Characterization of highly porous polymeric materials with pore diameters larger than 100 nm by mercury porosimetry and X-ray scattering methods.

Highly porous polymeric materials with pore sizes ranging from 100 nm to 1 microm are a very challenging class of materials not only to prepare synthetically (due to the high capillary pressures generated upon solvent removal) but also to characterize structurally. Through the examples of three different types of porous compounds synthesized in our laboratory (i) high-density melamine-based "MF-hd" with monomodal pore diameters around 500-900 nm, (ii) low-density melamine-based "MF-ld" with bimodal pore size distribution and average diameters around 2.3 microm and 350 nm, (iii) highly porous polyurethane "PU" with monomodal pore sizes around 150 nm, we confirm the limitations of mercury porosimetry as a means to investigate the architecture of materials with very high porosity (>80 vol %) and low compressive strength. Instead, a combination of high-resolution scanning electron microscopy and small-angle and ultrasmall-angle X-ray scattering (SAXS and USAXS, respectively) studies of these three types of materials helps in determining both the network and the pore structures. This work elucidates the need and applicability of the SAXS/USAXS techniques in characterizing such porous materials. For instance, the polyurethane specimens can only be quantitatively characterized by scattering techniques, the results of which are corroborated by high-resolution scanning electron microscopy observations.

Precursor structures in the crystallization/ precipitation processes of CaCO3 and control of particle formation by polyelectrolytes.

The formation of CaCO3 is usually discussed within the classical picture of crystallization, i.e. assuming that the formation of CaCO3 crystals proceeds via nucleation and growth. This may be true for the case of low supersaturation. In this work it is shown that the formation process is far more complex at high supersaturation, i.e. during precipitation. New insight into the mechanisms of precipitation is obtained by analyzing structure formation with a time resolution down to the millisecond range from the initiation of the reaction. The techniques used are scanning electron microscopy, electron diffraction, X-ray microscopy and cryo-transmission electron microscopy combined with a special quenching technique. It is seen that upon mixing CaCl2 and Na2CO3 solutions (0.01 M) first an emulsion-like structure forms. This structure decomposes to CaCO3-nanoparticles. These nanoparticles aggregate to form vaterite spheres of some micrometers in diameter. The spheres transform via dissolution and recrystallization to calcite rhombohedra. Once a suitable amount of additive, in our case polycarboxylic acid, is present during the precipitation the nanoparticles are stabilized against compact aggregation; instead they form flocs. This stabilization is either of a temporary nature if the amount of polymer is insufficient to cover the surface of the nanoparticles formed or more long lived if there is enough polymeric material present. By means of Ca-activity measurements it can be shown that the polymers are partially incorporated into the forming crystals.

Generation and characterization of test atmospheres with nanomaterials.

To ensure the product safety of nanomaterials, BASF has initiated an extensive program to study the potential inhalation toxicity of nanosize particles. As preparation work for upcoming inhalation studies, the following manufactured nanomaterials have been evaluated for their behavior in an exposure system designed for inhalation toxicity studies: titanium dioxide, carbon black, Aerosil R104, Aerosil R106, aluminum oxide, copper(II) oxide, amorphous silicon dioxide, zinc oxide, and zirconium(IV) oxide. As the physicochemical properties and the complex nature of ultrafine aerosols may substantially influence the toxic potential, the particle size, specific surface area, zeta potential, and morphology of each of the materials were determined. Aerosols of each material were generated using a dry powder aerosol generator and by nebulization of particle suspensions. The mass concentration of the particles in the inhalation atmosphere was determined gravimetrically and the particle size was determined using a cascade impactor, an optical particle counter, and a scanning mobility particle sizer. The dispersion techniques used generated fine aerosols with particle size distributions in the respiratory range. However, as a result of the significant agglomeration of nanoparticles in the test materials evaluated, no more than a few mass percent of the materials were present as single nanoparticles (i.e., < 100 nm). Considering the number, a greater percentage of nanoparticles was present. Based on the obtained results and experience with the equipment, a technical setup for inhalation studies with nanomaterials is proposed. Furthermore, a stepwise testing approach is recommended that also could reduce the number of animals used in testing.