About

Matthew “Mateo” Robbins is a lecturer in the Master of Environmental Data Science program at the Bren School of Environmental Science & Management at the University of California, Santa Barbara. His research has focused on network models of natural resource governance, sustainable fisheries, sea level rise adaptation, and the science of science communication. He teaches courses on machine learning and text analysis for environmental problems. Robbins joined the Bren School after completing a postdoctoral position at the Computational Communication Lab at UC Davis. He holds a PhD from the Graduate Group in Ecology at UC Davis, an MA in Cognitive Psychology from Washington University in St. Louis, and a BA in Psychology from Willamette University.

Research topics

• Materials science
• Physics
• Mechanics
• Composite material
• Condensed matter physics

Selected publications

• Advance Care Planning Self-Efficacy Scale

  PsycTESTS Dataset · 2024-01-01

  datasetSenior author
  PublisherDOI

• Transtheoretical Model Exercise Self-Efficacy Scale

  PsycTESTS Dataset · 2024-01-01

  datasetSenior author
  PublisherDOI

• Transtheoretical Model Exercise Barriers Scale

  PsycTESTS Dataset · 2024-01-01

  datasetSenior author
  PublisherDOI

• From Molecular to Multiasperity Contacts: How Roughness Bridges the Friction Scale Gap

  ACS Nano · 2023-01-23 · 15 citations

  articleOpen access

  The tangential force required to observe slip across a whole frictional interface can increase over time under a constant load, due to any combination of creep, chemical, or structural changes of the interface. In macroscopic rate-and-state models, these frictional aging processes are lumped into an ad hoc state variable. Here we explain, for a frictional system exclusively undergoing structural aging, how the macroscopic friction response emerges from the interplay between the surface roughness and the molecular motion within adsorbed monolayers. The existence of contact junctions and their friction dynamics are studied through coupled experimental and computational approaches. The former provides detailed measurements of how the friction force decays, after the stiction peak, to a steady-state value over a few nanometers of sliding distance, while the latter demonstrates how this memory distance is related to the evolution of the number of cross-surface attractive physical links, within contact junctions, between the molecules adsorbed on the rough surfaces. We also show that roughness is a sufficient condition for the appearance of structural aging. Using a unified model for friction between rough adsorbed monolayers, we show how contact junctions are a key component in structural aging and how the infrajunction molecular motion can control the macroscopic response.

  PublisherOA PDFDOI

• Breaking down brittle fragmentation: gaining theoretical insight with simulation

  2023-03-01

  articleOpen accessSenior author
  PublisherOA PDFDOI

• Universal behavior in fragmenting brittle, isotropic solids across material properties

  PubMed · 2023-06-20

  preprintOpen accessSenior author

  A bonded particle model is used to explore how variations in the material properties of brittle, isotropic solids affect critical behavior in fragmentation. To control material properties, a model is proposed which includes breakable two- and three-body particle interactions to calibrate elastic moduli and mode I and mode II fracture toughnesses. In the quasistatic limit, fragmentation leads to a power-law distribution of grain sizes which is truncated at a maximum grain mass that grows as a nontrivial power of system size. In the high-rate limit, truncation occurs at a mass that decreases as a power of increasing rate. A scaling description is used to characterize this behavior by collapsing the mean-square grain mass across rates and system sizes. Consistent scaling persists across all material properties studied, although there are differences in the evolution of grain size distributions with strain as the initial number of grains at fracture and their subsequent rate of production depend on Poisson's ratio. This evolving granular structure is found to induce a unique rheology where the ratio of the shear stress to pressure, an internal friction coefficient, decays approximately as the logarithm of increasing strain rate. The stress ratio also decreases at all rates with increasing strain as fragmentation progresses and depends on elastic properties of the solid.

  PublisherOA PDFDOI

• Universal behavior in fragmenting brittle, isotropic solids across material properties

  Physical review. E · 2023-09-12 · 5 citations

  articleOpen accessSenior author

  A bonded particle model is used to explore how variations in the material properties of brittle, isotropic solids affect critical behavior in fragmentation. To control material properties, a model is proposed which includes breakable two- and three-body particle interactions to calibrate elastic moduli and mode I and mode II fracture toughnesses. In the quasistatic limit, fragmentation leads to a power-law distribution of grain sizes which is truncated at a maximum grain mass that grows as a nontrivial power of system size. In the high-rate limit, truncation occurs at a mass that decreases as a power of increasing rate. A scaling description is used to characterize this behavior by collapsing the mean-square grain mass across rates and system sizes. Consistent scaling persists across all material properties studied, although there are differences in the evolution of grain size distributions with strain as the initial number of grains at fracture and their subsequent rate of production depend on Poisson's ratio. This evolving granular structure is found to induce a unique rheology where the ratio of the shear stress to pressure, an internal friction coefficient, decays approximately as the logarithm of increasing strain rate. The stress ratio also decreases at all rates with increasing strain as fragmentation progresses and depends on elastic properties of the solid.

  PublisherOA PDFDOI

• Effects of Coarse-Graining on Molecular Simulation of Craze Formation in Polymer Glass

  Macromolecules · 2022-02-01 · 25 citations

  article

  Crazing precedes the crack propagation in polymer glass and greatly increases the fracture toughness. We perform molecular dynamics simulations to study craze formation in glassy polystyrene (PS). The use of a structure-based coarse-grained (CG) model allows us to create and equilibrate a large-scale sample (≈ 71 nm × 71 nm × 71 nm) of well-entangled PS chains with molecular weight 10 times the entanglement threshold. The back-mapping of the CG sample to the united-atom (UA) representation generates a PS sample with fine atomistic details. The structural features of the craze fibrils in the CG and UA simulations are almost the same, and both correlate with the underlying entanglement network as in the traditional theoretical description, reflecting the preservation of structural correlations during the coarse-graining. The stress level in the CG simulation is reduced compared with the UA simulation, as the coarse-graining with fine atomistic details removed leads to a smoother potential energy landscape for craze formation. In both CG and UA simulations, the same large fraction (70%–80%) of the stress during craze formation is dissipative stress, suggesting the coarse-graining preserves the relative contributions of the energetic and dissipative components to the overall stress. The constant drawing stress is related to the surface tension and the average spacing between craze fibrils in the simulations, as in the traditional models of crazing. We also demonstrate a scale-bridging simulation protocol where the CG simulation is used to accelerate the craze formation, and the subsequent back-mapping to the UA simulation is used to recover the stress level.

  PublisherDOI

• Fractal geometry of contacting patches in rough elastic contacts

  Journal of the Mechanics and Physics of Solids · 2022-01-29 · 30 citations

  articleOpen accessSenior author

  Many naturally formed and processed surfaces are rough over a broad range of length scales. Surface roughness reduces the area of contact between solids, with ramifications for phenomena that depend on the geometry of the interface and the amount of direct contact, including friction and adhesion. In this work, we employ large-scale boundary-element simulations for nonadhesive, elastic solids to study the size dependence of contact patch mean pressure and geometry for patches formed between solids with self-affine fractal surface roughness across seven decades in patch area. Contact patches with diameters smaller than a crossover length scale of order the minimum wavelength of roughness are generally compact with simple geometries and bear pressures well described by Hertz theory. The patch pressure in contact patches larger than the crossover scale rises logarithmically before saturating at a finite value. Furthermore, the largest contact patches formed during our simulations are ramified and populated with regions out of contact, or bubbles, which reduce patch area and increase patch perimeter. As a result, we show that the mean contact diameter of the largest patches saturates, indicating that the patch contact area is proportional to the total patch perimeter. We quantify the effects of bubbles on patch area and perimeters as a function of Hurst exponent and contrast our findings with results of comparable bearing-area model calculations. The slow evolution of the mean patch pressure with patch size in our large-scale calculations explains the common observation that the global mean contact pressure depends on the structure of the roughness, the contact area, and even on system size.

  PublisherDOI

• Stressful situations: modeling granular fragmentation at high pressures.

  2022-10-01

  articleOpen accessSenior author

  Abstract not provided.

  PublisherOA PDFDOI

Recent grants

• Non-Equilibrium Systems: Spreading, Deformation, Adhesion and Friction

  NSF · $560k · 2005–2010

• MRI: Acquisition of 100TF Graphics Processor Laboratory for Multiscale/Multiphysics Modeling

  NSF · $382k · 2009–2013

• Deformation and Fracture of Disordered Solids: Mechanisms Underlying Macroscopic Behavior

  NSF · $580k · 2010–2015

• Contact, Adhesion and Friction: From Atomic Interactions to Macroscopic Behavior

  NSF · $520k · 2014–2019

• NIRT: Interfacial Forces in Active Nanodevices

  NSF · $1.1M · 2007–2013

Frequent coauthors

• Marek Cieplak

  Polish Academy of Sciences

  32 shared

• Lars Pastewka

  University of Freiburg

  30 shared

• Gary S. Grest

  Sandia National Laboratories

  29 shared

• Shiyi Chen

  Guangxi University of Chinese Medicine

  23 shared

• Ting Ge

  University of South Carolina

  23 shared

• Belita Koiller

  Universidade Federal do Rio de Janeiro

  23 shared

• Thomas C. O’Connor

  Carnegie Mellon University

  20 shared

• Binquan Luan

  IBM Research - Thomas J. Watson Research Center

  19 shared

Education

• PhD, Physics

  University of California Berkeley

  1983

• M.A., Physics

  Harvard University

  1977

• BA, Physics

  Harvard University

  1977