The ability of Lepidoptera, or butterflies and moths, to drink liquids from rotting fruit and wet soil, as well as nectar from floral tubes, raises the question of whether the conventional view of the proboscis as a drinking straw can account for the withdrawal of fluids from porous substrates or of films and droplets from floral tubes. We discovered that the proboscis promotes capillary pull of liquids from diverse sources owing to a hierarchical pore structure spanning nano-and microscales. X-ray phase-contrast imaging reveals that Plateau instability causes liquid bridges to form in the food canal, which are transported to the gut by the muscular sucking pump in the head. The dual functionality of the proboscis represents a key innovation for exploiting a vast range of nutritional sources. We suggest that future studies of the adaptive radiation of the Lepidoptera take into account the role played by the structural organization of the proboscis. A transformative two-step model of capillary intake and suctioning can be applied not only to butterflies and moths but also potentially to vast numbers of other insects such as bees and flies.

In situ characterization of minute amounts of fluids that rapidly change their rheological properties is a challenge. In this paper, the rheological properties of fluids were evaluated by examining the behavior of magnetic nanorods in a rotating magnetic field. We proposed a theory describing the rotation of a magnetic nanorod in a fluid when its viscosity increases with time exponentially fast. To confirm the theory, we studied the time-dependent rheology of microdroplets of 2-hydroxyethyl-methacrylate (HEMA)/diethylene glycol dimethacylate (DEGDMA)-based hydrogel during photopolymerization synthesis. We demonstrated that magnetic rotational spectroscopy provides rich physicochemical information about the gelation process. The method allows one to completely specify the time-dependent viscosity by directly measuring characteristic viscosity and characteristic time. Remarkably, one can analyze not only the polymer solution, but also the suspension enriched with the gel domains being formed. Since the probing nanorods are measured in nanometers, this method can be used for the in vivo mapping of the rheological properties of biofluids and polymers on a microscopic level at short time intervals when other methods fall short.

Optimized conditions for imaging and spectroscopic/elemental mapping of thin perfluorosulfonic acid (PFSA) ionomer layers in fuel cell electrodes by scanning transmission electron microscopy (STEM) have been investigated. The proper conditions were first identified using model systems of either Nafion ionomer-coated nanostructured thin film catalysts or thin films on nanoporous Si. These analysis conditions were then applied in a quantitative study of the ionomer through-layer loading for two differently-prepared electrode catalyst layers using electron energy loss (EELS) and energy dispersive X-ray spectroscopy (EDS) in the STEM. The electron-beam induced damage to the PFSA ionomer was quantified by following the fluorine mass loss with electron dose/exposure and was mitigated by several orders of magnitude using cryogenic specimen cooling and a higher incident electron voltage. Multivariate statistical analysis was applied to the analysis of both EELS and EDS spectrum images for data de-noising and unbiased separation of the independent components related to the catalyst, ionomer, and support distributions within the catalyst layers.Perfluorosulfonic acid (PFSA) ionomer is a key component within the electrode layers of polymer electrolyte fuel cells (PEFCs). The PEFC electrode layer is typically constructed at a ∼10 μm thickness and is comprised of a dispersed Pt nanoparticle catalyst supported on a highly structured carbon black support with a distributed PFSA ionomer film. This percolating solid polyelectrolyte in the electrode provides an efficient proton transport path to the active catalyst sites. The carbon and polymer occupy ∼20% volume fraction each in the electrode, which leaves ∼50-60% pore volume for transport of the reactant hydrogen/air and product water to/from the active Pt sites.Both the uniformity of the PFSA ionomer loading on a 100-nm length scale and the uniformity of the actual film thickness distribution surrounding the carbon support and catalyst nanoparticles on a 1-nm length scale are critical to electrode performance, and quantitative measurements of both these properties are highly desired. Scanning transmission electron microscopy (STEM) is an attractive tool for characterizing the distribution of ionomer within PEFC electrodes, especially when coupled with spectroscopic techniques such as electron energy loss spectroscopy (EELS) or energy dispersive X-ray spectroscopy (EDS). 1 While electron microscopy is more than capable of fulfilling the spatial resolution and chemical sensitivity requirements necessary for analysis of the PFSA ionomer, further method optimization of the STEM imaging and analysis parameters is required due to the beam-sensitive nature of the ionomer films.Fluorinated compounds, such as the PFSA ionomer, can be highly sensitive to electron beam radiation damage. 2 The high electron doses needed to acquire spectroscopic maps by either EDS or EELS can induce severe structural and chemical changes to the ionomer within the electrode, as previously demonstrated on PEF...

Robust, simple, and scalable touch- and brush-spinning methods for the drawing of nanofibers, core-shell nanofibers, and their aligned 2D and 3D meshes using polymer solutions and melts are discussed.

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We report on the development of a multifunctional magnetic rotator that has been built and used during the last five years by two groups from Clemson and Drexel Universities studying the rheological properties of microdroplets. This magnetic rotator allows one to generate rotating magnetic fields in a broad frequency band, from hertz to tens kilohertz. We illustrate its flexibility and robustness by conducting the rheological studies of simple and polymeric fluids at the nano and microscale. First we reproduce a temperature-dependent viscosity of a synthetic oil used as a viscosity standard. Magnetic rotational spectroscopy with suspended nickel nanorods was used in these studies. As a second example, we converted the magnetic rotator into a pump with precise controlled flow modulation. Using multiwalled carbon nanotubes, we were able to estimate the shear modulus of sickle hemoglobin polymer. We believe that this multifunctional magnetic system will be useful not only for micro and nanorheological studies, but it will find much broader applications requiring remote controlled manipulation of micro and nanoobjects.

3761wileyonlinelibrary.com single magnetic domain of the particle. The mean time between fl ips (the Neel relaxation time) depends on temperature. For many practical applications, the time of the experiment is orders of magnitude longer than the Neel relaxation time, so that the average particle magnetization is zero. The random fl ipping depends on temperature. At a given (generally low) temperature (termed the blocking temperature) the Neel relaxation time is the same as the characteristic time of the experiment, and thus above the blocking temperature the nanoparticle is superparamagnetic. The blocking temperature depends on the particle composition, size and shape. For example, for a 10 nm diameter spherical Fe 3 O 4 nanoparticle in a typical laboratory experiment the blocking temperature is far below 200 K, [ 2 ] thus the particles are superparamagnetic for most intended applications. Very low toxicity, low cost, simple and well-reproducible synthesis render iron oxide nanoparticles the most extensively used superparamagnetic nanomaterial.The response of a superparamagnetic particle to a magnetic fi eld and the experimental timeframe required for loss of the average magnetization has been intensively explored in numerous examples of stimuli-responsive nanostructures. The major advantage of materials based on magnetic particles is that the mechanism of response does not interfere with many other properties of the materials and that the magnetic fi eld (with a practical range on the order of 1 Tesla or less) is noninvasive for living organisms. The latter is a critical aspect for biomedical and other applications involving live species. The number of annual publications that utilize superparamagnetic nanoparticles is >1000 and rising. The rapid increase of interest in magnetic nanoparticles (MNPs) can be attributed to studies on magnetic imaging and drug delivery systems which built upon older research involving ferrofl uids. A number of excellent reviews have recently been published on the synthesis and applications of MNPs, [ 3 ] surface functionalization, [ 4 ] their biomedical applications, [ 3b , 5 ] applications in recyclable catalysts, [ 6 ] MNP toxicity, [ 7 ] and many others. [ 8 ] This review is focused on the surface functionalization of MNPs that can be used to either (a) generate nanostructured materials or to (b) add responsive properties to the materials. The goal of this review is to assemble the most practical and important information for material scientists working in the area of nanostructured materials with a focus on assembly using bottom-up methods. Magnetic fi eld induced forces can be tuned by the regulation of the magnetic fi eld direction, strength and gradient, which provide a large toolbox for the manipulation of nanoscale forces. [ 9 ] The structure of this article is as Magnetic fi eld imaging in living specimens with magnetic nanoparticles as contrasting agents has attracted signifi cant interest in the rapidly developing fi eld of nanomedicine. Developments in this fi eld ...

The enzymogel nanoparticle made of a magnetic core and polymer brush shell demonstrates a novel type of remote controlled phase-boundary biocatalysis that involves remotely directed binding to and engulfing insoluble substrates, high mobility, and stability of the catalytic centers. The mobile enzymes reside in the polymer brush scaffold and shuttle between the enzymogel interior and surface of the engulfed substrate in the bioconversion process. Biocatalytic activity of the mobile enzymes is preserved in the enzymogel while the brush-like architecture favors the efficient interfacial interaction when the enzymogel spreads over the substrate and extends substantially the reaction area as compared with rigid particles.