20 research outputs found
An artificial aquatic polyp that wirelessly attracts, grasps, and releases objects
The development of light-responsive materials has captured scientific attention and advanced the development of wirelessly driven terrestrial soft robots. Marine organisms trigger inspiration to expand the paradigm of untethered soft robotics into aqueous environments. However, this expansion toward aquatic soft robots is hampered by the slow response of most light-driven polymers to low light intensities and by the lack of controlled multishape deformations. Herein, we present a surface-anchored artificial aquatic coral polyp composed of a magnetically driven stem and a light-driven gripper. Through magnetically driven motion, the polyp induces stirring and attracts suspended targets. The light-responsive gripper is sensitive to low light intensities and has programmable states and rapid and highly controlled actuation, allowing the polyp to capture or release targets on demand. The artificial polyp demonstrates that assemblies of stimuli-responsive materials in water utilizing coordinated motion can perform tasks not possible for single-component devices. [Abstract copyright: Copyright © 2020 the Author(s). Published by PNAS.
Liquid crystal elastomer coatings with programmed response of surface profile
Stimuli-responsive liquid crystal elastomers (LCEs) with a strong coupling of
orientational molecular order and rubber-like elasticity, show a great
potential as working elements in soft robotics, sensing, transport and
propulsion systems. We demonstrate a dynamic thermal control of the surface
topography of LCE coatings achieved through pre-designed patterns of in-plane
molecular orientation. These patterns determine whether the LCE coating
develops elevations, depressions, or in-plane deformations. The deterministic
dependence of the out-of-plane dynamic surface profile on the in-plane
orientational pattern is explained by activation forces. These forces are
caused by two factors: (i) stretching-contraction of the polymer networks
driven by temperature; (ii) spatially varying orientation of the LCE. The
activation force concept brings the responsive LCEs into the domain of active
matter. The demonstrated relationship can be used to design programmable
coatings with functionalities that mimic biological tissues such as skin
Multistable Conventional Azobenzene Liquid Crystal Actuators Using Only Visible Light: The Decisive Role of Small Amounts of Unpolymerized Monomers
Azobenzene liquid
crystal polymers offer the potential to fabricate
autonomously operated actuators remotely controlled by light. Usually,
in fully polymerized actuators, only three different states can be
obtained: the initial state, the metastable light-actuated state,
and the recovered state, where the first and last states are identical
and stable. Here, we show that conventional azobenzene liquid crystal
polymers that retain a small amount of unpolymerized monomers can
exhibit multistable deformation states after manual bending and upon
irradiation. This nonbonded fraction of monomers migrates under the
influence of local stress gradients, such as those resulting from
bending, enabling the actuator to adapt its shape to counteract the
stresses induced manually or upon irradiation, resulting in stable
recovery states that differ from the initial shape. Oscillatory movement
of the azobenzenes and photosoftening facilitate monomer migration
and thus allow multiple stable shapes using only lower-energy blue
and green lights. Such materials have the potential for biomedical
and microfluidic applications where light-induced, multistable states
are desired and harmful UV-light needs to be avoided
Multistable Conventional Azobenzene Liquid Crystal Actuators Using Only Visible Light: The Decisive Role of Small Amounts of Unpolymerized Monomers
Azobenzene liquid
crystal polymers offer the potential to fabricate
autonomously operated actuators remotely controlled by light. Usually,
in fully polymerized actuators, only three different states can be
obtained: the initial state, the metastable light-actuated state,
and the recovered state, where the first and last states are identical
and stable. Here, we show that conventional azobenzene liquid crystal
polymers that retain a small amount of unpolymerized monomers can
exhibit multistable deformation states after manual bending and upon
irradiation. This nonbonded fraction of monomers migrates under the
influence of local stress gradients, such as those resulting from
bending, enabling the actuator to adapt its shape to counteract the
stresses induced manually or upon irradiation, resulting in stable
recovery states that differ from the initial shape. Oscillatory movement
of the azobenzenes and photosoftening facilitate monomer migration
and thus allow multiple stable shapes using only lower-energy blue
and green lights. Such materials have the potential for biomedical
and microfluidic applications where light-induced, multistable states
are desired and harmful UV-light needs to be avoided
Enhanced Thermal Conductivity in Oriented Polyvinyl Alcohol/Graphene Oxide Composites
[Image: see text] Polymer composites have attracted increasing interest as thermal management materials for use in devices owing to their ease of processing and potential lower costs. However, most polymer composites have only modest thermal conductivities, even at high concentrations of additives, resulting in high costs and reduced mechanical properties, which limit their applications. To achieve high thermally conductive polymer materials with a low concentration of additives, anisotropic, solid-state drawn composite films were prepared using water-soluble polyvinyl alcohol (PVA) and dispersible graphene oxide (GO). A co-additive (sodium dodecyl benzenesulfonate) was used to improve both the dispersion of GO and consequently the thermal conductivity. The hydrogen bonding between GO and PVA and the simultaneous alignment of GO and PVA in drawn composite films contribute to an improved thermal conductivity (∼25 W m(–1) K(–1)), which is higher than most reported polymer composites and an approximately 50-fold enhancement over isotropic PVA (0.3–0.5 W m(–1) K(–1)). This work provides a new method for preparing water-processable, drawn polymer composite films with high thermal conductivity, which may be useful for thermal management applications
Chemistry: Material marriage in electronics
Self-organizing molecules can form structures with useful electronic properties. These supramolecular materials combine the benefits of polymers with those of organic crystalline systems
Phases full of fullerenes
Self-assembled amphiphiles are more common in the realm of aqueous systems than in organic solvents. Their scope has now been expanded with the advent of 'hydrophobic amphiphiles' of p-conjugated–alkyl systems, which show various self-assembled phases similar to classical amphiphiles
Author Correction: Liquid crystal elastomer coatings with programmed response of surface profile
The original version of this Article contained errors in Figs. 1a, 2a, 3a, and 4b, in which the units on the scale bars incorrectly read ‘µm’ rather than the correct ‘nm.’ This has been corrected in both the PDF and HTML versions of the Article