RESUMO
Fabricating future materials by self-assembly of nano-building blocks programmed to generate specific lattices is among the most challenging goals of nanotechnology and has led to the recent concept of patchy particles. We report here a simple strategy to fabricate polystyrene nanoparticles with several silica patches based on the solvent-induced self-assembly of silica/polystyrene monopods. The latter are obtained with morphological yields as high as 99% by seed-growth emulsion polymerization of styrene in the presence of 100 nm silica seeds previously modified with an optimal surface density of methacryloxymethyl groups. In addition, we fabricate "magnetic" silica seeds by silica encapsulation of preformed maghemite supraparticles. The polystyrene pod, i.e., surface nodule, serves as a sticky point when the monopods are incubated in a bad/good solvent mixture for polystyrene, e.g., ethanol/tetrahydrofuran mixtures. After self-assembly, mixtures of particles with two, three, four silica or magnetic silica patches are mainly obtained. The influence of experimental parameters such as the ethanol/tetrahydrofuran volume ratio, monopod concentration and incubation time is studied. Further developments would consist of obtaining pure batches by centrifugal sorting and optimizing the relative position of the patches in conventional repulsion figures.
RESUMO
The intermetallic NdNiMg15 is the Mg-richest phase (more than 88 atom % of Mg) discovered in the Mg-Nd-Ni system. Its structure was determined by X-ray diffraction on single crystal with the following crystal data: tetragonal system, P4/ nmm, Z = 2, a = 10.0602(1) Å, c = 7.7612(2) Å, dcalc = 2.40 g·cm-3. Its structure is made of a three-dimensional framework of magnesium atoms showing channels filled by one-dimensional chain consisting of alternating Nd and Ni atoms along the c-axis. Anti-ferromagnetic ordering was observed with TN = 9 K, which is remarkably high considering the long distances between magnetic atoms, that is, Nd atoms. The effective magnetic moment µeff is equal to 3.58 µB, which is consistent with magnetic Nd3+ ions and weakly or nonmagnetic Ni atoms. Below TN, the M( H) curves show field-induced metamagnetic transitions at critical fields increasing with decreasing temperatures. The magnetic structure of NdNiMg15 was determined from neutron powder diffraction data by considering the propagation vector k = (1/2 1/2 0). This magnetic structure consists in ferromagnetic chains along the c-axis of Nd atoms carrying moments, only separated by Ni atoms. The chains are ferromagnetically coupled within planes perpendicular to the [110] direction, and these planes are anti-ferromagnetically coupled to neighboring planes forming a checkerboard-like magnetic structure.
