About

Bradley Chmelka is a professor in the Department of Chemical Engineering at the University of California, Santa Barbara. His research focuses on the correlation of macroscopic material properties and functions with molecular structure and dynamics, particularly in heterogeneous macromolecular solids. He specializes in the synthesis and characterization of self-assembled inorganic-organic and mesoporous materials for applications in catalysis, separations, and opto-electronic devices. His work also involves studying molecular dynamics and structure in hierarchically ordered polymers, liquid crystals, nanocrystals, and biominerals. Additionally, he develops and applies nuclear magnetic resonance spectroscopy methods to characterize the structure, dynamics, adsorption, transport, and reaction properties of new solid-state materials.

Research topics

• Chemical physics
• Physics
• Materials science
• Chemistry
• Nanotechnology
• Organic chemistry
• Optoelectronics
• Thermodynamics
• Optics
• Statistical physics
• Nuclear magnetic resonance

Selected publications

• Ba ²⁺ Complements Co ²⁺ Exchange as a Reporter of Al Proximity in CHA Zeolites

  Chemistry of Materials · 2026-03-07

  article

  Co2+ exchange is commonly used as a reporter of Al pair ensembles in zeolites. We combine density functional theory (DFT) calculations, statistical models, experimental titrations, and solid-state nuclear magnetic resonance (NMR) analyses to explore the utility of other 2+ ions as alternative reporters of proximal Al ensembles in the CHA zeolite. DFT calculations suggest that Ba2+ will exchange into both eight- (8MR) and six-membered (6MR) CHA rings equally effectively, distinct from Co2+, which exchanges solely into 6MR. Simulated titration curves highlight the potential for Co2+ and Ba2+ titrations to provide complementary information about specific proximal Al site ensembles as a function of Si/Al ratio. Experiments on CHA zeolites synthesized to express different Al distributions confirm that Ba2+ uptake exceeds that of Co2+ and that this uptake can be rationalized by Ba2+ ions that titrate both 8MR and 6MR Al pair sites. Comparisons of absolute ion uptakes and two-dimensional NMR analyses of Al proximity with predictions reveal previously unrecognized differences in Al siting rules under different syntheses. These findings demonstrate that complementary titrations using divalent cations of differing ionic radii provide additional resolution on Al–Al pair ensembles and the underlying rules that govern Al distributions on zeolite frameworks.

  PublisherDOI

• Hydroisomerization and hydrocracking over dual-function Pt/H+USY zeolite catalysts: Correlation of nanoscale compositions and structures with reaction kinetics

  Journal of Catalysis · 2026-02-27

  articleSenior authorCorresponding
  PublisherDOI

• Supporting dataset and scripts for "Ba2+ Complements Co2+ Exchange as a Reporter of Al Proximity in CHA Zeolites"

  Zenodo (CERN European Organization for Nuclear Research) · 2026-01-30

  datasetOpen access

  Dataset Description: This dataset includes all CONTCARs and python files used for energy analysis and titration simulations. It is organized as follows: 1. Divalent_Metals Folder CONTCARs files: Geometry optimized structure per divalent metal and Al pair configuration. Jupyter Notebook: Python-based notebook to generate Figure 2 and Figure S1 Dataset: ASE generate database with each performed DFT calculations 2. Z2Ba_vs_ZBaOH Folder CONTCARs files: Two folders with CONTCAR files used for evaluate the exchange energy between 2Al and 1Al site 3.Al_Distribution_and_Titration_Models Folder CURANTO: Python scripts with network-based Al distribution algorithm Jupyter Notebook: Python-based notebook to generate Al distribution samples. And notebook to generate the titration analysis plots.

  PublisherDOI

• Supporting dataset and scripts for "Ba2+ Complements Co2+ Exchange as a Reporter of Al Proximity in CHA Zeolites"

  Open MIND · 2026-01-30

  dataset

  Dataset Description: This dataset includes all CONTCARs and python files used for energy analysis and titration simulations. It is organized as follows: 1. Divalent_Metals Folder CONTCARs files: Geometry optimized structure per divalent metal and Al pair configuration. Jupyter Notebook: Python-based notebook to generate Figure 2 and Figure S1 Dataset: ASE generate database with each performed DFT calculations 2. Z2Ba_vs_ZBaOH Folder CONTCARs files: Two folders with CONTCAR files used for evaluate the exchange energy between 2Al and 1Al site 3.Al_Distribution_and_Titration_Models Folder CURANTO: Python scripts with network-based Al distribution algorithm Jupyter Notebook: Python-based notebook to generate Al distribution samples. And notebook to generate the titration analysis plots.

  DOI

• Divergent Mechanisms of SSZ-39 Crystallization Using Structurally Similar but Chemically Distinct Organic Structure-Directing Agents

  Journal of the American Chemical Society · 2025-06-02 · 6 citations

  article

  The role of an organic structure-directing agent on zeolite crystallization is conventionally interpreted based on the final, bulk crystal structure. However, few studies have examined their effect on the dynamics of zeolite crystal growth and restructuring, particularly with respect to the interzeolite transformations that are increasingly being exploited in zeolite synthesis. Herein, we compare two organic structure-directing agents that both direct the formation of the small-pore zeolite SSZ-39 (AEI). The organics have nearly identical molecular structures but exhibit distinct chemical compositions by virtue of a single heteroatom substitution. Our findings reveal that the organics have a dramatic impact on the crystallization kinetics, physicochemical properties, and catalytic performance of zeolite AEI prepared by the transformation of zeolite FAU parent crystals. The conventional quaternary ammonium structure-directing agent, “Pippy”, produces a distinct intermediate metastable structure with defects and anisotropic crystal shape that transitions into relatively thick zeolite AEI platelets with compromised hydrothermal stability. This transition is accompanied by an unusual morphological evolution from rod-like to platelet crystals that defies common Ostwald ripening processes. We demonstrate that a new quaternary ammonium-ether structure-directing agent, “Morphy”, produces thinner platelets of zeolite AEI and bypasses the defective intermediate observed for the conventional organic. Syntheses with Morphy produce a more hydrothermally stable product, which exhibits superior activity in the NH3 selective catalytic reduction of NOx used as a benchmark reaction for assessing structure–performance relationships.

  PublisherDOI

• Molecular Order and Disorder in the Semicrystalline Conjugated Polymer PBTTT and Donor–Acceptor Interactions in Bulk Heterojunction PBTTT:Fullerene Blends

  Macromolecules · 2025-07-28 · 2 citations

  articleSenior authorCorresponding

  The compositions and structures of the conjugated polymer poly(2,5-bis(3-hexadecylthiophen-2-yl)thienothiophene) (PBTTT-C16) are quantitatively measured and distinguished for the crystalline and disordered regions, as well as the intermolecular interactions between phenyl-C71-butyric acid methyl ester (PC71BM) and PBTTT moieties in bulk heterojunctions (BHJs). For PBTTT-C16, the long-range (>10 nm) crystalline order of lamellae is established by two-dimensional (2D) grazing-incidence small-angle X-ray scattering (GISAXS), while short-range (<1 nm) structures are characterized by using solid-state nuclear magnetic resonance (NMR) spectroscopy. In particular, 2D 1H{1H} double-quantum and 13C{1H} heteronuclear correlation NMR spectra reveal distinct intensity correlations for PBTTT-C16 that provide direct evidence for the presence of regions with well-ordered π–π-stacked conjugated backbones and interdigitated alkyl side chains, stacked backbones and disordered side chains, and amorphous regions of PBTTT-C16. Good agreement is found between the X-ray diffraction (XRD) and solid-state NMR analyses for 1H–1H distances between interlayer aromatic moieties (3.7 Å from XRD, 3.6 Å from 2D 1H{1H} NMR) and for the intermolecular C–H distances between the aromatic hydrogen atoms and terminal methyl carbon atoms (3.3–3.4 Å from XRD, 3.3 Å from 2D 13C{1H} NMR) in the crystalline regions. A larger mean 1H–1H distance of >3.8 Å between interlayer PBTTT backbones in less-ordered and disordered regions is determined by NMR, which is otherwise difficult to assess by XRD analyses alone. Combined solid-state NMR and density functional theory (DFT) results corroborate that the conjugated PBTTT-C16 backbones adopt nearly coplanar conformations in the ordered regions with a distribution of dihedral angles bisecting the thienothiophene moieties in the amorphous regions. The polar five-membered ring of the C70 fullerene in the PBTTT-C16:PC71BM blend was found to interact strongly with the aromatic thienothiophene protons of the semiconducting polymer, causing a strong π–π overlap of distinct moieties of the fullerene and polymer chain. The relative displacements of 1H chemical shifts by local ring currents and measurements of homonuclear 1H dipole–dipole couplings allow the molecular proximities between specific chemical moieties of the electron-donating PBTTT and the electron-accepting PC71BM species in the bimolecular BHJs to be established.

  PublisherDOI

• Kinetic photocycle description of photochemically induced dynamic nuclear polarization for dye-sensitized solid-state NMR spectroscopy

  AIP Publishing · 2025-01-01

  otherOpen access

  Solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) enables the amplification of the NMR signal in linked donor-acceptor (D-A) systems under light irradiation. At high fields, the effect relies on the creation of a transient a radical pair having a large initial spin order, which is spontaneously transferred to hyperfine-coupled nuclear spins and converted into polarization during the evolution of the system within the zero-quantum electron spin manifold. Previous quantum mechanical models to quantify the solid-state photo-CIDNP effect were based on a simplified representation of the D-A photocycle and did not account for the possibility of re-exciting the molecule after the radical pair state decays back to the molecular ground state. Here, we report a model for the quantification of solid-state photo-CIDNP using a unified master equation that spans all of the relevant photocycle states in Liouville space to account for their simultaneous evolution. The model accounts for multiple photocycle states interconnected by kinetic rates, with the various photocycle transitions described as spin-conserving Markovian processes. We then first apply the simplified model to identify conditions for solid-state ¹H photo-CIDNP at high magnetic fields (here, 9.4 T) and then, based on the information gathered in this way, we explore different cases with the unified model to identify potential design factors for second-generation D-A polarizing agents for dye-sensitized solid-state NMR experiments.

  PublisherDOI

• Diffusion in nanoporous materials with special consideration of the measurement of determining parameters (IUPAC Technical Report)

  Utrecht University Repository (Utrecht University) · 2025-01-01

  articleOpen access

  The random motion (the diffusion) of guest molecules in nanoporous host materials is key to their manifold technological applications and, simultaneously, a ubiquitous phenomenon in nature quite in general. Based on a specification of the different conditions under which molecular diffusion in nanoporous materials may occur and of the thus resulting relevant parameters, a survey of the various ways of the measurement of the determining parameters is given. Starting with a condensed introduction to the respective measuring principles, the survey notably includes a summary of the various parameters accessible by each individual technique, jointly with an overview of their strengths and weaknesses as well as of the respective ranges of observation. The presentation is complemented by basic relations of diffusion theory and molecular modeling in nanoporous materials, illustrating their significance for enhancing the informative value of each measuring technique and the added value attainable by their combination. By providing guidelines for the measurement and reporting of diffusion properties of chemical compounds in nanopores, the document aims to contribute to the clarification and standardization of the presentation, nomenclature, and methodology associated with the documentation of diffusion phenomena in nanoporous materials serving for catalytic, mass separation, and other relevant purposes.

  Publisher

• Kinetic photocycle description of photochemically induced dynamic nuclear polarization for dye-sensitized solid-state NMR spectroscopy

  AIP Publishing · 2025-01-01

  otherOpen access

  Solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) enables the amplification of the NMR signal in linked donor-acceptor (D-A) systems under light irradiation. At high fields, the effect relies on the creation of a transient a radical pair having a large initial spin order, which is spontaneously transferred to hyperfine-coupled nuclear spins and converted into polarization during the evolution of the system within the zero-quantum electron spin manifold. Previous quantum mechanical models to quantify the solid-state photo-CIDNP effect were based on a simplified representation of the D-A photocycle and did not account for the possibility of re-exciting the molecule after the radical pair state decays back to the molecular ground state. Here, we report a model for the quantification of solid-state photo-CIDNP using a unified master equation that spans all of the relevant photocycle states in Liouville space to account for their simultaneous evolution. The model accounts for multiple photocycle states interconnected by kinetic rates, with the various photocycle transitions described as spin-conserving Markovian processes. We then first apply the simplified model to identify conditions for solid-state ¹H photo-CIDNP at high magnetic fields (here, 9.4 T) and then, based on the information gathered in this way, we explore different cases with the unified model to identify potential design factors for second-generation D-A polarizing agents for dye-sensitized solid-state NMR experiments.

  PublisherDOI

• Supplementary Information

  AIP Publishing · 2025-01-01

  otherOpen access

  Supplementary Information

  PublisherDOI

Recent grants

• Collaborative Research: Reversible and Triggerable Self-Assembly of Photoresponsive Catanionic Vesicles

  NSF · $130k · 2008–2011

• MRI: Acquisition of an Integrated Dynamic Nuclear Polarization (DNP) Solid-State NMR Instrument with Unprecedented Sensitivity for Studies of Functional Materials

  NSF · $1.2M · 2014–2017

• INTERNATIONAL COLLABORATION IN CHEMISTRY: Local structures of heteroatom environments and their effects on the reactivities of alumino-and borosilicates

  NSF · $450k · 2009–2013

Frequent coauthors

• Galen D. Stucky

  University of California, Santa Barbara

  79 shared

• Shona M. Becwar

  University of California, Santa Barbara

  56 shared

• Sylvian Cadars

  Centre Européen de la Céramique

  55 shared

• David O. Scanlon

  54 shared

• Warda Rahim

  University College London

  52 shared

• Joseph K. Papp

  University of California, Berkeley

  51 shared

• Julija Vinckevičiūtė

  University of California, Santa Barbara

  51 shared

• Bryan D. McCloskey

  Lawrence Berkeley National Laboratory

  51 shared

Education

• PhD, Chemical Engineering

  University of California Berkeley

• Bachelor of Science, Chemical Engineering

  Arizona State University

Awards & honors

• Alfred P. Sloan Foundation Research Award (1996)
• David and Lucile Packard Foundation Award (1993)
• Camille and Henry Dreyfus Foundation Teacher-Scholar Award (…
• New Young Investigator Award, NSF Division of Materials Rese…
• NSF Division of Chemistry Post-doctoral Fellowship Award (19…