A positron annihilation study of carbon black and carbon-black-filled polybutadiene

Studies have been made on positron lifetimes in carbon blacks and carbon black filled polybutadiene. The results for the carbon blacks can be interpreted with the aid of the theoretical results of Brandt and Paulin: Phys. Rev. B5, 2430 (1972) and show that while positron annihilation occurs principally from a bound state, diffusion in the carbon black is extremely small. A numerical upper limit on the diffusion coefficient has been obtained. The data from the rubber is discussed with the aid of a specially developed extension of the previous theory. Here one finds that whereas the variations in the long-component intensity with carbon black loading can be very satisfactorily explained, there is again no evidence for any diffusion effects in the rubber, and an upper limit can be placed on the diffusion coefficient here also. Indeed the variation in the long-component intensity with particle size goes the opposite way to what one would expect if diffusion were dominant. This effect is attributed to the increase in the amount of bound rubber as the particle size is reduced, and the consequent increase in the number of annihilation sites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47030/1/339_2004_Article_BF00935908.pd

Evaluation of water properties in HEA–HEMA hydrogels swollen in aqueous-PEG solutions using thermoanalytical techniques

Hydrogels are polymeric materials used in many pharmaceutical and biomedical applications due to their ability to form 3D hydrophilic polymeric networks, which can absorb large amounts of water. In the present work, polyethylene glycols (PEG) were introduced into the hydrogel liquid phase in order to improve the mechanical properties of hydrogels composed of 2-hydroxyethylacrylate and 2-hydroxyethylmethacrylate (HEA–HEMA) synthesized with different co-monomer compositions and equilibrated in water or in 20 % water–PEG 400 and 600 solutions. The thermoanalytical techniques [differential scanning calorimetry (DSC) and thermogravimetry (TG)] were used to evaluate the amount and properties of free and bound water in HEA–HEMA hydrogels. The internal structure and the mechanical properties of hydrogels were studied using scanning electron microscopy and friability assay. TG “loss-on-drying” experiments were applied to study the water-retention properties of hydrogels, whereas the combination of TG and DSC allowed estimating the total amount of freezable and non-freezing water in hydrogels. The results show that the addition of viscous co-solvent (PEG) to the liquid medium results in significant improvement of the mechanical properties of HEA–HEMA hydrogels and also slightly retards the water loss from the hydrogels. A redistribution of free and bound water in the hydrogels equilibrated in mixed solutions containing 20 vol% of PEGs takes place

Erratum: Investigation of compatibility in syndiotactic poly(methyl methacrylate)/poly(vinyl chloride) blends (Macromolecules (1985) 18, 3, (388))

peer reviewed[No abstract available