Micellar formation by soft template electropolymerization in organic solvents

New fluorine-free low surface energy surfactants and surfaces

Modification and control of surface properties, such as surface tension γ at air-liquid (AL) interfaces and surface energy at solid-liquid (SL) surfaces, are at the heart of colloid and interface science. Certain applications require low or very low surface tensions γAL and surface energies γSL, for example and not limited to: microemulsification, aqueous foams for fire-fighting, hydrophobic, superhydrophobic and oleophobic surfaces to control spreading and wetting of aqueous and oily liquids on solids. In many cases low surface tensions/energies can only be obtained by employing perfluoroalkyl substances (PFAS) as surfactant or polymer additives or surface treatments. Although fluorocarbons and polymers have been employed for over 80 years, with many industrial and commercial benefits, it is now recognized that PFAS are very hazardous to the environment and health. Hence, in the coming years it will be necessary to phase out PFAS entirely, however, at present, there are very few viable alternatives available. This article outlines the chemical principles for designing F-free low surface energy (LSE) additives, and also covers the most recent advances in the quest for non-fluorinated surfactants and polymeric surface coatings.

Soft-Template Electropolymerization from Triphenylamine-Based Monomers: From Vertically Aligned Nanotubes to Nanomembranes

We report a bioinspired approach to tune surface nanostructures by soft-template electropolymerization in micellar condition. Monomers highly favoring π-stacking interactions are particularly interesting for depositing in one direction resulting in vertically aligned nanotubes. Here, for inducing very strong π-stacking interactions, a triphenylamine building block was selected and substituted by two substituents of different electronegativity (fluorine F and methoxy OMe). These synthons were di-substituted with various fully conjugated thiophene and carbazole derivatives. Here, all the monomers have high electrodeposition capacity except the monomers with thiophene in 3-position. Confirming previous works, electrochemical analyses in the electrodeposited films show the presence of monomers but with significant difference as a function of the used monomer. The surface structures are highly depending on the monomer structure while the depositions at constant potential lead to more ordered structures. With some of these monomers, densely packed nanotubes are created and their merger at high deposition charge, leading to nanomembranes. Their hydrophobicity and oleophobicity are also investigated and extremely various. Such materials could be used in the future in practical applications such as in oil/water separation membranes or in water-harvesting systems.

High-performance insulating materials with high breakdown strength and low permittivity for eco-friendly electrical equipment

High-performance insulating materials are essential for developing lightweight, compact, and green offshore wind power equipment. It has been shown that nanoporous structures can limit the development of electron avalanche, leading to a significant increase in the breakdown electric strength of dielectrics. Hence, we fabricated a polysiloxane nanoporous biopolymer insulating material (PNBIM) with the nanoporous structure that presents exceptionally high electrically insulating properties. Under a CO2 atmosphere, the breakdown electric strength of the PNBIM was remarkably improved, exhibiting 761.01 % enhancement relative to that of the pure gas gap. Moreover, the PNBIM demonstrates excellent dielectric performance, with a low dielectric constant (1.63) and dielectric loss (0.014), as well as high hydrophobicity and excellent thermal stability. The investigations revealed that the nanopores inside the material can effectively suppress gas discharge and improve the breakdown electric strength. This study widens our understanding of conventional insulating materials and provides a promising approach for exploring high-performance insulating materials provide valuable insights.

Influence of Polyfluorinated Side Chains and Soft-Template Method on the Surface Morphologies and Hydrophobic Properties of Electrodeposited Films from Fluorene Bridged Dicarbazole Monomers

A clear case of relationship between the monomer molecular structure and the capability of tuning the morphology of electrodeposited gas bubbles template polymer thin films is shown. To this end, a series of fluorene-bridged dicarbazole derivatives containing either linear or terminally branched polyfluorinated side chains connected to the fluorene subunit were synthesized and their electrochemical properties were investigated. The new compounds underwent electrochemical polymerization over indium tin oxide electrodes to give hydrophobic films with nanostructural and morphological properties strongly dependent on the nature of the side chains. Gas bubbles templated electropolymerization was next achieved by the addition of tiny amounts of water to the monomer solutions, without using surfactants. Within the investigated set of molecules, the nanostructural properties of the soft-templated films obtained from monomers bearing linear side chains could be fine-tuned by adjusting electrochemical parameters, leading to superhydrophobic surfaces.

Highly conjugated carbazole-based monomers for the control of nanotubular surface structures by soft template electropolymerization

In this work, a bioinspired approach is used to prepare nanotubular structures with tunable hydrophobicity and water adhesion by a soft template surfactant-free electropolymerization in organic solvent. Various highly conjugated carbazole-based molecules are used as monomer. The presence of water in the organic solvent enables the formation of porous and rough nanostructures. Their shapes depend essentially on the nature of the monomer and the way it polymerizes. Various morphologies were obtained from nanoparticles network to horizontally or vertically aligned nanotubes. The nanostructured surfaces reach superhydrophobic properties and their dynamical behavior varies with the monomer from sticky to slippery. For example, using 9,3′:6′,9″-tercarbazole (TC) very long nanotubes are observed but their number is higher at constant potential. At high deposition charge, it is observed that most of the tubes are even collapsed leading to a strong increase of surface hydrophobicity with apparent contact angle up to 143° with strong water adhesion comparable to rose petals or gecko foot.

A bioinspired approach to fabricate fluorescent nanotubes with strong water adhesion by soft template electropolymerization and post-grafting

HYPOTHESIS

In this original work, we aim to control both the surface wetting and fluorescence properties of extremely ordered and porous conducting polymer nanotubes prepared by soft template electropolymerization and post-grafting. For reaching this aim, various substituents of different hydrophobicity and fluorescence were post-grafted and the post-grafting yields were evaluated by surface analyses. We show that the used polymer is already fluorescent before post-grafting while the post-grafting yield and as a consequence the surface hydrophobicity highly depend on the substituent.

EXPERIMENTS

Here, we have chosen to chemically grafting various fluorinated and aromatic substituents using a post-grafting in order to keep the same surface topography. Flat conducting polymer surfaces with similar properties have been also prepared for determining the surface energy with the Owens-Wendt equation and estimating the post-grafting yield by X-ray Photoemission Spectroscopy (XPS) and Time of Flight Secondary Emission Spectrometry (ToF-SIMS). For example, using fluorinated chains of various length (C₄F₉, C₆F₁₃ and C₈F₁₇), it is demonstrated that the surface hydrophobicity and oleophobicity do not increase with the fluorinated chain length due to the different post-grafting yields and because of the presence of nanoroughness after post-grafting.

FINDINGS

These surfaces have high apparent water contact angle up to 130.5° but also strong water adhesion, comparable to rose petal effect even if there are no nanotubes on petal surface. XPS and ToF-SIMS analyses provided a detailed characterisation of the surface chemistry with a qualitative classification of the grafted surfaces (F6 > F4 > F8). SEM analysis shows that grafting does not alter the surface morphology. Finally, fluorescence analyses show that the polymer surfaces before post-treatment are already nicely fluorescent. Although the main goal of this paper was and is to understand the role of surface chemistry in tailoring the wetting properties of these surfaces rather than provide specific application examples, we believe that the obtained results can help the development of specific nanostructured materials for potential applications in liquid transport, or in stimuli responsive antimicrobial surfaces.