Charles M. Burns

Pervaporation separation of water/isopropanol mixture using sulfonated poly(ether ether ketone) (SPEEK) membranes: transport mechanism and separation performance

Abstract Homogeneous membranes based on sulfonated poly(ether ether ketone) (SPEEK) of different sulfonation degrees (SD) were tested for sorption and pervaporation dehydration of water/isopropanol mixtures in a wide range of feed composition. Coupled transport was observed in this pervaporation separation process, the permeation rate of isopropanol increases with the increase of water feed composition. A new transport mechanism considering the coupled transport was proposed, which assumes that there are two types of environments in SPEEK membranes, namely the hydrophilic environment A and hydrophobic environment B. Water can only dissolve in environment A, isopropanol can dissolve in both environments. According to this model, the water percentage in permeate is mainly determined by the relative diffusivity and relative concentration of water to isopropanol in environment A. Some other separation characteristics of the membranes are also discussed based on this mechanism.

Measurements of partition, diffusion coefficients of solvents in polymer membranes using rectangular thin-channel column inverse gas chromatography (RTCCIGC)

Abstract Rectangular thin-channel columns were designed to determine partition and diffusion coefficients of small molecular weight solvents in polymer membranes based on the inverse gas chromatography (IGC) technique. The advantage of using this novel column was analyzed in terms of uniform distribution of polymer thickness, ease of preparation of stationary phase (thin polymer layer), and repeated use of the column. A mathematical model was developed to describe the velocity profile of the carrier gas, and both the time- and location-dependent concentration profiles of solvent in the column. By using the moment analysis method, the partition coefficient and diffusion coefficient were related to the dimensionless first moment and dimensionless second central moment of the elution curve of the solvent, respectively. The first dimensionless moment of the elution curve was found to be independent of the carrier gas velocity, while the second central moment increased with the increase of the carrier gas velocity. Both these behaviors support the theoretical predictions. The diffusion and partition coefficients of ethanol were obtained on polymers of cellulose diacetate (CDA) and sulfonated poly(ether ether ketone) (SPEEK) with a sulfonation degree of 79% over different temperature ranges. Based on the Arrhenius formula, the diffusion activation energies and the solvent dissolution enthalpies in both polymers were also obtained. The diffusion coefficients of 1-propanol were also obtained using two different lengths of columns.

Determination of the Flory‐Huggins interaction parameter of polystyrene—polybutadiene blends by thermal analysis

Blends of polystyrene (PS) and polybutadiene (PBD) were investigated by differential scanning calorimetry. From the phase composition diagram of the blends, it appears that PBD dissolves more in the PS-rich phase than does PS in the PBD-rich phase. This result is consistent with the behavior of the specific heat increment at the glass transition temperature of PBD in the PS-PBD blends. From the measured glass transition temperature and apparent weight fractions of PS and PBD dissolved in each phase, values of the Flory—Huggins polymer—polymer interaction parameter (χ12) were determined to be 0.0040–0.0102 depending on the composition and molecular weights of the PS and the PBD. No significant difference in χ12 was observed among the blending methods. The composition-dependent value of the Flory—Huggins polymer—polymer interaction parameter was found to be similar to the value of χ12. The polymer—polymer interaction parameter appears to depend on the degree of polymerization of the polymers as well as on the apparent volume fraction of the polymers dissolved in each phase.

Copolymerization of ethylene and vinylcyclohexane using soluble Ziegler-Natta catalysts

Abstract The copolymerization of ethylene and vinylcyclohexane has been investigated using soluble catalytic systems Cp 2 ZrCl 2 MAO ( Cp = η 5 cyclopentadienyl ; MAO = methylaluminoxane ) and Cp 2 ZrMe 2 MAO at 70°C and room temperature. Under the reaction conditions employed, up to 1.7 mol% of vinylcyclohexane could be introduced into the polyethylene chains. The molecular structure and comonomer content of the copolymers were determined by 13C nuclear magnetic resonance. The comonomer content of the polymers was found to increase with the comonomer concentration in the feed. The comonomer was found to be mainly statistically distributed. With samples containing higher comonomer content, however, the formation of a relatively very small amount of short blocks was noted. The average molecular weights of the copolymers were lower than those of pure polyethylene prepared under identical conditions. As expected, the vinylcyclohexane decreased the melting point and crystallinity of the polymers.

Critical effect of pH on the formation of organic coatings on mild steel by the aqueous electropolymerization of 2-vinylpyridine

Coatings of poly(2-vinylpyridine) have been formed on mild steel substrates in aqueous medium by electrochemical polymerization of the 2-vinylpyridine monomer. The pH of the solution has been found to be critical for this electropolymerization coating process. At low pH (below 3.5), even with an efficient initiation reaction, the propagation process was impeded and no substantial polymer film was formed. At high pH (above 6.0), only a thin and irregular film formed due to the lack of an effective initiation reaction. Only when the solution pH is in the range of 4 to 5.5 can good quality coatings be formed on mild steel substrates. The detailed effects of the pH on the electropolymerization are discussed in terms of a proposed free radical polymerization mechanism. This research has also resolved the issue of some of the non-reproducible experimental results reported in the literature and confirmed the feasibility of forming poly(2-vinylpyridine) coatings on a mild steel substrate by electropolymerization of the monomer.

Confocal scanning laser microscopy of polymer coatings

A new nondestructive technique, confocal scanning laser microscopy (CSLM), is described that is used to characterize the topography and morphology of polymer coatings. The topography of the coating can be determined even when the coating is completely opaque. When the coating is not completely opaque, CSLM has the distinct advantage of also being able to distinguish between the coating surface and the substrate, thus enabling coating thickness to be determined over a wide range of areas. In this study CSLM was successfully applied to poly(2-vinylpyridine) coatings formed on mild steel substrates by in situ electropolymerization. Satisfactory morphological details were obtained for areas ranging from 200 × 200 μm to 4 × 4 mm. Quantitative measurements of the coating thickness and the surface roughness distribution were also carried out. Although several other nondestructive techniques for coating morphological analyses are available, CSLM has unique advantages in being able to provide simultaneous qualitative and quantitative information on coating surfaces as well as measurements over a wide range of surface areas. A comparison of CSLM with other popularly used methods is provided and the characteristics and limitations of the various techniques are discussed.

Electropolymerized poly(2-vinylpyridine) coatings as ion-exchange polymer modified electrodes

The effects of pH and of the nature and concentration of the electrolyte on the electrochemical behaviour of the Fe(CN)3−/4−6 charge-transfer reaction at a poly(2-vinylpyridine)-coated electrode formed by electropolymerization have been studied. Cyclic voltammetry during the Fe(CN)3−6 incorporation process was combined with measurement of the saturated concentration of the Fe(CN)3−6 confined in the films to investigate the electrochemical behaviour and the fundamental nature of the ion-exchange polymers. The poly(2-vinylpyridine) films formed by electropolymerization were found to have better properties (i.e., larger amount of Fe(CN)3−6 can be incorporated at various pH values and films are more chemically stable under acidic conditions) as polymer-modified electrodes than those formed by solvent evaporation. Of the various anions studied, ClO−4 was found to be distinct from the others (Cl−, NO−3, Br− and SO2−4). On the one hand, the polymer films exposed to ClO−4 are more dense and rigid than those exposed to other anions and show relatively little electroactivity. On the other hand, when the films are exposed to increasing concentrations of Cl−, the films become more swollen, thereby reducing the resistance within the film and enhancing the rate of charge-transfer from the outer film surface to the electrode surface.

Cyclic potential sweep electrolysis for formation of poly(2-vinylpyridine) coatings

A cyclic potential sweep (CPS) technique has been used to form coatings of poly(2-vinylpyridine) on mild steel substrates by electropolymerization of the monomer. This method can produce thick and uniform coatings of much higher quality than can be formed by other electrochemical methods such as galvanostatic electrolysis, constant cell-potential electrolysis and chronoamperometry. The range and rate of the potential sweep during the CPS are important for successful coating formation. Potential sweeps between −1.0 and −2.2 V vs SCE at rates from 10 to 50 mV s−1 have been found to be most suitable for the formation of poly(2-vinylpyridine) coatings. The essential reason for the successful application of the CPS technique to the electropolymerization process is the compatibility of the nature of the CPS process and the mechanism of 2-vinylpyridine electropolymerization.

Profiles of Spreading Sessile Drops of Viscous Polymer Melts

Abstract The profile or shape of spreading drops of viscous polymer melts has always raised some questions regarding the basic forces inherent in and controlling the wetting phenomenon. The occurrence and nonoccurrence of “projecting feet” for spreading sessile drops has puzzled experimentalists for some time. Recent work for a homologous polymer series, differing only in molecular weight and molecular weight distribution and examined over a wide temperature range, has emphasized that an advancing projecting foot does occur and is dependent upon the molecular weight of the polymer material. The projecting feet can be interpreted as an effect resulting from the viscoelastic response of the material which can occur when the molecular weight of the polymer is higher than the characteristic critical molecular weight of entanglement of the material. For low molecular weight polymers the strong interfacial forces are not impeded by the bulk viscous response of the material whereas the present evidence indicates...

Spreading of Viscous, Well-Wetting Liquids on Plane Surfaces

A semi-empirical equation has been developed to describe the wetting kinetics for the spreading of viscous sessile drops. The model has been successfully applied to polystyrene melts over a wide temperature range (150-240°C) as well as a significant molecular weight range (Mw from 10,000 to 353,000). Current literature models were found to be inadequate as a complete description of wetting kinetics. The present model and experimental results corroborate earlier predictions by Smith and by VanOene concerning the time dependence of the rate of spreading of a viscous liquid when surface tension effects are negligible. The present method has also been successfully applied to two other viscous liquids, glycerol and silicone oil. The model indicates the strong influence of melt viscosity on wetting kinetics.