Light-induced deformation of polymer networks containing azobenzene chromophores and liquid crystalline mesogens

Petrova, T. O.; Toshchevikov, Vladimir; Saphiannikova, Marina

doi:10.1039/c5sm00019j

Cited by 21 publications

(22 citation statements)

References 60 publications

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“…We have also excluded the possible influence of reduction of scalar order parameter of LC polymers upon UV exposure since similar deformations of microparticles are produced by visible light generating little amount of Z ‐azobenzenes (Figure S1, Supporting Information). On the contrary, the experimental data agrees with the building up high local mechanical stresses in azo‐polymer upon polarized light illumination which was theoretically predicted by Saphiannikova and co‐workers and experimentally demonstrated by Santer and co‐workers . The concept assumes that the (re)orientation of azobenzene fragments perpendicularly to light polarization leads to the reorientation of polymer backbone due to its strong coupling with side‐groups which causes the buildup an anisotropic internal stress .…”

Section: Resultssupporting

confidence: 84%

“…On the contrary, the experimental data agrees with the building up high local mechanical stresses in azo‐polymer upon polarized light illumination which was theoretically predicted by Saphiannikova and co‐workers and experimentally demonstrated by Santer and co‐workers . The concept assumes that the (re)orientation of azobenzene fragments perpendicularly to light polarization leads to the reorientation of polymer backbone due to its strong coupling with side‐groups which causes the buildup an anisotropic internal stress . As a result the elongation of polymer chains occurs along light polarization and further leads to material deformation.…”

Section: Resultssupporting

confidence: 84%

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Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Ryabchun

Bobrovsky

2019

Advanced Optical Materials

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into mechanical motion or work, such as photoactuation. [1][2][3][4][5] The funda mental importance of these phenomena occurring under the action of light, such as photofluidization, [6][7][8][9][10][11] photoimmo bilization, [6,12,13] formation of surface relief gratings, [14][15][16][17] and other complex 3D structures [10,[18][19][20][21][22][23][24] can help to develop photo responsive materials for versatile applications and will also improve and extend our knowledge in soft matter.The most extensively studied photo active materials usually contain azoben zene moieties as the lightresponsive unit. The properties of azobenzene such as high quantum yield and reversibility of E-Z photoisomerization, high fatigue resis tance, and large changes in molecular shape and dipole moment upon isomerization make it uniquely suitable as an active unit. Molecular shape changes of azobenzene can be harnessed on a macroscopic level by the embedding active molecules into hierarchically organized matter [25] and by confinement of the photoactive material in space, such as, spherical colloids which can selfassemble into 2D and 3D structures (photonic crys tals). The preparation and study of spherical micrometersized particles based on azobenzene polymers have been reported in a number of recent works revealing the importance for various optical microdevices, photonics, microfluidics, etc. [26][27][28][29][30][31][32][33][34][35][36][37][38] It has been demonstrated that polarized light irradiation results in elongation of these particles along the light polarization. Despite the interest to the research area, several issues like the mechanism and reversibility of microscopic shape changes are still elusive. Moreover, there are no reports on the influence of liquid crystal line (LC) ordering on the shapeshifting and optical properties of the particles, as well as the operation of microparticles has never been exploited to build materials with macroscopic functionalities.In the current work, we have developed a novel elastic composite material containing shapereconfigurable parti cles based on liquid crystalline polymer. We have used sty rene-ethylene-butylene-styrene triblock copolymer (SEBS, Figure 1a) as the elastic matrix which provides large deforma tion and low mechanical stiffness [39] and does not interfere to the deformation of embedded particles. Another important role of the matrix is its elasticity responsible for the compres sive forces experienced by the deformed particles which makes possible the shape to recover. The particles are made of liquid crystal copolymer PAAzo bearing mesogenic and azobenzene One of the key challenges of material science currently is the design of multifunctional "smart" materials combining features from both molecular and supramolecular levels. Pursuing the strategy of amplification and transduction of light-induced motion of small molecules (photoswitches) across increasing length scales to macroscopic level, a novel polymer composite based on shapereconfigurable microparticles is desig...

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Section: Resultssupporting

confidence: 84%

Section: Resultssupporting

confidence: 84%

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Ryabchun

Bobrovsky

2019

Advanced Optical Materials

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“…[36,37], where a light-induced transition from a uniaxial to the biaxial state has been predicted. The theory was then generalized for the case of a two-component polymer network containing both the azobenzenes and optically inert mesogens [38,39]. Application of the orientation potential to describe photomechanical properties of azobenzene-containing materials of different structures was discussed in detail in Ref.…”

Section: Introductionmentioning

confidence: 99%

“…The effects of bent cis-isomers were accounted for in the study [39], which allowed us to consider both the reorientation and dilution effects induced in the azobenzene LC elastomers by the polarized laser beam. The strength of each effect depends on the light wavelength and can be properly accounted for when the relative fractions of trans- and cis-isomers are known as a function of time at any wavelength in the absorption region of the azobenzenes.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of Ordering and Deformation in Photosensitive Azobenzene LC Networks

2018

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Azobenzene-containing polymer networks are unique compounds that are able to change their shape in response to light, which makes them prospective materials for photocontrollable nano-templates, sensors, microrobots, artificial muscles, etc. In present work, we study the kinetics of light-induced ordering and deformation in two-component polymer networks containing optically inert liquid crystalline (LC) mesogens and azobenzene chromophores. By this, we generalize our previous theory [J. Phys. Chem. Lett. 2017, 8, 1094–1098] devoted to the kinetics of photoizomerization in one-component azo-polymers without mesogenic inclusions. The kinetic equations of photoisomerization are used, taking into account the angular selectivity of the photoisomerization with respect to the polarization direction of the light E. After multiple trans-cis-trans photoisomerization cycles, the azobenzenes are reoriented preferably perpendicular to the vector E. This changes the ordering of the mesogens due to the orientational LC interactions between the components. The light-induced reordering is accompanied by network deformation. Time evolution of ordering and deformation is found as a function of the intensity of light and structural parameters of the LC azo-networks, which define the viscosity, the strength of the LC interactions between the components, the volume fraction of the azobenzene moieties, and the angular distribution of azobenzenes in polymer chains. Established structure-property relationships are in agreement with a number of experimental data.

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“…[a] Dr.J.M.I lnytskyi ogy, [18][19][20] but also the prediction of the number of new effects, such as appearance of biaxial order and biaxial deformation, in liquid crystals. [26,27] In spite of the clear success of the orientation approach, it is not obvious at all, whether the effective orientation potential is ag ood approximation of the complex stochastic switching between two isomerso fa zobenzene under polarized illumination. The first important question in this context is:C an the anisotropic stochastic photoisomerization process be reduced to any potentiala ta ll?T he second important question is: What is the role of the cis isomers in the reorientation process and whether they can be neglected at some illumination conditions?T his study aims to answer these two questions by comparing resultso fadirect simulation of the switching process under linearly polarized light with the resultso fa ni ndirect simulation based on the matching effective potential.…”

Section: Introductionmentioning

confidence: 99%

Reorientation Dynamics of Chromophores in Photosensitive Polymers by Means of Coarse‐Grained Modeling

Ilnytskyi

Saphiannikova

2015

ChemPhysChem

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We study the photoisomerization of azobenzene chromophores embedded into a polymer matrix by using coarse-grained simulations. Two types of beads are considered: t- and c-beads, which are rich in trans and cis isomers, respectively. Simulations combine deterministic (molecular dynamics) and stochastic (random-type switching) parts. The ratio between the characteristic times for photoinduced reorientation and for orientation relaxation is tuned to be of the order found in experiments. The essential features of the phenomenon: 1) the existence of a stationary state, and 2) anisotropic distribution of the orientations of t-beads (orientation hole-burning effect), are reproduced. We study population dynamics of c-beads and the strength of the orientation hole burning, depending on the illumination wavelength and its intensity. The form of the reorientation potential of the mean force acting on the t-beads is analyzed and its use is validated.

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Light-induced deformation of polymer networks containing azobenzene chromophores and liquid crystalline mesogens

Cited by 21 publications

References 60 publications

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Photocontrollable Deformations of Polymer Particles in Elastic Matrix

Kinetics of Ordering and Deformation in Photosensitive Azobenzene LC Networks

Reorientation Dynamics of Chromophores in Photosensitive Polymers by Means of Coarse‐Grained Modeling

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