排序方式: 共有35条查询结果,搜索用时 15 毫秒
21.
22.
M. Soccio M. Gazzano N. Lotti L. Finelli A. Munari 《Journal of Polymer Science.Polymer Physics》2009,47(14):1356-1367
Poly(butylene/diethylene naphthalate) copolymers (PBN‐PDEN) were synthesized in bulk according to the polycondensation procedure and examined by NMR, GPC, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and XRD. At room temperature they appeared as semicrystalline materials; the copolymerization caused a lowering in the Tg value, a decrement of Tm and of the crystallization rate. Pure α or β′ form was obtained at low and high DEN unit content, respectively; crystalline form transition never occurred in the solid state, analogously to PBN. After cooling from the melt, the pure α form was always evidenced in PBN‐PDEN10 and PBN‐PDEN20, whereas the pure β′ crystal phase develops in the copolymer containing 40 mol % DEN units, independently on the cooling rate. In the case of PBN‐PDEN30 a pure α or β′ form was obtained at low and high cooling rate, respectively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1356–1367, 2009 相似文献
23.
P. Finelli 《The European physical journal. Special topics》2008,156(1):183-190
A recently introduced relativistic nuclear energy density functional,
constrained by features of low-energy QCD, is extended
to describe the structure of hypernuclei.
The density-dependent mean field and the spin-orbit potential
of a Λ-hyperon in a nucleus,
are consistently calculated using the SU(3) extension of in-medium
chiral perturbation theory.
The leading long-range ΛN interaction arises from
kaon-exchange and 2π-exchange with a Σ-hyperon
in the intermediate state.
Scalar and vector mean fields, originating from in-medium changes
of the quark condensates, produce
a sizeable short-range spin-orbit interaction.
The model, when applied to oxygen as a test case,
provides a natural explanation for the
smallness of the effective Λ spin-orbit potential: an almost complete
cancellation between the background contributions (scalar and vector) and
the long-range terms generated by two-pion exchange. 相似文献
24.
Lotti N. Siracusa V. Finelli L. Munari A. Manaresi P. 《Journal of Thermal Analysis and Calorimetry》2001,66(3):827-840
Poly(2-hydroxyethoxybenzoate), poly(ε-caprolactone), and random poly(2-hydroxyethoxybenzoate/e-caprolactone) copolymers were
synthesized and characterized in terms of chemical structure and molecular mass. The thermal behavior was examined by DSC.
All the samples appear as semicrystalline materials; the main effect of copolymerization was lowering in the amount of crystallinity
and a decrease of melting temperature with respect to homopolymers. Flory's equation described well the T
m-composition data. Amorphous samples (in the 20–100%2-hydroxyethoxybenzoate unit concentration range) obtained by quenching
showed amonotonic decrease of the glass transition temperature T
g as the content of caprolactone units is increased. The Wood's equation described the T
g-composition data well.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
25.
The melting behaviour, the crystallization kinetics and the morphology of block poly(butylene/diethylene succinate) copolymers (PBSPDGS) were investigated by means of differential scanning calorimetry and hot stage optical microscopy. Multiple endotherms were evidenced in the PBSPDGS samples, due to melting and recrystallization processes, similarly to PBS. By applying the Hoffman-Weeks’ method, the of both the homopolymer and the copolymers was derived. The isothermal crystallization kinetics was analyzed according to the Avrami’s treatment. The copolymers with long PBS blocks are characterized by a very similar behaviour with respect to pure poly(butilene succinate), indicating that PBS macromolecular folding is not affected by the presence of non-crystallizable diethylene succinate blocks. On the contrary, the copolymers characterized by very short PBS block length were found to crystallize at a slower rate than the homopolymer. As a matter of fact, a higher value of the work of chain folding was also derived on the basis of Hoffman-Lauritzen nucleation theory. Anyway, in all cases the crystallization mechanism (heterogeneous nucleation and three-dimensional growth) was found to be the same. 相似文献
26.
The miscibility of poly(propylene succinate)/poly(propylene adipate) blends was investigated by means of DSC, WAXS and NMR techniques. Poly(propylene succinate) and poly(propylene adipate) were found to be completely immiscible in as blended-state. The miscibility changes upon extended mixing at elevated temperature: for enough long mixing time, the original two phases gradually merged into a single one because of transesterification reactions. The NMR analysis showed that the transesterifications led to block copolymers whose average sequence length decreased as the mixing time is increased at a fixed temperature. Upon very long mixing time (150 min), all PPS and PPA chains are fully transformed into a random copolymer characterized by a single amorphous phase. 相似文献
27.
28.
29.
We present the initial conditions for a decaying cosmological perturbation and study its signatures in the cosmic microwave background anisotropies and matter power spectra. An adiabatic decaying mode in the presence of components that are not described as perfect fluids (such as collisionless matter) decays slower than in a perfect-fluid dominated Universe and displays super-Hubble oscillations. Wilkinson Microwave Anisotropy Probe first year data constrain the decaying to growing ratio of scale invariant adiabatic fluctuations at the matter-radiation equality to less than 10%. 相似文献
30.
Influence of transesterification reactions on the miscibility and thermal properties of poly(butylene/diethylene succinate) copolymers 总被引:1,自引:0,他引:1
Poly(butylene/diethylene succinate) block copolymers (PBSPDGS), prepared by reactive blending of the parent homopolymers (PBS and PDGS) in the presence of Ti(OBu)4, were analyzed by 1H-NMR, TGA and DSC, in order to investigate the effects of the transesterification reactions on the molecular structure and thermal properties. 1H-NMR analysis evidenced the formation of copolymers whose degree of randomness increases with the mixing time. The thermal analysis of the melt-quenched samples showed that the melting peak, due to the crystalline phase of PBS, tends to disappear with increasing mixing time and therefore with decreasing the block length in the copolymers. As concern miscibility, a single homogeneous amorphous phase always occurred, independently on block length. Nevertheless, a phase separation, due to the tendency of the PBS blocks to crystallize, was evidenced in the copolymers with long butylene succinate sequences. The results obtained indicated that the block size had a fundamental role in determining the crystallizability and, therefore, phase behavior of the block copolymers. 相似文献