Sonja Krause

The earth's crust

The present structure of the earth consists of a largely molten core composed chiefly of iron and nickel, surrounded by lighter rocks. The outer few miles, the crust, is the only portion of the earth that is accessible, and is the source of most of the substances used in a technological society. This chapter describes the structure, composition, and evolution of earth crust, and the processes that take place in it. The volume of material to be mined and processed, the energy requirements, and the waste disposal problems clearly set economic and environmental restrictions on the minimum concentration that can be employed for large-scale use of any substance but the society generally uses atypical, high concentration sources for most of its mineral needs. Bacteria can also be used for recovery of metals from low-grade sources in an economical way through microbial mining. Surface rocks are subject to breakup and chemical change by several weathering processes including physical disintegration, chemical reactions, and biological effects that lead to soil formation. Soil is a vital substance but its degradation is of serious concern in terms of its impact on future food needs. Human activity frequently causes degradation of soil in ways that range from loss of nutrients to changes in physical character of the soil to contamination with toxic materials to loss of the soil itself. Different types of soils, their composition and process of formation, soil contamination, and methods of decontamination such as bioremediation, are also presented in the chapter.

An Electrorheological Fluid and Siloxane Gel Based Electromechanical Actuator: Working toward an Artificial Muscle

provided by the General Electric Silicones Division,Waterford, NY, was used. The PDMS gel was preparedStriated skeletal muscle responds to a nerve impulse by mixing equal parts of A and B and allowing thein less than 100 ms. In the past, polymeric gels (1) and mixture to cure. A swollen gel was made by mixingconducting polymers (2) have been investigated for use silicone fluid with the RTV 6136 before it had cured.as artificial muscle. However, the main problem with The gels had a cure time of about 1 h.these materials is their relatively slow response (œ3 The ERF used was a commercial sample, Rheobays).

Surface characterization of ethylene-vinyl acetate (EVA) and ethylene-acrylic acid (EAA) co-polymers using XPS and AFM

Abstract The air surfaces of ethylene-vinyl acetate (EVA) co-polymers with 9–70 wt% vinyl acetate (VA) and ethylene-acrylic acid (EAA) co-polymers with 3–20 wt% acrylic acid (AA) were studied using XPS at three take-off angles, representing three depths of penetration from 15–58 A. The semi-crystalline EVA and EAA co-polymers with high wt% ethylene (9–27.5 wt% VA) had higher percentages of VA at the surface than in the bulk, regardless of the type of sample preparation. Excess VA or AA at the surfaces of the annealed semi-crystalline films was probably the result of the rejection of VA or AA units from the growing crystallites. Spin and solution cast films generally had a greater percentage of VA at their surfaces than annealed films; this additional excess may be caused by the lower solubility of the ethylene units in the toluene used for casting, leaving a layer of the more soluble VA units on the air surfaces. Amorphous EVA co-polymer (50–70 wt% VA) annealed films showed an excess of ethylene at the surface. This occurred even though there are only very short sequences of ethylene in these co-polymers and was probably caused by the lower surface free energy of the ethylene repeat units with respect to the VA repeat units. The EAA co-polymers, all of which were semi-crystalline, always showed an excess of AA at the air surfaces, probably because of the rejection of the AA units by the crystallites. AFM bearing-ratio curves showed a fractional coverage of VA on 9EVA and 18EVA annealed surfaces of 0.885 and 0.927, respectively. When the XPS data were used with a simple model, which assumed a partial VA layer over a polyethylene layer at annealed co-polymer surfaces, a 2.0 A layer of VA on the 9EVA and 18EVA surfaces, with surface coverages of 0.91 and 0.96, respectively, was calculated, in reasonable agreement with the AFM bearing-ratio data.

Dilute solution properties of tactic polymethyl methacrylates I—Intrinsic viscosities of isotactic fractions

Abstract Intrinsic viscosities in acetone and in benzene solution were obtained on fractions of isotactic polymethyl methacrylate having M w &-M n ≈1·4 . The intrinsic viscosities in both solvents were higher than those of fractions of conventional free-radically initiated polymethyl methacrylate having comparable molecular weight. These data indicate that the isotactic molecules are more extended in solution than molecules of conventional polymethyl methacrylate. This conclusion is confirmed by data on the r.m.s. end-to-end distance of two of the fractions in acetone as determined from light scattering measurements.

Phase behaviour of poly(ethylene oxide)/poly(methyl methacrylate) blends containing alkali metal salts

Abstract The effect of alkali metal salts on the phase behaviour of poly(methyl methacrylate) (PMMA)/poly(ethylene oxide) (PEO) blends was studied using d.s.c. Addition of lithium trifluoromethane sulfonate (LiT) to the normally miscible PEO/PMMA blends induced phase separation with the formation of a crystalline PEO phase, a crystalline PEO/salt complex phase and an amorphous PMMA phase. When potassium thiocyanate was used instead of LiT the mixture separated into two amorphous phases. Phase separation in these blends was not merely a result of the expected PEO/salt interaction, but also of the interaction of the salt with the PMMA. The evidence for this second interaction comes from an observed increase in the PMMA glass transition temperature with the addition of salt. Weak shifts in the carbonyl peaks in the i.r. spectra of the PMMA in the PMMA/salt mixtures suggest that the oxygen atom in the carbonyl interacts with the cation in the salt.

N.m.r. investigation of interphases in dimethylsiloxane-styrene block copolymers: influence of block molecular weight

1 H n.m.r. relaxation data, determined via either wide-line 1 H n.m.r. or high-resolution solid-state 13 C n.m.r., were used to analyse the existence and extent of interphasic regions in dimethylsiloxane-styrene block copolymers. Results thus obtained have shown that copolymers having very short blocks possess relatively large interphases characterized by intermediate mobility. In addition, some styrene units are trapped in the dimethylsiloxane soft microphase. With increasing block molecular weights, the extent of the phase of intermediate mobility, as well as the percentage of styrene units trapped in the dimethylsiloxane soft microphase, decrease. In agreement with the conclusions previously deduced from d.s.c. experiments, and within the sensitivity of the n.m.r. technique, the samples with the longest blocks are sharply phase-separated.

IMPACT STRENGTH AND FRACTURE SURFACES OF INTERFACES BETWEEN POLYETHYLENE AND POLYPROPYLENE AND SOME ETHYLENE-CONTAINING COPOLYMERS

The impact strength of annealed interfaces between high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) and some ethylene-co-vinyl acetate (EVA) and ethylene-co-acrylic acid (EAA) copolymers was obtained using the Notched Izod test. The impact strengths of EVA-HDPE, EVA-LDPE, and EVA-PP interfaces using EVA copolymers with 9 to 27.5 wt % vinyl acetate (VA), and of EAA-PP interfaces using EAA with 3 to 20 wt % acrylic acid (AA), were all equal to or greater than those of the homopolymer used. However, the impact strengths of EAA-HDPE and EAA-LDPE interfaces were all lower than those of pure HDPE or LDPE, with the exception of 3EAA-LDPE. Scanning electron micrographs showed the presence of fibrils and/or voids, mostly on those copolymer-homopolymer fracture surfaces which had high impact strength. X-ray photoelectron spectroscopy of the fracture surfaces showed a greater calculated percentage of AA or VA on both the copolymer and homopolymer sides of the interface than in the bulk for most samples at 15 A penetration. This greater calculated percentage of AA or VA is probably due to chain scission during sample preparation or fracture, which results in additional acid or alcohol groups at the surface that are calculated as increased VA or AA content.

Effect of crystallization on the morphologies of block copolymer/homopolymer blends cast in an electric field

Blends of polystyrene (PS) and poly(styrene-b-ethylene oxide) (PS-b-PEO) were cast from a ternary solvent mixture containing 85% toluene, 10% tetrahydrofuran, and 5% methanol under conditions that favor crystallization of the PEO phase. Electric fields (2-14 kV/cm) were applied during casting to explore the possibility of morphology control by the field. It was observed that films cast in the absence of an electric field, in the temperature range of 0-25°C, from solutions initially cooled to 0°C were translucent. Their transmission electron micrographs exhibited thread-like, fibrillar structures. Micrographs of films cast in dc fields of 2-14 kV/cm at 16.3 ± 0.4°C also showed fibrillar structures, with the fibrils in the presence of fields greater than 8 kV/cm being substantially oriented in the field direction. We suggest that the morphologies developed under these conditions result from crystallization from preexisting crystal nuclei in the cooled solutions with the fibrillar crystals being oriented by the electric field. This method provides a possible way of processing anisotropic polymer blends.

Phase Separation in Styrene-α-Methyl Styrene Block Copolymers

In previous work from this laboratory, it has been shown that diblock and triblock copolymers of styrene, S, and α-methy1 styrene, MS, are homogeneous up to considerably higher molecular weights than are mixtures of the corresponding homopolymers (1,2). Homogeneity was inferred from the presence of a single Tg, intermediate between those of polystyrene, PS, and of poly (α-methyl styrene), PMS, in the samples. The glass transition temperatures were measured using DTA, DSC, and dilatometry. The same techniques showed that, if low molecular weight PS or PMS was mixed with one of the block copolymers, phase separation was always enhanced (3). The molecular weight and composition at which microphase separation occurred in the block copolymers could be predicted quite well using a theoretical treatment developed by one of us (4). The data indicated that the interaction parameter between PS and PMS was between 0.0030 and 0.0036 for samples with Mw/Mn < 1.3. Block copolymer samples with broader molecular weight distributions showed enhanced microphase separation, i.e., they exhibited microphase separation even when their Mw was so low that homogenity was predicted theoretically (4). Furthermore, the addition of homopolymer to the block copolymers always enhanced microphase separation, even though it was predicted (5) that the presence of very low molecular weight homopolymer should serve to compatibilize the system.

Soaps, synthetic surfactants, and polymers

This chapter reviews the chemical nature, synthesis, and environmental problems associated with biodegradable and nonbiodegradable organic compounds. Most of the polymers and surfactants in the detergents are made mainly from the chemicals derived from petroleum, and contain segments of linear or lightly branched hydrocarbon chains. Both soaps and synthetic detergents have similar structures, and their mechanisms of cleansing are also similar; however, zeolites of the detergents have environmental problems and they promote surface algal blooms. Microorganisms in the environment can utilize the energy of oxidation released by some hydrocarbons, soaps, and surfactants through β-oxidation. The chapter illustrates the microbial metabolism of hydrocarbons, soaps and synthetic detergents, and proposes guidelines to facilitate the understanding of microbial degradation of detergents. Although progress has been made in the synthesis of biodegradable polymers, these materials cost more, and in general, their properties are not as useful as those prepared from petroleum feedstock. A potential problem associated with biodegradable surfactants is the eutrophication of lakes that results from microbial degradation. The biodegradable replacements have solved the environmental problems associated with nonbiodegradable surfactants, and it is likely that biodegradable polymers assume an increasingly larger percentage of the polymer market.