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71.
72.
A general formalism for the dynamic scattering properties of cyclic polymers in good solvent conditions is presented. Single-chain dynamics are investigated in the framework of the Oseen tensor model with and without the preaveraging approximation. The chain swelling due to excluded volume interactions is introduced by a renormalization of the internal chain statistics of cyclic polymers. The relaxations of the concentration fluctuations are also described for both ring homopolymers and copolymers. © 1994 John Wiley & Sons, Inc. 相似文献
73.
Redouane?Belkorissat Ab ed daim?Kadoun Marc?Dupeyrat Brahim?Khelifa Christian?MathieuEmail author 《Mikrochimica acta》2004,147(3):135-139
The beam-gas interactions in the low-vacuum SEM is investigated through experimental and simulation approaches. An original experimental way to characterise the skirting is proposed. We obtained directly image distribution of the primary electron beam and the scattered electrons in the low-vacuum SEM. The experimental results are compared to the electron beam profile obtained with Monte-Carlo simulation. 相似文献
74.
Villetti M. A. Crespo J. S. Soldi M. S. Pires A. T. N. Borsali R. Soldi V. 《Journal of Thermal Analysis and Calorimetry》2002,67(2):295-303
The thermal degradation of sodium hyaluronate, xanthan and methylcellulose was evaluated by thermogravimetric and infrared
analysis. Kinetic parameters such as activation energy and pre-exponential factor were determined considering the Ozawa and
Freeman–Carroll methods. The results suggest changes in the degradation mechanism with the fraction of mass loss for both
the studied polysaccharides. The activation energy values determined by the Freeman–Carroll method are higher than those obtained
by the Ozawa method under the same conditions, probably because in the first method a first order reaction was assumed and
the thermal history effects were eliminated since only one TG curve was used to determine the kinetic parameters. Low thermal
stability was observed for polyanions e.g. sodium hyaluronate (Na-Hy) and xanthan(XT) in comparison with methylcellulose (MC)
which is a neutral polysaccharide. By infrared spectroscopy, it was observed that at low temperatures there occured only the
scission of the exocyclic groups for both polysaccharides and that the scission of strong links in the backbone occurred at
high temperatures, in agreement with the kinetic parameters determined for the degradation reaction.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
75.
A synthetic method with broad spectrum of application in the preparation of self‐organizing amphiphilic copolymers having poly(glycerol monomethacrylate) (PG2MA) as a hydrophilic part is herein reported. The approach relies on the facile preparation of silylated glycerol monomethacrylate (G2MA‐TMS) monomer, and its controlled atom transfer radical polymerization (ATRP) in organic media, which produced well‐defined (co)polymers with predictable molar mass and low dispersity, followed by desilylation. The wide scope of such a strategy was demonstrated by the successful synthesis of original polycaprolactone‐b‐poly(glycerol monomethacrylate) (PCL‐b‐PG2MA) diblock copolymers with the ability to self‐assemble into ordered structures (micelles and vesicles) in an aqueous medium.
76.
77.
Belmesnaoui Aqzzouz Redouane Nouira 《Rendiconti del Circolo Matematico di Palermo》2005,54(2):253-258
We give some sufficient and necessary conditions such that the vector lattice of continuous functions on a compact topological
space, not necessary metrizable, admits a locally convex and solid topology which is Lebesgue.
相似文献
78.
We characterize complete Hausdorff locally convex solid lattices (E,τ) satisfying the following property: for all operators such that 0?S?T and T precompact, the operator S2 is precompact. To cite this article: B. Aqzzouz, R. Nouira, C. R. Acad. Sci. Paris, Ser. I 337 (2003). 相似文献
79.
The relaxation frequency of the dynamic correlation function for a diblock cyclic copolymer in solution in the zero average condition is calculated in the presence of hydrodynamic interaction. The latter is introduced through the screened Oseen tensor where the hydrodynamic screening length is used as a parameter to determine the range of screening. Substantial differences with the case of linear homopolymer are found, especially in the low q range where the dynamics are much faster and correspond to nondiffusive processes as usually is the case for copolymer systems. As the screening length decreases the dynamics approach the Rouse behavior and the minimum of the relaxation frequency shifts to lower values. The proportionality constant of the relaxation frequency in the intermediate q range Γ(q) → q3/(kBTη0) is also investigated as a function of the screening length. © 1994 John Wiley & Sons, Inc. 相似文献
80.
Houga C Le Meins JF Borsali R Taton D Gnanou Y 《Chemical communications (Cambridge, England)》2007,(29):3063-3065
Dextran-b-polystyrene diblock copolymers forming miscellaneous spherical self-assemblies in water were obtained by chemical modification of the anomeric extremity of a commercial dextran followed by atom transfer radical polymerisation of styrene. 相似文献