From Chaos to Order: Evaporative Assembly and Collective Behavior

Subscriber access provided by UNIV OF DURHAM

Chemical and Dynamical Processes in Solution; Polymers, Glasses, and Soft Matter

From Chaos to Order: Evaporative Assembly and Collective Behavior in Drying Liquid Crystal Droplets Guang Chu, and Eyal Zussman J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.8b01866 • Publication Date (Web): 07 Aug 2018 Downloaded from http://pubs.acs.org on August 7, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

From Chaos to Order: Evaporative Assembly and Collective Behavior in Drying Liquid Crystal Droplets Guang Chu* and Eyal Zussman* NanoEngineering Group, Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 3200003, Israel Corresponding Author: Email: [email protected] (G. C.) Email: [email protected] (E. Z.)

ACS Paragon Plus Environment

1

The Journal of Physical Chemistry Letters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 20

ABSTRACT

The emergence of dynamic assembly and collective motion in living systems are marvels of nature which suggest universal principles for governing self-organization. By drying a drop of surfactant-stabilized liquid crystal emulsions, we present a simple form of evaporative assembly and collective motion in colloidal droplets. Driven by local evaporation flux distribution and capillary force, the dynamic mode in these swimming liquid crystal droplets are highly depended on their intrinsic configurations, exhibiting a macroscopic transition from chaotic to wellorganised. The combination of collective behavior, speed distribution, interparticle interaction, formation of topological defects and dislocations in a swarm of hexagonal ordered liquid crystal droplets produced a myriad of dynamical states, which suggest a means of mimicking the nonequilibrium state of living matter with controlled properties.

TOC GRAPHIC


2

Page 3 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Living systems are ubiquitous in nature and involve a wide range of length scales, ranging from macroscopic flock of birds to microscopic bacterial colonies, exhibiting complex coordinated behaviours, dynamic patterns and high-order structures that result from social interactions among individuals.1 In order to mimic the non-equilibrium biological collective behaviours, various kind of artificial active systems have been demonstrated, such as synthetic self-propelled colloids, bio-derived microrobot and passive particles in active fluid, etc.2-4 Among which, drying a drop of colloidal suspension might be one of the simplest ways to prepare a collective moving stream of particles. During the drying process, the drop edges are pinned to the substrate with capillary flow outward from the drop centre brings suspended particles to its edge, generating a directional collective movement of the colloids. After evaporation, the colloidal particles are concentrated and dried along the drop edge, and this phenomenon is referred to as coffee-stain effect.5-8 By using the methods of non-equilibrium hydrodynamics and statistical mechanics, one can precisely quantify and highlight the similarities between artificial and living matters in fluid motion and life-like complex behaviour.9 Liquid crystals (LCs) are anisotropic fluids that combine the long-range orientational ordering of crystal with high molecular mobility of liquid,10 which have been widely used as reconfigurable materials to sense their local environment, e.g., electric fields, temperature and mechanical shear.11-13 In particular, when LC phase is confined within micrometer-sized droplets that are dispersed in an aqueous surfactant dispersion, a colloidal LC emulsion is formed.14 For LC emulsion, the surface anchoring of LC molecule and corresponding LC-droplet configuration can be tuned either by the type of surfactant or the size of the droplet, generating adjustable LC colloids with various ordering.15 In addition, complex LC-mediated directional interparticle interactions are existed between each individual droplet, similar to the social interactions in


3


Page 4 of 20

living systems.16-18 Thus, the anisotropic LC-droplets may present additional opportunities to control the modes of collective motion in swimming droplets by application of extra interparticle forces as well as to manipulate their dynamic behaviours better than isotropic colloid particles. Recent studies demonstrate that evaporating a drop of colloidal LC can lead to the collective motion and dynamic assembly of the particles with the liquid crystalline ordering sustained.19-21 Therefore, the drying of LC emulsions with diffferent ordering in suspended droplets remains attractive for further investigation. Herein, we report the study on evaporative induced swimming LC-droplets that exhibit dynamic assembly and collective behaviours. These LC-droplets form a two-dimensional active schooling, which can move, sort, pair, merge and swarm throughout the drying evolution. The collective movements are driven by a combination of outward capillary flow and inward Marangoni stress and capillary force that autonomously convert energy available in suspension into droplet mechanical motion. It is noted that the structure of the suspended LC-droplets is important and can be used to control the way of collective motion, thus, strong long-ranged attractive interactions between colloidal droplets that lead to the formation of hexagonal packed and arrested droplet clusters on the air-water interface. The presented system not only provides new insight into the emerging order in active anisotropic fluids, but also shows the existence of far-from-equilibrium collisions of the swimming LC-droplets. The LC-droplets of 4-cyano-4′-pentylbiphenyl (5CB) in nematic ordering were investigated at room temperature. The preparation of polydispersed LC-droplets using sonication started with the addition of 5CB (25 µL) into 10 mL aqueous solution of surfactants. After emulsifying for 1 min, a stable LC-in-water emulsion was obtained (Figure 1a). Two kinds of surfactants zwitterionic 3-(N,N-dimethyl-myristyl-ammonio) propane-sulfonate (DMAPS) and


4

Page 5 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


non-ionic triblock copolymer Pluronic F127 were chosen as the stabilizing agent for LCdroplets, respectively, with the concentration of 0.5 wt% in solution. As shown in Figure 1b, DMAPS could cause a perpendicular anchoring of 5CB molecule at the LC-water interface, leading to a radial configuration of the nematic LC-droplet. In contrast, 5CB in Pluronic F127 solution underwent a planar anchoring at the droplet interface and generating LC-droplets with bipolar configuration.22 The change in ordering transition of 5CB in LC-droplets was attributed to the fact that amphipathic surfactants adsorb to and alter the orientational ordering of 5CB at LC-water interfaces, which were known as adsorbate-induced anchoring transition and involved a change in the LC anchoring energy induced by the amphiphile.23 The collective behaviour of the LC-droplets can be triggered by slowly evaporating a drop of LC emulsion on a glass surface. Evaporation occurs over the entire drop free-surface. At the beginning of drying process, the droplet contact line remained pinned to the substrate, with the contact angle gradually decreasing, which is known as the constant contact-radius mode.5, 6 It results in a capillary flow outward from the centre of the drop, which brought the suspended LCdroplets to its contact line (Figure 1c). The LC-droplets, both in radial and bipolar configurations, were efficiently transported to the edge, generating a ring-like structure along the air-water interface during evaporation (Figure 1d, 1e and Movie S1, S2, respectively). The LCdroplets with radial configuration formed hexagonal packed, quasi-static or arrested structures at the contact line, which due to the strong long-range, directional attractions between each individual droplet. However, the structure of bipolar LC-droplet aggregations was more loosely packed with non-uniform deposition. It is known that the attractive force (e.g., Van der Waals attraction) for two droplets increased with decreasing separation distance between them and reached large values at short distance (𝐹𝐴 ~ 𝑅⁄ℎ, where FA, R and h represented the attractive


5


Page 6 of 20

force, the diameter of the droplet and the distance between droplet, respectively). Due to the existence of short-ranged repulsive force between neighbouring droplets, the LC-droplet stay separately at the contact line and do not aggregate to form a flat LC film. The stronger attractions between radial LC-droplets as compared to between bipolar droplets, resulted from the coupling of orientational elasticity and capillary colloidal interactions.18 The difference in long-ranged attractive interactions between LC-droplets with radial and bipolar configurations were derived from their directional topological dipoles at the 5CB-aqueous interface, which were oriented either perpendicular to the surface or located at the droplet poles.24 For LC-droplets with radial configuration, the attractive forces were initially due to the dipole-induced many-body elasticcapillary interaction between droplets, generating a large area of 2D hexagonal cluster on a liquid-air interface at the contact line.25 Whereas, the bipolar LC-droplets exhibited an attraction force with one direction that along the topological dipole of the droplet,26 showing loosely packed linear chain assembly of the droplet which could be easily destroyed by the moving stream of subsequent droplet. In brief, the configurations of LC-droplets provide a convenient parameter to control the deposition in a certain arrangement, without additional modification of the droplet or altering the solvent chemistry.


6

Page 7 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. (a) Emulsifying 5CB by sonication in surfactant solution, generating stable LCdroplets in water. (b) The schematic illustrations (left) of director configurations observed for micrometer-sized nematic LC-droplets. The droplets, which stabilized by DMAPS and Pluronic F127, respectively, could cause a homeotropic and planar anchoring of 5CB molecules at the water-LC interface (right). (c) Schematic diagram of the evaporation process, depicting the capillary flow induced by pinned edges. During the evaporation process, the contact line remains pinned and the contact angle decreases (dashed line). The capillary flow (gray arrows), from the drop’s center to its edges, is induced to replenish fluid at the contact line. (d), (e) Polarized


7


Page 8 of 20

optical microscopy (POM) images of the distributions of 5CB droplets with radial (d) and bipolar (e) configurations at the contact line. As evaporation proceeded, instead of outward flow of individual LC-droplets, flocks of LC-droplets moved back from the edge to centre, leading to an inverted transport of the droplets. During the collective movements, four different kinds of moving states were observed for these active LC-droplets, e.g., resting, sliding, oscillating, and stopping state in which the droplet comes to rest after a short swimming period. In all these states, the collective motion of LCdroplets was maintained, reminiscent of dynamic hexagonal patterns predicted by self-propelled anisotropic particle flow.27 In order to gain an in-depth understanding of the moving LC system, the formation of dynamical clusters that spontaneously form, rearrange, and reassemble was tracked and analysed (Figure 2). Initially, individual LC-droplets with radial configuration, randomly swimming in the proximity of the droplets colony or undergoing directional migration from the centre to the edge, spontaneously formed a two-dimensional ordered structure which showed hexagonal pattern (Figure 2a). Multiple LC-droplets assembled into a hexagonal closely packed structure, wherein individual droplets were in contact with each other, but did not coalesce into a big droplet or spread into a LC film. During the assembly process, the cluster of LC-droplets schooling remained stationary without distinct motion and some of the individual droplets approached and joined to the cluster which due to the large attractive force between them. As the schooling of droplets grew bigger, a collective motion occurred, contrasting the fluid behaviour of single LC-droplet (Figure 2b and Movie S3). Schooling droplets swam in the same direction, i.e., perpendicular to the contact line with the direction from the edge to the centre, and exhibited a collective motion. However, most of the individual LC-droplets were moving in the opposite direction, from the centre to edge. This phenomenon implied a very


8

Page 9 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


conflictive interaction inside the suspension, namely, the outward swimming of individual LCdroplet was dominated by the capillary flow, while the inward collective motion of LC-droplets schoolings was the result of the Marangoni flow that was sufficiently large enough to overcome the self-pining of droplets at contact line. In addition, during the collective moving process we noted that some of the individual LC-droplets could be incorporated into the droplet schooling to expand the cluster (Movie S4). Besides, the resulting movements could be studied by evaluating the corresponding velocity field of these swimming droplets. Because all of the droplets inside the schooling moved at the same speed, the collective swimming of the LC cluster was about 16.4 µm/s, higher than the speed of adjacent individual LC-droplets (5.3 µm/s). The moving speed and orientation differences of LC-droplets in a drying drop of suspension were dependent on the interplay between the competing outward capillary flow and inward evaporative induced Marangoni stress. The collective motion of these clusters was visible for up to 2 min, after which they merged with adjacent clusters and slowed their movement until they became stationary. Small swimming droplets clusters migrated toward the edge of big droplet colony to minimize the elastic energy in system.28 Figure 2c shows the selected snapshots from the merging process of two LC clusters (Movie S5), exhibiting the strong long-range attractive interactions between two swimming LC clusters. The collective motion of LC cluster was slow when they were well separated (12.4 and 10.5 µm/s, respectively). However, as they gradually approached each other, the attractive force between the LC clusters went higher with the moving speed of these clusters increased and reached as maximum (18.5 µm/s) when the two clusters merged into a large periodic array, and then stopped with additional short swimming. During the merging process, the magnitude and direction of velocity for swimming clusters correlated strongly with the


9


Page 10 of 20

variation of attractive force throughout the entire process (Figure S1). This means that the attractive coupling force between droplets clusters exists at all times, with its magnitude inversely proportional to the approaching distance.29 The elastically strained regions of 5CB molecules in the vicinity of the droplet surface give rise to anisotropic interparticle attractive forces that drive the approaching of colloidal self-assembly in LC clusters.30 Besides, we found that the LC-mediated colloidal interactions can also be influenced by the topology of LC ordering inside the droplets. Thus, compared to the droplets with radial configuration, the LC clusters with bipolar configuration exhibited an entirely different mode of collective motion with the droplets packed in chaotic arrangement (Figure S2 and Movie S6). Sonication readily formed LC-droplets with broad size distributions, from 1 µm to 15 µm. In general, all of the droplets in suspension before evaporation were evenly distributed, moving randomly in Brownian motion, which due to the thermodynamic movement of water molecules (Figure S3 and Movie S7, S8). However, a droplet size gradient inside the LC clusters was observed during the swimming process, that is, the diameters of LC-droplets in the cluster border were smaller than those in the center (Figure 2d and Movie S9). The separation of LC-droplets may be due to the differences in drag forces during the collective motion.31 Such a mechanism for size sorting of colloidal droplets suspension is of interest for a wide range of applications. A sketch of the proposed mechanism for the collective motion of LC-droplets emulsion is shown in Figure 2e. For a drop of suspension drying on a glass substrate, some of the DMAPS molecules populate the water/air interface, with the hydrophobic tail pointing outward to the air. Due to the electrostatic repulsion between the hydrophilic heads of surfactant molecules, the preferred packing for DMAPS molecules at the curved interface is unlikely to be steric dense and uniform in equilibrium.32 Note that the rate of water evaporation at the contact line is faster than


10

Page 11 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


at the free surface of the drop, therefore, the surfactant molecules concentrate locally near the edge of the drop, leading to a decrease in the interfacial surface tension. Thus, this surface tension gradient along the curved drop surface, generates radially inward Marangoni flow along the air-water interface with the surface tension direction from low to high. On the other hand, it is known that the evaporation behavior of the droplet is largely affected by the particle deposition pattern. As evaporation progressing, more and more LC-droplets accumulate at the contact line and form a monolayer LC-droplets deposit on the substrate which increase the resulting capillary force. For the droplets at contact line, the accumulated droplets deform the interface, thus, the capillary force 𝐹𝑐 = 2𝜋𝑟𝜎(𝑐𝑜𝑠𝜃)2 (where 𝑟 is the diameter of the droplet, 𝜎 is the surface tension of the liquid-vapor interface and 𝜃 is the contact angle, respectively)33 rises up and acts on the accumulations that pointing to the drop centre and repelling the coffee-ring deposition at the contact line.34,

35

In the meantime, the LC-droplet clusters at contact line experience a

outward friction force 𝐹𝑓 on LC-droplet (droplet/glass substrate and droplet/fluid medium), which resists the corresponding opposite capillary force. If 𝐹𝑐 ≤ 𝑁𝐹𝑓 (N is the number of droplets in the cluster, 𝑁 =

2 −(𝑉 −𝑉 )𝜌 𝑎2 𝑅𝑝 −√𝑅𝑝 0 𝑝 𝑛

2𝑎

, where 𝑉0 and 𝑉𝑝 is the volume of the drop for

initial and pinned time, and 𝜌𝑛 is the density of droplet in emulsion, see detailed derivation process in Supporting Information), the LC-droplets are continuously transported to the contact line and accumulate there, resulting in an increase in the friction force and a densely packed droplet schooling. However, as evaporation going, when the resulting Marangoni stress along with the inward capillary force are strong enough to overcome the friction and drive the LCdroplet cluster to move inward to the centre, then the collective motion occurs. Thus, we deduce that the collective motion of LC-droplets schooling is driven by the surface tension gradient


11


Page 12 of 20

induced Marangoni stress along with capillary force, both in flow along the air-water interface and in inward driven force that prevail over the friction.

Figure 2. (a) POM image of the formation of LC-droplet schooling before collective moving. (b) An active LC-droplet schooling viewed on a large scale, which shows that the individual droplets and LC-droplet schooling are swimming in opposite directions. (c) Time evolution of the merging process of two LC-droplet schoolings during collective motion. (d) POM image of the LC-droplets cluster during collective motion. The diameters of the droplets near the contact line are smaller than those in the centre. The arrow indicate the gradient of increasing droplets diameters. (e) Sketch of the driven force for LC-droplets collective motion at the contact line, where 𝐹𝑐 and 𝐹𝑓 represent the capillary force and friction force, respectively.


12

Page 13 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Interestingly, we observed an unexpected collective order in the evolution of droplets motion. Initially, some defects were formed and retained in the formation and collective motion of the hexagonal LC-droplet colonies (Figure 3a, 3b and Movie S10). The density of defects in the LC cluster was sufficiently low, which derived from droplets having sizes that deviating significantly from the others (impurities in periodic droplets array), or droplets with the number of neighbors deviating from six (interstitial or vacancies in droplets array).36 During the collective motion of LC cluster, the droplets near defects disrupted their periodic ordering and rearranged into long-range dislocation line (Figure 3c and Movie S11). The defects in LC clusters produced high stress fields that interact with dislocations, acting as preferential sites for dislocation formation.37 Given that the dislocation dynamic in real crystals is an intermittent, stochastic and unpredictable event, these ordered dislocations nucleation at the defect region in LC clusters are unpredicted. When the swimming speed of the clusters slows down until eventually reaching zero, the dynamic states of the droplets in clusters are different from each other. Some of the droplets stop moving, while others continue moving further. As a consequence, the gradient speeds of these swimming droplets apply a compressive pressure on the moderative and static droplets, pressing the droplet boundary forward which forms an edge dislocation and rearranges the cluster ordering (Figure 3d). Remarkably, when the entire LC cluster was no longer moving, the edge dislocation could also be retained inside the periodic LCcluster, but with certain degree of droplet deformation which due to the contraction forces in LC (Figure 3e-g). This dislocation phenomenon between adjacent ordered LC-droplet boundaries might be attributed to the interfacial stress between LC-droplet, thus, stress in droplets boundaries at the interface was much larger than the average stress in the droplet lattice, with the stress source from anisotropic attractive interactions among individual LC-droplet.38 We


13


Page 14 of 20

concluded that the evolution of defects and dislocations in droplet boundaries during collective motion were strongly influenced by the inner stress between LC molecules. However, further research is still needed to elucidate the mechanism of dislocation dynamics in the collective motion process of LC-droplets schoolings.

Figure 3. Time evolution of the LC-droplets schooling during collective motion process. (a) POM image of the formation of topological defect in a schooling of LC-droplets. (b) POM image of the defects in LC-droplet schooling during collective motion. (c) POM image of the


14

Page 15 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


dislocation lines in LC-droplet schooling during collective motion. (d) The schematic description of the transition from topological defect to dislocation line in swimming LC-droplet schooling. (e) POM image of the moderative swimming LC-droplet schooling, which shows some dislocations in the static region. (f)-(g) POM images of the static LC-droplet schooling with different magnifications. It shows that the dislocation lines are preserved in the periodic droplets ordering. In summary, we demonstrated the self-assembly and collective behaviors of LC-droplets in surfactant solution, acting as two dimensional soft living crystals. The micrometer scaled LCdroplets exhibited either radial or bipolar configurations, which depended on the type of stabilized surfactants. By drying a drop of suspension on a glass surface, the suspended droplets autonomously exhibited mechanical motions that were driven by the outward capillary flow combined with inward Marangoni stress along with capillary force. Systematic analysis of the dynamic interactions and collective behavior of the swimming LC-droplet, showed the evolution of defects and dislocation formation in a periodic schooling of LC-droplets. In addition, due to the high solubility of 5CB, we think that these droplets can also be considered as ideal candidates to serve as cargo ships to transfer valuable nanomaterials (e.g., plasmonic nanoparticles) into particular position and orientation, opening new opportunities to fabricate novel metamaterials. These swimming LC-droplets can also serve as a rich platform for fundamental theoretical studies, seeking to understand biological active matter with hierarchically organized structure. Moreover, we anticipate that these intriguing swimming droplets could be extended to other LC systems with different phases and compositions, for example, smectic and chiral nematic LCs with controlled chirality, to achieve more sophisticated collective behavior than swimming nematic LC-droplet.


15


Page 16 of 20

ASSOCIATED CONTENT AUTHOR INFORMATION Author Contributions G. C. prepared the liquid crystal emulsions and carried out the experimental measurement and data analysis. G. C. and E. Z. designed and led the project. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Russell Berrie Nanotechnology Institute (RBNI), the Israel Science Foundation (ISF Grant No. 286/15). E.Z. acknowledges the financial support of the Winograd Chair of Fluid Mechanics and Heat Transfer at Technion. Supporting Information Additional experimental details and figures as well as movies are demonstrated in Supporting Information. This material is available free of charge via the Internet at http://pubs.acs.org.

REFERENCES (1) Vicsek, T.; Zafeiris, A. Collective Motion. Phys. Rep. 2012, 517, 71-140. (2) Palacci, J.; Sacanna, S.; Steinberg, A. P.; Pine, D. J.; Chaikin, P. M. Living Crystals of Light-Activated Colloidal Surfers. Science 2013, 339, 936-940. (3) Magdanz, V.; Sanchez, S.; Schmidt, O. G. Development of a Sperm-Flagella Driven Micro-Bio-Robot. Adv. Mater. 2013, 25, 6581-6588.


16

Page 17 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(4) Das, A.; Polley, A.; Rao, M. Phase Segregation of Passive Advective Particles in an Active Medium. Phys. Rev. Lett. 2016, 116, 068306. (5) Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Capillary Flow as the Cause of Ring Stains from Dried Liquid Drops. Nature 1997, 389, 827829. (6) Yunker, P. J.; Still, T.; Lohr, M. A.; Yodh, A. Suppression of the Coffee-Ring Effect by Shape-Dependent Capillary Interactions. Nature 2011, 476, 308-311. (7) Marín, Á. G.; Gelderblom, H.; Lohse, D.; Snoeijer, J. H. Order-to-Disorder Transition in Ring-Shaped Colloidal Stains. Phys. Rev. Lett. 2011, 107, 085502. (8) Malinowski, R.; Volpe, G.; Parkin, I. P.; Volpe, G. Dynamic Control of Particle Deposition in Evaporating Droplets by an External Point Source of Vapor. J. Phys. Chem. Lett. 2018, 9, 659-664. (9) Popkin, G. The Physics of Life. Nature 2016, 529, 16-18. (10) Prost, J. The Physics of Liquid Crystals; 2nd Edition. Oxford Univ. Press, 1995. (11) Shimoda, Y.; Ozaki, M.; Yoshino, K. Electric Field Tuning of a Stop Band in a Reflection Spectrum of Synthetic Opal Infiltrated with Nematic Liquid Crystal. Appl. Phys. Lett. 2001, 79, 3627-3629. (12) Coles, H. J.; Pivnenko, M. N. Liquid Crystal ‘Blue Phases’ with a Wide Temperature Range. Nature 2005, 436, 997-1000. (13) Cagnon, M.; Durand, G. Mechanical Shear of Layers in Smectic-A and Smectic-B Liquid Crystal. Phys. Rev. Lett. 1980, 45, 1418-1421. (14) Tjipto, E.; Cadwell, K. D.; Quinn, J. F.; Johnston, A. P.; Abbott, N. L.; Caruso, F. Tailoring the Interfaces between Nematic Liquid Crystal Emulsions and Aqueous Phases Via Layer-by-Layer Assembly. Nano Lett. 2006, 6, 2243-2248. (15) Miller, D. S.; Wang, X.; Abbott, N. L. Design of Functional Materials Based on Liquid Crystalline Droplets. Chem. Mater. 2013, 26, 496-506. (16) Poulin, P.; Stark, H.; Lubensky, T.; Weitz, D. Novel Colloidal Interactions in Anisotropic Fluids. Science 1997, 275, 1770-1773. (17) Loudet, J. C.; Barois, P.; Poulin, P. Collodial Ordering from Phase Separation in a Liquid-Crystalline Continuous Phase. Nature 2000, 407, 611-613. (18) Smalyukh, I. I.; Chernyshuk, S.; Lev, B.; Nych, A.; Ognysta, U.; Nazarenko, V.; Lavrentovich, O. Ordered Droplet Structures at the Liquid Crystal Surface and Elastic-Capillary Colloidal Interactions. Phys. Rev. Lett. 2004, 93, 117801. (19) Chu, G.; Vilensky, R.; Vasilyev, G.; Martin, P.; Zhang, R.; Zussman, E. Structure Evolution and Drying Dynamics in Sliding Cholesteric Cellulose Nanocrystals. J. Phys. Chem. Lett. 2018, 9, 1845-1851. (20) Davidson, Z. S.; Huang, Y.; Gross, A.; Martinez, A.; Still, T.; Zhou, C.; Collings, P. J.; Kamien, R. D.; Yodh, A. Deposition and Drying Dynamics of Liquid Crystal Droplets. Nat. Commun. 2017, 8, 15642. (21) Querner, C.; Fischbein, M. D.; Heiney, P. A.; Drndić, M. Millimeter-Scale Assembly of CdSe Nanorods into Smectic Superstructures by Solvent Drying Kinetics. Adv. Mater. 2008, 20, 2308-2314. (22) Liang, H. L.; Enz, E.; Scalia, G.; Lagerwall, J. Liquid Crystals in Novel Geometries Prepared by Microfluidics and Electrospinning. Mol. Cryst. Liq. Cryst. 2011, 549, 69-77.


17


Page 18 of 20

(23) Brake, J. M.; Mezera, A. D.; Abbott, N. L. Active Control of the Anchoring of 4 ‘-Pentyl4-Cyanobiphenyl (5CB) at an Aqueous-Liquid Crystal Interface by Using a Redox-Active Ferrocenyl Surfactant. Langmuir 2003, 19, 8629-8637. (24) Muševič, I.; Škarabot, M.; Tkalec, U.; Ravnik, M.; Žumer, S. Two-Dimensional Nematic Colloidal Crystals Self-Assembled by Topological Defects. Science 2006, 313, 954-958. (25) Nych, A.; Ognysta, U.; Pergamenshchik, V.; Lev, B.; Nazarenko, V.; Muševič, I.; Škarabot, M.; Lavrentovich, O. Coexistence of Two Colloidal Crystals at the Nematic-LiquidCrystal-Air Interface. Phys. Rev. Lett. 2007, 98, 057801. (26) Koenig, G. M.; Lin, I. H.; Abbott, N. L. Chemoresponsive Assemblies of Microparticles at Liquid Crystalline Interfaces. Proc. Natl. Acad. Sci. 2010, 107, 3998-4003. (27) Koch, D. L.; Subramanian, G. Collective Hydrodynamics of Swimming Microorganisms: Living Fluids. Annu. Rev. Fluid Mech. 2011, 43, 637-659. (28) Elgeti, J.; Winkler, R. G.; Gompper, G. Physics of Microswimmers-Single Particle Motion and Collective Behavior: A Review. Rep. Prog. Phys. 2015, 78, 056601. (29) Israelachvili, J. N. Intermolecular and Surface Forces; Academic press, 2011. (30) Muševič, I. Forces in Nematic Liquid Crystals: From Nanoscale Interfacial Forces to Long-Range Forces in Nematic Colloids. Liq. Cryst. 2009, 36, 639-647. (31) Hendarto, E.; Gianchandani, Y. B. Size Sorting of Floating Spheres Based on Marangoni Forces in Evaporating Droplets. J. Micromech. Microeng. 2013, 23, 075016. (32) Still, T.; Yunker, P. J.; Yodh, A. G. Surfactant-Induced Marangoni Eddies Alter the Coffee-Rings of Evaporating Colloidal Drops. Langmuir 2012, 28, 4984-4988. (33) Weon, B. M.; Je, J. H. Self-Pinning by Colloids Confined at a Contact Line. Phys. Rev. Lett. 2013, 110, 028303. (34) Weon, B. M.; Je, J. H. Capillary Force Repels Coffee-Ring Effect. Phys. Rev. E 2010, 82, 015305. (35) Sangani, A. S.; Lu, C.; Su, K.; Schwarz, J. A. Capillary Force on Particles near a Drop Edge Resting on a Substrate and a Criterion for Contact Line Pinning. Phys. Rev. E 2009, 80, 011603. (36) Gai, Y.; Leong, C. M.; Cai, W.; Tang, S. K. Spatiotemporal Periodicity of Dislocation Dynamics in a Two-Dimensional Microfluidic Crystal Flowing in a Tapered Channel. Proc. Natl. Acad. Sci. 2016, 113, 12082-12087. (37) Hull, D.; Bacon, D. J. Introduction to Dislocations; Butterworth-Heinemann, 2001. (38) Nazarenko, V.; Nych, A.; Lev, B. Crystal Structure in Nematic Emulsion. Phys. Rev. Lett. 2001, 87, 075504.


18

Page 19 of 20 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1 274x295mm (300 x 300 DPI)



TOC 114x64mm (300 x 300 DPI)


Page 20 of 20

From Chaos to Order: Evaporative Assembly and Collective Behavior

Recommend Documents