Neutron Reflectometry Study of Surface Segregation in an Isotopic Poly(ethylenepropylene) Blend: Deviation from Mean-Field Theory

Norton, Laura J.; Krämer, Edward J.; Bates, Frank; Gehlsen, Mark D.; Jones, Richard; Karim, Alamgir; Felcher, G. P.; Kleb, R.

doi:10.1021/ma00129a022

Cited by 45 publications

(75 citation statements)

References 9 publications

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“…These results are consistent with the predictions from a general linear response theory by Wu and Fredrickson for the effects of architectural asymmetry on binary blend surface thermodynamics [13]. While surface segregation involves entropic considerations including chain stretching and compositional variations [4,5,21,22], the linear response theory suggests these complex contributions to the driving force for segregation can be simply understood in terms of effective surface potentials for the ends and branch points. Surface segregation due to branching was observed experimentally by Walton and co-workers [14] using neutron reflectivity (NR) of blends of linear poly (methyl methacrylate) (PMMA), and branched random copolymer of methyl methacrylate and methoxy poly(ethylene glycol) monomethacrylate [P(MMA-rMnG)].…”

supporting

confidence: 87%

Surface segregation driven by molecular architecture asymmetry in polymer blends

Lee

Peri

et al. 2014

Phys. Rev. Lett.

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The contributions of chain ends and branch points to surface segregation of long-branched chains in blends with linear chains have been studied using neutron reflectometry and surface-enhanced Raman spectroscopy for a series of novel, well-defined polystyrenes. A linear response theory accounting for the number and type of branch points and chain ends is consistent with surface excesses and composition profile decay lengths, and allows the first determination of branch point potentials. Surface excess is determined primarily by chain ends with branch points playing a secondary role.

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supporting

confidence: 87%

Surface segregation driven by molecular architecture asymmetry in polymer blends

Lee

Peri

et al. 2014

Phys. Rev. Lett.

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“…A prediction of the density variation proximate to the surface is present in an earlier work by Cohen and Muthukumar 16 that contains a more detailed theoretical description of the surface free energies f s,i . Recent experiments by Norton et al 7 for surface segregation in PEP/ dPEP blends exhibit a flattening of the composition profile 17 over a range of roughly one-half the bulk correlation length, a feature not present in the earlier theories. A possible contribution to this near surface density flattening could arise from the competition between density variations proximate to the surface and from disparities in the surface free energy parameters f s,i driving the surface segregation, a mechanism requiring a ''compressible'' theory.…”

Section: Introductionmentioning

confidence: 80%

Analytic theory of surface segregation in compressible polymer blends

Freed

1996

The Journal of Chemical Physics

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We present an analytical theory for the competing influences of polymer-surface and polymerpolymer interactions, density and composition variations, and blend asymmetries on the surface profiles of a multicomponent polymer blend near an interacting, impenetrable interface. The theory is explicitly applied in the limit of small continuum model polymer-surface interaction parameters, a limit which still enables treating all qualitative behaviors of polymers that individually tend either to aggregate toward or to segregate from the surface. The formulation is based on an analytic combined self-consistent field-density functional theory for inhomogeneous polymer systems. The theory describes the compressible polymer system with a generic Gaussian chain-random mixing type model, which in the bulk phase reproduces a Sanchez-Lacomb-type description of the bulk thermodynamics. The analytic expressions for the density profiles, surface excesses, surface densities, and surface correlation lengths are all presented explicitly for binary compressible systems, but we note how to make the trivial extension to more components. The surface excess and surface correlation length are shown to diverge along the bulk phase spinodal, in rough accord with the increases found in recent experiments by Genzer and Composto. The relation between the continuum model interaction parameters and microscopic ͑e.g., lattice-model-type͒ interaction parameters is used to understand recent observations of a surface free energy that displays a higher than quadratic dependence on the surface composition and of the strong surface segregation exhibited by isotopic polymer blends.

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“…The experimental (b=V) profile is basically in good agreement with the predicted one but the former is slightly deviated from the exponential functional form predicted by the mean-field theory and is flattened near the surface. This phenomenon has been observed in other blend film surfaces, 8 however, explicit reasons for this phenomenon have not been clarified. There may be three reasons; one is the influence of surface confinement on local chain conformation of dPT and another is strong segregation of hydrophobic TMS groups on phenyl rings whose (b=V) value is higher than the other chemical groups due to deuteriums, and the other is the effect of the roughness of the film surfaces.…”

Section: Concentration Profile Of Pt/pi Blend Filmmentioning

confidence: 83%

Temperature Dependence of Surface Segregation in Miscible Polymer Blend of Poly(4-trimethylsilylstyrene)/Polyisoprene

Kawaguchi

Ohya

Torikai

et al. 2007

Polym J

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ABSTRACT:Surface segregation behavior in miscible polymer blend thin film of poly(4-trimethylsilylstyrene)(PT)/polyisoprene (PI) was investigated as a function of temperatures on the basis of contact angle and neutron reflectivity measurements. For all temperatures employed, PT, which is a lower surface free energy component, is segregated at the surface of the blend film due to the requirement for minimizing the total free energy of the system. A concentration profile near the blend film surface is in good agreement with the mean-field prediction at 373 K and 393 K, being much lower than the lower critical solution temperature (LCST) for the blend in bulk. It was confirmed that decay length, , and surface excess amount, z Ã , increase with increasing temperature. On the other hand, a concen- Controlling surface and interfacial structures of soft materials is important to many applications such as coating, wetting, adhesion, and lubrication etc. Many researchers have investigated surface segregation phenomena in miscible polymer blends theoretically and experimentally. [1][2][3][4][5][6][7][8][9][10][11][12][13] In miscible mixtures of two polymers having equivalent degree of polymerization, a lower surface energy component is known to be enriched at surface due to the requirement for minimization of the total free energy of the system. The concentration profile near the surface for such mixtures can be well expressed by mean-field and self-consistent mean-field models.1-7 This can be understood by taking into account thermodynamics at the surface.In general, a rubbery component is segregated at the surface from glassy/rubbery polymeric blends at room temperature. It is well recognized that polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend is the typical example in which the rubbery component, PVME, is preferentially segregated at the surface [14][15][16][17][18][19][20] even though both components are miscible each other in bulk. [21][22][23] Since a rubbery component possesses a lower density and/or a larger entropy, the surface free energy is relatively low in comparison with the glassy component unless any other enthalpic interactions. In reality, to our knowledge, no reports are known for the glassy/rubbery blends in which the glassy component is segregated at the surface.We have already found that poly(4-trimethylsilylstyrene) (PT), which is a glassy polymer as one of the PS derivatives, and polyisoprene (PI) with dominant 1,2-and 3,4-microstructures form a miscible polymer blend though PS and PI are a typical immiscible polymer blend. 24 Based on the small angle neutron scattering measurement and microscopic observation, it has been confirmed that the PT/PI blend exhibits a lower critical solution temperature (LCST) type phase diagram and is miscible at room temperature. These results indicate that miscibility of the blends can be drastically changed by introducing trimethylsilyl (TMS) groups into phenyl rings of PS. Thus, from the viewpoint of surface chemistry, PT is totally different from PS owing...

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Neutron Reflectometry Study of Surface Segregation in an Isotopic Poly(ethylenepropylene) Blend: Deviation from Mean-Field Theory

Cited by 45 publications

References 9 publications

Surface segregation driven by molecular architecture asymmetry in polymer blends

Surface segregation driven by molecular architecture asymmetry in polymer blends

Analytic theory of surface segregation in compressible polymer blends

Temperature Dependence of Surface Segregation in Miscible Polymer Blend of Poly(4-trimethylsilylstyrene)/Polyisoprene

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