Surface Segregation In Blends Research Articles

Surface segregation in blends of miscible amorphous polymers

The isothermal luminescence decay kinetics in near-surface nanolayers of plasma-activated bulk samples of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their miscible blends with weight ratios PS/PPO of 75/25 and 50/50 has been studied at 77 K. The intensities of isothermal luminescence (I) of homopolymer and blend surfaces have been compared. It has been found that the ratio between the luminescence intensities for PS and PPO (I(PS)/I(PPO)) may be as high as 50, while the luminescence intensities for the PS–PPO blends are close to I(PPO). The results obtained indicate that the PPO concentration in the surface layers of the blends is higher than that in the bulk.

Solvent‐ and interface‐induced surface segregation in blends of isotactic polypropylene with poly(ethylene‐co‐propylene) rubber

AbstractThe surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004

Effectiveχ and surface segregation in blends of star and linear polystyrene

The existence in blends of linear and star branched polystyrenes (PS) of a bulk thermodynamic interaction due to differences in macromolecular architecture has been demonstrated with small angle neutron scattering measurements. It has also been demonstrated that a regularly star-branched polystyrene material segregates preferentially to the surface of a blend of star and linear molecules.

Surface Enrichment in a Miscible Random Copolymer Blend: Influence of Polydispersity and Architecture

Neutron reflectivity and low-energy forward-recoil spectrometry were used simultaneously to monitor surface segregation in blends of poly(styrene-ran-acrylonitrile), dSAN23 and SAN27, having 23 and 27 wt % AN, respectively. Because of its lower AN content, dSAN23 was found to partition at the polymer/air interface, in agreement with the work of Mansfield et al. (Physica B 1991, 173, 207) and Kim et al. (Polymer 1995, 36, 2427). In contrast to the previous studies, this work explores surface segregation at high dSAN23 bulk volume fractions, φ∞ (i.e., φ∞ > 0.50). New results include the observation of a maximum dSAN23 surface excess (∼75 A) near φ∞ ≈ 0.35 and a dSAN23 surface volume fraction that approaches 1, rather than 0.75, as φ∞increases to 1. The dSAN23 profile deviates from the exponential profile predicted by Schmidt−Binder and self-consistent mean-field (SCMF) models. For φ∞ > 0.50, the profile displays a surface flattening not observed at low φ∞. The SCMF model is extended to account for polymer p...

Surface enrichment in thin films of PVC and PMMA

AbstractThe surface enrichment in thin bilayer films of poly(vinyl chloride) (PVC) and deuterated poly(methyl methacrylate) (PMMAd) was studied by neutron reflectometry, X‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS). In a layer system, where the PVC film is placed on top of a thin PMMA film, the PMMA chains migrate to the surface, although annealing of the films is performed below the glass transition temperature of PMMA. In addition, the surface segregation in blends of these materials was studied by XPS and SSIMS. In all cases PMMA is enriched at the surface. Results from the different techniques, probing different, sample depths, are consistent, if an exponential concentration profile of PMMAd at the surface is assumed. Concentration profiles at the surface are discussed with respect to theoretical models and diffusion coefficients are estimated.

Surface Segregation in Blends of Polystyrene and Perfluorohexane Double End Capped Polystyrene Studied by Static SIMS, ISS, and XPS

The surface composition of styrene polymers capped at one or both ends by perfluoro groups has been determined by ISS, XPS, and static SIMS. The homopolymers, with M(n) 29000-59000, have an excess of the perfluoro end groups at the surface that is inversely proportional to the chain length and is commensurate with one or both ends having perfluoro groups. In contrast, double perfluoro end capped homopolymers of M(n) similar to 9000 have only one of the perfluoro groups at the surface. In blends of perfluoro end capped styrene with hydrogen-terminated styrene, the fluorinated end cap causes the former to segregate to the surface. Nevertheless, the extents of segment segregation of single and double perfluoro end capped polymers of weights 29000-59000 are similar. For blends of perfluoro-capped polymer with M(n) 9000 in styrene of M(n) 30000, the molecular weight and perfluoro end caps both strongly influence the segment segregation. The concentration of fluorine at the surface of all the blends may be estimated from the homopolymer XPS data and the blend monomer composition determined by static SIMS.

Surface segregation in blends of styrene-acrylonitrile copolymers

We investigated the kinetic as well as thermodynamic aspects of surface segregation in blends of random copolymers of styrene and acrylonitrile (SAN) with different acrylonitrile contents (22.5 and 27.2 wt%) annealed at 163°C. A comparison was made with equilibrium data collected by Mansfield et al. on the same system using neutron reflectivity. The lower-AN-content SAN, which is labelled with deuterium (d-SAN), was observed to segregate to the vacuum/polymer interface. Time-of-flight and conventional forward recoil spectrometry were used to determine the depth profile of the deuterated component. The apparent diffusion coefficient D app controlling the segregation kinetics at a bulk volume fraction ω of d-SAN of 0.34 was obtained. It was smaller by a factor of approximately 1.5 than the mutual diffusion coefficient D app at =0.34 calculated without taking the expected thermodynamic slowing of diffusion into account. However, D app was larger than the measured D at =0.34 by a factor of approximately 3. The mean-field theory of Schmidt and Binder was employed to extract the Flory interaction parameter χ , which was found to be smaller than but close to its critical value χ c . The value of D computed using this χ value was in good agreement with the independently measured D at= 0.34.

Surface Segregation in Blends of Hydrogenous Polystyrene and Perfluorohexane End-Capped Deuterated Polystyrene, Studied by SSIMS and XPS

End capping a polystyrene with perfluorooctyldimethylchlorosilane is shown to strongly influence the surface segregation in blends of deuterated and hydrogenous polystyrenes. The surface composition, determined by SSIMS, of a low molecular weight blend containing 0.14 mole fraction deuterated polystyrene, end capped by proton donation from methanol, was only slightly increased compared to the bulk value, even after annealing for several days at 150°C. A low molecular weight blend containing the fluoro-end-capped deuteropolymer showed immediate surface segregation, which increased to give ca. 60% deuterated polymer at the surface after annealing

Surface segregation in blends containing poly(dimethylsiloxane)-polystyrene block copolymers

The surface composition of polystyrene blends containing poly(dimethylsiloxane)-polystyrene block copolymers have been analyzed using X-ray photoelectron spectroscopy (XPS), contact angle measurements, and time-of-flight secondary ion mass spectrometry (TOFSIMS). The three techniques showed the surface of the blend samples to be identical to pure poly(dimethylsiloxane) homopolymer, despite the fact that the systems each contained only a 2% bulk concentration of siloxane. The high surface sensitivity of TOFSIMS—which probes the samples to depths of a few angstroms—indicates an enrichment of-Si(CH3)3 groups at the surface. These are the terminal groups of the PDMS part of the block. Their enrichment at the surface of the samples is presumably due to their low surface energy, in addition to the tendency for end groups to be at the surface due to free volume considerations.

Effect of annealing time, film thickness, and molecular weight on surface enrichment in blends of polystyrene and deuterated polystyrene

SERS was used to investigate surface segregation in blends of polystyrene (PS) and deuterated polystyrene (DPS) by evaporating silver island films onto blend films before and after annealing at a temperature above the UCST. When blends consisted of PS and DPS with the same molecular weights, DPS segregated to the free surface during annealing at a temperature above the UCST. Moreover, the extent of surface segregation increased with increasing annealing time, the film thickness of the blends and the molecular weight of polymers in the blends

Surface segregation in blends of polystyrene and deuterated polystyrene

Surface-enhanced Raman scattering (SERS) has been used to investigate surface segregation in blends of high molecular weight polystyrene (PS) and deuterated polystyrene (DPS) (both having molecular weight 1 950 000) following annealing at temperatures above the upper critical solution temperature (UCST). Before annealing, the composition of the surface regions of the blends was similar to that of the bulk; after annealing, DPS segregated to the surface and the extent of surface segregation was related to the amount of DPS in the blends

Analysis of Surface Segregation in Blends of Acrylate Copolymer with Fluoro-Copolymer

The surface segregation of poly(2-ethylhexyl acrylate-co-acrylic acid-co-vinyl acetate) P(2EHA-AA-VAc)/poly(vinylidene fluoride-co-hexafluoro acetone) P(VDF-HFA) blends was investigated by FT IR in surface analysis, the miscibility of blends examined by both the Prigogine-Flory-Patterson’s theory and the thermo-photometry and surface tension γs. From 1 to ∼2μm of the surface in P(2EHA-AA-VAc)/P(VDF-HFA) (50/50) blend, the variation in P(VDF-HFA) concentration with increasing distance from the surface was observed by use of ATR-FT IR with incidence angle dependence. It was suggested that the surface segregation of P(VDF-HFA) took place in the blends. The P(2EHA-AA-VAc)/P(VDF-HFA) blends were revealed to be heterogeneous systems by the results of state parameters and thermo-photometry. The γs of P(2EHA-AA-VAc) and P(VDF-HFA) were evaluated according to Prigogine’s corresponding state theory, as extended for surfaces by Patterson and co-workers. The values of γs of P(2EHA-AA-VAc) and P(VDF-HFA) were 28.3 and 20.4 (dyn cm−1), respectively. Therefore, it was expected that surface segregation in P(2EHA-AA-VAc)/P(VDF-HFA) blends may occur, when the blend is immiscible and difference in γs between components is large.

Surface segregation of blends

Surface segregation of blends