About

Robert McLeod is a Professor and the Richard & Joy Dorf Endowed Professor in the Department of Electrical, Computer & Energy Engineering at the University of Colorado Boulder. His academic and research focus is on photonics and quantum engineering. He is associated with the College of Engineering and Applied Science and is involved in various interdisciplinary collaborations across departments such as Aerospace Engineering Sciences, Chemical & Biological Engineering, Civil, Environmental & Architectural Engineering, and others. His contact information includes an office at SEEC N321F and a lab at SEEC N2G3, with a phone number of 303-735-0997 and an email address at Robert.Mcleod@colorado.edu.

Research topics

• Materials science
• Computer Science
• Composite material
• Chemistry
• Artificial Intelligence
• Polymer chemistry
• Organic chemistry
• Polymer science
• Cell biology
• Physics
• Algorithm
• Computer graphics (images)
• Mathematics
• Optics
• Chemical engineering
• Nanotechnology
• Optoelectronics
• Biomedical engineering
• Biology
• Engineering
• Anatomy
• Computer vision

Selected publications

• High-Refractive-Index Halogenated Urethane Acrylates in Polyurethane for 2-Stage Material Applications

  ACS Applied Polymer Materials · 2026-03-17

  articleOpen accessSenior authorCorresponding

  High-refractive-index (HRI) monomers swollen in a rubbery host matrix to form 2-stage composite materials play a crucial role in modern optics applications and are constantly being redesigned to produce enhanced material properties. To aid in this effort, we report the synthesis of two HRI halogenated acrylate monomers and characterize their affinity for high-spatial-frequency photopatterning when swollen in a polyurethane matrix. Through refractive index measurements and high-resolution photopatterning, we show that these 2-stage films support submicrometer spatial frequencies with refractive index modulation n1 on the order of 0.01 and change in index upon polymerization Δn of 0.0023. Photopolymerization kinetics from FTIR fit a three-species kinetic model, where the dependence of the polymerization rate on incident light intensity reveals that the dominant termination kinetics in these 2-stage films is unimolecular termination, as opposed to the standard bimolecular. Critically, we show that photopatterning does not induce undesirable optical or mechanical properties such as haze, discoloration, stiffening of the films, or increased dispersion, making these materials suitable for photopatterning applications. High-fidelity holographic diffraction gratings and 2D photo-patterns with micron-scale features are presented to show proof of concept.

  PublisherDOI

• Dual-Cure Dynamic Networks for Mechanophotopatterning of Surface Topography

  Macromolecules · 2025-02-05 · 1 citations

  article

  Control of thin film surface features is critical in the fields of optics, biologics, electronics, and microfluidics, among others. Although facile in method, implementation of mechanophotopatterning has been chemically constrained, resulting in an undesired evolution or a limited processing window. This work overcomes these limitations by combining dynamic covalent chemistry to alter the surface relief with a dual-cure approach that increases the cross-link density and glass transition temperature following patterning to permanently fix the structure. The inclusion of a photosensitive dynamic covalent moiety, in the form of an allyl sulfide, allows for spatiotemporal stress relaxation control, and the associated formation of topographic patterns when the elastomer is exposed to light under strain. Typically, the resulting topography remains susceptible to undesirable evolution as the network’s dynamic capacity persists. To mitigate the residual dynamics, 65 wt % bisphenol A diglycidyl ether is included, in combination with a thermally latent acid, to facilitate a post-topography altering cationic polymerization which permanently fixes the topography through large changes in cross-link density and glass transition. Feature height of films fixed by this cure remain within 100 nm (<1% change), of their original dimensions.

  PublisherDOI

• Reducing Haze of Holographic Gratings Recorded in a Two-Stage Photopolymer

  Macromolecules · 2025-01-13 · 7 citations

  article

  The haze developed during the recording of holographic gratings was investigated and mitigated in a typical two-stage holographic photopolymer system where a high-refractive-index acrylate (1,3-bis(phenylthio)-2-propyl acrylate, i.e., BPTPA) was utilized as a writing monomer. An acrylate writing monomer (1,3-bis(phenylthio)-2-propyl urethane ethyl acrylate, i.e., BPTPUA) was proposed and synthesized to achieve a lower interaction parameter (χ) between the matrix and the writing monomer. Confirmed by theoretical predictions and experimental photolithography results, the formulation incorporating BPTPUA exhibited a significant improvement in miscibility between the two phases as compared to the analogue compound without a urethane, BPTPA. The higher miscibility led to dramatically lower haze of holographic gratings, due to which the quality of angular playback curves from holographic gratings improved from being strongly distorted to being well-matched with the Kogelnik coupled wave theory. Additionally, a higher light intensity reduced the haze remarkably due to the potential kinetic restriction for phase separation and lower molecular weight of the photopolymer formed. The molecular weight decrease at higher light intensity was confirmed experimentally, and the trend was fit by a theoretical calculation of the kinetic chain length. Using the fitted relationship, the free energy change of mixing was calculated and suggested that a higher light intensity improved the miscibility between the photopolymer and the matrix thermodynamically. Moreover, a reactive matrix was introduced to mitigate the haze development by forming covalent bonds between the two phases. With contributions from covalent attachment and BPTPUA as the writing monomer, haze as low as 0.5% was achieved in a 50 μm recording medium at an extremely high light intensity (200 mW/cm2) for holographic grating.

  PublisherDOI

• Ultrathin Screen‐Printed Plant Wearable Capacitive Sensors for Environmental Monitoring

  Advanced Sensor Research · 2025-01-28 · 11 citations

  articleOpen access

  Abstract Printable and wearable plant sensors offer an approach for collecting critical environmental data at high spatial resolution to understand plant conditions and aid land management practices. Here, screen printed capacitive devices that can measure relative humidity (RH) directly at the plant‐environment interface, are demonstrated in an ultra‐thin (&lt;6 µm) form factor. Using screen printing and a temporary tattoo transfer process, a simple technique is established to: 1) enclose printed electronic features between two layers of ethyl cellulose (EtC), 2) mount printed microparticle carbon‐based electronics onto a variety of plant structures, and 3) dramatically increase the capacitance and sensitivity for humidity sensors when compared to unencapsulated devices. This sandwich tattoo capacitor (STC) platform exhibits an RH sensitivity up to 1000 pF/%RH and stability while mounted to living plant leaves over several days. Electrochemical impedance spectroscopy (EIS) validates the formation of electric double layers within the EtC films that encapsulate the printed electrodes providing tunable capacitance values based on the ionic concentration of the device transfer fluid.

  PublisherOA PDFDOI

• 1,2-Dithiolane/yne photopolymerizations to generate high refractive index polymers

  Polymer Chemistry · 2025-01-01 · 6 citations

  articleOpen access

  Photoinitiated copolymerization of dithiolanes and alkynes results in copolymers with high refractive indices. Transmission holography performed via this reaction results in stable, high diffraction efficiency gratings with low haze, birefringence.

  PublisherOA PDFDOI

• Quantifying limits imposed by occlusions in volumetric additive manufacturing

  2025-03-19

  articleSenior author
  PublisherDOI

• Multi-criteria Decision Support for the Procurement of Retrofit Ventilation Systems in Educational Buildings

  Lecture notes in civil engineering · 2025-11-22 · 1 citations

  book-chapterSenior author
  PublisherDOI

• Tomography-driven registration of embedded objects for high-precision overprinting in volumetric additive manufacturing

  2025-03-19

  articleSenior author
  PublisherDOI

• High dimensionality volumetric additive manufacturing

  2025-03-19

  article1st authorCorresponding
  PublisherDOI

• Advancing the performance of dual-thiol holographic photopolymers via kinetic selectivity

  2025-06-02

  article

  Dual-thiol holographic photopolymers have been approached from various material schemes; however, optimal performance has yet to be developed, understood and explored. Exploiting the orthogonal nature of the base catalyzed thiol-Michael reaction and the radical mediated thiol-ene photopolymerization, two-stage dual-thiol materials were applied to form holographic photopolymers. Through thiol monomer selection, kinetic selectivity was applied to the thiol-Michael reaction pathway—opening the possibility of wider monomer selection. This approach enables one thiol to be chosen for the low refractive index matrix crosslinking agent, and a different thiol to be chosen for the high refractive index photopolymer. The flexibility of this technique facilitates one-pot synthesis of multiple different thiols while maintaining control and separation of the two thiol-click reactions. Herein, we expanded upon a previous approach using kinetic selectivity by pushing the performance of dual-thiol holographic photopolymers through driving up the refractive index contrast of the thiol monomers while exploring the fidelity of thiol-Michael selectivity. High refractive index thiol monomers previously developed are natural candidates to improve holographic photopolymer performance; however, the molecular composition that affects refractive index also impacts the reaction kinetics. By exploring the performance as indicated by the refractive index contrast while understanding the impact on the kinetic selectivity of such monomers, we present a more comprehensive approach to this dual-thiol holographic photopolymer approach.

  PublisherDOI

Recent grants

• GOALI: Projection Stereolithography of Gradient Viscoelastic Polymer Nanocomposites

  NSF · $415k · 2018–2022

• TCHCS: Hybrid RF/Optical ICs for High-Bandwidth Spread-Spectrum Communications

  NSF · $466k · 2007–2010

• GOALI: Holographic Passive Solar Concentration and Lighting

  NSF · $407k · 2013–2017

• Precision Organic Electrochemical Transistors for Single-Cell Electrophysiology

  NSF · $398k · 2015–2019

• EAGER: Shared Materials Plotter for Organic Robotics

  NSF · $30k · 2012–2013

Frequent coauthors

• Amy C. Sullivan

  University of Colorado Boulder

  40 shared

• Christopher N. Bowman

  University of Colorado Boulder

  23 shared

• Kelvin Wagner

  22 shared

• Marvin D. Alim

  University of Colorado Boulder

  19 shared

• Stephanie J. Bryant

  University of Colorado Boulder

  16 shared

• David J. Glugla

  University of Colorado Boulder

  15 shared

• Archish Muralidharan

  University of Colorado Boulder

  14 shared

• David B. Miller

  14 shared