Aqueous solutions of poly(vinyl acetate)-b-sodium polyacrylate (PVAc-b-NaPAA) block copolymers were characterized by capillary electrophoresis (CE). CE experiments reveal the presence of NaPAA dead chains, acetate ions (which are a byproduct of the hydrolysis of PVAc), and nonassociated copolymers (unimers). This fraction of unimers is dependent on the chemical composition of the copolymers and on the purification procedure. It remains constant when increasing copolymer concentration. The fraction of unimers was too high to correspond to a critical micellar concentration. Instead, this high content of unimers is likely due to the polydispersity in composition of the copolymers, sodium polyacrylate-rich copolymers being excluded from the micellization process. This interpretation is consistent with the study of the effect of temperature on the free copolymer fraction. Above a temperature threshold, the unimer population increases due to the destabilization of part of the micelles. Addition of a neutral surfactant leads to the formation of mixed micelles, the electrophoretic mobility of which can be modeled using recent theoretical developments on electrokinetic migration of composite objects.

We designed and synthesized new SmA* liquid crystals with different molecular architectures based on the chiral mesogen MR11, which was unsubstituted, or attached at one end and at both ends of a trisiloxane segment in the monosubstituted MSi3-MR11 and disubstituted DSi3-MR11 siloxanes, respectively. We studied the critical divergence of the magnetic susceptibility by measurements of the induced tilt angle Θind at the SmA*–SmC* transition. While all three SmA* liquid crystals presented a de Vries character, this was quite distinctive for DSi3-MR11 for which the critical exponent γ = 1.87 was maximal. X-ray diffraction experiments confirmed that the SmA*–SmC* transition occurred with essentially no layer shrinkage.

Disclinations in nematic liquid crystals usually adopt a straight shape in order to minimize their elastic energy. Once created in the course of a nonequilibrium process such as a temperature quench from the isotropic to the nematic phase, the topologically stable disclinations of half-integer strength either annihilate each other in pairs of opposite strength or form topologically unstable disclinations of integer strength. In this article, we demonstrate that the annihilation process can be inhibited and the defects can be deformed by an applied electric field. We study the disclination lines in the deep uniaxial nematic phase, located at the boundary between two different types of walls, the so-called π wall (a planar soliton stabilized by the surface anchoring) and the Brochard-Léger (BL) wall stabilized by the applied electric field. By changing the electric voltage, one can control the energy of director deformations associated with the two walls and thus control the deformation and dynamics of the disclination line. At small voltages, the disclinations are straight lines connecting the opposite plates of the cell, located at the two ends of the π walls. The π walls tend to shrink. When the voltage increases above EF, the Fréedericksz threshold, the BL walls appear and connect pairs of disclinations along a path complementary to the π wall. At E>2EF, the BL walls store sufficient energy to prevent shrinking of the π walls. Reconstruction of the three-dimensional director configuration using a fluorescent confocal polarizing microscopy demonstrates that the disclinations are strongly bent in the region between the π and the BL walls. The distortions and the related dynamics are associated with the transformation of the BL wall into two surface disclination lines; we characterize it experimentally as a function of the applied electric field, the cell thickness, and the sample temperature. A simple model captures the essential details of the experimental data.

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.

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.