Pressure-induced reentrant micellization of amphiphilic block copolymers in dilute aqueous solutions

The pressure-induced structural changes of a block copolymer, poly(2-ethoxyethoxyethyl vinyl ether)-block-poly(2-hydroxyethyl vinyl ether) (pEOEOVE-b-pHOVE) in aqueous solutions, were studied by means of small-angle neutron scattering (SANS) and dynamic light scattering (DLS) from atmospheric pressure up to 400 MPa. pEOEOVE-b-pHOVE formed a spherical micellar structure above 40 degrees C due to poor solubility of pEOEOVE. Micellization phase diagram was determined by DLS, and a covex-upward pressure-temperature (P-T) phase diagram was obtained having a peak around (P,T)=(150 MPa,48 degrees C). The SANS curves at 50 degrees C were analyzed as a function of P. The micellar core size decreased by pressurizing at low P's (P相似文献   

Modal Power Analysis for Two-Mode Fibers Illuminated by an Offset Beam Based on Near Field Pattern Measurement

A novel method for determining mode power distribution in a two-mode fiber illuminated by an offset beam by measuring the near field pattern on the test fiber endface is developed. This method utilizes the different field symmetries of the fundamental and the second order modes. Coupling efficiencies from a quasi Gaussian beam to the fundamental and the second order modes in a two mode fiber were measured by the new technique for various offset launching conditions, and were in good agreement with the theoretical ones.     

The incorporation of carboxylate groups into temperature‐responsive poly(N‐isopropylacrylamide)‐based hydrogels promotes rapid gel shrinking

Aqueous gel deswelling rates for copolymer hydrogels comprising N‐isopropylacrylamide (IPAAm) and 2‐carboxyisopropylacrylamide (CIPAAm) in response to increasing temperatures were investigated. Compared with pure IPAAm‐based gels, IPAAm–CIPAAm gels shrink very rapidly in response to small temperature increases across their lower critical solution temperature (their volume is reduced by five‐sixths within 60 s). Shrinking rates for these hydrogels increase with increasing CIPAAm content. In contrast, structurally analogous IPAAm–acrylic acid (AAc) copolymer gels lose their temperature sensitivity with the introduction of only a few mole percent of AAc. Additionally, deswelling rates of IPAAm–AAc gels decrease with increasing AAc content. These results indicate that IPAAm–CIPAAm copolymer gels behave distinctly from IPAAm–AAc systems even if both comonomers, CIPAAm and AAc, possess carboxylic acid groups. Thus, we propose that the sensitive deswelling behavior for IPAAm–CIPAAm gels results from strong hydrophobic chain aggregation maintained between network polymer chains due to the similar chemical structures of CIPAAm and IPAAm. This structural homology facilitates aggregation of chain isopropylamide groups for both IPAAm and CIPAAm sequences with increasing temperature. The incorporation of AAc, however, shows no structural homology to IPAAm, inhibiting chain aggregation and limiting collapse. A functionalized temperature‐sensitive poly(N‐isopropylacrylamide) hydrogel containing carboxylic acid groups is possible with CIPAAm, producing rapid and large volume changes in response to smaller temperature changes. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 335–342, 2001     

Thermally Induced Phase Transition of Crystalline Syndiotactic Polystyrene Studied by Molecular Dynamics Simulation

The structural phase transition between the polymorphs of syndiotactic polystyrene has been studied by means of molecular dynamics simulation. It was found that the initial δ_e form of the crystal structure was completely transformed into the γ form by thermal treatment. Not only the crystal structure but also the transition path are investigated at the molecular level for the first time.     

Fiber-packed needle-type sample preparation device designed for gas chromatographic analysis

A miniaturized sample preparation technique that uses a fine-fiber-packed needle as the extraction medium is reviewed, especially in relation to its application to the analysis of volatile organic compounds by gas chromatography. When the needle was packed longitudinally with a bundle of fine filaments (12 μm o.d.) which were also surface-coated with polymeric materials, successful sample preconcentration was obtained. Improved sensitivity was also established by introducing simultaneous derivatization reactions into the extraction process in the fiber-packed needle. The storage performance of the needle clearly demonstrated the potential of the technique for typical on-site sampling during environmental analysis. In this short review, the fiber-packed extraction needle developed by the authors is summarized along with applications that use the fiber-packed needle as a miniaturized extraction device.     

New Quenching Procedure for Preservation of Initial Polymer/Catalyst Particle Morphology in Ziegler–Natta Olefin Polymerization

Preservation of initial polymer/catalyst particle morphology under air, was examined using stopped‐flow Ziegler–Natta polymerization with various quenching conditions and post‐chemical treatments. The exposure of the initial particles to air caused the fast formation of cracks on the surface, finally leading to significant reformation of the particle shape, when polymerizing particles were washed with heptane at ?65 °C under N₂ or under CO₂. On the other hand, when the particles were washed with heptane containing an appropriate amount of tetrahydrofuran under CO₂, the particle morphology under air was almost completely maintained even after 1 h exposure. The present results are useful for various ex situ characterizations of unstable initial polymer/catalyst particles.

     

Rank of 3-tensors with 2 slices and Kronecker canonical forms

Tensor type data are becoming important recently in various application fields. We determine the rank of a 3-tensor with 2 slices in comparison with its Kronecker canonical form over the complex and real number field.     

Phase transition of L-Ser monohydrate crystal studied by (13)C solid-state NMR

We used gravimetric analysis (GA) and (13)C solid-state nuclear magnetic resonance (NMR) to study solid-phase transition from the transparent single crystal of L-serine (L-Ser) monohydrate to a turbid powder. We found that L-Ser monohydrate loses water molecules and transforms into an anhydrate, thus experimentally demonstrating Frey's assumption. Application of a handmade cross-polarization (CP) NMR probe with a saddle-type coil to the oriented crystal of the L-Ser monohydrate revealed the dehydration mechanism. Furthermore, the chemical shift tensor components of the carboxyl carbon in L-Ser monohydrate were determined. The difference in the tensor component of delta(22) between the monohydrate and anhydrate forms was more than 7 ppm, probably owing to differences in the hydrogen-bonding structure of each form.