Marco Giordano

Near-field optical writing on azo-polymethacrylate spin-coated films

We report on near-field optical writing and topographic reading of spin-coated azo-polymethacrylate films with subwavelength resolution. The sample is functionalized with photosensitive side chain azobenzene groups. These photochromes are locally illuminated at 325 and 488 nm through the aperture of a metalized tapered optical fiber. The printing on subwavelength scale is due to optically induced cooperative rearranging of the polymeric chain. It is read in situ in the surface topography imaged by shear-force microscopy. The stability of the optically produced pattern and the cycling characteristics of the photoisomerization of the azobenzene molecules make these samples suitable for optical nanolithography and high density optical data storage.

Optical nanowriting on azobenzene side-chain polymethacrylate thin films by near-field scanning optical microscopy

Optical writing and subsequent reading of information on thin films of azobenzene side-chain polymethacrylates on the 100-nm scale are demonstrated by near-field scanning optical microscopy (NSOM) with polarization control. Polarized blue light at 488 nm coupled to the NSOM aperture probe activates trans–cis–trans isomerization cycles of the side chains, causing their alignment and thus locally inducing optical birefringence. Red light at 690 nm with modulated polarization is coupled to the same aperture and used to detect optical anisotropy on the local scale. Lines of width on the 100-nm scale were optically inscribed and detected even with no concurrent topographic modification.

A generalization of mori's approach to the non-hermitean case: a new versatile theoretical tool for computational purposes

Abstract A suitable generalization of Moris approach allows us to build up a fast algorithm for evaluating slow-motion spectra It is then shown that this method permits an accurate evaluation of the spectroscopic effects of molecular inertia.

Scaling between the rotational diffusion of tracers and the relaxation of polymers and glass formers

The rotational dynamics of subnanometric molecular tracers in glass formers with low molecular weight and polymers is discussed by presenting electron spin-resonance and time-resolved fluorescence studies. It is shown that the reorientation of the tracer is fully or partially coupled to the host relaxation processes. The degree of coupling is well described by the fractional scaling between the correlation time of the tracer and the host timescales . The crossovers between the different regimes are sharp. Remarkably, one crossover occurs systematically very close to the splitting point of the dielectric relaxation or the critical temperature predicted by the mode-coupling theory of the glass transition.Abstract:Conservation equations are written for surface flows (either fluid or granular). The particularity of granular surface flows is then pointed out, namely that the depth of the flowing layer is not a priori fixed, leading to open equations. It is shown how some hypothesis on the flowing layer allows to close the system of equations. A possible hypothesis, similar to that made for a fluid layer, but inspired from granular flow experiments, is presented. The force acting on the flowing layer is discussed. Averaging over the flowing depth, as in shallow water theory, then allows to transform these conservation laws into equations for the evolution of the profile of a granular pile. Apart from their interest for building models, these conservation laws can be used to measure experimentally the effective forces acting on a flowing layer.

Linear and non-linear electron spin resonance study of the rotational diffusion of a molecular tracer in supercooled o-terphenyl

The long-time and the short-time rotational relaxation of a molecular tracer in supercooled o-terphenyl (OTP) have been studied by linear and non linear electron spin resonance (ESR) spectroscopy, respectively. At higher temperatures the related correlation times. τ 1 and τ s , are equal within the experimental errors, i.e. the relaxation is exponential, and well coupled to the viscosity. η. On cooling. τ s , and, at lower temperatures, τ 1 , are partially coupled to thc viscosity in agreement with the fractional Debye-Stokes-Einstein (DSE) law τ i α (η/T), i = 1. s with ξ i constant. For T < 330 K the rotational correlation function is not exponential.

Efficient characterization of the orientational ordering of ESR-active probes in supermolecular fluids

Supermolecular fluids often exhibit organized arrangements which order the orientations of solved ESR-active probe molecules. Due to the high microviscosity, the ESR line-shape of the probe virtually reflects the distribution of the resonating frequencies of the involved spin packets and then the degree of orientational order of the probe. An efficient strategy to get precise estimates of both the magnetic parameters of the probe molecule and the width of the spin packet from the ESR spectrum has been developed. This allows us to adjust only the strength of the effective orienting potential in the fit procedure. A study of the orientational ordering of cholestane probe molecule dissolved in side-chain polymeric mesophases provides accurate testing of the procedure.

A study of the Debye-Stokes-Einstein law in supercooled fluids

The reorientation of a nearly spherical paramagnetic tracer dissolved in supercooled o-terphenyl is studied by electron spin resonance in the range 200 K 300 K the rotational correlation time follows the Debye - Stokes - Einstein law. On decreasing the temperature, the rotational motion of the probe and the viscosity decouple. In particular, in the region around T = 290 K it is found that with .

Longitudinally detected electron spin resonance: Recent developments

Multiple-quantum spectroscopies are reviewed in the frame of electron paramagnetic resonance. Some properties of different nonlinear techniques are discussed for both transverse and longitudinal detection. The connections of effects recently presented with the procedure of longitudinal detection of electron paramagnetic resonance (LODESR) in presence of double transverse irradiation are stressed. Peculiarities of LODESR spectroscopy and its capabilities in facing problems related to relaxations in presence of very slow dynamic processes are evidentiated. Recent results show the vitality of the LODESR technique, that in the future could be applied to new fields, owing to experimental updating.

Rotational probe relaxation and scaling in fragile glass formers

Abstract The rotational dynamics of a stiff paramagnetic tracer dissolved in supercooled SALOL is investigated via electron spin resonance spectroscopy. The study shows that the molecular rotation follows different dynamical regimes as the temperature is lowered. In particular, on cooling through the critical temperature TC of the SALOL, the coupling between rotational relaxation and viscosity weakens and enhanced rotational diffusion is observed. In this temperature interval, the relationship between rotational correlation times and viscosity is fairly well described by a power law τ∝ηξ (Fractional Debye–Stokes–Einstein law). Activated reorientation is observed in the temperature region around the glass transition of the SALOL. The rotational dynamics of the tracer dissolved in SALOL are compared with its rotation in ortotherphenyl (OTP) investigated in previous studies, and a scaling procedure is proposed.

Structure and transport properties in organized polymeric materials

Synthesis of polymeric liquid crystals and blends electron spin resonance in polymeric liquid crystals nonlinear electron spin resonance in polymeric liquid crystals viscoelastic properties in polymeric liquid crystals collective and nuclear spin relaxation NMR studies of polymeric liquid crystals with different molecular architecture fluorescence polarization in oriented polymers infrared and Raman spectroscopy in polymeric liquid crystals liquid-crystalline polymers for electro-optical applications synthesis of electroconducting polymers structure and properties of electroconducting polymers dielectric relaxation in polymers mechanical properties in main chain polymers.