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We have synthesized doubly thermosensitive core-shell microspheres composed of chemically cross-linked poly(N-n-propyl acrylamide-co-styrene) (P(nPA-co-S)) with different styrene contents as the core and linear poly(N,N-diethyl acrylamide) (PDEA), poly(N-isopropyl acrylamide) (PiPA), or poly(N-isopropyl methacrylamide) (PiPMA) as the shells. The morphologies and swelling properties of the core and the core-shell microspheres have been studied. The P(nPA-co-S) copolymers have a similar volume phase transition temperature regardless of the styrene content, indicating a two-layer structure in the microspheres with a PS-rich inner core and a PnPA-rich outer layer resulting from soap-free emulsion polymerization in water. Upon the addition of the second shell composed of linear thermosensitive polymers, the core-shell microspheres display a two-step shrinking behavior when heated. The P(nPA-co-S) core exhibits a volume phase transition temperature at 13-15 degrees C, while the shells of PDEA, PiPA, and PiPMA have volume phase transition temperatures at 28, 32, and 42 degrees C, respectively. The core-shell microspheres are composed of three layers and possess two volume phase transition temperatures. 相似文献
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Bile acid-based polymers are promising new materials for biomedical applications. The determination of their molar mass, as for other novel polymers, has been difficult, due to the lack of suitable standards for size exclusion chromatography (SEC). In order to solve this problem, a family of main-chain bile acid-based oligo-esters has been synthesized by acyclic diene metathesis to be used as analogues in such analysis. These oligomers have been characterized by SEC, MALDI-TOF mass spectrometry and NMR spectroscopy. The results show that SEC with polystyrene standards tends to overestimate the molar mass of these materials and that a correction factor between 0.50 and 0.60 should be used for more accuracy. 相似文献
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F. Cousin J. Jestin G. Chaboussant S. Gautrot A. Menelle F. Ott 《The European physical journal. Special topics》2009,167(1):177-183
We demonstrate in this paper the possibilities offered by
Grazing Incidence Small Angle Neutron Scattering (GISANS) for the study of
solid/liquid interfaces. We present experimental results obtained by
Specular Neutron Reflectivity (SNR) and GISANS on a model system made of
silica nanospheres adsorbed on a silicon wafer by electrostatic interactions
both at solid/air interface and solid/liquid interfaces. At the solid/liquid
interface, we demonstrate that grazing incidence scattering enables to
discriminate the surface and the bulk scattering. The surface structure
factor derived from GISANS shows that the nanospheres are organized as a
repulsive liquid system, with a surface fraction occupation consistent with
values obtained by SNR. This original setup highlights a direct correlation
between the structure of the silica nanospheres in solution and their
organization on the surface: due to the strong electrostatic repulsions
between spheres, their organization at the surface is close to the
projection in 2D of the 3D organization of the nanospheres in solution. 相似文献
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