Publications (5)17.01 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Several series of unidimensional coordination polymers of formula [Zn(C(n)H(2n+1)trz)(3)](Cl)(2)·xH(2)O (n = 18, 16, 13, 11, 10, trz = 4-substituted-1,2,4-triazole), [Zn(C(18)H(37)trz)(3)](ptol)(2)·xH(2)O, [Fe(C(n)H(2n+1)trz)(3)](X)(2)·xH(2)O (n = 18, 16, 13, 10; X = Cl(-) or ptol(-), where ptol(-) = p-tolylsulfonate anion), and [Fe(C(18)H(37)trz)(3)](X)(2)·xH(2)O (X = C(8)H(17)PhSO(3)(-) and C(8)H(17)SO(3)(-)) are reported with their thermal, structural, and magnetic properties. Most of these materials exhibit thermotropic lamellar mesophases at temperatures as low as 410 K, as confirmed by textures observed by polarized optical microscopy. The corresponding phase diagrams deduced by differential scanning calorimetry are also reported. All iron-containing materials present a spin crossover phenomenon that occurs at temperatures ranging from 242 to 360 K, only slightly below the mesophase temperature domain, and remains complete and cooperative, even for the longer alkyl substituents. The use of stable diamagnetic Zn(II) analogues proves to be very useful to characterize the comparatively less stable and less crystalline Fe(II) analogues.
- [Show abstract] [Hide abstract] ABSTRACT: The gelation abilities toward organic solvents of a series of triazole-based coordination polymers of formula [M(C(n)trz)(3)]A(2) (M = Fe(II) or Zn(II); C(n)trz = 4-n-alkyl-1,2,4-triazole with n = 13, 16, 18; A = monovalent anions, abbreviated as MC(n)A) have been studied to form thermally responsive multifunctional metallogels, in particular for the iron polymers that present the spin-crossover phenomenon. Indeed thermo-reversible physical gels exhibiting thermally reversible magnetic and optical crossovers are formed in decane and toluene. The FeC(18)ptol/decane and FeC(18)ptol/toluene phase diagrams are described (ptol = p-toluene sulfonate anion), together with the rheological properties of the gels determined as a function of the solvent, the gelator concentration as well as temperature. Microscopic observations of the gel structure are correlated to the composition and rheological properties of the gels. Magnetic and thermal studies show that both the gel-liquid and spin-crossover phenomena can be adjusted through the composition of the gel mixture.
- [Show abstract] [Hide abstract] ABSTRACT: The flow behavior of a viscoelastic organogel is investigated using ultrasonic velocimetry combined with rheometry. Our gel presents a decreasing flow curve, i.e., the measured stress decreases as a function of the applied shear rate. Strikingly, we note that the local flow curve calculated from the velocity profiles also exhibits a decreasing part. We attribute this regime to the presence of a fracturing process and three-dimensional motions in the bulk of the sample.
- [Show abstract] [Hide abstract] ABSTRACT: We describe how high-frequency ultrasound can be used to measure and follow velocity profiles in complex fluids sheared in the Couette geometry with a 0.5–1 mm gap. The technique provides a spatial resolution of 40 m and velocity profiles can be recorded every second typically. Such ultrasonic velocimetry is coupled to a standard rheometer. The resulting “ultrasonic rheo-velocimeter” is tested on various complex fluids that display both inhomogeneous velocity profiles and temporal fluctuations close to a shear-induced transition: a lamellar phase, a triblock copolymer, a concentrated emulsion, and an organogel.
- [Show abstract] [Hide abstract] ABSTRACT: Using high-frequency ultrasonic velocimetry, we perform simultaneously rheological and local velocity measurements in a 75% wt. concentrated emulsion after a step-like shear rate applied for 3 h. Velocity profiles in the vicinity of the yield stress unveil the existence of transient inhomogeneous flows. However, approaching the equilibrium, banded states disappear and the emulsion flows homogeneously. At higher shear rates, we show that the local rheological behaviour evolves with the imposed shear rate. Changes in droplet concentration may be responsible for such a behaviour. We finally point out the presence of wall slip and investigate the evolution of the lubricating layers’ thicknesses with the shear stress.
University of BordeauxBurdeos, Aquitaine, France
Centre de Recherche Paul PascalPessac, Aquitaine, France