Role of hydration and micellar shielding in tuning the structure of single crystalline iron oxide nanoparticles for designer applications

Abstract

Different physicochemical properties of nanoscale iron oxides have been useful in enabling various applications. Desirable biochemical, magnetic, and catalytic properties result from the structure and size of the iron oxide polymorph particles. To produce monodispersed single crystalline particles, PS-b-P2VP reverse micelle templating has proven to be a convenient low temperature method. Here, Raman spectroscopy and quantitative nanomechanical mapping analysis are used to provide a full picture of the formation and transformation processes that occur within the reverse micelle templates. Surprisingly, shielding of the hygroscopic FeCl 3 precursor salt against hydration rather than complexation with the pyridine is responsible for the formation of 𝛾-Fe 2 O 3 particles. Additionally, micelle shielded nanoparticles not only exhibited a uniform size distribution and ordered dispersion, but also an increased transition temperature for the 𝛾 to 𝛼-phase transition, up to 700 • C, making them much more stable than traditional nanoparticles. Using these key understandings of particle formation, nanoparticles can be tuned with composition ranging from a purely spinel (𝛾-Fe 2 O 3 , Fe 3 O 4 ) to a purely hexagonal phase (𝛼-Fe 2 O 3 ), and varying ratios of the three phases, while maintaining a fixed particle size.Modifying parameters offer intriguing opportunities to tailor designer iron oxide nanoparticles for targeted applications with a facile and scalable technique.

Enhanced Stokes Shift and Phase Stability by Cosynthesizing Perovskite Nanoparticles (MAPbI3/MAPbBr3) in a Single Solution

“…[13] Typically for NP synthesis and size control, high-molecularweight polymers are chosen that form dense-core micelles, where the corona offers tight shielding against the environment. [20,37,38] Using lower-molecular-weight polymers results in the formation of a larger ballooning micelle structure with a looser corona of shorter PS chains, allowing easier infiltration of precursor salts [37] (see Figure S1, Supporting Information). However, the downside of such a micellar structure is lowered protection from hydration, as proven by Arbi et al, in the case of polymorphic iron oxide phase formation using different PS-b-P2VP diblock copolymer micelles.…”

“…However, the downside of such a micellar structure is lowered protection from hydration, as proven by Arbi et al, in the case of polymorphic iron oxide phase formation using different PS‐ b ‐P2VP diblock copolymer micelles. [ 37 ] The failure of MABr loading in the higher‐molecular‐weight PS‐ b ‐P2VP micelles results from its failure to infiltrate the densely packed polystyrene brushes in the corona. Using lower‐molecular‐weight polymers led to successful synthesis of NPs from MABr and PbBr 2 precursors; however, it also resulted in an uneven size and spatial distribution, as shown in Figure 1d.…”

Relationship between deposition techniques and nanoparticle dispersions for flexible and printed electronics

“…Therefore, to make any final conclusions about the effect of molecular weight on ordering and interparticle distance, an experiment that varies the concentration as well as the deposition parameters would be required. It is important to bear in mind that this approach to achieving larger interparticle distance may not be straightforward when making certain nanoparticles due to potential inadvertent effects on the crystal phase [36,49]. The sheer size of the design space with multiple variables underscores the care that must be taken to achieve tunability for such RMD arrays.…”

“…Typically, plasma etching of the two-dimensional arrays of loaded reverse micelles can be used to remove the polymer shell and expose the target nanoparticle [44] while maintaining the interparticle spacing and two dimensional order of the micellar templates (see SI figure S1 for an array of loaded reverse micelles and the resultant lanthanum oxide nanoparticles after plasma etching). Polystyrene-bpoly(2-vinylpyridine)(PS-b-P2VP) has proven to be a particularly useful and versatile template, due to its low critical micelle concentration [45,46], ability to complexate with many precursors [47,48], high stability with salt incorporation [35,47,49] and highly tunable self-assembly properties [50]. For interested readers, the general synthesis approach of using PSb-P2VP as a template to form nanoparticles has been reviewed elsewhere [45,[50][51][52].…”

“…However, processing modifications often require changes in the synthesis recipe which can have unintended side-effects that could significantly affect the final compositiontherefore the functionality-of the nanoparticles. For example, changing the molecular weight [49] or the concentration [36] of the polymer used has been seen to modify the observed crystallographic phase of the resultant nanoparticles. Additionally, modifying the solvent can result in an unravelling of the micelle, preventing the formation of ordered monodisperse arrays (see SI figure S2).…”