Tailored Anisotropic Magnetic Chain Structures Hierarchically Assembled from Magnetoresponsive and Fluorescent Components

Tunable Surface Wrinkling by a Bio-Inspired Polyamine Anion Coacervation Process that Mediates the Assembly of Polyoxometalate Nanoclusters

A bio-inspired method is used to render controlled wrinkling surface patterns on supramolecular architectures assembled from polyoxometalate (POM) clusters. It involves a polyamine-multivalent anion interaction generating positively charged coacervates, which while dictating the assembly of POM into spherical structures further facilitate an interesting surface morphogenesis with wrinkling patterns. This spontaneous surface wrinkling depends on the type of multivalent anion and the pH. As the polyamine-anion interaction becomes stronger, the wrinkles turn denser with lesser depth, which eventually undergoes post-buckling to engender a complex surface pattern. Interestingly, the order of influence exerted by different anions on the morphology follows the Hofmeister series. Moreover, the mild synthesis conditions keep the functional POM units dispersed in the sphere with a structural transformability to their lacunary form.

Capillary Force Driving Directional 1D Assembly of Patchy Colloidal Discs

Self-assembly from individual colloidal building units to complex superstructures provides a simple yet effective way for the fabrication of functional materials. A rational design of the unit interactions is essential for it to proceed in a desired manner. Here we show that nondirectional capillary force can be used for directional one-dimensional (1D) assembly of colloidal discs having a designed patch distribution, and colloidal discs with two liquid patches can assemble into long colloidal chains where the stacked colloidal discs have a well-matched configuration with parallel orientation. The length of the chains can be controlled by controlling the experimental parameters. We also found when liquid patches gradually turn into sticky patches, hydrophobic attraction comes into play and becomes dominant, which can also result in chains with continuously increasing length. This method opens an effective avenue for obtaining colloidal chains (or fibers), which can be adapted for the fabrication of other superstructures.

Microcapsule Structure with a Tunable Textured Surface via the Assembly of Polyoxomolybdate Clusters: A Bioinspired Strategy and Enhanced Activities in Alkene Oxidation

A polyamine-mediated bioinspired strategy to assemble Keggin-type phosphomolybdic acid (PMA) clusters is demonstrated for the fabrication of microcapsule (MC) structures with unique surface textures. It involves supramolecular aggregation of polyamines with multivalent anions, which then allows the assembly of negatively charged PMA into MCs in an aqueous medium under ambient conditions. Resembling the role of polyamines in biosilicification of diatoms, the polyamine-anion interaction is shown to be the key for the assembly process. It not only provides structural stability but also facilitates an interesting transition from a smooth to a wrinkled surface alongside a change in the Keggin form to its lacunary form depending on the pH of the medium. Moreover, the presence of isolated PMA units in the hybrid structure enables them to be active in catalyzing the aerobic oxidation of alkenes under solvent-free conditions with better selectivity and reusability. Hence, the assembly approach represents an effective way for heterogenization of PMA-based materials and is expected to find considerable application in the wider hybrid-cluster field.

Colloidal polymers with controlled sequence and branching constructed from magnetic field assembled nanoparticles

The assembly of nanoparticles into polymer-like architectures is challenging and usually requires highly defined colloidal building blocks. Here, we show that the broad size-distribution of a simple dispersion of magnetic nanocolloids can be exploited to obtain various polymer-like architectures. The particles are assembled under an external magnetic field and permanently linked by thermal sintering. The remarkable variety of polymer-analogue architectures that arises from this simple process ranges from statistical and block copolymer-like sequencing to branched chains and networks. This library of architectures can be realized by controlling the sequencing of the particles and the junction points via a size-dependent self-assembly of the single building blocks.

Anisotropic conductive films based on highly aligned polyimide fibers containing hybrid materials of graphene nanoribbons and carbon nanotubes

Anisotropic electrically conductive films (PI-GNR/CNT) consisting of highly aligned polyimide (PI) composite fibers with graphene nanoribbon (GNR) and carbon nanotube (CNT) (GNR/CNT) hybrids as nanofillers have been prepared by electrospinning. The GNR/CNT hybrids used here were prepared by one-step partial unzipping of multi-walled CNTs, in which, with the residual CNTs bonded on the randomly arranged GNR sheets, not only the aggregation of GNR sheets was greatly prevented but also an electrically conductive pathway with good conductivity was effectively formed with the CNTs acting as linking bridges between different GNRs. Due to the three-dimensional (3D) conductive network structure of the GNR/CNT hybrid and fine dispersion and alignment inside the PI fibers, as well as the good interfacial interaction between the GNR/CNT hybrid and the PI matrix, PI-GNR/CNT composite films exhibit a unique property of anisotropic electrical conductivity of 8.3 × 10(-2) S cm(-1) in the parallel direction along the fibers and 7.2 × 10(-8) S cm(-1) in the perpendicular direction, which may open the way for wide potential applications of anisotropic conductive nanomaterials in practical production and scientific research fields.

Preparation of highly anisotropic cobalt ferrite/silica microellipsoids using an external magnetic field

Magnetic cobalt ferrite/silica microparticles having both an original morphology and an anisotropic nanostructure are synthesized through the use of an external magnetic field and nanoparticles characterized by a high magnetic anisotropy. The association of these two factors implies that the ESE (emulsion and solvent evaporation) sol-gel method employed here allows the preparation of silica microellipsoids containing magnetic nanoparticles aggregated in large chains. It is clearly shown that without this combination, microspheres characterized by an isotropic distribution of the magnetic nanoparticles are obtained. While the chaining of the cobalt ferrite nanoparticles inside the silica matrix is related to the increase of their magnetic dipolar interactions, the ellipsoidal shape of the microparticles may be explained by the elongation of the sol droplets in the direction of the external magnetic field during the synthesis. Because of their highly anisotropic structure, these microparticles exhibit permanent magnetic moments, which are responsible, at a larger scale, for the existence of strong magnetic dipolar interactions. Therefore, when they are dispersed in water, the microellipsoids self-assemble into large and irregular chains. These interactions can be reinforced by the use of external magnetic field, allowing the preparation of very large permanent chains. This research illustrates how nanostructured particles exhibiting complex architectures can be elaborated through simple, fast, and low-cost methods, such as the use of external fields in combination with soft chemistry.

Assembly of multiple components in a hybrid microcapsule: designing a magnetically separable Pd catalyst for selective hydrogenation

In analogy to the role of long-chain polyamines in biosilicification, poly-L-lysine facilitates the assembly of nanocomponents to design multifunctional microcapsule structures. The method is demonstrated by the fabrication of a magnetically separable catalyst that accommodates Pd nanoparticles (NPs) as active catalyst, Fe3O4 NPs as magnetic component for easy recovery of the catalyst, and silica NPs to impart stability and selectivity to the catalyst. In addition, polyamines embedded inside the microcapsule prevent the agglomeration of Pd NPs and thus result in efficient catalytic activity in hydrogenation reactions, and the hydrophilic silica surface results in selectivity in reactions depending on the polarity of substrates.

Combining the best of two worlds: nanoparticles and nanofibers

The preparation and applications of nanoparticles and nanofibers are widely described in the literature. Both types of materials have specific advantages but also drawbacks. We discuss here the methods to fabricate nanofibers from nanoparticles and vice versa by template-free methods and colloid-electrospinning. Nanoparticles and nanofibers can be also synergistically combined to yield nanostructured constructs that display highly advantageous properties such as good mechanical integrity, double protection of encapsulated substances, or the possibility to co-encapsulate payloads with different polarities.

A new method for pH triggered curcumin release by applying poly(L-lysine) mediated nanoparticle-congregation

We introduce a novel method for encapsulation of curcumin by synthesizing microcapsule containing self-assembled nanoparticles using poly (L-lysine), trisodium citrate and silica sol. Such microcapsules can only be prepared in neutral and alkaline environment and unencapsulated curcumin can be effectively removed by simple centrifugation with encapsulation efficiency 57.34%. The particle sizes are in the range 0.7-3 μm with an effective diameter 1.05 μm. The structure of the microcapsules is dependent upon the solubility of curcumin in the solvent environment, the microcapsule are spherical when prepared in 10% acetone and bowl-shaped/conical when prepared in water suspension, however, the size of these curcumin encapsulated microcapsules remain similar. Fluorescence microscope images confirm that curcumin is predominantly concentrated within the shell wall of the capsules. Photophysical behavior of Micro-curcumin with respect to curcumin alone is evaluated. Release of curcumin is found to be triggered by pH where acidic environment trigger maximum release compared to basic and neutral conditions. Micro-curcumin is as stable as curcumin. Drug release efficiency is found to be 61.44% and the drug release profile of Micro-curcumin follow Higuchi model. It is also revealed that β-diketone group of curcumin responsible for scavenging activity is retained in the Micro-curcumin, thus suggesting applicability of such system as a poorly water soluble drug delivery vehicle. In contrast to other curcumin delivery systems, the presented method is easy, fast and does not need flow rate monitoring device. In addition poly (L-lysine) as a non-toxic and highly stable material that prevents metabolic degradation is used in the present preparation method.

Tailored Parallel Graphene Stripes in Plastic Film with Conductive Anisotropy by Shear-Induced Self-Assembly

We present a simple but efficient route to prepare a highly anisotropic conductive plastic thin film from the polypropylene/(styrene-ethylene/butadiene-styrene) triblock copolymer/graphene blend via shear-induced self-assembly. Under the shear-flow induction, GE nanosheets dispersed in the polymer matrix can spontaneously assemble into ordered parallel stripes, which endow the materials significantly conductive anisotropy. The electrical resistivity in the direction parallel to the graphene stripes is almost four orders of magnitude lower than that which is perpendicular to the stripes. This study provides a new method for the precise control of the organization of functional nano-objects in polymer matrix, which can be widely extended to the fabrication of other multifunctional anisotropic materials of interest in various fields.

Pyranine-induced self-assembly of colloidal structures using poly(allylamine-hydrochloride)

Complexes of dyes and polyelectrolytes have found widespread use in a variety of functional materials and interfaces. Here it is found that upon mixing the anionic dye pyranine and a cationic polyelectrolyte, poly(allylamine-hydrochloride), two different colloidal structures may form. Above a certain concentration of anionic dye, crosslinking of the polyelectrolyte is initiated, and the formation of sheet-like colloidal structures was observed. Addition of hydroxyl ions resulted in the formation of micron-sized spherical colloids. It was also found that the colloidal shape transition was accompanied by a significant red-shift in the fluorescence emission. Combining fluorescence measurements with studies of the particle size with time, it was found that red-shift was related to the crosslinking of the dye and the polyelectrolyte, and was not influenced significantly by the aggregation and particle growth. Further information about the colloidal behavior and stability was obtained by letting droplets dry and follow the kinetics of this process. It was found that the particles collapsed near the contact line and formed a ring deposit, in agreement with previous studies. However, unlike previous studies, the thickness of the ring deposit did not grow significantly with time, due to the peculiar process of formation found here.