Shape memory fiber spun with segmented polyurethane ionomer

The effect of cationic groups within hard segments on shape memory polyurethane (SMPU) fibers was studied and the cyclic tensile testing was conducted to assess the shape memory effect. Mechanical properties, hard segment crystallization, and dynamic mechanical properties of SMPU ionomer fibers composed of 1,4‐butanediol (BDO), N‐methyldiethanolamine (NMDA), 4,4′‐methylenebis(phenyl isocyanate) (MDI), and poly(butylene adipate)diol (PBA) were investigated using a universal tensile tester, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results demonstrate that only 2 wt% NMDA can significantly change the glass transition temperature of the soft segment phase. DSC shows that the ionic group within hard segments can facilitate the crystallization of hard segments in unsteamed SMPU ionomer fibers. But for steamed fiber specimens, this effect is insignificant. Moreover, the ionic groups in hard segments with different hard segment contents (HSC) have different effects. In unsteamed fibers with 64 wt% HSC, 2 wt% NMDA increases the glass transition of soft segments from 63.5 to 70.6°C. However, in fibers with 55 wt% HSC, the glass transition temperature is lowered from 46.7 to 33.5°C. The post‐treatment, high‐pressure steaming is an effective way to remove the internal stress and subsequently improve the dimensional stability of SMPU ionomer fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Shape memory effect and reversible phase crystallization process in SMPU ionomer

It is the first attempt to reveal the effect of reversible phase crystallization process on shape memory effect in shape memory polyurethane (PU) ionomer. Thereof the cyclic tensile testing was conducted with various cooling time to fix the temporary deformation for assessing shape memory function. The crystallization process of the reversible phase, poly (ε‐caprolactone) (PCL) in shape memory PU ionomers composed of different ionic group contents, 1,4‐butanediol, 4,4′‐methylenebis(phenyl isocyanate) and PCL, was investigated by using isothermal crystallization kinetics under the thermal routine similar to that for the cyclic tensile testing. The results demonstrate that the ionic groups within hard segments significantly slow down the crystal growth of the reversible phase. When the physical crosslink is strong enough, the crystallization rate would be a predominant factor determining the shape fixity ratio after various cooling time. Instead, when physical crosslink is weakening, the influence of crystallization rate is much less on the cooling time dependence of fixity. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and structure of the Li13 cage [[[O-P(mu-NtBu)]2Li2]3(LiCl)6Li(Cl/OnBu)0.5(thf)7], containing a [O-P(mu-NtBu)]2(2-) dianion

The hydrolysis of [ClP(mu-NtBu)]2 with H2O-Et3N in thf, followed by in situ lithiation with nBuLi gives the Li13 cage [[[O-P(mu-NtBu)]2Li2]3(LiCl)6Li(Cl/OnBu)0.5(thf)7], containing a [O-P(mu-NtBu)]2(2-) dianion that is isoelectronic with ligands of the type [(RN)P(mu-NR)]2(2-).     

Stimulated emission in ZnO nanostructures: A time-resolved study

Stimulated emission was studied using time-integrated and time-resolved photoluminescence in ZnO comb, tetrapod, and rod nanostructures. All the measurements were performed on ensembles of the nanostructures. The nanostructures were fabricated by vapor deposition (combs, tetrapods) and hydrothermal methods (rods). While stimulated emission was detected in all of the nanostructures, significant differences in the behavior of the stimulated emission, as well as the lasing threshold power, were found for different morphologies. The differences in the time evolution of the lasing spectra were particularly pronounced. The observed differences in the stimulated emission spectra of the three types of nanostructures in both exciton-exciton scattering and electron-hole plasma regimes are discussed.     

Structure formation in electromagnetically driven granular media

We report structure formation in submonolayers of magnetic microparticles subjected to periodic electrostatic and magnetic excitations. Depending on the excitation parameters, we observe the formation of a rich variety of structures: clusters, rings, chains, and networks. The dynamics and shapes of the structures are strongly dependent on the amplitude and frequency of the external magnetic field. We find that for pure ac magnetic driving the low-frequency magnetic excitation favors compact clusters, whereas high frequency driving favors chains and netlike structures. An abrupt phase transition from chains to a network phase was observed for a high density of particles.     

Crystal and molecular structure ofN,N′-diphenylpiperazine N,N′-dioxide octahydrate

The title compound isN,N-DiphenylpiperazineN,N-dioxide octahydrate, C₁₆H₃₄N₂O₁₀:M _r=414.46, orthorhombic, space groupPnma (No. 62),a=12.327(2),b=9.804(1),c=17.443(4) Å,V _c=2108.1(5) ų,Z=4. The structure was solved by the direct method and refined toR=0.056 for 3032 observed MoK reflections. In theN,N-dioxide molecule, all atoms except those of the methylene groups lie on a crystallographic mirror plane. The piperazine ring takes the chair form, with two N-O bonds oriented axially in atrans configuration. The crystal structure is characterized by strong hydrogen bonding between the water molecules, as well as between theN-oxide groups and water molecules, giving rise to a three-dimensional network structure composed of edge-sharing four-membered, five-membered, six-membered, and fourteen-membered rings.     

Chain length effect of alkanethiol self-assembled monolayers on the maximum spreading ratio of impacting water droplets

This paper presents a systematic study of de-ionized water droplets impact on five different self-assembled monolayer surfaces: octadecanethiol, hexadecanethiol, dodecanethiol, heptanethiol and pentanethiol. Our data for the maximum spreading diameter of water impacting on these surfaces were compared with those predicted from literature models. Of the models selected, the model [M. Pasandideh-Fard, S. Chandra, J. Mostaghimi, Phys. Fluids 8 (1996) 650] was modified and the results yielded a least mean error of 7.55 ± 1.73% in the determination of the maximum spreading diameter, which is among the best from those selected.