Small-angle neutron scattering from micelles of alkylpolyoxyethylene sulfate: Effect of chain length

Small-angle neutron scattering (SANS) data have been obtained for (i) a series of solutions of C _m H_2m+1(OCH₂–CH₂)₂SO₄Na, for m=18, 16, and 14; (ii) an approximately 0.07M solution of C₁₄H₂₉(OCH₂–CH₂)₂SO₄Na to which different amounts of NaCl were added; and (iii) a series of solutions of variable concentration of C₁₂H₂₅(OCH₂–CH₂)SO₄Na. The increase of the number of carbon atoms of the hydrocarbon chain produces a noticeable increase of the aggregation number of the micelles, while the salt tolerance decreases with increasing m. All the data can be described in terms of a monodispersed, charged, hard-spheres model interacting via a screened Coulombic potential, except the run at highest salt concentration, for which an ellipsoid model gives better results.     

Association models for alcohol-water mixtures

Alcohol-water mixtures are often used as model systems for the study of hydrophobic interactions. In this respect, their thermodynamic properties are of particular interest since precise data are available over the whole miscibility range and they lend themselves readily to theoretical modelling. Three association models have been used to fit the volume data taken from the literature for aqueous methonol, ethanol and n-propanol at various temperatures. A simple micellization equilibrium explains the general trends but fails to fit the reduced excess volumes at both ends of the mole fraction scale. Better fits are obtained if interaction parameters are introduced, but these two parameters cannot easily be rationalized. A double association model (one for the alcohol and one for the water) gives the best fit and all the parameters have a physical significance. However, the parameters extracted, e.g. aggregation numbers, and their trends with temperature are not always realistic. Despite their limitations, these models illustrate well with the kind of avenues that can be explored to fit and interpret the experimental data of these complex systems.     

Nusselt number correlations for heat transfer to small spheres in thermal plasma flows

Seven different equations predicting heat transfer rates to small spheres in plasma flows are examined considering argon and nitrogan as plasma gases from 300 to 21,000 K at 1 atm. For argon there is a general consensus up to 9000 K, beyond which wide deviations in behavior occur. For nitrogen, the seven correlations are in good agreement up to 4000 K, but show substantial deviations beyond this value. Comparisons with the sparsely available experimental data are made for argon from 300 to 17,000 K and for nitrogen up to 5500 K. Disagreement between the various correlations and experiment can exceed one order of magnitude.     

Electrochemical studies of Tl(I) crown-ether complexes in nonaqueous media

Summary Complexation equilibria of the Tl(I) ion with 18-crown-6 and dibenzo-18-crown-6 were studied polarographically in 10 nonaqueous solvents. The stability of the complexes is strongly influenced by the nature of solvents and varies with their Lewis basicities. It has been found that the logK _s value (K _s is the stability constant of the complex) can be well described by empirical relation logK _s=a DN+b, whereDN stands for the Gutmann donor number anda andb mark the regression coefficient. Addition of the second explanatory parameter, the acceptor number, is not statistically significant. This result is in agreement with the predominant role of Tl(I) ion solvation.

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Elektrochemische Untersuchungen von Tl(I)-Kronenetherkomplexen in nichtwäßrigen Medien

Zusammenfassung Es wurden die Komplexierungsgleichgewichte des Tl(I)-Ions mit 18-Krone-6 und Dibenzo-18-krone-6 polarographisch in 10 nichtwäßrigen Lösungsmitteln untersucht. Die Stabilität der Komplexe wird sehr stark vom Solvens beeinflußt, wobei eine starke Abhängigkeit von der Lewis-Basizität beobachtet wird. Es wurde festgestellt, daß die logK _s-Werte (K _s ist die Komplexstabilitätskonstante) gut mit der empirischen Beziehung logK _s=a DN+b beschrieben werden können, wobeiDN die Gutmann'sche Donorzahl unda undb die Regressionskonstanten bedeuten. Hinzunahme der Akzeptorzahl als zweiten Parameter bleibt statistisch insignifikant. Dieses Ergebnis stimmt mit dem dominierenden Einfluß der Tl(I)-Ionensolvatation überein.

     

Iminophosphanes: Unconventional Compounds of Main Group Elements

The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as “exotic” in main group chemistry. While the rich chemistry of P? C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry.     

Size of Micelles Determined by Static Fluorescence Quenching

We developed a new method to measure the average aggregation number of large rod-like micelles using static fluorescence self-quenching of a solubilized fluorophore. The method is based on the increase of self-quenching of micelle-solubilized pyrene through excimer formation. We consider the effect of random distribution of pyrene in micelles and the micellar size distribution. The measured average aggregation <n> _M is based on a new M-weighted raging similar to our exponential-weighted averaging in the transient decay method. We apply this method to study the effect of a large concentration of salt on the average aggregation behavior of sodium dodecyl sulfate (SDS) and cetyle tetraammonium bromide (CTAB). The sizes increase with increasing ionic concentrations. For SDS, we used the thermodynamic model developed by Missel et al. to calculate < n > _M which we compare with experimental results.     

Role of solvent in the compatibility of a vinylchloride–vinylacetate–maleic acid terpolymer and nitrocellulose blends

The compatibility of cast films of a vinylchloride–vinylacetate–maleic acid terpolymer (VMCH) and nitrocellulose (NC) blends is influenced by solvents. Transparent films of VMCH/NC blends are obtained when cast from solvents such as tetrahydrofuran or cyclohexanone, whereas hazy films are obtained when cast from solvents such as acetone or ethylacetate. Visible spectroscopy and phase morphology were used to analyse the compatibility–incompatibility of the blend. Differential scanning calorimetry (DSC) studies demonstrate that the transparent film is compatible, but the hazy film is incompatible. Fourier transform infra-red (FTIR) studies establish that a greater interaction is observed between the polymer pair in case of the compatible blend than in the case of the incompatible blend. A solvent dependency of blend compatibility is reflected in this study. The conformational state of the polymers in solution, which is responsible for the compatibility phenomena, may depend on the donor number and/or Taft-β value of the solvent. The greater the donor number and/or the Taft-β value, the higher may be the level of interaction between the solvent and the polymer molecules, which in turn may give a compatible blend after removal of the solvent.     

主成分-BP算法在近红外光谱法纸浆卡伯值测量中的应用研究

提出采用主成分-BP算法建立纸浆卡伯值近红外光谱法在线测量模型。结果表明,这种算法由于既考虑到了近红外光谱响应的非线性因素,又可防止BP算法在建模时出现“过拟合”的现象,利用该算法建立的纸浆卡伯值测量模型与一元回归,多元回归和主成分回归等线性方法相比,具有更高的预测精度。     

壳聚糖镍和壳聚糖镧配位聚合物的配位数研究

从ＩＲ、ＥＳＲ和ＸＰＳ的测试结果可知,Ｎｉ＾２＋或Ｌａ＾３＋与壳聚糖（ＣＳ）键节单元上的氨基Ｎ和仲羟基Ｏ发生配位反应,形成ＣＳ－Ｎｉ＾２＋或ＣＳ－Ｌａ＾３＋配位聚合物膜。通过电导率研究其配位数,发现Ｎｉ＾２＋或Ｌａ＾３＋可与壳聚糖的３个或５个键节单元配位。根据以上的实验可推定中心离子Ｎｉ＾２＋与壳聚糖３个键节单元上的氨基Ｎ和仲羟基Ｏ结合,形成六配位的ＣＳ－Ｎｉ配位聚合物Ｌａ＾３＋与壳聚糖５个键节单     

Electrochemical characteristics of the blended polymer electrolytes containing lithium salts

Blend-based polymer electrolytes composed of poly(ethylene oxide), poly(oligo[oxyethylene]oxysebacoyl), and lithium salts have been prepared. These polymer electrolytes have been investigated in terms of ionic conductivity, transport number, and interfacial characteristics of the lithium electrode in contact with the polymer electrolyte. The influences of the blend composition, the salt used, and its concentration on the electrochemical behavior were studied. © 1996 John Wiley & Sons, Inc.