ABSTRACT
Hollow microcapsules with the shell composed of biodegradable polyelectrolytes modified with the maghemite nanoparticles were fabricated by in situ synthesis. The nanoparticles were synthesized from the iron salt and the base directly on the capsule shells prepared by "layer by layer" technique. An average diameter of the capsule was about 6.7 µm while the average thickness of the capsule shell was 0.9 µm. XRD, HRTEM, Raman and Mössbauer spectroscopy data revealed that the iron oxide nanoparticles have the crystal structure of maghemite γ-Fe2O3. The nanoparticles were highly monodisperse with medium size of 7.5 nm. The Mössbauer spectroscopy data revealed that the nanoparticles have marked superparamagnetic behavior which was retained up to room temperature due to slow spin relaxation. Because of that, the microcapsules can be handled by an external magnetic field. Both these properties are important for target drug delivery. Based on the Mössbauer spectroscopy data, the spin blocking temperatures TB of about 90K was found for the particles with size D≤5 nm and TB≈250 K for particles with D≥6 nm. The anisotropy constants K were determined using the superparamagnetic approximation and in the low temperature approximation of collective magnetic excitation.
Subject(s)
Capsules/chemical synthesis , Magnetite Nanoparticles/chemistry , Capsules/chemistry , Ferric Compounds/chemistry , Microscopy, Electron, Transmission , Particle Size , Spectroscopy, Mossbauer , Spectrum Analysis, Raman , Temperature , X-Ray DiffractionABSTRACT
X-ray diffraction has been used to elucidate the structure and phase behavior of several liquid-crystalline dendrimers with a different surface topology of the terminal chains. This includes second-generation liquid-crystalline block and statistical dendrimers with mixed aliphatic and mesogenic terminal groups as well as homo-dendrimers of several generations containing only mesogenic end groups. The homo-dendrimers of generation one to four display a monolayer smectic phase, while the fifth generation shows a more ordered columnar phase. The block-dendrimer of the second generation has a bilayer smectic phase. The precise structure of the lamellar ordering has been determined by X-ray reflectivity from thin films on a substrate. The second-generation statistical dendrimer does not show any mesogenic phase. The observed phase behavior is discussed in terms of the frustration due to competition between the stiff geometry of the dendritic matrix and the close-packing conditions of the terminal chains.
ABSTRACT
Samples of synthetic NaCl crystals have been exposed to doses of electron irradiation up to 10(-2) TGy (1 Trad) at about 100 °C, and studied subsequently at T = 95 K by means of synchrotron radiation (SR). In addition to the earlier established Kurdjumov-Sachs orientation relationship (K-S OR) for Na precipitates, the following OR is revealed between solid chlorine and the host NaCl crystal system: [Formula: see text], [Formula: see text]. The size and shape of the Cl(2) precipitates has been studied as a function of the amount of radiation damage (i.e. the concentrations of Na and Cl(2)).
