Range Of Polymer Concentrations Research Articles

A polymer in an ionic liquid: Effect of the length of the cationic nonpolar tail on the character of interchain correlations

On the basis of the integral equation theory, we examine spatial correlations of flexible polymer chains dissolved in an ionic liquid. The effect of the concentration of a polymer on its structural properties is studied for different lengths of the nonpolar tail of the solvent cation. The structure of a polymer-containing ionic liquid is analyzed in the reciprocal space on the basis of calculated partial structure factors. In a wide range of polymer concentrations, for all the selected values of length of the cationic nonpolar tail, long-range liquid ordering and intermediate-range liquid ordering of polymer chains are observed. The dependences of the characteristic scale of ordering of macromolecules on their number density in solution are different for ionic liquids with different lengths of the cationic nonpolar tail.

Finite Length Effects for Osmotic Pressures of PEG Polymers

Previously we derived a one-parameter scaling-law equation of state for the osmotic pressures of polyethylene glycol (PEG) polymers in water, applicable over a broad range of polymer sizes and concentrations (J. Phys. Chem. B, 2009, 113, 3709). The derived equation is a non-virial linear combination of a low-concentration van’t Hoff (vH) term and a higher-concentration des Cloizeaux (dC) term. A single parameter α locates the crossover from dilute vH to semidilute dC behavior. The value of α was determined by an empirical fit to the concentration-dependent data of Rand et al. (loc.cit.) for PEGs of molecular weights ranging from 300 to 20,000 daltons. Appropriate scaling collapsed all the data onto a single curve that was well fit by our equation of state with the single parameter α = 0.49 ± 0.01. Now, by fitting α to the scaled osmotic pressures of each polymer separately, we find a small but systematic dependence of α on polymer size. As the number of monomers N increases, α(N) decreases monotonically toward an asymptotic value that we call α∗. The interaction strength of shorter polymers is thus larger than that of longer polymers. Because scaling theories assume polymers of infinite length, α∗ can be viewed as the value of α in the scaling limit. A correction-to-scaling formula derived from renormalization group theory provides an excellent fit to α(N) for PEG polymers, yielding α∗ = 0.43 ± 0.02. The present formulation for α(N) further improves the accuracy of the osmotic pressures of PEG polymers calculated by our equation of state.

Sol–gel transition of PEG–PAF aqueous solution and its application for hGH sustained release

We report a poly(ethylene glycol)–poly(L-alanine-co-L-phenylalanine) (PEG–PAF) aqueous solution as a polypeptide-based thermogelling system and its application as an injectable sustained release system for human growth hormone (hGH). The PEG–PAF aqueous solution underwent sol-to-gel transition at 16–34 °C in a polymer concentration range of 6.0–14.0 wt% as the temperature increased. Dynamic light scattering, circular dichroism, FTIR, and 13C-NMR spectra indicated that the secondary structure of PAF was preserved, however, PEG was dehydrated in the sol-to-gel transition temperature range. A micelle aggregation model was suggested for the sol-to-gel transition of the current PEG–PAF, similar to previous polyesters. The polymer was quite stable in water, and therefore, the molecular weight of the polymer did not significantly change and pH of the aqueous polymer solution was maintained at 7.2–7.8 during the 1 month storage of the polymer as an aqueous solution at room temperature. This point is clearly distinguished from previous thermogelling polymers based on polyesters, polyorthoesters, polyphosphazenes, poly(β-aminoester urethane)s, and polyanhydrides, which generate acid degradation products or can be degraded during storage as an aqueous polymer solution. Therefore, the current system can be used as a ready-to-use injectable implant for biomedical applications. When the polymer aqueous solution (0.5 mL) was injected into the subcutaneous layer of rats, the gel was formed by temperature-sensitive sol-to-gel transition, and the gel was completely eliminated from the implanted site in 1–5 ng mL−1in vivo, suggesting that the system is promising as a once-per-week delivery system for the hGH.

Buckling of an electrically charged liquid jet

The mechanism of fiber electrospinning from polymer solutions was theoretically studied. An equationdescribing the destabilization of an electricallycharged jet of a polymer solution was derived. Thebehavior of the jet cannot be explained without takinginto account its elasticity. It was concluded that theelectrospinning is possible only within a certain polymer concentration range. At too high polymer concentration, the jet elasticity is too high and the destabilization is suppressed. At too low polymer concentration, macromolecules are isolated and do not forma single entanglement network. The main parametersdetermining the electrospinning are the linear electriccharge density and Young’s modulus of the jet.Among commercial methods for producing chemical fibers, the electrospinning of nonwoven fibrousmaterials occupies a special place owing to its simplicity, high efficiency, process flexibility, and productdiversity [1–3]. The main advantage of this method isthe possibility of producing very thin fibers of diameter~1 μm and recently even down to 10 nm.Fibers are electrospin from a lowconductivitypolymer solution. A typical polymer concentration is~10%. An electric potential difference of ~3–20 kV isapplied between a receiving electrode and a meteringnozzle with the polymer solution. In nature, fiberelectrospinning is similar to electrospraying. Electrospinning was discovered in 1939 by N.A. Fuks andN.D. Rozenblyum in attempt to produce solid spherical aerosol particles of nitrocellulose from its acetonesolution. However, they suddenly observed a fiber generation mechanism by which a liquid jet flowing froma nozzle changed to strong continuous fibers of a stable cross section of ~1 μm instead of the expectedbreakup into drops. Let us now describe the processmechanism.A fiber is shaped only by electric forces. The electric field in a conductive material is known to be zero.On the surface of an electrically conductive liquid, acharge forms. The charge is acted by an electric fieldopposed by surface tension forces. At low fieldstrengths, the electric forces are weak and the liquidsurface remains stable. As the field strength isincreased, the electric forces increase, and at a certainelectric field strength, the surface tension forcesbecome weaker than the electrostatic forces. As aresult, the drop shape becomes unstable and the socalled Taylor cone forms. In the absence of a polymer,such instability leads to the detachment of the cone tipand the formation of charged drops, and in the case ofa polymer solution, a thin jet forms.Photography showed that, once leaving the nozzle,the jet is destabilized and ta kes the shape of a divergentconical helix [1, 4]. Having been formed, the jet gradually becomes increasingly wider and, at a certainmoment of time, is destabilized again. Up to four successive stages of jet destabilization were observed.The destabilization of the straightline jet isexplained by the Coulomb repulsion of like charges.Once the jet shape deviates from a straightline segment, a resultant of forces emerges (figure), causing anincrease in the fluctuation amplitude and, finally, theformation of the helix.The behavior of a 2% aqueous poly(ethylene oxide)(

KINETICS OF P - NITROPHENYL ACETATE HYDROLYSIS CATALYZED BY α- CHYMOTRYPSIN IN PRESENCE OF POLYETHYLENE GLYCOL

The effect of poly (ethyleneglycol) (PEG) addition on the rate of p-nitrophenyl acetate (PNPA) catalyzed by a- chymotrypsin has been measured in TRIS buffer at pH = 7.4. The presence of PEG (up to 30 % p/v) leads to an increase in the rate of the process. The effect of PEG is evident both, in the pre-steady state and steady state stages of the process. The reaction follows a Michaelis-Menten mechanism under all the conditions employed. The Michaelis constant slightly decreases and the catalytic rate constant slightly increases with PEG concentration over all the polymer concentration range employed (up to 30%). The decrease in the Michaelis constant suggests that the effect of the polymer is due to crowding.

Dynamic Structure Factor for Large Aggregate Clusters with Internal Motions: A Self-Consistent Light-Scattering Study on Conjugated Polymer Solutions

The aggregation properties of a standard conjugated polymer, poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), in two distinct solvents (chloroform and toluene) and a range of polymer concentrations (c = 0.1-3 mg/mL) have been unequivocally resolved using combined dynamic and static light scatterings (DLS/SLS). The prime challenges for analyzing this peculiar, practically important, solution system arise from the wide size distribution and unknown aggregate morphology, as well as pronounced interferences between translational and internal motions of aggregate clusters of considerably varying size. To cope with these central difficulties, we propose a self-consistent formulation for analyzing the dynamic structure factor in DLS experiment by extending an existing theory on free-draining bead-spring chains that explicitly accounts for internal fluctuations, along with two candidate form factors on Gaussian coil and rigid sphere, respectively, serving as two limiting cases to be discriminated in combined DLS and SLS measurements. Given that no accessibility to ultrasmall angular resolutions is a prerequisite, the suggested protocol can readily be carried out in conventional light-scattering apparatus. The present analyses unanimously support the rigid-sphere form factor in describing the entire set of light-scattering data on MEH-PPV solutions, differing from early small-angle neutron/X-ray scattering interpretations suggesting certain 2D fractal structures for the aggregation network. Scrutiny into the interior dynamics of aggregate clusters further disclosed that the segmental motions are noticeably more suppressed than for usual, nonaggregated polymer solutions, and no existing theories based on the bead-spring picture can yet capture the observed scaling behavior as manifested by the present data. Accordingly, we report several first-revealed properties of MEH-PPV solutions on the aggregate morphology, the size distribution (and mean size), mean aggregation number, and interior segmental dynamics, which serve as valuable information for linking solution properties with those for dried thin films in contemporary applications with conducting conjugated polymers.

A Comparative Study on Conventional Electrospinning and Emulsion Electrospinning of PLLA Nanofibers

Electrospinning is investigated by many groups around the world for constructing fibrous tissue engineering scaffolds. Incorporating biomolecules such as growth factors in fibers is becoming common for enhancing the biological performance of electrospun scaffolds. However, biomolecules may lose bioactivity if they are exposed to organic solvent during electrospinning. In emulsion electrospinning, an aqueous biomolecule solution is emulsified and water-in-oil emulsions are then electrospun into core-shell structured fibers, with biomolecules being contained in the core of fibers, which helps to avoid biomolecule-solvent contact and also reduce the initial burst release. In this investigation, for a comparative study, poly (L-lactic acid) was made into solid and core-shell structured fibers via conventional electrospinning and emulsion electrospinning, respectively. The two electrospinning techniques and resultant fibers were compared in terms of processing parameters (polymer concentration, applied voltage, working distance, etc.) and fiber characteristics (morphology, diameter, structure, etc.). Solvent properties such as conductivity and volatility affected fiber morphology and diameter. The polymer concentration range usable for emulsion electrospinning was narrower than that for conventional electrospinning owing to changes in viscosity.

Long- and Intermediate-Range Correlations in Polymer-Containing Ionic Liquids

Structure on long- and intermediate-length scales in polymer-containing ionic liquids is investigated on the basis of the polymer integral equation method. The structural features of flexible homopolymer chains and the ions of the solvent are analyzed in reciprocal space using partial structure factors. There is a range of polymer concentrations at which the long-range correlations of polymer chains are observed. When these correlations are pronounced, the decrease of the characteristic scale of the long-range polymer ordering with increasing polymer concentration fits a power law. The effect of adding polymer chains upon the ordering of the ions of the solvent is also considered. Upon addition of a polymer, it is shown that long-range correlations of ions can arise, although the intermediate-range ordering typical of pure ionic liquids remains dominant and stable. The dependence of the characteristic scale of the long-range ordering of the ions of the solvent on the polymer concentration also fits a power law.

Anti-CD22 Antibody Targeting of pH-responsive Micelles Enhances Small Interfering RNA Delivery and Gene Silencing in Lymphoma Cells

The application of small interfering RNA (siRNA) for cancer treatment is a promising strategy currently being explored in early phase clinical trials. However, efficient systemic delivery limits clinical implementation. We developed and tested a novel delivery system comprised of (i) an internalizing streptavidin-conjugated monoclonal antibody (mAb-SA) directed against CD22 and (ii) a biotinylated diblock copolymer containing both a positively charged siRNA condensing block and a pH-responsive block to facilitate endosome release. The modular design of the carrier facilitates the exchange of different targeting moieties and siRNAs to permit its usage in a variety of tumor types. The polymer was synthesized using the reversible addition fragmentation chain transfer (RAFT) technique and formed micelles capable of binding siRNA and mAb-SA. A hemolysis assay confirmed the predicted membrane destabilizing activity of the polymer under acidic conditions typical of the endosomal compartment. Enhanced siRNA uptake was demonstrated in DoHH2 lymphoma and transduced HeLa-R cells expressing CD22 but not in CD22 negative HeLa-R cells. Gene knockdown was significantly improved with CD22-targeted vs. nontargeted polymeric micelles. Treatment of DoHH2 cells with CD22-targeted polymeric micelles containing 15nmol/l siRNA produced 70% reduction of gene expression. This CD22-targeted polymer carrier may be useful for siRNA delivery to lymphoma cells.

Determination of the Flory Exponent by Study of Steady Shear Viscosity

The aim of the present work was to determine first the behavior of a neutral polymer, polyvinylpyrrolidone (Mw = 3,6 105 g/mol), in the dilute and semidilute regimes in water by a rotational concentric cylinder viscometer and then to deduce the Flory exponent. The absolute viscosity of the samples was directly determined from the shear stress–shear rate rheograms over a temperature range of 20°C–40°C and a polymer concentration range of 0.114–1.438 g/dl. The rheological nature of the polymer solutions was systematically analyzed, showing Newtonian behavior. Then, the intrinsic viscosity [η] was determined according to the Schultz–Blaschke equation. The overlapping concentration C* was determined by plotting the double logarithmic plots of reduced viscosity ηr versus polymer concentration C, yielding . The Flory exponents, ν, were deduced from viscosity measurements in the semidilute regime (ν = 0.544). In addition, the hydrodynamic radius, RH, was measured for different polymer molar mass (Mw (g/mol) = 10,000, 40,000, 50,000, and 360,000) by a dynamic light scattering technique at 25°C, yielding a Flory exponent at this temperature of 0.521. The obtained value was thus in agreement with that obtained by the rheological method in the semidilute regime with a relative deviation close to 4.5%.

New Excess Gibbs Energy Equation for Modeling the Thermodynamic and Transport Properties of Polymer Solutions and Nanofluids at Different Temperatures

A local composition model is developed for the representation of the excess Gibbs energy of polymer solutions. The model consists of two contributions due to the configurational entropy of mixing, represented by the Freed Flory–Huggins relation, and to the enthalpic contribution, represented by local compositions through nonrandom factor. The model is applied to correlate the solvent activity of binary polymer solutions. The new excess Gibbs energy equation was used along with the absolute rate theory of Eyring for modeling the dynamic viscosity of binary polymer solutions in the entire concentration range at different temperatures considering different molar mass of polymers. The fitting quality of new model has favorably been compared with polymer-NRTL, segment-based-liquid-NRTL, polymer-Wilson, polymer-NRF and polymer-NRF-Wilson models. The validity of the proposed model is especially demonstrated for the whole range of polymer concentrations at different temperatures using different molar masses of po...

Enzymatically Degradable Thermogelling Poly(alanine-co-leucine)-poloxamer-poly(alanine-co-leucine)

In the search for an enzymatically degradable thermogelling system, we are reporting poly(alanine-co-leucine)-poloxamer-poly(alanine-co-leucine) (PAL-PLX-PAL) aqueous solution. As the temperature increased, the polymer aqueous solution underwent sol-to-gel transition at 20-40 °C in a polymer concentration range of 3.0-10.0 wt %. The amphiphilic polymers of PAL-PLX-PAL form micelles in water, where the hydrophobic PALs form a core and the hydrophilic PLXs form a shell of the micelle. FTIR, circular dichroism, and (13)C NMR spectra suggest that the α-helical secondary structure of PAL is preserved; however, the molecular motion of the PLX significantly decreases in the sol-to-gel transition range of 20-50 °C. The polymer was degraded by proteolytic enzymes such as matrix metalloproteinase and elastase, whereas it was quite stable against cathepsin B, cathepsin C, and chymotrypsin or in phosphate-buffered saline (control). The in situ formed gel in the subcutaneous layer of rats showed a duration of ∼ 47 days, and H&E staining study suggests the histocompatibility of the gel in vivo with a marginal inflammation response of capsule formation. A model drug of bovine serum albumin was released over 1 month by the preset-gel injection method. The thermogelling PAL-PLX-PAL can be a promising biocompatible material for minimally invasive injectable drug delivery.

Membrane nanotubes induced by aqueous phase separation and stabilized by spontaneous curvature.

Tubular membrane structures are widespread in eukaryotic cells, but the mechanisms underlying their formation and stability are not well understood. Previous work has focused on tube extrusion from cells and model membranes under the application of external forces. Here, we present novel membrane/polymer systems, where stable tubes form in the absence of externally applied forces. Solutions of two water-soluble polymers, polyethylene glycol and dextran, were encapsulated in giant lipid vesicles, cell-size model systems. Hypertonic deflation induced phase separation of the enclosed solution. The excess membrane area created during the deflation process was stored in a large number of membrane nanotubes inside the vesicle. The tubes had a diameter below optical resolution and became visible only when fluorescently labeled. The tubes were rather stable: In the absence of external forces, they existed for several days. A theoretical analysis of the shapes of the deflated vesicles reveals that these shapes would be unstable if the membranes had no spontaneous curvature. Using the large separation of length scales between the tube diameter and the overall size of the vesicles, the spontaneous curvature can be calculated and is found to be about -1/(240 nm) for a certain range of polymer concentrations. The nanotubes could also be retracted back into the mother vesicle by increasing the membrane tension via micropipette aspiration of the vesicle. Membrane tubes, which can form and be retracted easily, should be relevant for lipid storage in cells.

The structure of percolated polymer systems: a computer simulation study

We studied the percolation process in a system consisting of long flexible polymer chains and solvent molecules. The polymer chains were approximated by linear sequences of beads on a two-dimensional triangular lattice. The system was athermal and the excluded volume was the only potential. The properties of the model system across the entire range of polymer concentrations were determined by Monte Carlo simulations employing a cooperative motion algorithm (CMA). The scaling behavior and the structure of the percolation clusters are presented and discussed.

Viscoelastic properties of highly concentrated maize starch solutions in DMSO

AbstractRheological measurements of highly concentrated dimethylsulfoxide (DMSO) starch solutions were performed. For all experiments commercial maize starch with different AM content was used. The research covered a wide range of polymer concentrations depending on linear fraction contribution and allowed to obtain a starch content up to 40% w/w. The analysis covered the time – concentration superposition method and fitting the continuous Maxwell model to the experimental data using Tikhonov regularization method. The results allowed statements about the viscoelastic behavior of non‐aqueous starch solutions, depending on their molecular structure. If the linear AM is the predominant component of the starch, the system behaves more elastic compared to those composed of branched AP. The effect of variation in molecular constitution is stronger than the effect of concentration of the dispersion. Additionally, the molecular masses of both fractions seems not to be the crucial factor for rheological properties as well as biopolymer solubility in DMSO. Relaxation spectra obtained from Maxwell model show the drift of the main peak to shorter relaxation times when the concentration of biopolymer is rising. The phenomenon testifies about the influence of starch concentration on elastic response of the system.

Comparison of two cationic polymeric flocculant architectures on the destabilization of negatively charged latex suspensions

Flocculation studies between cationic polymers and oppositely charged colloidal particles are reported in which both flocculation kinetics and floc structures are systematically investigated. The flocculation rate constant, stability ratio and kinetics laws are experimentally determined using particle counting for two polymer architectures; a cationic linear polymer and a two-branched polymer. Comparisons are also made using NaCl at different ionic concentrations for the destabilization of the colloidal particles. Detailed measurements of electrophoretic mobility and kinetics rate constants on varying the polymer dosage are reported. Results suggest that the polymer architecture plays important roles on the polymer dosage for the rapid destabilization of the colloidal suspension. The branched polymer at optimal dosage exhibits the highest flocculation rate constant, whereas on the other hand, the linear polymer concentration range of flocculation is larger. In both cases, polymer flocculation is more efficient by a factor of 5–6 than charge screening effects due to the presence of salt. Analysis of the stability ratio indicates that tele-bridging flocculation and electrostatic forces dictate the stability of the charged latex particle suspension. It is shown that the fractal concepts which are valid for aggregation processes are also applicable here and branched polymers as well as linear polymers yield to the formation of compact flocs in comparison to those obtained with salt.

Complexation of cationic polyelectrolyte with anionic phospholipid vesicles: Concentration, molecular weight and salt effects

The influence of cationic poly(diallyldimethylammonium chloride) on the morphology and phase behavior of anionic phospholipid vesicles was investigated using differential scanning calorimetry, fluorescent microscopy and light scattering technique. A wide range of polymer concentration has been examined for the first time. The polycation can bind electrostatically to the vesicles to compensate, neutralize and reverse the vesicular charge, depending on the molar ratio of cationic to anionic group R. For R < 1, charge compensation weakened the electrostatic repulsion between the lipid molecules, leading to formation of polymer-modified vesicles, each with an increased number of bilayers. The bilayer exhibits a rising main phase transition temperature from a gel to liquid crystalline state. This behavior persisted until R ≈ 1 around the neutralization condition, where the complexes became largest and precipitate. With R > 1, charge reversal took place, the complex size reduced. Interestingly, the main phase transition temperature was found for the first time to shift back towards the original value in the absence of polymer for large enough R. Although the thermal behavior was nearly independent of the polymer molecular weight, the complex morphology could be different.

Rheological behavior and microstructure of 2,2′-dioxy- 1,1′-binaphthylphosphazene R/S random copolymer

Solutions of a binaphthoxy phosphazene copolymer (containing chiral 2,2′-dioxy-1,1′-binaphthyl units with 50% R and S configurations distributed along the chains) in N-methyl pyrrolidone were studied by means of continuous flow experiments and small amplitude oscillatory flow tests. A sudden viscosity decrease was observed in the polymer concentration range (39–40 wt %), evidencing a liquid-crystalline polymer behavior. This has been confirmed by other rheological methods which have demonstrated that, for a sufficiently high concentration, the solutions of the binaphthoxy phosphazene copolymer give rise to a lyotropic system with formation of rigid rods (axial ratio of 10) stacked parallel to each other. The lyotropic properties of our binaphthoxy phosphazene copolymer are compatible with a regular helical structure, similar to that found for a homoleptic binaphthoxy phosphazene, which contains only S configuration. This suggests that the chains of 50% R/S binaphthoxy phosphazene copolymer are, in average, close to the strictly alternating R-S copolymeric structure of the syndiotactic isomer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010

Functional analysis of cellulose acetate flat membranes prepared via casting technique

Cellulosic membranes reflect better utilization of renewable resources with minimum impacts on the environment. Significant market for medium pressure application is encountered in water filtration and reclamation. Thus, endeavors are needed to balance advancement of cellulose membrane and manufacturing technology modification. Cellulose membranes have been prepared via phase inversion process from different blends of polymers/solvents/additives. The casting solutions comprising polymer concentration range from 15 to 25 wt%, and acetone, tetrachloroethane and N,N dimethyl formamide as solvents. Different samples of membranes have been prepared and tested using polymer with different acetyl contents. The prepared membranes have been characterized using scanning electron microscope (SEM). Further, performance indicators comprising: flux, operating time, permeability and selectivity has been investigated according to casting solution constituents and membrane matrix morphology. Operating pressures up to 50 bars has been applied. The results indicate that the appropriate polymeric content has been found to be between 20% and 22%. Enhanced performance is also observed in the presence of both polymethylhydrosiloxan (PMHS) and dibutyl phthalate (DBP) denoting better salt rejection. Almost all prepared membranes, could tolerate operating pressures up to 50 bars.

A polymer in an ionic liquid: Structural properties of a system during attraction between the polymer and cations of the ionic liquid

In terms of the polymer integral equation theory, structuring in ionic liquids containing flexiblechain polymers under the conditions of good solubility is studied for the first time. The influence of the polymer concentration on the structural properties of system components is studied at different lengths of polymer molecules. The structural organization of the ionic liquids is shown to be fairly stable after addition of the polymer. When there is attraction between the polar groups of cations of the ionic liquid and polymer molecules, the calculated structural factors suggest intermediate-range scales of polymer-component ordering. Given this, for any considered length of polymer molecules, there is a range of polymer concentrations in which the characteristic scale of ordering decreases with an increase in polymer density according to a power law.