Photochromic liquid-crystalline polymers. Main chain and side chain polymers containing azobenzene mesogens

Angeloni, A. S.; Caretti, Daniele; Carlini, Carlo; Chiellini, Emo; Galli, Giancarlo; Altomare, Angelina; Solaro, Roberto; Laus, Michele

doi:10.1080/02678298908033186

Cited by 151 publications

(83 citation statements)

References 32 publications

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“…The photosensitive polymer employed in this study is poly[[4-pentiloxy-3'-methyl-4'-(6-acryloxyexyloxy)] azobenzene] (denoted PA4 in the following) which has a glass phase with T g = 20°C and a nematic phase with clearing point T NI =92°C [14]. Multilayers of PA4 were prepared by the Langmuir Schaeffer (LS) technique.…”

Section: Samplementioning

confidence: 99%

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

Orsi

Cristofolini

Fontana

et al. 2011

Philosophical Magazine

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Section: Samplementioning

confidence: 99%

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

Orsi

Cristofolini

Fontana

et al. 2011

Philosophical Magazine

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“…The calibrated Rheometer was then employed to perform measurements on a particular polymerpoly[[4-pentiloxy-3'-methyl-4'-(6-acryloxyexylo xy)] azobenzene] henceforth called PA4, which has bulk Tg = 20°C and a nematic phase with clearing point T NI =92°C [18], Mw=19000 and whose optical properties are shown in the right panel of figure 4: the trans isomer is characterized by a strong absorption peak at wavelength 360n m, while the cis isomer has little absorption at this wavelength. This material has been already investigated by us both in bulk [19][20][21] and as molecular layers [5,22].…”

Section: Rheological Characterization Of a Photosensitive Azopolymermentioning

confidence: 99%

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Orsi

Cristofolini

Fontana

2011

Journal of Non-Crystalline Solids

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Abstract:We report the details of the construction and calibration of an ultra sensitive surface rheometer, inspired by the setup described in [C.F. Brooks et al Langmuir 15, 2450], which makes use of high resolution video tracking of the motion of a floating magnetized needle and is capable of measuring the viscoelastic response of a Langmuir monolayer with an accuracy of 10 -5 N/m. This instrument is then employed for the rheological characterization of a Langmuir monolayer of a photosensitive azobenzene polymer, which can be brought out of equilibrium by a suitable photoperturbation. The complex dynamic shear modulus G= G' + i G" is measured as a function of temperature and illumination power and wavelength. The reversible rheological ch anges induced in the film by photo-perturbation are monitored during time, observing a transition from a predominantly elastic (G' > G'') to a viscoelastic (G' ≈ G'') regime. These results are confirmed by comparison with independent measurements performed by us using other rheological techniques. Finally a discussion is made, taking into account the results of a recent x-ray photon correlation spectroscopy experiment on the same polymer in equilibrium and out of equilibrium.

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“…The measurements were performed as a function of temperature, energy dose, pump power and polarization, time. The sample we have studied is PMA4, the synthesis and calorimetric properties of which are published elsewhere [7]. The formula is shown in fig.1.…”

Section: Introductionmentioning

confidence: 99%

Photoinduced Morphological Changes and Optical Writing in a Liquid Crystalline Polymer on the Micron and Sub-Micron Scale

Camorani

Cristofolini

Galli

et al. 2002

GMCL

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In this paper we describe our recent work on optical effects due to photoinduced molecular reorientation in a side chain liquid crystalline polymer, namely azopolymethacrylate (PMA4). We have studied several kinds of optical effects on space scales ranging from the nanoscopic to macroscopic. In particular, we have built a computer controlled microscope-based apparatus to study photoinduced effects down to the micron scale in thin and ultrathin (Langmuir Blodgett) films of our material. Furthermore we measured the morphology and the photoinduced surface deformation by Atomic Force Microscopy in the submicron scale. INTRODUCTIONSide chain liquid crystalline polymers (LCP) based on the presence in the side chain of the azobenzene moiety have been the subject of intense study in recent years [1]. Of particular interest have been the optical effects due to the photoinduced cis-trans isomerization of the azobenzene. These effects have been studied due to their potential for optical writing applications and more specifically for entirely-optical high-density memories [2]. This class of materials features a rich and complex phenomenology, which makes them very interesting also from a fundamental point of view. Their dynamics is the result of the complex interplay between several types of interactions and processes: the mesogenic potential, the conformational main chain transitions, the glass transition, the molecular trans-cis isomerization [3]. The relative weight of such processes, and the coupling between side chain and main chain dynamics, depend of course not only on temperature, but it can be also externally influenced by optical pumping with light of the appropriate wavelength, polarization and intensity [4]. Moreover, when dealing with ultrathin films, coupling interactions between substrate (imposing a planar ordering to the polymeric main chain) and PLC become relevant. This gives rise-via a purely geometric effect-to an increased stability of the glassy phase upon heating [5], and correspondingly to an increase of the typical times characterising the back-to-equilibrium relaxation process This is of relevance also for the stability of the information optically written onto such thin films of azo-polymer. The combined action of the cis-trans photoisomerization and the nematic potential lead to collective molecular reorientation, hence to very high sensitivity of the sample to the optical writing beam. However it is not clear-and the subject of current investigationhow the nematic potential determines the collective character (and hence the length scale) of the molecular reorientation, on which the minimum addressable area depends, and hence the maximum information density possibly stored per surface unit. Although the basic microscopic mechanism for the production of optically oriented molecular

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Photochromic liquid-crystalline polymers. Main chain and side chain polymers containing azobenzene mesogens

Cited by 151 publications

References 32 publications

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

Microscopic dynamics in nanocomposite photosensitive films studied by X-ray photon correlation spectroscopy

Equilibrium and out-of-equilibrium dynamics in a molecular layer of azopolymer floating on water studied by Interfacial Shear Rheology

Photoinduced Morphological Changes and Optical Writing in a Liquid Crystalline Polymer on the Micron and Sub-Micron Scale

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