Polymeric Surfactant P84/Polyoxometalate α-PW12O403- A Model System to Investigate the Interplay between Chaotropic and Hydrophobic Effects

Low charge density nanometric ions were recently shown to bind strongly to neutral hydrated matter in aqueous solution. This phenomenon, called the (super-)chaotropic effect, arises from the partial dehydration of both the nano-ion and the solute, leading to a significant gain in enthalpy. Here, we investigate the chaotropic effect of the polyoxometalate α-PW12O403− on the triblock copolymer P84: (EO)19(PO)43(EO)19 with (EO)19 the polyethoxylated and (PO)43 the polypropoxylated chains. The combination of phase diagrams, spectroscopic (nuclear magnetic resonance) and scattering (small angle neutron/X-ray scattering) techniques revealed that: (i) below the micellization temperature of P84, PW12O403− exclusively binds to the propylene oxide moiety of P84 unimers; and (ii) above the micellization temperature, PW12O403− mostly adsorbs on the ethylene oxide micellar corona. The preferential binding of the PW12O403− to the PPO chain over the PEO chains suggests that the binding is driven by the chaotropic effect and is reinforced by the hydrophobic effect. At higher temperatures, copolymer micellization leads to the displacement of PW12O403− from the PPO chain to the PEO chains. This study deepens our understanding of the subtle interplay between the chaotropic and hydrophobic effects in complex salt-organic matter solutions

Polyoxometalates in the Hofmeister series

We propose a simple experimental procedure based on the cloud point measurement of a non-ionic surfactant as a tool for (i) estimating the super-chaotropic behaviour of polyoxometalates (POMs) and for (ii) establishing a classification of POMs according to their affinity towards polar surfaces

Influence of Chain Length and Double Bond on the Aqueous Behavior of Choline Carboxylate Soaps

In preceding studies, we demonstrated that choline carboxylates ChCm with alkyl chain lengths of m = 12 - 18 are highly water-sol. (for m = 12, sol. up to 93 wt. % soap and 0 °C). In addn., choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concn., the following phases were found: micellar phase (L1), discontinuous cubic phase (I1' and I1''), hexagonal phase (H1), bicontinuous cubic phase (V1), and lamellar phase (Lα). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aq. phase behavior of choline soaps with C8 and C10 chain-lengths (choline octanoate and choline decanoate) and with a C18 chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologs mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar soln. phase. In addn., choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better soly. in water and a decrease of the solubilization temp. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar soln. phase in the binary phase diagram of choline octanoate viscosity and cond. measurements were also carried out. [on SciFinder(R)

Thermotropic Phase Behavior of Choline Soaps

Choline carboxylates (ChCm with m = 12-18) are simple biocompatible anionic surfactants with very low Krafft temps., possessing a rich aq. phase behavior. In the present work, we have investigated the thermotropic mesomorphism of anhyd. ChCm salts for m = 12-18. Transition temps. and enthalpies detd. by differential scanning calorimetry reveal that all investigated compds. exhibit three different phases between -20 and 95 °C. The phases were further characterized by optical polarizing microscopy, NMR spin-spin relaxation, and X-ray scattering measurements. The nature of the phases was identified with increasing temp. as cryst., semicryst., and liq.-cryst. lamellar. Even long-chain choline carboxylates (m = 18) were found to melt into a lamellar liq.-cryst. phase below 100 °C. Accordingly, with choline as counterion in simple fatty acid soaps, not only the water soly. is considerably enhanced but also the m.ps. are substantially reduced, hence facilitating thermotropic mesomorphism at temps. between 35 and 95 °C. Thus, simple choline soaps with m = 12-18 may be classified as ionic liqs

Nanostructures in clear and homogeneous mixtures of rapeseed oil and ethanol in the presence of green additives

Ethanol and rapeseed oil are mixed in the presence of tributyl citrate, 2,5-dimethylfuran, 2-methylfuran, 2-methyl tetrahydrofuran, methyl tert butyl ether, ethyl tert butyl ether, FAME-rapeseed biodiesel, 1-heptanol, and 2-ethylhexyl nitrate, at 25 °C (298.15 K). All these additives come or can be obtained completely or partially from plants. The obtained ternary phase diagrams show a large domain of clear and homogeneous solutions and a liquid two-phase system due to the partial solubility of rapeseed oil and ethanol. All the tested additives have thus an evident cosolvent behavior for ethanol and rapeseed oil. In all the studied systems, the possible presence of nanostructures is checked with dynamic light scattering (DLS) and confirmed using static light scattering (SLS). In the system rapeseed oil/ethanol/1-heptanol, the presence of nanostructures is definitely established performing small-angle neutron scattering (SANS). The true geometry of these nanostructures could not be detected, but systematic conductivity measurements starting with the binary melt 1-heptanol/rapeseed oil in the presence of LiClO4 adding ethanol show clearly a continuous transition from ethanol-in-rapeseed oil to rapeseed oil-in-ethanol mixtures passing through a bicontinuous medium

Emergence of surfactant-​free micelles from ternary solutions

Curious effects ranging from enzyme activity to anomalies in evapn. rates that have been known for over fifty years suggest the existence and thermodn. stability of surfactant-free micelles. Only recently, joint X-ray, light and neutron scattering expts. have demonstrated that aggregates and bulk pseudo-phases coexist in presumably normal solns., in which a water insol. component is solubilized in a certain domain of concn. of a hydrotrope component like ethanol. Nevertheless, nothing is known about the mol.-level shape and structure of such aggregates. In this work we characterize mixts. of octanol, ethanol, and water by mol. dynamics simulations. For compns. in the "pre-ouzo" region (close to the single phase stability limit) we observe micelle-like aggregates that are clearly distinct from simple crit. d. fluctuations. We define an ethanol partition in the pseudo-phase from an integral of the van der Waals dispersion energy term. From this partition, octanol-rich aggregates swollen with ethanol appear with an emerging interface. Ethanol is present in the water pseudo-phase with an exponential decay similar to the one predicted by Marcelja and Radic forty years ago

Nanostructuring in ethanol/"ethanolotrope"​/rapeseed oil automotive biofuels

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