Fundamental constants explain submillimeter liquid shear forces.

From fundamental physical constants to the identification of liquid shear elasticity, over the past decade, new ways have emerged to understand viscosity.

Microscopic Analysis of the Water/Glycerol/EO30PS System in Bulk and on a Solid Substrate.

Surfactant systems are often employed in cosmetic formulations where they dry on skin as a surface, thereby becoming increasingly concentrated systems. To better understand this drying process, we focused on the difference of self-assembled structures of the water/glycerol/polyoxyethylene (30) phytosteryl ether (EO30PS) system in bulk and on a solid substrate because the interaction between the substrate and the surfactant may have a substantial effect on the self-assembly, which may be related to the bulk structure but in detail may also differ strongly from the bulk situation. In bulk, small-angle neutron scattering (SANS) experiments showed that with increasing loss of water, the degree of ordering increases but changes of the aggregate structure are rather small.

Collective Effects in Ionic Liquid [emim][Tf2N] and Ionic Paramagnetic Nitrate Solutions without Long-Range Structuring.

Mesoscopic shear elasticity has been revealed in ordinary liquids both experimentally by reinforcing the liquid/surface interfacial energy and theoretically by nonextensive models. The elastic effects are here examined in the frame of small molecules with strong electrostatic interactions such as room temperature ionic liquids [emim][Tf2N] and nitrate solutions exhibiting paramagnetic properties. We first show that these charged fluids also exhibit a nonzero low-frequency shear elasticity at the submillimeter scale, highlighting their resistance to shear stress.

Structural Characterization of Nonionic Surfactant Micelles with CO/Ethylene Oxide Head Groups and Their Temperature Dependence.

Using CO as a resource in the production of materials is a viable alternative to conventional, petroleum-based raw materials and therefore offers great potential for more sustainable chemistry. This study presents a detailed structural characterization of aggregates of nonionic dodecyl surfactants with different amounts of CO substituting ethylene oxide (EO) in the head group. The micellar structure was characterized as a function of concentration and temperature by dynamic and static light scattering and, in further detail, by small-angle neutron scattering (SANS).

Capillary-size flow of human blood plasma: Revealing hidden elasticity and scale dependence.

The dynamical mechanical analysis of blood generally uses models inspired by conventional flows, assuming scale-independent homogeneous flows and without considering fluid-surface boundary interactions. The present experimental study highlights the relevance of using an approach in line with physiological reality providing a strong interaction between the fluid and the boundary interface. New dynamic properties of human blood plasma are found: a finite shear elastic response (solid-like property) is identified in nearly static conditions, which also depends on the scale (being reinforced at small scales).

Highlighting Thermo-Elastic Effects in Confined Fluids.

The recent identification of a finite shear elasticity in mesoscopic fluids has motivated the search of other solid-like properties of liquids. We present an innovative thermal approach of liquids. We identify a dynamic thermo-elastic mesoscopic behavior by building the thermal image produced by different liquids upon applying a low frequency mechanical shear field.

Identification of Thermal Response of Mesoscopic Liquids under Mechanical Excitation: From Harmonic to Nonharmonic Thermal Wave.

In the conventional picture, the temperature of a liquid bath in the quiescent state is uniform down to thermal fluctuation length scales. Here we examine the impact of a low-frequency shear mechanical field (hertz) on the thermal equilibrium of polypropylene glycol and liquid water away from any phase transition confined between high-energy surfaces. We show the emergence of both cooling and heating shear waves of several tens of micrometers widths varying synchronously with the applied shear strain wave.

Universal ' ∼ Law for the Low-Frequency Shear Modulus of Confined Liquids.

Liquids confined to sub-millimeter scales have remained poorly understood. One of the most striking effects is the large elasticity revealed using good wetting conditions, which grows upon further decreasing the confinement length, . These systems display a low-frequency shear modulus in the order of 1-10 Pa, contrary to our everyday experience of liquids as bodies with a zero low-frequency shear modulus.

Do Deep Eutectic Solvents Form Uniform Mixtures Beyond Molecular Microheterogeneities?

We have performed small-angle neutron scattering in a momentum transfer range (0.05 < < 0.5 Å) to study long-range order and concentration fluctuations in deep eutectic solvents (DESs) and their aqueous solutions.

Strain-induced violation of temperature uniformity in mesoscale liquids.

Thermo-elasticity couples the deformation of an elastic (solid) body to its temperature and vice-versa. It is a solid-like property. Highlighting such property in liquids is a paradigm shift: it requires long-range collective interactions that are not considered in current liquid descriptions.

Changes in Phase Behavior from the Substitution of Ethylene Oxide with Carbon Dioxide in the Head Group of Nonionic Surfactants.

Nonionic ethylene oxide (EO)-based surfactants are widely employed in commercial applications and normally form gel-like liquid crystalline phases at higher concentrations, rendering their handling under such conditions difficult. By incorporating CO units in their hydrophilic head groups, the consumption of the petrochemical EO was reduced, and the tendency to form liquid crystals was suppressed completely. This surprising behavior was characterized by rheology and studied with respect to its structural origin by means of small-angle neutron scattering (SANS).

Structural control of polyelectrolyte/microemulsion droplet complexes (PEMECs) with different polyacrylates.

The ionic assembly of oppositely charged polyelectrolyte-surfactant complexes (PESCs) is often done with the aim of constructing more functional colloids, for instance as advanced delivery systems. However, PESCs are often not easily loaded with a solubilisate due to intrinsic restrictions of such complexes. This question was addressed from a different starting point: by employing microemulsion droplets as heavily loaded surfactant systems and thereby avoiding potential solubilisation limitations from the beginning.

Temperature-dependent structure and dynamics of highly-branched poly(N-isopropylacrylamide) in aqueous solution.

Small-angle neutron scattering (SANS) and neutron spin-echo (NSE) have been used to investigate the temperature-dependent solution behaviour of highly-branched poly(N-isopropylacrylamide) (HB-PNIPAM). SANS experiments have shown that water is a good solvent for both HB-PNIPAM and a linear PNIPAM control at low temperatures where the small angle scattering is described by a single correlation length model. Increasing the temperature leads to a gradual collapse of HB-PNIPAM until above the lower critical solution temperature (LCST), at which point aggregation occurs, forming disperse spherical particles of up to 60 nm in diameter, independent of the degree of branching.

More room for microphase separation: An extended study on binary liquids confined in SBA-15 cylindrical pores.

The confinement of liquid mixtures in porous channels provides new insight into fluid ordering at the nanoscale. In this study, we address a phenomenon of microphase separation, which appears as a novel fascinating confinement effect for fully miscible binary liquids. We investigate the structure of tert-butanol-toluene mixtures confined in the straight and mono-dispersed cylindrical nanochannels of SBA-15 mesoporous silicates (D = 8.

A journey through the phase diagram of a pharmaceutically relevant microemulsion system.

Hypothesis: The phase behavior and the properties of water, oil, surfactant, and cosurfactant mixtures depend on the fine balance of different forces, among them the bending energy of the amphiphilic film. Thus, it should be possible to control the structural evolution of nonionic microemulsions by the cosurfactant content and the hydration of the surfactant headgroup.

Experiments: An extensive investigation of the pseudoternary phase diagram of mixtures of water, isopropyl palmitate, polyoxyethylene (10) oleyl ether Brij 97 (C18E10), and butanol is presented for two different cosurfactant concentrations, thereby varying the hydrophilicity of the amphiphile.

Bringing to Light Hidden Elasticity in the Liquid State Using In-Situ Pretransitional Liquid Crystal Swarms.

The present work reveals that at the sub-millimeter length-scale, molecules in the liquid state are not dynamically free but elastically correlated. It is possible to "visualize" these hidden elastic correlations by using the birefringent properties of pretransitional swarms persistent in liquids presenting a weak first order transition. The strategy consists in observing the optical response of the isotropic phase of mesogenic fluids to a weak (low energy) mechanical excitation.

Organogels based on 12-hydroxy stearic acid as a leitmotif: Dependence of gelation properties on chemical modifications.

Various compounds based on the structural leitmotif of 12-hydroxy stearic acid (HSA) were studied with respect to their ability to form organogels. They were modified by ethoxylation in order to avoid the acid group of HSA, which is unwanted for many of the applications of organogels. In this paper, it is shown that the rheological performance of organogels depends strongly on the extent of ethoxylation, exhibiting an optimum at intermediate degrees of ethoxylation.

Highlighting a Cooling Regime in Liquids under Submillimeter Flows.

The shear flow of ordinary liquids is for the first time observed at the submillimeter scale by thermal imaging. We report on microinfrared experiments, showing that liquids as important as water flowing on wetting surfaces produce cooling, while the academic view would foresee heating production. This apparent counterintuitive cooling effect shows that the increase of the internal energy due to the flow can result in different shapes, including a cooling process, before reaching the conventional heating regime at higher shear rates.

Identification of a low-frequency elastic behaviour in liquid water.

This article deals with the identification of solid-like properties measured at room temperature at a sub-millimetre length scale in liquid water. At a macroscopic scale, normal liquids (i.e.

Structure of reverse microemulsion-templated metal hexacyanoferrate nanoparticles.

The droplet phase of a reverse microemulsion formed by the surfactant cetyltrimethylammonium ferrocyanide was used as a matrix to synthesize nanoparticles of nickel hexacyanoferrate by adding just a solution of NiCl2 to the microemulsion media. Dynamic light scattering and small-angle neutron scattering measurements show that the reverse microemulsion droplets employed have a globular structure, with sizes that depend on water content. Transmission electron microscopy and electron diffraction are used to obtain information about the structure of the synthesized nanoparticles.

The use of highly ordered vesicle gels as template for the formation of silica gels.

A spontaneously forming gel of unilamellar vesicles based on sodium oleate (Na oleate) and 1-octanol as amphiphiles has been employed as a template in the formation of a silica gel formed by the hydrolysis of the inorganic precursor tetraethyl orthosilicate (TEOS). Up to about 10 wt % TEOS can be incorporated into this vesicle gel without phase separation and in a fully homogeneous formation process by simple mixing of the components. The process itself relies solely upon the self-organizing properties of this amphiphilic template system.

Growth and branching of charged wormlike micelles as revealed by dilution laws.

The successive transitions of morphology in aqueous solutions of interacting micelles are directly evidenced by the position q* of the correlation peak of the small angle neutron scattering profiles. As the volume fraction Phi increases, q* successively fits to the dilution laws expected for spheres and cylinders, and eventually gets close to the one expected for sheets when the micelles get branched. Data in between the swelling laws are quantitatively analyzed in terms of aggregation number and junction density.

New light on old wisdoms on molten polymers: conformation, slippage and shear banding in sheared entangled and unentangled melts.

The flow of viscoelastic materials is usually interpreted as resulting from intramolecular properties. Typically, the non-linear flow behaviour and sluggish relaxation dynamics in entangled polymers are interpreted by a disentanglement process. This molecular interpretation has never been validated by direct observation.

Shear-induced isotropic to nematic transition of liquid-crystal polymers: identification of gap thickness and slipping effects.

The shear-induced isotropic-nematic transition is a generic property of liquid-crystalline polymer melts which is identified by the emergence in the isotropic phase of a strong birefringence above a critical shear rate. Although spectacular, this transition cannot be explained on the basis of a conventional approach (coupling with pretransitional fluctuations or with viscoelastic relaxation times). We investigate the asymptotic rheo-optical behavior of the shear-induced phase.