Ribal Georges Sabat

Temperature dependence of the complete material coefficients matrix of soft and hard doped piezoelectric lead zirconate titanate ceramics

We have used resonance methods to determine the variation of all the independent piezoelectric, elastic, and dielectric material coefficients, as well as the corresponding electromechanical coupling factors, of soft and hard doped piezoelectric lead zirconate titanate (PZT) ceramics with compositions near the morphotropic phase boundary, as a function of temperature ranging between −165 and 195°C. The material coefficients were obtained by analyzing the fundamental resonance of the impedance or admittance spectra as a function of frequency for several sample resonance geometries. The piezoelectric coefficients d33, −d31, and d15, as well as the dielectric permittivity coefficients e11T and e33T, generally increased with temperature for both soft and hard PZT samples. However, the elastic compliance coefficients s11E, −s12E, s33E, and s55E exhibited abnormal variations seen as broad peaks over parts of the tested temperature range. Additionally, thermal hystereses were observed in all the studied material ...

Disperse and disordered: a mexylaminotriazine-substituted azobenzene derivative with superior glass and surface relief grating formation

Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.

Surface relief grating growth in thin films of mexylaminotriazine-functionalized glass-forming azobenzene derivatives

Azobenzene-containing materials exhibit various photomechanical properties, including the formation of surface relief gratings (SRG) when irradiated with two interfering laser beams. In a recent study, a novel glass-forming derivative of Disperse Red 1 (DR1) with a mexylaminotriazine group was synthesized in high yield with a simple and efficient procedure, and showed the ability to form high-quality amorphous thin films with a high resistance to crystallization. Irradiation of films of this material yielded SRG with growth rates comparable to other reported azo materials. Herein, a series of closely related molecular glasses containing azobenzene chromophores with various absorption maxima ranging from 410 to 570 nm were synthesized, and their physical and photomechanical properties were studied. All materials studied showed the ability to form stable glassy phases, and irradiation with lasers emitting at various wavelengths allowed to perform a comparative study of SRG growth within a series of analogous chromophores.

Quasistatic dielectric and strain characterization of transparent relaxor ferroelectric lead lanthanum zirconate titanate ceramics

The relative permittivity and dielectric loss tangent of transparent lead lanthanum zirconate titanate (PLZT) (9.5/65/35) and (9.0/65/35) ceramics were measured as a function of temperature, ranging from −60 to 100 °C, and as a function of frequency, ranging from 0.12 to 5000 kHz. Diffuse maxima were observed in the complex permittivity plots of both PLZT compositions. These maxima correspond to phase transitions from ferroelectric to paraelectric and finally to cubic in the PLZT crystal structure. Second, a Sawyer–Tower circuit was used to determine the electric displacement of each ceramic composition as a function of a dc bias field, ranging from −1.7 to 1.7 MV/m. Third, a Polytech vibrometer was used to measure the longitudinal ac strain response of (9.5/65/35) and (9.0/65/35) PLZT ceramics under various dc bias and ac electric fields with a 120 Hz driving frequency. A maximum piezoelectric strain of 0.8×10−3 m/m occurred for a 0.64 mm thick (9.5/65/35) PLZT at 1.1 MV/m dc and 1.09 MV/m ac peak to pea...

Surface Plasmon-Induced Band Gap in the Photocurrent Response of Organic Solar Cells

A 260 nm layer of organic bulk heterojunction blend of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene [6,6]-phenyl C61-butyric (PCBM) was spin-coated in between aluminum and gold electrodes, respectively, on top of a laser inscribed azo polymer surface-relief diffraction grating. Angle-dependent surface plasmons (SPs) with a large band gap were observed in the normalized photocurrent by the P3HT-PCBM layer as a function of wavelength. The SP-induced photocurrents were also investigated as a function of the grating depth and spacing.

Superimposed surface-relief diffraction grating holographic lenses on azo-polymer films

Various superimposed chirped relief gratings, acting as diffracting holographic lenses, were photo-inscribed on azo-polymer films upon exposure to the interference pattern of a plane and a curved laser light wavefronts. Depending on the configuration used, this resulted in incident light being focused independently of polarization along the 0th or 1st diffracted order of the grating. The focal point and focalization angle of the resulting holographic lenses were easily tuned during the fabrication process. Furthermore, a dual-focus chirped holographic lens grating was fabricated and shown to exhibit a far-field interference pattern.

Supramolecular Complexes of Multivalent Cholesterol‐Containing Polymers to Solubilize Carbon Nanotubes in Apolar Organic Solvents

Copolymers of 2-ethylhexyl acrylate (EHA) and cholesteryloxycarbonyl-2-hydroxymethacrylate (CEM) were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Supramolecular complexes of these copolymers with carbon nanotubes (CNTs) were soluble in THF, toluene, and isooctane. The colloidal solutions remained stable for months without aggregation. The rationale for the choice of CEM was based on the high adsorption energy of cholesterol on the CNT surface, as computed by DFT calculations. Adsorption isotherms were experimentally measured for copolymers of various architectures (statistical, diblock, and star copolymers), thereby demonstrating that 2-5 cholesterol groups were adsorbed per polymer chain. Once the supramolecular complex had dried, the CNTs could be easily resolubilized in isooctane without the need for high-power sonication and in the absence of added polymer. Analysis by atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated that the CNTs were devoid of bundles. The supramolecular complexes could also be employed in an inverse emulsion polymerization of 2-hydroxyethylmethacrylate (HEMA) in isooctane and dodecane, thereby leading to the formation of a continuous polymeric sheath around the CNTs. Thus, this technique leads to the formation of very stable dispersions in non-polar organic solvents, without altering the fundamental properties of the CNTs.

Photoactive/Passive Molecular Glass Blends: An Efficient Strategy to Optimize Azomaterials for Surface Relief Grating Inscription

Irradiation of azomaterials causes various photophysical and photomechanical effects that can be exploited for the preparation of functional materials such as surface relief gratings (SRGs). Herein, we develop and apply an efficient strategy to optimize the SRG inscription process by decoupling, for the first time, the important effects of the azo content and glass transition temperature (Tg). We prepare blends of a photoactive molecular glass functionalized with the azo Disperse Red 1 (gDR1) with a series of analogous photopassive molecular glasses. Blends with 10 and 40 mol % of gDR1 are completely miscible, present very similar optical properties, and cover a wide range of Tg from below to well above ambient temperature. SRG inscription experiments show that the diffraction efficiency (DE), residual DE, and initial inscription rate reach a maximum when Tg is 25-40 °C above ambient temperature for low to high azo content, respectively. Indeed, for a fixed 40 mol % azo content, choosing the optimal Tg enables doubling the SRG inscription rate and increasing DE 6-fold. Moreover, a higher azo content enables higher DE for a similar Tg. Spectroscopy measurements indicate that the photo-orientation of DR1 and its thermal stability are maximal with Tg around 70 °C, independent of the azo content. We conclude that the SRG potential of azomaterials depends on their capability to photo-orient but that the matrix rigidity eventually limits the inscription kinetics, leading to an optimal Tg that depends on the azo content. This study exposes clear material design guidelines to optimize the SRG inscription process and the photoactivity of azomaterials.

Temperature dependence of the dielectric, elastic and piezoelectric material constants of lead zirconate titanate (PZT) ceramics

Resonance methods were used to determine the variation of several piezoelectric, elastic and dielectric constants, as well as the corresponding electromechanical coupling factors of soft and hard doped Pb(ZrxTi1-x)O3 (PZT) ceramics, with compositions near the morphotropic phase boundary (MPB), as a function of temperature ranging from −165 °C to 195 °C. The material constants were obtained by analyzing the fundamental resonance of the impedance or admittance spectra as a function of frequency for several sample resonance geometries. The piezoelectric constants d33 and −d31, as well as the dielectric constants εT33, generally increased with temperature for both soft and hard PZT samples. However, the elastic constants sE11 and -sE12 exhibited abnormal variations seen as broad peaks over parts of the tested temperature range. Furthermore, thermal hystereses were observed in all the studied material constants during the heating and cooling cycles. Finally, it was noted that, overall, the material constants of soft PZT varied significantly more than those of hard PZT under changing temperature conditions.

Erasure of surface relief gratings in azobenzene molecular glasses by localized heating using a CO2 laser

A thermo-optical process was developed for the erasure of surface relief gratings (SRG) inscribed on various films of mexylaminotriazine molecular glasses functionalized with different azobenzene chromophores, as well as azobenzene polymer films. Irradiation of the samples with a CO2 laser beam causes localized heating of the soda lime substrate, which is then transferred to the azobenzene films, causing complete erasure of the gratings while the temperature of each film was monitored in real time. The erasure temperature has been found to be strongly correlated with the respective glass transition temperature (Tg) of the materials. Therefore, complete and partial all-optical erasure of gratings was successfully demonstrated and occurred in under a minute for azobenzene molecular glass films and under 3 minutes for azo-polymer films. Finally, gratings were shown to erase in specific patterns through the use of a metallic mask.