Printing spongy all-in-liquid materials

Printing structured networks of functionalized droplets in a liquid medium enables engineering collectives of living cells for functional purposes [1, 2], bacterial ecology [3], and promises enormous applications in processes ranging from energy storage [4, 5] to drug delivery [6, 7]and tissue engineering [8]. Current approaches are limited to drop-by-drop printing [1, 2] or face limitations in reproducing the sophisticated internal features of a structured material and its interactions with the surrounding media [6, 9–11]. Here, we report on a simple approach for creating stable liquid filaments of silica nanoparticle dispersions and use them as inks to print all-in-liquid materials that consist of a network of droplets. Silica nanoparticles stabilize liquid filaments at Weber numbers two orders of magnitude smaller than previously reported in liquid-liquid systems by rapidly producing a concentrated microemulsion zone at the oil-water interface. We experimentally demonstrate that the printed aqueous phase is emulsified in-situ; consequently, a 3D structure is achieved with flexible walls consisting of layered microemulsions. The tube-like printed features have a spongy texture resembling miniaturized versions of “tube sponges” found in the oceans. A scaling analysis based on the interplay between hydro-dynamics and emulsification kinetics reveals that liquid filaments are formed when emulsions are generated and remain at the interface during the printing period. We demonstrate the utilization of filaments of the nanoparticle dispersions for printing fluidic channels and propose to use them as lab-on-a-chip devices.

Low-Temperature Atmospheric Pressure Plasma Processes for the Deposition of Nanocomposite Coatings

Low-temperature atmospheric pressure (AP) plasma technologies have recently proven to offer a range of interesting opportunities for the preparation of a variety of nanocomposite (NC) coatings with different chemical compositions, structures, and morphologies. Since the late 2000s, numerous strategies have been implemented for the deposition of this intriguing class of coatings by using both direct and remote AP plasma sources. Interestingly, considerable progress has been made in the development of aerosol-assisted deposition processes in which the use of either precursor solutions or nanoparticle dispersions in aerosol form allows greatly widening the range of constituents that can be combined in the plasma-deposited NC films. This review summarizes the research published on this topic so far and, specifically, aims to present a concise survey of the developed plasma processes, with particular focus on their optimization as well as on the structural and functional properties of the NC coatings to which they provide access. Current challenges and opportunities are also briefly discussed to give an outlook on possible future research directions.

Magnetic Guiding with Permanent Magnets: Concept, Realization and Applications to Nanoparticles and Cells

The idea of remote magnetic guiding is developed from the underlying physics of a concept that allows for bijective force generation over the inner volume of magnet systems. This concept can equally be implemented by electro- or permanent magnets. Here, permanent magnets are in the focus because they offer many advantages. The equations of magnetic fields and forces as well as velocities are derived in detail and physical limits are discussed. The special hydrodynamics of nanoparticle dispersions under these circumstances is reviewed and related to technical constraints. The possibility of 3D guiding and magnetic imaging techniques are discussed. Finally, the first results in guiding macroscopic objects, superparamagnetic nanoparticles, and cells with incorporated nanoparticles are presented. The constructed magnet systems allow for orientation, movement, and acceleration of magnetic objects and, in principle, can be scaled up to human size.

Molecular Assembly in Block Copolymer-Surfactant Nanoparticle Dispersions: Information on Molecular Exchange and Apparent Solubility from High-Resolution and PFG NMR

Internally structured block copolymer-surfactant particles are formed when the complex salts of ionic-neutral block copolymers neutralized by surfactant counterions are dispersed in aqueous media. Here, we report the 1H NMR signal intensities and self-diffusion coefficients (D, from pulsed field gradient nuclear magnetic resonance, PFG NMR) of trimethyl alkylammonium surfactant ions and the poly(acrylamide)-block-poly(acrylate) (PAAm-b-PA) polyions forming such particles. The results reveal the presence of an “NMR-invisible” (slowly exchanging) fraction of aggregated surfactant ions in the particle core and an “NMR-visible” fraction consisting of surface surfactant ions in rapid exchange with the surfactant ions dissociated into the aqueous domain. They also confirm that the neutral PAAm blocks are exposed to water at the particle surface, while the PA blocks are buried in the particle core. The self-diffusion of the polyions closely agree with the self-diffusion of a hydrophobic probe molecule solubilized in the particles, showing that essentially all copolymer chains are incorporated in the aggregates. Through centrifugation, we prepared macroscopically phase-separated systems with a phase concentrated in particles separated from a clear dilute phase. D values for the surfactant and block copolymer indicated that the dilute phase contained small aggregates (ca. 5 nm) of surfactant ions and a few anionic-neutral block copolymer chains. Regardless of the overall concentration of the sample, the fraction of block copolymer found in the dilute phase was nearly constant. This indicates that the dilute fraction represented a tail of small particles created by the dispersion process rather than a true thermodynamic solubility of the complex salts.

Mesocrystals from Platinum Nanocubes

Platinum nanoparticles are widely known for their numerous electrochemical and catalytic applications. Enhanced or novel properties that may arise when ordering such particles in a highly defined manner, however, are still subject to ongoing research, as superstructure formation on the mesoscale is still a major challenge to be overcome. In this work, we therefore established a reproducible method to fabricate micrometer-sized superstructures from platinum nanocubes. Through small-angle X-ray scattering and electron diffraction methods we demonstrate that the obtained superstructures have a high degree of ordering up to the atomic scale and, therefore, fulfill all criteria of a mesocrystal. By changing the solvent and stabilizer in which the platinum nanocubes were dispersed, we were able to control the resulting crystal habit of the mesocrystals. Aside from mesocrystal fabrication, this method can be further utilized to purify nanoparticle dispersions by recrystallization with respect to narrowing down the particle size distribution and removing contaminations.

Evaluation of the Photocatalytic Activity of Water-Based TiO2 Nanoparticle Dispersions Applied on Historical Painting Surfaces

This paper aims at assessing the use of nanomaterials in painting conservation and in cleaning practices that could be alternative to the traditional ones to overcome the limits of new green materials. Titanium dioxide nanoparticles have been spread and studied on historical painting surfaces with good results. In particular, the properties of TiO2 nanoparticles have been considered useful for self-cleaning and protective purposes against the accumulation of dirt and dust that represents the first phase in deterioration of historical painting surfaces. TiO2 nanoparticles, prepared in distilled water by Pulsed Laser Ablation in Liquids, were applied on painting mock-ups realized in the laboratory according to old recipes and using historical binders and pigments. The surface characteristics of the painting were investigated by contact angle measurement and by Atomic Force Microscopy. The optical and aesthetical compatibility of the colloidal dispersions with the painting was assessed by spectrophotometry, and then the cleaning efficiency was evaluated by discoloration of a dye under ultraviolet irradiation, at fixed time intervals, using colorimetric technique. Because of the high reactivity of nanoparticles, the possibility of degrading the painting surface, together with the chromatic marker, was examined by colorimetric measurements. The evaluation of the color changes is important for all the materials belonging to cultural heritage, especially painting, for which the color modification induced by protective and/or cleaning interventions could irremediably compromise the work of art.