The manipulation of small amounts of liquids has applications ranging from biomedical devices to liquid transfer. Direct light-driven manipulation of liquids, especially when triggered by light-induced capillary forces, is of particular interest because light can provide contactless spatial and temporal control. However, existing light-driven technologies suffer from an inherent limitation in that liquid motion is strongly resisted by the effect of contact-line pinning. Here we report a strategy to manipulate fluid slugs by photo-induced asymmetric deformation of tubular microactuators, which induces capillary forces for liquid propulsion. Microactuators with various shapes (straight, ‘Y’-shaped, serpentine and helical) are fabricated from a mechanically robust linear liquid crystal polymer. These microactuators are able to exert photocontrol of a wide diversity of liquids over a long distance with controllable velocity and direction, and hence to mix multiphase liquids, to combine liquids and even to make liquids run uphill. We anticipate that this photodeformable microactuator will find use in micro-reactors, in laboratory-on-a-chip settings and in micro-optomechanical systems.
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This work was supported by the National Natural Science Foundation of China (51225304, 21134003 and 21273048) and by the Shanghai Outstanding Academic Leaders Plan (15XD1500600). We thank Y. Xu, X. Liu and E. Chen for assistance with 2D-WAXD measurements; G. Guan, S. Yan and L. Gao for help with TEM tests; H. Guo and X. Feng for assistance with the analytical model and the related calculation; Z. Dai and Q. Liu for assistance with the calculation of the moving speed of slugs; F. Guo and Y. Zhao for help with static CA tests; and Y. Gong for assistance with dynamic CA tests.
The authors declare no competing financial interests.
Reviewer Information Nature thanks D. Baigl, D. J. Broer and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
a, AFM topographic image of the LLCP film. b, The line profile along the white line in a, showing that the thickness of one lamella and two lamellas is 4.38 nm and 8.53 nm, respectively.
a, Photographs showing preparation of the healed LLCP fibre. The two cut pieces of the fibre (left) were overlapped for a length of 5 mm and covered by two glass slides (middle). Then, the fixed fibres were put into an oven and healed for 1 h at 55 °C (right). b, Photographs demonstrating the strength of a virgin and healed LLCP fibre (left and right, respectively). The inset in the left photograph shows that the fibre has a clip at each end; the upper clip is hung below an iron beam, and the bottom clip is loaded (weight w) with many iron rings strung together by an iron wire. The healed fibre supports a load of 51.52 g, while the virgin fibre is loaded with 55.53 g. c, Photographs demonstrating the toughness of a LLCP fibre. The LLCP fibre was stretched to 22 times its initial length by a tensile machine (Instron model 5943) (Supplementary Video 2). Left, unstretched; right, stretched.
The sequence of photographs shows the unloaded TMA (left) buckling under an external force without damage. The buckled TMA (middle) spontaneously recovered its initial shape when the external force was released (right). This buckling was repeated for 30 cycles without any damage to the TMA (Supplementary Video 3). The TMA was clipped between the tips of a pair of tweezers, and was buckled by the opening and closing of the tweezers. The diameter of the TMA is 0.5 mm.
Extended Data Figure 4 Light-induced motion of a solid–liquid slug consisting of acetic ether and polyethylene microspheres.
Top, a sequence of side-on photographs (at times of 0, 3, 6 and 7 s) showing the mixing of acetic ether (ethyl acetate) and PE (polyethylene) microspheres in the slug that occurs when the TMA photodeforms (Part 4 in Supplementary Video 4). Bottom, schematic illustration of vortex circulation in the slug. The diameter of the polyethylene microspheres is ~35 μm. The length of the open arrows denotes the intensity of 470-nm light.
This sequence of side-on photographs (at times 0, 15, 25 and 45 s) shows that benzophenone (~0.03 mg) within an ethanol (~0.3 μl, 75 vol%) slug dissolves little over a period of 45 s without the light irradiation.
Extended Data Figure 6 Schematics demonstrating the mechanism of photoalignment of azobenzene mesogens under linear polarized blue light.
Left, trans-azobenzene molecules with their transition moments parallel to the polarization direction of the light are effectively activated to their excited states, which is followed by trans–cis isomerization (middle); but molecules with their transition moments perpendicular to the polarization direction of actinic light are inactive towards isomerization. The cis–trans isomerization of azobenzene molecules is also induced by the light. After repetition of many trans–cis–trans isomerization cycles, trans-azobenzene molecules have reoriented to be perpendicular to the polarization direction of the actinic light, and hence inactive towards the incident radiation (right); this production of a net population of trans-azobenzene molecules aligned perpendicularly to the light polarization is known as the ‘Weigert effect’.
Extended Data Figure 7 Effect of irradiation on the 2D-WAXD patterns of the flat TMA wall cut and flattened out into a plane.
a, b, Before (a) and after (b) irradiation. A higher intensity and a longer irradiation time of the 470-nm light are employed in this 2D-WAXD measurement compared with those in the experiments on light-induced liquid motion in the TMA, which ensures that most of the azobenzene mesogens in the flat wall are reorientated along the light propagation direction. Thus, the 2D-WAXD signal of the flat wall is strong enough to be detected. The X-ray beam is applied from the lateral side of the wall and parallel to the plane of the wall. 2θ denotes the diffraction angle and d represents the lateral distance between the azobenzene mesogens. Yellow arrows denote the horizontal direction of the flat TMA wall.
Extended Data Figure 8 Light-driven liquid motion on irradiation by 470-nm light that has been attenuated by passing through lean pork.
The white and green arrows indicate the leading edge and the trailing edge of a silicone oil slug, respectively. The length of the open arrows denotes the intensity of 470-nm light. The volume of the silicone oil slug is 0.2 μl; the thickness of the lean pork and the glass slide is ~1 mm and 1.2 mm, respectively. Part 6 of Supplementary Video 9 shows this process in full.
This file contains Supplementary Methods, a Supplementary Discussion, legends for Supplementary Videos 1-9 and Supplementary References. (PDF 1335 kb)
This file contains the Source Data for Extended Data Table 1. (XLSX 22 kb)
The slug of silicone oil is moving when the TMA is perpendicularly irradiated with attenuated 470-nm light. The moving direction of the slug is controllable by varying the attenuated direction of 470-nm light. In order to prevent the bending of the TMA, it is adhered to the substrate by epoxy adhesive. There is an optical filter between the TMA and the camera lens to filter light below 530 nm, which effectively eliminates the dazzle of 470-nm light. The volume of the silicone oil is ~ 0.2 μL. The diameter of the TMA is 0.5 mm. The video is shot from lateral side of the TMA. (MP4 3024 kb)
The LLCP fiber is stretched by an Instron Universal Testing Machine (Model 5943) at a deformation rate of 60 mm min-1 in air. The mechanical parameters such as stress and strain are live displayed by a digital panel while the fiber is stretched. (MP4 3634 kb)
Upon external force, the TMA is buckled with a large magnitude of deformation. After removing the external force, the curved TMA self-recovers to the initial shape. (MP4 7622 kb)
Part 1 Propelling various pure liquids by the TMAs: Upon irradiation of attenuated 470-nm light, the TMAs propel ethanol, water, acetone, ethyl acetate and hexane, respectively. The video is shot from lateral side of the TMA. Part 2 Propelling train of silicone oil slugs by the TMA. Upon irradiation of attenuated 470-nm light, the train of silicone oil slugs is self-propelled in the photodeformed TMA. The video is shot from lateral side of the TMA. Part 3 Propelling emulsion by the TMA. Upon irradiation of attenuated 470-nm light, the emulsion made of rapeseed oil and silicone oil is self-propelled in the photodeformed TMA. The video is shot from lateral side of the TMA. Part 4 Propelling a solid-liquid fluid by the TMA. Upon irradiation of attenuated 470-nm light, the liquid-solid fluid prepared by dispersing polyethylene microspheres in acetic ether is self-propelled in the photodeformed TMA. It is noted that the fluid is self-mixing when the TMA photodeforms. The video is shot from lateral side of the TMA. Part 5 Propelling gasoline by the TMA. Upon irradiation of attenuated 470-nm light, the TMA propels a gasoline slug. The video is shot from lateral side of the TMA. Part 6 Propelling various biomedical liquids by the TMA. Upon irradiation of attenuated 470-nm light, the TMA propels bovine serum albumin solution, phosphate buffer solution, cell culture medium and cell suspension, respectively. The video is shot from lateral side of the TMA. (MP4 22355 kb)
Upon irradiation of attenuated 470-nm light, benzophenone (~ 0.03 mg) completely dissolves in ethanol (75 vol%) within 45 s. The video is shot from lateral side of the TMA. (MP4 2576 kb)
Propelling a silicone oil slug to capture and convey a polyethylene microsphere through the photodeformation of the TMA.
The video is shot from lateral side of the TMA. (MP4 1516 kb)
The higher the light intensity, the larger the cross section area; therefore, when irradiated with the 470-nm light whose intensity is attenuated along the axial direction, the TMA deforms to an asymmetric cone-like geometry. After turning off the light source, the TMA returns to its initial size. The video is shot from lateral side of the TMA. (MP4 3234 kb)
When irradiated with 470-nm light perpendicularly to the long axis of the TMA, the TMA deforms. After turning off the light source, the TMA returns to its initial size. Such reversible deformation on interval irradiation with 470-nm light repeats over 100 cycles without obvious fatigue. The video is shot from lateral side of the TMA. (MP4 1388 kb)
Part 1 Propelling a silicone oil slug over a long distance by the TMA. Upon irradiation of attenuated 470-nm light, a silicone oil slug is propelled and constantly moved 57 mm in the photodeformed TMA. The video is shot from lateral side of the TMA. Part 2 Light-driven uphill motion of a silicone slug in the TMA. Upon irradiation of attenuated 470-nm light, a silicone oil slug overcomes gravity and self-propels on a 17° incline in the photodeformed TMA. The video is shot from lateral side of the TMA. Part 3 Light-driven motion of a silicone slug in the serpentine TMA. Upon irradiation of attenuated 470-nm light, the silicon oil slug moves with S-shaped trajectory in the serpentine TMA. Part 4 Light-driven motion of a silicone oil slug in the helical TMA. Upon irradiation of attenuated 470-nm light, the silicone oil slug moves with helical trajectory in the helical TMA. Part 5 Light-driven fusion of two silicone oil slugs in the Y-shaped TMA. Upon irradiation of attenuated 470-nm light, a silicone oil slug is propelled to the junction of the Y-shaped TMA by photodeformation and combined with another silicone oil slug at the junction. Part 6 Light-driven motion of a silicone oil slug upon irradiation of attenuated 470-nm light transmitting through a piece of pork. The incident light at 470-nm transmitted through the pork drives a silicone oil slug moving with the average speed of 0.048 mm s-1 in the photodeformed TMA. The video is shot from lateral side of the TMA. (MP4 16116 kb)
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Lv, Ja., Liu, Y., Wei, J. et al. Photocontrol of fluid slugs in liquid crystal polymer microactuators. Nature 537, 179–184 (2016). https://doi.org/10.1038/nature19344
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