Ion specific tuning of nanoparticle dispersion in an ionic liquid: a structural, thermoelectric and thermo-diffusive investigation.

Dispersions of charged maghemite nanoparticles (NPs) in EAN (ethylammonium nitrate) a reference Ionic Liquid (IL) are studied here using a number of static and dynamical experimental techniques; small angle scattering (SAS) of X-rays and of neutrons, dynamical light scattering and forced Rayleigh scattering. Particular insight is provided regarding the importance of tuning the ionic species present at the NP/IL interface. In this work we compare the effect of Li+, Na+ or Rb+ ions. Here, the nature of these species has a clear influence on the short-range spatial organisation of the ions at the interface and thus on the colloidal stability of the dispersions, governing both the NP/NP and NP/IL interactions, which are both evaluated here. The overall NP/NP interaction is either attractive or repulsive. It is characterised by determining, thanks to the SAS techniques, the second virial coefficient A2, which is found to be independent of temperature. The NP/IL interaction is featured by the dynamical effective charge ξeff0 of the NPs and by their entropy of transfer SNP (or equivalently their heat of transport ) determined here thanks to thermoelectric and thermodiffusive measurements. For repulsive systems, an activated process rules the temperature dependence of these two latter quantities.

Thermodiffusion of citrate-coated γ-Fe2O3 nanoparticles in aqueous dispersions with tuned counter-ions - anisotropy of the Soret coefficient under a magnetic field.

Under a temperature gradient, the direction of thermodiffusion of charged γ-Fe2O3 nanoparticles (NPs) depends on the nature of the counter-ions present in the dispersion, resulting in either a positive or negative Soret coefficient. Various counter-ions are probed in finely tuned and well characterized dispersions of citrate-coated NPs at comparable concentrations of free ionic species. The Soret coefficient ST is measured in stationary conditions together with the mass-diffusion coefficient Dm using a forced Rayleigh scattering method. The strong interparticle repulsion, determined by SAXS, is also attested by the increase of Dm with NP volume fraction Φ. The Φ-dependence of ST is analyzed in terms of thermophoretic and thermoelectric contributions of the various ionic species. The obtained single-particle thermophoretic contribution of the NPs (the Eastman entropy of transfer sNP) varies linearly with the entropy of transfer of the counter-ions. This is understood in terms of electrostatic contribution and of hydration of the ionic shell surrounding the NPs. Two aqueous dispersions, respectively, with ST > 0 and with ST < 0 are then probed under an applied field H[combining right harpoon above], and an anisotropy of Dm and of ST is induced while the in-field system remains monophasic. Whatever the H[combining right harpoon above]-direction (parallel or perpendicular to the gradients and ), the Soret coefficient is modulated keeping the same sign as in zero applied field. In-field experimental determinations are well described using a mean field model of the interparticle magnetic interaction.

Thermodiffusion of repulsive charged nanoparticles - the interplay between single-particle and thermoelectric contributions.

Thermodiffusion of different ferrite nanoparticles (NPs), ∼10 nm in diameter, is explored in tailor-made aqueous dispersions stabilized by electrostatic interparticle interactions. In the dispersions, electrosteric repulsion is the dominant force, which is tuned by an osmotic-stress technique, i.e. controlling of osmotic pressure Π, pH and ionic strength. It is then possible to map Π and the NPs' osmotic compressibility χ in the dispersion with a Carnahan-Starling formalism of effective hard spheres (larger than the NPs' core). The NPs are here dispersed with two different surface ionic species, either at pH ∼ 2 or 7, leading to a surface charge, either positive or negative. Their Ludwig-Soret ST coefficient together with their mass diffusion Dm coefficient are determined experimentally by forced Rayleigh scattering. All probed NPs display a thermophilic behavior (ST < 0) regardless of the ionic species used to cover the surface. We determine the NPs' Eastman entropy of transfer and the Seebeck (thermoelectric) contribution to the measured Ludwig-Soret coefficient in these ionic dispersions. The NPs' Eastman entropy of transfer sNP is interpreted through the electrostatic and hydration contributions of the ionic shell surrounding the NPs.

Thermoelectricity and thermodiffusion in charged colloids.

The Seebeck and Soret coefficients of ionically stabilized suspension of maghemite nanoparticles in dimethyl sulfoxide are experimentally studied as a function of nanoparticle volume fraction. In the presence of a temperature gradient, the charged colloidal nanoparticles experience both thermal drift due to their interactions with the solvent and electric forces proportional to the internal thermoelectric field. The resulting thermodiffusion of nanoparticles is observed through forced Rayleigh scattering measurements, while the thermoelectric field is accessed through voltage measurements in a thermocell. Both techniques provide independent estimates of nanoparticle's entropy of transfer as high as 82 meV K(-1). Such a property may be used to improve the thermoelectric coefficients in liquid thermocells.

Accumulation and aggregate formation of mutant superoxide dismutase 1 in canine degenerative myelopathy.

Canine degenerative myelopathy (DM) is an adult-onset progressive neurodegenerative disorder that has recently been linked to mutations in the superoxide dismutase 1 (SOD1) gene. We generated a polyclonal antibody against canine SOD1 to further characterize the mutant SOD1 protein and its involvement in DM pathogenesis. This antibody (SYN3554) was highly specific to canine SOD1 and had the ability to reveal distinct cytoplasmic aggregates in cultured cells expressing canine mutant SOD1 and also in the spinal neurons of symptomatic homozygotes. A similar staining pattern was observed in asymptomatic homozygotes. SOD1 aggregates were not detected in the spinal neurons of heterozygotes; the accumulation of SOD1 was also detected in the reactive astrocytes of homozygotes and heterozygotes to a similar extent. Our results support the hypothesis that the cytoplasmic accumulation and aggregate formation of the mutant SOD1 protein, especially in astrocytes, are closely associated with the pathogenesis of DM. Therefore, this disease is regarded as a spontaneous large-animal model of SOD1-mediated amyotrophic lateral sclerosis in humans.

A simply designed cell for thermal conductivity measurements of low vapor-pressure liquids.

We have built a simply designed cell for the measurement of the thermal conductivity of liquids under steady state conditions from room temperature to about 60 °C. Thermal conductivities measured in the range between 0.2 and 0.7 Wm(-1) K(-1) show deviations of a few percent from reference thermal-conductivity data. The cell is made of two concentric parallel plates separated by a 0.44 mm thick sample. It is easily assembled and loaded with the sample for a quick and routine use.

Huge Seebeck coefficients in nonaqueous electrolytes.

The Seebeck coefficients of the nonaqueous electrolytes tetrabutylammonium nitrate, tetraoctylphosphonium bromide, and tetradodecylammonium nitrate in 1-octanol, 1-dodecanol, and ethylene-glycol are measured in a temperature range from T = 30 °C to T = 45 °C. The Seebeck coefficient is generally of the order of a few hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here we report huge values of 7 mV/K at 0.1 M concentration for tetrabutylammonium nitrate in 1-dodecanol. These striking results open the question of unexpectedly large kosmotrope or "structure making" effects of tetraalkylammonium ions on the structure of alcohols.

Intrinsic low temperature paramagnetism in B-DNA.

We present an experimental study of magnetization in lambda-DNA in conjunction with structural measurements. The results show the surprising interplay between the molecular structures and their magnetic property. In the B-DNA state, lambda-DNA exhibits paramagnetic behavior below 20 K that is nonlinear in an applied magnetic field whereas, in the A-DNA state, it remains diamagnetic down to 2 K. We propose orbital paramagnetism as the origin of the observed phenomena and discuss its relation to the existence of long range coherent transport in B-DNA at low temperature.

Curvature elasticity of multilamellar lipid bilayers close to the chain-melting transition.

We directly measured curvature elasticity of dipalmitoylphosphatidylcholine multilamellar bilayers close to the chain-melting transition using the method of electric-field-induced bending deformation of the cylindrical tubes. The result shows that the bending modulus, kappa(c), decreases remarkably at temperatures close to the melting transition temperature. This reflects a softening of the bilayer resulted from the area fluctuations as predicted theoretically. However, the decrease of kappa(c) near the transition is far smaller than that predicted. This is due to the experimental method and the narrow transition width of the multilamellar bilayers. Nevertheless, the result obtained gives direct evidence of the kappa(c) reduction predicted for multilamellar membranes in the transition regime. Below about 41 degrees C, almost of all cylindrical tubes cannot response to the electric field, indicating a very large bending rigidity.

Absence of residual quasiparticle conductivity in the underdoped cuprate YBa2Cu4O8.

We report measurements of the in-plane thermal conductivity kappa of the stoichiometric underdoped cuprate YBa2Cu4O8 (Y124) below 1 K. kappa(T) is shown to follow a simple phononic T3 dependence at the lowest temperature T for both current directions, with a negligible linear quasiparticle contribution. This observation is in marked contrast with behavior reported in optimally doped cuprates, and implies that extended zero-energy (or low-energy) quasiparticles are absent in Y124.

Frequency dependence of electric-field-induced orientation of myelin tubes.

Orientation induced by an alternating electric field was studied for myelin tubes of egg phosphatidylcholine (egg-PC) in water and in KCl electrolyte solution. The orientation was also studied for myelin tubes of egg-PC/cholesterol mixtures in water. The orientation effect was measured by the bending curvature of myelin tubes with hairpin-like deformation at frequencies between 10 kHz and 20 MHz. The bending deformation of egg-PC myelin tubes in water decreased abruptly with a decreasing frequency within the low-frequency range below 100 kHz, and shrinkage of myelin tubes was often observed. The bending deformation decreased as the frequency was increased in a higher frequency range. The profile of the frequency dependence for egg-PC in KCl solution was similar to that in water but shifted towards a higher frequency. At low KCl concentrations below 3 mM, the relaxation frequency increased proportionally with increasing an KCl concentration, which was due to a proportional increase in the conductivity of the surrounding medium. Similar profiles of the frequency dependence were observed for egg-PC/cholesterol mixtures but with no shift in the relaxation frequency. These data in the high-frequency range fitted well with calculations based on theoretical equations for the electric-field-induced orientation of nonspherical particles. The conductivity of myelin tubes was estimated to be in the order of 10(-4) S/m in water and of 10(-3) S/m at the low KCl concentrations. The bending modulus of a bilayer membrane was estimated to be (1.0 +/- 0.5) x 10(-19) J for egg-PC in water. No change in the bending modulus was observed for egg-PC in KCl solution. However, for egg-PC/cholesterol mixtures in water, the bending modulus abruptly increased to (1.8 +/- 0.5) x 10(-19) J at a cholesterol concentration of 40 mol%.