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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

Structure and properties of a PCAD@AG actuator.(a) Chemical structure of the composite film and mechanism of water exchange. (b,c) Appearance of the hybrid film before (b) and after exposure to humidity from the surface (c). The length of the scale bar, 2 cm. (d,e) AFM images of the surface topography of dry film (d) and changes that occur on exposure of the film to humid air (e). (f) ATR−infrared spectra showing that the contact (lower) surface of a PCAD@AG film placed on a D2O-wetted substrate (filter paper) undergoes faster adsorption of D2O relative to the non-contact surface. (g) Time-dependent ATR–infrared spectra of film saturated by dipping in D2O for 10 s and kept in air (the excess D2O was wiped out from the surface). The spectra show rapid release of D2O and concomitant adsorption of H2O from the surroundings. (h) Variation of the weight of the PCAD@AG film with relative humidity of the air. Note that the film was not saturated with water in this experiment. (i) Typical stress–strain curves of films of PCAD@AG and non-doped AG before and after adsorption of water. (j) Typical patterns of deflection of the tip of a PCAD@AG film exposed to humidity, ultraviolet light and heat. The inset shows snapshots of the reversible humidity-driven bending. Note that the heat-induced bending is irreversible. (k–m) Effects of load weight, temperature and thickness on the turnover frequency (F, number of flips over time) of PCAD@AG film. The s.d. from three measurements are shown as error bars. AFM, atomic force microscopy; ATR, attenuated total reflection.
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f1: Structure and properties of a PCAD@AG actuator.(a) Chemical structure of the composite film and mechanism of water exchange. (b,c) Appearance of the hybrid film before (b) and after exposure to humidity from the surface (c). The length of the scale bar, 2 cm. (d,e) AFM images of the surface topography of dry film (d) and changes that occur on exposure of the film to humid air (e). (f) ATR−infrared spectra showing that the contact (lower) surface of a PCAD@AG film placed on a D2O-wetted substrate (filter paper) undergoes faster adsorption of D2O relative to the non-contact surface. (g) Time-dependent ATR–infrared spectra of film saturated by dipping in D2O for 10 s and kept in air (the excess D2O was wiped out from the surface). The spectra show rapid release of D2O and concomitant adsorption of H2O from the surroundings. (h) Variation of the weight of the PCAD@AG film with relative humidity of the air. Note that the film was not saturated with water in this experiment. (i) Typical stress–strain curves of films of PCAD@AG and non-doped AG before and after adsorption of water. (j) Typical patterns of deflection of the tip of a PCAD@AG film exposed to humidity, ultraviolet light and heat. The inset shows snapshots of the reversible humidity-driven bending. Note that the heat-induced bending is irreversible. (k–m) Effects of load weight, temperature and thickness on the turnover frequency (F, number of flips over time) of PCAD@AG film. The s.d. from three measurements are shown as error bars. AFM, atomic force microscopy; ATR, attenuated total reflection.

Mentions: Agarose (AG) was selected as elastic hydrogel matrix. While AG has an extraordinary capacity for water adsorption with swelling capacity of ∼93% (ref. 20), the low melting point renders this material mechanically inapt for application as films are soft and collapse without external support. To attain concomitant mechanical robustness and photochemical response, a multifunctional photoresponsive poly(ethylene glycol) (PEG)-conjugated azobenzene derivative (PCAD) was prepared, characterized and embedded in the AG matrix (Fig. 1a; for details of the synthetic protocol see Supplementary Methods and Supplementary Fig. 1)2122. As shown in Fig. 1a, the structure of the active component PCAD was designed to incorporate azobenzene units as chromophores/mechanophores for light harvesting and actuation, diethylene glycol as flexible component that provides elasticity, terephthalates as connecting functional groups that are also capable of hydrogen bonding, and PEG units for enhanced miscibility with the host matrix. The robust azobenzene unit was selected as photoactive component based on its well-known capability to effectively actuate polymers by trans–cis isomerization. For efficient energy harvesting and transduction to the matrix, two azobenzene units were incorporated into the backbone of PCAD. This number of chromophores was optimal, since incorporation of a single azobenzene unit afforded a semi-solid product and soft hybrid material with pronounced propensity for adhesion to the surface of the base, which strongly alleviated its performance in response to ultraviolet light. Higher number of azobenzene units, on the other hand, resulted in poor solubility and posed difficulties with preparation of the hybrid. Using terephthalate units as connectors, the two azobenzene units were coupled with each other through a tetra(terephthaloyl-diethylene glycol) segment as flexible linker. The flexibility and the short length of the central diethylene glycol unit were essential to provide conditions for simultaneous isomerization of both azobenzene chromophores without imposing mutual steric hindrance or conjugation-related constraints while retaining sufficient overall rigidity for actuation. The terephthalate connectors were also expected to facilitate the interaction with the host by providing additional sites for hydrogen bonding. Using another pair of terephthalates as connectors, the long and flexible PEG tails were introduced at both ends for improved miscibility, processability and elasticity of the hybrid film.


Photogated humidity-driven motility.

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

Structure and properties of a PCAD@AG actuator.(a) Chemical structure of the composite film and mechanism of water exchange. (b,c) Appearance of the hybrid film before (b) and after exposure to humidity from the surface (c). The length of the scale bar, 2 cm. (d,e) AFM images of the surface topography of dry film (d) and changes that occur on exposure of the film to humid air (e). (f) ATR−infrared spectra showing that the contact (lower) surface of a PCAD@AG film placed on a D2O-wetted substrate (filter paper) undergoes faster adsorption of D2O relative to the non-contact surface. (g) Time-dependent ATR–infrared spectra of film saturated by dipping in D2O for 10 s and kept in air (the excess D2O was wiped out from the surface). The spectra show rapid release of D2O and concomitant adsorption of H2O from the surroundings. (h) Variation of the weight of the PCAD@AG film with relative humidity of the air. Note that the film was not saturated with water in this experiment. (i) Typical stress–strain curves of films of PCAD@AG and non-doped AG before and after adsorption of water. (j) Typical patterns of deflection of the tip of a PCAD@AG film exposed to humidity, ultraviolet light and heat. The inset shows snapshots of the reversible humidity-driven bending. Note that the heat-induced bending is irreversible. (k–m) Effects of load weight, temperature and thickness on the turnover frequency (F, number of flips over time) of PCAD@AG film. The s.d. from three measurements are shown as error bars. AFM, atomic force microscopy; ATR, attenuated total reflection.
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f1: Structure and properties of a PCAD@AG actuator.(a) Chemical structure of the composite film and mechanism of water exchange. (b,c) Appearance of the hybrid film before (b) and after exposure to humidity from the surface (c). The length of the scale bar, 2 cm. (d,e) AFM images of the surface topography of dry film (d) and changes that occur on exposure of the film to humid air (e). (f) ATR−infrared spectra showing that the contact (lower) surface of a PCAD@AG film placed on a D2O-wetted substrate (filter paper) undergoes faster adsorption of D2O relative to the non-contact surface. (g) Time-dependent ATR–infrared spectra of film saturated by dipping in D2O for 10 s and kept in air (the excess D2O was wiped out from the surface). The spectra show rapid release of D2O and concomitant adsorption of H2O from the surroundings. (h) Variation of the weight of the PCAD@AG film with relative humidity of the air. Note that the film was not saturated with water in this experiment. (i) Typical stress–strain curves of films of PCAD@AG and non-doped AG before and after adsorption of water. (j) Typical patterns of deflection of the tip of a PCAD@AG film exposed to humidity, ultraviolet light and heat. The inset shows snapshots of the reversible humidity-driven bending. Note that the heat-induced bending is irreversible. (k–m) Effects of load weight, temperature and thickness on the turnover frequency (F, number of flips over time) of PCAD@AG film. The s.d. from three measurements are shown as error bars. AFM, atomic force microscopy; ATR, attenuated total reflection.
Mentions: Agarose (AG) was selected as elastic hydrogel matrix. While AG has an extraordinary capacity for water adsorption with swelling capacity of ∼93% (ref. 20), the low melting point renders this material mechanically inapt for application as films are soft and collapse without external support. To attain concomitant mechanical robustness and photochemical response, a multifunctional photoresponsive poly(ethylene glycol) (PEG)-conjugated azobenzene derivative (PCAD) was prepared, characterized and embedded in the AG matrix (Fig. 1a; for details of the synthetic protocol see Supplementary Methods and Supplementary Fig. 1)2122. As shown in Fig. 1a, the structure of the active component PCAD was designed to incorporate azobenzene units as chromophores/mechanophores for light harvesting and actuation, diethylene glycol as flexible component that provides elasticity, terephthalates as connecting functional groups that are also capable of hydrogen bonding, and PEG units for enhanced miscibility with the host matrix. The robust azobenzene unit was selected as photoactive component based on its well-known capability to effectively actuate polymers by trans–cis isomerization. For efficient energy harvesting and transduction to the matrix, two azobenzene units were incorporated into the backbone of PCAD. This number of chromophores was optimal, since incorporation of a single azobenzene unit afforded a semi-solid product and soft hybrid material with pronounced propensity for adhesion to the surface of the base, which strongly alleviated its performance in response to ultraviolet light. Higher number of azobenzene units, on the other hand, resulted in poor solubility and posed difficulties with preparation of the hybrid. Using terephthalate units as connectors, the two azobenzene units were coupled with each other through a tetra(terephthaloyl-diethylene glycol) segment as flexible linker. The flexibility and the short length of the central diethylene glycol unit were essential to provide conditions for simultaneous isomerization of both azobenzene chromophores without imposing mutual steric hindrance or conjugation-related constraints while retaining sufficient overall rigidity for actuation. The terephthalate connectors were also expected to facilitate the interaction with the host by providing additional sites for hydrogen bonding. Using another pair of terephthalates as connectors, the long and flexible PEG tails were introduced at both ends for improved miscibility, processability and elasticity of the hybrid film.

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