Range Of Polymer Concentrations Research Articles

Effect of Composition of HPAM/Chromium(III) Acetate Gels on Delayed Gelation Time

A delayed crosslinking system employed with hydrolyzed polyacrylamide (HPAM) and chromium acetate was developed for high profile control in low-temperature reservoirs. The crosslinking system formed strong gel at polymer concentration range of 3000–5000 mg/L, and the gelation time was delayed to 8–30 days, which offered the crosslinking system enough time to flow into deep water-producing zones and plug large pore paths, forcing follow-up fluids to enter low-permeability layer and reduce disproportionate permeability. The effect of polymer hydrolysis degree, polymer concentration, pH, and crosslinker concentration on delaying gelation time was evaluated using bottle testing. Meanwhile, sand-packed tube displacement experiments revealed the plugging performance of delayed crosslinking system. According to Fourier transform infrared spectroscopy (FTIR) analysis, as well as crosslinking mechanism between polymer and chromium acetate, the delayed mechanism of crosslinked system demonstrated that due to stronger affinity of acetate complexes as a ligand, its substitution in situ by carboxylate group of polyacrylamide slowed down the initial rate-determining step of crosslinking reaction.

Stabilization of self‐assembled microdroplets using short chain alcohols

ABSTRACTThe condensation of water vapor on a volatile polymeric solution leads to a porous surface after evaporation of both solvent and water. However, the stabilization of the water microdroplet is of great importance, which can be achieved using specific polymer or adding a third substance to the polymer solution. Short chain alcohols (methanol, ethanol, and n‐propanol) are utilized to fabricate a self‐assembled porous honeycomb film of linear, low molecular weight polystyrene using the breath figure technique. A combination of breath figure processing and the effect of alcohol on a water droplet can stabilize the pattern and make pores on the surface of the polymer film. The quality of the porous honeycomb film is strongly dependent on the type of alcohols and the concentration of polymer. In a specific range of polymer and alcohol concentration, pores cover all the surface of the polymer film. This method offers the possibility of producing a honeycomb structure with no trace of additive residual after the fabrication process and avoiding polymer modification. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 709–718

Vapour pressure osmometry determination of water activity of binary and ternary aqueous (polymer + polymer) solutions

Precise water activity measurements at T=308.15K were carried out on several binary (water+polymer) and ternary {water+polymer (1)+polymer (2)} systems using the vapour pressure osmometry (VPO) technique. Polymers were polyethylene glycol 400 (PEG400), polyethylene glycol 6000 (PEG6000), polypropylene glycol 400 (PPG400), polyvinylpyrrolidone (PVP) and dextran (DEX). The water activity results obtained were used to calculate the vapour pressure of solutions as a function of concentration and the segment-based local composition models, NRTL and Wilson, were used to correlate the experimental water activity values. It was found that, for the polymer concentration range studied here, the values of the water activity obtained for the binary (water+polymer) solutions decrease in the order DEX>PVP>PEG6000>PPG400>PEG400. Furthermore, water activities of solutions of each polymer in the aqueous solutions of (5, 10, 15 and 20)% (w/w) other polymers investigated were also measured at T=308.15K. The ability of polymer (1) in decreasing the water activity of binary {water+polymer (2)} solutions was discussed on the basis of the (polymer+water) and {polymer (1)+polymer (2)} interactions.

Pressure-driven microfluidic flow-focusing of air through a surfactant-doped dilute polymer liquid

In this paper, we present experimental results on the formation of air bubbles in a non-Newtonian liquid. Flow-focusing technology with pressure-driven fluid pumping is used to demonstrate and study the bubble production process. The liquid phase consists of aqueous polyacrylamide at concentrations ranging from 0.01 to 0.10 wt%. Additionally, the solution contains sodium lauryl sulfate, an anionic surfactant, at concentrations ranging from 0.01 to 0.10 wt%. We report on bubble production with pressure ratios (dispersed/continuous phases) ranging from 0.6 to 0.9; the range spans from the minimum ratio required to produce bubbles to the pressure ratio required to produce an air jet. Within this range of pressure ratios, the bubbles lengths are polydisperse, a clear deviation from previous studies involving Newtonian continuous phase fluids. Although the continuous phase contains two additives, we deduce that the polymer is mainly responsible for this change in behavior from Newtonian fluids. The addition of surfactant though provides a means of manipulating this behavior for a certain range of polymer concentrations. We characterize the efficiency of the surfactant by performing a mass transport analysis using Schmidt (Sc), Sherwood (Sh), and Reynolds (Re) numbers. Despite this observation, the average bubble lengths follow trends established for Newtonian fluids.

The Modification of Rheological Properties of Sodium Bentonite-water Dispersions with Low Viscosity CMC Polymer Effect

Due to their exceptional rheological properties, bentonites are used in different branches of industry, such as in drilling fluids, dyes, pharmaceuticals, paper, cement, nanocomposites, polymer composites, and ceramics. In the use of bentonite in different applications, the addition of carboxymethyl cellulose (CMC) sodium salt is recommended to optimize the rheological properties of the suspension. In this study, the effect of carboxymethyl cellulose on the rheological properties of Na-bentonite suspensions was investigated in the polymer concentration range of 0.02–0.50 wt%. The addition of carboxymethyl cellulose to the bentonite dispersions resulted in significant increase in the dispersion viscosity. The advantage of carboxymethyl cellulose is that the desired rheological properties can be obtained with less bentonite by adding carboxymethyl cellulose polymer and the undesirable effects of high bentonite concentrations can be avoided. The viscosity of 8.0 wt% pure bentonite dispersions was achieved by adding 0.10 wt% carboxymethyl cellulose to 4.0 wt% bentonite dispersions. The combined flow behaviors of Bingham and shear thickening observed for the 4.0 wt% pure bentonite dispersion was shifted toward the shear thinning profile with a yield stress in the presence of the carboxymethyl cellulose. This yield stress increased substantially with carboxymethyl cellulose concentration. In addition, the thixotropic behavior of bentonite dispersions was significantly enhanced by adding carboxymethyl cellulose polymer.

Single Polymer Dynamics in A Random Flow

SummaryThe dynamics and conformations of a single fluorescently stained T4 DNA molecule are studied in a random flow of elastic turbulence created by the same unlabeled molecules. The explored polymer concentration covers the dilute and semi‐dilute unentangled regimes, according to the measurement of the longest relaxation time by extension relaxation of single polymer chains. The criterion of the coil‐stretch transition was found to be close to the theoretically predicted value. Using measured polymer stretching statistics and its known elastic properties, the elastic stress in elastic turbulence is obtained over a broad range of Weissenberg number and polymer concentration. The existing theory of elastic turbulence is disproved by the measurements of the elastic stress and the degree of polymer stretching. The role of increasing shear rate on polymer extension and angular statistics in a random flow is also studied and compared with theory and numerical simulations.

Viscoelastic analysis of single-component and composite PEG and alginate hydrogels

Hydrogels, three-dimensional hydrophilic polymer networks, are appealing candidate materials for studying the cellular microenvironment as their substantial water content helps to better mimic soft tissue. However, hydrogels can lack mechanical stiffness, strength, and toughness. Composite hydrogel systems have been shown to improve upon mechanical properties compared to their singlecomponent counterparts. Poly (ethylene glycol) dimethacrylate (PEGDMA) and alginate are polymers that have been used to form hydrogels for biological applications. Singlecomponent and composite PEGDMA and alginate systems were fabricated with a range of total polymer concentrations. Bulk gels were mechanically characterized using spherical indentation testing and a viscoelastic analysis framework. An increase in shear modulus with increasing polymer concentration was demonstrated for all systems. Alginate hydrogels were shown to have a smaller viscoelastic ratio than the PEGDMA gels, indicating more extensive relaxation over time. Composite alginate and PEGDMA hydrogels exhibited a combination of the mechanical properties of the constituents, as well as a qualitative increase in toughness. Additionally, multiple hydrogel systems were produced that had similar shear moduli, but different viscoelastic behaviors. Accurate measurement of the mechanical properties of hydrogels is necessary in order to determine what parameters are key in modeling the cellular microenvironment. Open image in new window

Stability of manganese dioxide by guar gum in the absence or presence of surfactants

Stability of the manganese dioxide (MnO2) suspensions by non-ionic guar gum (GG) in the absence or presence of the surfactants: anionic sodium dodecyl sulphate (SDS), cationic hexadecyltrimethylammonium bromide (CTAB) and non-ionic Triton X-100 (t-octylphenoxypolyethoxyethanol) and their equimolar mixtures (SDS/TX-100; CTAB/TX-100) was measured using turbidity. The obtained results of the manganese dioxide suspensions stability were discussed together with the adsorption data and with the data concerning the thicknesses of the adsorption layers. In order to gain more information about the structure of the electric double layer surface charge density and the zeta potential measurements were performed. The obtained results show that the addition of guar gum to the MnO2 suspensions increases MnO2 stability. The larger this increase is, the higher is the concentration of the polymer (concentration range 10–200 ppm). Moreover, the addition of single surfactants also causes the increase in the effectiveness of stabilizing the manganese dioxide suspensions. The reason for that is formation of multilayer complexes between the polymer and the surfactants. In such a system both the adsorption of polymer and the thickness of polymer adsorption layer increase. The greatest increase in the stability of MnO2/GG suspensions was provided by the mixture of anionic and non-ionic surfactants due to a strong synergistic effect. Also, mixing the polymer and two surfactants reduces the stability of the suspension.

Hybrid Nanomaterial Complexes for Advanced Phage-guided Gene Delivery.

Developing nanomaterials that are effective, safe, and selective for gene transfer applications is challenging. Bacteriophages (phage), viruses that infect bacteria only, have shown promise for targeted gene transfer applications. Unfortunately, limited progress has been achieved in improving their potential to overcome mammalian cellular barriers. We hypothesized that chemical modification of the bacteriophage capsid could be applied to improve targeted gene delivery by phage vectors into mammalian cells. Here, we introduce a novel hybrid system consisting of two classes of nanomaterial systems, cationic polymers and M13 bacteriophage virus particles genetically engineered to display a tumor-targeting ligand and carry a transgene cassette. We demonstrate that the phage complex with cationic polymers generates positively charged phage and large aggregates that show enhanced cell surface attachment, buffering capacity, and improved transgene expression while retaining cell type specificity. Moreover, phage/polymer complexes carrying a therapeutic gene achieve greater cancer cell killing than phage alone. This new class of hybrid nanomaterial platform can advance targeted gene delivery applications by bacteriophage.

Activation Energy for Mobility of Dyes and Proteins in Polymer Solutions: From Diffusion of Single Particles to Macroscale Flow

We measure the activation energy Ea for the diffusion of molecular probes (dyes and proteins of radii from 0.52 to 6.9 nm) and for macroscopic flow in a model complex liquid-aqueous solutions of polyethylene glycol. We cover a broad range of polymer molecular weights, concentrations, and temperatures. Fluorescence correlation spectroscopy and rheometry experiments reveal a relationship between the excess of the activation energy in polymer solutions over the one in pure solvent ΔEa and simple parameters describing the structure of the system: probe radius, polymer hydrodynamic radius, and correlation length. ΔEa varies by more than an order of magnitude in the investigated systems (in the range of ca. 1-15 kJ/mol) and for probes significantly larger than the polymer hydrodynamic radius approaches the value measured for macroscopic flow. We develop an explicit formula describing the smooth transition of ΔEa from the diffusion of molecular probes to macroscopic flow. This formula is a reference for the quantitative analysis of specific interactions of moving nano-objects with their environment as well as active transport. For instance, the power developed by a molecular motor moving at constant velocity u is proportional to u2exp(Ea/RT).

Comparison of concentration dependence of mechanical modulus in two biopolymer gel systems using scaling analysis

Concentration dependence of mechanical modulus of two biopolymer systems, i.e., xanthan-locust bean (X/L) mixture and fish muscle protein (surimi) was evaluated and compared at a wide range of polymer concentrations. A small amplitude oscillatory shear test was performed to measure changes in storage (G') modulus during gelation and after gelation. Critical concentration (Cc) of the X/L mixture and surimi gel was determined to be 0.15 g/100 mL of solvent and 2.04 g/100 g of solvent, respectively. Reduced concentration (CR=CL/Cc) was used to compare the power-law dependence of modulus of the two systems. The elasticity exponent of the X/L mixture and surimi gel was determined to be 2.4 and 1.97, respectively. The concentration dependence of two biopolymer gel systems such as physical gels (X/L) and chemicals gels (fish muscle protein) theoretically demonstrated that the difference of flexibility of junctions in the networks might distinguish the elasticity of each gel.

NMR water self‐diffusion and relaxation studies on sodium polyacrylate solutions and gels in physiologic ionic solutions

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca2+ and Na+. Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na+ on the mobility of water molecules was practically undetectable. By contrast, addition of Ca2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced.

Influence of polyvinylpyrrolidone on the interaction between water and methanol

Abstract - The present work aims to determine the influence of a dissolved polymer, polyvinylpyrrolidone, on the interaction between water and methanol . First, the dynamic viscosities were measured for polymer solutions by a rotational concentric cylinder at 25 °C and for the polymer concentration range from 0.1 to 0.6 g/dl. The results show a polynomial dependence of the viscosity on polymer concentration. On the hypothesis of a quasi-binary system, a pseudo Grumberg-Nissan constant, ' dp , was introduced to quantify the interaction between unlike molecules in the presence of polymer. The interaction between unlike molecules due to the presence of the polymer was quantified by the deviation of the Grumberg-Nissan constant, '' δ= −dd d p pp . Generally, this constant is negative which means that the interactions between water and methanol decrease in the presence of polyvinylpyrrolidone at 25 °C. The presence of the polymer induces a perturbation of the dynamic equilibrium between free and complexed molecules.

Light scattering behavior and the kinetics of pressure-induced phase separation in solutions of poly(ε-caprolactone) in acetone + CO2 binary fluid mixtures

The miscibility and the kinetics of pressure-induced phase separation in solutions of poly(ε-caprolactone) (PCL) in acetone + CO2 binary fluid mixtures have been studied at pressures up to 28 MPa and temperatures up to 410 K using a unique high pressure view-cell equipped with a dual set of pistons and dual set of sapphire windows. One set of the windows separated by 25.4 mm allows the assessment of the phase state and is used to monitor the transmitted light intensities. The second set of windows separated by 50 μm is used to monitor the scattered light intensities over a wide range of scattering vector q (from 0.35 to 4 μm−1) which allows the assessment of the mechanism of phase separation. Investigations have been carried out for a wide range of polymer concentrations, from 2.0 to 34.9 wt%, while holding the acetone-to-CO2 (wt:wt) ratio in each solution at a constant value of 2:1. The dual set of pistons that are employed which are synchronized and motorized create a churn-like action in the cell insuring effective mixing, even at the high polymer concentrations by translating the cell content across a magnetically-coupled rotating mixer impeller. The piston actions assure also that the solution is effectively introduced into the narrow gap between the scattering windows, and refreshed. The solutions at off-critical concentrations undergo pressure-induced phase separation via nucleation and growth mechanism which shows circular symmetric patterns in their light scattering patterns. For these solutions, the Debye–Bueche type scattering function was used to analyze the domain size of the new phase that forms and develops after a pressure quench. The phase separation in solutions at or near the critical polymer concentrations (9.0–15.0 wt%) proceeds via spinodal decomposition which is characterized by the formation and evolution of the spinodal ring patterns corresponding to a maximum in the angular variation of the scattered light intensities. The results in early stage of the spinodal decomposition were described by the linearized Cahn theory. The variation of the scattered light intensity maximum Im and its location in scattering vectors qm with time in the later stage of the spinodal decomposition obey power-law scaling according to Im ∼ tβ and qm ∼ t−α. The results for the 9.0 and 12.0 wt% solutions show that β/α changes its value from β/α > 3 to β/α ≈ 3 with time, indicating the progression of the spinodal decomposition from intermediate to late stage.

Drop breakage and coalescence in the toluene/water dispersions with dissolved surface active polymers PVA 88% and 98%

The influence of two PVAs of the same molecular weight (13,000–23,000) and different degree of hydrolysis equal to 88% and 98% on breakage and coalescence of toluene droplets in the liquid/liquid dispersion were considered for PVA concentration range 0.001–0.01%. Analysis of experimental results shows that drop coalescence is significant only in the system containing 0.001% PVA. Drop coalescence for polymer concentration range 0.002–0.01% is strongly limited. Therefore, population balance was solved using breakage and coalescence expressions with assumed partially mobile drop interfaces for the lowest PVA concentration. For c≥0.002% drop size distributions were properly predicted using only breakage model. Multifractal formalism was used to take into account intermittent character of turbulence and explain drop behavior. Larger drop size reduction by PVA of lower degree of hydrolysis observed experimentally was confirmed by the model.

Dominant role of wormlike micelles in temperature-responsive viscoelastic properties of their mixtures with polymeric chains

Temperature effects on the rheological properties of viscoelastic solutions containing entangled wormlike micelles of potassium oleate and hydrophobically modified polyacrylamide were studied in a wide range of polymer concentrations. A very pronounced drop of viscosity by four orders of magnitude was observed at heating from 20 to 78°C both in the presence and in the absence of polymer indicating that the wormlike micelles are mainly responsible for this effect. The highly thermosensitive behavior was attributed to the shortening of micellar chains induced by heating. Although the decrease in viscosity is almost the same for both surfactant and surfactant/polymer systems, the absolute values of the viscosity in the presence of polymer are by few orders of magnitude higher, which is due to the formation of a common network of entangled polymer and micellar chains. As a result, the added polymer allows one to get highly temperature responsive system that keeps viscoelastic properties in a much wider range of temperatures, which makes it very promising for various practical applications.

Rheological and hydrodynamic properties of cellulose acetate/ionic liquid solutions

Rheological properties of cellulose acetate/1-ethyl-3-methylimidazolium acetate (EMIMAc) solutions are studied using shear dynamic and steady state rheology in a large range of polymer concentrations (from 0.1 to 10wt.%) and temperatures (from 0°C to 80°C). Master plots for storage and loss moduli and for dynamic viscosity were built and shift parameters determined. Cellulose acetate/EMIMAc behaves as a classical polymer solution and obeys Cox–Merz law. Cellulose acetate intrinsic viscosity [η] was determined as a function of temperature and compared with the literature data for cellulose acetates dissolved in other solvents and cellulose dissolved in EMIMAc. Cellulose acetate intrinsic viscosity turned out to be much less temperature sensitive than that of cellulose. Specific viscosity-C[η] master plot was built: the slopes in log–log scale are 1.2 and 3.1 in dilute and semi-dilute regions, respectively. The activation energy as a function of concentration follows a power-law dependence.

Measuring the Grafting Density of Nanoparticles in Solution by Analytical Ultracentrifugation and Total Organic Carbon Analysis

Many of the solution phase properties of nanoparticles, such as their colloidal stability and hydrodynamic diameter, are governed by the number of stabilizing groups bound to the particle surface (i.e., grafting density). Here, we show how two techniques, analytical ultracentrifugation (AUC) and total organic carbon analysis (TOC), can be applied separately to the measurement of this parameter. AUC directly measures the density of nanoparticle-polymer conjugates while TOC provides the total carbon content of its aqueous dispersions. When these techniques are applied to model gold nanoparticles capped with thiolated poly(ethylene glycol), the measured grafting densities across a range of polymer chain lengths, polymer concentrations, and nanoparticle diameters agree to within 20%. Moreover, the measured grafting densities correlate well with the polymer content determined by thermogravimetric analysis of solid conjugate samples. Using these tools, we examine the particle core diameter, polymer chain length, and polymer solution concentration dependence of nanoparticle grafting densities in a gold nanoparticle-poly(ethylene glycol) conjugate system.

Confinement-Induced Solidification of Colloid-Polymer Depletion Mixtures

Using a model colloid-polymer suspension, we show that confinement induces solidification in attractive colloidal suspensions via a fundamentally different route from that active in hard sphere colloidal suspensions. For a range of polymer concentrations, the suspensions undergo a phase transition from a colloidal fluid of clusters to a colloidal gel as confinement increases while polymer and particle concentration are held constant. In both fluid- and solidlike attractive suspensions, effects of confinement on the structure and dynamics appear at much larger thicknesses than for hard-sphere suspensions. The solidification does not originate from structuring of the colloids by the walls. Instead, by analyzing cluster size distributions in the fluid phase and particle dynamics in the gel phase as a function of confinement, we find that the strength of the effective interparticle attraction increases as the samples are confined. We show that the increase in the effective attraction can be understood as a consequence of the increasing importance of excluded volume due to the walls to the free energy of the polymer as confinement is increased.

Preparation, characterization and performance of a novel PVDF/PMMA/TPU blend hollow fiber membrane for wastewater treatment

Polyvinylidene fluoride (PVDF)/polymethylmethacrylate (PMMA)/thermoplastic polyurethane (TPU) blend hollow fiber membranes were successfully prepared by the wet-spinning method with the loading of PMMA and TPU in a range of polymer concentrations varying from 0 to 20 wt% and at a total polymer concentration of 16 wt%. The influence of the addition of PMMA and TPU on the morphologies and the properties of such prepared membranes was investigated through FTIR-ATR, SEM, viscosity measurements, UF experiments and mechanical strength tests. Based on the experimental results, the compatibility of the PVDF, PMMA and TPU blend was best under the conditions of the PVDF-rich phase. The elongation at break of the membrane increased to a maximum of 146% with increase in the TPU concentration to 20 wt% in dope solution. The addition of PMMA increased the water permeation flux from 120 to 195 L/(m(2) h) initially. The flux then decreased when PMMA concentration was increased to over 10 wt%. The membranes obtained at optimized blending ratio were applied to the dyeing process wastewater filtration. During continuous filtration for 8 h, the flux was stabilized at about 20 L/(m(2) h) at 0.1 MPa. The reduction in COD(Cr), turbidity and color were about 63, 84 and 63% respectively.