Reversal of the isotopic effect in the surface behavior of binary polymer blends
- Department of Materials Science and Engineering, Polymer Science Program, Pennsylvania State University, University Park, Pennsylvania (United States)
- IBM Almaden Research Center, 650 Harry Road, San Jose, California (United States)
We report neutron reflectivity measurements on the surface behavior of isotopic polystyrene blends of symmetric and disparate molecular weights near an air surface. For the symmetric blends we find, in agreement with past findings, that the segments of the deuterated polymer always partition to the air surface. These results, which are driven purely by energetic effects, can then be modeled in the framework of a mean-field lattice theory with a constant surface energy difference parameter. In contrast, for the asymmetric blends we find that the segments of either polymer can partition to the surface, and the controlling variable is the disparity in the molecular weights of the two components. These new results, which cannot be predicted with the constant density lattice models utilized for symmetric blends, can be modeled if one balances the energetic preference of placing the deuterated segments near the surface with entropic effects, which are caused by the presence of a density gradient at the air surface, preferring the surface segregation of the short chains. These findings emphasize the need for the inclusion of free-volume effects when modeling the segregation to a free surface, and we show that a recent mean-field compressible lattice model does capture these effects adequately.
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 6771417
- Journal Information:
- Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 98:5; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360602 -- Other Materials-- Structure & Phase Studies
360606* -- Other Materials-- Physical Properties-- (1992-)
AIR
ASYMMETRY
BINARY MIXTURES
COHERENT SCATTERING
COMPRESSIBILITY
DEUTERIUM COMPOUNDS
DIFFRACTION
DISPERSIONS
FLUIDS
GASES
HYDROGEN COMPOUNDS
INTERFACES
ISOTOPE EFFECTS
ISOTOPES
MATERIALS
MEAN-FIELD THEORY
MECHANICAL PROPERTIES
MIXTURES
MOLECULAR WEIGHT
NEUTRON DIFFRACTION
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PETROCHEMICALS
PETROLEUM PRODUCTS
PLASTICS
POLYMERS
POLYOLEFINS
POLYSTYRENE
POLYVINYLS
SCATTERING
SEGREGATION
SURFACE PROPERTIES
SYNTHETIC MATERIALS
WETTABILITY