Poly(vinylidene fluoride) film formation with electrospray deposition has been studied with support of a droplet evaporation model. The input parameters of the model consist basically of the solvent, the solute concentration, the flow rate, and the solution conductivity. The model provides the droplet size, the solute concentration, the droplet velocity, and the shear stress of the droplet at impact as a function of the distance between the nozzle and the substrate. With some additional experimental information such as the size change of the film with spray distance and the viscosity of the solution, the growth rate of the film and the shear rate of the droplet at impact can be determined. Growth rate is shown to define distinct regimes of film formation. In those regimes, only a single factor or a limited number of factors controls the film morphology. The most important factors include the shear rate and the surface energy. It is found that at a specific range of growth rates only the shear rate determines the morphology of the polymer film. Growth rate, as the defining quantity of film morphology, is not limited to polymer solutions. Therefore, the growth rate, in combination with the control factors mentioned above, functions as a general framework through which understanding and control of film formation with electrospray deposition can be improved.

The self-diffusion coefficients have been determined for five generations of poly(propylene imine) dendrimers in methanol at three different temperatures5, 25, and 45 °Cover the whole concentration range. Pulsed field gradient spin echo NMR has been used. The Stokes−Einstein hard sphere radii have been calculated in the zero concentration limit. They were equal, within error, to the radii found from the viscosity. The high-generation dendrimers have three concentration regimes:  a dilute, a semidilute, and a concentrated regime. For the lower generations, only a dilute and a semidilute regime can be found. In the dilute regime, the self-diffusion coefficient decreases as a function of the concentration. In the semidilute regime, this decrease continues. In part of the semidilute and in the concentrated regime diffusion was very slow, and we were not able to measure the long time self-diffusion coefficient. As the transition from semidilute to concentrated solutions corresponds to a decrease of the radius of the dendrimer, dendrimers in concentrated solutions can be considered as collapsed though still separate molecules. The behavior in the semidilute and the concentrated regimes is very different from polymer diffusion.

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The rate of adsorption of positively charged poly(propylene imine) dendrimers on glass, an oppositely charged surface, has been studied as a function of generation and charge (by systematic adjustment of pH and ionic strength) using scanning angle reflectometry and an impinging-jet cell. A comparison of the mass transport conditions for this geometry and the bulk long-time self-diffusion coefficient obtained from pulsed field gradient NMR experiments shows that a sticking probability of the order of 3% is needed to relate the diffusion toward the surface with the long-time self-diffusion in the bulk. The adsorption kinetics were mostly diffusion/convection controlled with a linear dependence on the bulk concentrations up to 10 mg/L at pH 7 and in 0.1 M NaCl. At higher bulk concentrations there is a drop in concentration dependence into a 1/3 power law dependence. This crossover concentration shifts to higher concentrations with decreasing pH (increasing dendrimer charge).

The colligative properties of poly(propylene imine) dendrimers in methanol have been investigated with low-angle laser light scattering and vapor pressure osmometry. The molecular weights and second virial coefficients of the first five generations have been determined. The molecular weights have been found to agree with the theoretically expected values. Effective radii have been obtained from the second virial coefficient, viscosity, and the partial specific volume. Both pair interaction and viscous state of the particles are considered in terms of effective volumes. The fifth generation shows the most pronounced hard-sphere interaction probably reinforced by Coulombic repulsion. The viscosity behavior of these dendrimers is like nondraining spheres. All radii grow almost linearly with the generation number. Together with the exponential growth of their molecular weights, this excludes a power law dependence of molecular weight and radius; i.e., these dendrimers are not self-similar. This also explains the maximum in the viscosity.

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