Liquid Membrane Separations of Metal Cations Using Macrocyclic Carriers

Abstract

The selectivity in water and methanol solvents of macrocyclic crown ether ligands toward univalent and bivalent cations is well known. Incorporation of these ligands into chloroform liquid membranes separating water and salt solution phases results in a system showing selective cation transport. The cation transport rates of single cations across these liquid membranes have been correlated with equilibrium constant values for cation-macrocycle interaction in methanol. This correlation has been extended to binary cation mixtures of Cs⁺ with Li⁺, Na⁺, K⁺, and Rb⁺. A model for cation transport from these cation mixtures has been reduced to an equation which gives good agreement between measured and predicted transport rates across our liquid membranes.     

Influence of interface chemistry and network density on interfacial ion transport kinetics for styrene/acrylate copolymer coated zinc and iron substrates

n-Butyl acrylate/styrene copolymer films were applied on iron and zinc surfaces. The kinetics of interfacial ion transport and cathodic delamination were tracked by in situ Scanning Kelvin Probe (SKP) measurements. A destabilisation of the interface was detected for latex network structures with an increased degree of cross-linking. In contrast, a reduction of the average macromolecular chain length resulted in films with higher resistance to interfacial ion transport. No comparable effect of the polymer structure was detectable when latex films were applied on zinc. Calculated coefficients for water diffusion through the bulk polymer partially supported the SKP results obtained on iron.     

Potential induced pH change: Towards electrochemical coating of medical implants by organic nanoparticles

The electrochemical deposition of organic nanoparticles on conducting surface, such as a coronary stents, in the absence of a polymeric matrix is demonstrated. A novel approach, whereby pH-responsive organic nanoparticles coagulate on a conducting surface as a result of applying positive potential, has been studied. Specifically, latex nanoparticles stabilized by sodium oleate in aqueous solutions were deposited by applying a positive potential that oxidized the water and caused the decrease of pH on various conducting surfaces. It was found that the applied potential, its duration and the concentration of the dispersed nanoparticles govern the deposition characteristics of the coating.This generic approach allows coating objects with complex geometries with thickness ranging from nanometers to microns and therefore can be utilized for coating medical and other devices as well as for controlling drug release.     

Rheology of sterically stabilized dispersions and latices

Steric stabilization is a method that is often used to properly disperse small particles. It can be applied in aqueous as well as non-aqueous media. The rheological properties of sterically stabilized dispersions are discussed here. The various controlling parameters and the physical mechanisms involved are reviewed. Brownian hard spheres are used as a reference. Scaling relations are presented that make it possible to reduce data sets and to predict properties. Viscosity, yield stress, shear thickening and viscoelasticity are included. The rheological properties are also related to the fundamental colloidal properties of the dispersions under consideration. Quantitative results are available for monodisperse spherical particles, although the effects of particle size distribution can sometimes be predicted also quite well. In other cases the procedures presented here can be used qualitatively to predict viscosities.     

Electrochemical impedance spectroscopy study of waterborne coatings film formation

In order to establish electrochemical impedance spectroscopy (EIS) as a viable quantitative method for characterization of latex film formation, three waterborne acrylate and styrene–acrylate polymer dispersions were periodically analyzed during a course of 2 weeks. Impedance spectra were fitted on the base of equivalent circuit consisting of a capacitor in parallel with a Warburg element representing film capacitance and the extent of ion diffusion through the film. Calculated EIS parameter values showed a decrease in Warburg diffusion over time, which is a result of particle coalescence and in agreement with the established theory of latex film formation. Atomic force microscopy (AFM) of the samples showed a smoothing of the surface and blurring of interparticle boundaries which confirmed that EIS can be used to study film formation of latex.     

Polypyrrole nanocoatings of poly(styrene-co-methacrylic acid) particles

In this study the properties of polypyrrole (PPy) nanocoating over poly(styrene-co-methacrylic acid) (PS-MAA) particles were investigated. Monodisperse PS-MAA templates were obtained by free surfactant emulsion polymerization. The addition of methacrylic acid into the monomer feed mixture reduced particle size, ionic charge and hydrophobicity of the template surface. Correlations between template sizes and compositions, PPy confinement (granularity, shell size, etc.) and electrical conductivity, σ, are discussed. After dissolving the PPy/PS-MAA composites in tetrahydrofurane, PPy void spheres are obtained proving the core-shell nature of the coated particles. Bare styrene templates show densely packed PPy coatings and electrical conductivities near 7 S cm⁻¹ at high PPy loadings; on the contrary, at the same PPy mass percentage, the richer methacrylic acid particles show low packed PPy grains and conductivities that fall to 0.8 S cm⁻¹. In core-shell particles the PPy mass per unit area, Γ, is the key parameter which determines the insulator-conductor transition for any particle size. The conductivity values of PPy/PS-MAA composites follow a percolation law: σ∝t(Γ−Γc), with a critical threshold Γ_c=(0.262 ± 0.002)×10⁻⁶ g cm⁻². The critical exponent obtained t = 1.98 ± 0.07 agrees with the predicted value t = 2.0 for three-dimensional lattices of random resistors.     

常温下自交联核壳乳液的制备

本文合成了两亲性加成-断裂链转移(RAFT)试剂,2-{[(十二烷基)硫代甲酰基]硫烷基}丙酸(RAFT-1),并作为加成-断裂链转移试剂用于丙烯酸和丙烯酸正丁酯(等量)的可控自由基共聚合,得到聚合度为10的两亲型嵌段共聚物(RAFT-2)。利用RAFT-2作为反应性表面活性剂,制备了核-壳型聚(丙烯酸丁酯-双丙酮丙烯酰胺)乳液。所得乳液颗粒的分布较窄且稳定,固含量可达45%以上,平均粒径为50nm左右。利用核-壳乳液和少量的交联剂(己二酸及二酰肼)制备了乳液薄膜,发现交联反应随着水分的蒸发而不断进行,并最终形成坚韧而透明的交联薄膜。     

High solids content emulsion polymerisation without intermediate seeds. Part III. Reproducibility and influence of process conditions

The reproducibility and robustness of a unseeded process for the production of high solid content, low viscosity latex are examined. A series of runs showed that the experiments are very reproducible both in terms of the particle size distribution and the shear viscosity of the final latex. It is also shown that it is the surfactant concentration and feed profiles that are the most sensitive issues in maintaining product specifications since they control the rate of generation of small particles.     

水分散有机硅－聚氨酯嵌段共聚物合成性能及应用的研究

合成了水分散有机硅－聚氨酯嵌段共聚物乳液，研究了反应动力学、共聚物的性能及应用．首先由八甲基环四硅氧烷以膨润土为催化剂，醋酐为分子量调节剂合成分子量为端羟基聚硅氧烷齐聚物，再使之与甲苯二异氰酸酯及聚乙醇（ＰＥＧ）于丙酮中反应制得端异氰酸酯基的有机硅－聚氨酯预聚体（ＰＳｉ－ＰＥＵ）．将此预聚体用３－（Ｎ－甲基二乙醇氯化铵）－１，２－环氧丙烷扩链，加水乳化即得阳离子型的有机硅－聚氨酯嵌段共聚物（ＰＳｉ－ＰＵ）水乳液．此种水乳液是一种优良的织物整理剂可用以改善织物的表面性能、吸湿性和永久抗静电效果，同时可提高织物的力学性能和耐磨性能．     

附聚胶乳的附聚机理的研究

研究了用由丙烯酸正丁酯一丙烯酸共聚物组成的附聚胶乳(B)附聚聚合物胶乳(A)的附聚机理。随着附聚胶乳(B)用量的增加,出现两个附聚峰,提出了这两个附聚峰相应的附聚机理。