Polymère supramoléculaire | EPFL Graph Search

Un polymère supramoléculaire est une large molécule (macromolécule) dont la structure est composée d'assemblages d'unités monomères reliés par des liaisons non covalentes. Ces dernières sont des interactions secondaires réversibles et directionnelles. Elles comprennent la force de van der Waals, la liaison hydrogène, l'empilement π-π, la coordination métallique, la liaison halogène, la liaison chalcogène et l'interaction hôte-invité. La direction et la force des interactions non-covalentes sont précisément ajustées de sorte que le réseau de molécules se comporte comme un polymère en solution diluée et concentrée (c'est-à-dire qu'il se comporte d'une manière qui peut être décrite par les théories de la physique des polymères), ainsi que dans la phase solide. Dans les polymères conventionnels, les unités monomères sont liées par des liaisons covalentes fortes et ont d'excellentes propriétés en tant que matériaux ; cependant, des températures et des pressions élevées sont requises pour leur transformation en raison de l'enchevêtrement du polymère dans la masse fondue hautement visqueuse. Les polymères supramoléculaires combinent de bonnes propriétés de matériau avec de faible viscosité à l'état fondu, ce qui les rend plus faciles à manipuler que les polymères conventionnels. De plus, certains polymères supramoléculaires ont des caractéristiques uniques, telles que la capacité d'auto-cicatrisation des fractures. Bien que les polymères covalents puissent être recyclés, leurs fortes liaisons covalentes ne se désintègrent jamais et affectent négativement l'environnement sous forme de déchets plastiques. Ainsi, les polymères supramoléculaires sont de plus en plus populaires en raison de leur potentiel pour la conception de matériaux réactifs, adaptatifs, auto-cicatrisants et respectueux de l'environnement. vignette|459x459px|Motifs monomères et types d'interactions utilisés pour la préparation de polymères supramoléculaires. Le concept moderne de polymères est attribué à Hermann Staudinger, qui a confirmé l'existence de molécules ultra-longues liées de manière covalente en 1920, qu'il a appelées « macromolécules ».

Mechanistic Insight into Supramolecular Polymerization in Water Tunable by Molecular Geometry

Lukas Pfeifer, Fan Xu

Supramolecular self-assembly in water based on non-covalent bonding is attracting major attention due to the potential of hydrogels and aqueous polymers in biomedical applications. Although supramolecular polymerization in organic solvents is well established, the key design features, the assembly mechanisms in water and achieving control over the aggregate structures remain challenging. Here, we present the assembly and disassembly of geometrical isomers of a stiff-stilbene bis-urea amphiphile (SA) in pure water. A remarkable feature of this system is that the (E)-isomer forms supramolecular polymers in both pure water and organic solvents. Taking advantage of this unique property, the hydrophobic effect was studied by comparing the supramolecular assembly in both systems. The assembly process in water follows an enthalpy-driven nucleation-elongation (cooperative) supramolecular polymerization mechanism with a standard Gibbs free energy (Delta G degrees = -53 kJ mol(-1)) double the value of the one found in toluene. We attributed this distinctive feature to the hydrophobic effect in water. Furthermore, we discovered an isomer-dependent assembly process, which can be used to control aggregation in aqueous media. Due to the substantial geometric difference between (E)-SA and (Z)-SA, we compared their assembly in water to study the influence of different driving forces involved in the process. The supramolecular polymerization of (E)-SA was cooperatively influenced by hydrogen bonding, pi-stacking, and hydrophobic effects, whereas the assembly of (Z)-SA was mainly driven by hydrophobic effects. As a result, the fiber length of (E)-SA in water is much longer than that of (Z)-SA, presenting opportunities for geometrical control of aggregation in aqueous media. [GRAPHICS]

CHINESE CHEMICAL SOC2022

Design of Surface-Supported Bio-inspired Networks for CO2 and O2 Activation at Room Temperature

Daniel Eduardo Hurtado Salinas

The structure of a biological system defines its function. Therefore, nature has developed sophisticated systems that catalyze chemical reactions that are vital for life on earth. For instance, the photosynthesis is a biological process that is partially regulated by the metallo-enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase), whose function is to catalyze the capture and transfer of CO2 into organic molecules. This carboxylation reaction occurs at the active site, where a magnesium ion (Mg2+) is bound to organic molecules with carboxylate (COO-) and amine (NH2) functional groups. In the last decades, supramolecular chemistry has proven to be a valid approach to replicate the structural characteristics of these natural metal-organic systems. Metal atoms and organic molecules are used as building blocks to form two-dimensional (2D) metal-organic networks (MONs) on metal surfaces, through a self-assembly process that occurs spontaneously. In these systems the molecules bind to the metal centers and control their oxidation states that, as found in metallo-enzymes, is crucial to perform a catalytic task. Therefore, these supramolecular assemblies show promising features to be explored for heterogeneous catalysis. The main objective of this thesis is to reverse the structure-function equation, that is: instead of finding specific functions of well-known 2D structures for future applications, 2D structures are designed to reproduce the specific functions of well-known bio-systems. Thus, inspired in the structure of the active site of RuBisCO, 2D Mg-based supramolecular assemblies are rationally designed on Cu(100) or Mg(0001) surfaces at room temperature (RT) as a platform for CO2 adsorption. This work is the first study of self-assembly of alkaline earth metal atoms (Mg) with organic molecules ((1,4-benzenedicarboxylic acid (TPA) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)) on metal surfaces. The first part of this thesis investigates the self-assembly of TAPT molecules. Scanning Tunneling Microscopy (STM) and High Resolution X-ray Photoemission Spectroscopy (HR-XPS) demonstrate that the molecules typically semi-deprotonate to form MONs with the adatoms from the host substrates. The exposure of these structures to CO2 results in the carboxylation of the amino groups. The second part proves that the COOH moieties of TPA molecules fully-deprotonate to form homo-molecular structures. The incorporation of Mg adatoms result in ionic MONs, which reproduce the carboxylate environment of the active site of RuBiSCO. STM, XPS and Density Functional Theory (DFT) analyze the structural changes, the chemical reactions and charge transfer during either the CO2 or O2 adsorption on the Mg2+ centers. The last part focusses on the co-deposition of both molecules to form 2D metallic-hetero-molecular networks with Mg2+ centers. The role of the Mg2+ centers as active sites for molecular adsorption and model systems for gas storage is studied. STM reveals that CO2 partially modifies the network towards a configuration that resembles the active site of RuBisCO. The formation of 3D structures to enhance CO2 adsorption is also evaluated.

EPFL2018

Nanoscale Lithography and Thermometry with Thermal Scanning Probes

Samuel Zimmermann

Thermal scanning probe lithography (t-SPL) is an advanced lithography technique in which a heated atomic force microscope tip locally modifies a sample material. Due to the nanometer-sized tip apex diameter, t-SPL enables patterning of sub-10 nm structures at a low cost compared to electron beam or extreme ultraviolet lithography techniques. In the first part of this dissertation, two novel materials are investigated as a resist for t-SPL, which have in common that fast heating and cooling rates are required to modify them. The first material is a fluorescent supramolecular polymer, which exhibits thermoresponsive luminescence due to reversible aggregation of excimer-forming fluorophores. At temperatures above 180 °C under ultraviolet light, the material fluoresces in green and when cooled down to room temperature, a spectral shift towards red emission takes place due due to aggregation of the fluorescent moieties. Unlike at the macroscale, where the fast aggregation of the fluorophores prevent kinetical trapping of the green fluorescent high-temperature state, the heating and cooling rates (on the order of 10^8 K/s) accessible by t-SPL are fast enough to freeze the green fluorescent state. The thermomechanical properties of the supramolecular glass are analyzed by nanoindentation with a heated probe and the self-healing behavior of the material is used to selectively write and erase indents. It is demonstrated that t-SPL patterning enables the fabrication of topographical and fluorescent structures with interesting properties. The second material is silk fibroin, a protein extracted from silk produced by the larvae of bombyx mori moths or certain spiders. The polymorphic structure of silk fibroin enables a solubility contrast between the amorphous and cross-linked phase. In this work, water-insoluble silk fibroin thin films are fabricated by spin coating and immersion in ethanol. During t-SPL patterning, local heating of of silk fibroin at high heating rates induces water-solubility. The resolution and line edge roughness are compared to the molecular size of the resist, which poses the ultimate resolution limit. In addition, grayscale lithography with silk is demonstrated. Silk fibroin is also explored as a resist for dry etching by demonstration of a pattern transfer from t-SPL fabricated patterns in silk fibroin into silicon oxide. A second part of the thesis concerns the planning and assembly of a setup for nanoscale thermometry in combination with thermal scanning probes, and implementation of the necessary software. The construction of a dedicated setup to perform nanometer scale thermometry at the tip of a cantilever is motivated by the difficulty to measure or calculate the temperature at the tip during operation. Among many nanoscale thermometry techniques, fluorescence based thermometry using nanodiamonds with nitrogen vacancy defects has been evaluated as promising. The components and the assembly of the setup, consisting of a excitation laser, an inverted optical microscope, a single photon detector and stages for scanning, are described and discussed. Initial results of thermometry with micrometer particles are presented and measurements with nanoparticles on a heated tip are shown. Good agreement with experiments from literature was found.

EPFL2018