Copolymers of N -alkyl- and N -arylalkylacrylamides with acrylamide: influence of hydrophobic structure on associative properties. Part II: rheological behaviour in semi-dilute 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.
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.
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. #
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.
1984
Dilute solution viscosity of a series of random copolymers of acrylamide (AM) with sodium-2acrylamido-2-methylpropane sulfonate (NaAMPS) and with sodium-2-sulfoethylmethacrylate (NaSEM) has been studied using a four-bulb shear dilution capillary viscometer. The hydrodynamic volume of the copolymers in aqueous media was determined as a function of salt concentration, temperature, shear rate, and time. A linear relationship was observed between the intrinsic viscosity [9]0 and the reciprocal of the square root of ionic strength in sodium chloride solutions, with salt concentrations varying from 0.043M to 0.257M. Negative temperature coefficients for [9]o indicate a decrease in the hydrodynamic volume of the ionic polymer molecules with increasing temperature. The relative zero-shear-intrinsic-viscosity change in distilled water to 0.257M sodium chloride aqueous media is used to elucidate viscosity-structure relatbnships. A maximum value is reached for this parameter at a composition of about 30 mol % of ionic comonomers for AM-NaAMPS and AM-NaSEM copolymer series.
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).
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
Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions
Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile-methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion poly-merization technique. The polymerization conditions were adjusted in such a way to produce polymers with similar composition and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were investigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhibited the longest relaxation time (λ) at low and medium frequencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ω c) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logGʹ versus logG data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer.