Nonsphere Drop Impact Assembly of Graphene Oxide Liquid Crystals

Nonsphere Drop Impact Assembly of Graphene Oxide Liquid Crystals Qiuyan Yang,†,§ Yanqiu Jiang,†,§ Dongyu Fan,† Kan Zheng,† Jiayi Zhang,‡ Zhen Xu,*,† Weiquan Yao,† Qingxu Zhang,† Yihu Song,† Qiang Zheng,† Liwu Fan,‡ Weiwei Gao,† and Chao Gao*,† Downloaded via BUFFALO STATE on July 17, 2019 at 06:23:08 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

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MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Zhejiang University, 38 Zheda Road, Hangzhou 310027, People’s Republic of China ‡ State Key Laboratory of Clean Energy Utilization, Zhejiang University, 38 Zheda Road, Hangzhou 310027, People’s Republic of China S Supporting Information *

ABSTRACT: Creating long-lived topological textured liquid crystals (LCs) in confined nonspherical space is of significance in both generations of structures and fundamental studies of topological physics. However, it remains a great challenge due to the fluid character of LCs and the unstable tensional state of transient nonspheres. Here, we realize a rich series of topological textures confined in nonspherical geometries by drop impact assembly (DIA) of graphene oxide (GO) aqueous LCs. Various highly curved nonspherical morphologies of LCs were captured by gelator bath, generating distinct out-ofequilibrium yet long-lived macroscopic topological textures in 3D confinement. Our hydrodynamic investigations on DIA processes reveal that the shear-thinning fluid behavior of LCs and the arrested GO alignments mainly contribute to the topological richness in DIA. Utilizing the shaping behavior of GO LCs compared to other conventional linear polymers such as alginate, we further extend the DIA methodology to design more complex yet highly controllable functional composites and hybrids. This work thus reveals the potential to scale production of uniform yet anisotropic materials with rich topologic textures and tailored composition. KEYWORDS: drop impact assemble, liquid crystals, graphene oxide, nonsphere morphology, topological texture

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means to achieve rich nonspherical geometries that are induced by complex liquid movements.37−41 Isotropic molecules and colloids have been studied in the vortex rings generated by drop impact for a century,27−38 but capturing the intriguing textures of the LC within the generated nonspheres still remains difficult. Here, we achieve rich long-lived topological LC textures confined in multiple nonspherical morphologies by drop impact assembly (DIA) of graphene oxide (GO) LCs. The dynamics of GO LCs as well as the formation mechanism for nonspherical LC morphologies during drop impact are in situ investigated by high-speed polarized optical imaging. The formation of rich morphologies and topological configurations is mainly ascribed to the non-Newtonian shear-thinning behavior of GO LCs and the arrestment of two-dimensional

iquid crystals (LCs) are ubiquitous in natural and artificial systems. Manipulating their topological configurations and textures is significant for fundamental studies of both the LC itself and LC-based materials.1−10 Confining LCs inside three-dimensional (3D) spaces can impose strong deformation of the LC and becomes an option to generate liquid crystalline topological structures with rich functions,11−24 which alternatively serves as an analogy to other fine scale or active systems that are hard to experimentally monitor.23 To date, the exploration on 3D LC topological structures has focused on confinement in high symmetrical space, such as spheres, ellipsoids, and toroids.11−25 However, LC topological structures confined in spaces with broken spherical symmetry still remain mysterious,24 due to the experimental difficulty to restrict fluid LCs within nonspheres, confinement that usually induces a highly distorted topological configuration. Drop impact, referring to the dynamic process when a liquid droplet strikes a liquid surface,25−36 has been recognized as a simple © XXXX American Chemical Society

Received: May 21, 2019 Accepted: July 10, 2019 Published: July 10, 2019 A

DOI: 10.1021/acsnano.9b03926 ACS Nano XXXX, XXX, XXX−XXX

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Figure 1. GO LC architectures assembled by DIA. (a) Illustration of the drop impact assembly approach. (b, c) Photograph (between crossed polarizers) of (b) jellyfishes (2 mg/g GO droplets impacting from a 40 mm height) and (c) caps (3 mg/g GO droplets impacting from 30 mm) by DIA. The formed structures exhibit distinctive birefringence between crossed polarizers. They are mass produced yet monodispersed with the size polydisperse index below 1.0074, as demonstrated in the 400 mL bottles in the right column. (d) Photographs between crossed polarizers of GO shapes collected at different heights and GO concentrations. (e) Phase diagram of GO shapes drawn from (d). Inset stars represent the height of the GO droplet detached from the nozzle. Scale bars: 5 mm.

conditions; (ii) ordered LCs with a shear-thinning fluid character adopt rich topological structures through DIA;42−44 (iii) the introduction of gelation agents such as calcium ions ensures capturing highly tensional nonspherical geometries; and (iv) the colloidal GO aqueous solution is selected as the model drop fluid since it forms lyotropic LCs at a very low concentration (i.e., ∼0.1 wt %) and can transform into a hydrogel state immediately after contacting with an aqueous ionic gelator in the liquid reservoir.45−49 All these key factors ensure the realization of long-lived topological LC structures confined inside nonspherical geometries. GO LC Nonspherical Structures via the DIA Approach. Single-layer GO sheets utilized for DIA have an average lateral size of 38.7 μm and C/O ratio of 1.87 (Figure S1). The huge aspect ratio (∼4 × 104) of GO enables the spontaneous formation of LCs at a concentration down to 1

GO alignments by divalent ions. The DIA strategy demonstrates advantages of easy operability, fine controllability, high reproducibility, and mass productivity for fabricating nonspherical LC structures. With the comprehensive understanding on the drop impact dynamic differences between GO and other conventional linear polymers such as alginate, we further extend the DIA methodology to design more complex yet highly controllable functional composites and hybrids.

RESULTS AND DISCUSSIONS Designing Strategy. We propose a DIA strategy to realize rich geometries of an LC fluid based on four considerations (Figure 1a): (i) the drop impact system provides a dynamic platform to generate nonspherical geometries, which is facile and scalable without complex requirements for operation B


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Figure 2. Various morphologies of GO LC by DIA. Different shapes of GO LCs constructed by DIA: (a) teardrops, (b) hazelnuts, (c) caps, (d, f) jellyfishes, and (e) sunflower-like. Top row of each image: 3D shapes (red), the orientation of GO sheets in cross-section profiles (red dash), and cross-section director fields (gray dash). Bottom row of each image: Polarized optical images and SEM images. Scale bar: 500 μm.

mg/mL, guaranteeing the high deformation capability of droplets during DIA. Besides, GO contains carboxylic acid functional groups with a zeta potential ranging from −70 to −30 mV, which provide many cross-linkable sites for multivalent cations, such as Ca2+, Mg2+, and Cu2+.50 Experimentally, GO LCs were dropped into an aqueous bath, especially in the presence of gelation reagents (450 mM CaCl2). The drop impact with the bath surface shaped GO LC droplets into a rich series of uniform geometries beyond spheres,51 such as rings (also named donuts), jellyfishes, caps, sunflowers, and teardrops (Figure 1a). These shapes are highly controllable by adjusting the collecting heights (h, the distance between the nozzle tip and the bath surface) from 5 to 130 mm and the concentration of GO LCs (c) from 1 to 8 mg/g (Figures S5−S12), as guided by the depicted phase diagrams in Figure 1d and e. A higher h results in more complex morphologies, and the height thresholds for different morphologies increase upon the increase of GO concentration. Despite that drop impact has already been utilized to achieve polymeric and colloidal nonspheres,27−38 the range of geometries achieved here is richer. Further combining the DIA concept with an industrially viable wet-spinning technique allows us to continuously produce intriguing yet uniformly shaped macroparticles on a large scale (Movies S1, S2). The mass-produced geometries exhibited bright birefringence patterns under polarizers for the localized orientation of GO LCs (Figure 1b,c and Figure S2). Almost all the particles were uniformly dispersed in size despite the complexity of shapes and high productivity (around 2500 particles per nozzle in an hour). For example, the size of both jellyfishes and caps demonstrated an extremely narrow polydisperse distribution index lower than 1.0074 (Figures S3, S4). Such a DIA strategy generally demonstrates various advantages in operability, controllability, reproducibility, and

large-scale productivity for the fabrication of anisotropic macrostructures. Topological Configuration of GO LC in Nonspherical Confinement. Intriguing topological structures of LCs were formed concurrently within those anisotropic spaces. Order normally can contribute great macroscopic properties and thus is preferential for functional materials design. For instance, the arch structures in caps, as revealed by the typical Maltese crosses under polarizers and the cross-section scanning electronic microscopy (SEM) images (Figure 2c and Figure S13), allow their superior elasticity to withstand 70% compression for more than 5000 cycles (Figure S14). Unlike other microstructures that demonstrated superelasticity by multiscale deformation of elastic units, the outstanding elasticity of caps was contributed by folding and unfolding of layer-like shells. As long as the rims are intact, the compressed caps recover their original shapes. The macroscopically ordered alignment of GO sheets is also exhibited in the wing of jellyfishes and the middle of teardrops, hazelnuts, flowers, and jellyfishes (Figure 2 and Figure S15). All those topological structures were “frozen” out of equilibrium states of GO LCs, which are normally believed to be unstable according to the thermal equilibrium theory of LCs10,24,52 but long-lived here mainly due to the Ca2+-induced gelation. The nonsphere confinement in DIA propels the complexity and variety of materials design with their physical properties. Formation Mechanism of Various Morphologies Achieved by DIA. To understand the formation mechanism of these morphologies and their internal topological structures during DIA, the dynamic drop impact processes of GO LCs were investigated via a high-speed imaging between polarizers (Figure 3a). The visualization of the dynamic shaping process was largely enhanced benefiting from the birefringence of GO droplets. That, on the contrary, was one great challenge for the C


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Figure 3. Height effect of DIA. (a) Schematic of the setup combined with polarizers for high-speed imaging to track DIA of GO LCs. (b) High-speed images of GO (with the concentration of 3 mg/g) drop impact from different height (from 10 to 130 mm). A higher height induces greater deformation in stage I as well as a larger degree of upward dragging in stage II. The right columns show the top view and side view of formed shapes under crossed polarizers corresponding to observation in Figure 1d.

and larger area of interfaces from the resulting GO−air, the GO−bath, and the bath−air. When the maximum depth is reached at a given h, air craters begin to withdraw, classified as the starting point for the stage II. At the same time, the retracting interface drags GO droplets, particularly the free side exposed to the air crater, to shrink backward and even to move upward along the air−liquid interface. Such a phenomenon becomes distinctive for higher h cases, beyond 40 mm for 3 mg/g droplets. Stage III starts as the droplets completely detach from the air craters. No obvious shape change was observed in this stage when the GO concentration is higher than 3 mg/g, whereas a further downward movement of GO LC droplets occurred in both stages II and III at diluted GO dispersions (2 mg/g in Figure S18). Overall, the increased kinetic energy at higher h is dissipated through more extensive LC phase deformation, giving rise to more complex topologies. The concentration of GO LCs plays a major role on the extent to which the droplet can curve downward in stage I, move upward in stage II, and further flow downward in stage III (Figure 4 and Movies S4 and S6−S8). GO droplets with a higher concentration have a larger viscosity (Supplementary

conventional drop impact system, due to the low contrast between the droplets and the reservoir liquid.27 Dye additives were often required for high-resolution imaging in those cases, such as the alginate solution droplets (Figure S16). Snapshots in Figure 3b demonstrate the effect of height h on DIA of GO LCs (see also in Movies S3−S5). We divide the dynamic processes into three stages to simplify the discussion. GO droplets were first curved between the air and liquid in stage I, resulting in air craters as the kinetic energy could overcome the surface energy of the liquid, the bending energy of GO droplets, and also the interfacial energies of air− droplet/droplet−liquid.53 Notice that the gravity and buoyant effects are negligible here, because the bath density was already tuned to be close to that of the GO droplets by adding ethanol (Figure S17, Tables S1 and S2). Therefore, the curved extent in this stage depends on the primary kinetic energy that is 1 proportional to h (i.e., 2 mv 2 = mgh, where v is the velocity of the drop impacting the pool). Accordingly, a higher primary kinetic energy drives a bigger air crater, meaning a greater GO spreading degree/deformation at a given GO concentration D


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Figure 4. GO concentration effect. High-speed images and schemes of GO drop impact processes from 60 mm (a) and 5 mm (b) height. Droplets with low GO concentration (below 3 mg/g) undergo an inertia downward flow due to their low viscosity and thus high mobility of GO LCs, while concentrated GO droplets can stand a higher surface retraction force in stage II, and no further downward movement appears in stage III.

S22) or turned from nonspheres to spheres in a Ca2+ bath after drop impact (Figure 5a). In the latter case, the downward curving of an alginate droplet in stage I and II was greatly impeded by the fast Ca2+ cross-linking; a thin compact shell subsequently formed around the droplets in stage III, which greatly slowed down the diffusion of Ca2+ ions for further solidification to the inner liquid58 and finally caused the deformed droplets to turn back to spheres under the interfacial tension. We tried other bivalent cations as gelators: GO droplets formed caps at h = 30 mm in 450 mM Ba2+, supersaturated Zn2+, and supersaturated Cu2+ coagulation baths (Figure S23). By contrast, alginate droplets still failed to form long-lived nonspheres in all the above-mentioned ion gelation baths. The great capability of GO LCs for nonsphere formation is intrinsically attributed to their typical shear thinning nonNewtonian character. Rheological analysis (Figure 5b and Figure S24) demonstrates that the viscosity of GO LCs is 3 orders of magnitude higher than that of alginate at a near-zero shear rate, but achieves the same order of magnitude with the latter as the shear rate increases over 100 s−1. Such a behavior enables GO LCs to deform easily into various nonspherical intermediates under high shear rates, such as 100−1000 s−1 for different drop impact h from 5 to 130 mm, in stage I and II, and the high shear viscosity in the near-zero region endows GO LC droplets with a high modulus (Figure S24) to well maintain the deformed shapes for a long enough time as the shearing effect fades in stage III. In addition, different from densely cross-linked shells formed on the drop surface of alginate,58 the remaining space between GO gelation networks

Figure 19), which hinders the deformation during the whole dynamic process, particularly above 7 mg/g (Figure 4a). Shifting to another extreme case in which h was greatly lowered, for example to 5 mm (Figure 4b), at which droplets still did not completely detach from the nozzle as it contacted the pool surface (Figures S20 and S21), only diluted GO droplets (below 3 mg/g) curved downward in stage I. No deformations (at high h) were found for highly concentrated ones. As a consequence, caps formed at low GO concentrations of 2 and 3 mg/g, and teardrop or hazelnut shapes were directly collected when the GO concentration is higher than 4 mg/g. The confined GO LC topologies remembered their dynamic flow histories (Figure 4). When GO LCs were extruded from the nozzle and exposed to air (Figure S21), their prealignment direction along the tube wall turned parallel to the surface of the droplet due to the anchoring effect by the air−water interface.54−57 The orientations of GO LCs were directly retained inside the teardrop and hazelnut droplets (Figure 2a,b). Curving in stage I on the preoriented droplets gives rise to parallel alignments along the shell inside the caps (Figure 2c). Further upward movements of GO LCs in stage II induced by withdrawing the air crater, on the contrary, results in perpendicular alignments to the bottom, as well as more topological defects, inside flower- and jellyfish-like shapes (Figure 2d−f). Shaping Behavior of GO LCs. To further demonstrate the deformation mechanism of GO LCs, we did comparable DIA experiments on conventional linear polymers such as alginate. In stark contrast with stable nonspheres in GO LCs, alginate droplets either completely dissolved in pure water (Figure E


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Figure 5. Different shaping capabilities of GO and alginate. (a) High-speed images and POM images of GO (3 mg/g), a GO−alginate mixture (50 wt % of GO), and alginate (3 mg/g with 0.1% methyl blue) drop impact into the coagulation bath (450 mM Ca2+) from a 30 mm height. (b) Steady shearing viscosities with shear rate and (c) optical images of GO−alginate composites (3 mg/g) at different GO mass fractions (0, 20, 50, 80%) and collecting heights (10, 30, 50, 100 mm). Scale bar: 10 mm.

allows ionic coagulators to transport from the outer to the inner space for further solidification on deformed droplets.59 A GO LC composite with alginate shows the same drop impact behavior as the neat GO system. In particular, the GO−alginate mixture solution containing GO of more than 50% demonstrated typical shear-thinning character of neat GO. In this GO mass fraction range, the spherical recovery trend of alginate was greatly depressed and a greater deforming degree of GO−alginate droplets was observed (Figure 5c and Figures S25 and S26). Notably, as the mass fraction of GO decreased below 20%, the zero-shear-rate viscosity of the GO− alginate mixture was much decreased and composite droplets almost turned back to spheres. These observations further declare the decisive role of the GO LCs for anisotropic structure formation. Composites and Hybrid Structure Design. GO LCs were directly used as templates for shaping other materials that are hard to shape into nonspheres solely by DIA. For instance, caps were obtained in all cases of GO−carbon nanotubes (Figure S27), GO−poly(vinylidenefluoride-co-trifluoroethylene) (Figure S28), and GO−iron oxide nanoparticles (Figure S29). We also extended the DIA methodology to achieve more complex yet highly controlled anisotropic composite and hybrid structures (Figure 6a−c and Figures S30 and S31). Janus and amber-like types were achieved by effectively utilizing the different shaping behavior of GO LCs with alginate, adjusting the type of titrating nozzles (shoulder to shoulder or coaxial), collecting heights, and the GO to alginate

ratio. In DIA, GO phases normally retained deformed shapes, but alginate recovered to spherical ones. Such a technique thus offers a simple and robust procedure to achieve smart hybrid structures that are difficult to create from other emulsion-based methods.60 We demonstrated one of the potential applications of these DIA structures in Figure 6d, by showing that magnetic stimuli responses combined with chemical/drug loading were simply designed for controllable targeting release, by selectively adjusting the content of the two phases. In principle, the composition, structure, and functionality of hybrids are easily customized at will by selecting composite components that have the desired interactions with the host GO LC. Hydrodynamic Analyses for GO Shaping in DIA. GO LCs demonstrated rich outer geometries and inner topological structures by the DIA method. The Weber number, We, a dimensionless number defined by ρv2D/σ (where ρ is the density of droplets, D is the droplet diameter, and σ is the surface tension) in traditional fluid mechanics, is also utilized here to define the thresholds for transition among different shapes (Figure 7). The boundary We value between the cap and jellyfish formation regions is a notable one because it can also be considered as the traditional threshold for splashing (Figure 3 and Figure S18). We found such a threshold of We is not a constant number, different from that of Newtonian fluids (such as 64 for the We threshold value of water between the vortex and splashing during drop impact),27,61 but increases monotonically with the GO concentration (Figure 7, Movies S4 and S6−S8). This observation that GO can suppress the F


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Figure 6. Anisotropic composites and hybrid structures. (a) Schematic illustration of the nozzle with two parallel flow channels, optical images, and cartoon of the formed GO−alginate (with the same spinning speed) anisotropic hybrid structures. (b) Schematic illustration of the coaxial nozzle with the alginate flowing through the inner channel at 4 times the spinning speed of GO, optical images under two cross placed polarizers of the formed GO−alginate structures from different heights (30, 50, and 100 mm), and a cartoon of the phase separation between GO and the alginate. (c) Schematic illustration of the coaxial nozzle with GO flowing through the inner channel and optical images under two cross polarizers of the formed amber-like GO−alginate structures prepared at different GO to alginate spinning speed ratios (1/ 50, 1/20, and 1/10). (d) Chemical/drug loading with the magnetic stimuli responses controlled releasing ability. All alginates were labeled with methylene blue. The GO LC appears brown to the eye and exhibits a bright yellow birefringence under polarizers. Scale bar: 1 mm for zoomed-in images and 10 mm for zoomed-out images.

nonspherical GO shapes. (ii) The GO LC provides a platform for distinct inner topological structures inside nonspherical confinement upon fabrication conditions. (iii) The birefringence character of LCs under polarizers greatly enhanced the visibility of high-speed imaging, guaranteeing the in situ hydrodynamic shaping observation, a deep understanding of the dynamics of the LC drop impact system, and more precise discussions on the mechanism of the nonsphere formation. The shear-thinning LC fluid character plays a pivotal role for nonspherical topology formation. This conclusion suggests that the DIA approach is also applicable for other typical shearthinning yet cross-linkable materials, such as thermotropic LCs, cellulose, MXenes, boron nitride, and transitional metal dichalcogenides.47 Similarly, alginate utilized for complex composite and hybrid structure design with GO LCs can also extend to rich polymers, indicating the vast possibility to achieve customized structures with different composition and functionality for broad applications beyond the provided one in Figure 6, such as controllable mass transmission, targeting catalysis, adsorption and separation, and sustained drug release. Besides, these out-of-equilibrium LC topological states provide macroscopic platforms for further in situ structural analysis and theoretical simulations and thus fundamental studies on the interplay between curvature, defects, and order in other fine or

Figure 7. Weber number thresholds for shape control in DIA of GO LCs. We thresholds exhibit dependence on GO concentration and increase with the increase of GO concentration.

splashing of fluid implies significant applications in fluidrelated industrial production that requires enhanced or weakened splashing. The typical LC character of GO solutions functions mainly in three ways in DIA. (i) The shear-thinning liquid properties enable GO droplets to deform easily under high shear stress in stages I and II and maintain the deformed shapes as the shear is released in stage III, allowing various uniform yet intriguing G


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of GO droplets, rheological behaviors of GO dispersions, optical images and SEM images of GO composited architectures, density of GO dispersions and coagulation baths (PDF) Movie S1: DIA process of 2 mg/mL GO dispersion from 40 mm height. (MP4) Movie S2: DIA process of 3 mg/mL GO dispersion from 30 mm height (MP4) Movie S3: DIA process of 3 mg/mL GO dispersion from 20 mm height (MP4) Movie S4: DIA process of 3 mg/mL GO dispersion from 60 mm height (MP4) Movie S5: DIA process of 3 mg/mL GO dispersion from 100 mm height (MP4) Movie S6: DIA process of 2 mg/mL GO dispersion from 60 mm height (MP4) Movie S7: DIA process of 5 mg/mL GO dispersion from 60 mm height (MP4) Movie S8: DIA process of 7 mg/mL GO dispersion from 60 mm height (MP4)

CONCLUSIONS In summary, we proposed a facile DIA approach to the scalable fabrication of multiple nonspherical LC morphologies with typical 2D colloidal GO LCs. The DIA methodology demonstrates advantages of easy operability, fine controllability, high reproducibility, and mass productivity. The topological configurations of LCs inside the nonsphere confinement are highly curvature focusing, forming rich textures in 3D space. The non-Newtonian shear-thinning fluid behavior of LCs and the arrested GO alignments enable the shaping capability of GO LCs in DIA. Effectively utilizing such a shaping difference between GO LCs and isotropic solutions, we also designed and fabricated rich composites/ hybrid structures with high control over composition, morphology, and functionality for broad applications. Our work thus extends the structure design and further functional device fabrication based on colloidal LCs. MATERIALS AND METHODS Materials and DIA Process. Single-layer GO sheets (≥99.5%) with an average lateral size of 30−50 μm were purchased from Hangzhou Gaoxi Technology Co., Ltd. (www.gaoxitech.com). A droplet of GO aqueous solution with a certain concentration was steadily extruded from a nozzle (inner diameter of 1 mm) and dropped into an ethanol aqueous solution with CaCl2 (450 mM). The pumping rate was kept at 1 mL/min (∼2500 droplets/hour per nozzle). To investigate the effect of GO concentration on the DIA process, GO aqueous solutions with concentrations ranging from 1 to 8 mg/mL were utilized to fabricate nonsphere drops. On the other hand, the height between the needle and the bottom liquid surface was adjusted from 5 to 130 mm to investigate the effect of collecting heights on the DIA process. Moreover, the composition of the liquid pool solution was changed including the ethanol to water ratio (from 1:9 to 9:1) to investigate the effect on the drop impact. The drop impact of alginate, CMC, GO−alginate, GO−CMC, GO−CNT, and GO−iron oxide nanoparticles (3 or 7 mg/g aqueous solution) followed the above-mentioned procedure. In the case of GO-P(VDFTrFE), polymers were dissolved in dimethylformamide, and a mixture of isopropanol and phenixin was utilized as the target liquid reservoir. Characterization. The photos of samples were collected with a Canon EOS700D, and two crossed polarizers were used for the observation of their birefringence. A strain-controlled rheometer (ARES-G2, TA Instruments, USA) with a steel cone−plate geometry (40 mm diameter, 2° cone angle, gap 50 μm) was used to measure the dynamic rheological responses of the GO aqueous solution in steady shear. The temperature was controlled at 26 °C by using a Peltier system. Surface tensions were determined using a CTS-200 system (Mighty Technology Pvt. Ltd., China) fitted with a drop shape analyzer. The measurement of zeta potential was performed on a ZET-3000HS apparatus. The droplet impacting processes were videotaped by a high-speed camera (NAC-GX1 featuring 500/1000 frames per second).

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ASSOCIATED CONTENT

(1) Hasan, M.; Kane, C. Colloquium: Topological Insulators. Rev. Mod. Phys. 2010, 82, 3045−3067. (2) Dennis, M. R.; King, R. P.; Jack, B.; O’Holleran, K.; Padgett, M. J. Isolated Optical Vortex Knots. Nat. Phys. 2010, 6, 118−121. (3) Hall, D. S.; Ray, M. W.; Tiurev, K.; Ruokokoski, E.; Gheorghe, A. H.; Möttönen, M. Tying Quantum Knots. Nat. Phys. 2016, 12, 478−483. (4) McConney, M. E.; Martinez, A.; Tondiglia, V. P.; Lee, K. M.; Langley, D.; Smalyukh, I. I.; White, T. J. Topography from Topology: Photoinduced Surface Features Generated in Liquid Crystal Polymer Networks. Adv. Mater. 2013, 25, 5880−5885.

Corresponding Authors

*E-mail: [email protected] (Z.X.). *E-mail: [email protected] (C.G.). ORCID

Qiuyan Yang: 0000-0002-4647-299X Zhen Xu: 0000-0001-9282-9753 Chao Gao: 0000-0002-3893-7224 Author Contributions §

Q. Yang and Y. Jiang contributed equally to this work.

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work is supported by the National Natural Science Foundation of China (Nos. 51533008, 21325417, 51603183, and 51703194), National Key R&D Program of China (No. 2016YFA0200200), Fujian Provincial Science and Technology Major Projects (No. 2018HZ0001-2), Hundred Talents Program of Zhejiang University (188020*194231701/113), Key Research and Development Plan of Zhejiang Province (2018C01049), the Fundamental Research Funds for the Central Universities (Nos. 2017QNA4036 and 2017XZZX001-04), and China Postdoctoral Science Foundation (2017M621927). We thank Yunlong Xu and Hongpeng Han for help with the collection and discussion on the rheological results. REFERENCES

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.9b03926. Characterizations of GO, photograph images and statistical data of different nonsphere architectures, optical images of GO shapes collected under different conditions, POM and SEM images of GO caps, compression tests of GO caps, high-speed optical images H


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Nonsphere Drop Impact Assembly of Graphene Oxide Liquid Crystals

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