William Wang Laboratory for Soft Matter Research
Funding
External Funding Sources
National Science Foundation
Award #: 2227991 (Link to award page)
Project Title: Collaborative Research: Inkjet Printing Framework by Droplet Impact-induced Ink Release from Liquid Crystal Receiving Substrate.
Sponsoring Organization: NSF, Civil, Mechanical and Manufacturing Innovation (CMMI), Advanced Manufacturing
PI: Wang, X.
Start and End Date: 2023/07/01 - 2026/06/30
Amount of Award from Contract Source: $358,360
We thank the NSF and Program Manager Dr. Linkan Bian for their support!
Award #: 2339425 (Link to award page)
Project Title: CAREER: Controlling Chain Conformation in Amorphous Polymers through Soft Nanoscale Confinement.
Sponsoring Organization: NSF, Division Of Materials Research (DMR), Polymers
PI: Wang, X.
Start and End Date: 2024/08/01 - 2029/07/31
Amount of Award from Contract Source: $666,742
We thank the NSF and Program Manager Dr. Andrew Lovinger for their support!
Internal Funding Sources
Sustainability Institute
Project Title: Design of Low-Cost Thermoelectric Materials Based on MXene/Carbon Composites.
Sponsoring Organization: OSU Sustainability Institute
PI: Wang, X.
Start and End Date: 2020/07/01 - 2021/06/30
Amount of Award from Contract Source: $25,000
We thank the Ohio State University Sustainability Institute for their financial support!
Project Title: Development of a Biobased Packaging Film Made From Food Waste and Designed with Accelerated Degradation Capabilities in Landfills.
Sponsoring Organization: OSU Sustainability Institute
PI: Pascall, M.
Co-PIs: Wang, X.; Yousef, A.; Ezeji, T.
Start and End Date: 2023/05/01 - 2024/08/31
Amount of Award from Contract Source: $25,000
We thank the Ohio State University Sustainability Institute for their financial support!
Sustainability Institute and The Wexner Medical Center
Project Title: Sustainable Materials and Zero Waste
Sponsoring Organization: OSU Sustainability Institute, OSU Wexner Medical Center, OSU Facilities Operations and Development.
Start and End Date: 2022/03/01 - 2023/06/30
PI: Gabel, L.
Co-PI: Wang, X.
Amount of Award from Contract Source: $175,000; Wang amount: $150,000
We thank the Ohio State University Sustainability Institute and the Wexner Medical Center for their financial support!
Institute for Materials and Manufacturing Research
Project Title: Design of Low-Cost Thermoelectric Materials Based on MXene Composites.
Sponsoring Organization: OSU Institute for Materials Research Kickstart Facility Grant
PI: Wang, X.
Start and End Date: 2021/04/15 - 2022/04/14
Amount of Award from Contract Source: $2,500
We thank the Ohio State University Institute for Materials and Manufacturing Research for their financial support
Project Title: Deformation Behavior of Nano-Architectured Liquid Crystal Elastomers.
Sponsoring Organization: OSU Institute for Materials Research Kickstart Facility Grant
PI: Wang, X.
Start and End Date: 2020/04/15 - 2021/04/14
Amount of Award from Contract Source: $2,500
We thank the Ohio State University Institute for Materials and Manufacturing Research for their financial support!
Project Title: Effect of Polymer Chain Sequence and Architecture on Phase Behavior and Thermomechanical Response of Liquid Crystalline Copolymers Consisting of Oblate and Prolate Liquid Crystal Monomers.
Sponsoring Organization: OSU Institute for Materials Research
PI: Wang, X.
Start and End Date: 2022/06/07 - 2023/09/06
Amount of Award from Contract Source: $40,000
We thank the Ohio State University Institute for Materials and Manufacturing Research for their financial support!
Project Title: Topological Dipole Lattices in Geometrically Confined Nematic Liquid Crystals.
Sponsoring Organization: OSU Institute for Materials Research Kickstart Facility Grant
PI: Wang, X.
Start and End Date: 2024/01/01 - 2024/12/31
Amount of Award from Contract Source: $2,500
We thank the Ohio State University Institute for Materials and Manufacturing Research for their financial support!
Research
Background:
Liquid crystals (LCs) are widely known for their use in liquid crystal displays (LCDs). Indeed, LCDs represent one of the most successful technologies developed to date using a responsive soft material: An electric field is used to induce a change in the ordering of the LC and thus a change in the optical appearance. Over the past decade, however, research has revealed the fundamental underpinnings of a potentially far broader and more pervasive uses of LCs for the design of responsive soft material systems. These systems involve a delicate interplay between the effects of surface-induced ordering, the elastic strain of LCs, and the formation of topological defects and are characterized by a chemically complex and diverse range of nano- and micrometer-scale geometry that goes well beyond previous investigations. As a representative class of structural fluids, LCs combine properties commonly associated with crystalline solids (i.e., long-range orientational ordering of constituent molecules) and isotropic liquids (i.e., high mobility of constituent molecules). Thermotropic LCs can adopt a rich palette of positional order (i.e., the extent to which the molecules show translational symmetry, such as an ordered or lattice structure) and orientational order (i.e., the measure of the tendency of the molecules to align along the same direction) of constituent molecules (so-called mesogens).
Scheme of common LC mesophases
Lab Goals:
Theranostics require a programmable combination of imaging modalities, diagnostics, and therapeutics for the precise treatment of cancer or infection sites. Soft robots are an ideal choice for theranostics due to their lower weight, higher thermodynamic efficiency, biocompatibility, biomimicry, and more applicable mechanical properties, compared to traditional hard robots. To date, most soft robots face two main challenges regarding the choice and development of materials, dictated by the requirements of their applications: (1) the design of nanoscale soft robots capable of both programmable locomotion and the controlled release of chemicals and (2) the ability to control and tune the soft robots using a wireless, non-invasive external stimulus as common stimuli, such as heat, light, and electric fields, are not suitable for non-invasive biomedical applications. Our group’s career goal is to design and synthesize miniature, responsive soft material-based robots that are capable of programmable locomotion, selective catalysis, and programmable chemical release for targeted theranostics, which can be actuated using non-invasive stimuli such as electromagnetic waves.
Current Research Areas:
Chemical and Biosensors:
The intrinsic molecular order of the mesogens in the LC phases enables a broad range of functional and responsive systems based on water–LC interfaces that are capable of sensing chemicals, transporting fluids, and synthesizing particles. As a reflection of this evolution, the community investigating LC-based materials now relies heavily on concepts from colloidal and interfacial science. Recent advances in colloidal and interfacial phenomena involving LCs have enabled the design of new classes of soft matter that respond to stimuli as broad as light, airborne pollutants, bacterial toxins in water, mechanical interactions with living cells, molecular chirality, and more.
The outbreak of the coronavirus disease in 2019 (COVID-19), caused by the novel severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), spread rapidly and evolved into a global pandemic. SARS-CoV-2 has an incubation period of 2–7 days during which infected individuals present no obvious symptoms, and the transmission of the SARS-CoV-2 virus has been shown to peak on or before symptom onset. To efficiently control such pre-symptomatic transmission, rapid, robust, and inexpensive tests should be performed on a large fraction of the population. Nucleic acid tests on the viral RNAs swabbed from a patient’s throat or nasal passage, typically in the form of a reverse-transcription polymerase chain reaction (RT-PCR) test, are effective for the detection of the SARS-CoV-2 virus. This RT-PCR test is considered to be the “gold standard” for clinical diagnosis. A promising alternative approach to RT-PCR is the isothermal amplification method, which mainly contains two techniques: loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA). However, these methods require both long characterization times and specialized equipment.
Recently, we reported the design of LC-based sensors for the reliable detection of SARS-CoV-2 RNA. Specifically, a partially self-assembled monolayer of cationic surfactants is formed at an aqueous–LC interface, followed by the adsorption of a 15-mer ssDNA probe with a complementary sequence to the SARS-CoV-2 virus at the cationic surfactant-laden aqueous–LC interface. We demonstrate that the ordering transition in the formed LC surface strongly depends on the targeted nucleotide sequence. The minimum concentration of SARS-CoV-2 RNA that can drive an ordering transition in the LC film is seven orders of magnitude lower than that of the base pair-mismatched severe acute respiratory syndrome (SARS) RNA. Furthermore, we designed and fabricated a LC-based SARS-CoV-2 RNA point-of-care detection kit, with an obtained response that is visible to the naked-eye without any additional equipment, and a smartphone-based app to enhance the overall accuracy of the test result readout and to avoid user error. Overall, these results revealed principles by which LCs and RNA can be coupled at cationic surfactant-decorated aqueous interfaces, and hints at new routes by which the RNA of a pathogenic virus can be rapidly and easily sensed using LCs with both a high sensitivity and a high selectivity.
Selected Publication:
Xu, Y.; Rather, A. M.; Song, S.; Fang, J.-C.; Dupont, R. L.; Kara, U. I.; Chang, Y.; Paulson, J. A.; Qin, R.; Bao, X.; Wang, X. Ultrasensitive and Selective Detection of SARS-CoV-2 Using Thermotropic Liquid Crystals and Image-Based Machine Learning. Cell Reports Physical Science 2020, 1, 100276. Link to article
Sliding and Chemical Release:
Understanding water droplet behaviors at surfaces, such as wetting and mobility, is extremely important in soft condensed matter physics. The wetting phenomenon at solid surfaces has been widely studied both theoretically and experimentally. Surface topography has been demonstrated to significantly impact the wettability and mobility of water droplets. For instance, a water droplet easily spreads on a flat glass substrate but takes on a spherical droplet shape on a lotus leaf (known as the superhydrophobic effect). The distinct behaviors of water droplets on solid substrates with different surface energies and roughness’s can be understood by water–solid intermolecular interactions at both smooth and micro- or nanostructured surfaces. Compared with solid surfaces, water droplets exhibit different behaviors at the surface of immiscible liquids. For example, an extraordinary mobility of water droplets can be achieved by lubricating the micro- or nanostructured solid surfaces infused with a chemically matched isotropic oil film to obtain a slippery lubricant-infused porous surface (SLIPS). Although SLIPS have shown anti-biofouling and anti-icing properties, current SLIPS rely exclusively on isotropic lubricants such as silicone oils and perfluorinated oils, which inherently lack both long-range positional and orientational order. The effect of molecular order in complex and structured fluids on the properties of SLIPS (e.g., wetting, sliding, and bouncing of water droplets on liquid surfaces), however, remains unknown.
The intrinsic molecular order of the mesogens in LC phases enables a broad range of functional and responsive systems based on water–LC interfaces that are capable of sensing chemicals, transporting fluids, and synthesizing particles. Although LCs are a particularly promising class of anisotropic structured fluids that can offer unprecedented responsiveness and functionalities to conventional isotropic liquid-based SLIPS, past studies have reported water droplet-induced dewetting of LC films coated on conventional hydrophobic surfaces, such as silane-functionalized substrates and polymeric multilayers. This instability is due to the amphiphilic molecular structure of the LC, i.e., having both nonpolar (e.g., alkane and phenyl groups) and polar regions (e.g., nitrile and ester groups), thus conventional hydrophobic surfaces are inadequate to stabilize LC films against dewetting caused by water droplets.
Our group uses porous LC polymeric networks to stabilize thermotropic LC mesogens to overcome the aforementioned issue of water-induced LC dewetting. We find that the mobility of water droplets on these LC-based surfaces depends only on the positional order of the LC: water droplets are pinned to the LC surfaces in the smectic A phase, whereas droplets can freely slide without pinning on LC surfaces in both nematic and isotropic phases. Moreover, we experimentally and theoretically demonstrated that the mesogenic orientational order of the LC surface plays a pivotal role in the release of chemicals from the LC surface to droplets. Finally, we demonstrated that as a consequence of the inherent decoupling between a droplet’s mobility and the release of cargo from the LC, LC-based open surface microfluidic platforms can capture and precipitate heavy metal ions in droplets of water on the LC surfaces without hindering the droplets’ mobilities. Our work provides novel design principles for fabricating anisotropic liquid-based open surface microfluidics that enable promising applications including liquid droplet-based chemical synthesis and medical diagnostics.
Selected Publication:
38. Xu, Y.; Rather, A. M.; Yao, Y.; Fang, J.-C.; Mamtani, R. S.; Bennett, R. K. A.; Atta, R. G.; Adera, S.; Tkalec, U.; Wang, X. Liquid Crystal-Based Open Surface Microfluidics Manipulate Liquid Mobility and Chemical Composition On Demand. Science Advances, 2021, 7, eabi7607. Link to article
Soft polymeric materials with complex shape transformations in response to environmental cues have shown great potential in applications ranging from drug delivery to soft robotics. A variety of polymeric materials, including hydrogels, shape memory polymers, and dielectric elastomers have been reported to exhibit stimuli-responsive shape deformations. The intrinsic mechanical properties of the above isotropic shape changing polymers, however, are typically the same in all directions, leading to isotropic deformations. Liquid crystal elastomers (LCEs) capitalize on the interplay between the self-association of liquid crystal (LC) functional groups and the entropic conformation of polymer backbones, resulting in phase-dependent macroscopic shape deformations. LC moieties can be incorporated into polymer chains as either part of the polymer backbone (main-chain LCE) or the pendant functional group (side-chain LCE), seen in Figure 1 below. Previous studies have shown that in LC phases, the conformation of LC polymer chains can deviate from statistically spherical random coils, depending on the configuration of the pendant LC functional groups. For prolate LC polymers, polymer backbones align along the orientation of the mesogenic groups (called the director), resulting in a longer radius of gyration parallel to the LC director (R∥) than that perpendicular to the LC director (R⊥). This anisotropy gives rise to a uniaxial contraction of the respective LCE parallel to the LC director above the LC–isotropic phase transition temperatures (TLC–I). In contrast, for oblate LC polymers in LC phases, the radius of gyration parallel to the director is shorter than the radius perpendicular, that is R∥ < R⊥, which results in a uniaxial elongation of the LCE parallel to the director above the TLC–I, both seen in Figure 2 below. Though the polymer chain conformation and the consequent shape deformations of LCEs made purely of one configuration of LC monomer, either prolate or oblate, have been extensively studied, to the best of our knowledge, the effect of the copolymerization of LC monomers with different configurations on the polymer conformation and the consequent LCE shape deformation remains hidden.
Figure 1. Different LCEs: (A) main-chain, (B) side-on side-chain, (C) end-on side-chain
Figure 2. Polymer chain conformation and consequent shape deformation of LC polymers made of different configurations of LC monomers: (A) prolate with R∥ > R⊥ and (B) oblate with R∥ < R⊥ in LC phases.
We focused on the synthesis of random LC copolymers consisting of a combination of prolate and oblate reactive LC monomers. We demonstrated that the orientational order of the LC functional groups is destabilized in random LC copolymers consisting of both prolate and oblate monomers, whereas a random insertion of the same configuration of LC monomers, e.g., oblate monomers, preserves the packing of the LC pendant groups on the polymer backbone. Furthermore, we illustrated the control over both the direction and magnitude of the thermally triggered shape deformations of random LC copolymers by tuning LC monomer configurations and chemical compositions. Overall, our results not only provided insights into how LC monomer configurations and the chemical composition of random LC copolymers affect the thermal and mechanical properties of LCEs through the coupling among LC pendant groups, but also demonstrated a new design principle to program the deformation behaviors of LCE structures by patterning local LC monomer configurations, an example can be seen in Figure 3 below. We are currently studying LC copolymers in block chain sequence and bottlebrush chain architecture.
Figure 3. Control over the deformation behavior of LCEs through patterning LC monomers with different configurations. The double-headed arrow indicates the LC director.
Selected Publication:
Xu, Y.; Dupont, R. L.; Yao, Y.; Zhang, M.; Fang, J.-C.; Wang, X. Random Liquid Crystalline Copolymers Consisting of Prolate and Oblate Liquid Crystal Monomers. Macromolecules 2021, 54, 5376-5387. Link to article
Our group has focused on the design and synthesis of nanoscale LCE structures capable of programmable locomotion and selective catalytic reactions for targeted theranostics. To achieve this goal, our group has attempted to synthesize nanostructures using non-liquid crystalline polymers. In the first thrust of the research, we created cochlea-inspired polydimethylsiloxane (PDMS) polymeric nanowire structures to retard penetrating cracking and significantly increase the stretchability of metal film-based sensors. Mechanical strain-induced penetrating cracking, which refers to the formation of cracks propagating perpendicularly to the strain and running throughout a whole conducting metal film, causes lower tolerable strains (the maximum detectable strain at which penetrating cracks form and disable the sensor) of metal film-based wearable electronic devices and thus inherently limits their application for monitoring a full range of activities. We find that this polymeric nanowire structured surface outperforms its flat counterparts in stretchability (130% versus 30% tolerable strain) and maintains a high sensitivity (minimum detection of 0.005% strain) in response to an external stimuli such as sound and mechanical forces. The enlarged stretchability is attributed to the two-stage cracking process induced by the synergy of micro-voids and nano-voids. In-situ observation confirms that at low strains micro-voids between nanowire clusters guide the process of crack growth, whereas at large strains, new cracks are randomly initiated from nano-voids among individual nanowires.
Bioinspired hierarchical assembly of PDMS nanowires. Nanowire-structured Pt films for detection of soft gripper’s locomotion and sound. MV denotes micro-voids whereas NV denotes nano-voids.
In the second thrust of research, we reported the use of hyper-crosslinked polymers for the synthesis of polystyrene-based hollow porous polymeric nanosphere frameworks (HPPNFs) as highly efficient yolk-shell structured catalysts. This approach involves the encapsulation of ligand-free metal nanoparticles within the hyper-crosslinked HPPNFs, giving rise to remarkable catalytic activity as well as an outstanding reusability with respect to hydrogenation. By tuning the molecular size of the reactant, we demonstrated an intrinsic size-selectivity precisely defined by the HPPNF-based catalyst. Because the solvent polarity determines the porosity of the HPPNFs, it provides guidance to design a novel class of responsive and functional soft materials for use in catalysis technology. Our current research is focused on the design and synthesis of LCE nanostructures for programmable locomotion and selective catalysis.
The synthesis process of metal nanoparticle-loaded HPPNFs. TEM micrographs and size-dependent selectivity of hydrogenation by Pd-loaded HPPNFs.
Selected Publications:
Xu, Y.; Yao, Y.; Yu, H.; Shi, B.; Gao, S.; Zhang, L.; Miller, A. L.; Fang, J.-C.; Wang, X.; Huang, K. Nanoparticle-Encapsulated Hollow Porous Polymeric Nanosphere Frameworks as Highly Active and Tunable Size-Selective Catalysts. ACS Macro Letters 2019, 8, 1263-1267. Link to article
Miao, W.; Yao, Y.; Zhang, Z.; Ma, C.; Li, S.; Tang, J.; Liu, H.; Liu, Z.; Wang, D.; Camburn, M. A.; Fang, J.-C.; Hao, R.; Fang, X.; Zheng, S.; Hu, N.; Wang, X. Micro-/Nano-Voids Guided Two-Stage Film Cracking on Bioinspired Assemblies for High-Performance Electronics. Nature Communications 2019, 10, 3862. Link to article
Although the rapid popularization of wireless electronic devices has significantly improved the quality of human lives, it has led to the release of redundant electromagnetic (EM) waves into the environment as EM pollution. EM pollution interferes with device-to-device communication, which can be detrimental for a variety of applications ranging from self-driving vehicles to remote surgical operations. Hence, harvesting the excess EM waves and converting them into thermal energy using a material design strategy (based on the materials intrinsic dielectric relaxation and conductive loss) provides a feasible solution to address EM pollution. The design criteria for an ideal EM absorber includes strong EM absorption (calculated by reflection loss (RL)), wideband effective absorption (fE; frequency region with RL < –10 dB, corresponding to > 90% EM absorption), a small thickness (referring to the thickness of absorption layer made by dispersing the EM absorber into a matrix), and a low mass density (lightweight).
In the past decade, the design of EM absorbers based on 2D nanomaterials has attracted a vast amount of attention because of their unique atomic arrangements. First, the electronic structure of 2D nanomaterials, such as their electrical conductivity, can be tuned over a wide regime, e.g., ranging from a wide bandgap semiconducting behavior to a metallic electrical conductivity. Second, confined transport of carriers within 2D atomic layers leads to both a directional movement with high mobility and a weak electronic scattering, which are beneficial to the conductive loss behavior. Third, the intrinsically high specific surface area of 2D nanomaterials provides a rich palette of avenues for tuning the polarization relaxation loss behavior. While promising, most popular 2D nanomaterials such as MoS2, Ti3C2Tx (Tx referring to the dipole groups) and graphitic carbon nitride (g-C3N4) exhibit a narrow fE (e.g., ≤ 2.0 GHz).
Recently, we reported a combined defect engineering strategies to tune the electronic structure of 2D g-C3N4 nanosheets to enhance their EM absorption performance by creating nanopores which efficiently tuned their electronic structure and enriched the active edges for the subsequent element doping. Next, phosphorus (P) and sulfur (S) were doped into the nanoporous g-C3N4, giving rise to both a conductive loss and a continuous polarization relaxation loss. Finally, we demonstrated that the S/P-doped nanoporous g-C3N4 exhibited a broad fE value of 6.0 GHz at a thickness below 2.0 mm at room temperature and a good thermal stability (e.g., fE of > 4.0 GHz at a thickness of 1.2 mm at 150 oC). Overall, the results reported in this work revealed new principles by which metal-free 2D nanomaterials can be modified to serve as a novel class of high-performance and wideband EM absorbers at a wide range of temperatures.
Modifications of 2D g-C3N4 nanosheets and electromagnetic wave absorption at a wide range of temperatures.
Selected Publication:
Lv, H.; Zhou, X.; Wu, G.; Kara, U. I.; Wang, X. Engineering Defects in 2D g-C3N4 for Wideband, Efficient Electromagnetic Absorption at Elevated Temperature. Journal of Materials Chemistry A In press. Link to article
Publications and Works
- Rather, A. M.; Xu, Y.; Dupont, R. L.; Wang, X. Polymeric Membranes in Wastewater Treatment. In Title: Nanoscale Engineering of Biomaterials: Properties and Applications; Pandey, L., Hasan, A. Eds; Springer Nature; 2022, 487-515. Link to book chapter
Group Members
New Year Potluck - Jan 24, 2020:
From left to right around the table: Xiaodi Zhou, Dr. Hualiang Lyu, Robert Dupont, Ufuoma Kara, Rajdeep Mamtani, Dr. Xiaoguang Wang, Dr. Adil Rather, Dr. Zhangcheng Gao, Jen-Chun Fang, Dr. Yang Xu
Lab celebration of Rajdeep's new job at Merck - March 15, 2022:
From left to right: Asher Vokoun, Weichen Deng, Robert Dupont, Meng Zhang, Rajdeep Mamtani, Ufuoma Kara, Dr. Xiaoguang Wang
Microscopes
Surface Chemistry
Material Synthesis
Twin and Single Screw Extruders
Other Equipment
