About

Robert Hickey is an Associate Professor of Materials Science and Engineering at Penn State University. He received his B.S. in Chemistry from Widener University in 2007 and his Ph.D. in Chemistry from the University of Pennsylvania in 2013. During his doctoral studies at UPenn, he worked in the laboratory of Prof. So-Jung Park, focusing on controlling the morphology and materials properties of colloidal aggregates composed of inorganic nanoparticles and amphiphilic diblock copolymers, with biomedical applications. His research experience includes a summer research stint at Ewha Womans University in Seoul, South Korea, and postdoctoral work at the University of Minnesota in the labs of Professors Frank Bates and Tim Lodge, where he studied the self-assembly and phase behavior of ternary polymer blends and their application to polymer electrolyte systems involving Li+ ion diffusion. His research interests center on the synthesis and characterization of nanocomposite materials, particularly hybrid inorganic/polymeric materials. His lab focuses on creating hierarchical, supramolecular structures through the bottom-up assembly of nanocrystals and polymers, aiming to develop materials with properties relevant to optical, magnetic, electronic, and catalytic technologies. Robert Hickey is associated with the Penn State Intercollege Graduate Degree Program in Materials Science and Engineering, fostering cross-disciplinary collaboration. His notable contributions include receiving the American Physical Society’s John H. Dillon Medal in 2025.

Research topics

• Composite material
• Nanotechnology
• Materials science
• Computer Science
• Chemical engineering
• Crystallography
• Chemistry
• Organic chemistry

Selected publications

• 3D-printable bilayer-stabilized jammed emulsions as scalable biological tissue mimics

  ChemRxiv · 2025-03-05

  preprintOpen access

  We present Jammed Interconnected Bilayer Emulsions (JIBEs) as a class of tissue-like materials with macroscopic scalability and rapid fabrication, comprising millions to billions of bilayer-separated aqueous compartments. These materials closely mimic the organizational structure and properties of biological tissues. Our rapid self-assembly method for producing JIBEs generates milliliter- to deciliter-scale volumes within minutes representing over 10,000-fold improvement in the fabrication speed of droplet-based artificial tissues compared to existing droplet-based methods, enabling the creation of a truly macroscopic material. The method is highly adaptable to a wide range of amphiphiles, including lipids and block-copolymers, providing flexibility in tailoring JIBEs for diverse applications. The jammed architecture of JIBEs imparts unique properties, such as direct 3D-printabilty into aqueous solutions or onto air-exposed surfaces. Their membrane-bound structure also allows functionalization with biological and artificial nanochannels, enabling the material to exhibit the specific properties of the incorporated channels. In this work, we demonstrate three key features of JIBEs using distinct ion channels: tunable conductance, selective transport, and memristance. Incorporating an E. coli outer membrane protein increased ionic conductance by approximately 4,400-fold compared to non-functionalized tissues. Introducing a peptide-based transporter produced ion-selective membranes capable of discriminating ammonium over sodium at a ratio greater than 15:1. Finally, incorporating a model voltage-gated pore enabled the construction of a massively networked memristive device. We propose that functionalizing JIBEs with additional membrane proteins or synthetic ion channels could unlock a broad range of applications, including separations, energy generation and storage, neuromorphic computing, tissue engineering, drug delivery, and soft robotics.

  PublisherOA PDFDOI

• Porous hierarchically ordered hydrogels demonstrating structurally dependent mechanical properties

  Nature Communications · 2025-04-22 · 31 citations

  articleOpen accessSenior author

  While hierarchical ordering is a distinctive feature of natural tissues and is directly responsible for their diverse and unique properties, efforts to synthesize biomaterials have primarily focused on using molecular-based approaches with little emphasis on multiscale structure. Here, we report a bottom-up self-assembly process to produce highly porous hydrogel fibers that resemble extracellular matrices both structurally and mechanically. Physically crosslinked nanostructured micelles form the walls of micrometer-sized water-rich pores with preferred orientation along the fiber direction. Low elastic moduli (<1 kPa), high elasticity (extending by more than 12 times the initial length), non-linear elasticity (e.g., hyperelasticity), and completely reversible extension are derived from unevenly distributed strain between the micrometer-sized pores and the polymer chains, which is reminiscent of cellular solids. Control of the material microstructure and orientation over many orders of magnitude (e.g., nm–μm), while holding the nanostructure constant, reveals how the multiscale structure directly impacts mechanical properties. Hierarchical ordering is critical for preparing biomimetic materials, but control of multiscale structure over many length scales is limited. Here, the authors report on a bottom-up assembly process for producing highly porous hydrogel structures where structure dictates bulk properties.

  PublisherOA PDFDOI

• Nanoparticle Loading in Swollen Polymer Gels: An Unexpected Thermodynamic Twist

  Nano Letters · 2025-02-17 · 2 citations

  articleSenior authorCorresponding

  Tailoring polymer gel functionality by loading small molecules and nanoparticles is critical for drug delivery and tissue regeneration. Typically, solute loading in gels correlates with the degree of solvent swelling, which is controlled by the cross-link density and polymer/solvent interactions. However, the general assumption that the degree of swelling is the primary factor for nanoparticle loading is incorrect. Here, we demonstrate that the pairwise interactions between the polymer, solvent, and solute dictate the solute loading in gels. We performed gel loading studies of ligand-stabilized gold nanoparticles using different solvents, polymer network hydrophobicity, and cross-link densities, and found that nanoparticle distribution between polymer and solvent correlate with calculated thermodynamic partition coefficients. Despite previous assumptions that the maximum nanoparticle loading occurs at the highest degree of gel swelling, we reveal that nanoparticles preferentially load into gels with lower solvent swelling if ligand/polymer interactions are more favorable than ligand/solvent interactions.

  PublisherDOI

• 3D-printable bilayer-stabilized jammed emulsions as scalable biological tissue mimics

  ChemRxiv · 2025-02-04 · 2 citations

  preprint

  We present Jammed Interconnected Bilayer Emulsions (JIBEs) as a class of tissue-like materials with macroscopic scalability and rapid fabrication, comprising millions to billions of bilayer-separated aqueous compartments. These materials closely mimic the organizational structure and properties of biological tissues. Our rapid self-assembly method for producing JIBEs generates milliliter- to deciliter-scale volumes within minutes representing over 10,000-fold improvement in the fabrication speed of droplet-based artificial tissues compared to existing droplet-based methods, enabling the creation of a truly macroscopic material. The method is highly adaptable to a wide range of amphiphiles, including lipids and block-copolymers, providing flexibility in tailoring JIBEs for diverse applications. The jammed architecture of JIBEs imparts unique properties, such as direct 3D-printabilty into aqueous solutions or onto air-exposed surfaces. Their membrane-bound structure also allows functionalization with biological and artificial nanochannels, enabling the material to exhibit the specific properties of the incorporated channels. In this work, we demonstrate three key features of JIBEs using distinct ion channels: tunable conductance, selective transport, and memristance. Incorporating an E. coli outer membrane protein increased ionic conductance by approximately 4,400-fold compared to non-functionalized tissues. Introducing a peptide-based transporter produced ion-selective membranes capable of discriminating ammonium over sodium at a ratio greater than 15:1. Finally, incorporating a model voltage-gated pore enabled the construction of a massively networked memristive device. We propose that functionalizing JIBEs with additional membrane proteins or synthetic ion channels could unlock a broad range of applications, including separations, energy generation and storage, neuromorphic computing, tissue engineering, drug delivery, and soft robotics.

  PublisherDOI

• Polyzwitterionic Material Structure and Dielectric Properties

  Langmuir · 2025-04-07 · 3 citations

  articleSenior authorCorresponding

  There is a growing need for flexible, high-dielectric-constant materials that move beyond current polar solvent swelling and nanofiller approaches to advance energy storage and actuator applications. Here, we synthesized a series of statistical copolymers consisting of polybutyl acrylate-co-poly(2-(dimethylamino)ethyl acrylate), which were then converted into polyzwitterions to explore the impact of zwitterions on the material structure and dielectric properties. The DMAEA residues in each copolymer were quaternized using 1,4-butane sultone to yield polyzwitterions through postpolymerization modification. The functionalization of the copolymers with zwitterions increases the static dielectric constant of the materials (i.e., ∼9.3 at 80 °C) compared with the unquaternized materials. The strong dipolar interactions between zwitterions lead to aggregation, resulting in the appearance of either a second glass-transition temperature or the softening of the zwitterion aggregates. Although the zwitterions increased the dielectric constant of the materials, the zwitterion-rich aggregates are posited to restrict zwitterion mobility, precluding the maximum material dielectric constant. The reported findings position polyzwitterions as promising next-generation dielectric materials, potentially broadening applications in flexible electronics and energy-efficient devices.

  PublisherDOI

• Boosting Discharge Energy Density of Commercially Available Polyethylene via Post-Polymerization Modification

  Macromolecules · 2025-12-01

  articleSenior authorCorresponding

  Enhancing polymer dielectric properties is critical for more efficient and reliable energy storage, sensors, and actuators. However, achieving high dielectric constant and low dielectric loss tangent in polymer materials is challenging without incurring higher cost in comparison to polyolefins that are widely used as dielectric materials. Here, we demonstrate postpolymerization modification (PPM) of linear low-density polyethylene (LLDPE) by using azide–alkyne click chemistry to covalently attach polar amines and zwitterions to the backbone, dramatically improving dielectric performance. Amine- and zwitterion-functionalized LLDPE exhibited greater dielectric constants (εs = 12 and 5.6, respectively) than unfunctionalized LLDPE (εs = 2.8). Moreover, the trade-off in functionalizing LLDPE was minimal with the dielectric loss tangent (tan δ) increasing from 0.0002 to 0.007–0.17 at 1 kHz and 30 °C and a modest reduction in the breakdown strength. Electric displacement–electric field loop studies indicate that the discharge energy density (Ud) of amine-modified LLDPE (Ud = 1.59 J/cm3 at 150 MV/m with a high efficiency of 83.5%) outperforms that of poly(vinylidene fluoride), a high-performance ferroelectric polymer, and is 7 times greater than that of the pristine LLDPE. PPM provides a versatile approach to enhance the dielectric properties of commercially available polyolefins for capacitor applications through covalent attachment of polar functionality.

  PublisherDOI

• Binding-Induced Bond Polarization in Polymer Solutions to Drive Micelle and Vesicle Formation

  Macromolecules · 2024-12-20 · 1 citations

  articleSenior authorCorresponding

  Driving self-assembly through donor–acceptor interactions to create nanostructured materials is a key feature of supramolecular chemistry; however, the connection between molecular-level changes and larger-scale organization is still unknown. Here, we propose the concept of Lewis adduct binding-induced bond polarization, where the formation of the Lewis adduct leads to a large dipole (here estimated to be 12.5 D), significantly altering the intermolecular interactions between different species and inducing self-assembly. Specifically, a diblock copolymer, poly(2-(dimethylamino)ethyl methacrylate)-polystyrene (PDMAEMA-PS), self-assembles into nanostructured colloidal aggregates on the addition of the Lewis acid tris(pentafluorophenyl) borane (BCF) in toluene. The morphology of the nanostructured colloidal structures is controlled by tuning the block mole fraction of the poly(Lewis base) (polyLB, i.e., PDMAEMA) within the diblock copolymer, resulting in spherical micelles, vesicles, and large compound vesicles with an increasing PDMAEMA block mole fraction. The self-assembly is driven by binding-induced bond polarization during Lewis adduct formation, where the degree of bond polarization of the Lewis adducts is quantified by measuring the dielectric constant of adduct mixtures. We propose that the large dipole formed because of the Lewis adduct leads to substantial changes in the polymer–solvent interactions, driving the self-assembly. The reported findings regarding the Lewis adduct-induced self-assembly in polymer systems have far-ranging potential implications in supermolecular chemistry.

  PublisherDOI

• Polymer macroligands passivate halide perovskite surfaces

  RSC Applied Polymers · 2024-01-01 · 5 citations

  articleOpen accessSenior authorCorresponding

  Polymers with nitrogen-containing groups act as polymer macroligands that will preferentially bind to and passivate perovskite surface, resulting in enhanced optical properties.

  PublisherOA PDFDOI

• From Fully Stretched to Collapsed Chains: Bottlebrush Polymer Grafted Particles

  Macromolecules · 2024-10-08 · 7 citations

  articleSenior authorCorresponding

  Macromolecular architecture is a critical parameter in tuning polymer material properties. Although the implementation of nonlinear polymers in different applications has grown over the years, polymer grafted surfaces such as nanoparticles have traditionally been composed of linear thermoplastic polymers, with a limited number of examples demonstrating a diversity in polymer architectures. In an effort to combine polymer architecturally dependent material properties with polymer grafted particles (PGPs), as opposed to conventional methods of tuning polymer grafting parameters, such as the number of chains per surface area (i.e., polymer graft density), a series of bottlebrush grafted particles were synthesized using surface-initiated ring-opening metathesis polymerization (SI-ROMP). These bottlebrush PGPs are composed of glassy, semicrystalline, and elastomeric polymer side chains with controlled backbone degrees of polymerization (Nbb) at relatively constant polymer graft density on the surface of silica particles with diameters equaling approximately 160 or 77 nm. Bottlebrush polymer chain conformations, evaluated by measuring the brush height of surface grafted polymer chains in solution and the melt, undergo drastic changes in their macromolecular dimensions in different environments. In solution, brush heights increase linearly as a function of Nbb, consistent with fully stretched chains, which is confirmed using cryogenic transmission electron microscopy (cryo-TEM). Meanwhile, brush heights are consistently at a minimum in the melt, indicative of chains collapsed on the particle surface. The conformational extremes for grafted bottlebrush polymers are unseen in any linear polymer chain system, highlighting the effect of macromolecular architecture and surface grafting. Bottlebrush grafted particles are an exciting class of materials where diversifying polymer architectures will expand PGP material design rules that harness macromolecular architecture to dictate properties.

  PublisherDOI

• Enhancing the dielectric constant of zwitterionic liquids via dipole moment and anion chemistry

  The Journal of Chemical Physics · 2024-07-01 · 11 citations

  articleOpen accessSenior author

  The dielectric constant is a critical parameter in many energy-related applications. Typically, increasing the dielectric constant of soft materials involves adding high dielectric constant polar liquids or inorganic fillers, but there are limitations to this approach due to safety concerns with volatile and flammable solvents and the agglomeration of inorganic fillers. An alternative approach is to add zwitterionic liquids that exhibit exceptionally high dielectric constants with negligible volatility. Here, we report the synthesis of a series of zwitterionic liquids containing an imidazolium cation, exhibiting the highest dielectric constant among all organic molecules (∼350 at 293 K). The cation-anion linkage was tailored in a wide range between three and nine carbons, rendering the zwitterion dipole from 25 to 52 D. Comparing the dielectric constant for zwitterions with different anions (i.e., sulfonylimide, sulfonate, and carboxylate) reveals the beneficial impacts of the delocalized sulfonylimide anion vs the carboxylate anion due to the enlarged molecular dipole and more homogenous liquid morphology. Molecular dipole and liquid morphology are identified as the keys to developing high dielectric constant zwitterionic liquids. The extremely high dielectric constant accessible with the proposed molecular design paves new avenues for developing high dielectric constant zwitterions that act as dielectricizers.

  PublisherOA PDFDOI

Recent grants

• CAREER: Enabling the Design of Versatile Hybrid Materials using Polymerization-Induced Nanostructural Transitions

  NSF · $600k · 2020–2025

• DMREF/Collaborative Research: Computationally Driven Design of Synthetic Tissue-Like Multifunctional Materials

  NSF · $408k · 2021–2025

• Collaborative Research: Controlling Nanoscale Self-Assembly via Binding-Induced Polarization

  NSF · $275k · 2022–2025

Frequent coauthors

• Chao Lang

  South China University of Technology

  35 shared

• Jacob A. LaNasa

  Center for Integrated Nanotechnologies

  25 shared

• Woochul Song

  Pohang University of Science and Technology

  23 shared

• Manish Kumar

  20 shared

• Frank S. Bates

  University of Minnesota

  18 shared

• Timothy P. Lodge

  University of Minnesota

  17 shared

• Timothy M. Gillard

  15 shared

• Michael A. Hickner

  Pennsylvania State University

  14 shared

Education

• PhD, Chemistry

  Univeristy of Pennsylvania

  2013

• B.S., Chemistry

  Widener University

  2007

Awards & honors

• American Physical Society’s John H. Dillon Medal, 2025