Microscopic transport properties in liquid crystalline polymeric matrices: dependence on the thermal history

Andreozzi, Laura; Fontana, M. P.; Francia, Francesco; Giordano, Marco; Leporini, Dino; Rateo, M.

doi:10.1016/0022-3093(94)90603-3

Cited by 10 publications

(8 citation statements)

References 15 publications

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“…In polyacrylates and poly-methacrylates the pumping of the photo-isomerization transition yields several potentially useful optical effects with very high sensitivity [6][7][8]. The vibrational and diffusive dynamics can be altered by the optical pump [9,10] and the phenomenology of the glass transition has been extensively studied by calorimetric, dynamical analysis and ESR relaxation measurements [11]. Extensive photo-mechanical effects have also been observed in azopolymers, including photo induced expansion and a change in the viscoelastic properties [12].…”

Section: Introductionmentioning

confidence: 99%

Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy

et al. 2010

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We report the results of X-ray photon correlation spectroscopy (XPCS) experiments on Langmuir Blodgett multilayers of a photosensitive azo-polymer. Time correlation functions have been measured at different temperatures and momentum transfers (q) and under different illumination conditions (darkness, UV or visible). The correlation functions are well described by the Kohlrausch-Williams-Watts (KWW) form with relaxation times that are proportional to q -1 , which in other systems have been explained in terms of intermittent rearrangements [L. Cipelletti et al., Phys. Rev. Lett. 84, 2275-2278] or random dipolar interactions within an elastic medium [J.-P. Bouchaud and E. Pitard, Eur. Phys. J. E 6, 231-236 (2001)]. The characteristic relaxation times follow the well known Vogel-Fulcher-Tammann law describing the temperature dependence of the bulk viscosity of this polymer. UV photoperturbation accelerates the relaxation dynamics, in qualitative agreement with the fluidification effect of UV photo-perturbation previously observed by surface rheometry, and is used to drive the system out of equilibrium. Transient dynamics is characterized, by the variance  of the two-times correlation functions. A clear peak in  appears at a well defined time  C which scales with q -1 and with the ageing time, in a similar fashion as previously reported in colloidal suspensions [O. Dauchot et al., Phys. Rev. Lett. 95, 265701 (2005)]. From an accurate analysis of the correlation functions we could demonstrate a temperature dependent cross-over from KWW compressed to simple exponential behaviour, which is modified by the fluidification due to the optical pumping of the cis-trans isomerisation of the side-chain azobenzene group.

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Section: Introductionmentioning

confidence: 99%

Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy

et al. 2010

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“…• C [7]. Thin layers of this material were prepared by cast solution in chloroform, for thicknesses of 1-5 µm, or by Langmuir-Blodgett deposition, for thicknesses of up to 0.4 µm.…”

Section: Experimental Techniquesmentioning

confidence: 99%

Molecular relaxation in a photosensitive liquid-crystalline polymeric glass former

Cristofolini

Facci

Camorani

et al. 1999

J. Phys.: Condens. Matter

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Abstract. We have measured the relaxation to equilibrium in the supercooled nematic phase upon approach to T g of a fragile liquid-crystalline photosensitive polymeric glass former. Perturbation is introduced in a non-conventional way by optical pumping (orientation) of the nematic polydomain phase. Relaxation back to equilibrium is followed both on the microscopic scale, by means of depolarized time-resolved Raman experiments, and on the macroscopic scale, by means of quartz crystal microgravimetry.

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“…3 we compare the results concerning z,, as drawn from both ESR and NLESR, for PAl annealed 10 days at T = T~ + 5 K. Experimental evidence shows that the spin probes are confined in the residual amorphous fraction of the semi-crystalline PAl [7]. We note i) NLESR provides in the range 10-9-10 -1~ s data on z, of higher quality than ESR does around 10-7s.…”

Section: If F(t)~-exp[-t/~] Then Resr~r Nlesr Instead If F(t) Has mentioning

confidence: 90%

“…The samples were preliminarly heated above the isotropization temperature for 10 hours and then quenched to below the glass transition temperature. To start crystallization, samples were annealed at T = Tg + 5 K. Further details may be found elsewhere [7]. ESR measurements were carried out by using a Bruker spectrometer E R200D equipped with an X band bridge supplying at 0 dB 200mW, a NMR gaussmeter ER035M and gas flow variable temperature unit.…”

Section: If F(t)~-exp[-t/~] Then Resr~r Nlesr Instead If F(t) Has mentioning

confidence: 99%

“…This case is of some interest in that it is known that the spin probe is confined in the residual amorphous part of the PLC [7], so that one can selectively characterize the constraints that the crystalline fraction exerts on the amorphous one. The Electron Spin Resonance spectroscopy has been extensively used for a long time to study the orientation dynamics of guest paramagnetic molecules dissolved in low molar mass fluids [6].…”

Section: -Introductionmentioning

confidence: 98%

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A linear and non-linear electron spin resonance study of orientational relaxation in semi-crystalline polymeric liquid crystals

1994

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(ricevuto il 28 Ottobre 1994)Summary. --Linear and non-linear Electron Spin Resonance spectroscopies have been designed to study the decay of the orientation correlations on different time scales. The reorientation of radicals (,,spin probes,O dissolved in host phases (in the present case a polymeric liquid crystal (PLC)) may be investigated in the time window 10 -11-10 -5 s. Evidence of the non-exponential regression of fluctuations is given. The temperature dependence of the correlation time of the spin probe orientation is discussed in the case of semi-crystalline PLCs and contrasted with the case of amorphous PLCs.

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Microscopic transport properties in liquid crystalline polymeric matrices: dependence on the thermal history

Cited by 10 publications

References 15 publications

Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy

Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy

Molecular relaxation in a photosensitive liquid-crystalline polymeric glass former

A linear and non-linear electron spin resonance study of orientational relaxation in semi-crystalline polymeric liquid crystals

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