No abstract

Self-aggregation of eight dimethyl-di-N-octylammonium salts ([DiC(8)]) has been investigated as a function of the nature of the counteranion. Tensiometry, conductimetry, and [DiC(8)]-selective electrode measurements highlighted three different behaviors and led to a rationalization of the aggregation process depending on the counteranion: "hydrophilic" anions (MoO(4)(2-), WO(4)(2-), SO(4)(2-), F(-)) give only unimers and micelles, whereas less hydrated anions form unimers, dimers, and either one micelle-like structure (NO(3)(-), Br(-)) or two micelle-like structures (CH(3)SO(3)(-), Cl(-)). Small-angle neutron and dynamic light scattering confirms the unusual behavior of [DiC(8)][Cl], which forms two types of aggregates: (i) disk or vesicles between 10 and 30 mM and (ii) ellipsoidal micelles above 30 mM. For [DiC(8)][MoO(4)(2-)], the formation of ellipsoidal micelles is supported between 10 and 300 mM. Finally, shapes and sizes of the aggregates are confirmed by molecular dynamic experiments.

A series of short chain dialkyldimethylammonium amphiphiles ([DiC(n)][X] and [DiC(n)]2[X] with n = 6, 8, or 10) has been investigated as a function of the nature of the counteranion [X] (Cl(-) and Br(-) as classical references and MoO4(2-) and WO4(2-) as catalytic anions). Critical aggregation concentrations (CACs) in water were determined by surface tension measurements, and the binary phase diagrams of the surfactant/water systems were established using polarized optical microscopy (POM) and small angle X-ray scattering (SAXS). The evolution of microstructures and lyotropic phases were discussed in terms of surfactant chain length and counterion effect. A cubic phase region was observed for the divalent counteranions associated with the intermediate chain length, i.e., [DiC8]2[MoO4] and [DiC8]2[WO4]. Finally, the fish diagrams reflecting the polyphasic microemulsion phase behavior of the water/amphiphile/oil ternary systems were established using the carbon number of mono- and dichlorinated n-alkanes as a scan variable. The amphiphile efficiency was also discussed according to the chain length and the nature of the counterions. The hydrophilic-lipophilic behavior of the amphiphiles was evaluated on the basis of the fish diagrams allowing their classification according to the Hofmeister anion sequence. The unusual behavior of [DiC8][Cl] and [DiC8]2[MO4] (M = W or Mo) is highlighted by all experiments: these compounds are clearly intermediates between hydrotropes, [DiC6] cation, and surfactants, [DiC10] cation.

Starch, an abundant and low-cost plant-based glucopolymer, has great potential to replace carbon-based polymers in various materials. In order to optimize its functional properties for bioplastics applications chemical groups need to be introduced on the free hydroxyl groups in a controlled manner, so an understanding of the resulting structure-properties relationships is therefore essential. The purpose of this work was to study the multiscale structure of highly-acetylated (degree of substitution, 0.4 < DS ≤ 3) and etherified starches by using an original combination of experimental strategies and methodologies. The molecular structure and substituents repartition were investigated by developing new sample preparation strategies for specific analysis including Asymmetrical Flow Field Flow Fractionation associated with Multiangle Laser Light Scattering, Nuclear Magnetic Resonance (NMR), Raman and Time of Flight Secondary Ion Mass spectroscopies. Molar mass decrease and specific ways of chain breakage due to modification were pointed out and are correlated to the amylose content. The amorphous structuration was revealed by solid-state NMR. This original broad analytical approach allowed for the first time a large characterization of highly-acetylated starches insoluble in aqueous solvents. This strategy, then applied to characterize etherified starches, opens the way to correlate the structure to the properties of such insoluble starch-based materials.