Regulating the modulus of a chiral liquid crystal polymer network by light

Kumar, Kamlesh; Schenning, Albertus P. H. J.; Broer, Dirk J.; Liu, Danqing

doi:10.1039/c6sm00114a

Cited by 70 publications

(77 citation statements)

References 35 publications

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“…The onset of fluidization is consistent with previous reports on UV-induced amorphization of azobenzene-based polymer films17, and softening in pure crystals of azobenzene molecules1041424344 and azobenzene-doped elastomers283145, which has been attributed to the higher free volume requirements of the cis bent conformation compared with the trans isomer2746. We therefore postulate that blue light-induced fluidization facilitates the co-alignment of kinetically-trapped, randomly arranged mesostructured domains in the trans -azoTAB:PAA particles such that the irregular particles of trans -azoTAB:PAA are reconfigured into hexagonal platelets with well-defined low energy faces.…”

Section: Discussionsupporting

confidence: 91%

“…Long-distance mass transport is usually inhibited in these systems because of immobilization of the azobenzene molecules into crystalline arrays or via covalent attachment to crosslinked polymer chains31, which in turn limit the extent of light-induced shape transformations. In contrast, the bottom-up assembly of photoactive materials based on non-covalent bonding between linear polymers and mesogens293233 could be advantageous for photo-induced long-range molecular motion due to the weaker bonding interactions.…”

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confidence: 99%

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Light-induced dynamic shaping and self-division of multipodal polyelectrolyte-surfactant microarchitectures via azobenzene photomechanics

Martin

Sharma

Harniman

et al. 2017

Sci Rep

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Light-induced shape transformations represent a fundamental step towards the emergence of adaptive materials exhibiting photomechanical behaviours. Although a range of covalent azobenzene-based photoactive materials has been demonstrated, the use of dynamic photoisomerization in mesostructured soft solids involving non-covalent co-assembly has received little attention. Here we prepare discrete micrometre-sized hydrated particles of a hexagonally ordered polyelectrolyte-surfactant mesophase based on the electrostatically induced co-assembly of poly(sodium acrylate) (PAA) and trans-azobenzene trimethylammonium bromide (trans-azoTAB), and demonstrate unusual non-equilibrium substrate-mediated shape transformations to complex multipodal microarchitectures under continuous blue light. The microparticles spontaneously sequester molecular dyes, functional enzymes and oligonucleotides, and undergo self-division when transformed to the cis state under UV irradiation. Our results illustrate that weak bonding interactions in polyelectrolyte-azobenzene surfactant mesophases can be exploited for photo-induced long-range molecular motion, and highlight how dynamic shape transformations and autonomous division can be activated by spatially confining azobenzene photomechanics in condensed microparticulate materials.

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Section: Discussionsupporting

confidence: 91%

mentioning

confidence: 99%

Light-induced dynamic shaping and self-division of multipodal polyelectrolyte-surfactant microarchitectures via azobenzene photomechanics

Martin

Sharma

Harniman

et al. 2017

Sci Rep

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“…For linear azo polymers, multiple mechanisms have been proposed [41]. Whereas with the azo polymer networks (azo-LCN), free volume generation in a glassy material seems to fit most of experimental data, this solution comes under question in light of the recent findings showing that also mechanical properties of the polymer network change upon illumination [110]. Recent research also shows an influence of temperature upon irradiation.…”

Section: Discussionmentioning

confidence: 82%

“…Recent research also shows an influence of temperature upon irradiation. This leads to photothermal effects described as photo-softening [42,[110][111][112]. A full understanding of the driving mechanism in the creation of surface structures in azo polymers is sought to improve or fabricate new surface topography changing coatings.…”

Section: Discussionmentioning

confidence: 99%

Light-Triggered Formation of Surface Topographies in Azo Polymers

et al. 2017

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Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the surface topography is controllable by light. The topographies form without the use of a solvent, and can be designed to remain static or have dynamic properties, that is, be capable of reversibly switching between different states. The topographical changes can be induced by using linear azo polymers to produce surface-relief gratings. With the ability to address specific regions, interference patterns can imprint a variety of structures. These topographies can be used for nanopatterning, lithography or diffractive optics. For cross-linked polymer networks containing azobenzene moieties, the coatings can form topographies that disappear as soon as the light trigger is switched off. This allows the use of topography-forming coatings in a wide range of applications, ranging from optics to self-cleaning, robotics or haptics.

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“…For systems undergoing a considerable temperature increase under strong intensities [30,33], one needs to take the selfheating into account since the characteristic fall-back time of the cis azobenzene, τ, decreases with temperature, leading to reduced light parameters α and β [see Eq. (4)], and thus affects the light attenuation and the constants in Eq.…”

Section: Prl 119 057801 (2017) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 99%

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

Liu

Onck

2017

Phys. Rev. Lett.

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Azobenzene-embedded liquid crystal polymers can undergo mechanical deformation in response to ultraviolet (UV) light. The natural rodlike trans state azobenzene absorbs UV light and isomerizes to a bentlike cis state, which disturbs the order of the polymer network, leading to an anisotropic deformation. The current consensus is that the magnitude of the photoinduced deformation is related to the statistical building up of molecules in the cis state. However, a recent experimental study [Liu and Broer, Nat. Commun. 6 8334 (2015).] shows that a drastic (fourfold) increase of the photoinduced deformation can be generated by exposing the samples simultaneously to 365 nm (UV) and 455 nm (visible) light. To elucidate the physical mechanism that drives this increase, we develop a two-light attenuation model and an optomechanical constitutive relation that not only accounts for the statistical accumulation of cis azobenzenes, but also for the dynamic trans-cis-trans oscillatory isomerization process. Our experimentally calibrated model predicts that the optimal single-wavelength exposure is 395 nm light, a pronounced shift towards the visible spectrum. In addition, we identify a range of optimal combinations of twowavelength lights that generate a favorable response for a given amount of injected energy. Our model provides mechanistic insight into the different (multi)wavelength exposures used in experiments and, at the same time, opens new avenues towards enhanced, multiwavelength optomechanical behavior.

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Regulating the modulus of a chiral liquid crystal polymer network by light

Abstract: We provide a methodology to change the state of matter from hard and glassy to soft and rubbery by light.

Cited by 70 publications

References 35 publications

Light-induced dynamic shaping and self-division of multipodal polyelectrolyte-surfactant microarchitectures via azobenzene photomechanics

Light-induced dynamic shaping and self-division of multipodal polyelectrolyte-surfactant microarchitectures via azobenzene photomechanics

Light-Triggered Formation of Surface Topographies in Azo Polymers

Enhanced Deformation of Azobenzene-Modified Liquid Crystal Polymers under Dual Wavelength Exposure: A Photophysical Model

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