Ferrofluidic aqueous two-phase system with ultralow interfacial tension and micro-pattern formation

Abstract

Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10−2 N m−1, leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10−6 N m−1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.

Thermodynamically controlled multiphase separation of heterogeneous liquid crystal colloids

“…1 c, d). The influence and colloidal behavior of adding guest additives into LCPS of CNC suspensions or LLPS of PEG-dextran solutions has been widely studied 37 – 42 , also in the case of mixing the two systems with each other. Previously, we have established that the CNC nanoparticles can maintain their cholesteric order with the existence of PEG and dextran, while the resulting two CNC-polymers dispersions are immiscible when mixed, giving rise to water-in-water emulsions comprising hierarchical CNC assemblies 43 , 44 .…”

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

“…It was known that high interface tension was beneficial to the anchorage of nanoplates [ 44 , 45 ], but it simultaneously led to difficult spread-assembly of nanoplates, resulting in crumple and uneven structures [ 32 ]. ATPS possessed two distinct interfacial properties, which had a low interfacial tension (0.001 mN m −1 ) that was two orders of magnitude less than that of oil–water system, and semi-confined interface zone (tens of micrometer) that was three orders of magnitude higher than that of oil–water system [ 28 ].…”

Chaotic Model of Brownian Motion in Relation to Drug Delivery Systems Using Ferromagnetic Particles

“…Wetting of certain substrates can also cause bifurcation in thin ferrofluid layers. To avoid agglomeration, the magnetic particle should be coated with a shell of a suitable material [30,31]. In relation to the coating, ferrofluid is divided into two main groups: surfactant, if the coating is a surfactant molecule, and ionic, if it is an electric shell [30,31].…”

“…The particles are most often hematite, Fe 2 O 3 , or magnetite, Fe 3 O 4 , and they need to be stabilized due to high surface energy by adding a polymer or ionic component (surfactant). Usually, such stable particles are about 10 nm in diameter, and their surface energy is reduced by long-chain surfactants which, thanks to the long chains, prevent agglomeration, or the same charge on the surface of magnetic particles leads to a mutual repulsion, preventing agglomeration [30]. Ferrofluid particles do not precipitate even for a long time, they do not agglomerate and they do not separate from liquids even by applying an extremely strong magnetic field.…”

“…To avoid agglomeration, ferrofluid particles are coated [30,31]. Depending on the coating, ferrofluids are divided into two groups: surfactant-coated ferrofluids and electrostatically stabilized ferrofluids [31].…”