Structure and properties of hydrophobically end-capped poly(ethylene oxide) solutions in the presence of monovalent and divalent cations

Hydrophobically modified poly(ethylene oxide), HMPEO, was studied in concentrated salt solutions. The influence of salts was compared to the effect of temperature on poly(ethylene oxide), PEO. As expected, the addition of monovalent cations (Na(+), K(+)) has the same effect as an increase in temperature in agreement with the thermodynamic properties of PEO: a decrease in solubility, micelle size, and viscosity was observed. Moreover, the intensity of neutron scattering peaks (characteristic of the semi-dilute solutions of these associative polymers) increases due to the collapse of PEO coronae in micelles. Very peculiar behavior was observed in the presence of divalent cations (Ca(2+), Mg(2+)): larger micelle aggregates and higher viscosities, relaxation times, and activation energies were observed by dynamic rheology. This behavior is attributed to interactions between divalent cations and oxygen in PEO backbones close to the micelle core, which may reinforce intermicellar bridges.     

Aqueous solution behavior of new thermoassociative polymers

A new kind of water-soluble polymer was obtained by grafting side chains, characterized by a phase separation on heating (Lower Critical Solution Temperature LCST), on a hydrosoluble backbone. For semidilute solutions, the side chains associate as the temperature exceeds a critical temperature (T _ass), which is close to their LCST. Microdomains are formed which act like physical crosslinking units between the main chains, and an increase in the aqueous solution viscosity is observed. Systems based on 2-Acrylamido-2-methyl propane sulfonic acid (AMPS) backbone and polyethylene oxide (PEO) side chains were developed. Their rheological behavior in both dilute and semi-dilute states was studied by varying differents parameters such as polymer and salt concentrations, grafting ratio, etc. Fluorescence measurements indicate the formation of hydrophobic microdomains on heating, in agreement with the thickening properties of the solutions.     

Thermal transitions in associating aqueous block copolymers: light scattering,rheology and spectroscopy

Solutions containing a polyoxy-ethylene/polyoxy-propylene/polyoxy-ethylene (PEO–PPO–PEO) block copolymer, indicated as F68, in water were investigated as a function of composition and temperature. Hydrogen nuclear magnetic resonance (¹H NMR) line width, chemical shift, self-diffusion, spin-lattice relaxation times, laser light scattering and rheological methods were used. The monomer–micelle equilibrium and the micelle–liquid crystalline phase transitions depend on the F68 content in the mixture and temperature. Significant changes in light scattering intensity and apparent hydrodynamic radius are associated to micelle formation above the critical micellar temperature (CMT). According to a Contin analysis, this behaviour is reflected in the presence of two populations in the intensity–intensity autocorrelation functions. The contributions due to molecules and micelles can be evaluated separately. No such effects are observed below the CMT. Micelle onset is also associated to variations in ¹H NMR spectra, affecting the chemical shift, line width and spin-lattice relaxation time of the PPO methyl protons and self-diffusion, as well. Spin-lattice relaxation times of PEO chains, conversely, change significantly at temperatures close to the micelle–liquid crystalline thermal transition. Similar results were obtained from the line width of ²H NMR spectra as a function of T. Significant changes in both viscous and elastic modulus were also observed and ascribed to PPO dehydration, at the CMT, as well as to squeezing and dehydration of PEO units in liquid crystal formation, respectively.     

Structure and interactions of block copolymer micelles of Brij 700 studied by combining small-angle X-ray and neutron scattering

Spherical micelles of the diblock copolymer/surfactant Brij 700 (C(18)EO(100)) in water (D(2)O) solution have been investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS and SANS experiments are combined to obtain complementary information from the two different contrast conditions of the two techniques. Solutions in a concentration range from 0.25 to 10 wt % and at temperatures from 10 to 80 degrees C have been investigated. The data have been analyzed on absolute scale using a model based on Monte Carlo simulations, where the micelles have a spherical homogeneous core with a graded interface surrounded by a corona of self-avoiding, semiflexible interacting chains. SANS and SAXS data were fitted simultaneously, which allows one to obtain extensive quantitative information on the structure and profile of the core and corona, the chain interactions, and the concentration effects. The model describes the scattering data very well, when part of the EO chains are taken as a "background"contribution belonging to the solvent. The effect of this becomes non-negligible at polymer concentrations as low as 2 wt %, where overlap of the micellar coronas sets in. The results from the analysis on the micellar structure, interchain interactions, and structure factor effects are all consistent with a decrease in solvent quality of water for the PEO block as the theta temperature of PEO is approached.     

Interactions between block copolymers and single-walled carbon nanotubes in aqueous solutions: a small-angle neutron scattering study

The amphiphilic copolymers of the Pluronic family are known to be excellent dispersants for single-walled carbon nanotubes (SWCNT) in water, especially F108 and F127, which have rather long end-blocks of poly(ethylene oxide) (PEO). In this study, the structure of the CNT/polymer hybrid formed in water is evaluated by measurements of small-angle neutron scattering (SANS) with contrast variation, as supported by cryo-transmission electron microscopy (cryo-TEM) imaging. The homogeneous, stable, inklike dispersions exhibited very small isolated bundles of carbon nanotubes in cryo-TEM images. SANS experiments were conducted at different D(2)O/H(2)O content of the dispersing solvent. The data for both systems showed surprisingly minimal intensity values at 70% D(2)O solvent composition, which is much higher than the expected value of 17% D(2)O that is based on the scattering length density (SLD) of PEO. At this near match point, the data exhibited a q(-1) power law relation of intensity to the scattering vector (q), indicating rodlike entities. Two models are evaluated, as extensions to Pederson's block copolymer micelles models. One is loosely adsorbed polymer chains on a rodlike CNT bundle. In the other, the hydrophobic block is considered to form a continuous hydrated shell on the CNT surface, whereas the hydrophilic blocks emanate into the solvent. Both models were found to fit the experimental data reasonably well. The model fit required special considerations of the tight association of water molecules around PEO chains and slight isotopic selectivity.     

Cylindrical micelles from the aqueous self-assembly of an amphiphilic poly(ethylene oxide)-b-poly(ferrocenylsilane) (PEO-b-PFS) block copolymer with a metallo-supramolecular linker at the block junction

A supramolecular AB diblock copolymer has been prepared by the sequential self-assembly of terpyridine end-functionalized polymer blocks by using Ru(III)/Ru(II) chemistry. By this synthetic strategy a hydrophobic poly(ferrocenylsilane) (PFS) was attached to a hydrophilic poly(ethylene oxide) (PEO) block to give an amphiphilic metallo-supramolecular diblock copolymer (PEO/PFS block ratio 6:1). This compound was used to form micelles in water that were characterized by a combination of dynamic and static light scattering, transmission electron microscopy, and atomic force microscopy. These complementary techniques showed that the copolymers investigated form rod-like micelles in water; the micelles have a constant diameter but are rather polydisperse in length, and light scattering measurements indicate that they are flexible. Crystallization of the PFS in these micelles was observed by differential scanning calorimetry, and is thought to be the key behind the formation of rod-like structures. The cylindrical micelles can be cleaved into smaller rods whenever the temperature of the solution is increased or they are exposed to ultrasound.     

Physicochemical studies on hydrophobic PEO‐PPO‐PEO triblock copolymer micelles in SDS micellar environment

The shape, size, aggregation, hydration, and correlation times of water insoluble PEO‐PPO‐PEO triblock copolymer micelles with sodium dodecylsulfate (SDS) micelles were investigated using transport studies and dynamic light scattering technique. From the conductance of micellar solutions of the polymer in 25 mM SDS and 5 mM NaCl, the hydration of polymer micelles were determined using the principle of obstruction of electrolyte migration by the polymer. The asymmetry of the micellar particles of polymer and polymer‐SDS mixed micellar systems in 5 mM NaCl and their average axial ratios were calculated using intrinsic viscosity and hydration data obeying Simha–Einstein equation. Hydration number and micellar sizes were variable with temperature. The shape of the polymer micelles has been ellipsoidal rather than spherical. The micellar volume, hydrodynamic radius, radius of gyration, diffusional coefficients as well as translational, rotational and effective correlation times have been calculated from the absolute values of the axes. The partial molal volume of polymer micelles has also been determined and its comparison with the molar volume of pure polymer suggested a volume contraction due to immobilization of the water phase by the hydrophilic head groups of the polymer. The thermodynamic activation parameters for viscous flow favor a more ordered water structure around polymer micelles at higher temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2410–2420, 2007     

聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质的研究

采用核磁共振 (NMR)、动态激光光散射 (DLS)、透射电子显微镜 (TEM )等方法研究了规整性聚甲基丙烯酸甲酯接枝聚氧乙烯共聚物溶液性质 ,研究表明两亲接枝共聚物在选择性溶剂中可形成球状胶束 ,溶液的浓度、温度和聚合物结构等因素影响其胶束的大小、形态     

Structure and rheology of hyperbranched and dendritic polymers. II. Effects of blending acetylated and hydroxy‐terminated poly(propyleneimine) dendrimers with aqueous poly(ethylene oxide) solutions

The effect of adding acetylated poly(propyleneimine) dendrimers to the structure and rheology of aqueous solutions of high molecular weight poly(ethylene oxide) (PEO) was investigated by rheology and small‐angle neutron scattering in a temperature range of 10–40 °C. In the semidilute regime, the steady shear rheology of PEO solutions was unmodified by the addition of dendrimers at a comparable weight concentration. At the highest concentrations studied, the addition of acetylated dendrimers suppressed the onset of a low‐frequency elastic modulus at the lowest temperature investigated. For comparison, the addition of PEO of a comparable molecular weight at the same weight fraction resulted in a milder suppression but, unlike the dendrimers, greatly increased the solution viscosity. The addition of acetylated dendrimers to a semidilute PEO solution at 10 °C substantially reduced the solution turbidity. These effects on the rheology and optical properties were confirmed by small‐angle neutron scattering measurements of the molecular structure of the mixture. Additional SANS measurements in the dilute regime (0.1 wt % PEO) showed quantitatively that the dendrimers decorated the PEO chains in a necklace structure, such as that observed previously for micelles. The results suggested a mechanism of rheology modification whereby the dendrimers disrupted the association network structure in the PEO solution at lower temperatures by preferentially associating with the PEO chains in solution. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 874–882, 2000     

A Facile Method to Form a Densely Grafted PEO‐b‐P4VP Brush on Gold Surface

Here we report a facile method for the preparation of a PEO₁₁₃‐b‐P4VP₉₃ brush on gold surface with a grafting density as high as 1.32 chains/nm²; the P4VP blocks were physically adsorbed on gold surface forming an inner layer while the PEO blocks stretched towards the solution forming PEO brush. PEO₁₁₃‐b‐P4VP₉₃ micelles with P4VP core and PEO shell formed in methanol/water mixed solvents were used as the precursor. By adsorbing PEO₁₁₃‐b‐P4VP₉₃ micelles from pure water, in which the density of the micelles is the largest, maximum amount of the micelles was adsorbed onto gold surface, and the adsorbed micelles existed as individual domains on the surface. To prepare the polymer brush with a density as high as possible, we annealed the adsorbed micelles by methanol/water mixed solvent at the volume fraction of methanol (VF) of 20%, which was the proper proportion at which the core‐forming P4VP chains began to be flexible but the integrity of the micelles was remained. At this volume fraction, almost all the adsorbed micelles originally existing as individual domains were transformed into a dense polymer brush.     

Hierarchical mesostructures of biodegradable triblock copolymers via evaporation-induced self-assembly directed by alkali metal ions

Hierarchical mesostructures of poly(ε-caprolactone)-b-poly(ethylene oxide)-b-poly(ε-caprolactone) (PCL-PEO-PCL) triblock copolymers have been grown from evaporation-induced self-assembly directed by alkali metal ions. The self-assembly process began with a dilute homogeneous solution of the triblock copolymers in a mixture of tetrahydrofuran (THF) and water. THF preferentially evaporated under reduced pressure and induced the formation of amphiphilic polymer micelles. The spherical polymer micelles formed both in deionized water and NaOH aqueous solution. However, different mesostructures were discovered during the film depositing process for scanning electron microscopy observation. The polymer micelles were observed for the deposition sample in deionized water while sisal-like hierarchical mesostructures resulted from the film deposition of polymer micelles in NaOH aqueous solution. The sisal-like mesostructures and their formation process were observed through scanning electron microscopy, transmission electron microscopy, fluorescent microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Detailed study revealed that during evaporation-induced self-assembly of PCL-PEO-PCL amphiphilic triblock copolymer directed by alkali metal ions, the sodium ions and polymer micelles increasingly concentrated in NaOH aqueous solution and the solvent quality for the diblock progressively decreased, which resulted in the stronger coordination between alkali metal ions and PEO ligands in the block copolymer and PEO segment crystallization.     

Phase behavior and local dynamics of concentrated triblock copolymer micelles

We report a neutron-scattering study to characterize the ordering and local dynamics of spherical micelles formed by the triblock copolymer polyethylene oxide (PEO)--polypropylene oxide (PPO)--polyethylene oxide (Pluronic) in aqueous solution. The study focuses on two Pluronic species, F68 and F108, that have the same weight fraction of PEO but that differ in chain length by approximately a factor of 2. At sufficiently high concentration, both species undergo a sequence of phase changes with increasing temperature from dissolved chains to micelles with liquid-like order to a cubic crystal phase and finally back to a micelle liquid phase. A comparison of the phase diagrams constructed from small-angle neutron scattering indicates that crystallization is suppressed for shorter chain micelles due to fluctuation effects. The intermediate scattering function I(Q,t)I(Q,0) determined by neutron spin echo displays a line shape with two distinct relaxations. Comparisons between I(Q,t)I(Q,0) for fully hydrogenated F68 chains in D2O and for F68 with deuterated PEO blocks reveal that the slower relaxation corresponds to Rouse modes of the PPO segments in the concentrated micelle cores. The faster relaxation is identified with longitudinal diffusive modes in the PEO corona characteristic of a polymer brush.     

The effect of poly(ethylene oxide) on the characteristics of Triton X-100/1-butanol/ n-octane/water reverse micelles

 Nonionic poly(oxyethylene) surfactant with about ten ethylene oxide units and 1-butanol have been studied in reverse micelles with one nonpolar solvent(n-octane) at different water contents in the presence and in the absence of poly (ethylene oxide) (PEO) using two absorption probes, methyl orange and methyl blue MB and one spin probe, 5-doxylstearic acid. The study has focused attention on the effect of the addition of PEO on the phase behavior of the system, the state of water in the reverse micelles, and the locus of PEO solubilized in reverse micelles. In the presence of PEO, some PEO segments may penetrate into the interface close to the palisade layer of the reverse micelles and then replace some water molecules, which results in a less close arrangement between the chains of surfactants as well as between alcohol molecules. Received: 13 April 1999/Accepted in revised form: 5 November 1999     

Interactions between cellulose nanocrystals and anionic and neutral polymers in aqueous solutions

Physical structures of aqueous cellulose nanocrystal (CNC) suspensions in anionic polyelectrolyte carboxymethyl cellulose (CMC) and non-ionic poly(ethylene oxide) (PEO) were investigated by studying their cross polarized, polarized optical microscope (POM) images and dynamic light scattering, zeta potential, ¹H spin–lattice relaxation nuclear magnetic resonance (NMR) data. The presence of anionic CMC and nonionic PEO in CNC suspensions led to two different kind of interactions. Semi-dilute CNC suspensions showed first gel-like behavior then phase separation by adding only semi-dilute un-entangled CMC polymer solutions, whereas the addition of PEO didn’t cause any significant change. POM images showed the phase transitions of CNC suspensions in the presence of CMC solutions from the isotropic state to nematic and chiral nematic phases. Dynamic light scattering, zeta potential and ¹H spin–lattice relaxation NMR data presented further arguments to explain polymer-CNC interactions in CMC and PEO solutions. ¹H NMR solvent relaxation technique determined the adsorption and depletion interactions between polymers and CNC. The minima in spin–spin specific relaxation rate constant showed the depletion of CNC nanoparticles in CMC. It is believed that the depletion flocculation was the case for the effects of CMC polymer chains in CNC suspensions. PEO was adsorbed on CNC surfaces and caused only weak depletion interactions due to the presence of soft particles.     

Complexation of poly(acrylic acid) and poly(ethylene oxide) investigated by enhanced Rayleigh scattering method

The method of enhanced Rayleigh scattering spectroscopy (ERS) was developed to investigate the complexation of poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO) in semidilute polymer solutions. Based on the Ornstein‐Zernike equation, the relationship between macromolecular static correlation length and ERS intensity was presented. Moreover, the ERS spectra were calculated by the moving window two‐dimensional (MW2D) correlation spectroscopy to get detailed information of the polymer complexation. The results indicated that the ERS spectroscopy characteristics of the polymer mixtures have similar trend, and the ERS intensity promptly increases as the macromolecular chains contract. The increase of ERS intensity showed that the degree of complexation between PAA and PEO increases when the pH value decreases. The complexation results from the collapse of macromolecular chains, which is induced by the PAA chains contracting and the enhanced association between PAA and PEO chains because of the hydrogen bond formation. In addition, the association resulting from the complexation of PAA and PEO in solution was demonstrated by the MW2D correlation spectroscopy. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1847–1852, 2010     

Pinch-off dynamics and extensional relaxation times of intrinsically semi-dilute polymer solutions characterized by dripping-onto-substrate rheometry

Stream-wise velocity-gradients associated with extensional flows arise in thinning liquid necks spontaneously formed during jetting, printing, coating, spraying, atomization, and microfluidic-based drop formation. In this contribution, we employ Dripping-onto-Substrate (DoS) rheometry protocols to measure the extensional rheology response of intrinsically semi-dilute polymer solutions by visualizing and analyzing capillary-driven thinning of a columnar neck formed between a nozzle and a sessile drop. We show that extensional viscosity that quantifies the resistance to stream-wise velocity gradients is orders of magnitude higher than the shear viscosity. Although shear flows only weakly perturb the chain dimensions, extensional flows can strongly stretch and orient the chains, thus influencing both intra- and inter-chain interactions. We find that the extensional relaxation times for intrinsically semi-dilute PEO solutions in a good solvent for five different molecular weights increase linearly with concentration, exhibiting a stronger concentration dependence than observed for dilute solutions, or anticipated by blob models, developed for relaxation of weakly perturbed chains in a good solvent. The observed distinction between the concentration-dependent relaxation dynamics of intrinsically dilute and semi-dilute solutions arises due the complex influence of stretching, conformational anisotropy, and polymer concentration on excluded volume and hydrodynamic interactions of flexible, highly extensible polymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1692–1704     

Surface Reconstruction by a Coassembly Approach

Materials with switchable surfaces, capable of changing surface properties under external stimuli, are playing a pivotal role in many applications, such as tissue engineering, biosensors, and drug/protein delivery. In this research silica particles with patterned and switchable surfaces are fabricated. Surface micelles on silica particles are formed by coassembly of polymer brushes and “free” block copolymer chains in a selective solvent. The cores of the surface micelles are crosslinked by anthracene photodimerization. After quaternization of the coronae, amphiphilic surface micelles are prepared. The surface micelles are able to rearrange in different media. After treatment with an organic solvent, the surfaces of silica particles are occupied by hydrophobic polymer components; in aqueous solution, the positively charged polymer chains are on the surfaces. The switching of the surface micelles results in changes in surface composition and wetting behaviors.     

FORMATION OF FLOWER-LIKE AGGREGATES FROM SELF-ASSEMBLING OF MICELLES WITH PEO SHELLS AND CROSS-LINKED POLYACRYLAMIDE CORES

Amphiphilic block copolymers,poly(ethylene oxide)-b-poly(N-acryloxysuccinimide) (PEO-b-PNAS) with various molecular weights have been successfully synthesized by atom transfer radical polymerization (ATRP) of NAS using functionalized PEO (PEO-Br) as ATRP macroinitiator.The self-assembling of the block copolymers in water,which is a good solvent for PEO and a non-solvent for PNAS.yielded spherical core-shell micelles with PNAS as core and PEO as shell.The cross-linked reaction of oxysuccinimide in PNAS ch...     

Mixed solvent effect on lithium-coordination to poly(ethylene oxide)

This article presents a comparative study of the structure formation of poly (ethylene oxide) PEO/Li complexes in aqueous and acetonitrile solutions using small-angle neutron scattering (SANS). We demonstrate that in acetonitrile solutions, Li-cations coordinate to the ether–oxygen of the monomeric unit, and this results in charging and stretching of the polymer chains. This is found to be in contrast to aqueous solutions, where the ions remain free in solution. In particular, we demonstrate that the “binding” and “screening” regimes that were observed in case of PEO/K⁺ solutions in acetonitrile are also found in the respective PEO/Li⁺ solutions. The addition of water to solutions in acetonitrile increasingly diminishes the ion-coordination to the polymer, eventually resulting in neutral polymer chains at water contents above ϕ*_water = 30% (w/v). The preferential adsorption of water on PEO in mixtures of acetonitrile and water is evidenced by the pronounced stretching of polymer chains, in particular, at a water content of ϕ_water = 25% and 33.33% (w/v) where complete stretching of the chains is observed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3642–3650, 2006