Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides

Resistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX , with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine ( AMTPA ), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide ( NTCDI ) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide ( BTCDI ) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI . The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX . At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI . Combining these results and our previous study on perylenebisimide ( PBI ), we concluded that memory characteristics could be tailored by changing the conjugation length ( PBI > NTCDI > BTCDI ) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

High resolution‐HMBC (HR‐HMBC), a new method for measuring heteronuclear long‐range coupling constants

A useful pulse sequence for measuring long‐range C? H coupling constants (J_{C? H}) named high resolution‐HMBC (HR‐HMBC) has been developed. In this pulse sequence, the J‐scaling pulse [(nt₁)/2? 180° (H/C) ? (nt₁)/2] is incorporated after the spin evolution period, and then followed by an ¹H 180° pulse to reverse the magnetization of J_{C? H} couplings. As a result, splittings of the cross peaks due to the long‐range J_{C? H} are realigned with separations of nJ_{C? H} along the F₁ dimension, and thus even the small long‐range J_{C? H} values can easily be determined. The efficiency of measuring the long‐range J_{C? H} using the proposed pulse sequences has been demonstrated in application to the complicated natural product, portmicin. Copyright © 2010 John Wiley & Sons, Ltd.     

Three‐component negative‐type photosensitive polyimide precursor based on poly(amic acid), a crosslinker,and a photoacid generator

A new negative‐working and alkaline‐developable photosensitive polyimide precursor based on poly(amic acid) (PAA), 4,4′‐methylenebis[2,6‐bis(hydroxymethyl)]phenol (MBHP) as a crosslinker, and a photoacid generator (5‐propylsulfonyloxyimino‐5H‐thiophen‐2‐ylidene)‐2‐(methylphenyl)acetonitrile (PTMA) has been developed. PAA was prepared by ring‐opening polymerization of pyromellitic dianhydride with 4,4′‐oxydianiline. The photosensitive polyimide precursor containing PAA (65 wt %), MBHP (25 wt %), and PTMA (10 wt %) showed a clear negative image featuring 10 μm line and space patterns when it was exposed to 436 nm light at 100 mJ·cm^?2, post‐exposure baked at 130 °C for 3 min, followed by developing with a 2.38 wt % aqueous tetramethylammonium hydroxide solution at 25 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 593–599, 2005     

Angioarchitecture of tumors induced by two different cloned cell lines established from a transplantable rat malignant fibrous histiocytoma.

Angiogenesis, a biologic process whereby endothelial cells divide and migrate to form new blood vessels, is a key step in tumor growth, invasion, and metastasis. In the present study, we investigated the differences in angioarchitecture between two different tumors induced by cloned cell lines (MT-8 and MT-9), derived from a transplantable rat malignant fibrous histiocytoma, by scanning electron microscopy of vascular corrosion casts. During a 3-week observation period after implantation, the growth of MT-8 tumors appeared to be faster than that of MT-9 tumors. Histologically, MT-8 tumors were of the uniformly undifferentiated sarcoma type arranged in characteristic organoid structures, and MT-9 tumors showed a storiform growth pattern. In MT-8 tumors, neovascularization occurred by sprouting at postimplantation (PI) week 1, and the newly formed capillaries gradually became more tortuous. In MT-9 tumors, at PI week 1, the corrosion casts of newly formed capillaries mainly showed a wavy course but no finger-like outgrowths of capillaries were seen. At PI weeks 2 and 3, the sprouting was seen specifically in MT-9 tumors, forming basket-like structures and glomeruloid structures of capillaries. These results indicate that angiogenesis or angioarchitecture of MT-8 tumors is different from that of MT-9 tumors, depending on the differences in their tumor histology and by the features like absence or presence of basket-like structures and glomeruloid structures of capillaries.     

Construction of a dimethyl sulfoxide sensor based on dimethyl sulfoxide reductase immobilized on a au film electrode.

A novel dimethyl sulfoxide (DMSO) sensor using DMSO reductase and film electrodes was constructed. The Au and Ag electrodes were fabricated on slide glass by vacuum deposition and the application of a photolithographic technique. The micro-chamber (4 x 50 x 1 mm, volume 200 microl) was fabricated on a poly(dimethylsiloxane) (PDMS) polymer. The Pt electrode was implanted in a PDMS polymer. DMSO reductase was immobilized on a Au film electrode with bovine serum albumin (BSA)-glutaraldehyde. This sensor could determine DMSO in an unpurged aqueous solution with glucose oxidase (GOD) and catalase (CAT) for oxygen removal. The DMSO sensor showed a linear response within 1 mM DMSO with a correlation coefficient of 0.999. The detection limit was 200 microM (3sigma), and the sensitivity was 23.8 mA M(-1) cm(-2). The relative standard deviations at each concentration were within 3.6%.     

Study on interaction between Tb(III) and poly(N-isopropylacrylamide)

A new kind of the thermo-sensitive and fluorescent complex of poly(N-isopropylacrylamide) (PNIPAM) and Tb(III) was synthesized by free radical polymerization, in which PNIPAM was used as a polymer ligand. The complex was characterized by using X-ray photoelectron spectroscopy (XPS), ultraviolet-visual (UV), Fourier transform infrared (FT-IR) and fluorescence spectroscopy. The results from the experiments indicated that there is a strong interaction between PNIPAM and Tb(III), leading to a decrease in the electron density of nitrogen and oxygen atoms and an increase in the electron density of Tb(III) in the PNIPAM containing Tb(III) by contrast with PNIPAM and Tb(III), respectively, meanwhile, exhibiting that the Tb(III) is mainly bonded to oxygen atoms in the polymer chain of PNIPAM and formed the complex of PNIPAM-Tb(III). After forming the PNIPAM-Tb(III) complex, the emission fluorescence intensity of Tb(III) in the PNIPAM-Tb(III) complex is significantly enhanced because the effective intramolecular energy transfer from PNIPAM to Tb(III). Especially, the emission intensity of the fluorescence peak at 547 nm can be increased as high as 145 times comparing with that of the pure Tb(III). The intramolecular energy transfer efficiency for fluorescence peak at 547 nm can reach as high as 68%. The fluorescence intensity is related the weight ratio of Tb(III) and PNIPAM in the PNIPAM-Tb(III) complex. When the weight ratio is 1.4%, the maximum fluorescence enhancement can be obtained. Nevertheless, the lower critical solution temperature of PNIPAM containing a low content of Tb(III) has not obviously changed after the formation of the complex of PNIPAM-Tb(III) by the interaction between PNIPAM and Tb(III). This novel thermosensitive and fluorescence characterization of the PNIPAM-Tb(III) complex may be useful in the fluorescence systems and the biomedical field.     

Spectrophotometric determination of titanium with o-carboxyphenylfluorone in cationic micellar media, and its equilibrium and kinetic studies

Spectrophotometric determination of titanium(IV) was accomplished with o-carboxyphenylfluorone (OCPF) in the presence of hexadecyltrimethyl ammonium chloride (HTAC) under strongly acidic media. In the determination of titanium(IV), Beer's law was obeyed in the range of 24-340 ng mL⁻¹ with an effective molar absorption coefficient (at 530 nm) and relative standard deviation of 2.24 × 10⁵ dm³ mol⁻¹ cm⁻¹ and 0.64% (n = 8), respectively. The severe interference of iron ions was easily eliminated by the addition of ethylenediaminetetraacetic acid (EDTA); the effects of other foreign substances were low. Equilibrium and kinetic studies under analytical conditions were investigated to quantitatively evaluate the reaction mechanism. The obtained orange complex is considered to be Ti(OCPF)₄. Its stability log K_f and rate constant K_obs are 16.88 and 1.65 × 10⁻² s⁻¹, respectively. It is suggested that the color of the complex is related to the species of OCPF in the solution.