2010
DOI: 10.1103/physreve.82.031804
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Slow dynamics in an azopolymer molecular layer studied by x-ray photon correlation spectroscopy

Abstract: 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… Show more

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Cited by 29 publications
(34 citation statements)
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References 48 publications
(76 reference statements)
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“…The dynamic shear modulus |G| shows a reversible switching from the more fluid cis-PA4 film, reached under UV illu mination, to the trans-PA4 film induced by blue light. This change in shear modulus is in qualitative agreement with the evolution of XPCS relaxation times in PA4 films as reported in [23]. In the same paper we also analysed the out of equilibrium d ynamics finding quantitative agreement on the time scales needed for the system to reach equilibrium after photoperturbation, which incidentally agree also with the time scale needed for molecular reorganization as probed by pump-probe photoinduced birefringence measurements [19].…”
Section: Figure 4 Left: Compression Isotherms Of Pa4 At T=19°c In Dasupporting
confidence: 86%
“…The dynamic shear modulus |G| shows a reversible switching from the more fluid cis-PA4 film, reached under UV illu mination, to the trans-PA4 film induced by blue light. This change in shear modulus is in qualitative agreement with the evolution of XPCS relaxation times in PA4 films as reported in [23]. In the same paper we also analysed the out of equilibrium d ynamics finding quantitative agreement on the time scales needed for the system to reach equilibrium after photoperturbation, which incidentally agree also with the time scale needed for molecular reorganization as probed by pump-probe photoinduced birefringence measurements [19].…”
Section: Figure 4 Left: Compression Isotherms Of Pa4 At T=19°c In Dasupporting
confidence: 86%
“…A priori, the combination of the results of such measurements to yield a comprehensive picture is complicated by the different space scales involved, spanning from the centimeter scale for the ISR down to fractions of a micron in the case of XPCS. However, in most cases, those macroscopic and microscopic quantities have been found to agree, as, e.g., in floating polymeric layers [17,26]. A counterexample of this is found even in simple phospholipid monolayers; their macroscopically liquid and mainly viscous phase may exhibit a complex and mainly elastic response when probed on the micron scale [28].…”
Section: Introductionmentioning
confidence: 93%
“…In the former case, a deformation is applied from outside, as in the oscillating barriers technique [23] and in interfacial shear rheology (ISR), in which a magnetized needle is used to induce shear deformation [24,25]. In the latter case, mechanical properties are deduced from the spontaneous fluctuations recorded, e.g., by dynamic light scattering or by XPCS experiments [17,26,27]. A priori, the combination of the results of such measurements to yield a comprehensive picture is complicated by the different space scales involved, spanning from the centimeter scale for the ISR down to fractions of a micron in the case of XPCS.…”
Section: Introductionmentioning
confidence: 99%
“…Indeed, characteristics of the glass-transition physics like cooperative motions called dynamic heterogeneities were reported to be generated during the motion of various motors [38][39][40][41][42]. The photo-fluidization and softening of the host material, or transient liquid-like behaviors, were also reported by different groups experimentally and by simulations [38,[43][44][45][46] with particular motors.…”
Section: Introductionmentioning
confidence: 88%