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Photogated humidity-driven motility.

Zhang L, Liang H, Jacob J, Naumov P - Nat Commun (2015)

Bottom Line: Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light.A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min(-1).The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself.

View Article: PubMed Central - PubMed

Affiliation: New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.

ABSTRACT
Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day-night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min(-1). The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

No MeSH data available.


Related in: MedlinePlus

Mechanism of photogated humidity-driven actuation.(a) With intramolecular photogating of humidity-driven actuation, the units that respond to humidity and light are part of the same molecule. While action of stimulus 1 (exposure to humidity) alone induces bending, action of stimulus 2 (exposure to light) prevents the bending driven by stimulus 1. (b) With intermolecular photogating, such as that in PCAD@AG, the units that respond to humidity and light are different molecules coupled by intermolecular interactions. Action of stimulus 1 (humidity) induces bending. Action of stimulus 2 (light) prevents the bending by isomerization and decreases the affinity of AG for adsorption of water. Note that stimulus 1 also affects the hydrogen bonding network between PCAD and AG. (c) Mechanism of photogating of humidity-induced motility. The trans form of azobenzene groups in a PCAD@AG film bent by humidity is converted to the cis form. Exposure to humidity facilitates the isomerization of the cis to the trans form and prevents bending. (d,e) Photoinduced actuation gated by humidity monitored by ultraviolet–vis spectroscopy. In d, the sample was first exposed to ultraviolet light for 2 s whereby the trans form (the characteristic strong peak in the visible region) was partially converted to the cis form that was thermally stable in the dark. As shown in e, on exposure to humidity, the cis form was reverted completely to the trans form in <4 s, and thus the humidity counterbalanced the isomerization of the chromophore. (f,g) Evidence of the humidity-induced actuation gated by light. In f, a water droplet sits on the PCAD@AG film at a contact angle of 76°. As shown in g, irradiation with ultraviolet light increased the contact angle to 86° and enhanced the hydrophobicity of the surface, thus alleviating the propensity of the material for adsorption of water.
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f5: Mechanism of photogated humidity-driven actuation.(a) With intramolecular photogating of humidity-driven actuation, the units that respond to humidity and light are part of the same molecule. While action of stimulus 1 (exposure to humidity) alone induces bending, action of stimulus 2 (exposure to light) prevents the bending driven by stimulus 1. (b) With intermolecular photogating, such as that in PCAD@AG, the units that respond to humidity and light are different molecules coupled by intermolecular interactions. Action of stimulus 1 (humidity) induces bending. Action of stimulus 2 (light) prevents the bending by isomerization and decreases the affinity of AG for adsorption of water. Note that stimulus 1 also affects the hydrogen bonding network between PCAD and AG. (c) Mechanism of photogating of humidity-induced motility. The trans form of azobenzene groups in a PCAD@AG film bent by humidity is converted to the cis form. Exposure to humidity facilitates the isomerization of the cis to the trans form and prevents bending. (d,e) Photoinduced actuation gated by humidity monitored by ultraviolet–vis spectroscopy. In d, the sample was first exposed to ultraviolet light for 2 s whereby the trans form (the characteristic strong peak in the visible region) was partially converted to the cis form that was thermally stable in the dark. As shown in e, on exposure to humidity, the cis form was reverted completely to the trans form in <4 s, and thus the humidity counterbalanced the isomerization of the chromophore. (f,g) Evidence of the humidity-induced actuation gated by light. In f, a water droplet sits on the PCAD@AG film at a contact angle of 76°. As shown in g, irradiation with ultraviolet light increased the contact angle to 86° and enhanced the hydrophobicity of the surface, thus alleviating the propensity of the material for adsorption of water.

Mentions: The mechanism of control over the motility of PCAD@AG with light raises a question regarding the underlying mechanism, where the hindrance of motion can occur at a molecular level, as a result of entanglement of the molecular changes induced by the two stimuli, or at a macroscopic level, as a result of the action of two independent but opposing forces. In a conventional intramolecularly gated system, such as are some thermally controlled photochromic molecules, the gating is accomplished by exerting control over the effect of one of the stimuli (light) by action of the other (heat), both stimuli operating on sensing units that are located on the same molecule (for a schematic of a hypothetical intramolecularly photogated hygroresponsive system, see Fig. 5a). The switching induced by the gated stimulus can be directly controlled by activation of the gating stimulus. PCAD@AG is a hybrid material and can be considered an intermolecularly gated system, in the sense that the two sensing units are represented by two chemically distinct albeit coupled (through intermolecular interactions) molecules. Namely, each of the two components (PCAD and AG) is a sensing unit that responds to different stimulus. The two units are connected and communicate with each other through an extensive hydrogen bonding network (Fig. 5b). In effect, changes induced by the effect of external stimulus on one of the components affect the other component indirectly, through the hydrogen bonded linkages. Consequently, exposure of the hygroresponsive component (AG) to humidity can switch that component between two states (‘dry' and ‘wet'). Application of light to the photoresponsive component (PCAD), on the other hand, switches that component from ‘dark' to ‘light' state and prevents the first component (AG) from switching between the ‘dry' and ‘wet' states, thereby effectively gating its response. An additional complication in this two-component system comes from the fact that not only does water adsorption affect the hygroresponsive component (AG) by direct hydration, but it does so by partial disruption of the hydrogen bonding linkages between AG and PCAD (Fig. 5b).


Photogated humidity-driven motility.

Zhang L, Liang H, Jacob J, Naumov P - Nat Commun (2015)

Mechanism of photogated humidity-driven actuation.(a) With intramolecular photogating of humidity-driven actuation, the units that respond to humidity and light are part of the same molecule. While action of stimulus 1 (exposure to humidity) alone induces bending, action of stimulus 2 (exposure to light) prevents the bending driven by stimulus 1. (b) With intermolecular photogating, such as that in PCAD@AG, the units that respond to humidity and light are different molecules coupled by intermolecular interactions. Action of stimulus 1 (humidity) induces bending. Action of stimulus 2 (light) prevents the bending by isomerization and decreases the affinity of AG for adsorption of water. Note that stimulus 1 also affects the hydrogen bonding network between PCAD and AG. (c) Mechanism of photogating of humidity-induced motility. The trans form of azobenzene groups in a PCAD@AG film bent by humidity is converted to the cis form. Exposure to humidity facilitates the isomerization of the cis to the trans form and prevents bending. (d,e) Photoinduced actuation gated by humidity monitored by ultraviolet–vis spectroscopy. In d, the sample was first exposed to ultraviolet light for 2 s whereby the trans form (the characteristic strong peak in the visible region) was partially converted to the cis form that was thermally stable in the dark. As shown in e, on exposure to humidity, the cis form was reverted completely to the trans form in <4 s, and thus the humidity counterbalanced the isomerization of the chromophore. (f,g) Evidence of the humidity-induced actuation gated by light. In f, a water droplet sits on the PCAD@AG film at a contact angle of 76°. As shown in g, irradiation with ultraviolet light increased the contact angle to 86° and enhanced the hydrophobicity of the surface, thus alleviating the propensity of the material for adsorption of water.
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f5: Mechanism of photogated humidity-driven actuation.(a) With intramolecular photogating of humidity-driven actuation, the units that respond to humidity and light are part of the same molecule. While action of stimulus 1 (exposure to humidity) alone induces bending, action of stimulus 2 (exposure to light) prevents the bending driven by stimulus 1. (b) With intermolecular photogating, such as that in PCAD@AG, the units that respond to humidity and light are different molecules coupled by intermolecular interactions. Action of stimulus 1 (humidity) induces bending. Action of stimulus 2 (light) prevents the bending by isomerization and decreases the affinity of AG for adsorption of water. Note that stimulus 1 also affects the hydrogen bonding network between PCAD and AG. (c) Mechanism of photogating of humidity-induced motility. The trans form of azobenzene groups in a PCAD@AG film bent by humidity is converted to the cis form. Exposure to humidity facilitates the isomerization of the cis to the trans form and prevents bending. (d,e) Photoinduced actuation gated by humidity monitored by ultraviolet–vis spectroscopy. In d, the sample was first exposed to ultraviolet light for 2 s whereby the trans form (the characteristic strong peak in the visible region) was partially converted to the cis form that was thermally stable in the dark. As shown in e, on exposure to humidity, the cis form was reverted completely to the trans form in <4 s, and thus the humidity counterbalanced the isomerization of the chromophore. (f,g) Evidence of the humidity-induced actuation gated by light. In f, a water droplet sits on the PCAD@AG film at a contact angle of 76°. As shown in g, irradiation with ultraviolet light increased the contact angle to 86° and enhanced the hydrophobicity of the surface, thus alleviating the propensity of the material for adsorption of water.
Mentions: The mechanism of control over the motility of PCAD@AG with light raises a question regarding the underlying mechanism, where the hindrance of motion can occur at a molecular level, as a result of entanglement of the molecular changes induced by the two stimuli, or at a macroscopic level, as a result of the action of two independent but opposing forces. In a conventional intramolecularly gated system, such as are some thermally controlled photochromic molecules, the gating is accomplished by exerting control over the effect of one of the stimuli (light) by action of the other (heat), both stimuli operating on sensing units that are located on the same molecule (for a schematic of a hypothetical intramolecularly photogated hygroresponsive system, see Fig. 5a). The switching induced by the gated stimulus can be directly controlled by activation of the gating stimulus. PCAD@AG is a hybrid material and can be considered an intermolecularly gated system, in the sense that the two sensing units are represented by two chemically distinct albeit coupled (through intermolecular interactions) molecules. Namely, each of the two components (PCAD and AG) is a sensing unit that responds to different stimulus. The two units are connected and communicate with each other through an extensive hydrogen bonding network (Fig. 5b). In effect, changes induced by the effect of external stimulus on one of the components affect the other component indirectly, through the hydrogen bonded linkages. Consequently, exposure of the hygroresponsive component (AG) to humidity can switch that component between two states (‘dry' and ‘wet'). Application of light to the photoresponsive component (PCAD), on the other hand, switches that component from ‘dark' to ‘light' state and prevents the first component (AG) from switching between the ‘dry' and ‘wet' states, thereby effectively gating its response. An additional complication in this two-component system comes from the fact that not only does water adsorption affect the hygroresponsive component (AG) by direct hydration, but it does so by partial disruption of the hydrogen bonding linkages between AG and PCAD (Fig. 5b).

Bottom Line: Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light.A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min(-1).The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself.

View Article: PubMed Central - PubMed

Affiliation: New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.

ABSTRACT
Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day-night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min(-1). The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

No MeSH data available.


Related in: MedlinePlus