排序方式: 共有6条查询结果,搜索用时 46 毫秒
1
1.
I. Barandiaran D. Katsigiannopoulos E. Grana A. Avgeropoulos A. Eceiza G. Kortaberria 《Colloid and polymer science》2013,291(9):2173-2180
Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount. 相似文献
2.
Artiaga R. Garcia A. Garcia L. Varela A. Mier J. L. Naya S. Grana M. 《Journal of Thermal Analysis and Calorimetry》2002,70(1):199-207
The nickel-titanium alloys are usually known as Shape Memory alloys because of their ability to return to some previously
defined shape or size when subjected to the appropriate thermal procedure. Mechanical properties of a nickel titanium wire
were investigated by DMTA using cylindrical tension mode. The Young"s modulus, the maximum strain and residual deformation
have been calculated. Recovery of previously deformed samples was observed in constant stress temperature ramp tests. Relaxation
stress behaviour at temperatures above the austenitic transformation has been studied. The strain and frequency ranges of
linear response have been determined by dynamic experiments. Strain amplitude of 0.1% and frequency of 1 Hz have been chosen
for the temperature ramp dynamic experiments. A big change between 65 and 95°C is observed in the storage modulus. The values
of E' at temperatures below and above the transition are essentially constant. Finally, the effects of the frequency at different
temperatures have been examined.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Dimitrios Katsigiannopoulos Eftychia Grana Apostolos Avgeropoulos Pedro M. Carrasco Ignacio Garcia Ibon Odriozola Evmorfia Diamanti Dimitrios Gournis 《Journal of polymer science. Part A, Polymer chemistry》2012,50(6):1181-1186
We report the synthesis of a composite material comprised of poly(4‐vinylpyridine) (P4VP) grafted on multiwall carbon nanotubes (MWCNTs) and the preparation of a nanohybrid via quaternization of the nitrogen atom per monomeric unit of the polymer chains. 4‐Vinylpyridine was polymerized anionically using high vacuum techniques and was reacted with MWCNTs under vacuum to be grafted on the polymer segments. The composite material was soluble in common solvents and the dispersion of the carbon nanotubes was improved after quaternization due to the formation of polymeric ionic liquid (PIL) of the MWCNTs‐g‐[P4VP‐r‐poly(4ViEtPy+Br‐)] type. The successful synthesis was confirmed with Fourier‐transform infrared and Raman spectroscopies, whereas differential scanning calorimetry was adopted to verify the stability of the polymer's glass transition temperature before and after grafting on the MWCNTs. Moreover, thermogravimetric analysis was used for examining the thermal stability and the PIL formation of the composite. Energy dispersive spectroscopy measurements confirm the precipitation of silver bromide when the MWCNTs‐g‐[P4VP‐r‐poly(4ViEtPy+Br‐)] is reacted with silver nitrite indicating the successful quaternization and formation of the appropriate PIL. High temperature size exclusion chromatography was used for the determination of the molecular characteristics (average molecular weight by number $\overline M _n$ , polydispersity I) of the homopolymer obtained from the filtration of the composite material. Finally, field‐emission scanning electron microscopy was used to verify the successful grafting of the polymer to the MWCNTs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
4.
Alvaro Leonel Robles Grana Hortensia Maldonado-Textle Jos Romn Torres-Lubin Claude St Thomas Ramn Díaz de Len Jos Luis Olivares-Romero Luis Valencia Francisco Javier Enríquez-Medrano 《Molecules (Basel, Switzerland)》2021,26(15)
Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ < 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates. 相似文献
5.
Tei Newman-Lehman Roberto Grana Kalyanasundaram Seshadri Forman Williams 《Proceedings of the Combustion Institute》2013,34(2):2147-2153
Knowledge of combustion of hydrocarbon fuels with nitrogen-containing oxidizers is a first step in understanding key aspects of combustion of hypergolic and gun propellants. Here an experimental and kinetic-modeling study is carried out to elucidate aspects of nonpremixed combustion of methane (CH4) and nitrous oxide (N2O), and ethane (C2H6) and N2O. Experiments are conducted, at a pressure of 1 atm, on flames stabilized between two opposing streams. One stream is a mixture of oxygen (O2), nitrogen (N2), and N2O, and the other a mixture of CH4 and N2 or C2H6 and N2. Critical conditions for extinction are measured. Kinetic-modeling studies are performed with the San Diego Mechanism. Experimental data and results of kinetic-modeling show that N2O inhibits the flame by promoting extinction. Analysis of the flame structure shows that H radicals are produced in the overall chain-branching step 3H2 + O2 ? 2H2O + 2H, in which molecular hydrogen is consumed. Hydrogen is also consumed in the overall step N2O + H2 ? N2 + H2O where stable products are formed. Inhibition of the flames by N2O is attributed to competition between these two overall steps. 相似文献
6.
Mariana Grana 《International Journal of Theoretical Physics》1999,38(4):1359-1371
We formulate a phenomenological model where theinflaton fluctuations are treated as a fluid. Byapplying the hydrodynamic equations to this fluid werecover the conventional result that relates thespectrum of density fluctuations in the inflaton fieldat reentering the horizon to the spectrum offluctuations at the time a scale leaves the horizon.Moreover, through the equivalent viscosity of the fluidwe obtain a Reynolds number that suggeststurbulent motion, which implies that mode–modecoupling in the inflaton field cannot be neglected. Forde Sitter inflation the resulting spectrum usingturbulence theory is scale invariant on all scales ofinterest. This suggests that the hypothesis of anextremely weakly coupled inflation could be relaxedwithout affecting the predictions of themodel. 相似文献
1