We synthesized a chiral mesogen AC11 and two different siloxanes MSi2-AC11 and DSi3-AC11 derived from it by a hydrosilylation reaction. The effects of varying the molecular architecture were investigated with special attention being devoted to the occurrence of the de Vries SmA* phase. Strong hints that all the three molecules follow the scenario suggested by de Vries were found in the behavior of the susceptibility by studies of their electrooptical response in the SmA* phase. In particular, DSi3-AC11 containing two mesogens interconnected by a siloxane spacer presented a critical exponent γ as high as 1.97, indicating a practically pure de Vries behavior. Temperature-dependent X-ray analysis revealed that the three materials underwent a small layer shrinkage at the SmA*–SmC* transition.

The behavior of lamellar materials under strain is not yet completely understood, either for large shears where macroscopic defects (onions, focal conic domains) are formed, or even in small-strains experiments where the deformation is ruled by dislocations. We have developed a micro-plasticity experiment, in which we impose a controlled strain to an homeotropic smectic A sample and observe, under microscope, the associated motion of edge dislocations (a dynamical extension of the well-known experiment [1] at rest described in R. B. Meyer et al., Phys. Rev. Lett. 41, 1393 (1978)). We note that edge dislocations are strongly pinned by screw dislocations. We explain how this pinning is at the origin of a yield strain. We furthermore study the dynamics of climbing edge dislocations and evidence a morphological transition from a jerky motion to a viscous regime. We clarify the role of the pinning in this transition.

New perfluoroalkylated acrylic monomers with a biphenyl core and hydrocarbon spacer (CH2)m of various length (m = 0, 6, 11) were synthesized from biphenol. Phase transitions of monomers and intermediates isolated in the course of the synthesis were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Whereas most fluoroacrylic monomers and low molecular weight precursors displayed thermotropic behavior (whatever the length of the spacer), the polymers did not retain the ability to form mesophases. Moreover, the bulk organization of the fluorinated side groups was diminished strongly for polymers in comparison with the corresponding fluorinated monomers. Nevertheless, it was demonstrated that an intermediate length of the spacer (–CH2)6, could favor the organization of the rigid perfluoroalkylated biphenyl side groups in the bulk.

Drosophila thoracic mechanosensory bristles originate from cells that are singled out from 'proneural' groups of competent epithelial cells. Neural competence is restricted to individual sensory organ precursors (SOPs) by Delta/Notch-mediated 'lateral inhibition', whereas other cells in the proneural field adopt an epidermal fate. The precursors of the large macrochaetes differentiate separately from individual proneural clusters that comprise about 20-30 cells or as heterochronic pairs from groups of more than 100 cells, whereas the precursors of the small regularly spaced microchaetes emerge from even larger proneural fields. This indicates that lateral inhibition might act over several cell diameters; it was difficult to reconcile with the fact that the inhibitory ligand Delta is membrane-bound until the observation that SOPs frequently extend thin processes offered an attractive hypothesis. Here we show that the extension of these planar filopodia--a common attribute of wing imaginal disc cells--is promoted by Delta and that their experimental suppression reduces Notch signalling in distant cells and increases bristle density in large proneural groups, showing that these membrane specializations mediate long-range lateral inhibition.

In lyotropic systems, the sponge and the lamellar phases possess the same local structure: a membrane made of a bilayer of surfactants. In the quasiternary lyotropic system CPCl/brine/hexanol, the bilayer is continuous through the interface between the lamellar and the sponge phases. A model based on this phenomenon has predicted a very low value of the interfacial free energy. The study of hydrodynamic relaxation time of distorted spherical lamellar droplets gives an estimation of the interfacial tension value. Results confirm the validity of the model and the dependence on membrane volume fraction is explained by a simple scaling law.

Deformation and tank-treading motion of flaccid vesicles in a linear shear flow close to a wall are quantitatively studied by light microscopy. Velocities of bounded vesicles obey Goldman's law established for rigid spheres. A progressive tilt and a transition of unbinding of vesicles are evidenced upon increasing the shear rate, gamma;. These observations disclose the existence of a viscous lift force, F(l), depending on the viscosity eta of the fluid, the radius R of the vesicle, its distance h from the substrate, and a monotonous decreasing function f(1-v) of the reduced volume v, in the following manner: F(l) = eta(gamma)(R(3)/h)f(1-v). This relation is valid for vesicles both close to and farther from the substrate.