Morphological Tuning of Nanostructured Hydroxyapatite (HAp) Porous Microgranules by Evaporation-Induced Assembly.

Porous biocompatible microgranules, such as hydroxyapatite (HAp), are potential candidates for various bio-medical applications including drug delivery and remediation. Using the principle of evaporation-induced assembly in contact free dispersion droplets, we have synthesized porous micrometric HAp granules consist of interlocked ellipsoidal nanoparticles. We have shown that the shape of the microgranules can be tuned from spherical to doughnut solely by controlling the drying temperature during assembly. The structure and interparticle correlation in the synthesized granules have been probed by electron microscopy and small-angle scattering. The observed morphological transition has been attributed to the buckling of elastic shell made of interlocked HAp nanoparticles. Alteration of granular morphology at higher drying rate does not affect the local packing fraction of the correlated HAp nanoparticles in the granules. The absorption of bovine serum albumin protein by the synthesized granules has been tested as a potential application.

Neutron diffraction evidence for kinetic arrest of first order magneto-structural phase transitions in some functional magnetic materials.

Neutron diffraction measurements, performed in the presence of an external magnetic field, have been used to show structural evidence for the kinetic arrest of the first order phase transition from (i) the high temperature austenite phase to the low temperature martensite phase in the magnetic shape memory alloy Ni37Co11Mn42.5Sn9.5, (ii) the higher temperature ferromagnetic phase to the lower temperature antiferromagnetic phase in the half-doped charge ordered compound La0.5Ca0.5MnO3 and (iii) the formation of glass-like arrested states in both compounds. The cooling and heating under unequal fields protocol has been used to establish phase coexistence of metastable and equilibrium states, and also to demonstrate the devitrification of the arrested metastable states in the neutron diffraction patterns. We also explore the field­temperature dependent kinetic arrest line TK(H), through the transformation of the arrested phase to the equilibrium phase. This transformation has been observed isothermally in reducing H, as also on warming in constant H. TK is seen to increase as H increases in both cases, consistent with the low-T equilibrium phase having lower magnetization.