Light scattering study of stereocomplex behaviour in solutions of poly(methyl methacrylate)

The behaviour of mixtures of iso- and syndiotactic poly(methyl methacrylate) (PMMA) as a function of time and polymer whole concentration in several solvents has been studied by light scattering and laser light scattering. The different solvents investigated in this study are acetonitrile, ethyl acetate, dimethylformamide (DMF), tetrahydrofuran (THF) and 1,4-dioxane. We have found that the last one behaves as a weakly complexing solvent, while the others show a complexing power decreasing from acetonitrile to THF.An increase in polymer whole concentration induces a higher aggregation of the macromolecular coil, while the compaction process of stereocomplex particles is not strongly influenced. The influence of time in stereocomplex behaviour depends on the nature of the solvent employed. In strongly complexing solvents there is initially a strong increase in the aggregation process and a decrease in compaction. However, in weakly complexing solvents these kinetic processes are less important.     

The determination of total phosphorus in seawater by nitrate oxidation of the organic component

A method is presented for the determination of total phosphorus dissolved in seawater by magnesium nitrate oxidation of the organic component concomitant with depolymerization of polyphosphate residues, followed by the standard molybdate colorimetric determination of the liberated orthophosphate. This method gave 93–100% recovery of phosphorus from inorganic metaphosphate and polyphosphate, phosphate esters and anhydrides, nucleotide-P, phospholipid and phosphonates. It is shown to be superior to the perchlorate-oxidation or high-intensity u.v.-irradiation methods for quantitative P recovery from phosphonates and polyphosphates, while proving equal in P recovery to the autoclave-requiring persulfate-oxidation method.     

The influence of silicon on properties of deposited Ni-Cr films

Multicomponent alloy thin films based on Ni-Cr with a high silicon content were deposited in a high vacuum onto ceramic flat substrates and investigated. After annealing in air the Ni-Cr-Si films show a high stability. It has been found that the temperature coefficient of resistance has values around zero in a range of the film composition from 5 to 20 at.% Ni, from 20 to 40 at.% Cr and from 50 to 65 at.% Si. This range of the film composition is suitable for the production of metal film resistors by means of sputtering.     

Photocurrent and decay time studies of solution-sprayed Cd0.8Zn0.2S films from liquid nitrogen to room temperature

The photocurrent of solution-sprayed Cd_0.8Zn_0.2S films and its dependence on temperature and light intensity were determined and a detailed investigation of the photocurrent decay was carried out. The photocurrent is almost independent of temperature at low temperatures and increases exponentially to a maximum at about 250 K. The decay times are shorter at low temperatures than at room temperature and they also depend on the light intensity.     

Ultrafiltration cell for sorption and biodegradation experiments

The knowledge about sorption and biodegradation of trace organics in soils and sediments of low organic carbon content, such as ground water aquifers, is still meagre. In an attempt to develop a tool to study mechanisms of interactions between low-molecular weight compounds, bacteria, organic polymers and clay minerals, an ultrafiltration membrane cell was designed to be operated either in batch or continuous flow mode. The cell and its maintenance are described, and its performance illustrated by experiments with p-chloroaniline (PCA) in suspension with a microbial polysaccharide and a bentonite clay. PCA at a concentration of about 50 μgl⁻¹ demonstrated sorption only to bentonite, and only after protonation. The reproducibility of the experiments was high resulting in a minimal detectable sorption of PCA of 0.56%. The high sensitivity, reproducibility and replicability of this cell approach are particularly applicable to the current efforts to gain a better understanding of sorption and biodegradation processes in the saturated subsurface.     

The industrial role in risk assessment

Industry has a major role in the assessment and management of risk to society from its operations. Much of the basic knowledge of manufacturing operations, product distribution, use and ultimate disposal of products and byproducts resides in industry. Basic data on the health and environmental effects of materials in commerce has been generated by industry. This information must be utilized in the evaluation of risk so that appropriate management decisions can be made. Experience gained in the industrial sector with risk assessment and management should be of value to government in its oversight role on behalf of society. There is growing realization in both industry and government of the need for more effective communication of risk to the general public in the context of management decisions.     

A mass spectrometric investigation of the thermal oxidative reactivity of ethylene glycol

The thermal oxidative stability of ethylene glycol was investigated over the temperature range of 100–126°C. Aqueous ethylene glycol were heated in sealed tubes in the presence of metallic copper and without metal. Mass spectrometric analysis was used to determine the rates of O₂ consumption and CO₂ evolution during heating. Copper had a catalytic effect of the glycol degradation. It was found that the rate limiting step in the thermal oxidative process was not related to oxygen consumption, suggesting that the rate limiting step involved the formation of a free radical which subsequently reacts with O₂. The evolution of CO₂ continued to occur after total consumption of the O₂. This suggested that the CO₂ is evolved from one of the thermal oxidation products of ethylene glycol.