Hydrophobically Modified Alkali-soluble Emulsion Research Articles

Pyrene Excimer Kinetics in Micellelike Aggregates in a C20-HASE Associating Polymer

We have carried out time-resolved fluorescence quenching experiments, using pyrene derivatives as probes, on aqueous solutions of a hydrophobically modified alkali-soluble emulsion (HASE) polymer 1. This polymer is a 1:1 copolymer of ethyl acrylate and methacrylic acid, containing 1 mol % of a macromonomer with a C20H41 group at the end of an oligo(ethylene oxide) (EO32) spacer. The experiments we describe establish that the polymer 1 at full neutralization in water forms two different types of hydrophobic domains. When various pyrene derivatives are employed as probes, they partition between the two environments and exhibit different fluorescence decay times in the different types of domains. For experiments carried out at elevated probe concentration where excimer formation is important, proper analysis of the data is possible only if the solutions are deaerated. The data are fitted to a series of models invoking the presence of a single hydrophobic domain and two different hydrophobic domains. Only the...

Rheological Properties of Semidilute Hydrophobically Modified Alkali-Soluble Emulsion Polymers in Sodium Dodecyl Sulfate and Salt Solutions

The rheological properties of semidilute hydrophobically modified alkali-soluble emulsion polymers in the presence of 0.4 M NaCl and various concentrations of anionic surfactant were investigated. The viscosity profile consists of a zero-shear Newtonian region at low stresses and a shear-thickening region at intermediate stresses, followed by a catastrophic decrease in the viscosity at moderate to high stresses. The viscosity and the dynamic modulus peaked at c/cmc of ∼11, in contrast to 1 in the absence of NaCl. The activation energies determined at the zero-shear and the shear-thickening regime (denoted by Ea0 and Ea,max respectively) increase to a maximum and subsequently decrease as a function of surfactant concentration. Two critical SDS concentrations defined by the crossover of the Ea curves (at ∼0.001 and 0.009 M SDS) are related to the balance in the inter- and intramolecular association.

Single Chain Characterization of Hydrophobically Modified Polyelectrolytes Using Cyclodextrin/Hydrophobe Complexes

The characterization of hydrophobically modified alkali-soluble emulsions (HASE) using conventional techniques such as gel permeation chromatography or static light scattering is difficult because of the hydrophobic association. Two different approaches were taken to prevent the hydrophobic association of HASE polymers in aqueous solution: (1) hydrolyze the polymer to dislodge the hydrophobic constituents, and (2) use methyl-β-cyclodextrin, which has a hydrophobic cavity and a hydrophilic outer shell, to shield the hydrophobes from associating. Using these two approaches, the molecular weight (Mw), hydrodynamic radius (Rh), and radius of gyration (Rg) of single chains of these polymers were determined using gel permeation chromatography (GPC) and dynamic (DLS) and static (SLS) light scattering techniques. The molecular weight of the control polymer (i.e., polymers with similar composition but with no hydrophobe) is found to be ∼7.0 × 105 g/mol. The molecular weights of these polymers with C8, C16, and C20 hydrophobes were found to be ∼2.0 × 105 g/mol. By comparing GPC and SLS results, we were able to determine that, except for one chemical site, branching or grafting did not occur in the polymer chain during synthesis.

Calorimetric Studies of Model Hydrophobically Modified Alkali-Soluble Emulsion Polymers with Varying Spacer Chain Length in Ionic Surfactant Solutions

The binding behavior of SDS onto several model hydrophobically modified alkali-soluble emulsion (HASE) polymers with different spacer chain length was studied using the isothermal titration calorim...

Model Alkali-Soluble Associative (HASE) Polymers and Ionic Surfactant Interactions Examined by Isothermal Titration Calorimetry

Isothermal titration calorimetry was used to examine the energetics of surfactant aggregation in the absence and presence of hydrophobically modified alkali-soluble emulsion (HASE) polymers. The binding behavior of SDS onto several model HASE polymers with C1, C8, C12, C16, and C20 hydrophobes was investigated. A 0.1 wt % HASE polymer solution was titrated with a 0.1 M SDS solution. For all the SDS/polymer systems, pronounced endothermic differential enthalpic curves are observed. Thermodynamic parameters such as enthalpy and entropy change of aggregation confirm that the process for the binding of SDS to the hydrophobic junction is entropy-driven. The Gibbs energy of binding of SDS onto the model polymers increases from −2.9 kJ/mol for C1 hydrophobe to −4.2 kJ/mol for C20 hydrophobes. The critical aggregation concentration and the negative enthalpy of aggregation decrease with increasing polymer hydrophobicity.

Rheological and microcalorimetric studies of a model alkali-soluble associative polymer (HASE) in nonionic surfactant solutions

Rheological experiments were carried out on a 1 wt % hydrophobically modified alkali-soluble emulsion (HASE) solutions at pH ∼ 9 in the presence of nonionic polyoxyethylene ether type surfactant (C 12 EO 23 ). The low shear viscosity and dynamic moduli increases at c > cmc until they reach a maximum at a critical concentration, c' of approximately 1 mM (∼ 17 times the cmc of free surfactant) and then decrease. The dominant mechanism at cmc < c < c m is an increase in the number of intermolecular hydrophobic junctions and a strengthening of the overall associative network structure. Above c m , the disruption of the associative network causes a reduction in the number of junctions and strength of the overall network structure. The influence of C 12 EO 23 on HASE before cmc could not be detected macroscopically by the rheological technique. However, isothermal titration calorimetry enables the determination of complex binding of surfactant to the polymer. Isothermal titration of C 12 EO 23 into 0.1 wt % HASE indicates that the C 12 EO 23 aggregation in water and 0.1 wt % HASE polymer solutions is entropically driven. A reduction in the critical aggregation concentration (cac) confirms the existence of polymer-surfactant interactions. The hydrophobic micellar junctions cause a decrease in the ΔH and AS of aggregation of the nonionic surfactant.

Potentiometric titration and dynamic light scattering of hydrophobically modified alkali soluble emulsion (HASE) polymer solutions

Download options Please wait... Article information DOI https://doi.org/10.1039/A910302N Article type Paper Submitted 23 Dec 1999 Accepted 06 Mar 2000 First published 10 Apr 2000 Download Citation Phys. Chem. Chem. Phys., 2000,2, 1967-1972 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Potentiometric titration and dynamic light scattering of hydrophobically modified alkali soluble emulsion (HASE) polymer solutions C. Wang, K. C. Tam, R. D. Jenkins and D. R. Bassett, Phys. Chem. Chem. Phys., 2000, 2, 1967 DOI: 10.1039/A910302N To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author C. Wang K. C. Tam R. D. Jenkins D. R. Bassett

Network structure of a model HASE polymer in semidilute salt solutions

The effects of salt and temperature on a model hydrophobically modified alkali-soluble emulsion (HASE) associative polymer were investigated. The shear viscosities and viscoelastic properties decrease continuously as the salt concentration is increased. The decrease is attributed to the shielding of charged polyelectrolyte backbones by excess cations, which causes the “stiff” polymer backbone to shrink, leading to the destruction of intermolecular junctions. Smaller individual polymer clusters with predominantly intramolecular associations are then formed. At moderate deformation rates, the solutions exhibit a shear-thickening behavior, which is attributed to the conversion of intramolecular to intermolecular junctions [Tam et al. Polymer 1999, 40, 6369]. The activation energy determined from the zero-shear viscosity decreases with the salt concentrations, while that obtained from the maximum viscosity increases until 0.6M NaCl, beyond which it decreases. This trend indicates that the strength of the network is greater in the shear-thickening region due to the larger proportion of intermolecular junctions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1486–1496, 2001

Microstructure of Dilute Hydrophobically Modified Alkali Soluble Emulsion in Aqueous Salt Solution

The microstructure of a model HASE associative polymer in aqueous salt solution is complex and has not been defined until now. On the basis of the results from static and dynamic light scattering studies, a physical model describing the microstructure of a model HASE polymer in aqueous salt solution is proposed. The model HASE polymer contains a copolymer backbone of equal moles of methacrylic acid (MAA) and ethyl acrylate (EA) with 1 mol % of C16H33 hydrophobic modified macromonomer distributed randomly along the backbone. In very dilute aqueous solutions (0.005−0.1 wt %), two decay modes are observed in the relaxation time distribution function. The fast and the slow modes correspond to the translational diffusion of the unimers and the polymer aggregates (consisting of about five polymer chains), respectively. The polymer aggregate is formed by association of the hydrophobic macromonomer via a closed association mechanism. When the polymer concentration increases, the polymer aggregates grow in size. The fractal dimension, df, decreases with increasing polymer concentrations, indicating that the aggregates are becoming less compact. At the same time, when the polymer concentration exceeds 0.1 wt %, the unimers are transformed to oligomers consisting of two or more polymer chains.

Effects of Temperature on the Flow Dynamics of a Model HASE Associative Polymer in Nonionic Surfactant Solutions

The interaction between a model hydrophobically modified, alkali-soluble emulsion (HASE) polymer and a nonionic surfactant, C12EO4, was investigated in this work. The addition of the nonionic surfactant increases the viscosity and moduli of the polymer up to the maximum concentration of 0.1 M. The low-shear viscosity, plateau modulus, and hence the effective junction density increase linearly with surfactant concentration up to 0.01 M. However, above 0.01 M, the plateau modulus tapers off while the rise in viscosity becomes steeper. From the Arrhenius plots of both the low-shear viscosity and longest relaxation time, the activation energy of dissociation of the hydrophobes from the aggregated junction for the pure HASE polymer was found to be of the order of 50 kJ mol-1. In the presence of 0.00025-M surfactant, an increase in the activation energy of approximately 10% was observed, and results from the enhancement of the hydrophobic junctions by the surfactant molecules. At higher surfactant concentration...

Evaluation of intrinsic viscosity measurements of hydrophobically modified polyelectrolyte solutions

The dilute solution properties of the hydrophobically modified alkali-soluble emulsion (HASE) were examined using the intrinsic viscosity method. The HASE model systems with essentially the same chemical structure and molecular weight but different numbers of carbon in hydrophobe were synthesized for this study. The effects of ionic strength on the intrinsic viscosity measurement of HASE systems were studied. The ionic strength of the dilute polymer solution was found to influence the degree of hydrophobic association and the size of the micellar clusters during dilution. The variations of the above factors were experimentally found to have significant effects on the accuracy, reliability and repeatability of the intrinsic viscosity and Huggins coefficient.

Stability of a model alkali-soluble associative polymer in the presence of a weak and a strong base

Hydrophobically modified alkali-soluble emulsion (HASE) polymer is solubilized by the addition of a base. When the pH is increased to greater than 6.5, methacrylic acids on the polymer backbone are neutralized and the carboxylated latex polymer goes into solution causing a large increase in the viscosity due to inter-molecular associations of the hydrophobes. The stability of the viscosity of the polymer solution at pH in the range 9–10 was studied in the presence of a strong (NaOH) and a weak [1-amino-1-methylpropanol (AMP)] base. No change in the viscosity or the moduli was observed for the polymer in AMP. Reduction in the viscous and elastic properties of the polymer solution in NaOH was observed after 4 weeks. Such small changes are detectable using the superposition of oscillation on the steady shear technique. The decrease in the viscoelastic properties is attributed to the hydrolysis reaction of the urethane groups of the macromonomer, which resulted in a decrease in the number of hydrophobes per polymer chain. It is recommended that a weak base be used to neutralise the HASE polymer in order to avoid the possibility of compositional changes in the polymer after neutralisation for more than 6 weeks.

Effects of salt on the intrinsic viscosity of model alkali-soluble associative polymers

The effects of salt on four model hydrophobically modified alkali-soluble emulsion (HASE) associative polymers were studied. Their reduced viscosities in aqueous solution at different salt concentrations (10−4 to 10−1 M) were measured and the corresponding intrinsic viscosities were determined. The results show that the intrinsic viscosity at any given salt concentration decreases as the hydrophobicity of the hydrophobes (i.e., n in the side chain CnH2n+1) increases. The interpretation is that stronger intra-molecular association of the more hydrophobic macromonomer leads to smaller polymer molecular coils. An increase of salt content in the solution causes the reduced viscosities of all the model polymers to decrease. This is believed to be the result of excess positive ions in solution which have a shielding effect and reduce the mutual repulsion of the charges along the polymer backbone. In dilute solution the hydrophobic associations of the model associative polymers are predominantly intra-molecular. The addition of salt to the polymer solutions hinders the inter-molecular interaction of the model polymers. The increase in salt content also leads to an increase of intra-molecular aggregations of the hydrophobes of the model associative polymers. Stiffness indices such as the stiffness parameter B and the persistence chain length were used to correlate the polymer conformation of the model associative polymers in NaCl solutions.