Redox polymerization of 2-hydroxyethyl methacrylate (HEMA). I. Influence of surfactants on polymerization kinetics

Oxidation of ferrous orthophenanthroline (FeP) by peroxydiphosphate (PP) in aqueous medium at pH 1 was followed spectrophotometrically. Kinetic analysis has shown that oxidation occurs via the formation of an intermediate complex between FeP and PP. Equi-librium and rate constants were calculated. Influence of surfactants on the oxidation of FeP by PP was also Investigated. The equilibrium constant for complex formation was found to be higher in the presence of surfactants. The enhanced complex formation has been attributed to the ionic interactions between the charged surfactant and the ionic species in the reaction medium. Polymerization of HEMA initiated by the redox system,FeP/PP, was carried out in aqueous medium, under the conditions of excess reductant over oxidant and excess oxidant over reductant. The polymerization followed different mech-anisms under these conditions; with excess oxidant, the growing polymer radicals underwent oxidative termination, while with excess reductant, primary radical termination was pre-ferred. The effect of surfactants on the aqueous polymerization of HEMA using the redox system FeP/PP was also investigated. In addition to the decrease in rate, the polymerization followed a different mechanism in the presence of surfactants, the growing radicals ter-minated by mutual interaction. © 1995 John Wiley & Sons, Inc.     

Intercalation and exchange reactions of clay minerals and non-clay layer compounds

Presently, a large variety of layered materials are synthesized that are able to intercalate neutral guest molecules or to exchange inorganic and organic ions for interlayer ions. Several of these materials are also found as minerals.The intracrystalline reactivity of a few selected compounds will be described and compared to clay minerals:

A proton NMR study on aggregation of cationic surfactants in water: effects of the structure of the headgroup

 ¹H NMR chemical shifts of solutions of the following cationic surfactants in D₂O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride, CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δ_mon and the micelle δ_mic. ¹H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant solutions in H₂O, allowing for the difference in structure between D₂O and H₂O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH₂ group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol^-1. Values of (δ_mic–δ_mon) for the surfactant groups at the interface, e.g., CH₃–(CH₂)₁₅–N+(CH₃)₂ and within the micellar core, e.g., CH₃–(CH₂)₁₅–N⁺ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl, and CDPhPrACl. Received: 23 February 1996 Accepted: 29 August 1996     

Packings and stationary phases for biopolymer separations by HPLC

Summary Packings and stationary phases applied to high resolution separations of proteins, enzymes, and nucleic acids must satisfy a series of distinct criteria that are different from those usually required by HPLC of low molecular weight non-biologically active analytes. These requirements have been met through substantial improvements in classical gel media together with novel developments in silica supports, and have led to a family of products with tailor-made and reproducible properties. Supports consisting of cross-linked organic gels, and inorganic materials (mostly silicas) are now available with graduated particle sizes, pore sizes, porosities and surface areas as well as non-porous beads. A whole range of stationary phases, such as reversed phase, hydrophobic interaction, ion exchanger and affinity packings, were designed for application as chemical sensors for biopolymer recognition in adsorptive chromatography. The phase systems are operated in the gradient mode, giving high resolution and high peak capacities. In addition, aqueous liquid-liquid partitioning systems have been developed for the fractionation of proteins and nucleic acids. Size exclusion media complete the set of HPLC variants enabling a discrimination of proteins according to their size and shape in an isocratic elution mode. Basically, protein purification and isolation is a multistage process where-by the HPLC variants are combined in a logistic sequence, utilizing the different selectivities of the phase systems and thus maximising resolution, speed and throughput.     

连接基团链长度对季铵盐二聚表面活性剂C12-s-C12·2Br在水溶液中胶团化行为的影响

用电导法、稳态荧光法和粘度法研究了二聚表面活性剂C12-s-C12*2Br分子中的连接基团链长度(s=2, 3, 4, 6)对其在水溶液中聚集行为的影响. 实验发现, C12-s-C12*2Br的胶团生成能力远比其单体C12TABr强得多, 前者cmc值较后者降低一个数量级. 胶团聚集数N随表面活性剂浓度c的增大而增大, 其中当s=2时的N值在c=7.7 mmol/L后开始急剧增大. 计算结果表明, 此时胶团形状发生了明显变化, 形成了椭球形的胶团. 粘度测定结果也证实了这一点.     

Wetting of surfactant solutions by alkanes.

Ellipsometry, surface tensiometry, and contact-angle measurement have been used to study the transition between partial wetting and pseudo-partial wetting of surfactant solutions by alkanes. In the partial wetting regime, the air-water surface tension is the same with and without alkane. In the pseudo-partial wetting regime, the air-water surface tension is lowered by the presence of alkane, showing that oil is solubilised into the surfactant monolayer. A discontinuous change in the coefficient of ellipticity with increasing surfactant concentration provides unequivocal evidence for the first-order nature of the wetting transitions. Ellipsometry has been used to explore the generality of wetting transitions of alkanes (dodecane, hexadecane, and squalane) on surfactant solutions [dodecyltrimethylammonium bromide, tetredecyltrimethylammonium bromide, dibucaine hydrochloride, and Aerosol OT (AOT)]. Of the systems studied, only hexadecane on AOT solutions did not show a wetting transition. Excess alkane remains as a lens on the surface of the surfactant solutions at all concentrations, but the contact angle is a minimum at the wetting transition. A semiquantitative model for the variation of the contact angle with surfactant concentration is provided.     

A simple adsorption model for ionic surfactants

In the past, few theoretical attempts have been made to describe quantitatively the adsorption of ionic surfactants at liquid interfaces. Well-known adsorption isotherms due to Frumkin or Hill–de Boer cannot respond to the specific electrostatic and geometric properties of the surfactant molecules. Our approach is based on a combination of the Gouy–Chapman theory with a modified Frumkin isotherm. The modification implies that the system is free to choose an optimal head group area and an optimal arrangement of the surfactant molecules in the interface as a function of bulk concentration. Interaction energies between neighbouring adsorbed surfactant molecules and between surfactant and water molecules are taken into consideration. The minimum of the Gibbs free energy of the system is equivalent to a minimal interfacial tension. Thus, the thermodynamically stable isotherm can be obtained as the lower envelope of the family of σ versus ln c isotherms resulting from different choices of the model parameters, including the area per molecule. According to the Gibbs equation, the Γ versus ln c adsorption isotherm is obtained as the derivative of this envelope. By variation of the model parameters, the envelope of the calculated adsorption isotherms can be fitted to experimental data of the interfacial tension versus bulk concentration. A computer program is used to calculate the σ versus c and the Γ versus ln c curves as well as to fit the parameters. Received: 28 October 1999/Accepted: 8 February 2000     

盐酸溶液中阴离子表面活性剂在铝表面上的吸附

用失重法研究了盐酸溶液中阴离子表面活性剂十二烷基磺酸钠（ＤＳＡＳＳ），十二烷基苯磺酸钠（ＤＢＳＡＳ）以及十二烷基硫酸钠（ＳＤＳ）在铝表面上的吸附作用，提出这种吸附作用与铝的失重量有关，且符合Ｌａｎｇ－ｍｕｉｒ方程，计算出吸附热，吸附熵和吸附自由能等热力学参数。认为这种吸附主要靠静电作用，根据接触角的变化讨论了阴离子表面活性剂分子在铝表面上的吸附取向。     

C12-s-C12•2Br和C12En混合水溶液的胶团化行为

季铵盐二聚表面活性剂C12 s C12•2Br（s=2、3、4、6）和非离子表面活性剂C12E10或C12E23在水溶液中生成混合胶团.其临界胶团总浓度cmcT值介于二元复配体系中各组分的临界胶团浓度和之间.当添加少量非离子型表面活性剂（在水溶液中的摩尔分数α2=0.1）时,混合胶团中C12E10或C12E23的摩尔分数均已超过0.35;随着溶液中非离子型表面活性剂含量的增大,混合胶团中逐渐以C12E10或C12E23成分为主.     

Analytical study of highly condensed non ionic surfactants. Separation on cation exchangers

Summary This study was aimed at optimizing the separation of non-ionic surfactants, resulting from the condensation of ethylene oxide with natural fatty alcohols in the C₁₆ and C₁₈ range (saturated and unsaturated), and presenting a high degree of condensation, i.e. 20 and 25 ethylene oxide units (Brij 99 and KM 25). The cation exchange stationary phase is a partially ionized silica, conditioned in different ways. We have studied the influence of the nature of cations on the separation selectivity. Cations studied included alkali metals (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺), alkaline earth metals (Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), transition metals (Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Cu²⁺), and quaternary ammonium (NH ₄ ⁺ , NMe ₄ ⁺ ) ions as well as a proton (acetic acid). The influences of ionic strength, pH and addition of cosolvent were examined. A study of the influence of temperature on the system selectivity evidenced a strong interdependance of these two parameters. The optimized conditions [mobile phase: CH₃CN/H₂O (92/8), pH 7.4, sodium acetate 5.10^–3 M; temperature gradient between 25 and 50°C] allowed for the first time the distributions of Brij 99 and KM 25 to be obtained.