (HAuCl4 x 3H2O) in aqueous solution. The concentration of P85 block copolymer was varied from 0.5 to 2 wt% at fixed temperature (30 degrees C) in presence of HAuCl4 x 3H2O in the range of 0.002 to 0.2 wt% for each P85 concentration. The surface plasmon resonance in the time-dependent UV-visible spectra reveals that increase in the block copolymer concentration increases the yield of the gold nanoparticles but decreases their stability. Both small-angle neutron scattering (SANS) and dynamic light scattering (DLS) show that the number density of block copolymer micelles increase almost linearly with the concentration, which is related to result in higher numbers of nucleation centers and therefore increase in the yield of gold nanoparticles. The fact that increase in the number density of nanoparticles also increases the chances of aggregation and this tends to decrease the stability at higher block copolymer concentration. Transmission electron microscopy (TEM) images confirm the larger sizes of the nanoparticles formed in these systems at higher concentrations.

Preparation and characterization of PVDF–HFP copolymer hollow fiber membranes for membrane distillation

Poly(vinylidene fluoride- co-hexafluoropropylene) (PVDF–HFP) hollow fiber membranes were prepared by the dry/wet spinning technique at different copolymer concentrations from 17 to 24 wt%. All the spinning parameters were kept constant except the copolymer concentration. The temperature of both the internal and external coagulants was maintained at 40ºC. The effects of the copolymer concentration on the morphological properties of the hollow fibers were studied in terms of external and internal diameter and scanning electron microscopy (SEM). It was found that the thickness of all tested hollow fibers did not change significantly. An evolution of the cross-section structure with the increase of the copolymer concentration was detected. The cross-section of the hollow fiber prepared with the lowest copolymer concentration exhibited a finger-like structure in both the external and internal layers disappearing in the internal layer as the copolymer concentration increases. Finally, a sponge-like structure is formed through all cross-section of the hollow fiber prepared with the highest concentration. This may be explained based on the decrease of the coagulation rate with the increase of the copolymer concentration in the dope solution.

Pluronic L64 Micelles near Cloud Point: Investigating the Role of Micellar Growth and Interaction in Critical Concentration Fluctuation and Percolation

The structure and the properties of the (Ethylene Oxide)(13)(Propylene Oxide)(30)(Ethylene Oxide)(13) (Pluronic L64, MW approximately 2900) micelles have been studied in the aqueous medium by small angle neutron scattering (SANS), dynamic light scattering (DLS) and viscometry measurements. The aqueous solutions of this triblock copolymer are unique among the pluronic solutions in showing critical concentration fluctuations and a concomitant enhancement in viscosity on approaching their cloud point. So far these results have been attributed solely to the presence of attractive interaction between the spherical L64 micelles. Recent theoretical studies, on the other hand, suggest that L64 micelles prefer a prolate ellipsoidal structure to sphere (Bedrov et al. Langmuir 2007, 23, 12032) and have a predominantly repulsive intermicellar interaction. A comparative analysis of our SANS data based on the spherical and prolate ellipsoidal structure shows that the L64 micelles can be best described by a prolate ellipsoidal structure, the aspect ratios of which increase progressively with increase in temperature. This, together with our viscosity and DLS studies, suggests that the enhanced viscosity of the copolymer solution near the cloud point arises largely due to the anisotropic growth of the micelles to the worm-like structures. The role of the intermicellar attractive interaction has thus been limited to the observed critical concentration fluctuation, and its effect decreases progressively with increase in copolymer concentration. It has also been shown that the water structure making salts like NaCl reduces the micellar growth temperature and helps in forming worm-like micelles at the room temperature. These studies thus identify the effect of micellar growth and interaction in determining the properties of the copolymer solution near the cloud point, which are the first of its kind in the case of the pluronics.

Sphere-to-rod transition of short-chain PEO- b-PDMS- b-PEO in aqueous solution induced by copolymer concentration

A short-chain triblock copolymer EO 9-DMS 7-EO 9 was synthesized by coupling reaction of allyl-terminated poly(ethylene oxide) and Si–H-terminated poly(dimethylsiloxane). The structure and purity of synthesized copolymer was carefully characterized. Self-assembly behavior of EO 9-DMS 7-EO 9 triblock copolymer in water was investigated. And it was found that along with the increase of copolymer concentration, morphology of self-assembled aggregates transits from sphere to rod. A plausible understanding of the morphology transition for the investigated triblock copolymer was proposed.

Ultrafast Infrared Heating Laser Pulse-Induced Micellization Kinetics of Poly(ethylene oxide)−Poly(propylene oxide)−Poly(ethylene oxide) in Water

The heating-induced micellization of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic PE10300) triblock copolymer chains was studied by ultrasensitive differential scanning calorimetry, laser light scattering, and fluorescence spectrometry with a fluorescent probe, 8-anilino-1-naphthalenesulfonic acid ammonium salt. The critical micellization temperatures obtained from the three methods are similar. The micellization kinetics was studied in terms of changes in the fluorescence and Rayleigh scattering intensities after an ultrafast infrared heating laser pulse (approximately 10 ns)-induced temperature jump. The increases in the fluorescence and Rayleigh scattering intensities in the millisecond range can be well described by a single-exponential equation, corresponding to the incorporation of individual triblock copolymer chains (unimers) into large spherical micelles. The increase in copolymer concentration or the initial solution temperature decreases the characteristic transition time. In general, the fluorescence measurement has a better signal-to-noise ratio but leads to a transition time that is slightly shorter than that from the corresponding Rayleigh scattering measurement for a given copolymer solution.

Rheological behavior of acrylonitrile/ammonium acrylate copolymer solutions

AbstractAmmonium acrylate was first used as a comonomer to copolymerize with acrylonitrile. The viscosity behavior of dimethyl formamide solutions of acrylonitrile/ammonium acrylate copolymer was studied, and the rheological kinetics of the solutions were studied for comparison. It was shown that the solutions behaved the same as a Newtonian flow as the rotor speed increased beyond 12 rpm. With an increase in temperature, the apparent viscosity of acrylonitrile/ammonium acrylate copolymer solutions showed a trend of decreasing. The changes in the apparent flow‐activation energy of solutions (Eη) calculated by the Arrhenius equation became less prominent along with the changes in the molecular weight of the acrylonitrile/ammonium acrylate copolymers. Eη increased continuously with an increase in copolymer concentration. The viscosity of copolymer solutions decreased continuously as the concentrations of KCl and NaCl increased up to 0.015 mol/L, and then it increased. The Eη showed an obvious trend of decreasing with the addition of alkali salts, and the changes in the Eη containing NaCl were more prominent than those of solutions containing KCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2320–2324, 2007

Diffusion coefficient of DMF in acrylic fiber formation

AbstractA H2O/dimethyl formamide (DMF) mixture was used as the coagulation bath of wet‐spun process for acrylic fibers. Diffusion coefficient of DMF in the protofibers prepared by acrylonitrile/acrylamide copolymers was determined. It has been found that diffusion coefficient of DMF outflow of the protofibers prepared by acrylonitrile/acrylamide copolymers synthesized by solution polymerization is highest compared with those of acrylonitrile/acrylamide copolymers synthesized by H2O/DMF mixture suspension polymerization and aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMF decreases continuously. Diffusion coefficient of DMF increases along with the bath temperature, but the changes in diffusion coefficient values are less prominent as temperature goes beyond 55°C. When DMF concentration in the coagulation bath was 50%, the value of the diffusion coefficient of DMF was minimal. Diffusion coefficient of DMF increases along with jet stretch minus ratio increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3616–3619, 2006

Rheological kinetics of acrylonitrile/amino ethyl‐2‐methyl propenoate copolymer solutions in dimethyl sulfoxide

AbstractViscosity behavior of dimethyl sulfoxide solutions of acrylonitrile (AN)/amino ethyl‐2‐methyl propenoate (AEMP) copolymer was discussed. Rheological kinetics of the solutions was studied in contrast. It is shown that the solutions behave the same as Newtonian flow as the rotor speed goes beyond 12 rpm. With an increase of temperature, the apparent viscosity of AN/AEMP copolymer solutions shows a trend of decrease. The changes of the apparent flow activation energy of solutions calculated by Arrhenius equation become less prominent along with the changes of the molecular weight of AN/AEMP copolymers. The apparent flow activation energy of the copolymer solutions increases continuously with an increase of copolymer concentration. The viscosity of copolymer solutions decreases continuously as the concentrations of KCl and NaCl up to 0.02 mol L−1, and then it increases. the apparent flow‐activation energy of AN/AEMP copolymer solutions shows an obvious trend of decrease with addition of alkali salts and the changes of the apparent flow‐activation energy of solutions containing NaCl are more prominent than those of solutions containing KCl. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2972–2976, 2006