DODAB and DODAC bilayer-like aggregates in the micromolar surfactant concentration domain

In the millimolar concentration domain (typically 1 mM), dioctadecyldimethylammonium bromide and chloride (DODAX, X representing Br⁻ or Cl⁻ counterions) molecules assemble in water as large unilamellar vesicles. Differential-scanning calorimetry (DSC) is a suitable technique to obtain the melting temperature (T _m) characteristic of surfactant bilayers, while fluorescence spectroscopy detects formation of surfactant aggregates, like bilayers. These two techniques were combined to investigate the assembly of DODAX molecules at micromolar concentrations, from 10 to 100 μM. At 1 mM surfactant, T _m ≈ 45 °C and 49 °C, respectively, for DODAB and DODAC. DSC and fluorescence of Nile Red were used to show the formation of DODAX aggregates, at the surfactant concentration as low as 10 μM, whose T _m decreases monotonically with increasing DODAX concentration to attain the value for the ordinary vesicles. The data indicate that these aggregates are organized as bilayer-like structures.     

Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites.It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer (). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer .     

锂离子电池正极材料LiMnO_2的电化学阻抗谱研究

通过球形扩散模型给出了一种测定锂离子在电极材料中固相表观扩散系数的计算方法(修正Warburg阻抗法),研究了LiMnO_2电极的交流阻抗和锂离子的扩散行为.研究表明,材料合成温度影响电极反应表面电荷传递和材料中的锂离子扩散特性.用熔盐浸渍法在500℃保温12h合成的LiMnO_2正极材料的锂离子表观扩散系数为1.49×10~(-10)cm~2/s.     

Improvement in toughness of poly(l-lactide) (PLLA) through reactive blending with acrylonitrile-butadiene-styrene copolymer (ABS): Morphology and properties

Poly(l-lactide) (PLLA) was melt-blended with acrylonitrile-butadiene-styrene copolymer (ABS) with the aim of enhancing impact strength and elongation at break of PLLA, but not sacrificing its modulus and stiffness significantly. However, PLLA and ABS were found to be thermodynamically immiscible by simply melt blending and the formed blends show deteriorated mechanical properties. The reactive styrene/acrylonitrile/glycidyl methacrylate copolymer (SAN-GMA) by incorporating with ethyltriphenyl phosphonium bromide (ETPB) as the catalyst was used as the in situ compatibilizer for PLLA/ABS blends to improve the compatibility between PLLA and ABS. The reactive process during melt blending was investigated by Fourier transformed infra-red (FTIR). It showed that the epoxide group of SAN-GMA reacted with PLLA end groups under the mixing conditions and that the addition of ETPB accelerated the reaction. Phase structure and physical properties of the compatibilized blends were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic mechanical analysis (DMA), tensile tests and impact property measurements. It was found that the size of ABS domains in PLLA matrix is significantly decreased by addition of the reactive compatibilizer. The dynamic mechanical analysis revealed markedly shifted glass transition temperatures for both PLLA and ABS, indicating the improved compatibility between PLLA and ABS. The mechanical tests showed the compatibilized PLLA/ABS blends had a very nice stiffness-toughness balance, i.e., the improved impact strength and the elongation at break with a slightly loss in the modulus.     

Real Time Electrochemical Monitoring of DNA/PNA Dissociation by Melting Curve Analysis

An immobilization‐free electrochemical method is reported for real‐time monitoring of the DNA hybrid dissociation between a ferrocene labeled peptide nucleic acid (PNA) and a fully‐complementary or single‐base‐mismatched DNA. This method takes advantages of electrostatic charge characteristics and interactions among the neutrally charged PNA, the negatively charged DNA and the negatively charged electrode surface made of indium tin oxide (ITO). When a ferrocene labeled PNA (Fc‐PNA) sequence is hybridized to a complementary DNA strand, electrostatic repulsion between the negatively charged PNA/DNA hybrid and the negative ITO surface retards the diffusion of the electroactive Fc to the electrode, resulting in a much reduced electrochemical signal. On the other hand, when the Fc‐PNA is dissociated from the hybrid at elevated temperatures, the neutrally charged Fc‐PNA easily diffuses to the electrode with an enhanced electrochemical signal. Therefore, an electrochemical melting curve of the Fc‐PNA/DNA hybrid can be obtained by measuring the Fc signal with the increasing temperature. This strategy allows monitoring of the dissociation of the DNA hybrid in real time, which might lead to a simple detection method for single nucleotide polymorphism (SNP) analysis.     

SrF2和BaF2熔化温度的分子动力学模拟

利用壳层模型分子动力学方法,考虑萤石结构分子中的预熔化现象,对SrF2和BaF2的分子动力学模拟熔化温度进行修正,获得了高压下SrF2和BaF2的熔化温度．同时给出了300K、0．1MPa-7GPa和10．1MPa-3GPa时SrF2和BaF2的状态方程,与已有研究结果的最大误差分别为0．3％和2．2％．计算所得SrF2和BaF2常压下的熔点与已有的实验结果符合较好．对于SrF2和BaF2分子体积变化和已有的熔化模拟的差别也做了比较和讨论．     

中介尺度Au纳米团簇熔化的分子动力学模拟

采用分子动力学模拟技术，研究了原子个数为16～8628的 Au纳米团簇的熔化过程.采用 Johnson的EAM (embedded atom method) 模型,模拟结果表明，金属纳米团簇存在一中介尺度区域.对Au纳米团簇而言，当原子个数N >456时，团簇的热力学性质与团簇尺寸呈线性关系，熔化首先从表面开始，逐步向中心区域推进，且满足Tmb－Tmc(N)＝aN(－1/3)的关系.另外，计算了中介区域的团簇的尺寸、熔化温度、表面能、熵、焓等热力学量以及均方根位移（RMSD）等动力学量，为研究纳米团簇提供定量数据.     

PVCH-PE-PVCH三嵌段共聚物在超临界CO2中的熔融再结晶行为

本研究组在前期研究中发现, 改变溶剂的挥发速率可以调节体系中PE结晶和PVCH玻璃化之间的竞争, 进而调节PE结晶的受限程度. 超临界二氧化碳(scCO2)是一种非极性溶剂, 其对无定形聚合物(如PS)有很强的溶胀作用, 可显著降低聚合物的玻璃化转变温度, 提高原来被冻结的高分子链的活动能力. PVCH的分子结构与PS相似, 研究结果表明, scCO2对PVCH组分也有很强的溶胀能力, 导致PVCH的玻璃化转变温度降低, 从而可以改变PE嵌段的受限状态. 本文研究了PVCH-PE-PVCH在scCO2中的熔融再结晶行为.     

Molecular Dynamic Simulation of Melting Points of Trans-1,4,5,8-tetranitro-1,4,5,8-tetraazadacalin (TNAD) with Some Propellants

Molecular dynamic simulation was employed to predict the melting points Tm of TNAD/HMX, TNAD/RDX, TNAD/DINA, and TNAD/DNP systems (tans-1,4,5,8-tetranitro-1,4,5,8-tetraazadacalin (TNAD), dinitropiperazine (DNP), cyclotetramethylenete-tranitroamine (HMX), cyclotrimethylenetrinitramine (RDX), and N-nitrodihydroxyethy-laminedinitrate (DINA)). Tm was determined from the inflexion point on the curve of mean specific volume vs. temperature. The result shows that the Tm values of TNAD/HMX, TNAD/RDX, and TNAD/DINA systems are 500, 536, and 488 K, respectively. The TNAD/DNP system has no obvious Tm value, which shows the system is insoluble. Us-ing Tm, the solubility of the four systems was analyzed. The radial distribution functions of the four systems were analyzed and the main intermolecular forces between TNAD and other energetic components are short-range interactions. The better the solubility is, the stronger the intermolecular interaction is. In addition, the force field energy at different temperature was also analyzed to predict Tm of the four systems.     

聚丙烯接枝己内酯型增容剂的合成及其共混增容应用

以含悬挂羟基的聚丙烯为引发剂,辛酸亚锡为催化剂催化己内酯开环聚合,成功制备了一系列支链为聚己内酯的功能化接枝聚丙烯,并通过核磁共振、红外光谱、示差扫描量热（DSC）和广角X射线衍射（WAXD）等技术手段对聚合物进行了明确的结构表征。 研究了反应温度和时间对接枝反应的影响,结果表明,最佳反应温度为90 ℃,通过改变接枝时间可以调控己内酯链段的长度。 将成功接枝的功能化聚丙烯用做聚丙烯与尼龙-6共混体系的增容剂,并通过扫描电子显微镜（SEM）观察的方法考察了该增容剂对共混体系的影响。 SEM 显示增容剂的加入显著地降低了界面张力,减小了分散相的尺寸,增强了界面的粘结性。