Binding Characteristics of Hydrophobic Ethoxylated Urethane (HEUR) and an Anionic Surfactant: Microcalorimetry and Laser Light Scattering Studies

Rheological Behavior of HEUR Mixtures in Aqueous Media

Three S-G HEUR thickeners were synthesized by a step growth polymerization technique of poly (ethylene oxide) (PEO) and dicyclohexylmethane – 4,40-diisocyanate (H12MDI) and then end capped with two monofunctional aliphatic alcohols. These polymers were mixed together according to the hydrophilic and hydrophobic nature of their segments. Based on this, two sets of associating polymers were introduced. In one set, the samples had identical hydrophobic segments while in the other one, hydrophilic segments were similar. The steady shear viscosity profiles of aqueous solutions of all models were determined. In addition, aqueous binary mixtures with various ratios of the S-G HEUR models were studied using steady state and dynamic rheometry. It is suggested that combinations of associating polymers with different size of hydrophobic segments and similar hydrophilic segments produce an associative polymer-like behavior. However, the combination of those with similar long hydrophobic segments and different hydrophilic segments at similar weight ratio in solution falls short of displaying an associative polymer – like behavior.

Interactions between a series of pyrene end-labeled poly(ethylene oxide)s and sodium dodecyl sulfate in aqueous solution probed by fluorescence

The interactions between a series of poly(ethylene oxide)s covalently labeled at both ends with pyrene pendants (PEO(X)-Py2, where X represents the number-average molecular weight of the PEO chains and equals 2K, 5K, 10K, and 16.5K) and an ionic surfactant, namely, sodium dodecyl sulfate (SDS), in water were investigated at a fixed pyrene concentration of 2.5 μM corresponding to polymer concentrations smaller than 21 mg/L and with an SDS concentration range between 5 × 10(-6) and 0.02 M, thus encompassing the 8 mM critical micelle concentration (CMC) of SDS in water. The steady-state fluorescence spectra showed that the I1/I3 ratio decreased from 1.73 ± 0.06 for SDS concentration smaller than 2 mM where pyrene was exposed to water to 1.43 ± 0.03 for SDS concentration greater than 6 mM where pyrene was incorporated inside SDS micelles. The ratio of excimer-to-monomer emission intensities (the IE/IM ratio) of all PEO(X)-Py2 samples remained constant at low SDS concentrations, then increased, passed through a maximum at the same SDS concentration of 4 mM before decreasing to a plateau value that is close to zero for PEO(10K)-Py2 and PEO(16.5K)-Py2 but nonzero for PEO(2K)-Py2 and PEO(5K)-Py2. The pyrene end groups of these two latter samples could not bridge two different micelles due to the short PEO chain, and excimer was formed by intramolecular diffusion inside the same SDS micelle. Time-resolved fluorescence decays of the pyrene monomer and excimer of the PEO(X)-Py2 samples were acquired at various SDS concentrations and globally fitted according to the "Model Free" analysis over the entire range of SDS concentration. The molar fractions of various excited pyrene species and the rate constant of pyrene excimer formation retrieved from the analysis of fluorescence decays were obtained as a function of SDS concentration. Interactions between SDS and PEO could not be detected by isothermal titration calorimetry, potentiometry with a surfactant selective electrode, and conductance measurements.

Investigation of the Thickening Efficiency of HEUR on the Behavior of Two Different Latex Types

A hydrophobically modified ethoxylated urethane (HEUR) as a thickener was synthesized using poly (ethylene glycol), Dicyclohexylmethane diisocyanate (H12MDI) and cethyl alcohol via step growth polymerization technique. The molecular weight of the thickener was determined by GPC, and its behavior in aqueous solution was studied. The steady shear experiments were carried out by mixture of the synthesized thickener with two resins. These resins had different nature; one with hydrophilic and the other with both hydrophilic and hydrophobic segmental structure. The result showed the type of resin can be effective in the thickening efficiency of HEUR thickener.

Supramolecular complex of [60]fullerene-grafted polyelectrolyte and surfactant: mechanism and nanostructures

Water-soluble, pH-responsive mono- and di-[60]fullerene end-capped poly(acrylic acid)s (PAA-C60 and C60-PAA-C60) were synthesized using the atom transfer radical polymerization technique. Isothermal titration calorimetry, dynamic light scattering, UV-vis spectroscopy, and transmission electron microscopy were employed to study the supramolecular complexation between fullerene end-capped PAAs and nonionic surfactant, polyethylene glycol (9-10) tert-octylphenyl ether, also known as Triton X100 (TX100) at different pH values. At pH < 4, TX100 bound specifically to C60 domains driven by hydrophobic and pi-pi interactions between TX100 and fullerene molecules. The binding was exothermic, and the magnitude of the interaction decreased gradually with increasing pH. The amount of polymer-bound TX100 was proportional to the fullerene content, which was approximately 1.3 and approximately 2.5 mM for 5 mM (concentration of carboxylic groups) PAA-C60 and C60-PAA-C60, respectively. Morphological transformations resulting in the formation of polymer/surfactant complex (PSC) precipitates in the course of binding were observed for both polymers. The PSC of PAA-C60 possessed a dense spherical structure, whereas the PSC of C60-PAA-C60 possessed a lamellar stacking structure. The PSC precipitates resolubilized in excess amounts of TX100 to form stable aggregates.

Morphological transformation of [60]fullerene-containing poly(acrylic acid) induced by the binding of surfactant

Water-soluble pH-responsive [60]fullerene end-capped poly(acrylic acid) (PAA85-b-C60) was synthesized using atom-transfer radical polymerization (ATRP) technique. The unusual morphological transformation of the polymer induced by the binding of nonionic surfactant Triton X-100 (TX100) at different degrees of neutralization (alpha) was investigated using isothermal titration calorimetry (ITC), UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). For the 5 mM (monomer concentration) polymer solution at pH < 4, approximately 1.3 mM TX100 binds specifically to C60 domains of the polymeric micelles driven by hydrophobic interaction, which induces a structural transformation of the polymer from a large compound micelle with a radius of 110 nm to a dense precipitated spherical polymer/surfactant complex (PSC) with a radius of 500 nm. The precipitates are resolubilized by a wetting layer of TX100 in excess surfactant (> 1.7 mM in the polymer solution). The binding is significantly weakened and the complexation is disrupted with increasing pH, where the interaction completely ceased at pH > 6.

Surfactant/Nonionic Copolymer Interaction: A SLS, DLS, ITC, and NMR Investigation

The interactions between an oxyphenylethylene-oxyethylene nonionic diblock copolymer with the anionic surfactant sodium dodecyl sulfate (SDS) have been studied in dilute aqueous solutions by static and dynamic light scattering (SLS and DLS, respectively), isothermal titration calorimetry (ITC), and 13C and self-diffusion nuclear magnetic resonance techniques. The studied copolymer, S20E67, where S denotes the hydrophobic styrene oxide unit and E the hydrophilic oxyethylene unit, forms micelles of 15.6 nm at 25 degrees C, whose core is formed by the styrene oxide chains surrounded by a water swollen polyoxyethylene corona. The S20E67/SDS system has been investigated at a copolymer concentration of 2.5 g dm(-3), for which the copolymer is fully micellized, and with varying surfactant concentration up to approximately 0.15 M. When SDS is added to the solution, two different types of complexes are observed at various surfactant concentrations. From SLS and DLS it can be seen that, at low SDS concentrations, a copolymer-rich surfactant mixed micelle or complex is formed after association of SDS molecules to block copolymer micelles. These interactions give rise to a strong decrease in both light scattering intensity and hydrodynamic radius of the mixed micelles, which has been ascribed to an effective reduction of the complex size, and also an effect arising from the increasing electrostatic repulsion of charged surfactant-copolymer micelles. At higher surfactant concentrations, the copolymer-rich surfactant micelles progressively are destroyed to give surfactant-rich-copolymer micelles, which would be formed by a surfactant micelle bound to one or very few copolymer unimers. ITC data seem to confirm the results of light scattering, showing the dehydration and rehydration processes accompanying the formation and subsequent destruction of the copolymer-rich surfactant mixed micelles. The extent of interaction between the copolymer and the surfactant is seen to involve as much as carbon 3 (C3) of the SDS molecule. Self-diffusion coefficients corroborated light scattering data.

Size Control of Styrene Oxide−Ethylene Oxide Diblock Copolymer Aggregates with Classical Surfactants: DLS, TEM, and ITC Study

The interactions between the diblock copolymer S(15)E(63) and the surfactants sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDeS), and sodium octyl sulfate (SOS) have been investigated by dynamic light scattering (DLS), transmission electron microscopy (TEM), and isothermal titration calorimetry (ITC). The surfactants with the same headgroup differentiate in their chain length. At 20 degrees C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6 nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO or E) corona. The different copolymer/surfactant systems have been studied at a constant copolymer concentration of 2.5 g dm(-3) and in a vast range of surfactant concentrations, from 7.5 x 10(-6) up to 0.75 M. When SDS and SDeS are added to the block copolymer solution, different regions are observed in the DLS data: at low surfactant concentrations (c < 1.0 x 10(-4) M), single surfactant molecules associate with the copolymer micelle, probably the former being solubilized in the micelle core, leading to a certain disruption of the mixed micelle due to repulsive electrostatic interactions between surfactant headgroups followed by a stabilization of the mixed micelle. At higher concentrations (1.0 x 10(-4) < c < 0.1 M), two types of copolymer-surfactant complexes coexist: one large copolymer-rich/surfactant complex and one small complex consisting of one or a few copolymer chains and rich in surfactants. At higher SDS and SDeS concentrations, complete disintegration of mixed micelles takes place. In contrast, SOS-S(15)E(63) interactions are less important up to surfactant concentrations of 0.05 M due to its higher hydrophilicity, reducing the hydrophobic interactions between surfactant alkyl chains and copolymer micelles. At concentration larger than the critical aggregation concentration (cac) of the system, 0.05 M, disruption of copolymer micelles occurs. These regions have been confirmed by transmission electron microscopy. On the other hand, the titration calorimetric data for SDS and SDeS present an endothermic increase indicating the formation of mixed copolymer-rich-surfactant micelles. From that point, important differences in the ITC plot for both surfactants are present. However, the ITC curve obtained after titration of a SOS solution in the copolymer solution is quite similar to that of its titration in water.

Comparative studies on the micellization of sodium bis(4-phenylbutyl) sulfosuccinate and sodium bis(2-ethylhexyl) sulfosuccinate and their interaction with hydrophobically modified poly(acrylamide)

The micellization process of sodium bis(4-phenylbutyl) sulfosuccinate (SBPBS) has been studied compared to that of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) by surface tension, steady-state fluorescence, microcalorimetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements. Meanwhile, the interaction of these two surfactants with hydrophobically modified poly(acrylamide) (HMPAM) was investigated. The results show that the surface tension at the critical micelle concentration (cmc) of SBPBS and the micropolarity probed by pyrene in SBPBS aggregates are both larger than those of AOT. The enthalpy change of micellization (DeltaH(mic)) of AOT is endothermic, while it is exothermic for SBPBS. Strong pi-pi interaction among the adjacent phenyl groups of SBPBS molecules is likely the cause for the above properties of SBPBS. Moreover, vesicles are observed for AOT and SBPBS by DLS and TEM, especially for AOT, whose micelle-vesicle transition has been first confirmed by its calorimetric curve. In the surfactant-HMPAM systems, the critical aggregation concentration (cac), the saturation concentration of aggregation (C(2)), and the thermodynamic parameters of binding have also been determined. The conclusion may be drawn that the binding strength of SBPBS onto HMPAM is stronger than that of AOT.

Behavior of a Styrene Oxide−Ethylene Oxide Diblock Copolymer/Surfactant System: A Thermodynamic and Spectroscopy Study

Co-micellization of the diblock copolymer oxyphenylethylene/oxyethylene (S(17)E(65)) with the anionic surfactant sodium dodecyl sulfate (SDS) was investigated in aqueous solution using light scattering, transmission electron microscopy, isothermal titration calorimetry (ITC), and density measurements. Upon the addition of the surfactant, changes in the physicochemical properties of the micellized block copolymer take place due to interactions between the surfactant and the copolymer. Mixed micelles of copolymer and surfactant are formed and the size of the mixed aggregates changes in dependence of the amount of SDS. At a certain limiting concentration of SDS, only small rich-surfactant-copolymer aggregates and free surfactant micelles are observed in solution, as confirmed by the thermodynamic data obtained by ITC and transfer volumes. Thus, it seems that the presence of surfactant can be a tool to control the size and properties of block copolymer aggregates in solution.

Isothermal titration calorimetry and dynamic light scattering studies of interactions between gemini surfactants of different structure and Pluronic block copolymers

The interactions between triblock copolymers of poly(ethylene oxide) and poly(propylene oxide), P103 and F108, EO(n)PO(m)EO(n), m=56 and n=17 and 132, respectively, and m-s-m type gemini surfactants, m=8, 10, 12, and 18, and s = 3, 6, 12, and 16, have been studied in aqueous solution using isothermal titration calorimetry and dynamic light scattering techniques. The enthalpograms of F108 as a function of surfactant concentration show one broad peak at polymer concentrations C(p) < or = 0.50 wt%, below the cmc of the copolymer at 25 degrees C. It is attributed to interactions between the surfactant and the triblock copolymer monomer. DLS results show hydrodynamic radii (R(h)) initially consistent with copolymer monomers that change to values consistent with gemini surfactant micelles as the surfactant concentration is increased. In P103 solutions at C(p) > or = 0.05 wt%, two peaks appear in the enthalpograms, and they are attributed to the interactions between the gemini surfactant and the micelle or monomer forms of the copolymer. An origin-based nonlinear fitting program was employed to deconvolute the two peaks and to obtain estimates of peak properties. An estimate of the fraction of copolymer in aggregated form was also obtained. The enthalpy change due to interactions between the surfactants and P103 aggregates is very large compared to values obtained for traditional surfactants. This suggests that extensive reorganization of copolymer aggregates and surrounding solvent occurs during the interaction. DLS results for the P103 systems containing C(p) > or = 0.05% show evidence of very large aggregates in solution, likely P103 micelle clusters. The transitions observed in the hydrodynamic radii are consistent with a breakdown of micelle clusters with addition of gemini surfactant, followed by mixed micelle formation and/or deaggregation into monomer P103. This is followed by interactions similar to those typically observed in surfactant-nonionic polymer systems. Mechanisms for the interaction and the observed structural changes are discussed.

Isothermal titration calorimetric studies on the temperature dependence of binding interactions between poly(propylene glycol)s and sodium dodecyl sulfate

Isothermal titration calorimetry (ITC) is a sensitive research tool for examining the binding interactions between surfactant and polymer where the differential enthalpy during the binding process is monitored. In addition to the critical micelle concentration (cmc) and the micellization enthalpy (deltaHm), the effective micellar charge fraction (beta) of the ionic surfactant micellization process can also be determined from ITC thermograms. Poly(propylene glycol) (PPG) exhibits a lower critical solution temperature (LCST) ranging from 15 to 42 degrees C, depending on the molecular weights. We report, for the first time, the binding interactions between sodium dodecyl sulfate (SDS) and 1,000, 2,000 and 3,000 Da PPGs, where different binding mechanisms are in operation, depending on the temperature. At temperatures lower than the LCST, the binding interactions are similar to those of SDS and low molecular weight poly(ethylene glycol)s (MW < 3500 Da). At temperatures greater than the LCST, the binding interactions are dominated by direct solubilization of PPG chains into mixed micellar cores. At temperatures near the LCST, the binding interactions are controlled by the balance ofthe PPG solubilization at low SDS concentrations and polymer-induced micellization at high SDS concentrations.

Association behavior of poly(methyl methacrylate-block-methacrylic acid) in aqueous medium

The atom transfer radical polymerization technique was used to synthesize the poly(methyl methacrylate-block-methacrylic acid) (P(MAA-b-MMA)) copolymer in order to study the aggregation behavior in aqueous solution over the course of neutralization. Combinations of static and dynamic light scattering (SLS, DLS) and potentiometric titration techniques were used to investigate the size and shape of the micelle at various degrees of neutralization (alpha). By comparing the effect of different polymer chain length with similar MMA/MAA ratio on the aggregation behavior during neutralization, we found relatively strong entanglement of long MMA polymer chains. The comparison between the different MMA/MAA ratios showed that longer MMA chains produced more entanglements. Conductometric titration was used to determine the counterion condensation phenomenon during the course of neutralization. At a critical micellar charge density observed at alpha approximately 0.4, Na+ ions are condensed on the polymer chains. The amount of condensed Na+ was evaluated by the conductivity change, yielding the condensation ratio when the polymer was completely neutralized.