Pulsed laser deposition of a thin conjugated-polymer film

Thin films of poly(3-octylthiophene), P3OT, were deposited by pulsed laser ablation method. Infrared spectroscopy indicates that the major chemical structure of P3OT survived the ablative process. In addition, the films exhibit enhanced linear and non-linear optical responses as compared with the spin-coated P3OT films. Our results demonstrate the potential of laser ablation in producing π-conjugated polymer films of high quality.     

Thiazole-containing benzo-crown ethers: a new class of ammonium-selective ionophores

A new class of crown ethers containing heterocyclic units has been designed to develop synthetic NH4+-selective ionophores whose resulting potentiometric properties in solvent polymeric membranes are superior or at least comparable to those of nonactin. It was found that the derivatives of thiazole containing dibenzo-18-crown-6 (1; TDB18C6) incorporated in PVC-based membranes provide enhanced NH4+ selectivities over alkali metal cations, especially over Na+, compared to those of the nonactin-doped membranes: for example, the selectivity coefficients, log K(POT)NH4+J (J = Li+, Na+, K+), for the 2-nitrophenyloctyl ether (NPOE) plasticized PVC membranes doped with the hexyl chain-substituted TDB18C6 (2) were -4.9, -3.9, and -1.3, while those for the same type of membranes with nonactin -4.4, -3.0, and -1.0, respectively. Unlike other synthetic NH4+-selective neutral carriers reported to date, TDB18C6-type compounds result in potentiometric performance highly comparable to that of the nonactin-based ones except their slightly higher detection limits (approximately 3 x 10(-6) vs 7 x 10(-7)). The complex formation between TDB18C6 and NH4+ was identified from 1H NMR spectra. The 1:1 complex formation constant of TDB18C6 with NH4+ in solvent polymeric membranes estimated using the method suggested by Bakker et al. and the NH4+ selectivity coefficient over K+ (K(POT)NH4+,K+) are approximately 200 times smaller than that of nonactin (1.8 x 10(7) vs 3.6 x 10(9)).     

Potentiometric evaluation of solvent polymeric carbonate-selective membranes based on molecular tweezer-type neutral carriers

Potentiometric properties of the ion-selective electrodes) based on highly plasticized PVC membranes doped with the carbonate-selective cholic acid (CA) derivatives have been measured. The carbonate-selective neutral carriers have been prepared by coupling one to three trifluoroacetobenzoyl (TFAB) groups to a cholic acid derivative which has three hydroxyl linkers lining on the C3, C7, and C12 positions of its rigid steroidal ring structure. The membranes based on cholic acid derivatives with two TFABs [3,7-bis(TFAB)CA, 3,12-bis(TFAB)CA, and 7,12-bis(T-FAB)CA] exhibited remarkably improved carbonate selectivity, indicating that the bis(FAB)CAs behave like molecular tweezers for the carbonate ion. For example, 3,12-bis(TFAB)CA resulted in 10-300-fold-enhanced carbonate selectivity over other anions (e.g., salicylate, ClO4-, SCN-, (HPO4)2-, NO3-, NO2-, Br-, and Cl-) compared to that of the neutral carriers with a single TFAB group. The distances between the carbonate binding centers of bis(TFAB)CAs, i.e., the carbonyl carbons of the two TFAB groups, are in the 7.3-7.9-A range at the AM1 level semiempirical calculation, which is too far for the carbonate ion to form direct covalent bonding. The fast atom bombardment mass spectra of bis(TFAB)CAs show that significant fractions of the compounds are either mono- or dihydrated before complexing the carbonate ion. These findings seem to suggest that bis(TFAB)CAs recognize the incoming carbonate ion by forming both covalent and hydrogen bonding between the hydrated and unhydrated TFAB groups. The analytical utility of the carbonate-selective electrode based on 3,12-bis(TFAB)-CA has been demonstrated by measuring the total carbon dioxide in human serum in the presence of lipophilic anion interferents, e.g., salicylate.     

One-component room temperature vulcanizing-type silicone rubber-based calcium-selective electrodes

New calcium-selective membranes for all-solid-state ion sensors are developed with a highly adhesive one-component room temperature vulcanizing-type silicone rubber (RTV-1-type SR) matrix. The membranes are formulated with 21.6 wt % bis(2-ethylhexyl) adipate, 0.3 wt % tetradodecylammonium tetrakis(p-chlorophenyl)borate (ETH 500), 0.1 wt % potassium tetrakis(p-chlorophenyl)borate, and 0.8 wt % calcium-selective neutral carrier ETH 129 or ETH 1001. Plasticizer added to the RTV-1-type SR matrix not only decreases the bulk membrane resistance but also increases the solubility of electroactive components incorporated in the membrane without significantly deteriorating its adhesive strength. It is found that the lipophilic salt ETH 500 remarkably enhances the calcium selectivity of ETH 129 or ETH 1001 ligands in the SR matrix; the selectivity coefficients ([Formula: see text] by separate solution method, where j = Li(+), Na(+), K(+), or Mg(2+)) for the optimized membranes were below 10(-5). Potentiometric characteristics of planar-type Ag electrodes coated with optimized RTV-1-type SR membranes, e.g., response slope 29.0 ± 0.5 mV/decade, detection limit below 5.0 × 10(-7) M a(Ca)((2+)), and 2-3 mV of potential drift per day, were virtually the same as those of the corresponding poly(vinyl chloride) membrane-based conventional electrodes, but with greatly enhanced sensor-to-sensor reproducibility and lifetime (3-9 weeks).     

用当代飞行时间二次离子质谱分析航天器污染

随着对航天器长寿命和高可靠性的要求日益提高，其污染问题已引起国内外高度重视。在监测污染物总量的基础上，需要有效的分析手段确定污染物的化学成分才能判断污染源。用当代飞行时间二次离子质谱仪器（TOF-SIMS）对我国地面空间环境模拟污染的典型样品进行了探索性实验，结果表明：与国内外现有的检测手段相比，当代TOF-SIMS最适于样品量有限的航天污染物的成份分析；具有高质量分辨的TOF—SIMS，对航天污染物包含的所有元素、同位素和化合物具有指纹鉴别能力；成像分析可解析出污染物形成历史的一些相关信息。TOF-SIMS有望在航天污染系统工程中发展成为一种独具特色的航天污染检测新技术。     

Frost formation on a cold surface under turbulent flow

This study presents a mathematical model to predict the frosting behavior on a cold surface under turbulent flow. The model consists of the standard κ–ε model for turbulent flow and the diffusion equation for the frost layer. The numerical results show that turbulent flow promotes the growth of the frost layer on the cold surface, compared to the laminar flow. Increase in air velocity has little effect on mass transfer under turbulent flow, while frost growth under laminar flow is influenced by the air velocity. With constant air humidity, the frost layer thickness increases with decreasing air temperature, while the relationship for the frost density is reversed. The effect of the air temperature on the mass flux is negligible, compared to the other frosting parameters.     

Syntheses of Mn3O4 and LiMn2O4 nanoparticles by a simple sonochemical method

Mn₃O₄ and LiMn₂O₄ nanoparticles were prepared by a simple sonochemical method which is environmentally benign. First, Mn₃O₄ nanoparticles were prepared by reacting MnCl₂ and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min. Second, LiOH was coated onto the resulting Mn₃O₄ under the same sonochemical conditions as above. The thickness of coated LiOH on Mn₃O₄ obtained from the reaction ratio of 3:1 between LiOH and Mn₃O₄ was about 4.5–5.5 nm range. Then, by heating those LiOH-coated Mn₃O₄ particles at the relatively low temperature of 300–500 °C for 1 h, they were transformed into phase-pure LiMn₂O₄ nanoparticles of about 50 to 70 nm size in diameter.     

Characterization of Edge Contact: Atomically Resolved Semiconductor–Metal Lateral Boundary in MoS2

Despite recent efforts for the development of transition‐metal‐dichalcogenide‐based high‐performance thin‐film transistors, device performance has not improved much, mainly because of the high contact resistance at the interface between the 2D semiconductor and the metal electrode. Edge contact has been proposed for the fabrication of a high‐quality electrical contact; however, the complete electronic properties for the contact resistance have not been elucidated in detail. Using the scanning tunneling microscopy/spectroscopy and scanning transmission electron microscopy techniques, the edge contact, as well as the lateral boundary between the 2D semiconducting layer and the metalized interfacial layer, are investigated, and their electronic properties and the energy band profile across the boundary are shown. The results demonstrate a possible mechanism for the formation of an ohmic contact in homojunctions of the transition‐metal dichalcogenides semiconductor–metal layers and suggest a new device scheme utilizing the low‐resistance edge contact.     

COPNA树脂的合成及其复合材料耐热性研究

以三种不同的油浆为原料 ,在酸性催化剂存在下 ,与对苯二甲醇反应 ,得到三种缩合多环多核芳烃 (COPNA)树脂。以COPNA树脂、酚醛、环氧树脂为基体 ,与碳纤维复合 ,通过模压成型 ,得到三种不同基体的复合材料。比较考察了COPNA树脂的软化点、残炭、β树脂含量等粘结性参数以及树脂 /碳纤维复合材料的耐热性能。经分析认为 ,得到的COPNA树脂可达到工业粘结剂的要求 ,具有很好的粘结作用 ;以COPNA树脂为基体的碳纤维复合材料 ,表现出很好的耐热性 ,这为COPNA树脂的应用提供了一个很好的方向。     

25th Anniversary Article: Rational Design and Applications of Hydrogels in Regenerative Medicine

Hydrogels are hydrophilic polymer‐based materials with high water content and physical characteristics that resemble the native extracellular matrix. Because of their remarkable properties, hydrogel systems are used for a wide range of biomedical applications, such as three‐dimensional (3D) matrices for tissue engineering, drug‐delivery vehicles, composite biomaterials, and as injectable fillers in minimally invasive surgeries. In addition, the rational design of hydrogels with controlled physical and biological properties can be used to modulate cellular functionality and tissue morphogenesis. Here, the development of advanced hydrogels with tunable physiochemical properties is highlighted, with particular emphasis on elastomeric, light‐sensitive, composite, and shape‐memory hydrogels. Emerging technologies developed over the past decade to control hydrogel architecture are also discussed and a number of potential applications and challenges in the utilization of hydrogels in regenerative medicine are reviewed. It is anticipated that the continued development of sophisticated hydrogels will result in clinical applications that will improve patient care and quality of life.