A 3D-Printed Molecular Ferroelectric Metamaterial

A 3D-printed molecular ferroelectric metamaterial

Yong Hua,1, Zipeng Guob,1, Andrew Ragonesea,1, Taishan Zhuc, Saurabh Khujea, Changning Lia, Jeffrey C. Grossmanc, Chi Zhoub,2, Mostafa Nouha,2, and Shenqiang Rena,d,e,2

aDepartment of Mechanical and Aerospace Engineering, The State University of New York at Buffalo, Buffalo, NY 14260; bDepartment of Industrial and Systems Engineering, The State University of New York at Buffalo, Buffalo, NY 14260; cDepartment of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; dDepartment of Chemistry, The State University of New York at Buffalo, Buffalo, NY 14260; and eResearch and Education in Energy Environment & Water Institute, The State University of New York at Buffalo, Buffalo, NY 14260

Edited by Thomas E. Mallouk, University of Pennsylvania, University Park, PA, and approved September 21, 2020 (received for review July 2, 2020) Molecular ferroelectrics combine electromechanical coupling and high loading of solid functional component is required to afford electric polarizabilities, offering immense promise in stimuli- functionalities in printed structures (19), while this challenges the dependent metamaterials. Despite such promise, current physical homogeneity and viscosity stability for ultimate printability of the realizations of mechanical metamaterials remain hindered by the feedstock. Additive manufacturing and its design space in func- lack of rapid-prototyping ferroelectric metamaterial structures. tional ferroelectric materials are particularly limited due to the Here, we present a continuous rapid printing strategy for the vol- limitation of ferroelectric solid component loading. In addition, the umetric deposition of water-soluble molecular ferroelectric meta- mechanical flexibility and ferroelectricity of printed materials are materials with precise spatial control in virtually any three- diminished as a result of randomly organized components (20, 21). dimensional (3D) geometry by means of an electric-field–assisted Therefore, a seamless integration of additive manufacturing, mo- additive manufacturing. We demonstrate a scaffold-supported lecular ferroelectric materials, and metamaterial design would ferroelectric crystalline lattice that enables self-healing and a provide the ultimate solution to unlock the functional material and reprogrammable stiffness for dynamic tuning of mechanical exotic structural properties of molecular ferroelectric metamaterials metamaterials with a long lifetime and sustainability. A molecu- for unprecedented emerging applications. lar ferroelectric architecture with resonant inclusions then ex- Here, we unravel a printable mechanical metamaterial of imi- hibits adaptive mitigation of incident vibroacoustic dynamic dazolium perchlorate (ImClO4) (2, 22, 23), a transparent molec- loads via an electrically tunable subwavelength-frequency band ular ferroelectric with superior electromechanical coupling and gap. The findings shown here pave the way for the versatile ad- reprogrammable stiffness. We propose a continuous rapid 3D ENGINEERING ditive manufacturing of molecular ferroelectric metamaterials. printing technique which can reduce the manufacturing time of ferroelectrics from hours down to minutes. Different from con- molecular ferroelectrics | mechanical metamaterials | hydrogel | additive ventional inorganic or organic–inorganic ferroelectrics (24, 25), manufacturing | three-dimensional printing the ionic nature of molecular ferroelectrics enables high solu- bility in water, ensuring a highly dense and transparent precur- olution-processable molecular ferroelectrics, which show sor. We optically pattern the 3D architecture scaffolds through Sferroelectric properties approaching inorganic perovskites, have amassed much recent attention due to their lightweight, Significance tunable electrooptic and electromechanical coupling effects (1–5). Spontaneous polarization and the ability to switch the electromechanical activity by an external electric or mechanical Molecular ferroelectrics, which show the ability to switch the stimulus is of prime importance, establishing the basis for many electromechanical activity by an external electric field, estab- metamaterial technologies (6–8). Over the past decade, elastic lish the basis for mechanical metamaterial technologies. De- metamaterials with resonant inclusions have gained significant spite their theoretical promise, such mechanical metamaterials remain hindered by the lack of adaptive stimuli-responsive traction owing to their unique response to incident dynamic “ ” loads, ranging from subwavelength band gaps (9–11), back- materials which can be effectively tuned on demand across scattering immune wave guides (12, 13), and topological time and length scales. Here, we unravel a printable mechani- pumps (14–16), to the design of logic gates, nonreciprocity, and cal metamaterial of imidazolium perchlorate with superior diodelike formations (17, 18). Despite their theoretical promise, electromechanical coupling and reprogrammable stiffness. We such mechanical metamaterials remain hindered by the lack of propose a continuous rapid three-dimensional (3D) printing technique which can reduce the manufacturing time of ferro- adaptive stimuli-responsive materials which can be effectively electrics from hours down to minutes. The printed molecular tuned “on demand” across the time and length scales dictated by ferroelectric metamaterial structure is then shown to enable a such metamaterials. On the other hand, heterogeneous meta- tunable-frequency vibration-isolating architecture. This study material structures and systems have been shown to produce paves the way for rationally designed 3D-printable molecular tailorable properties beyond those of the constitutive materials ferroelectric metamaterials. (ferroelectrics) owing to the unique geometrical and topological

material reorganization. However, the hallmark feature of such Author contributions: Y.H., Z.G., A.R., C.Z., M.N., and S.R. designed research; Y.H., Z.G., metamaterials is a hierarchical architecture which often exhibits A.R., and T.Z. performed research; Y.H., Z.G., A.R., C.L., T.Z., and J.C.G. contributed new highly complicated internal features, rendering these exotic reagents/analytic tools; Y.H., Z.G., A.R., T.Z., C.Z., and M.N. analyzed data; and Y.H., Z.G., structures extremely challenging, if not impossible, to achieve A.R., T.Z., S.K., J.C.G., C.Z., M.N., and S.R. wrote the paper. with traditional manufacturing processes. The authors declare no competing interest. Three-dimensional (3D) printing has been hailed as an emerging This article is a PNAS Direct Submission. advanced manufacturing paradigm, providing a large potential to Published under the PNAS license. rapidly fabricate highly complicated metamaterial structures with a 1Y.H., Z.G., and A.R. contributed equally to this work. wide variety of materials owing to its elegant concept of layer by 2To whom correspondence may be addressed. Email: [email protected], mnouh@ layer deposition. However, 3D printing is mainly limited to creating buffalo.edu, or [email protected]. complex geometries of nonfunctional structures. The competition This article contains supporting information online at https://www.pnas.org/lookup/suppl/ between printability and functionality has been identified as the doi:10.1073/pnas.2013934117/-/DCSupplemental. main limitation of 3D printing in functional materials. Generally, a

www.pnas.org/cgi/doi/10.1073/pnas.2013934117 PNAS Latest Articles | 1of7 Downloaded by guest on September 29, 2021 stereolithography (SLA) 3D printing for selective volumetric desired ferroelectric performance by changing the concentration crystallization of ionic ImClO4 precursor. The SLA-printed water- of ImClO4 or the ratio of PEGDA. Thus, we prepare the pre- soluble ferroelectric precursor and photopolymerizable material cursor with saturated ImClO4 solution and low volume ratio of with a highly porous yet tough polymer network serve as an ex- PEGDA (5 vol %). Finally, dried printed samples with around cellent carrier to in situ crystalize and organize molecular ferro- 50 vol% ratio of ImClO4 are obtained. electric crystals. The patterned scaffold is then dehydrated under a In general, the crystal growth in a liquid environment is con- biased electric field to crystallize ImClO4 with the desired polar- trolled by two processes: the diffusion of ions through the liquid ization orientation. The printed molecular ferroelectrics also ex- phase to the growth front and the reorganization of crystal grains hibit a self-healing ability from the overloaded mechanical and into the polycrystal. In our experiments, the diffusion of ions electric field (26, 27). The printed molecular ferroelectric meta- should not be the limiting factor because of the highly concen- material structure is then shown to enable a tunable-frequency trated ImClO4 precursor solution and large pore size of the vibration-isolating architecture. This study paves the way for ra- hydrogel scaffold. Thus, the crystal grain reorganization is the tionally designed 3D-printable molecular ferroelectric materials limiting step during the growth. By applying a biased electric for mechanical metamaterials. field, we can organize the orientation of small grains formed C Results right after the nucleation. As shown in Fig. 1 , the dehydration process was conducted under an electric field, which was applied 3D Fabrication Process. Three-dimensional SLA printing enables to obtain a high-quality polycrystal with a preferred polarization the creation of volumetric architectures consisting of nanoscale orientation of ImClO . The small single-crystal ImClO grains feature size using programmed automation processes (28–30). 4 4 can merge into a large polycrystalline structure with preferred By analogy, we inferred that this SLA strategy could be incor- crystal orientation as water continuously and slowly evaporates porated for the volumetric design of ferroelectric metamaterials if the following fundamental prerequisites are met: transparent under the biased electric field. Printed ImClO4 with and without ferroelectric precursor for the curing light and sufficient curing the biased electric field are denoted as the printed and control depth, light-sensitive polymers, and sufficient density to trigger sample, respectively, in the following discussion. electromechanical coupling and ferroelectricity. If these chal- Structural and Optical Properties. As shown in Fig. 2A, the printed lenges can be addressed by molecular ferroelectrics, a rapid 3D sample maintains its geometry with uniform shrinkage after it is fabrication strategy would allow control over the geometry, B feature size, and polarization direction of molecular ferroelectric fully dried. Fig. 2 shows its in situ resistance measurement metamaterials. Fig. 1A illustrates the schematic diagram of SLA during the drying, while the resistance escalates continuously until the formation of the ImClO4 crystal. As shown in Fig. 2C,if printing for molecular ImClO4 ferroelectrics with high dimensional accuracy, structural complexity, and high throughput. The the biased electric field is applied together with drying, the obtained sample shows the preferred orientations with the dif- molecular ferroelectric ImClO4 crystal is water-soluble and can mix with photopolymerizable material to achieve transparent fraction peaks at 22.36° and 24.62° representing the (210) and printable precursor ink solution with a viscosity of 1.70 cSt (SI (102) planes, respectively. A high diffraction intensity for the Appendix, Table S1 and Fig. S3) (31). The transparent and highly (102) planes suggests that its preferred growth orientation concentrated ferroelectric precursor solution plays a key role in matches with its polarization axis for the pronounced ferroelec- the SLA printing as its low diffraction index can facilitate light tric properties (22), confirmed by our theoretical modeling (SI penetration and prevent light scattering. This ultimately allows Appendix, Figs. S7–S9). Since the ferroelectric ordering tem- for a reliable, accurate, and efficient 3D printing process. perature of ImClO is far above its crystallization temperature, A 4 In the bottom-up SLA process (Fig. 1 ), a smaller traction the anisotropic energy associated with this ferroelectric state is force between the structure being printed and the material large enough to align the grains under the electric field (SI Ap- container is the vital factor in printing speed and reliability (32), pendix, Supporting Text 5). The anisotropic energy leads to the and such force is linearly proportional to viscosity (33). rotation of the crystal nucleus parallel to the external electric Therefore, the low viscosity of the precursor material enables field. Moreover, the scaffolds not only have superlative intrinsic continuous rapid printing, which reduces the manufacturing properties, such as optical transparency and light weight, but time from hours to minutes for the same structure (Movie S1). they are also geometrically compatible with the ImClO4 crystal. This represents a game-changing molecular ferroelectric SI Appendix manufacturing technique and offers the unique advantages of A cubic ImClO4 sample ( , Fig. S4) is printed for the prevention of hydrogel dehydration and printing failure, as optical measurement. Similar to the single crystal (2, 23), the printed ImClO4 is transparent in the visible range (Fig. 2D) with well as process efficiency and structural accuracy. During SI Appendix printing (Fig. 1C), the precursor solution is exposed to ultra- a large energy band gap of 4.1 eV ( , Fig. S8). The violet (UV) light, and poly(ethylene glycol) diacrylate transparency of the printed sample renders it a promising can- (PEGDA) is then cross-linked to form the scaffold network didate for electrooptic devices (2). with the encapsulated ions of the ImClO precursor. As shown 4 Dielectric, Ferroelectric, and Electromechanical Coupling Properties. in Movie S1, a complex geometric structure (Schwarz primitive A structure, 25 × 25 × 25 mm3)canbeprintedin8minasopposed Fig. 3 shows the temperature dependence of dielectric per- to 3 h by conventional methods. The large pore size of the mittivity of the ImClO4 single crystal, the printed sample, and the scaffold (about a few micrometers, SI Appendix,Fig.S5)pro- control sample, which all show the characteristic sharp dielectric vides higher controllability and flexibility. Additionally, the anomalies around the phase transition temperature. The second- electrical resistance measurement (SI Appendix,Fig.S6) shows order phase transition occurs at 375 K from the paraelectric to that the as-printed sample is electrically conductive due to the the ferroelectric phase, suggesting that the transition is not abundance of ions. Dehydration then crystallizes molecular influenced by the crystallization process. However, these samples ferroelectric ImClO4, while the polymer skeleton holds the as- show distinct dielectric behavior around the first-order phase printed structure after water evaporation due to the elasticity of transition (around 210 K with large hysteresis as shown in SI the PEGDA polymer network (34). It has to be mentioned that a Appendix, Fig. S10). The peaks of dielectric permittivity for the high loading of molecular ferroelectric component is required to first-order transition in the printed sample indicate that the applied maintain the high polarization in printed structures. The volume electric field improves its crystal order with the dielectric anomaly ratio of ferroelectric phase can be easily tuned to serve for the appearing at 237 and 222 K, respectively. More importantly, its

2of7 | www.pnas.org/cgi/doi/10.1073/pnas.2013934117 Hu et al. Downloaded by guest on September 29, 2021 ENGINEERING 3 Fig. 1. Schematic figure for 3D fabrication process. (A) Schematic diagram for manufacturing ImClO4 (Schwarz primitive structure, 25 × 25 × 25 mm )bythe SLA method. The digital projection printing setup (SI Appendix, Fig. S1) was utilized to project dynamic digital masks on the photocurable polymer composite solution. The UV light used has a wavelength of 385 nm and the control of image projection was achieved through a dynamic micromirror device. (B) The

traditional SLA printing method for ferroelectrics based on the precursor prepared by mixing the ImClO4 powder with UV-sensitive resin (Anycubic Inc). (C) Schematic figure for the new hydrogel-based printing method for the ImClO4 crystal. The hydrogel sample with the desired ImClO4 solution can be obtained by directly printing from precursor made with the desired ImClO4 water solution. The crystallization process for the printed sample is performed based on the printed hydrogel which was dried in the air under an electric field. (Inset) SEM image for the printed ImClO4.

dielectric permittivity shows anabruptjumpat222K,suggesting Fig. 3E and Movie S2, the degraded ImClO4 can be dissolved the single-crystal–like ferroelectric properties. into ImClO4 solution and lead to the formation of the − The ferroelectricity can be attributed to the small permanent hydrogel state containing Im+ and ClO ions. Additional − 4 dipole moment of the slightly distorted ClO4 anion together electrical-field assistant drying process could help to recover with the contribution from the off-center displacement of the its ferroelectric property. imidazolium cations (SI Appendix, Fig. S9). We further carried out the polarization vs. electric-field hysteresis loops (P-E loops) Metamaterial Simulation. The printed ferroelectric ImClO4 is at room temperature. As shown in Fig. 3B, the polarization of expected to show response to an external electric field, particu- the ImClO4 single crystal, the printed sample, and the control larly a change in material stiffness due to the ferroelectric sample are 1.49, 0.22, and 0.08 μC/cm2 at 3-kV/cm poling electric alignment in the direction of the external field. To investigate field, respectively. As shown in SI Appendix, Fig. S11, the Raman this property, the stress–strain curves of the printed sample are ’ spectrum for printed ImClO4 suggests that the chemical bonding recorded under varying electric-field strength and its Young s is not influenced by the scaffold when compared with the modulus is measured, as presented in Fig. 3D and SI Appendix, ’ ImClO4 single crystal. The thermogravimetric analysis (TGA) Table S2. These experiments demonstrate an initial Young s measurement shows one broad decomposition temperature modulus of 12.0 MPa in the absence of electric field and varia- range from 500 to 700 K; such broad decomposition can be tion in elastic modulus up to 25% as the field strength increases considered as a combination of the decomposition temperature from 0 to 2,000 V/cm (Fig. 3D and SI Appendix, Table S2), for ImClO4 and PEGDA. The 50% volume ratio for printed demonstrating significant programmable tunability in the ferro- ImClO4 is projected to decrease its polarization. In comparison, electric material stiffness. This successful design of a printed the 3D-printed PEGDA does not show any P-E loop behavior molecular ferroelectric material opens up new avenues in the (SI Appendix, Fig. S12), suggesting that the measured polariza- increasingly popular domain of active electroacoustic meta- tion originated from the ImClO4 phase. Often, ferroelectric materials with highly responsive and tunable mechanical prop- property degradation could appear in ferroelectrics due to erties. To illustrate an application of this tunable material, a electrical conduction under repetitive cycling or high, local “hard–soft–hard” locally resonant metamaterial (LRM) is electric field. As shown in Fig. 3C, the degraded sample shows architected with the printed molecular ferroelectric material as lower polarization when compared with printed ImClO4.But the filler component, in which the soft printed ferroelectric is here, the water-based printable ferroelectrics provide an ef- attached to stiffer matrix and resonator elements to form each fective way toward self-healing: the printed sample with de- unit cell of the periodic structure. This LRM comprises multiple graded ferroelectric property could be healed by dissolving into such unit cells in a two-dimensional (2D) array and is schemat- the ImClO4 solution followed by recrystallization. As shown in ically depicted in Fig. 4A.

Hu et al. PNAS Latest Articles | 3of7 Downloaded by guest on September 29, 2021 Fig. 2. Three-dimensionally–printed ImClO4.(A) Optical images showing the dimension change during the drying process. The yellow-colored dye was added to the precursor of 0.002 wt % in order to have a detailed visualization of the printed part. (B) In situ time-resistance measurement for the printed sample

during the drying process. (Insets) Optical images for the printed sample during the drying process. (C) XRD patterns for the ImClO4 single crystal, printed ImClO4 drying under an electric field (printed ImClO4 crystal), and printed ImClO4 drying without an electric field (control sample). (D) Transmittance spectra for printed ImClO4, PEGDA, and the ImClO4 crystal. (Inset) Optical images demonstrate the transparency of printed ImClO4; green laser light can penetrate the sample from right to left. (Inset) Schematic figure shows that the laser light is parallel to the direction of applied electric field during dehydration process.

Cubic ImClO4 sample (SI Appendix, Fig. S4) is used for optical measurement.

An illustration of the behavior of this ferroelectric meta- higher frequencies, while little to no electric field strengths of material is presented in SI Appendix, Fig. S16, showing the fre- 0 and 300 V/cm yield a lower-frequency band gap for the same quency response from 500 to 2,000 Hz at three distinct geometry and configuration, thus causing an incident excitation measurement locations (SI Appendix, Fig. S16A) and illustrating of the same frequency to lie both inside and outside the for- the array’s vibration profile both outside (M1, 630 Hz) and inside bidden regime depending on electric-field strength (Fig. 4 C and (M2, 845 Hz) the emergent frequency band gap (SI Appendix, D and Movie S3). Furthermore, a change in field strength from Fig. S16B) using aluminum and brass as the matrix and resonator 0 to 2,000 V/cm instigates a band gap shift from 759–1,266 Hz to materials, respectively (material properties are provided in SI 847–1,411 Hz (SI Appendix, Table S2), culminating in an 11.6% Appendix, Table S3). The metamaterial is excited via transverse increase in center band gap frequency corresponding to the z-directional flexural waves at the bottom corner of the array maximum change in electric-field strength. which propagate in the xy plane of the structure, permitted to propagate through the metamaterial at pass-band frequencies Conclusion but forbidden in the frequency band gap indicated by the shaded We demonstrate a 3D-printed molecular ferroelectric meta- region of SI Appendix, Fig. S16A. SI Appendix, Fig. S16A pits the material architecture via additive manufacturing, which exhibits displacement response of the finite metamaterial (top portion; optical transparency, ferroelectricity, and a self-healing ability. generated from a finite-element model) against the wave dis- The ability to restore ferroelectric and electromechanical cou- persion behavior of an infinite array of the constitutive unit cell pling properties opens up opportunities to greatly enhance the (bottom portion; predicted via a Bloch-wave band structure). durability and reliability of mechanical metamaterials. The me- The band gap calculated from the dispersion analysis spans the chanical properties of the printed metamaterial are also shown – SI Appendix 759 1,266-Hz range ( , Table S2) and provides ex- to be dynamically tunable by an external electric field. Finally, a cellent agreement with the displacement transfer function cap- locally resonant architecture is designed with the printed mo- tured in the frequency response. lecular ferroelectric metamaterial, yielding a tunable range of Using this passive configuration as a benchmark, the meta- frequencies within which incident loads are exponentially sup- ’ material s versatility is then expanded by exploiting the sensitivity pressed. Our study shows that printed molecular ferroelectric ’ of the printed ferroelectric material s elastic modulus to an ex- metamaterials are of particular interest for mechanical isola- ternally applied electric field. Different simulated scenarios for tion and dispersive wave manipulation under incident dynamic electric field strengths of 0, 300, 700, and 2,000 V/cm are loads, notably without the need for hard-wired setups (35), depicted in Fig. 4, showing the response and band gap shift at the shunt circuits (36), spinning parts (37), and motor-driven same measurement locations used in SI Appendix, Fig. S16 B ’ components (38), which cannot be readily scaled to most (Fig. 4 ) and demonstrating the change in the metamaterial s practical applications. displacement field at a single fixed frequency of 810 Hz (Fig. 4C). Fig. 4D presents a direct quantitative comparison Materials and Methods between the displacement transfer function and the electric-field Detailed descriptions of the experimental procedures and analyses are strength at the three measurement locations, demonstrating an provided in SI Appendix, Materials and Methods. In brief, ImClO4 was syn- ability to fully control the elastic deformation level in prescribed thesized by allowing the imidazole base dissolved in distilled water to react regions by selectively tuning the external stimulation. Due to the with perchloric acid. UV-vis absorption and transmittance spectra were col- increased stiffness of the soft ferroelectric filler, large electric- lected using an Agilent Cary 7000 UV-Visnear-IR spectrophotometer. The field strengths of 700 and 2,000 V/cm drive the band gap to crystal structure was characterized by X-ray diffraction (XRD; Rigaku Ultima

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Fig. 3. Dielectric, ferroelectric, and electromechanical coupling properties of printed ImClO4 with self-healing ability. (A) Temperature dependence of dielectric permittivity for ImClO4 single crystal, printed ImClO4, and control sample. (B) P-E loops at 5 Hz for ImClO4 single crystal, printed ImClO4 dried in the air, and printed ImClO4 dried in the air under a biased electric field. (C) P-E loops at 5 Hz under different electric fields for printed ImClO4 dried in the air. (D) Electric-field dependence of elastic modulus for printed ImClO4.(E) Optical images showing the self-healing process. (Scale bar, 10 mm.) The printed ImClO4 is degraded due to electric loading. Self-healing ability can be realized by immersing the degraded sample in the desired ImClO4 solution. Then, the new sample with well-crystallized structure can be obtained after performing the electric-field assistant drying process. The yellow-colored dye was added to the precursor of 0.002 wt % in order to have a detailed visualization of the printed part.

IV instrument operating with a Cu Ka radiation). The microstructure exam- characterization was performed with a Radiant Ferroelectric Tester Precision ination was performed in a field emission gun scanning electron microscope LC. The temperature dependence of dielectric constant was measured in a (JSM 7001F, JEOL). Compression experiments for the 3D-printed sample Quantum Design Physical Property Measurement System with a Radiant were performed with a Mark-10 universal testing machine. Ferroelectric High Voltage Cryogenic Probe and an Agilent 4294A impedance analyzer.

Hu et al. PNAS Latest Articles | 5of7 Downloaded by guest on September 29, 2021 Fig. 4. Tunable metamaterial generation using printed ferroelectric material. (A) Configuration of metamaterial array and unit cell highlighting the ferroelectric material as the filler component of each cell. (B) Displacement transfer functions and shifted band gaps (BGs) numerically simulated with various applied electric-field strengths. (Experimentally determined elastic moduli with applied electric-field strength shown in Fig. 3D and SI Appendix, Table S2 were utilized to model the effects of the applied electric field on the metamaterial; shaded regions indicate band gaps.) (C) Simulated vibration responses at 810 Hz demonstrating the tunability of the metamaterial’s displacement field under various electric fields. (D) Direct comparison between displacement transfer function and electric field strength at 810 Hz at the three simulated measurement locations.

The SLA printing process was performed with a custom-built SLA printer, Division of Materials Sciences and Engineering, under Award DE-SC0018631 utilizing a bottom-up configuration. (Physical properties of molecular electronic crystals). The US Army Research Office supports S.R. under Award W911NF-18-2-0202 (Self-assembly of Data Availability. All study data are included in the article and SI Appendix. organic crystals). M.N. acknowledges support of this work from the US National Science Foundation through Awards 1904254 and 1847254. M.N. and S.R. ACKNOWLEDGMENTS. Work at the University at Buffalo (S.R.) was sup- acknowledge support from the NY State Center of Excellence in Material ported by the US Department of Energy, Office of Basic Energy Sciences, Informatics. Y.H. acknowledges support from Yunru Zhang in figure design.

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