Romain Valentin

Biosurfactant-mediated one-step synthesis of hydrophobic functional imogolite nanotubes

Imogolites are aluminosilicate nanotubes that attract a particular interest due to their insulating properties, surface reactivity and shape-selective properties in catalysis. Although being available in nature, synthetic protocols have been developed since the 70s to obtain large amounts of this particular mineral without purification processes. In particular, surface functionalized imogolites are currently studied for their application as a dispersant in hydrophobic matrixes like polymers. With respect to known synthetic processes, natural imogolite is produced by using either milli- or deci-molar amounts of aluminium salts in solution while surface functionalized imogolites are systematically prepared in two steps: imogolite synthesis followed by surface functionalization mainly using phosphonic acids. Here, we propose a new one-step synthesis involving a cheap, widely-used, non-toxic surfactant, glycerol α-monolaurate (MG) and centimolar aluminium concentrations. In the presence of Al3+ cations, MG forms an emulsion, and the subsequent addition of tetraethoxysilane leads to the formation of imogolite nanotubes within 3 days at neutral pH under hydrothermal conditions. An interesting, new, lamellar long-range order of the nanotubes can then be achieved after 10 days. Under similar conditions, blank tests performed on MG-free systems result in the formation of proto-imogolite. Based on the combination of highly selective 29Si, 27Al and 1H solid-state NMR experiments and additional synthesis using lauric acid (LA) and glycerol, a mechanism of formation is proposed based on MG dissociation and LA binding on the outside surface of the nanotubes. As a result, our process provides imogolite with unprecedented hydrophobic surface properties that offer new perspectives for these materials as nanoscale fillers in, e.g., polymeric media.

Pure short-chain glycerol fatty acid esters and glycerylic cyclocarbonic fatty acid esters as surface active and antimicrobial coagels protecting surfaces by promoting superhydrophilicity

Pure glycerol fatty acid esters and glycerylic cyclocarbonic fatty acid esters have an amphiphilic structure, giving these biomolecules a broad range of physico-chemical and biological properties. Physico-chemical properties depend on chain lengths, odd or even carbon numbers on the chain, and glyceryl or cyclocarbonic polar heads. The spectrum of melting-point values for these molecules is large. Surface-activity is very important and through determination of the critical aggregation concentration (CAC), some fatty-acid esters are considered as solvo-surfactant biomolecules. Coupling these self-aggregation and crystallization properties, superhydrophilic surfaces were obtained. An efficient durable water repellent coating of various metallic and polymeric surfaces was allowed. Moreover, these fatty acid esters promoting superhydrophilicity showed biological activity against Gram positive, Gram negative, and yeast-like micro-organisms. Such surfaces coated by self-assembled fatty acid esters in a stable coagel state present a novel solution to surface-contamination risks from pathogen proliferation.

Recycled bio-sourced glycerol and diglycerol for asphalt release agents (ARA)

The objective of this study is to develop bio-sourced waste chemicals for use as asphalt release agents. Glycerol was extracted from bio-sourced waste and transformed by transesterification into the surfactants undecenoates of glycerol (MUG) and undecenoates of diglycerol (MUDG). They were composed of glycerol, monoglycerol, diglycerol, triglycerol, tetraglycerol and water. The formulations were mixed separately with water at quantities of 5–50%, along with acetone and commercial bio-sourced ARAs in order to observe the effects. The formulations were subjected to performance testing with the asphalt slide test, finding significant reduction in adhesion for a number of different formulations. The interaction of the formulations with bitumen was tested by the bitumen degradation test, which was combined with FTIR–ATR analysis, finding that the formulations do not dissolve the bitumen, but rather were adsorbed by the bitumen. The effects on asphalt mix of the best performing formulation, MUG at 20% in water, was tested by indirect tensile strength, determining that the formulation was acceptable for use in the field.