About

The Balsara lab at UC Berkeley, led by Professor Nitash P. Balsara, aims to foster a collaborative and inclusive environment where the whole is greater than the sum of its parts. The lab supports diversity within the group and welcomes each other's viewpoints and backgrounds.

Research topics

• Computer Science
• Engineering
• Engineering physics
• Geology
• Archaeology
• Library science
• Geography
• Systems engineering
• Nuclear physics
• Chemistry
• Physics
• Materials science
• Process engineering
• Paleontology
• Electrical engineering
• Nanotechnology

Selected publications

• Atomic-Scale Imaging Reveals Polar-π Interactions in Two-Dimensional Molecular Superlattices

  Journal of the American Chemical Society · 2026-03-18

  article

  Controlling coassembly of synthetic oligomers into binary superlattices at the atomic level is challenging. We report a strategy for programming polar-π interactions in oligomeric peptoids, a class of sequence-defined peptidomimetics, facilitating the formation of homogeneous two-dimensional (2D) superlattices. N-2-phenylethyl and N-(2-perfluorophenyl)ethyl side chains, similar in size, but with contrasting electrostatic characteristics, were introduced at defined sequence positions to generate favorable dipolar aromatic interactions. The resulting nanosheets exhibit different crystal motifs depending on the side chain interactions: systems containing only one type of aromatic side chain form a parallel V-shaped motif driven by π–π interactions, whereas a combination of both types of aromatic side chains, either within one backbone or through the coassembly of two distinct peptoids, adopt an antiparallel V-shaped superlattice with higher thermal stability, driven by polar-π interactions. Cryogenic transmission electron microscopy directly resolved the packing arrangement of perfluorophenyl and phenyl rings in individual nanosheet superlattices, confirming that intermolecular polar-π interaction dominates the superlattice motifs and increases lattice stability. Molecular dynamics simulations and density functional theory calculations further substantiate the energetic favorability of polar-π interactions over π–π interactions, rationalizing the formation of homogeneous superlattices with enhanced thermal stability. Our discoveries establish a design principle for binary coassembly using sequence-defined oligomers, which enables control over unit cell geometry, lattice stability, and molecular registration through aromatic side chain polarization and sequence control. This ability to program atomic-scale binary superlattices opens new avenues for designing functional 2D soft materials.

  PublisherDOI

• Conductivity-Driven Origin of the Limiting Current in Concentrated Electrolytes

  ACS Energy Letters · 2026-03-26

  articleSenior authorCorresponding

  Next-generation electrolyte materials are hindered by their ability to support high currents essential for fast-charge and high-power battery applications. The maximum current supported by an electrolyte, the limiting current, is dictated by the formation of concentration gradients across the electrolyte under an electric field. Most of the literature attributes the onset of the limiting current in concentrated electrolytes to the salt concentration at the positive electrode approaching the solubility limit. Here, we leverage operando X-ray transmission imaging to measure spatiotemporal salt concentration profiles of a polymer electrolyte in a lithium–indium symmetric cell at a current exceeding the limiting current. The measurement of concentration profiles enables mapping the spatiotemporal electric potential, which comprises an ohmic contribution, governed by conductivity, and an overpotential related to maintaining concentration gradients. We find that a precipitous drop in conductivity at the positive electrode drives the divergence of electric potential, rather than a thermodynamic solubility limit.

  PublisherDOI

• Minimizing Interfacial Resistance between Polymer Electrolytes and Metal Electrodes Using Applied Current

  ACS Energy Letters · 2026-01-15

  articleSenior authorCorresponding

  Reducing the interfacial resistance between different phases in electrochemical systems is crucial for enabling practical applications. In this work, we proposed a process for reducing the interfacial resistance between polymer electrolytes and metal electrodes. Thus far in the literature, the lowest interfacial resistance reported in these systems is 15 Ω·cm2. In this study, assembled and preconditioned symmetric cells with lithium–indium alloy electrodes showed similar values. The current through the cell was increased in steps up to the limiting current. This resulted in a permanent decrease of the interfacial resistance to values as low as 1 Ω·cm2, a value that is comparable to that of optimized lithium-ion batteries. The proposed process is general, and it could be applied to any combination of polymer electrolytes and metal electrodes.

  PublisherDOI

• Mapping Spatiotemporal Solvent Velocity from Measured Concentration Gradients in a Polarized Electrolyte

  Journal of The Electrochemical Society · 2025-01-21 · 6 citations

  articleOpen accessSenior author

  The electric-field induced motion of neutral species impedes the efficacy of electrochemical devices. By combining operando X-ray transmission measurements with continuum mechanics, we have developed a methodology for determining the velocity of neutral solvent molecules under an applied field. The X-ray transmission experiments were used to determine ion concentration profiles as a function of space and time in a polymer electrolyte. The unsteady state solvent mass balance equation was solved numerically with experimental concentration profiles to map spatiotemporal solvent velocities. We compare our experimentally derived results with predictions made with concentrated solution theory. We use the cation transference number as the only adjustable parameter to match experimental measurements of both concentration and solvent velocity. Our approach may be used to determine solvent velocity with any operando technique used to measure time-dependent ion concentration profiles.

  PublisherOA PDFDOI

• Tracking Spatiotemporal Electric Potential in Batteries Using High-Resolution <i>Operando</i> X-ray Transmission Imaging

  The Journal of Physical Chemistry C · 2025-11-03 · 3 citations

  articleSenior author
  PublisherDOI

• Ion Transport in Concentrated Crosslinked Solid Polymer Electrolytes

  Journal of The Electrochemical Society · 2025-12-01

  articleOpen accessSenior author

  Crosslinking polymers is a common approach to create mechanically stable solid materials such as polymer electrolytes for lithium batteries. In conventional liquid electrolytes, the solvent molecules move freely to accommodate the field-induced motion of ions. However, in crosslinked polymer electrolytes, the rearrangement of polymer segments is constrained by the deformation limits of the network. Herein, we develop a new transport model that accounts for both the formation of concentration gradients and the elasticity of the electrolyte. The elasticity is incorporated by adding an additional term related to the entropy of crosslinked strands to the electrochemical potential of the salt. The resulting Crosslink Model contains two adjustable parameters: <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="script">N</mml:mi> </mml:math> , the average number of monomers in a strand, and λ crit , the maximum strain the network can sustain. These solid-like constraints produce singularities in the governing transport equations, fundamentally altering the concentration profiles. Plateaus in salt concentrations emerge near the electrodes, and network elasticity introduces a strain overpotential. When compared to a Baseline Model ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="script">N</mml:mi> </mml:math> → ∞, equivalent to concentrated solution theory), which predicts steepest gradients near the electrodes, both models yield similar current–voltage relationships. Model predictions are compared to electrochemical data for a poly(ethylene oxide)-based crosslinked polymer electrolyte.

  PublisherDOI

• Cooperative Role of Mixed Solvent in the Evaporation-Induced Self-Assembly of Polypeptoid Nanocrystals

  ACS Applied Nano Materials · 2025-06-16 · 2 citations

  articleOpen access

  Peptoids, or polypeptoids, are biomimetic polymers that can self-assemble into nanocrystals for biomedical and biotechnological applications. Polypeptoid nanocrystals can be prepared by evaporation-induced self-assembly, but the roles of solvent components for this process have long been overlooked at the molecular level, leaving a tunable parameter for improving self-assembly protocols. This work utilized molecular dynamics simulations to study the effects of water and the commonly used tetrahydrofuran (THF) on the assembly of nanosheets from molecules of acetylated diblock polypeptoid, poly(N-decylglycine)-b-poly(N-2-(2-(2-methoxyethoxy)ethoxy) ethylglycine), abbreviated as Ac-Ndc10-Nte10. To probe the stages of self-assembly, isolated molecules and preassembled nanofibers/nanosheets were simulated in pure THF, water, and their mixtures, respectively. The assembly energies show that the THF/water mixture has a greater tendency to form nanosheets than pure water. In a THF/water mixture, polypeptoids were found more uncoiled in isolated states, less compact in disordered agglomerates, and with reduced requirement for the Nte block to cover hydrophobic Ndc surfaces in the nanocrystals. Mixed solvent is vital to initiating self-assembly, as THF assists in the opening of coiled polypeptoid molecules, while water provides the thermodynamics to aggregate and ultimately form nanocrystals. To obtain wider nanosheets, it is recommended that some THF be maintained in the aqueous solvent before it becomes exhausted by evaporation. Near the nanosheet surface, the THF concentration is higher than that in bulk solution (3–4 times in 4 M THF/water). The strong adsorption of THF indicates the self-assembly in a de facto mixed solvent. These results are expected to guide the refinement of evaporation-induced self-assembly protocols for polypeptoid nanocrystals.

  PublisherDOI

• Key Intermediate Nanostructures in the Self-Assembly of Amphiphilic Polypeptoids Revealed by Cryo-TEM

  Macromolecules · 2025-04-09 · 4 citations

  article

  Amphiphilic copolypeptoids are known to form a variety of nanostructures (fibers, tubes, sheets, etc.), but the assembly mechanisms and key intermediates remain underexplored. This study investigates the intermediate structures formed during the early stages of self-assembly in diblock copolypeptoids using cryo-transmission electron microscopy (cryo-TEM). We focused on two diblock copolypeptoids, one with a free N-terminus and the other with a capped N-terminus, which ultimately form less-ordered nanofibers and well-ordered nanosheets, respectively. Through cryo-TEM imaging of vitrified solutions at various time points during the self-assembly process, the study identified micelles and vesicles as key intermediate structures. Notably, the formation of vesicles as intermediates is unusual in crystallization-driven self-assembly and suggests a unique pathway in polypeptoid self-assembly. The study provides direct imaging evidence of key intermediates in polypeptoid self-assembly, advancing the understanding of their self-assembly mechanisms.

  PublisherDOI

• Comparing Li-/Na- Ion Transport in Polymer Electrolytes

  ECS Meeting Abstracts · 2025-11-24

  article

  All-solid-state batteries (ASSB) using solid-phase electrolytes are considered a promising next generation chemistry in terms of larger energy density and improved safety compared to conventional Li-ion batteries. Among many candidates for solid electrolytes, polymers have gained a lot of attention because of the mechanical deformability allowing them to maintain good contacts with electrodes in ASSBs over extended cycles. Furthermore, given many studies having demonstrated the enhancement in transport properties of polymers by compositing with other types of electrolytes (e.g., ceramic), polymers are an attractive option for enabling ASSBs. Despite these advantages, there are still under-explored questions critical to expand the utilization of polymers in ASSBs regarding 1) ions transport in polymers considering the solvent drag effect, and 2) the distinct behaviors of ions in polymers dissolving different types of salts (i.e., Li- and Na-ion based electrolytes). In the present study, poly-ethylene oxides (PEO) with either LiTFSI or NaTFSI salts are modeled with concentration solution theory. Through experimental characterizations, concentration-dependent transport and thermodynamic properties of PEOs dissolving respective salts are determined, which are leveraged for the continuum modeling. Interactions between anions, cations, and solvent are considered in simulations to describe the ion transport in Li/PEO-LiTFSI/Li or Na/PEO-NaTFSI/Na cells during cycling. Lastly, the resultant overpotential across each electrolyte system is predicted. The physical picture grasped in this work will enable more accurate modeling of polymer electrolytes towards building both Li- and Na-ion based solid-state batteries. Figure 1

  PublisherDOI

• Three-Dimensional Crystals Assembled by Linear Oligopeptoids

  Nano Letters · 2025-07-28 · 1 citations

  article

  The rational construction of three-dimensional (3D) crystalline lattices from synthetic short-chain polymers remains a significant challenge due to the lack of inherent driving forces to enable crystal growth in all three dimensions. Here, we report the design of 3D peptoid crystals from linear peptoid hexamers, derived from amphiphilic diblock sequences that typically form crystalline two-dimensional (2D) nanosheets. By removing the amorphous domains and tuning the chain termini, crystalline lamellae up to 500 nm thick were achieved, far exceeding the thickness of typical nanosheets (on the order of a few nanometers). These 3D crystals form via the stacking of unit cells with lattice parameters similar to those in 2D nanosheets, where terminal groups, particularly compact C-terminal moieties, facilitate vertical growth and enhance crystallinity. This study highlights the importance of atomic precision in terminus chemistry for achieving long-range ordering and isotropic crystal growth in the design of macroscale crystals from oligomeric peptoids.

  PublisherDOI

Recent grants

• ELECTROCHEMICAL CONTROL OF BLOCK COPOLYMER SELF-ASSEMBLY

  NSF · $225k · 2006–2009

• Collaborative Research: Electronic and Ionic Transport in Block Copolymers

  NSF · $201k · 2010–2013

• DMREF: Collaborative Research: Next-Generation Nanostructured Polymer Electrolytes by Molecular Design

  NSF · $400k · 2013–2017

• Collaborative Research: Thermodynamics and Ion Transport in Block Copolymer/Lithium Salt Mixtures

  NSF · $320k · 2010–2014

• Collaborative Research: Thermodynamics, Grain Structure, and Ion Transport in Block Copolymer/Salt Mixtures

  NSF · $300k · 2015–2019

Frequent coauthors

• Bruce A. Garetz

  New York University

  125 shared

• Megan L. Ruegg

  Lawrence Berkeley National Laboratory

  114 shared

• Xi Jiang

  Lawrence Berkeley National Laboratory

  113 shared

• Jacqueline A. Maslyn

  Lawrence Berkeley National Laboratory

  101 shared

• Irune Villaluenga

  University of the Basque Country

  95 shared

• Enrique D. Gomez

  Pennsylvania State University

  89 shared

• David M. Halat

  University of California, Berkeley

  85 shared

• Whitney S. Loo

  Lawrence Berkeley National Laboratory

  85 shared

Awards & honors

• National Science Foundation Young Investigator Award (1994)
• Sigma Xi Distinguished Faculty Research Award, Polytechnic U…
• 3M Non-Tenured Faculty Award (1996)
• Engineer of the Year, American Institute of Engineers of Ind…
• John H. Dillon Medal, American Physical Society Award for Po…