Effect of Hydrogen-Bonding Complexation on the Interfacial Behavior of Poly(isoprene)− b -Poly(ethylene oxide) and Poly(isoprene)− b -Poly(acrylic acid) Langmuir Monolayers (original) (raw)
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Langmuir, 2005
A polystyrene-b-poly(ethylene oxide) (PS-b-PEO) (MW) 141k, 11.4 wt% PEO) diblock copolymer in the hydrophobic regime was spread from chloroform solutions of various concentrations at the air-water interface, and the resultant monolayers were transferred to glass substrates and imaged using atomic force microscopy. Monolayers prepared under identical conditions were also characterized at the airwater interface via Langmuir compression isotherms. The effects of spreading solution concentration on surface features, compressibility, and limiting mean molecular area were determined, revealing several interesting trends that have not been reported for other systems of PS-b-PEO. Spreading solutions g0.50 mg/mL resulted almost exclusively in dot and spaghetti morphologies, with no observed continent features, which have been commonly found in more hydrophobic systems. For lower spreading solutions, e0.25 mg/mL, we observed a large predominance of two novel surface morphologies, nanoscale rings and chains. The surface pressure (π)-area (A) isotherms also exhibited a unique dependence on the spreading solution concentration, with limiting mean molecular areas and isothermal compressibilities of PS-b-PEO monolayers increasing below a critical concentration of spreading solution, suggesting a greater contribution from the PEO blocks. These results suggest that PS chain entanglement prior to solvent evaporation plays an important kinetic role in the extent of PEO adsorption at the air-water interface and in the morphologies of the resulting self-assembled surface aggregates.
Structural Analysis of PEO−PBO Copolymer Monolayers at the Air−Water Interface
Langmuir, 2006
X-ray reflectivity (XR) and grazing incidence X-ray diffraction (GIXD) have been used to examine an oxyethyleneb-oxybutylene (E 23 B 8 ) copolymer film at the air-water interface. The XR data were fitted using both a one-and a two-layer model that outputted the film thickness, roughness, and electron density. The best fit to the experimental data was obtained using a two-layer model (representing the oxyethylene and oxybutylene blocks, respectively), which showed a rapid thickening of the copolymer film at pressures above 7 mN/m. The large roughness values found indicate a significant degree of intermixing between the blocks and back up the GIXD data, which showed no long range lateral ordering within the layer. It was found from the electron density model results that there is a large film densification at 7 mN/m, possibly suggesting conformational changes within the film, even though no such change occurs on the pressure-area isotherm at the same surface pressure.
Langmuir, 2005
The dilatational rheological properties of monolayers of poly(ethylene oxide)-poly(propylene oxide)poly(ethylene oxide)-type block copolymers at the air-water interface have been investigated by employing an oscillating ring trough method. The properties of adsorbed monolayers were compared to spread layers over a range of surface concentrations. The studied polymers were PEO26-PPO39-PEO26 (P85), PEO103-PPO40-PEO103 (F88), and PEO99-PPO65-PEO99 (F127). Thus, two of the polymers have similar PPO block size and two of them have similar PEO block size, which allows us to draw conclusions about the relationship between molecular structure and surface dilatational rheology. The dilatational properties of adsorbed monolayers were investigated as a function of time and bulk solution concentration. The time dependence was found to be rather complex, reflecting structural changes in the layer. When the dilatational modulus measured at different concentrations was replotted as a function of surface pressure, one unique master curve was obtained for each polymer. It was found that the dilatational behavior of spread (Langmuir) and adsorbed (Gibbs) monolayers of the same polymer is close to identical up to surface concentrations of ≈0.7 mg/m 2. At higher coverage, the properties are qualitatively alike with respect to dilatational modulus, although some differences are noticeable. Relaxation processes take place mainly within the interfacial layers by a redistribution of polymer segments. Several conformational transitions were shown to occur as the area per molecule decreased. PEO desorbs significantly from the interface at segmental areas below 20 Å 2 , while at higher surface coverage, we propose that segments of PPO are forced to leave the interface to form a mixed sublayer in the aqueous region.
The Journal of Physical Chemistry B, 2012
By use of a combined experimental and theoretical approach, a model poly(ethylene oxide) (PEO) brush system, prepared by spreading a poly(ethylene oxide)− poly(n-butyl acrylate) (PEO−PnBA) amphiphilic diblock copolymer onto an air−water interface, was investigated. The polymer segment density profiles of the PEO brush in the direction normal to the air−water interface under various grafting density conditions were determined by using the neutron reflectivity (NR) measurement technique. To achieve a theoretically sound analysis of the reflectivity data, we used a data analysis method that utilizes the self-consistent field (SCF) theoretical modeling as a tool for predicting expected reflectivity results for comparison with the experimental data. Using this data analysis technique, we discovered that the effective Flory−Huggins interaction parameter of the PEO brush chains is significantly greater than that corresponding to the θ condition in Flory−Huggins solutions (i.e., χ PEO−water (brush chains)/ χ PEO−water (θ condition) ≈ 1.2), suggesting that contrary to what is more commonly observed for PEO in normal situations (χ PEO−water (free chains)/χ PEO−water (θ condition) ≈ 0.92), the PEO chains are actually not "hydrophilic" when they exist as polymer brush chains, because of the many body interactions that are forced to be effective in the brush situation. This result is further supported by the fact that the surface pressures of the PEO brush calculated on the basis of the measured χ PEO−water value are in close agreement with the experimental surface pressure−area isotherm data. The SCF theoretical analysis of the surface pressure behavior of the PEO brush also suggests that even though the grafted PEO chains experience a poor solvent environment, the PEO brush layer exhibits positive surface pressures, because the hydrophobicity of the PEO brush chains (which favors compression) is insufficient to overcome the opposing effect of the chain conformational entropy (which resists compression).
Langmuir, 1996
Spread monolayers of poly(styrene)-poly(ethylene oxide) diblock copolymers (PSm-PEOn, m ) 38, n ) 90, 148, 250, and 445) have been studied at the air-water interface by measuring the surface pressurearea (π-A) isotherms at several temperatures. The π-A isotherms exhibit several regions which can be ascribed to different conformations of the polymer chains: a pancake structure at low surface pressures and high areas when the isolated chains are adsorbed by both the PS globule and the PEO segments at the interface; an intermediate structure, quasi-brush, when the PEO segments are solubilized in the subphase; and finally a brush developed at low surface areas when the PEO chains are obliged to stretch away from the interface to avoid overlapping. At surface pressures near 10 mN/m there is a transition between a high-density pancake and the quasi-brush regime. The compression and the subsequent expansion curves superpose at the transition and quasi-brush regions but not at the brush and pancake stages. This points to a high cohesion in the brush structure after compression and to some irreversible entanglement and hydration of the PEO chains when immersed in the subphase. These two local hystereses depend differently on the PEO chain length and temperature. The hysteresis observed at high surface pressures (brush conformation) decreases with the PEO length and temperature, whereas the low surface pressure hysteresis (pancake) increases with PEO chain length, decreases with temperature in the range 283-298 K, and increases in the range 298-315 K. A negative mean transition entropy change was obtained from the temperature dependence of the quasi-SSAL-quasi-brush transition. The results indicate that the extensive properties of the present diblock copolymers at the interface, such as the pancake limiting area and the mean transition entropy, when expressed by PEOmer, are independent of the PEO length.
Langmuir : the ACS journal of surfaces and colloids, 2017
We describe the surface behavior of PS-b-PAA monolayers at the air/water interface using N,N-dimethyformamide (DMF) as spreading solvent. At low pH, when the PAA blocks are neutral, the surface pressure versus molecular area isotherm shows a pseudoplateau associated with the presence of remaining spreading solvent molecules in the monolayer, as we described in a former study (Guennouni et al., Langmuir, 2016). We show here that the width of the plateau decreases when increasing pH up to its complete disappearance at high pH, when PAA blocks are fully charged, although two regimes of compressibilities on the isotherm still exist. A refined structural study at pH 9 combining specular neutron reflectivity (SNR), grazing-incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy (AFM) in liquid measurements shows that (i) PAA blocks are stretched in solution, as expected from polyelectrolyte brushes in the osmotic regime; (ii) the system undergoes a spinodal decomposit...
Langmuir, 2004
PEE212-PEO112 diblock copolymer monolayers are studied at the air/water interface. At large molecular areas, with X-ray reflectivity, PEE domains are observed, which are partly immersed into the water. The domain thickness increases on compression (28 to 40 Å). With off-specular X-ray reflectivity, an average domain radius of 750 Å is found, but there are also smaller domains. Due to these space constraints, most PEO blocks form a brush beneath the PEE domains. Only a few PEO blocks form a corona surrounding the domains and adsorb flatly onto the air/water interface. The PEO desorption transition is observed at the typical pressure of 9 mN/m, when the flatly adsorbed PEO is compressed at a domain fraction of 95%.
Internal Interface of a Compressed PEE−PEO Diblock Copolymer Monolayer
Langmuir, 2003
Amphiphilic block copolymers consisting of a fluid hydrophobic (poly(ethyl ethylene), PEE) and a hydrophilic (poly(ethylene oxide), PEO) block form monolayers at the air/water interface. With X-ray and neutron reflectivity, the density profile of PEE432-PEO484 was investigated. It was found that the polymer adsorption layer consists of a homogeneous PEE and a solubilized PEO block, which can be laterally compressed by a factor of 3. The PEE thickness increases in inverse proportion to the molecular area, and the PEO brush follows the scaling law predicted for a brush in a good solvent. However, the stretching of the two blocks roughens the PEE-PEO interface, causing a transition from a PEO monolayer adsorbed to a hydrophobic interface (0.8-1.1 nm thick) to a PEE-PEO/water interfacial layer of 3 nm thickness. This transition of the interfacial layer highlights the rich phase behavior of amphiphilic block copolymers, which resembles that of lipids and nonionic surfactants.
Polymer International, 2014
Lithium cations are known to form complexes with the oxygen atoms of poly(oxyethylene) chains. The effect of Li + on the surface properties of three block-copolymers containing poly(oxyethylene) (PEO) have been studied. Two types of copolymers have been studied, a water soluble one of the pluronic family, PEO-b-PPO-b-PEO, PPO being poly(propyleneoxyde), and two water insoluble ones: PEO-b-PS and PEO-b-PS-b-PEO, PS being polysty rene. In the case of the pluronic the adsorption kinetics, the equilibrium surface tension isotherm and the aqueous/air surface rheology have been measured, while for the two insoluble copolymers only the surface pressure and the surface rheology have been studied. In all the cases two different Li + concentrations have been used. As in the absence of lithi um ions, the adsorption kinetics of pluronic solutions shows two processes, and becomes faster as [Li + ] increases. The kinetics is not diffusion controlled. For a given pluronic concentration the equilibrium surface pressure increases with [Li + ], and the isotherms show two surface phase transitions, though less marked than for [Li + ] = 0. A similar behavior was found for the equilibrium isotherms of PEO-b-PS and PEO-b-PS-b-PEO. The surface elasticity of these two copolymers was found to increase with [Li + ] over the whole surface concentration and frequency ranges studied. A smaller effect was found in the case of the pluronic solutions. The results of the pluronic solutions were modeled using a recent theory that takes into account that the molecules can be adsorbed at the surface in two different states. The theory gives a good fit for the adsorption ki netics and a reasonably good prediction of the equilibrium isotherms for low and intermediate concentrations of pluronic. However, the theory is not able to reproduce the isotherm for [Li + ] = 0. Only a semi-quantitative prediction of the surface elasticity is obtained for [pluronic] 6 1 Â 10 À3 mM.
Monolayers of diblock copolymer at the air-water interface: the attractive monomer-surface case
European Physical Journal B, 1998
We have studied both experimentally and theoretically the surface pressure isotherms of copolymers of polystyrene-polyethyleneoxide (PS-PEO) at the air-water interface. The SCMF (single chain meanfield) theory provides a very good agreement with the experiments for the entire range of surface densities and is consistent with the experiments if an adsorption energy per PEO monomer at the air-water interface of about one kBT is taken. In addition, the chain density profile has been calculated for a variety of surface densities, from the dilute to the very dense ones. The SCMF approach has been complemented by a mean-field approach in the low density regime, where the PEO chains act as a two-dimensional layer. Both theoretical calculations agree with the experiments in this region.