Synthesis of Multifunctional Micrometer‐Sized Particles with Magnetic, Amphiphilic, and Anisotropic Properties

Choi, Siyoung Q.; Jang, Se Gyu; Pascall, Andrew J.; Dimitriou, Michael; Kang, Tae Gon; Hawker, Craig J.; Squires, Todd M.

doi:10.1002/adma.201003604

Cited by 56 publications

(48 citation statements)

References 48 publications

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“…For a given surface viscosity, the Boussinesq number,

Bo = \frac{2 η_{s}}{a η}

for the needle (a ∼ 1 mm) was ∼ 20 times smaller than that of the 100 μm microbuttons (a ∼ 50 μm) used in the current experiments (69). This limits the minimum surface viscosity that can be measured to ∼ 1-10 μPa-s-mfor needle instruments (5, 47, 68-71), compared to the ∼ 0.1 μPa-s-m with the microbutton rheometer (9-13, 55). With the microbutton rheometer, we find that the actual range of surface viscosity in these phase-separated systems is four orders of magnitude or more (Fig.…”

Section: Discussionmentioning

confidence: 95%

“…Circular ferromagnetic probes (microbuttons) of diameter 100 um, thickness 1 μm, with “button holes” of diameter 3.5 μm were fabricated by photolithography (11, 55), followed by an electron-beam evaporated layer of nickel on one side, followed by a 10 nm layer of gold. The entire wafer was dipped into a 1.0 mM solution of perfluorooctanethiol (Sigma, St. Louis, MO) in ethanol to form a hydrophobic self-assembled monolayer on the gold.…”

Section: Methodsmentioning

confidence: 99%

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Interfacial rheology of coexisting solid and fluid monolayers

et al. 2017

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Biologically relevant monolayer and bilayer films often consist of micron-scale high viscosity domains in a continuous low viscosity matrix. Here we show that this morphology can cause the overall monolayer fluidity to vary by orders of magnitude over a limited range of monolayer composition. Modeling the system as a two-dimensional suspension in analogy to classic three-dimensional suspensions of hard spheres in a liquid solvent explains the rheological data with no adjustable parameters. In monolayers with ordered, highly viscous domains dispersed in a continuous low viscosity matrix, the surface viscosity increases as a power law with the area fraction of viscous domains. Changing the phase of the continuous matrix from a disordered fluid phase to a more ordered, condensed phase dramatically changes the overall monolayer viscosity. Small changes in the domain density and/or continuous matrix composition can alter themonolayerviscosity by orders of magnitude.

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“…For a given surface viscosity, the Boussinesq number,

Bo = \frac{2 η_{s}}{a η}

Section: Discussionmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

Interfacial rheology of coexisting solid and fluid monolayers

et al. 2017

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“…Circular ferromagnetic probes (microbuttons, Fig. 4) of diameter 20 μm, thickness 1 μm, with "button holes" of diameter 3.5 μm were fabricated by photolithography as described elsewhere (13). Briefly, a sacrificial layer (Omnicoat; MicroChem Corp.) was deposited onto a silicon wafer (4 inch; Rockwood) followed by a 1-μm-thick layer of photoresist (SU-8; MicroChem Corp.).…”

Section: Methodsmentioning

confidence: 99%

Effect of cholesterol nanodomains on monolayer morphology and dynamics

Kim

Choi

Zell

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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At low mole fractions, cholesterol segregates into 10-to 100-nmdiameter nanodomains dispersed throughout primarily dipalmitoylphosphatidylcholine (DPPC) domains in mixed DPPC:cholesterol monolayers. The nanodomains consist of 6:1 DPPC:cholesterol "complexes" that decorate and lengthen DPPC domain boundaries, consistent with a reduced line tension, λ. The surface viscosity of the monolayer, η s , decreases exponentially with the area fraction of the nanodomains at fixed surface pressure over the 0.1-to 10-Hz range of frequencies common to respiration. At fixed cholesterol fraction, the surface viscosity increases exponentially with surface pressure in similar ways for all cholesterol fractions. This increase can be explained with a free-area model that relates η s to the pure DPPC monolayer compressibility and collapse pressure. The elastic modulus, G′, initially decreases with cholesterol fraction, consistent with the decrease in λ expected from the line-active nanodomains, in analogy to 3D emulsions. However, increasing cholesterol further causes a sharp increase in G′ between 4 and 5 mol% cholesterol owing to an evolution in the domain morphology, so that the monolayer is elastic rather than viscous over 0.1-10 Hz. Understanding the effects of small mole fractions of cholesterol should help resolve the controversial role cholesterol plays in human lung surfactants and may give clues as to how cholesterol influences raft formation in cell membranes.surface rheology | isotherms | free-volume model | AFM M inute fractions of cholesterol lead to dramatic changes in dipalmitoylphosphatidylcholine (DPPC) monolayer morphology (Figs. 1-3) (1, 2) and have equally dramatic effects on monolayer dynamic properties. One weight percent cholesterol reduces the surface viscosity, η s , of DPPC monolayers by an order of magnitude, and 2 wt% reduces η s by two orders of magnitude . Atomic force microscopy (AFM) images and microrheological data show that the cholesterol is segregated to lineactive, locally disordered nanodomains that are dispersed in and separate ordered, primarily DPPC domains. As a result, the monolayer retains many of the features of pure DPPC monolayers including a high collapse pressure, high compressibility, and so on, while having significantly lower surface viscosity. This surface viscosity effect suggests a role for cholesterol in lung surfactant (LS), a lipid-protein monolayer necessary to reduce the surface tension in the lung alveoli during respiration (Fig. S1) (3, 4). At present, even the existence of cholesterol in native LS is questioned, because the lung lavage required to harvest LS inevitably causes blood and cell debris to be coextracted, potentially contaminating LS with cholesterol (5). This lack of consensus over the role of cholesterol is reflected in the composition of replacement lung surfactants for neonatal respiratory distress syndrome (NRDS), which occurs in 20,000-30,000 premature births each year (6). Survanta and Curosurf, two clinically approved animalextract replacement surfact...

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“…Multi-component hybrid magnetic nanoparticles such as the dumbbell or core-satellite type are successfully synthesized by solution-based methods (Hao et al, 2010). Non-spherical magnetic particles of disk, triangular, rectangular, rice, worm or boomerang shape can be fabricated within the nanometerto-micrometer size range via photolithographic or microfluidic processes (Choi et al, 2011;Suh et al, 2012). Such nanoscale fabrication techniques can be applied for more profound understanding of the mechanism of shape-related heterogeneous flocculation.…”

Section: Perspectives and Future Directionsmentioning

confidence: 99%