层状液晶凝胶对微泡沫的稳定作用

以非离子表面活性剂单硬脂酸甘油酯(GMS)制备出稳定的微泡沫. 采用偏光显微镜、冷冻断裂蚀刻透射电子显微镜(FF-TEM)、差示扫描量热仪(DSC)和流变仪对其表面活性剂溶液相态、泡沫体系的微观结构、相变行为和流变性进行研究以探索微泡沫的稳定机理. 实验结果表明, 表面活性剂分子吸附在气泡界面, 发生晶化形成有序、紧密排列的层状液晶凝胶相液膜, 该液膜具有较强的刚性, 能抵抗由Laplace附加压力驱使的气泡溶解和聚并行为. 微泡沫可稳定10个月, 无明显的相分离和气泡破裂现象. 其稳定作用机理是通过影响泡沫排液过程, 增强Gibbs-Marangoni效应, 从而提高了气泡液膜强度, 减缓了气相扩散速率.     

聚丙烯鱼眼与晶点的成因

聚乙烯 (PE)、聚氯乙烯 (PVC)、聚苯乙烯(PS)、聚丙烯 (PP)等高分子材料在加工成型为薄膜时 ,常会出现气泡或小粒子 ,因气泡形状与鱼眼(Fisheyes)相似 ,故得名 .有关鱼眼的成因 ,都认为与挤出混合不均一或与高分子融体的污染有关 [1～ 4 ] ,也有人从 GPC的数据推测与聚丙烯的低分子成份有关 [5] ,但未用具体样品进行研究 .本文的鱼眼是指 PP在制作编织袋过程中出现的小气泡 ,此气泡随薄膜吹塑比增大而增大 ,在拉伸方向呈现中部最薄的鱼眼 ,是吹塑过程中的爆破点 .使 PP编织丝的强度达不到应有的要求而影响质量 .本文的晶点是指在膜上…     

电化学控制产生纳米氧气气泡及其对电化学聚合吡咯形貌的影响

利用原位电化学原子力显微镜(in-situ EC-AFM)研究了纳米氧气气泡在高定向热解石墨(HOPG)表面的电化学控制产生与生长. AFM原位图像表明电化学产生的氧气在HOPG表面形成了纳米气泡, 并且纳米气泡的产生与生长可以通过改变外加电压和反应时间来进行控制. 随后, 研究了电化学产生的纳米氧气气泡对于在HOPG表面电化学聚合吡咯反应的影响, 结果表明伴随聚合反应过程产生的纳米氧气气泡使得生成的聚吡咯膜表面形成了气泡状的缺陷.     

原电池负极上的副反应探析

在原电池中 ,理论上 ,是在负极上发生氧化反应 ,在正极上发生还原反应 ,电子由负极通过外电路流向正极。但是 ,实际进行原电池的实验时 ,往往有副反应发生 ,即负极上也发生还原反应。以Cu -Zn原电池为例 ,如图 1装置 ,理论上的反应是 :负极 (Zn) :Zn%D 2e%D Zn2 +　 (氧化反应 )　　正极 (Cu) :2H++ 2e-H2 ↑　 (还原反应 )其现象应该是 ,在正极上有气泡产生 ,而负极逐渐消耗 ,没有气泡出现。但是 ,实际上 ,正极和负极上通常都有气泡产生 ,即负极上也有氢离子得电子的副反应发生。由于副反应的存在 ,原电池的效率就大大降低了。图 1对于…     

气泡最大压力法测定溶液表面张力实验装置的改进

国内物理化学实验用气泡最大压力法测定溶液表面张力的装置不足之处是:毛细管内的气泡很难以单个方式出现,常常是连串产生,造成压力计内液面连续跳动,液面高度差难以读准(本实验的关键是要测准压力计差△h),对数据处理引入较大误差。针对上述不足,我对原装置进行了改进:将装置中的滴液漏斗换成注射器,通过控制抽气速度快慢来控制毛细管内气泡产生,改进后的装置如图所示。用改进的装置优点在于:(1)能够很好地控制毛细管内产生单个气泡,使得压力计中液面不会连续跳动;(2)气泡的产生和读数能同步进行,做到每产生一个气泡读一次数,能十分准确读出压力差     

水中悬浮气泡法研究水合物生长动力学

提出了利用测定温度、压力与水中悬浮气泡表面上水合物生长速度的关系, 以获得普遍适用的水合物生成动力学数据的新实验方法. 采用Gibbs自由能差作为反应推动力对所测的甲烷、二氧化碳气泡水合物生长动力学数据进行了关联, 取得了较好的效果. 对实验中发现的新现象进行了描述和解释.     

纳米气泡电化学研究进展

纳米气泡广泛存在于许多自然现象和工业生产过程,其自身具有独特的物理化学性质.由于涉及气体反应的纳米电催化及能源转化技术的迅速发展,有关纳米气泡的电化学研究越来越受研究者的关注.针对电极界面纳米气泡的研究不仅有助于实现对气泡行为的调控,指导催化剂电极界面的合理设计以提高电催化效率,也可以从科学上去了解纳米催化剂本征电催化机制与特性,同时还能加深对相变成核这一基本物理化学现象的理解.本文重点综述了电极界面上微纳气泡的电化学研究方法和进展,介绍了基于纳米圆盘电极和电化学池显微镜的单个纳米气泡电化学研究方法,并分析了界面纳米气泡的动态稳定性机制.我们还概括了近年来光学显微术用于电化学产生的微纳气泡的成像研究.最后我们讨论了本领域的主要挑战并展望了未来的发展趋势.     

固液界面纳米气泡研究

固液界面纳米气泡是近十年来表面科学的重要发现之一。从利用原子力显微镜(AFM)在固液界面上观察到纳米气泡以来,科学工作者们已经证实了纳米气泡在固液界面上存在。由于其在微机电系统(MEMS)、微生化系统、表面科学、流体动力学等领域潜在的应用价值,各国学者们对纳米气泡的自身性质及影响因素已经开展了多方面的研究。但纳米气泡稳定性(反常的长寿)的原因仍然是未解决的问题之一。本文综述了纳米气泡的形成及影响因素,重点评述了纳米气泡稳定性理论,包括线张力理论、动态平衡理论、杂质理论和克努森气体理论等。同时,介绍了固液界面纳米气泡的应用,并展望了未来研究的重点和方向。     

检测器(Ⅲ)

3使用及故障的排除如前述,检测器是一种将物质的量变化转变成电信号,并由记录或处理装置进行处理的仪器,出现的所有问题大多也是依据记录下的信号图（色谱图）来判断解决的。在有正确的判断和解决方法之前,一个非常重要的问题是色谱图的记录要绝对准确。但有一个极易造成混淆的现象是气泡的干扰。3．l气泡在液相色谱泵的章节中我们谈到了气泡会对液相色谱分析造成较大的困难,检测器中气泡所带来的麻烦也决不会低于在泵中的困扰,因此对气泡决不可大意。气泡通过流动池时,在色谱图上可能形成一个尖锐的峰,也可能形成像正常色谱峰的峰…     

超疏水网状结构对水中气泡的转移作用

通过一步浸泡法制得了超疏水网状结构. 采用环境扫描电镜(ESEM)、X光电子能谱(XPS)和傅里叶变换红外光谱(FTIR)分别对超疏水网状结构的微观形貌和化学组成进行了表征, 结果表明, 超疏水的网状结构是由连续排列的类菊花状结构堆积而成的, 组成花瓣的微簇是具有层状结构的Cu[CH3(CH2)12COO]2. 借助高速照相机研究了超疏水网状结构表面与水中气泡的相互作用行为规律, 发现该超疏水网状结构对水中气泡产生转移作用, 而亲水的网状结构则不具备该特性.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.