Premium
Solvent diffusion in silica/poly[styrene‐ co ‐(acrylic acid)] core‐shell microspheres by pulsed field gradient NMR techniques
Author(s) -
Jiang Binbo,
Yang Yong,
Du Lijun,
Mattea Carlos,
Wang Jingdai,
Stapf Siegfried,
Yang Yongrong
Publication year - 2014
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.40161
Subject(s) - pulsed field gradient , polymer , acrylic acid , materials science , diffusion , polymer chemistry , styrene , chemical engineering , membrane , polystyrene , analytical chemistry (journal) , chemistry , copolymer , chromatography , composite material , thermodynamics , biochemistry , physics , engineering
Polymer‐coated SiO 2 particles are prepared by precipitation of poly[styrene‐ co ‐(acrylic acid)] on SiO 2 microspheres through an improved phase inversion method. The diffusion resistance of the polymer membrane was considered to be the critical reason for producing tailor‐made polyethylene by catalysts supported on these polymer‐coated particles. This paper employs pulsed field gradient NMR (PFG‐NMR) to distinguish diffusion of n ‐hexane in different regimes, i.e., in the space between each particle, the pores in SiO 2 and the polymer shell, by their respective diffusion coefficients. By varying the observation time, the time scale of the molecular exchange is discussed. A three‐region ansatz was used to interpret the exchange and diffusion in polymer‐coated SiO 2 system, and was compared with results acquired with noncoated particles. At long diffusion times, the mean‐squared displacement, and thus the averaged self‐diffusion coefficient, of hexane in the system of polymer‐coated SiO 2 particles is significantly reduced. The PSA membrane is identified as an efficient barrier against molecular exchange between the pores in SiO 2 and the intraparticle space. Consistently, the relaxation measurements indicated that the mobility of n ‐hexane molecules, especially the rotation of n ‐hexane, was limited by the PSA membrane. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40160.