Magnetic Resonance and Mössbauer Studies of Superparamagnetic γ‐Fe₂O₃ Nanoparticles Encapsulated into Liquid‐Crystalline Poly(propylene imine) Dendrimers

Abstract

We present the first results of electron magnetic resonance (EMR) and Mössbauer spectroscopy studies of γ-Fe(2)O(3) nanoparticles (NPs) incorporated into liquid-crystalline, second-generation dendrimers. The mean size of NPs formed in the dendrimers was around 2.5 nm. A temperature-driven transition from superparamagnetic to ferrimagnetic resonance was observed for the sample. Low-temperature blocking of the NP magnetic moments has been clearly evidenced in the integrated EMR line intensity and the blocking temperature was about 60 K. The physical parameters of magnetic NPs (magnetic moment, effective magnetic anisotropy) have been determined from analyses of the EMR data. The effective magnetic anisotropy constant is enhanced relative to bulk γ-Fe(2)O(3) and this enhanced value is associated with the influence of the surface and shape effects. The angular dependence of the EMR signal position for the field-freezing sample from liquid-crystalline phase showed that NPs possessed uniaxial anisotropy, in contrast to bulk γ-Fe(2)O(3). Mössbauer spectroscopy determined that fabricated NPs consisted of an α-Fe core and a γ-Fe(2)O(3) shell.

Liquid crystalline poly(propylene imine) dendrimer-based iron oxide nanoparticles

“…According to our results 24 and those published by other groups 25,39,40 it is possible to conclude that maghemite NPs are electrostatically coupled with reactive (amido and amino) nitrogen periphery atoms and incorporated among the branches of a PPI dendrimer.…”

“…According to the literature, 17 dendrimer-based MIO NPs can be synthesized using different strategies: (1) dendrimer-stabilized MIO NPs (DSNPs), whereby dendrimers are used as stabilizers to surround or protect the MIO NPs, and the MIO NPs are formed in situ; 18,19 (2) dendrimer-assembled MIO NPs (DANPs), where functionalized dendrimers are assembled onto the surface of preformed MIO NPs via specic physical or chemical interactions; [20][21][22] (3) dendrimer-entrapped MIO NPs (DENPs), in which the dendrimers are used as templates to synthesize MIO NPs in situ; [23][24][25][26] (4) MIO NP-cored dendrimers, whereby the dendrimers grow from the MIO NP cores via a step-wise divergent synthesis approach; 27 and (5) nal position dendron-assembled MIO NPs, where dendrons are assembled or graed onto the preformed MIO NPs. 28,29 Recently a unique interior structure of dendrimers was suggested allowing them to be used as templates to entrap different metal and semiconductor NPs.…”

“…28,29 Recently a unique interior structure of dendrimers was suggested allowing them to be used as templates to entrap different metal and semiconductor NPs. In our previous works, to create dendritic nanocomposites or DENPs, Domracheva et al [24][25][26] developed a convenient approach according to which, at rst complexes of Fe(III) ions with liquid-crystalline second generation poly(propylene imine) (PPI) dendrimers reduce by N 2 H 2 Fe(III) to Fe(II) then react with NaOH to obtain dendrimer-Fe(OH) 2 intermediates, that nally oxidize to form the target dendrimer-entrapped Fe 2 O 3 NPs. In works of Domracheva and co-authors 30,31 the observation of quantum size effects was described: inuence of the size of the semiconductor g-Fe 2 O 3 NPs on optical properties and inuence of pulsed laser irradiation on superparamagnetic properties of g-Fe 2 O 3 NPs.…”

Modified nano Fe2O3-epoxy composite with enhanced mechanical properties

“…It has been widely used in catalysts, pigments, drug delivery, electrochemical activity, microwave adsorption, magnetic devices and aerospace fields. Nowadays, Fe 2 O 3 -based nanocomposites have been intensively investigated [24][25][26][27][28]. Among of them, [29].…”

Liquid Crystalline Polymers as Tools for the Formation of Nanohybrids

“…The ferromagnetic properties of Co NPs were also studied. By using a similar strategy, Domracheva et al (2011) prepared superparamagnetic γ-Fe 2 O 3 nanoparticles by oxidation of a second generation polypropylene imine LC dendrimer-iron (II) complex in THF solution. NPs with an average diameter of about 2.5 nm encapsulated within the LC dendrimer were obtained.…”