Dynamic elasticity of triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) on a water surface

Dilatational viscoelasticity of adsorbed and spread films of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer at the air-water interface is studied by the capillary waves and oscillating barrier techniques. At the surface pressure below 10 mN/m, dynamic surface properties of these films coincide with those of poly(ethylene oxide). At higher surface pressures, the results obtained indicate the desorption of poly(propylene oxide) segments from the monolayer and their interaction with poly(ethylene oxide) segments in an aqueous phase. At a surface pressure close to 19 mN/m, the behavior of adsorbed and spread poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) films becomes different. The real part of dynamic surface elasticity of spread films tends toward its maximum value (20 mN/m) and, upon further compression, films begin to dissolve. At the same time, the surface elasticity of adsorbed films decreases nearly twofold upon the achievement of the maximum value that testifies the formation of looser structure of the surface layer.     

Surface Dynamic Elasticity of Amphiphilic Block Copolymer Monolayers on a Water Surface

The methods of longitudinal and transverse surface waves and of oscillating barrier were used to measure a surface dynamic elasticity of the monolayers of poly(ethylene oxide) and polystyrene block copolymers spread on water within the frequency range of 0.007–520 Hz. At low surface concentrations, the properties of monolayers are determined by the poly(ethylene oxide) block. Upon further monolayer compression, the transition to the regime of polymer brush occurs when the surface dynamic elasticity increases dramatically. Change in the molecular weight of poly(ethylene oxide) block does not lead to the qualitative change in the dependence of surface properties on the degree of monolayer compression. Surface viscosity in the regime of brush significantly differs from the results of calculations made by Buzzaet al. [26]. Possible reasons for this difference are discussed.     

Dynamic Surface Properties of Poly(vinylpyrrolidone) Solutions

The dynamic surface tension and the complex dynamic surface elasticity of poly(vinylpyrrolidone) (PVP) solutions were measured in the concentration range 10(-5) wt% up to about 1 wt%. The surface tension changed slowly with time at low (<10(-4) wt%) and high concentrations (>0.1 wt%). At low concentrations this is a consequence of the slow transport by diffusion of PVP molecules from the depth of the bulk phase to the surface. At high concentrations the time effect is unexpected and probably the result of PVP contamination of high surface activity. The dynamic surface elasticity of PVP solutions gradually decreases with increasing concentration up to the range of high concentrations (>0.1 wt%) where an abrupt increase in the elasticity caused by the adsorbed impurity is observed. At low and medium concentrations the viscoelastic behavior of PVP adsorbed films is similar to that of the previously investigated poly(ethylene oxide) and poly(ethylene glycol) films and is determined by the number of loops and tails protruding into the bulk phase.     

Nanostructured latex films from poly(butyl methacrylate) latex cross-linked with poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock macro-cross-linker

Biphasic polymer latexes were synthesized by a seeded swelling and polymerization method. The latexes were composed of a poly(butyl methacrylate) core and a poly(ethylene oxide) rich shell cross-linked with poly(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) triblock diol diacrylate macro-cross-linker. Nanostructured films were obtained by annealing the biphasic polymer latexes at a temperature between the glass-transition temperatures of the core latex and the cross-linked poly(ethylene oxide) based shell. Atomic force microscope images of the latex film revealed that the poly(butyl methacrylate) core phase is confined in the poly(ethylene oxide)-rich continuous phase with the form of separate nanosized spheres.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为,在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响.根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为,解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因:(1)相比PDMS涂层,蛋白质与PEG涂层的结合能量较低,使其结合更加疏松;(2)蛋白质吸附到材料表面要克服表面水化层分子引起的能障,PEG表面与水分子之间结合紧密,结合水难于脱附,造成蛋白质在其表面的吸附需要克服更高的能量,不利于蛋白质的吸附.     

溶菌酶蛋白在聚合物防污膜表面的吸附

采用分子动力学模拟方法比较了溶菌酶蛋白在两种典型聚合物防污材料聚乙二醇(PEG)和聚二甲基硅氧烷(PDMS)表面的吸附行为, 在微观上探讨了聚合物膜表面性质对蛋白质吸附的影响. 根据蛋白质与聚合物膜之间的相互作用、能量变化及表面水化层分子的动力学行为, 解释了PEG防污涂层相对于PDMS表面具有更佳防污效果的原因: (1) 相比PDMS涂层, 蛋白质与PEG涂层的结合能量较低, 使其结合更加疏松; (2) 蛋白质吸附到材料表面要克服表面水化层分子引起的能障, PEG表面与水分子之间结合紧密, 结合水难于脱附, 造成蛋白质在其表面的吸附需要克服更高的能量, 不利于蛋白质的吸附.     

Surface dilational moduli of poly (ethylene oxide), poly (methyl methacrylate), and their blend films

Surface dilational moduli of poly (ethylene oxide) (PEO), poly (methyl methacrylate) (PMMA), and compatible PEO/PMMA blend films spread at the air-water interface were investigated as a function of surface concentration. The surface dilational modulus of an expanded PEO film increased as the surface concentration increased to 0.4mg/m(2), which corresponds to the limiting surface area of PEO. After peaking at this value, the surface dilational modulus decreased with an increase in the PEO concentration. Lissajous orbits of PEO films exhibited positive hysteresis loops for all surface concentration ranges. On the other hand, the surface dilational modulus of a condensed PMMA film steeply increased as the surface concentration increased. Lissajous orbits of PMMA films changed from positive hysteresis loops to negative loops at the surface concentration at which the surface pressure reached in the plateau region. The magnitude of the surface dilational modulus of PMMA was larger than that of PEO at a fixed surface concentration. The surface dilational moduli of the PEO/PMMA blend films increased with the total surface concentration and their magnitudes were less than those of the individual PMMA films and larger than those of the individual PEO films at fixed surface concentrations. Lissajous orbits of the PEO/PMMA blend films also changed from positive hysteresis loops to negative loops beyond the surface concentration at which the plateau surface pressure of PEO was attained.     

Surface Dilatational Elasticity of Pulmonary Surfactant Solutions in a Wide Range of Surface Tensions

This work is devoted to the dynamic properties of adsorption films of pulmonary surfactant and a spread monolayer of dipalmitoylphosphatidylcholine, which is the main component of the mixed surfactant. The surface dilatational elasticity of the aforementioned systems has been determined using a recently proposed approach, which is based on the analysis of a response of a system to large deformations of a surface, and a modified Langmuir trough, which excludes solution leakage under barriers. At low surface tensions (below 30 mN/m) corresponding to those in pulmonary alveoles, the surface elasticity of a pulmonary surfactant adsorption film is half that of the spread dipalmitoylphosphatidylcholine monolayer. This may, in the former case, be related to the displacement of components with lower surface activity from the surface upon film compression.     

Interactions between hen egg-white lysozyme, PEG2,000, and PLA50 at the air-water interface

In this paper, we compared the efficiency of polymer films, made of a poly(ethylene glycol) (PEG2,000)/poly(d,l-lactide) (PLA50) mixture, or a PEG2,000-PLA50 copolymer, to prevent adsorption of a model protein, the hen egg-white lysozyme (HEWL), at the air-water interface. This was achieved by analyzing the surface pressure/surface area curves, and the X-ray reflectivity data of the polymer films spread on a Langmuir trough, obtained in absence or in presence of the protein. For both the mixture and the copolymer, the amount of protein adsorbed at the air-water interface decreases when the density of the polymer surface coverage increases. It was shown that even in a condensed state, the polymer film made by the mixture can not totally prevent HEWL molecules to adsorb and penetrate the polymer mixed film, but however, protein molecules would not be directly exposed to the more hydrophobic phase, i.e. the air phase. It was also shown that the configuration adopted by the copolymer at the interface in its condensed state would prevent adsorption of HEWL molecules for several hours; this would be due in particular to the presence of PEG segments in the interfacial film.     

Surface modification of HDPE, PP, and PET films with KMnO4/HCl solutions

Surface modification of high-density-polyethylene (HDPE), polypropylene (PP), and poly(ethylene terephthalate) (PET) films was promoted by potassium permanganate solutions in HCl acidic medium using eight conditions by varying time, temperature, and oxidative solution concentration. This oxidation system introduced different amounts of carbonyl-carboxyl and hydroxyl groups onto the polymer surfaces. Drop water contact angle, FTIR, TGA, and SEM were used to assess oxidation efficiency and the surface changes suffered by the polymer film. The hydrophilicity of films obtained by contact angle was analyzed using a 2³ factorial design in Design-Expert^® program to obtain the main effects, the variance, and the interaction between the effects in action in the oxidation process.     

Size effects on miscibility and glass transition temperature of binary polymer blend films

After determining the size dependent miscibility of binary polymer blend films using molecular dynamics simulation and thermodynamics, the size dependent glass transition temperatures Tg(w,D) of several polymer blend films in miscible ranges are determined by computer simulation and the Fox equation where w is the weight fraction of the second component and D denotes thickness of films. The Tg(w,D) function of a thin film can decrease or increase as D decreases depending on their surface or interface states. The computer simulation results are consistent with available experimental results and theoretical results for polymer blend films of PPO/PS [poly(2,6-dimethyl-1,4-phenylene oxide)/polystyrene] and stereoregular PMMA/PEO [poly(methyl methacrylate)/poly(ethylene oxide)]. The physical background of the above results is related to the root of mean square displacement of thin films in their different regions.     

Surface rheology of PEO-PPO-PEO triblock copolymers at the air-water interface: comparison of spread and adsorbed layers

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 approximately 0.7 mg/m2. 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 A(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.     

Investigations on poly(methyl methacrylate)-poly(ethylene oxide) hybrid polymer electrolytes with dioctyl phthalate, dimethyl phthalate and diethyl phthalate as plasticizers

Plasticizers can be used to change the mechanical and electrical properties of polymer electrolytes by reducing the degree of crystallinity and lowering the glass transition temperature. The transport properties of gel-type ionic conducting membranes consisting of poly(ethylene oxide) (PEO), poly(methyl methacrylate) (PMMA), LiClO₄ and dioctyl phthalate, diethyl phthalate or dimethyl phthalate (DMP) are studied. The polymer films are characterized by X-ray diffraction, Fourier transform infrared and impedance spectroscopic studies. It is found that the addition of DMP as the plasticizer in the PEO-PMMA-LiClO₄ polymer complex favours an enhancement in ionic conductivity. The maximum conductivity value obtained for the solid polymer electrolyte film at 305 K is 3.529×10^{– 4} S cm^–1. Electronic Publication     

Adsorption of water-soluble polymers with surfactant character. Dilational viscoelasticity

A brief summary of dilational surface viscoelatic properties of spread and adsorbed surfactant polymer films at the air-water interface is reported. The viscoelastic moduli have been measured as a function of frequency and surface pressure. The combination of several techniques, oscillating drop and barrier experiments and electrocapillary waves (ECW), has allowed us to investigate a broad frequency range. The dynamic elasticity epsilon shows a slight change with frequency and a noticeable pressure dependence for both kinds of monolayers. In the spread films, elasticity increases steeply with surface pressure, and reaches a constant value before the polymer begins to dissolve into the bulk. On the other hand, the adsorbed films exhibit a pronounced elasticity maximum, followed by a considerable decay when a loose surface structure is formed. The position of the maximum depends on the polymer chemical composition and molecular weight. The results on the overlapping surface pressure range confirm the dynamic equivalence of spread and adsorbed monolayers. At low surface concentration, the agreement between static and dynamic elasticity is quite satisfactory, but the values diverge considerably at higher surface pressures. The loss modulus omegakappa decreases monotonically with increasing omega, becoming zero (it can even take apparent negative values) for the highest frequencies. The frequency dependence of the elasticity has been well described by the diffusive control model of Lucassen-van den Tempel (LVT). However, its predictions for omegakappa do not coincide with the experimental data. The differences between experimental and theoretical values increase at low frequencies.     

Surface characteristics of a self-polymerized dopamine coating deposited on hydrophobic polymer films

This study aims to explore the fundamental surface characteristics of polydopamine (pDA)-coated hydrophobic polymer films. A poly(vinylidene fluoride) (PVDF) film was surface modified by dip coating in an aqueous solution of dopamine on the basis of its self-polymerization and strong adhesion feature. The self-polymerization and deposition rates of dopamine on film surfaces increased with increasing temperature as evaluated by both spectroscopic ellipsometry and scanning electronic microscopy (SEM). Changes in the surface morphologies of pDA-coated films as well as the size and shape of pDA particles in the solution were also investigated by SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface roughness and surface free energy of pDA-modified films were mainly affected by the reaction temperature and showed only a slight dependence on the reaction time and concentration of the dopamine solution. Additionally, three other typical hydrophobic polymer films of polytetrafluoroethylene (PTFE), poly(ethylene terephthalate) (PET), and polyimide (PI) were also modified by the same procedure. The lyophilicity (liquid affinity) and surface free energy of these polymer films were enhanced significantly after being coated with pDA, as were those of PVDF films. It is indicated that the deposition behavior of pDA is not strongly dependent on the nature of the substrates. This information provides us with not only a better understanding of biologically inspired surface chemistry for pDA coatings but also effective strategies for exploiting the properties of dopamine to create novel functional polymer materials.     

Surface forces in foam films from ABA block copolymer: a dynamic method study

The thinning of foam films from aqueous solutions of an ABA triblock copolymer of polyethylene oxide and polypropylene oxide (average molecular weight 14,000 g/mol) is studied experimentally. The dependence of the surface forces on film thickness is obtained by the dynamic method of Scheludko and Exerowa.The total surface force measured in foam films (radius 60–70 m) from 10^–5 M (0.014 wt%) polymer solution with 0.1 M NaCl is positive at thicknesses from about 800 down to 460 . The electrostatic repulsion is negligible while the contribution of van der Waals attraction is small (within 15%). Therefore a positive surface force component predominates. Most probably it arises from steric interactions between the hydrophilic polyethylene oxide tails of the polymer. The dynamic method appears to be a suitable technique for exploring the stabilization of foam films from ABA copolymers.     

Thermal diffusivity of polymer films by pulsed photothermal radiometry

We have developed a pulsed photothermal radiometry technique for determining the thermal diffusivity parallel to the surface of a polymer film that involves flashing a line-shaped laser beam on the surface of the sample at right angle to its length, and monitoring the temperature change with time at a distance from the line source using an infrared detector. Combining this with our previous laser-flash radiometry method for thermal diffusivity measurement perpendicular to the film surface, we can now measure the thermal diffusivity of a polymer film along all directions. These two techniques have been used to study uniaxially and biaxially oriented poly(ethylene terephalate) and uniaxially drawn ultrahigh molecular weight polyethylene films. For uniaxially oriented poly(ethylene terephalate), the thermal diffusivity along the draw direction is substantially higher than that in the transverse direction, which in turn, is slightly higher than that in the thickness direction. For a polyethylene film with a draw ratio of 200, the axial thermal diffusivity is extremely high, being about five times that of stainless steel. The anisotropy of the thermal diffusivity of this film exceeds 90. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1621–1631, 1997     

Surface interpenetrating networks of polyacrylamide in poly(ethylene terephthalate) as a means of surface modification

Surface interpenetrating network (IPN) polymers are emerging hybrid materials in which the surface of existing polymers can be modified to preserve their chemical structure and bulk properties. A detailed structural characterization of poly(ethylene terephthalate) (PET) thin films on nanoscopically flat silicon wafers has been carried out by Scanning Probe Microscopy (SPM) and X-ray photoelectron spectroscopy (XPS). Examination of the surface of spin-coated annealed PET film by the SPM in tapping mode revealed a two-phase structure. One phase appeared as a dense crystalline fraction of the polymer while the other was identified as amorphous. These findings were supported by Differential Scanning Calorimetry (DSC), which recognized the crystallinity of annealed PET film at 30%. Modification of the PET surface with interpenetrating polyacrylamide (PAM) increased the roughness of the surface with uniform properties. The depth profiling with XPS revealed that PAM interpenetration extended down to 7.2 nm, confirming a three-dimensional character of the polymer modification, with a relative mass concentration of PAM at about 30.7% in the IPN interface.     

Surface properties of bottle-brush polyelectrolytes on mica: effects of side chain and charge densities

Surface properties of a series of cationic bottle-brush polyelectrolytes with 45-unit-long poly(ethylene oxide) side chains were investigated by phase modulated ellipsometry and surface force measurements. The evaluation of the adsorbed mass of polymer on mica by means of ellipsometry is complex due to the transparency of mica and its birefringence and low dielectric constant. We therefore employed a new method to overcome these difficulties. The charge and the poly(ethylene oxide) side chain density of the bottle-brush polymers were varied from zero charge density and one side chain per segment to one charge per segment and no side chains, thus spanning the realm from a neutral bottle-brush polymer, via a partly charged brush polyelectrolyte, to a linear fully charged polyelectrolyte. The adsorption properties depend crucially on the polymer architecture. A minimum charge density of the polymer is required to facilitate adsorption to the oppositely charged surface. The maximum adsorbed amount and the maximum side chain density at the surface are obtained for the polymer with 50% charged segments and the remaining 50% of the segments carrying poly(ethylene oxide) side chains. It is found that brushlike layers are formed when 25-50% of the segments carry poly(ethylene oxide) side chains. In this paper, we argue that the repulsion between the side chains results in an adsorbed layer that is non-homogeneous on the molecular level. As a result, not all side chains will contribute equally to the steric repulsion but some will be stretched along the surface rather than perpendicular to it. By comparison with linear polyelectrolytes, it will be shown that the presence of the side chains counteracts adsorption. This is due to the entropic penalty of confining the side chains to the surface region.     

Electrosurface properties of poly(ethylene terephthalate) films irradiated by heavy ions and track membranes based on these films

The streaming potential method realized in a slit-like setup using 10^–4–10^–2 mol/L KCl solutions has been employed to study the electrosurface characteristics of poly(ethylene terephthalate) films, both initial and irradiated by heavy ions, as well as track membranes with pore sizes of 50 and 210 nm made from these films. Their ζ potentials and surface charges have been calculated. The data obtained suggest that irradiation of the polymer films by heavy ions reduce the ζ potential and surface charge. However, as a result of film etching during the preparation of the track membranes, the ζ potential and surface charge increase and exceed the corresponding values for the initial film.