The shape of the interstitial air film between noncoalescing liquids and between a drop and a solid surface is detected by means of laser interferometry. Alternative optical techniques are exploited to reveal the film profile and absolute thickness and its dynamical behavior. In particular, the thickness of the film is measured, by means of an angle shift method, in the case of a drop resting on a solid surface; further experiments, based upon reflectometry, show that stable noncoalescence may be realized both under steady and time-dependent conditions of the interfaces. A light deflection technique, coupled with image analysis, is exploited to detect the features of the film unsteadiness. The related Fourier spectra are explicitly calculated. The procedure for the determination of the film thickness is explained with the aid of a specific numerical code that is able to simulate the interference fringe patterns generated by thin films. The results presented herewith are explained in terms of theory of lubrication, exploiting the experimental data as boundary conditions that allow one to uncouple the stress–balance equations at the interfaces and the lubrication equations and solve only the latter ones.

(Pro-Pro-Gly) 10 is one of the most widely studied collagen polypeptide models. Microgravity crystal growth of (Pro-ProGly) 10 was carried out in the Advanced Protein Crystallization Facility aboard the Space Shuttle Discovery during the STS-95 mission. Crystals were successfully grown in all experiments, using both dialysis and free-interface diffusion methods. The quality of the microgravity-grown crystals and of groundgrown counterparts was assessed by X-ray synchrotron diffraction. Microgravity-grown crystals exhibited a signi®cant improvement in terms of dimensions and resolution limit. As previously reported, crystals were orthorhombic, space group P2 1 2 1 2 1 . However, the diffraction pattern showed weak re¯ections, never previously measured, that were consistent with new unit-cell parameters a = 26.9, b = 26.4, c = 182.5 A Ê . This allowed the derivation of a new model for the arrangement of the triple-helical molecules in the crystals.

Single chains of the collagen model polypeptide with sequence (Pro-Pro-Gly)(10), hereafter referred to as (PPG)(10), aggregate to form rod-shaped triple helices. Crystals of (PPG)(10) were grown in the Advanced Protein Crystallization Facility (APCF) both onboard the International Space Station (ISS) and on Earth. The experiments allow the direct comparison of four different crystallization environments for the first time: solution in microgravity ((g), agarose gel in (g, solution on earth, and gel on earth. Both on board and on ground, the crystal growth was monitored by a CCD video camera. The image analysis provided information on the spatial distribution of the crystals, their movement and their growth rate. The analysis of the distribution of crystals reveals that the crystallization process occurs as it does in batch conditions. Slow motions have been observed onboard the ISS. Different to Space-Shuttle experiment, the crystals onboard the ISS moved coherently and followed parallel trajectories. Growth rate and induction time are very similar both in gel and in solution, suggesting that the crystal growth rate is controlled by the kinetics at the interface under the used experimental conditions. These results provide the first data in the crystallogenesis of (PPG)(10), which is a representative member of non-globular, rod-like proteins.

Mach-Zehnder interferometry is applied to quantitatively characterize growth of lysozyme crystals in microgravity. Experiments were performed by the Free Interface Diffusion technique into APCF FID reactors using large seeds. Tracking of the experiments using interferometry allowed to monitor the onset of supersaturation and the seed growth. A large and stable concentration depletion zone around the growing crystal developed, whose time evolution was analyzed. The interferograms were analyzed taking into account finite thickness of the cell by integrating the concentration over the straight lines through the optical path. It was concluded that there may be a quasi-steady state growth mode at the stage when the spacial concentration distribution did not change but its absolute value over all the cell was slowly diminishing. From this portion of the data, an estimate was made of the dimensionless parameter beta R/D where beta is the face kinetic coefficient, R is the effective crystal size and D is the lysozyme diffusivity in solution, as followed from the steady state model. For the assumed quasi steady state data portion, the parameter varies between 0.7 and 0.9 suggesting mixed diffusion-interface kinetic controlled growth.

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