Doping of lyotropic smectics with non magnetic particles : comparison with ferrosmectics

International audienceThe first examples of doped lyotropic mesophases, or amphicolloids, have been realized recently by doping a smectic quaternary mixture of cyclohexane/water/sodiumdodecyl sulfate/pentanol with magnetic particles (“ferrosmectic” phases). We present here the obtention of similar smectic phases where the doping particles are nonmagnetic and the first experiments on these phases (texture, phase diagram). The comparison of the three systems studied here (magnetic and nonmagnetic dopedphases, and the initial undoped lamellar phase) shows that the modifications induced in doped phases by the presence of the particles are not dominated by the magnetic interactions

Doping of lyotropic smectics with non magnetic particles : comparison with ferrosmectics

International audienceThe first examples of doped lyotropic mesophases, or amphicolloids, have been realized recently by doping a smectic quaternary mixture of cyclohexane/water/sodiumdodecyl sulfate/pentanol with magnetic particles (“ferrosmectic” phases). We present here the obtention of similar smectic phases where the doping particles are nonmagnetic and the first experiments on these phases (texture, phase diagram). The comparison of the three systems studied here (magnetic and nonmagnetic dopedphases, and the initial undoped lamellar phase) shows that the modifications induced in doped phases by the presence of the particles are not dominated by the magnetic interactions

Composites copolymères-nanoparticules : I. Période lamellaire dans le régime des “petites nanoparticules"

In the new composite materials made of lamellar diblock copolymer and ferrofluidics, the lamellar period $L$ is experimentally shown to depend on the volume fraction $\Phi$ of nanoparticles according to: $L=L_0(1+\Phi/3)$, where $L_0=L(\Phi=0)$, while $L=L_0(1+\Phi)$ was rather expected. Knowing that the particles are exclusively located into one of the two polymeric components, we show that these two laws can be established in a simple way from two different assumptions about the spatial distribution of nanoparticles in the host layers. The hypothesis of particles confined in the center of the layers is finally rejected.Une étude expérimentale nous montre que dans les nouveaux matériaux composites élaborés récemment à partir de copolymères diblocs lamellaires et de ferrofluides, la période lamellaire $L$ varie avec la fraction volumique de nanoparticules d'une façon à peu près bien décrite par une loi $L=L_0(1+\Phi/3)$, où $L_0=L(\Phi=0)$, alors qu'on attendait plutôt $L=L_0(1+\Phi)$. Sachant les nanoparticules localisées dans l'une des deux espèces du copolymère, nous montrons comment ces deux lois s'obtiennent théoriquement à partir de deux hypothèses fortes très différentes sur la distribution des particules à l'intérieur des domaines hôtes. Celle qui conduit à des prédictions infirmées par l'expérience est finalement écartée

Lyotropic ferronematics: Magnetic orientational transition in the discotic phase

We report the synthesis of lyotropic ferronematics with a content of magnetic nanoparticles ($\rm \sim 6 \;nm$) up to 1 vol.%. In the ferrodiscotic phase we observe a magnetic Frederiks transition with critical fields about two orders of magnitude lower than that for an undoped lyotropic system. A model accounting for the magnetic polarization behavior of the studied ferronematics is presented

Diblock copolymers adsorbed at a water-oil interface

We probe the conformation of a diblock copolymer layer adsorbed at the surface of water-in-oil emulsion droplets at various concentration of a molecular surfactant. The diblock copolymer is made of a hydrophobic polybutadiene part linked to a hydrophilic polyethylene oxide one. The measure provides the equilibrium thickness of the polymer layer that is obtained with two different techniques, i.e. dynamic light scattering and force measurements. The structure of the layer is shown to change from a "mushroom"conformation in which the adsorbed chains form independent Gaussian coils to a conformation where they interact and extend in the continuous phase. The transition from one regime to the other is progressive as the ratio surfactant/polymer bulk concentration varies