Unexpected Polymorphism and Unique Particle Morphologies from Monodisperse Droplet Evaporation

The particle sizes, morphologies, and structures are presented for succinic acid particles formed from the evaporation of uniform droplets created with a vibrating orifice aerosol generator. Particle sizes are monodisperse, and solvent choice is found to be the dominant factor in determining the final morphology and structure. The external particle morphologies range from round to cap shaped, while the surface roughness ranges from fairly smooth to extremely rough and pitted. Internally, the particles have significant void space and noticeable crystals. X-ray diffraction confirms that the particles are crystalline. Thus, the morphologies of the particles take on a crystal filled structure that is unique in comparison to previous particles formed through droplet evaporation. The structure of the particles contains β succinic acid; however, the particles formed from water also contain α succinic acid. α Succinic acid has not previously been able to be formed from solution at near atmospheric conditions. The unique morphologies and ability to identify unexpected polymorphs provide for a potential tool to not only enhance particle engineering but also to identify metastable polymorphs.

Effect of substrate surface roughening and cold spray coating on the fatigue life of AA2024 specimens

The effects of cold spray coating and substrate surface preparation on crack initiation under cyclic loading have been studied on Al2024 alloy specimens. Commercially pure (CP) aluminum feedstock powder has been deposited on Al2024-T351 samples using a cold-spray coating technique known as high velocity particle consolidation. Substrate specimens were prepared by surface grit blasting or shot peening prior to coating. The fatigue behavior of both coated and uncoated specimens was then tested under rotating bend conditions at two stress levels, 180 MPa and 210 MPa. Scanning electron microscopy was used to analyze failure surfaces and identify failure mechanisms. The results indicate that the fatigue strength was significantly improved on average, up to 50% at 180 MPa and up to 38% at 210 MPa, by the deposition of the cold-sprayed CP-Al coatings. Coated specimens first prepared by glass bead grit blasting experienced the largest average increase in fatigue life over bare specimens. The results display a strong dependency of the fatigue strength on the surface preparation and cold spray parameters

Understanding Bile Micelle Chiral Interactions

Bile salts are known to aggregate into micelles in biological systems; however, the fundamental structure and dynamics of bile molecule micelle formation are poorly understood. Previous studies have established that the bile salt cholate is capable of performing chirally selective micellar electrokinetic capillary chromatography (MEKC) separations of model racemic binaphthyl compounds 1,1¿-binaphthyl-2,2¿-diyl hydrogen phosphate (R,S-BNDHP) and 1,1¿-bi-2-naphthol (R,S-BN). Nuclear magnetic resonance (NMR) has been established as a complementary technique for understanding chiral selectivity and micelle formation events based on changes in proton chemical shifts of the probe molecules BNDHP and BN as well as of cholate. This work investigated the effects of the probe molecule, the alkali cation identity and temperature on cholate micelle aggregation and MEKC separations of R,S-BN and R,S-BNDHP. The probe molecule was found to mediate micelle formation by MEKC and proton NMR. A low (0.1 mM) concentration of probe was found to have minimal effects on micellization events detected by proton NMR while higher probe concentration (2.5 mM) was found to mediate micellization causing micellization events to occur at lower cholate concentrations. This work also investigated the effects of alkali counterion on chiral separation. Generally, counterions with larger crystal cationic radius were found to cause greater chiral separation power. NMR data suggest that protons near the surface of the cholate micelle are most sensitive to the cation identity, suggesting a model of improved separation based on the cation sterically inhibiting binding of one isomer. Finally, the effect of temperature on MEKC separation was investigated. Separation power of R,S-BN and R,S-BNDHP appeared to increase linearly with temperature for 22.0 mM to 50.0 mM pH 12.0 cholate. In total, these results indicate that cholate aggregation is dependent on multiple conditions. Understanding the roles that these factors play in influencing cholate micellization can inform better separation in MEKC.