Constant time steady gradient NMR diffusometry using the secondary stimulated echo

A pulse sequence producing a second stimulated echo is suggested for the compensation of relaxation and residual dipolar interaction effects in steady gradient spin echo diffusometry. Steady field gradients of considerable strength exist in the fringe field of NMR magnets, for instance. While the absolute echo time of the second stimulated echo is kept constant throughout the experiment, the interval between the first two radiofrequency pulses is augmented leading to a modulation of the amplitude of that second stimulated echo by self-diffusion only. The unique feature of this technique is that it is of a single-scan/single-echo-signal nature. That is, no reference signals neither of the same pulse sequence nor of separate experiments are needed. The new method was tested with poly(ethylene oxide) melts and proved to provide reliable data for (time dependent) self-diffusion coefficients down to the physical limit (D approximately 10(-15)m(2)/s) when flip-flop spin diffusion starts to become effective.     

偶氮基染料掺杂薄膜的双光子图象存储

研究了偶氮基染料掺杂薄膜ＭＯ－ＰＶＡ和ＥＯ－ＰＶＡ的双光子存储特性。在对薄膜用Ａｒ＾＋激光作预激发下实现了Ｈｅ－Ｎｅ激光的红光存储。获得了实时和短时存储照片。光电记录存储曲线，分析了双光四能级系统的存储机制。实现确定了最佳预激发功率约为０．２８Ｗ／ｃｍ＾２，最小Ｈｅ－Ｎｅ光可存储功率密度低于０．２Ｗ／ｃｍ＾２。     

The effect of PVA (Bi2O3-doped) interfacial layer and series resistance on electrical characteristics of Au/n-Si (110) Schottky barrier diodes (SBDs)

Two types of Schottky Barrier Diodes (SBDs) with and without PVA (Bi₂O₃-doped) polymeric interfacial layer, were fabricated and measured at room temperature in order to investigate the effects of the PVA (Bi₂O₃-doped) interfacial layer on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (Φ_B0), series resistance (R_s) and interface-state density (N_ss). Electrical parameters of these two diodes were calculated from the current-voltage (I-V) characteristics and compared with each other. The values of Φ_B0, n and R_s for SBDs without polymeric interfacial layer are 0.71 eV, 1.44 and 4775 Ω, respectively. The values of Φ_B0, n and R_s for SBDs with PVA (Bi₂O₃-doped) polymeric interfacial layer are 0.74 eV, 3.49 and 10,030 Ω, respectively. For two SBDs, the energy density distribution profiles of interface states (N_ss) were obtained from forward-bias I-V measurements by taking the bias dependence of R_s of these devices into account. The values of N_ss obtained for the SBD with PVA (Bi₂O₃-doped) polymeric interfacial layer are smaller than those of the SBD without polymeric interfacial layer.     

微接触印刷法制造聚合物多层次准三维立体微结构

直接用聚合物稀溶液作为“印墨”进行微接触印刷,制作了诸如聚苯乙烯和聚甲基丙烯酸甲酯等聚合物的微细结构,通过重复交叉盖印得到多层次准三维立体微结构,并用可聚合的双(甲苯磺酸)-2,4-己二炔-1,6-二醇脂的丙酮稀溶液作微接触印刷,观察了微条纹上的聚合.对聚合物溶液的微接触印刷的过程中溶剂挥发等因素的影响进行了观察分析,结果表明,溶剂挥发时间对微图形的准确复制是十分重要的,过长或过短的溶剂挥发时间都不利于得到清晰精确的微结构.     

Selective surface chemistry of allyl alcohol and allyl aldehyde on Si(1 0 0)2×1: Competition of [2 + 2] CC cycloaddition with O-H dissociation and with [2 + 2] CO cycloaddition in bifunctional molecules

Competition between the CC functional group with the OH group in allyl alcohol and with the CO group in allyl aldehyde in the adsorption and thermal chemistry on Si(1 0 0)2×1 has been studied by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), as well as density-functional theory (DFT) calculations. The similarities found in the C 1s and O 1s spectra for both molecules indicate that the O-H dissociation product for allyl alcohol and [2 + 2] CO cycloaddition product for allyl aldehyde are preferred over the corresponding [2 + 2] CC cycloaddition products. Temperature-dependent XPS and TPD studies further show that thermal evolution of these molecules gives rise to the formation of ethylene, acetylene, and propene on Si(1 0 0)2×1, with additional CO evolution only from allyl alcohol. The formation of these desorption products also supports that the [2 + 2] CC cycloaddition reaction does not occur. In addition, the formation of SiC at 1090 K is observed for both allyl alcohol and allyl aldehyde. We propose plausible surface-mediated reaction pathways for the formation of these thermal evolution products. The present work illustrates the crucial role of the Si(1 0 0)2×1 surface in selective reactions of the Si dimers with the O−H group in allyl alcohol and with the CO group in allyl aldehyde over the CC functional group common to both molecules.     

Rheological Behaviors and Properties of Poly (Ether Ether Ketone) In-Situ Blends: Effect of Chemical Structure of Added Thermotropic Liquid Crystalline Polyarylates

Abstract

Two kinds of thermotropic liquid crystalline polyesters (TLCP) with different chemical structures were used as flow modifiers during the melt spinning of poly (ether ether ketone). One of TLCPs, named PAT-S, was a kind of aromatic polyester synthesized from 4-acetoxybenzoicacid and 6-hydroxy-naphthoic acid, and the other one named, PEEKAR, was a block copolymer based on poly (ether ether ketene) (PEEK) oligomers and PAT-S oligomers. The effects of the chemical structures of the prepared TLCPs on the rheological behavior of the TLCP/PEEK blends were measured by rheological measurements, and then the structure and properties of the TLCP/PEEK in-situ blend fibers were studied by a series of methods, including differential scanning calorimetry (DSC), wide angle X-ray diffraction (WRXD), optical microscopy (OM), scanning electron microscopy (SEM), orientation degree tests, mechanical properties tests, etc. The results showed that the melt viscosity of PEEK could be effectively reduced by nearly 20% by adding a small amount of PEEKAR or PAT-S with the viscosity reducing effect of PEEKAR on PEEK being greater than that of PAT-S; this was mainly caused by the better compatibility between PEEK and PEEKAR because of the similar segment structures. The crystallinity of the PEEK fibers increased by nearly 50% with addition of both TLCPs, indicating that both the PEEKAR and PAT-S could serve as nucleating agent as well. The results from the morphology analysis clearly proved that PEEKAR had a better compatibility with the PEEK resin compared with PAT-S. The tensile strength of the PEEK fibers could be improved to some extent by adding PEEKAR, while it was obviously reduced after adding PAT-S.     

Ultrasound triggered cell death in vitro with doxorubicin loaded poly lactic-acid contrast agents

Traditional chemotherapy generally results in systemic toxicity, which also limits drug levels at the area of need. Two ultrasound contrast agents (UCA), with diameters between 1–2 μm in diameter and shell thicknesses of 100–200 nm, composed of poly lactic-acid (PLA), one loaded by surface adsorption and the other loaded by drug incorporation in the shell, were compared in vitro for potential use in cancer therapy. These poly lactic-acid (PLA) UCA platforms contain a gas core that in an ultrasound (US) field can cause the UCA to oscillate or rupture. Following a systemic injection of drug loaded UCA with external application of US focused at the area of interest, this platform could potentially increase drug toxicity at the area of need, while protecting healthy tissue through microencapsulation of the drug. In vitro toxicity in MDA-MB-231 breast cancer cells of the surface-adsorbed and shell-incorporated doxorubicin (Dox) loaded UCA were examined at 5 MHz insonation using a pulse repetition frequency of 100 Hz at varying pressure amplitudes. Both platforms resulted in equivalent cell death compared to free Dox and US when insonated at peak positive pressure amplitudes of 1.26 MPa and above. While no significant changes in cell death were seen for surface adsorbed Dox-UCA with or without insonation, cell death using the platform with Dox incorporated within the shell increased from 16.12% to 25.78% (p = 0.0272), approaching double the potency of the platform when insonated at peak positive pressure amplitudes of 1.26 MPa and above. This mechanism is believed to be the result of UCA rupture at higher insonation pressure amplitudes, resulting in more exposed drug and shell surface area as well as increased cellular uptake of Dox containing polymer shell fragments. This study has shown that a polymer UCA with drug housed within the shell may be used for US-triggered cell death. US activation can be used to make a carrier significantly more potent once in the area of need.     

红外光谱法测定聚(乳酸-苯丙氨酸)共聚物的含量

分别以苯丙氨酸和乳酸为原料合成了3-苯甲基-2,5-吗啉二酮(PMD)与丙交酯(LA),以PMD和LA作为聚合单体经开环聚合分别得到PMD均聚物(PPMD)、丙交酯均聚物(PLA)及聚(乳酸-苯丙氨酸)共聚物。对合成的均聚物进行红外分析,确定1 671.53和870.82 cm-1处的吸收峰分别为PPMD和PLA的特征峰。根据以上两种特征吸收峰并以朗伯-比耳定律为理论依据,建立了利用红外光谱法测定聚(乳酸-苯丙氨酸)共聚物含量的方法。实验测定的标准工作曲线为y=0.055 67x+0.1091,r=0.999 3。利用该标准工作曲线定量测定了共聚物组分含量,其结果与1H NMR测定值一致,相对误差在2％以内,证明红外光谱法可方便、快捷地测定聚(乳酸-苯丙氨酸)共聚物组分含量,且适用于其他聚(乳酸-氨基酸)共聚物的含量测定,具有一定的实用性及推广性。     

Proton induced modification in Poly(ethylene terephthalate)

A systematic investigation of 62 r MeV proton irradiated Poly(ethylene terephthalate) (PET) has been carried out using Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction spectroscopy. The experiments revealed a restoration of the crystalline matrix and simultaneous decrease in thermal stability in the irradiated polymer as a function of dose, indicating that PET underwent both degradation and cross-linking by proton irradiation.