Preparation and magnetoviscosity of nanotube ferrofluids by viral scaffolding and ALD on porous templates

Abstract

Current models for magnetoviscosity suggest that replacing the spherical nanoparticles of a conventional ferrofluid with magnetic nanotubes would lead to a stronger field-induced viscosity enhancement and a much-improved stability against shear thinning -two important parameters for technological exploitation of the magnetoviscous effect. We report the development of positive and negative templating strategies for the synthesis of magnetic nanotubes out of a variety of materials. Our positive template is Tobacco mosaic virus (TMV) -in natural form or genetically engineered to express specific surface chemistries and lengths -which we exploit as a template for the electroless deposition (ELD) of nanosized clusters of nickel and as a scaffold for magnetic particles in a conventional ferrofluid. Our negative templating strategy employs porous anodic aluminum oxide (AAO) as a substrate for the atomic layer deposition (ALD) of a conformal coating of iron oxide, offering precise control over the length and wall thickness of the resulting nanotubes. Both strategies were scaled up to produce the mass quantities of uniform-aspect-ratio nanotubes that are needed for macroscopic ferrofluid volumes. The magnetoviscosity of these ''nanotube ferrofluid'' samples was studied as a function of applied magnetic field and shear frequency, and a particularly strong effect was found to be induced by viral scaffolding.

Electroless synthesis of 3 nm wide alloy nanowires insideTobacco mosaic virus

“…The particles are isolated from plants, wet chemically sensitized/activated with Pd(II) catalyst, and metallized with Co(II) and Fe(II) in suspension. deposition (ELD) can offer an alternative [3,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. While the ELD of Cu and Ni has been very well investigated since they are employed for various products, many other metals qualify for investigation too [24].…”

“…One of the best known templates is porous alumina [18], while extremely small diameters can be reached in micelles (<2 nm) [25], or in microtubuli [21,22].…”

Nanoscale device architectures derived from biological assemblies: The case of tobacco mosaic virus and (apo)ferritin

“…61,118) For deposits that are much thicker than the virion, prolonged deposition produces smooth tubes. 119) An important criterion for applications is chemical stability. While Au and Pt generally do not oxidize in air, NiFe forms a very thin passivating oxide layer, Ni oxidizes slowly, and pure Co oxidizes rapidly.…”

Ferrofluids: Synthetic Strategies, Stabilization, Physicochemical Features, Characterization, and Applications

“…[236] Wu et al demonstrated these strategies for synthesizing mass quantities of uniform-aspect-ratio magnetic nanotubes needed for macroscopic FF volumes that enhanced their magnetoviscosity (Figure 15). [237 Using TMV as a positive template for the electroless deposition of nanosized clusters of nickel, they observed the presence of Ni layers having nonhomogeneous thickness (< 20 nm) dominated by grain boundaries formed by the coalescence of neighboring Ni clusters. Magnetometry measurements performed on Ni-TMV particles exhibited a coercivity of 90 Oe, which is near to that of bulk Ni (100 Oe) though its saturation magnetization was very low ( % 0.004 emu g À1 ).…”

“…The enhancement in FF magnetoviscosity (left) and improved resistance to shear thinning (right) of a commercial FF supplemented with TMV-derived bioadditives. Reproduced with permission from reference [237]. Copyright 2010 American Chemical Society.…”