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  • 1
    Electronic Resource
    Electronic Resource
    Surface phase behavior in binary polymer mixtures. I. Miscibility, phase coexistence, and interactions in polyolefin blends (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8786-8794 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have used composition depth profiling of polymer bilayers, based on nuclear reaction analysis, to determine miscibility, phase coexistence, and critical temperatures in mixtures of random olefinic copolymers of mean composition E1−x/EEx; here E is the ethylene group −(C4H8)−, EE is the ethylethylene group −[C2H3(C2H5)]−, and one of the copolymers is partially deuterated. The components in each binary mixture have different values x1,x2 of the EE fraction. Using a simple Flory–Huggins mixing model, our results enable us to extract an interaction parameter of the form χ(x1,x2,T)=A(x1,x2)/T, where for given x1,x2, A is a constant. Calculated binodals using this form fit our measured coexistence curves well, while allowing χ a weak composition dependence improves the fit further. Within the range of our parameters, our results suggest that in such binary polyolefin mixtures the interaction parameter increases roughly linearly with the extent of chemical mismatch expressed as the difference in degree of ethyl branching between the two components. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471568
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  • 2
    Electronic Resource
    Electronic Resource
    Surface phase behavior in binary polymer mixtures. II. Surface enrichment from polyolefin blends (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8795-8806 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using nuclear reaction analysis, we have measured the enrichment by one of the components at the surface of a binary mixture of random olefinic copolymers, with components of monomer structure E1−x1EEx1 and E1−x2EEx2. Here E and EE are the linear ethylene and branched ethylethylene groups (C4H8) and [C2H3(C2H5)], respectively, and x represents the fraction of the EE group randomly distributed on the chains. We examined 12 different couples covering a range x=0.38–0.97. The mixtures, whose thermodynamic behavior was established in our earlier paper, were cast in the form of films on both a silicon and on a gold-covered silicon surface, and were investigated in the one-phase region of the binodal in the vicinity of the critical temperature. We find that it is always the more flexible component—the one with a shorter statistical step length, corresponding to the higher ethylethylene fraction (higher x)—that is enriched at the polymer/air surface. Within our resolution neither component is enriched at the polymer/solid interface. These results show clearly that enthalpic rather than entropic factors dominate the surface potential driving the surface enrichment. For two of the mixtures we determined the excess of the surface-preferred species as a function of mixture composition along an isotherm in the one-phase region of the binodal. A consistent description of our data in terms of a mean-field model is provided by including in the surface potential a term in the mixture composition gradient at the polymer surface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471569
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  • 3
    Electronic Resource
    Electronic Resource
    The effects of confinement and surface interactions on coexistence in a binary polymer mixture (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 5229-5238 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the composition-distance profile across a film consisting of two thin layers (200–600 nm) of a model binary isotopic mixture of deuterated polystyrene (dPS) and protonated polystyrene (hPS), coexisting with each other near their equilibrium compositions below the critical temperature for phase demixing for this pair. Profiles were determined normal to the silicon wafer on which the bilayer is mounted using nuclear reaction analysis, both for an uncoated silicon surface and for one coated with a gold layer. Measurements reveal that when both layers are thick relative to the characteristic width w (∼100 nm) of the interfacial region between them, the coexisting compositions about the interface are close to their bulk values as determined earlier for this system. When the dimensions of the layers are made comparable with w, however, interactions with the confining surfaces may significantly modify the composition profile of the coexisting layers about the interface. This effect is marked at the polymer/silicon interface as a result of its interactions with one of the components (dPS), but is absent for a gold-coated surface in an identical geometry due to the much weaker influence of the surface. Our results are discussed in detail in terms of mean-field models of mixing in polymeric mixtures, and enable quantitative determination (using a Cahn construction approach) of the interaction parameters both at the polymer–air and polymer–silicon interfaces. Though we are not able to calculate in a completely a priori fashion the coexistence profiles as a function of the film thickness, we propose an approximate approach which provides good agreement of calculated composition profiles with those determined experimentally over the range of parameters in our experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463821
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