Phoretic Self-Propulsion Moran, Jeffrey L; Posner, Jonathan D
Annual review of fluid mechanics,
01/2017, Volume:
49, Issue:
1
Journal Article
Peer reviewed
Open access
It is well-known that micro- and nanoparticles can move by phoretic effects in response to externally imposed gradients of scalar quantities such as chemical concentration or electric potential. A ...class of active colloids can propel themselves through aqueous media by generating local gradients of concentration and electrical potential via surface reactions. Phoretic active colloids can be controlled using external stimuli and can mimic collective behaviors exhibited by many biological swimmers. Low-Reynolds number physicochemical hydrodynamics imposes unique challenges and constraints that must be understood for the practical potential of active colloids to be realized. Here, we review the rich physics underlying the operation of phoretic active colloids, describe their interactions and collective behaviors, and discuss promising directions for future research.
Colloidal Self Assembly
In article number 2211197, Dwaipayan Chakrabarti and co‐workers report on the self‐assembly of enantiomorphic single colloidal gyroid crystals in silico from designer chiral ...patchy spheres. Each of these crystals is shown to support a complete photonic bandgap, whilst also exhibiting rich chiroptical properties. This computational study introduces single colloidal gyroids as attractive targets for chiral photonic crystals operating at optical frequencies. Image credit: Wesley Flavell.
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Stability of colloidal particles contributes to the turbidity in the water column, which significantly influences water quality and ecological functions in aquatic environments especially shallow ...lakes. Here we report characterization, origin and aggregation behavior of aquatic colloids, including natural colloidal particles (NCPs) and total inorganic colloidal particles (TICPs), in a highly turbid shallow lake, via field observations, simulation experiments, ultrafiltration, spectral and microscopic, and light scattering techniques. The colloidal particles were characterized with various shapes (spherical, polygonal and elliptical) and aluminum-, silicon-, and ferric-containing mineralogical structures, with a size range of 20–200 nm. The process of sediment re-suspension under environmentally relevant conditions contributed 78–80% of TICPs and 54–55% of NCPs in Lake Taihu, representing an important source of colloids in the water column. Both mono- and divalent electrolytes enhanced colloidal aggregation, while a reverse trend was observed in the presence of natural organic matter (NOM). The influence of NOM on colloidal stability was highly related to molecular weight (MW) properties with the high MW fraction exhibiting higher stability efficiency than the low MW counterparts. However, the MW-dependent aggregation behavior for NCPs was less significant than that for TICPs, implying that previous results on colloidal behavior using model inorganic colloids alone should be reevaluated. Further studies are needed to better understand the mobility/stability and transformation of aquatic colloids and their role in governing the fate and transport of pollutants in natural waters.
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•Characterization, origin and aggregation behavior of shallow-lake colloids were studied.•Aquatic colloids had Al-, Si- and Fe-containing mineralogical structures with diverse conformation.•Sediment re-suspension contributed 78–80% of TICPs and 54–55% of NCPs in lake waters.•HMW-NOM greatly enhanced colloidal stability of TICPs compared to LMW-NOM.•Colloidal behavior analyses based on model inorganic colloids and bulk NOM should be reevaluated.
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"The possibility of using colloidal silver and gold as condensors for electron storage in artificial photosynthesis has prompted the recent renewed interest in these areas." This statement by Fendler ...and co-workers in 1983 is even more relevant in today's science and technology. In this
tutorial review
we summarize research regarding the use of light in the synthesis of metallic nanoparticles. We describe how light of different energies induces a variety of chemical events that culminate in the nucleation and growth of metal nanocrystals. Light can thus be used as a handle to direct metal nanocrystal growth and improve tunability and reproducibility.
The presence of light in chemical synthesis of plasmonic nanoparticles offers promising tools for colloidal nanofabrication.
Colloidal particles with site-specific directional interactions, so called “patchy particles”, are promising candidates for bottom-up assembly routes towards complex structures with rationally ...designed properties. Here we present an experimental realization of patchy colloidal particles based on material independent depletion interaction and surface roughness. Curved, smooth patches on rough colloids are shown to be exclusively attractive due to their different overlap volumes. We discuss in detail the case of colloids with one patch that serves as a model for molecular surfactants both with respect to their geometry and their interactions. These one-patch particles assemble into clusters that resemble surfactant micelles with the smooth and attractive sides of the colloids located at the interior. We term these clusters “colloidal micelles”. Direct Monte Carlo simulations starting from a homogeneous state give rise to cluster size distributions that are in good agreement with those found in experiments. Important differences with surfactant micelles originate from the colloidal character of our model system and are investigated by simulations and addressed theoretically. Our new “patchy” model system opens up the possibility for self-assembly studies into finite-sized superstructures as well as crystals with as of yet inaccessible structures.
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•Stable HA-Cd(II) nanocolloids formed at high C/Cd ratios.•Electrostatic interactions controlled the stability of HA-Cd(II) nanoparticles.•Colloid transport model can well describe the mobility of ...HA-Cd(II) colloids.•Stable HA-Cd(II) colloids can travel a large distance in column.
Humic acid (HA), a principal constituent of natural organic matter (NOM), manifests ubiquitously across diverse ecosystems and can significantly influence the environmental behaviors of Cd(II) in aquatic systems. Previous studies on NOM-Cd(II) interactions have primarily focused on the immobilization of Cd(II) solids, but little is known about the colloidal stability of organically complexed Cd(II) particles in the environment. In this study, we investigated the formation of HA-Cd(II) colloids and quantified their aggregation, stability, and transport behaviors in a saturated porous media representative of typical subsurface conditions. Results from batch experiments indicated that the relative quantity of HA-Cd(II) colloids increased with increasing C/Cd molar ratio and that the carboxyl functional groups of HA dominated the stability of HA-Cd(II) colloids. The results of correlation analysis between particle size, critical aggregation concentration (CCC), and zeta potential indicated that both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions contributed to the enhanced colloidal stability of HA-Cd(II) colloids. Column results further confirmed that the stable HA-Cd(II) colloid can transport fast in a saturated media composed of clean sand. Together, this study provides new knowledge of the colloidal behaviors of NOM-Cd(II) nanoparticles, which is important for better understanding the ultimate cycling of Cd(II) in aquatic systems.
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The paper shows the results of method development identification of colloidal silver nanoparticles on the components of the Raman spectra, using the conditions information uncertainty decision to ...increase the reliability evaluating the presence nanoparticles at the surface polyester fibers.
The rheological properties of a colloidal suspension are a function of the concentration of the colloids and their interactions. While suspensions of passive colloids are well studied and have been ...shown to form crystals, gels, and glasses, examples of energy‐consuming “active” colloidal suspensions are still largely unexplored. Active suspensions of biological matter, such as motile bacteria or dense mixtures of active actin–motor–protein mixtures have, respectively, reveals superfluid‐like and gel‐like states. Attractive inanimate systems for active matter are chemically self‐propelled particles. It has so far been challenging to use these swimming particles at high enough densities to affect the bulk material properties of the suspension. Here, it is shown that light‐triggered asymmetric titanium dioxide that self‐propel, can be obtained in large quantities, and self‐organize to make a gram‐scale active medium. The suspension shows an activity‐dependent tenfold reversible change in its bulk viscosity.
A large‐scale application of active chemical nanomotors is demonstrated. The active motors self‐organize to change the microstructure of the suspension. This results in a change of the bulk viscosity of the suspension, which can be reversibly tuned by an order of magnitude, thus forming an active optorheological medium.
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Photocatalytically active, multi‐chambered, biomolecule‐based microspheres were prepared by hierarchical co‐assembly of simple dipeptides and porphyrins. The colloidal microspheres are highly ...hydrated and consist of a network of J‐aggregate nanoscale substructures that serve as light‐harvesting antennae with a relatively broad spectral cross‐section and considerable photostability. These optical properties can be exploited in photocatalytic reactions involving inorganic or organic species. Taken together, these structural and functional features suggest that soft porous biomolecule‐based colloids are a plausible photosynthetic model that could be developed towards demonstrating aspects of primitive abiotic cellularity.
Simple but multifunctional: Photocatalytically active microspheres with highly hydrated, accessible multi‐chambered interiors have been prepared by cooperative self‐assembly of simple dipeptides and porphyrins (see picture). They serve as a plausible photosynthetic model that could be potentially developed towards studying aspects of primitive abiotic cellularity.
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