Microfluidic dialysis on the beamline: experiment and theory

Biological small angle x-ray solution scattering requires sufficient sample concentration to yield good signal while at the same time avoiding interparticle interference or the formation of unwanted oligomers or aggregates. The mere act of concentrating some samples risks rendering them unfit for SAXS measurements and the limit to which a sample may be concentrated before problems occur is often unknown a priori; aggregation is not generally regarded as a reversible process. At the same time, sample behavior at high concentrations is increasingly important not just for characterization of equilibria, or e.g. applications in the pharmaceutical industry, but also for understanding potential molecular crowding effects. We have constructed a microfluidic dialysis setup that permits on-demand concentration of protein samples at the beamline. Rather than generating dilution series to explore concentration effects, this approach produces true "concentration series", efficiently working from dilute sample upward. We experimentally demonstrate that useful concentrations can be achieved on practical timescales and that buffer exchange can be performed. Convection-diffusion modeling shows that the dialysis chip may actually retard aggregates, thus resulting in some degree of incidental sample purification. Based on model projections, the theoretical limits and potential of chip-dialysis will be described.

Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glass

Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He+implantation over an energy range of 1 to 2 MeV to give a uniform distribution over ∼1 µm depth. The implanted dose was varied from 9 × 1013to 2.8 × 1016 ions cm−2, corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus–Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15 Å and from 10−3to 10−1, respectively, as the dose increased from 9 × 1013to 2.8 × 1016 cm−2. The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix.

Ultrafine nanostructure of partially crystallized bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8

Bulk amorphous Zr54.5Ti7.5Al10Cu20Ni8was investigated by means of small-angle neutron scattering and high-resolution electron microscopy. Partially crystallized states were generated by annealing. The scattering data were analyzed in terms of a model taking into account both properties of the particles and interparticle interference. The mean radius of the particles is 1.3 nm. They are surrounded by a depletion zone with mean thickness of 2.6 nm. The volume fraction of the particles is estimated from the interparticle interference effect; its upper limit after annealing at 653 K for 4 h is 12%. Electron microscopy confirms the size determined from the scattering data and shows that the particles are crystalline.

Insight into the Formation of Ultrafine Nanostructures in Bulk Amorphous Zr54.5 Ti7.5Al10Cu20Ni8

ABSTRACTBulk amorphous Zr54.5 Ti7.5Al10Cu20Ni8 is investigated by means of smal-angle neutron scattering (SANS), differential-scanning calorimetry (DSC), high-resolution electron microscopy (HREM) and other methods. The formation of ultrafine nanostructures in the glassy phase is observed and explained by a new model. Structura fluctuations of randomly distributed partialy ordered domains grow during annealing just below the glass transition temperature by local re-ordering. During anneaing the DSC gives evidence for a increasing volume fraction of the localy ordered domains. At high volume fractions of impinging domains a percolation threshold on the interconnected domain boundaries occurs and enhanced diffusion becomes possible. At that stage SANS measurements lead to satistically significant scattering data. The SANS signals are anayzed in terms of a model taking into account spherica particles surrounded by diffusion zones and interparticle interference effects. The mean radius of the nanocrystaline particles is determined to 1 nm and the mean thickness of the depletion zone is 2 nm. The upper limit for the volume fraction after annealing at 653 K for 4hours is about 20 %. Electron microscopy confirms the size and shows that the particle are crystaline.

Small Angle X-Ray Scattering (Saxs) Study of Coarsening Kinetics in an Aluminum-Lithium Alloy

Coarsening kinetics was studied in a A190. 6 Li9. 4 alloy aged at 100°C, 128°C, 165°C, 178 ° C, and 209 °C. The time-dependent behavior of the average precipitate radius followed t1/3 behavior. The precipitate/ matrix interfacial energy obtained from analysis of the kinetic constant was 0.015 J/M2 and was largely independent of temperature. The scattering curves exhibit interparticle interference which prevents us from calculating a particle size distribution.