Observation of Temperature Induced Plasma Frequency Shift in an Extremely Large Magnetoresistance Compound LaSb

We report an optical spectroscopy study on LaSb, a compound recently identified to exhibit extremely large magnetoresistance. Our optieal measurement indicates that the material has a low carrier density. More inter- estingly, the study reveals that the plasma frequency increases with decreasing temperature. This phenomenon suggests either an increase of the conducting carrier density or/and a decrease of the effective mass of carriers with decreasing temperature. We attribute it primarily to the latter effect. Two possible scenarios on its physical origin are examined and discussed. The study offers new insight into the electronic structure of this compound.

Temperature-Induced Transformation from Large Compound Vesicles to Worm-like Aggregates by ABC Triblock Copolymer

Two triblock polymers, tetraaniline-block-poly（N-isopropyl acrylamide）-block-poly（hydroxyethyl acrylate） （TA-b-PNIPAM-b-PHEA） and TA-b-PHEA-b-PNIPAM, were synthesized with unambiguous structure by a two step method. The difference of these two diblock polymers is the connection order of carboxyl group to block, e.g., carboxyl group to PNIPAM block for PNIPAM-b-PHEA and to PHEA block for PHEA-b-PNIPAM. Secondly, block tetraaniline was linked to the diblock polymer through amidation to yield the corresponding triblock copolymer. Both of them have almost the identical chemical compositions. The only difference is the connection order of each block in the triblock polymers. When they were self-assembled at 45℃ in a suitable solution, both of their aggregates have spherical shape with slight defects on their surface with the average diameter of about 400 nm. However, when their aggregate dispersion was cooled down to 20 ℃, only TA-b-PHEA-b-PNIPAM＇s morphology changed, forming worm-like aggregates with the diameter of about 100-200 nm transformed from spherical ag- gregates. Both amphiphilic property and position of each block in this triblock copolymer are very essential for this morphology transformation. Since the worm-like aggregates presented here by our group have hollow structure in- side, its controlled release properties for doxorubicin were evaluated. Drug release experiment indicated that along with the temperature changes, the rearrangement of the intermediate layer structure caused morphology change in aggregate, thus accelerating the speed of drug release.

Shear Induced Morphological Transformation of Large Compound Micelles Formed by Glutathione End-capped Poly（4-vinylpyridine）

Here we report novel shear-sensitive polymeric large compound micelles （LCMs） formed by self-assembly of glutathione end-capped poly（4-vinylpyridine） （GP4VP） in water containing 4 vol% methanol. The amphiphile prefers to form the kinetieally stabilized LCMs due to the small length ratio of the hydrophilic part to the hydrophobic part; the encapsulation of the hydrophilic part within LCMs causes only a small enthalpy loss from a thermody- namic view. Sheared by vortex flows generated by vigorous stir, the LCMs evolve to thick wall vesicles, thin wall vesicles, broken vesicles and ＂pearl-necklace＂ structures consecutively. The high flexibility of the LCMs and the internal tension caused by the encapsulation of the hydrophilic part are responsible for the high shear sensitivity of the LCMs.