Properties of hydrophobically modified polyacrylamide with low molecular weight and interaction with surfactant in aqueous solution (original) (raw)
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Rheology of aqueous solutions of hydrophobically modified polyacrylamides and surfactants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using as hydrophobic monomers n-decylacrylamide and t-octyl-acrylamide. The synthesized polymers contained between 0.5 and 1.5 mol.% of the hydrophobic groups. Shear rheology experiments showed a viscosity enhancement for most copolymers in comparison with the homopolymers due to intermolecular hydrophobic associations, which lead to shear thickening for copolymers with 1 mol.% or more hydrophobic groups. An increase in the ionic strength of the solutions strengthens these hydrophobic associations. The addition of an anionic surfactant (sodium dodecyl sulfate, SDS) produced viscosity increases due to intermolecular bridging caused by the formation of mixed micelles between the hydrophobic groups and the surfactant. Higher surfactant concentrations lead to a viscosity reduction due to electrostatic screening of associations between hydrophobic side groups of different chains. The same behavior was observed in the spherical micelle concentration regime for the cationic surfactant cetyltrimethylammonium p-toluenesulfonate (CTAT), but at higher surfactant concentrations, entanglements between the copolymers and worm-like micelles lead to further increases in solution viscosity.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Viscosity data are reported for aqueous solutions of a series of acrylamide-based co-and terpolymers with added surfactants. Polymer composition is systematically varied through ionic content (acrylic acid monomer content and solution pH) and hydrophobicity (alkylacrylamide content and alkyl chainlength). Surfactants used were sodium dodecylsulfate (SDS), diethylhexyl sulfosuccinate (AOT), dodecyltrimethyl ammoniumbromide (DTAB) and nonionic surfactants. For the anionic surfactant SDS, a surfactant selective electrode was used to obtain binding isotherms of SDS with the polymers. The experiments show that in the presence of anionic surfactants, the solutions exhibit a dramatic increase in solution viscosity at concentrations around the surfactant CMC, attributed to interpolymer crosslinking through the formation of mixed micelles involving the hydrophobes from different polymer chains and the surfactant molecules. The viscosity enhancement is found to increase with increasing hydrophobicity of the hydrophobe and decreases with increasing AA incorporation in the polymer. The ionic fraction of the polymer chain (AA) also plays an important role in unfolding the polymer chain through electrostatic repulsion contributing to the viscosity increases at high solution pH. Both rheology and EMF-derived binding isotherms suggest that the viscosity maximum occurs at a low ratio of bound surfactant and hydrophobe monomers of approximately two surfactant molecules per hydrophobe. #
European Polymer Journal, 2007
The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2-phenoxylethyl acrylate (POEA) (<1.0 mol %) at the octane-water interfaces were investigated by means of two methods: the interfacial tension response to sinusoidal area variations and the relaxation of an applied stress. The dependencies of interfacial dilational modulus and phase angle on the polymer concentration were explored. The influence of sodium dodecyl sulfate (SDS) on the dilational viscoelastic properties of polymer solutions was studied. The results obtained by oscillating barriers method showed that the dilational modulus passed through a maximum value with increasing polymer concentration, while the phase angle decreased with increasing concentration below 200 ppm, then showed very low concentration dependence up to 3000 ppm, and increased dramatically above it. When SDS was added to the aqueous phase, the dilational modulus passed through a maximum with increasing SDS concentration, while the change of phase angle depended on the polymer bulk concentration. The results obtained by the relaxation of an applied stress show that two main relaxation processes exist in the interface at low bulk concentration below the critical aggregation concentration: one is the fast process involving the exchange of hydrophobic microdomains between the proximal region and distal region in the interface with a characteristic time value from several tens of seconds to several seconds at different bulk concentration; the other is the slow relaxation process involving conformational changes of polymer chain in the interface with characteristic time value from 1000 s to several tens of seconds, depending on the bulk concentration. However, there is only one main relaxation process controlling the dilational properties above c*: a fast relaxation process with the characteristic relaxation time of less than 1 s, which is believed to be related to the associations formed by hydrophobic microdomains. Anionic surfactant SDS can influence the dilational properties of polymer solutions by the following ways: first, SDS can absorb onto the interface and bind to the hydrophobic microdomains to change the characteristic times and contributions of the existed relaxation processes of polymer chains; second, SDS can provide a new fast relaxation process involving the exchange of SDS molecules between monomers and mixed micelles in interface. The information on relaxation processes obtained from interfacial tension relaxation measurements can explain the results from dilational viscoelasticity measurements very well. The negative phase angles have been obtained in some case. It is believed that the in-interface slow relaxation process, which sometimes dominates the dilational viscoelasticity of polymer film, is responsible for this phenomenon in our employed experimental method.
Journal of Colloid and Interface Science, 2009
Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using poly(propylene glycol) monomethacrylate, PPGMA, as hydrophobic monomer and sodium dodecyl sulfate, SDS, as surfactant. The hydrophobic monomer to surfactant ratio was varied during micellar synthesis to obtain different hydrophobic block lengths. It was found that the rheology of HMPAM/SDS solutions depends both on the ratio of PPGMA to surfactant and on the concentration of surfactant used in the micellar copolymerization. Also, the rheological behavior of the copolymer solutions was studied as a function of SDS addition and temperature. In the presence of SDS, an increase in zero-shear viscosity was observed that depended on polymer and surfactant concentration. At the highest SDS concentration, the copolymer did not reach the viscosity value exhibited by the solution without surfactant. In the presence of surfactant, HMPAM solutions exhibited a small thermo-thickening behavior when the temperature increases from 25 to 50 • C. Our rheological results evidence that the properties of HMPAM aqueous solution as a function of temperature, are a consequence of the rheological response of both components within the copolymer chain, i.e., hydrophilic (acrylamide) and lateral lower critical solution temperature (LCST) sequences (PPO).
New approach to the molecular characterization of hydrophobically modified polyacrylamide
Polymer, 2004
A new approach to the molecular characterization of hydrophobically associating copolymers of acrylamide is developed. It is based on the study of associative properties: the formation of intermolecular aggregates was followed by dynamic and static light scattering (DLS and SLS), while the formation of hydrophobic domains was detected by fluorescence spectroscopy with pyrene as a probe. In aqueous media, hydrophobic aggregation begins at concentrations much lower than the overlap concentration. The addition of co-solvent, acetonitrile, shifts the aggregation to the semi-dilute region. The dissolution of hydrophobic aggregates is controlled both by fluorescence spectroscopy with pyrene as a probe and by DLS and SLS. Absolute M w values are measured by SLS in mixed solvent of optimal composition. Molecular weight distribution (MWD) is characterized by GPC using calibration with secondary standards characterized by SLS. This approach allowed us to follow MWD evolution during a micellar copolymerization of acrylamide, N-nonylacrylamide and acrylic acid. It is found that the molecular weight heterogeneity remarkably growths with the increase of conversion. q
Properties of hydrophobically associating polyacrylamides: influence of the method of synthesis
Macromolecules, 1993
Hydrophobically modified water-soluble polymers have been prepared by radial copolymerization of acrylamide and ethylphenylacrylamide as the hydrophobic comonomer. Three methods of synthesis in aqueous media have been investigated (i) a 'micellar" process in which the presence of a surfactant ensures the solubilization of the hydrophobic monomer; (ii) a 'homogeneous" process wherein a miscible cosolvent is used; (iii) a "heterogeneous" process, without additive to solubilize the insoluble monomer. The properties of the copolymers in dilute and semidilute aqueous solutions strongly depend on the conditions of the synthesis. Copolymers prepared by the homogeneous and heterogeneous processes behave like homopolyacrylamide; i.e., hydrophobic interactions do not occur significantly. Copolymers obtained by micellar copolymerization exhibit improved thickening properties due to intermolecular hydrophobic associations. These differences can be directly related to the copolymer microstructure, i.e., to a random or blocky distribution of the hydrophobic units. The blockmess of the copolymer can be adjusted by varying the [hydrophobel/[micellel ratio at a constant hydrophobe level. Thus, it is possible to control the association degree and therefore the rheological properties. Fluorescence studies, using pyrene as a probe, reveal the formation of hydrophobic microdomains which corroborate the rheological results.
Advances in Colloid and Interface Science, 1999
. The characteristic features of hydrophobically-modified polyacrylamides HMPAM prepared by a micellar polymerization technique are reviewed. This method of synthesis leads to copolymers in which the hydrophobic units are randomly distributed as small blocks in the acrylamide backbone. Special emphasis is put on the improvement of the technique so that well characterized and homogeneous samples are synthesized. The effect of the various parameters controlling the rheological behavior of HMPAM is thoroughly analyzed. In particular, it is shown that a determining factor for a good thickening ability is the copolymer microstructure, i.e. the hydrophobe distribution. Some recent advances are presented towards a better understanding of the association structure, thus allowing the design of tailored materials with good controllable rheological properties. ᮊ
Polymer, 2002
Dilute and semi-dilute solution properties of polyacrylamide (PAM) and its hydrophobically modified analogues (HAPAMs) in both pure water and brine were compared by means of viscometry, light scattering and fluorescence spectrometry. In dilute solution, large differences in reduced viscosity and apparent molecular weight M wapp of HAPAMs were found between pure water and 0.1 M NaCl solutions, while no significant differences were observed for PAM. In addition, in pure water, intrinsic viscosity and M wapp of HAPAMs are higher than those of PAM. In semi dilute regime, with increasing salinity, the reduced viscosity of PAM remains almost unchanged, whereas enhanced viscosity was observed for the HAPAM polymers in both monovalent and divalent cation aqueous environment. HAPAM solutions behave as classical shear-thinning fluid in pure water, whereas addition of NaCl induces shear-thickening response for these polymers. The experimental results are interpreted in terms of the hydrophobe distribution and its influence on the formation of intra-and intermolecular associations. The differences between the behaviors described in this paper and those usually obtained with HAPAMs characterized by a blocky hydrophobe distribution are discussed. q
Synthesis in inverse emulsion and associating behavior of hydrophobically modified polyacrylamides
Journal of Applied Polymer Science, 2004
An inverse free-radical emulsion polymerization technique was used to prepare copolymers of acrylamide and two different hydrophobic comonomers: N, Ndihexylacrylamide (diC6) or N,. The products of the reaction were high molecular weight hydrophobically modified water-soluble polymers (HMWSPs) encapsulated within water droplets dispersed in an organic medium. A comparison of the copolymer compositions prepared under different experimental conditions showed that the level of incorporation of diPh in the final copolymer depended strongly on its localization in the emulsion (aqueous or oil phase) and on the nature of the redox initiator pair (water-soluble or oil-soluble). The rheological properties of the HMWSPs in aqueous solution were investigated as a function of the comonomer content and the nature of the initiator, using steady-flow experiments. The thickening properties were found to be directly correlated to the conditions of synthesis and were optimal when the initiator and the hydrophobic comonomer were located in two distinct phases. An examination of the viscosity as a function of shear rate showed that these solutions exhibit typical characteristics of hydrophobically associative polymers.
Journal of colloid and interface science, 2017
The rheological control of suspensions is of key interest in the formulation design. A chemically cross-linked hydrophobically modified poly(acrylic acid) (HMCL-PAA), used as rheology modifier, is pH sensitive and shows swelling behavior above a critical pH due to the ionization of the acrylic acid groups. At low pH, HMCL-PAA suspensions are liquid and turbid. The binding of surfactants to HMCL-PAA, at low pH conditions, can result in significant changes on rheology and transparency of the polymeric suspensions, due to the swelling of the microgel particles. The influence of surfactants addition on the rheological properties and transparency of HMCL-PAA suspensions was determined. A systematic study was performed using different types of surfactants (ionic, non-ionic and zwitterionic). The gelation efficiency of HMCL-PAA suspensions at low pH is strongly dependent on surfactant architecture: ionic surfactants are found to be much more efficient than non-ionic or zwitterionic surfact...