Reconfigurable Anisotropic Coatings via Magnetic Field‐Directed Assembly and Translocation of Locking Magnetic Chains

A method for the generation of remotely reconfigurable anisotropic coatings is developed. To form these coatings, locking magnetic nanoparticles (LMNPs) made of a superparamagnetic core and a two‐component polymer shell are employed. Two different polymers form phase‐separated coaxial shells. The outer shell provides repulsive interactions between the LMNPs while the inner shell exerts attractive forces between the particles. Applying a non‐uniform magnetic field, one gathers the particles together, pushing them to come in contact when the internal shells could effectively hold the particles together. When the magnetic field is turned off, the particles remain locked due to these strong interactions between internal shells. The shells are thus made stimuli‐responsive, so this locking can be made reversible and the chains can be disintegrated on demand. In a non‐uniform magnetic field, the assembled chains translocate, bind to the solid substrate and form anisotropic coatings with a “locked” anisotropic structure. The coatings can be constructed, aligned, realigned, degraded, and generated again on demand by changing the magnetic field and particle environment. The mechanism of the coating formation is explained using experimental observations and a theoretical model.     

In situ trace analysis of oil in water with mid-infrared fiberoptic chemical sensors

The determination of trace amounts of oil in water facilitates the forensic analysis on the presence and origin of oil in the aqueous environment. To this end, the present study focuses on direct sensing schemes for quantifying trace amounts of oil in water using mid-infrared (MIR) evanescent field absorption spectroscopy via fiberoptic chemical sensors. MIR transparent silver halide fibers were utilized as optical transducer for interrogating oil-in-water emulsions via the evanescent field emanating from the waveguide surface, and penetrating the surrounding aqueous environment by a couple of micrometers. Unmodified fibers and fibers surface-modified with grafted epoxidized polybutadiene layers enabled the direct detection of crude oil in a deionized water matrix at the ppm level to ppb concentration level, respectively. Thus, direct chemical sensing of crude oil IR signatures without any sample preparation as low as 46 ppb was achieved with a response time of a few seconds.     

Transparent hydrophobic organic-inorganic nanocomposite films

Hydrophobic, transparent organic-inorganic hybrid coatings were synthesized by the incorporation of SiO₂ nanoparticles in a matrix of 3-glycidoxypropyltrimethoxysilane (GPTS) and tetramethyl orthosilicate (TMOS) followed by overlaying isobutyltrimethoxysilane (IBTMS) film for enhanced hydrophobicity. Scanning probe microscopy, ellipsometry and contact angle measurements were used to study their morphology, thickness and surface properties. GPTS and TMOS sol with SiO₂ nanoparticles resulted in rough but transparent surface of homogeneous monolayer of ∼40 nm. The rough surface mimicking lotus leaf was chemically modified with a layer of IBTMS resulting in the contact angle of nearly 130°. Morphology as well as contact angles were dependent on the thickness of IBTMS hydrophobic coating layer. Process of creating rough but transparent and durable layer loaded with SiO₂ particles demonstrates the feasibility of meeting all three desired characteristics of transparency, durability and superhydrophobicity.     

Nanoporous artificial proboscis for probing minute amount of liquids

We describe a method of fabrication of nanoporous flexible probes which work as artificial proboscises. The challenge of making probes with fast absorption rates and good retention capacity was addressed theoretically and experimentally. This work shows that the probe should possess two levels of pore hierarchy: nanopores are needed to enhance the capillary action and micrometer pores are required to speed up fluid transport. The model of controlled fluid absorption was verified in experiments. We also demonstrated that the artificial proboscises can be remotely controlled by electric or magnetic fields. Using an artificial proboscis, one can approach a drop of hazardous liquid, absorb it and safely deliver it to an analytical device. With these materials, the paradigm of a stationary microfluidic platform can be shifted to the flexible structures that would allow one to pack multiple microfluidic sensors into a single fiber.     

The effects of concentration-dependent morphology of self-assembling RADA16 nanoscaffolds on mixed retinal cultures

RADA16 self-assembling peptide nanofiber scaffolds (SAPNSs) have been shown to have positive effects on neural regeneration following injury to the central nervous system in vivo, but mechanisms are unclear. Here we show that RADA16 SAPNSs form scaffolds of increasing fiber density with increasing peptide concentration which in turn has a concentration-dependent effect on neurons and astrocytes in mixed retinal cultures. Importantly, we report that the final nanoscale fiber architecture is an important factor to consider in designing scaffolds to promote regeneration in the central nervous system.     

Oily Nanocoatings

Tribological performance of molecular thermoplastic elastomeric films grafted onto a silicon surface was enhanced by adding a minute amount of paraffinic oil, which was adsorbed by the rubber matrix. The nanocomposite films show bimodal distribution of the surface elastic modulus, caused by the nanodomain structure. Minute amounts of oil, trapped within the rubber phase after evaporation, modified the nanotribological properties of these layers. We observed a significant decrease of the friction coefficient by 40%, along with a lower elastic modulus of the rubber phase. We suggest that under high shear stresses and sliding velocity, oil molecules can be compressed out of the bulk to the surface, facilitating instant local lubrication of the contact area.     

Field-directed self-assembly with locking nanoparticles

A reversible locking mechanism is established for the generation of anisotropic nanostructures by a magnetic field pulse in liquid matrices by balancing the thermal energy, short-range attractive and long-range repulsive forces, and dipole-dipole interactions using a specially tailored polymer shell of nanoparticles. The locking mechanism is used to precisely regulate the dimensions of self-assembled magnetic nanoparticle chains and to generate and disintegrate three-dimensional (3D) nanostructured materials in solvents and polymers.     

Synthesis and behavior of the polymer covering on a solid surface. II. Effect of the adsorbent particle size on adsorption

Adsorption of poly(5-tert-butylperoxy-5-methyl-1-hexen-3-yne-co-maleic anhydride) and poly(styrene-co-maleic anhydride) on the various ultrafine powders (TiO₂, ZnO, Al₂O₃, CaCO₃, aerosil, and quartz powder) was studied. Plateau adsorption amount per unit surface of adsorbent (a^s) decreased with the decreasing of particle size of the adsorbent. The a^s-molecular mass relationship was different for copolymers of low and high molecular mass. The fractal dimension D = 2.5 of adsorbent surface was determined if the particle radius was less than 2.5 μm. Fractal behavior was explained by aggregation of particles. Due to the aggregation the interparticle space (pore) in the area of contact of neighboring particles is inaccessible for the polymer and accessible for the solvent. The experimental isotherm with maximum was employed for estimation of the volume of inaccessible pores 2.4 cm³/g for suspension of aerosil. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 299–305, 1998     

Biodegradable plastics from animal protein coproducts: Feathermeal

This work describes the properties of plastics made from partially denatured proteins produced by the animal coproduct (rendering) industry and these plastics' fabrication. Specifically, plastic samples from partially denatured feathermeal protein were successfully produced by a compression‐molding process. The modulus (stiffness) of the material obtained was found to be comparable with that of commercial synthetic materials, such as polystyrene, but was found to have lower toughness characteristics, which is a common phenomenon among plastics produced from animal and plant proteins. A reversible stress–strain property was observed over the yield region. Plastic‐forming conditions for undenatured animal proteins, such as albumen and whey proteins, were also formulated for fabricating plastics out of these proteins' blends with feathermeal proteins. The resultant plastic samples that were developed of biomacromolecular blends, such as feathermeal/whey and feathermeal/albumen, demonstrated improved mechanical properties, specifically tensile strength, when compared with neat plastics from feathermeal proteins. The values for the stiffness of the feathermeal/whey blends deviated from simple mixing rule and showed a synergistic effect. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthetic Hydrophilic Materials with Tunable Strength and a Range of Hydrophobic Interactions

The ability to vary, adjust, and control hydrophobic interactions is crucial in manipulating interactions between biological objects and the surface of synthetic materials in aqueous environment. To this end a grafted polymer layer (multi‐component mixed polymer brush) is synthesized that is capable of reversibly exposing nanometer‐sized hydrophobic fragments at its hydrophilic surface and of tuning, turning on, and turning off the hydrophobic interactions. The reversible switching occurs in response to changes in the environment and alters the strength and range of attractive interactions between the layer and hydrophobic or amphiphilic probes in water. The grafted layer retains its overall hydrophilicity, while local hydrophobic forces enable the grafted layer to sense and attract the hydrophobic domains of protein molecules dissolved in the aqueous environment. The hydrophobic interactions between the material and a hydrophobic probe are investigated using atomic force microscopy measurements and a long‐range attractive and contact‐adhesive interaction between the material and the probe is observed, which is controlled by environmental conditions. Switching of the layer exterior is also confirmed via protein adsorption measurements.