Re-entrant transition of aluminum-crosslinked partially hydrolyzed polyacrylamide in a high salinity solvent by rheology and NMR (original) (raw)
Related papers
Energy & Fuels, 2014
There is booming interest in the application of nanoparticles for enhanced oil recovery. In this work, a polymer nanoparticle that is generated by cross-linking a high-molecular weight partially hydrolyzed polyacrylamide with aluminum(III) and known as linked polymer solution (LPS) has been studied. The size and conformational state of LPS particles are influenced by the concentration of Al(III). To the best our knowledge, there is no current established method for determining the conformational state, i.e., single coiled particle, coil aggregates, or gel, for a polymer solution with a high molecular weight (>10 × 10 6 Da) and a low concentration (<1000 ppm). In this work, therefore, the phase transition of LPS is investigated by employing two-dimensional 1 H− 1 H nuclear magnetic resonance (nuclear Overhauser effect spectroscopy and diffusion ordered spectroscopy), UV−visible spectroscopy, and oscillatory rheological methods. Each method is limited to determining the conformational state; however, the combined methods provided a consistent tool for mapping various interactions regarding the conformational changes of LPS as a function of Al(III) concentration. The results of our study revealed that the phase transition is a stepwise process; the transition from a random polymer coil to structured coils (intramolecular cross-linking) was observed by reduction of the hydrodynamic radius and an increase in the rate of diffusion, followed by coil aggregates as a function of Al 3+ concentration. Ultimately, networked weak gels are formed by coil aggregates (intermolecular cross-linking) above the threshold concentration.
Theoretical study of chain transfer to solvent reactions of alkyl acrylates
The journal of physical chemistry. A, 2014
This computational and theoretical study deals with chain transfer to solvent (CTS) reactions of methyl acrylate (MA), ethyl acrylate (EA), and n-butyl acrylate (n-BA) self-initiated homopolymerization in solvents such as butanol (polar, protic), methyl ethyl ketone (MEK) (polar, aprotic), and p-xylene (nonpolar). The results indicate that abstraction of a hydrogen atom from the methylene group next to the oxygen atom in n-butanol, from the methylene group in MEK, and from a methyl group in p-xylene by a live polymer chain are the most likely mechanisms of CTS reactions in MA, EA, and n-BA. Energy barriers and molecular geometries of reactants, products, and transition states are predicted. The sensitivity of the predictions to three hybrid functionals (B3LYP, X3LYP, and M06-2X) and three different basis sets (6-31G(d,p), 6-311G(d), and 6-311G(d,p)) is investigated. Among n-butanol, sec-butanol, and tert-butanol, tert-butanol has the highest CTS energy barrier and the lowest rate co...
Journal of the Brazilian Chemical Society, 2011
Uma poliacrilamida hidrofobicamente modificada e dois dos seus derivados parcialmente hidrolisados, contendo grupos hidrofóbicos e carboxila, foram preparados por polimerização micelar e pós-hidrólise. A massa molar, o segundo coeficiente do virial e o raio de giração foram determinados por espalhamento de luz estático (SLS). O espalhamento de luz dinâmico (DLS) e o espalhamento de raios-X a baixos ângulos (SAXS) foram utilizados respectivamente para determinar a formação de agregados e o tipo de empacotamento das cadeias em regime semi-diluído. O comportamento das soluções, em regime diluído e semi-diluído foi estudado por viscosimetria e reologia. A poliacrilamida modificada hidrofobicamente apresentou tendência à formação de agregados devido aos grupos hidrofóbicos, mas essa agregação não foi suficiente para aumentar a viscosidade aparente. Embora os derivados parcialmente hidrolisados não apresentassem a mesma tendência para agregação, eles apresentaram um comportamento anisotrópico devido à introdução de densidade de carga sobre a cadeia polimérica, a qual levou a uma conformação mais alongada da macromolécula e maior viscosidade. A hydrophobically-modified polyacrylamide and two partially hydrolyzed derivatives containing hydrophobic and carboxylic groups were prepared by micellar polymerization and posthydrolysis. The molecular weight, second virial coefficient and radius of gyration were determined by static light scattering (SLS). Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were employed to determine the aggregate formation and type of chain packing in the semidilute regime, respectively. The behavior of solutions in dilute and semidilute regimes was also studied by viscometry and rheology. The hydrophobically-modified polyacrylamide showed a tendency to form aggregates due to the hydrophobic groups, but not enough to increase apparent viscosity. The partially hydrolyzed derivatives did not show the same aggregate-forming tendency. Rather, they exhibited anisotropic behavior, due to the charge density introduced into the polymer chain, which led to a more elongated macromolecular conformation and higher viscosity.
Kinetics of the Crosslinking of Polyacrylamide with Cr(III). Analysis of Possible Mechanisms
The Journal of Physical Chemistry, 1994
Rheological measurements have been performed on a system of a partially hydrolyzed polyacrylamide (€-PAM) with Cr(II1) as a cross-linking agent. A soYgel phase diagram of the system has been established. The scaling properties of the gel have been investigated varying the cross-link concentration at a fixed polymer concentration, measuring the dynamic storage modulus, G', after the reaction was completed. The variation of final storage modulus versus Cr(II1) concentration is described by the percolation model, giving a scaling exponent for G' of 1.9. Combining the percolation model description with a traditional kinetic approach for first-order reactions, the kinetics of gelation were determined from measured time dependence of G'. Comparison has been made to measurements by W-v i s spectroscopy on the same systems. The measurement of G' provides additional mechanistic information about the gelation process. It indicates that the observed biphasic natures of the first-order plots from rheology and spectroscopy measurements are due to a side reaction. The cross-linking is believed to proceed through a rate-determining introduction of the first HPAM to Cr(II1).
The Canadian Journal of Chemical Engineering, 2021
Inorganically crosslinked polymers have been intensively implemented for conformance control treatments in oil and gas wells at low temperatures (<90 C) because of their faster gelation time compared to organically crosslinked gels. Crosslinkers such as chromium acetate are known to be toxic, and aluminium-based alternatives have been introduced. This study aims to investigate the impact of aluminium acetate (AlAc) particle size on the gelation kinetics of polyacrylamide (PAM)-based gels at a pH of 5 and temperature of 75 C. Moreover, bentonite is used as an additive to delay the crosslinking of PAM/AlAc gels. Reducing the particle size increases the specific surface area of the particles and provides more crosslinking sites. Therefore, lower PAM concentrations (up to 5 wt.%) could be used without AlAc settling. Using 7 wt. % PAM/1 wt.% AlAc with sizes of 25 and 48 μm revealed a crosslinking time of 17 and 115 min, respectively. The addition of bentonite at low crosslinker concentrations (0.5-1 wt.%) did not decrease the gel strength of 7 wt.% PAM/1 wt. % AlAc significantly. The gelation time was extended after adding 1 wt.% bentonite to the formulation where the delay was attributed to the adsorption of AlAc on the bentonite surface that was illustrated by molecular simulation.
2013
The aim of this study was to investigate the kinetic properties of hydrolyzed polyacrylamide gel. The hydrolyzed polyacrylamide was synthesized by free radical mechanism. The optimum molecular weight for the gel preparation was then obtained after examination of various factors such as average molecular weight, initiator concentration and reaction time in the gelation process. The main interaction which creates supramolecular gel is metal ligand coordination between carboxylate groups and chromium ions, and amide groups. These bonds were confirmed by FTIR and UV-Visible spectra techniques. Furthermore, the XRD showed crystalline structure in the gel.
Formation and Structure of Cross-Linked Polyacrylates
ACS Symposium Series, 1994
Models developed to describe free radical crosslinking polymerizations may be divided into three classes: statistical models, kinetic descriptions, and kinetic gelation simulations. This paper provides a comparison of the three types of models by describing the approach, assumptions, strengths, and limitations of each when applied to lightly crosslinked systems. The greatest strength of the statistical approach arises from the wealth of post-gel structural information that can be obtained, however these models have difficulty accounting for history-dependent effects. Kinetic descriptions may properly describe history-dependent reaction non-idealities, but are unable to account for localized effects that are prevalent in highly crosslinked systems. The kinetic gelation simulations may describe topological constraints and localized effects but are of limited use for lightly crosslinked polymers due to their inability to accurately account for molecular motions. In recent years there has been considerable interest in water-swellable "superabsorbing" polymers capable of absorbing and holding large amounts of water. These polymers have found extensive commercial application as sorbents in personal care products such as infant diapers, feminine hygiene products, and incontinence products (7 ,2), and have received considerable attention for a variety of more specialized applications including matrices for enzyme immobilization (3), biosorbents in preparative chromatography (3), materials for agricultural mulches (4), and matrices for controlled release devices (5). The interest in superabsorbing polymers is illustrated by the popularity of the ACS symposium upon which this volume is based, as well as the recent proliferation of research articles on the topic (for reviews, see references 1-7).
The Journal of Physical Chemistry A, 2013
This article presents a computational study of chain transfer to monomer (CTM) reactions in self-initiated high-temperature homopolymerization of alkyl acrylates (methyl, ethyl, and n-butyl acrylate). Several mechanisms of CTM are studied. The effects of the length of live polymer chains and the type of monoradical that initiated the live polymer chains on the energy barriers and rate constants of the involved reaction steps are investigated theoretically. All calculations are carried out using density functional theory. Three types of hybrid functionals (B3LYP, X3LYP, and M06-2X) and four basis sets (6-31G(d), 6-31G(d,p), 6-311G(d), and 6-311G(d,p)) are applied to predict the molecular geometries of the reactants, products and transition sates, and energy barriers. Transition state theory is used to estimate rate constants. The results indicate that abstraction of a hydrogen atom (by live polymer chains) from the methyl group in methyl acrylate, the methylene group in ethyl acrylate, and methylene groups in n-butyl acrylate are the most likely mechanisms of CTM. Also, the rate constants of CTM reactions calculated using M06-2X are in good agreement with those estimated from polymer sample measurements using macroscopic mechanistic models. The rate constant values do not change significantly with the length of live polymer chains. Abstraction of a hydrogen atom by a tertiary radical has a higher energy barrier than abstraction by a secondary radical, which agrees with experimental findings. The calculated and experimental NMR spectra of dead polymer chains produced by CTM reactions are comparable. This theoretical/computational study reveals that CTM occurs most likely via hydrogen abstraction by live polymer chains from the methyl group of methyl acrylate and methylene group(s) of ethyl (n-butyl) acrylate.