Fractionated Crystallization Kinetics and Polymorphic Homocrystalline Structure of Poly(L-lactic acid)/Poly(D-lactic acid) Blends: Effect of Blend Ratio

Stereocomplex (SC) crystallization has been an effective way to improve the physical performances of stereoregular polymers. However, the competition between homo and SC crystallizations can lead to more complicated crystallization kinetics and polymorphic crystalline structure in stereocomplexable polymers, which influences the physical properties of obtained materials. Herein, we select the medium-molecular-weight (MMW) poly(_L-lactic acid)/poly(_D-lactic acid) (PLLA/PDLA) asymmetric blends with different PDLA fractions (f_D=0.01–0.5) as the model system and investigate the effects of f_D and crystallization temperature (T_c) on the crystallization kinetics and polymorphic crystalline structure. We observe the fractionated (i.e., multistep) crystallization kinetics and the formation of peculiar β-form homocrystals (HCs) in the asymmetric blends under quiescent conditions, which are strongly influenced by both f_D and T_c. Precisely, crystallization of β-form HCs is favorable in the MMW PLLA/PDLA blends with high f_D (≥0.2) at a low T_c (80–100 °C). It is proposed that the formation of metastable β-form HCs is attributed to the conformational matching between β-form HCs and SCs, and the stronger constrain effects of precedingly-formed SCs in the early stage of crystallization. Such effects can also cause the multistep crystallization kinetics of MMW PLLA/PDLA asymmetric blends in the heating process.

     

含TEMPO配合物的合成、表征、谱学性质及光猝灭机理

A novel Pt(Ⅱ)-based metallointercalator terpyridine complex linked with a 2, 2, 6, 6-tetramethyl-1-piperidinyl N-oxide (TEMPO) derivative was prepared by a reaction between 4'-TEMPO-terpyridine (L) and a Pt(Ⅱ) salt. This complex presented unusual luminescence quenching owing to the effect of the stable nitroxide radical. The crystal structure of[Pt(terpy-TEMPO)Cl]Cl·H₂O·CH₃OH (terpy=2, 2':6', 2"-terpyridine) was elucidated by X-ray crystallography. Additionally, the effect of TEMPO on the photophysical properties of[Pt(terpy-TEMPO)Cl] Cl·H₂O·CH₃OH was investigated by UV-Vis, fluorescence emission, and electron paramagnetic resonance (EPR) spectroscopy. Data from the absorption and luminescence properties (298 K) of the[Pt(terpy-TEMPO)Cl]⁺ complex indicated the presence of two groups of typical bands:an intense band B with distinct vibronic structures (270-350 nm, ε>10⁴ dm³·mol^-1·cm^-1) and a less intense band A (370-450 nm, ε~10³ dm³·mol^-1·cm^-1). These two bands are generally assigned to ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT) excited states, respectively. Furthermore, efficient photoluminescent quenching behavior was observed in the emission spectra of this complex system. Quantum calculations of the molecular energy gaps and bands were performed by Gaussian 09 software. The calculated results verified that TEMPO greatly affects the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Thus, the relationship between efficient photoquenching and molecular structure was theoretically interpreted. EPR results indicated that when TEMPO is attached to a macrocyclic terpyridine platinum complex, e.g., [Pt(terpy)Cl]⁺, the terpyridine platinum complex does not affect the hyperfine coupling constant (A value) and g factor (g values) but the rotation and relaxation times of the TEMPO radical.     

液/固界面多肽分子组装精细结构的扫描隧道显微镜研究

介绍了与蛋白构象病相关的淀粉样多肽分子组装结构的研究进展.综述了在固体、溶液以及界面等不同状态下多肽分子组装结构的表征方法,对于扫描隧道显微技术(STM)在解析多肽分子界面组装结构方面的研究进展进行了重点评述,主要包括在液/固界面上的多肽分子组装结构的精细特征,界面诱导的多肽构象转变,调节分子、染料等与多肽组装结构的相互作用模式和位点识别等.     

介孔尺度及结构对混合硝酸盐热输运特性的影响

米用分子动力学方法模拟介孔尺度和结构对混合硝酸盐热输运特性的影啊.便用Material Studio软件分别建立不同尺度、两种结构的混合硝酸盐模型以及达到共晶状态的不同比例的NaNO₃-KNO₃模型,通过对模型进行运算并整理计算结果,对纳米尺度下混合硝酸盐热输运特性的微观机理进行分析.结果表明:太阳盐的相变温度随着纳米孔尺度的增大呈现先增加后减小的趋势,最终与宏观尺度下的熔点一致;阳离子的比例对混合硝酸盐的相变温度有很大的影响,且纳米线结构也会改变硝酸盐的相变温度.硝酸盐的体热膨胀系数随着介孔尺度的增大而减小,随着NaNO₃含量的增加而增大,随着介孔结构的改变而改变.离子之间的相互作用的增强会使导热率增大,但对定压比热容没有太大影响.