Monolayers of hydrogen-bonded polymer blends at the air–water interface: poly(vinylacetate)+poly (4-hydroxystyrene (original) (raw)
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Journal of Colloid and Interface Science, 1999
The Langmuir surface balance technique has been used to study the interfacial behavior of six structurally different poly(oxyethylene) (POE)-based polymer surfactants at the air-water interface. On a pure water subphase the surfactants have collapse surface pressures dependent on the POE chain length. The surfactant monolayers collapse at well-determined surface pressures, and the lower POE chain-length surfactants collapse at higher pressures than those with high POE content. This difference vanishes as increasing amounts of salt are added to the subphase. The ⌸Aisotherms are smooth, which is normal for polymeric surfactants. A closer analysis of the isotherms reveals characteristic behavior that can be attributed to structural differences. Similarities in thermodynamic behavior suggest that the molecular orientation is the same despite the structural differences. A new expression for the compressibility factor is developed to explain the relationship between this parameter and surface pressure for polymeric monolayers.
Macromolecules, 1993
Mixed films formed by an insoluble polymer, poly(dimethylsi1oxane) (PDMS), placed on the surface of aqueous solutions of two different soluble surfactants are studied by a variety of different methods: surface tension isotherms, ellipsometry complemented by the neutron reflectivity experiments presented in part 2, and direct observations of the surface via the Brewster angle microscope. A vertical separation into superimposing surfactant and polymer layers is exhibited, with mixing between the layers depending on the surfactant. On one but not the other of the surfactant solutions studied, a lateral separation of the polymer monolayer is also observed, into domains similar to those previously observed on pure water. The collapse of the monolayer into a three-dimensional state with increasing polymer concentration occurs more smoothly than on water.
Poly(methyl methacrylate) monolayers at the air–water interface
Materials Letters, 2005
Several poly(methyl methacrylate) (PMMA) molecules with various chain numbers has been synthesised using Emulsifier-free emulsion polymerisation method. Langmuir -Blodgett thin film technique is an excellent method to investigate the surface behaviours of organic monolayers at the air -water interface. In this study, PMMA molecules have been studied at the air -water interface using Langmuir -Blodgett thin film method. Area per molecule for several PMMA molecules is found to be between 0.29 T 0.01 and 0.98 T 0.01 nm 2 . The surface pressure -area graphs were taken in two stages i.e. during the first compression of the monolayer and also during the second compression of the same monolayer before the collapsed stage of the monolayer. It is also found that first surface pressure -area graph for the first compressing of the monolayer at the water surface is different than the surface pressure -area graph obtained after a decompression of the monolayer. Isotherm graphs show that long alkyl chain groups of these molecules may cause aggregation behaviours on water surface and a model for the behaviour of PMMA molecules on the air -water interface due to surface interactions has been proposed. D
The European Physical Journal B, 1998
Equilibrium surface tension measurements have been carried out on mixed solutions of a nonsurface active polyelectrolyte (polyacrylamide sulfonate) and cationic surfactants. A strong synergistic lowering of the surface tension is found in the concentration range where no appreciable complexation of surfactant and polymer occurs in the bulk solution (as seen from viscosity measurements). The surface tension decrease does not depend upon the polymer molecular weight, and there is a limited influence of the surfactant chain length. The influence of the degree of charge of the polymer is more important: for small degree of charge, the complexation is less cooperative, and the structure of the surface complex is looser.
Dilational rheology of monolayers of a miscible polymer blend: From good- to poor-solvent conditions
European Physical Journal E, 2002
The viscoelastic moduli (elasticity and dilational viscosity) of monolayers of PVAc + P4HS has been studied over a broad frequency range (0.1 mHz-200 kHz) using a combination of relaxation and capillary-waves techniques. The analysis of the surface pressure, the elasticity and the viscosity on the semidilute regime show that the air-water interface is a good solvent for the monolayers of PVAc-rich blends, and a poor (near-Θ) solvent for the monolayers of P4HS-rich blends. The solvent quality changes continuously over a broad concentration range. The results of viscoelastic moduli show that there is a broad relaxation process in the low-frequency range ( ω
Interfacial and Monolayer Properties of Poly(vinylcaprolactam)
Langmuir, 2000
The surface properties of a polydisperse poly(vinycaprolactam) (48 kDa) have been studied at the air/ water and hexane/water interfaces. Adsorption of the polymer at both interfaces shows substantial timedependent surface tension lowering at remarkably low concentrations in the aqueous phase. This adsorption is increased by addition of electrolyte, which also lowers the lower consolute temperature (LCT) of the polymer in solution. Adsorption is endothermic, corresponding with the approach to the LCT as the temperature is raised. Spreading of the polymer at the air/water interface from aqueous solutions is near quantitative. The surface pressure-area isotherms indicate extensive coiling in the monolayer at low pressures and looping of the polymer monolayer into the aqueous phase in the higher pressure range.
Journal of Colloid and Interface Science, 2008
The monolayer formed at an air/water interface by the synthetic non-ionic surfactant, 1,2-di-O-octadecyl-rac-glyceryl-3-(ω-methoxydodecakis (ethylene glycol)) (2C 18 E 12) has been characterized using Langmuir trough measurements, Brewster angle microscopy (BAM), and neutron reflectometry. The BAM and reflectometry studies were performed at four different surface pressures (π) in the range 15-40 mN/m. The BAM studies (which give information on the in-plane organisation of the surfactant layer) demonstrate that the 2C 18 E 12 molecules are arranged on the water surface to form distinct, approximately circular, 5 µm diameter domains. As the surface pressure is increased these domains retain their size and shape but are made progressively more close-packed, such that the monolayer is made more or less complete at π = 40 mN/m. The neutron reflectometry measurements were made to determine the structure of the interfacial surfactant layer at π = 15, 28, 34 and 40 mN/m, providing information on the thickness of the 2C 18 E 12 alkyl chains', head groups' and associated solvent distributions (measured along the surface normal), along with the separations between these distributions, and the effective interfacial area per molecule. Partial structure factor analyses of the reflectivity data show that the effective interfacial area occupied decreases from 217 Å 2 per 2C 18 E 12 molecule at π = 15 mN/m down to 102 Å 2 at π = 40 mN/m. There are concomitant increases in the widths of the surfactant's alkyl chains' and head groups' distributions (modelled as Gaussians), with the former rising from 12 Å (at π = 15 mN/m) up to 19 Å (at π = 40 mN/m) and the latter rising from 13 Å (at π = 15 mN/m) up to 24 Å (at π = 40 mN/m). The compression of the monolayer is also shown to give rise to an increased surface roughness, some of which is due to the thermal roughness caused by capillary waves, but with a significant contribution also coming from the intrinsic/structural disorder in the monolayer. At all surface pressures studied, the alkyl chains and head groups of the 2C 18 E 12 are found to exhibit a significant overlap, and this increases with increasing π. Given the various trends noted on how the structure of the 2C 18 E 12 monolayer changes as a function of π , we extrapolate to consider the structure of the monolayer at π > 40 mN/m (making comparison with its single chain (C n E m) counterparts) and then relate these findings to the observations recorded on the structure and solute entrapment efficiency of 2C 18 E 12 vesicles.
Monolayers of some ABA block-copolymers at the airwater interface
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1996
Monolayers of non-ionic ABA block-copolymers at the air-water interface have been investigated by means of the Langmuir surface balance technique. The A-and B-blocks of the polymer are biodegradable polyester and poly(ethylene oxide) (PEO) chains, respectively. The interfacial properties such as surface pressure and area per molecule have been measured for polymers with variable A-blocks and a constant B-block. The results showed that there is a dependence between the critical and extrapolated areas per molecule and the length of the A-blocks. The results were interpreted by a modified equation of state for gases in two dimensions which suggested that the final polymer chain conformation was adopted relatively early during the compression and that the B-block was displaced away from the interface only with the two B-block monomers that are bound to the A-blocks anchored at the interface. The parameter, i, characterising the interaction between the molecules at the interface, was an approximately linear function of the molecular weight and the size of the A-blocks, and when extrapolated to the molecular weight corresponding to a pure B homopolymer a value close to the value for a B homopolymer monolayer was obtained. Interpretation of the results by an equation of state developed by Gaines indicated different monolayer compositions in the high and low compressibility regions, showing that the B-block is displaced away from the interface above a surface pressure of approximately 9 mN m-I which is the collapse surface pressure of a pure PEO monolayer. A comparison between this model and a modified Semenov model showed only a small contribution to the surface pressure from the polymer chain conformational changes, in line with the suggestion that the polymer chain adopts the final conformation at relatively high areas.
Behavior of DSPC/DSPE-PEG2000 mixed monolayers at the air/water interface
Colloids and Surfaces A: Physicochemical and …, 2002
Lateral interactions in L-a-distearoyl phosphatidylcholine (DSPC)/distearoylphosphatidyl-ethanolamine-poly(ethylene glycol)2000 (DSPE-PEG2000) mixed monolayers were studied by measuring lateral film pressure Á/mean molecular area (P Á/A) isotherms. Application of thermodynamic analysis to these isotherms reveals fundamental behavior of these mixed films on the water subphase. The results show that DSPC and DSPE-PEG2000 are miscible and exhibit nonideal mixed behavior at the interface. The mixed film are energetically stable if the molar fraction of DSPE-PEG2000 (X DSPE-PEG2000) is greater than 5 mol% and the most stable composition was found at X DSPE-PEG2000 0/7 mol%. Relaxation phenomenon was observed at constant film pressure. Compressibility for this system was estimated as well. It is concluded that mixed film are rather stable even at high surface pressure and the addition of DSPE-PEG2000 into DSPC monolayer make the film become more expanded and slight more compressible, except at X DSPE-PEG2000 0/5 mol%. The findings of this study corroborates well with those of the lipid Á/PEG2000 liposomes.
The Journal of Physical Chemistry B, 2009
The effect of hydrogen-bonding complexation on the interfacial behavior of poly(isoprene)-b-poly(ethylene oxide) (PI-b-PEO) diblock copolymer at the air-water interface has been investigated by Langmuir balance and neutron reflectivity. PI-b-PEO forms Langmuir monolayers with PI as the anchoring block. Introduction of a second diblock, poly(isoprene)-b-poly(acrylic acid) (PI-b-PAA) yields PI-b-PEO/PI-b-PAA mixed layers with interfacial behavior that is pH-dependent. At pH 10.0 and 5.7, the compression (π-A) isotherms exhibit three regions that are characteristic of PEO-type tethered layers, (i) a low-pressure 2-D "pancake" region (region I), (ii) a pseudoplateau where PEO segments desorb and are immerse in the subphase (region II), and (iii) a steep pressure rise region commonly considered as the "brush" regime (region III). At pH 2.5, on the other hand, the π-A isotherm shows only two regions, (I) and (III). This novel behavior is attributed to hydrogen-bonding complexation between the undissociated carboxylic acids and the PEO, forming very compact layers. It appears that desorption of PEO segments is hindered as a consequence of this complexation. Furthermore, no brush-like structure is observed in region III of the isotherml; thus, the steep rise in surface pressure in this case arises primarily from interactions of the anchoring block. The hydrogen-bonded complex of PI-b-PEO/PI-b-PAA monolayers thus shows enhanced surface stability.