Interfacing Langmuir-Blodgett and Pickering Emulsions for the Synthesis of 2D Nanostructured Films: Applications in Copper Ion Adsorption.

This research focuses on developing a 2D thin film comprising a monolayer of silica nanoparticles functionalized with polyethyleneimine (PEI), achieved through a novel integration of Langmuir-Blodgett (L-B) and Pickering emulsion techniques. The primary aim was to create a nanostructured film that exhibits dual functionality: iridescence and efficient metal ion adsorption, specifically Cu(II) ions. The methodology combined L-B and Pickering emulsion polymerization to assemble and stabilize a nanoparticle monolayer at an oil/water interface, which was then polymerized under UV radiation to form an asymmetrically structured film. The results demonstrate that the film possesses a high adsorption efficiency for Cu(II) ions, with the enhanced mechanical durability provided by a reinforcing layer of polyvinyl alcohol/glycerol. The advantage of combining L-B and Pickering emulsion technology is the ability to generate 2D films from functional nanoparticle monolayers that are sufficiently sturdy to be deployed in applications. The 2D film's practical applications in environmental remediation were confirmed through its ability to adsorb and recover Cu(II) ions from aqueous solutions effectively. We thus demonstrate the film's potential as a versatile tool in water treatment applications owing to its combined photonic and adsorptive properties. This work paves the way for future research on the use of nanoengineered films in environmental and possibly photonic applications focusing on enhancing the film's structural robustness and exploring its broader applicability to other pollutants and metal ions.

Asymmetrically Nanostructured 2D Janus Films Obtained from Pickering Emulsions Polymerized in a Langmuir-Blodgett Trough.

Low-dimensional structures, such as two-dimensional (2D) Janus films, can be useful in studying fundamental interactions or in applications at the nanoscale. In this work, we report the fabrication of 2D polymer Janus films consisting of one smooth and another nanostructured facet on which silica nanoparticles (NPs) are self-assembled in a compact monolayer shield. The 2D films are made from Pickering emulsions of monomers in water, stabilized by NPs, which are spread over the surface of the water in a Langmuir-Blodgett trough. Following the spreading of the colloidosomes, oil droplets stabilized by NPs collapse, and the interfaces reorganize such that the NP monolayer is found exclusively at the oil/water interface. Upon compression followed by UV polymerization, a 2D solid film is formed, with one smooth and another nanostructured face. The film can be removed from the surface of the water and handled with tweezers. The 2D films exhibit different surface properties on the two sides, such as differences in water wettability. On the nanostructured side, water wettability can be tuned by tuning the surface energy of the nanoparticles, namely by changing their surface functional groups. Upon removal of NPs, the surface can be patterned with an array of circular traces.

Monitoring the Surface Energy Change of Nanoparticles in Functionalization Reactions with the NanoTraPPED Method.

Performing chemical functionalization on the surface of nanoparticles underlies their use in applications. Probing that a physicochemical transformation has indeed occurred on a nanoparticles' surface is rather difficult. For this reason, we propose that a macroscopic parameter, namely the surface energy γ, can monitor the physicochemical transformations taking place at the surface of nanoparticles. Determining the surface energy of macroscopic surfaces is trivial, but it is very challenging for nanoparticles. In this work we demonstrate that the Nanoparticles Trapped on Polymerized Pickering Emulsion Droplet (NanoTraPPED) method can be successfully deployed to monitor the evolution of surface energies γ, with its γp polar and γd dispersive components of the silica nanoparticles at each stage of two surface reactions: (i) amination by siloxane chemistry, coupling reaction of a 2,4-dihydroxy benzaldehyde and formation of a Schiff base ligand, followed by coordination of metal ions and (ii) epoxide ring opening and formation of azide. The change in surface energy and its components are discussed and analyzed for each step of the two reactions. It is observed that large variations in surface energy are observed with the complexity of the molecular structure attaching to nanoparticle surface, while functional group replacement leads to only small changes in the surface energies.

Role of Surface Energy of Nanoparticle Stabilizers in the Synthesis of Microspheres via Pickering Emulsion Polymerization.

Polymer microspheres are important for a variety of applications, such as ion exchange chromatography, catalyst supports, absorbents, etc. Synthesis of large microspheres can be challenging, because they cannot be obtained easily via classic emulsion polymerization, but rather by more complex methods. Here, we present a facile method for obtaining polymer microspheres, beyond 50 µm, via Pickering emulsion polymerization. The method consists in creating oil-in-water (o/w) Pickering emulsion/suspension from vinyl bearing monomers, immiscible with water, whereas silica nanoparticles (NPs), bearing glycidyl functionalities, have a stabilizing role by adsorbing at the monomer/water interface of emulsion droplets. The emulsion is polymerized under UV light, and polymer microspheres decorated with NPs are obtained. We discovered that the contact angle of the NPs with the polymer microsphere is the key parameter for tuning the size and the quality of the obtained microspheres. The contact angle depends on the NPs' interfacial energy and its polar and dispersive contributions, which we determine with a newly developed NanoTraPPED method. By varying the NPs' surface functionality, we demonstrate that when their interfacial energy with water decreases, their energy of adhesion to water increases, causing the curvature of the polymer/water interface to decrease, resulting in increasingly larger polymer microspheres.

NanoTraPPED-A New Method for Determining the Surface Energy of Nanoparticles via Pickering Emulsion Polymerization.

Surface energy with its polar and disperse components describes the physicochemical state of nanoparticles' (NPs) surfaces, and can be a valuable parameter for predicting their bulk behavior in powders. Here, we introduce a new method, namely, Nanoparticles Trapped on Polymerized Pickering Emulsion Droplets (NanoTraPPED), for measuring the surface energy of a series of silica NPs bearing various surface functional groups. The method consists in creating Pickering emulsions from vinyl bearing monomers, immiscible with water, whereas NPs of interest have a stabilizing role, and in the process, become trapped at the monomer/water interface of emulsion droplets. The Pickering emulsion is polymerized, and polymer microspheres (colloidosomes) decorated with NPs are obtained. NanoTraPPED relies on measuring contact angles from the immersion depth of nanoparticles at the interface of various polymer colloidosomes with the electron microscope. The contact angle values are used as input for the Owens-Wendt-Rabel-Kaelble (OWRK) model, to quantitatively determine the total surface energy with water γNP/water, air γNP, and the corresponding polar and dispersive interaction components of NPs carrying -NH2, -SH, -OH, -CN and -C8 surface functional groups, ranking these according to their polarity. Our findings were confirmed independently by calculating the interfacial desorption energies of NPs from contact angles.

National and Gender Measurement Invariance of the Utrecht-Management of Identity Commitments Scale (U-MICS): A 10-Nation Study With University Students.

The purpose of this study was to examine the psychometric properties of the Utrecht-Management of Identity Commitments Scale (U-MICS), a self-report measure aimed at assessing identity processes of commitment, in-depth exploration, and reconsideration of commitment. We tested its factor structure in university students from a large array of cultural contexts, including 10 nations located in Europe (i.e., Italy, the Netherlands, Poland, Portugal, Romania, and Switzerland), Middle East (i.e., Turkey), and Asia (i.e., China, Japan, and Taiwan). Furthermore, we tested national and gender measurement invariance. Participants were 6,118 (63.2% females) university students aged from 18 to 25 years (Mage = 20.91 years). Results indicated that the three-factor structure of the U-MICS fitted well in the total sample, in each national group, and in gender groups. Furthermore, national and gender measurement invariance were established. Thus, the U-MICS can be fruitfully applied to study identity in university students from various Western and non-Western contexts.