Temperature-Controlled Switchable Photochromism in Solid Materials.

A novel strategy to achieve thermally switchable photochromism in solid materials is reported, which relies on the preparation of polymeric core-shell capsules containing solutions of photochromic dyes in acidic phase-change materials. Upon changing the phase (solid or liquid) of the encapsulated medium, one of the two photochromic states of the system is selectively stabilized on demand, allowing for reversible interconversion between direct and reverse photochromism when thermally scanning through the melting temperature of the phase-change material. This strategy, which does not require the addition of external agents or chemical modification of the dyes, proved to be general for different spiropyran photochromes and to be applicable to the fabrication of a variety of functional materials by simply embedding the capsules obtained into a solid matrix of choice.

Covalent Grafting of Coordination Polymers on Surfaces: The Case of Hybrid Valence Tautomeric Interphases.

We have developed a novel approach for grafting coordination polymers, structured as nanoparticles bearing surface reactive carboxylic groups, to amino-functionalized surfaces through a simple carbodiimide-mediated coupling reaction. As a proof-of-concept to validate our approach, and on the quest for novel hybrid interphases with potential technological applications, we have used valence tautomeric nanoparticles exhibiting spin transition at or around room temperature. SEM and AFM characterization reveal that the nanoparticles were organized chiefly into a single monolayer while X-ray photoelectron spectroscopy (XPS) measurements confirm that the nanoparticles retain a temperature-induced electronic redistribution upon surface anchorage. Our results represent an effective approach towards the challenging manufacture of coordination polymers.

Encapsulation and sedimentation of nanomaterials through complex coacervation.

HYPOTHESIS: Nanoparticles removal from seawage water is a health and environmental challenge, due to the increasing use of these materials of excellent colloidal stability. Herein we hypothesize to reach this objective through complex coacervation, a straightforward, low-cost process, normally accomplished with non-toxic and biodegradable macromolecules. Highly dense polymer-rich colloidal droplets (the coacervates) obtained from a reversible charge-driven phase separation, entrap suspended nanomaterials, allowing their settling and potential recovery. EXPERIMENTS: In this work we apply this process to highly stable aqueous colloidal dispersions of different surface charge, size, type and state (solid or liquid). We systematically investigate the effects of the biopolymers excess and the nanomaterials concentration and charge on the encapsulation and sedimentation efficiency and rate. This strategy is also applied to real laboratory water-based wastes. FINDINGS: Long-lasting colloidal suspensions are succesfully destabilized through coacervate formation, which ensures high nanomaterials encapsulation efficiencies (~85%), payloads and highly tranparent supernatants (%T ~90%), within two hours. Lower polymer excess induces faster clearance and less sediments, while preserving effective nanomaterials removal. Preliminary experiments also validate the method for the clearance of real water residuals, making complex coacervation a promising scalable, low-cost and ecofriendly alternative to concentrate, separate or recover suspended micro/nanomaterials from aqueous sludges.

Synthesis of Nanoscale Coordination Polymers in Femtoliter Reactors on Surfaces.

In the present work, AFM-assisted lithography was used to perform the synthesis of a coordination polymer inside femtoliter droplets deposited on surfaces. For this, solutions of the metal salt and the organic ligand were independently transferred to adjacent tips of the same AFM probe array and were sequentially delivered on the same position of the surface, creating femtoliter-sized reaction vessels where the coordination reaction and particle growth occurred. Alternatively, the two reagents were mixed in the cantilever array by loading an excess of the inks, and transferred to the surface immediately after, before the precipitation of the coordination polymer took place. The in situ synthesis allowed the reproducible obtaining of round-shaped coordination polymer nanostructures with control over their XY positioning on the surface, as characterized by microscopy and spectroscopy techniques.

Surface-confined molecular coolers for cryogenics.

An excellent molecule-based cryogenic magnetic refrigerant, gadolinium acetate tetrahydrate, is here used to decorate selected portions of silicon substrate. By quantitative magnetic force microscopy for a variable applied magnetic field near liquid-helium temperature, the molecules are demonstrated to hold their magnetic properties intact, and therefore their cooling functionality, after their deposition. These results represent a step forward towards the realization of a molecule-based micro-refrigerating device at very low temperatures.

Mn12 single molecule magnets deposited on µ-SQUID sensors: the role of interphases and structural modifications.

Direct measurements of the linear ac susceptibility and magnetic relaxation of a few Mn12 monolayers deposited on a µ-SQUID sensor are reported. In order to integrate the molecules into the device, DPN has been the technique of choice. It enabled the structuration of the molecules on the most sensitive areas of the sensor without the need for any previous functionalization of the molecule or the substrate, while controlling the number of molecular units deposited on each array. The measurements reveal that their characteristic SMM behaviour is lost, a fact that is attributed to molecular distortions originated by the strong surface tensions arising at the molecular interphases.

Multiplexed arrays of chemosensors by parallel dip-pen nanolithography.

Miniaturized combined arrays of three different pH indicators allowing for sensitive, robust and broad-range acidity detection are prepared by parallel dip-pen nanolithography, which proves the potential of this technique to fabricate multiplexed platforms at the micro- and nanoscale that can act as sensors.