A description is given of the molecular and morphological structure of polyvinylidene fluoride and from this description a classical model is proposed for calculating the piezoelectric and pyroelectric properties. The model consists of an array of crystal lamellae with a net moment from aligned dipoles in the crystals and compensating space charge on the crystal surfaces. The results for no compensation and complete compensation essentially bracket experimentally observed results and indicate that the largest contribution to the activity of this polymer arises from bulk dimensional changes rather than from changes in molecular dipole moments.

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This paper discusses the difference between the experimentally observed angle of Hertzian cone cracks and the angle defined by the trajectories of the preexisting stress fields. It is argued that there is no reason why these angles should be the same, as has usually been assumed. A finite element method has been used to model the growth of cracks in the Hertzian stress fields. In this model, the crack is incrementally advanced along the direction of maximum strain energy release, as calculated by the evolving, rather than the preexisting, stress fields. For the modeled Hertzian indentation system, a cone crack is observed to grow, but at an angle which is significantly different from that defined by the normal to the maximum preexisting tensile stress. The angle of the cone crack, as grown in the model, is in excellent agreement with observations on experimentally grown cone cracks in glass, with the same Poisson's ration. It is proposed that, in general, cracks will grow along paths that result in the maximum release of strain energy. For asymmetric, nonuniform preexisting stress fields, such paths do not necessarily coincide with the normal to the maximum preexisting tensile stress.

The electrostatic charge properties of commercial metered dose inhaler (MDI) aerosols, including Ventolin ᭨ , Flixotide ᭨ , Tilade ᭨ and QVAR ᭨ , sampled through new and detergent-coated AeroChamber ᭨ Plus spacers were studied using a modified 13-stage electrical low pressure impactor (ELPI) with aerodynamic cutoff diameters ranging from 0.028 to 10.07 m. Aerosol particles deposited on the impactor stages according to their aerodynamic diameters and their charges were simultaneously measured by the electrometers. The deposited drug mass was assayed chemically using HPLC. The surface potential on the inner spacer wall was measured with an electrostatic probe before and after aerosol actuation. High surface potentials were found on the new spacers whereas the detergent-coated spacers had minimal charges due to the conductive coating. MDI aerosol charges were decreased when spacers were used but the charge profiles of the aerosols were not altered qualitatively. New spacers had the lowest throat deposition, fine particle dose, and net aerosol and fine particle charges as a result of high spacer retention. These trends were partially reversed by the detergent-coated spacers. In general, the charge per mass of drug (charge-to-mass ratio) for particles from detergent-coated spacers was higher than those from new spacers. This was thought to be due to the reduction of electrostatic deposition inside the spacer thus leading to particles carrying higher charges being sampled. The calculated number of elementary charges per drug particle ranged from zero to several hundred, which is sufficiently high to potentially affect lung deposition. The ELPI provided high resolution charge profiles on MDI aerosols delivered through spacers. ᭧

A method is discussed for measuring the separate spatial distributions of fixed charge and permanent polarization in a uniform insulator. Changes in the potential difference across the insulator are measured when a known nonuniform time-dependent temperature perturbation is established through the sample thickness. The contributions to the measured signal from real charge and polarization charge have the same form, but are weighted differently. Deconvolution of the experimental data, therefore, yields a linear combination of the spatial distributions of real and polarization charges. These two distributions can be separated by utilizing the temperature dependence of these weighting factors.