About

Ioannis Chasiotis is a professor at the University of Illinois at Urbana-Champaign, affiliated with the Micro and Nanotechnology Laboratory. He holds a Ph.D. in Aeronautics with a minor in Materials Science from the California Institute of Technology, where he also earned his M.S. in Aeronautics. His academic background includes a Diploma in Chemical Engineering from Aristotle University of Thessaloniki, Greece. Chasiotis's research focuses on experimental mechanics at the nanoscale, including atomic force microscopy, mechanics of thin films, MEMS, NEMS, fibers, and nanofibers, as well as the mechanics of interfaces and time-dependent mechanics of soft and biological materials. His work also encompasses high fidelity 3D printing of polymers, metals, and ceramics, with applications in aerospace materials, digital transformations, and sustainability. Throughout his career, he has contributed significantly to the understanding of nanostructured materials, impact-resistant polymers, and biological fibrils, earning numerous awards and recognition, including the Presidential Early Career Award for Scientists and Engineers (PECASE) and fellowships in professional societies.

Research topics

• Composite material
• Materials science
• Nanotechnology
• Structural engineering
• Chemistry
• Thermodynamics
• Biophysics

Selected publications

• The nonlinear elastic deformation of liquid inclusions embedded in elastomers

  Journal of the Mechanics and Physics of Solids · 2025-03-30 · 8 citations

  articleOpen accessCorresponding

  Elastomers filled with liquid inclusions — as opposed to conventional solid fillers — are a recent trend in the soft matter community because of their unique range of mechanical and physical properties. Such properties stem, in part, from the very large deformations that the underlying liquid inclusions are capable of undergoing. With the objective of advancing the understanding of the mechanics of this emerging class of materials, this paper presents a combined experimental/theoretical study of the nonlinear elastic deformation of initially spherical liquid inclusions embedded in elastomers that are subjected to quasistatic mechanical loads. The focus is on two fundamental problems, both within the limit regime when elasto-capillarity effects are negligible: ( i ) the problem of an isolated inclusion and ( i i ) that of a pair of closely interacting inclusions. Experimentally, specimens made of a polydimethylsiloxane (PDMS) elastomer filled with either isolated or pairs of initially spherical liquid glycerol inclusions are subjected to uniaxial tension. For the specimens with pairs of inclusions, three orientations of the two inclusions with respect to the direction of the applied macroscopic tensile load are considered, 0°, 45°, and 90°. The liquid glycerol is stained with a fluorescent dye that permits to measure the local deformation of the inclusions in situ via confocal laser scanning fluorescent microscopy. Theoretically, a recently developed framework — wherein the elastomer is considered to be a nonlinear elastic solid, the liquid comprising the inclusions is considered to be a nonlinear elastic fluid, and the interfaces separating the elastomer from the liquid inclusions can feature their own nonlinear elastic behavior (e.g., surface tension) — is utilized to carry out full-field simulations of the experiments. Inter alia , the results show that the deformation of liquid inclusions is significantly non-uniform and strongly influenced by the presence of other liquid inclusions around them. Interestingly, they also show that the large compressive stretches that localize at the poles of the inclusions may result in the development of creases.

  PublisherDOI

• High-Speed Atomic Force Microscopy for In-Situ Full-Field Measurement of Large Deformations

  Experimental Mechanics · 2025-12-04 · 1 citations

  articleOpen accessSenior author

  Abstract Background Atomic Force Microscopy (AFM) is widely used for high-resolution imaging and for probing the contact mechanics and multiphysics of materials at the nanoscale. However, its application to quantitative, full-field finite deformation studies of soft materials remains unexplored. Objective This work focuses on accurate high-speed, high-resolution AFM imaging of polydimethylsiloxane (PDMS) specimens in order to compute full-field strains with nanoscale spatial resolution. Methods The AFM cantilever dynamics were optimized for accurate high-speed imaging through independent control of the cantilever resonance frequency and spring constant, and by active Q-control. A miniature mechanical testing device was developed to fit inside a compact AFM, thereby enabling simultaneous mechanical loading and nanoscale imaging via a symmetric specimen stretching mechanism. Full-field in-plane strain fields from PDMS specimens subjected to finite deformations were extracted via Digital Image Correlation (DIC) from AFM images obtained during incremental specimen stretching. Results This experimental methodology successfully enables low error AFM imaging of PDMS at 100 Hz scan rate, signifying a 100-fold reduction in image acquisition time compared to previous studies using AFM to measure strain fields. The imaging repeatability, assessed with the aid of DIC, was accurate within 0.5% error in mean strain. Full-field strains derived from high-speed AFM images of PDMS specimens tested in situ under an AFM, agreed very well with macroscale optical measurements, including Poisson’s ratio calculations obtained up to the point of specimen failure. Conclusion The results of this study illustrate the feasibility of high-speed AFM as a quantitative tool for nanoscale full-field strain analysis, offering new opportunities for probing the large deformation mechanics of soft materials.

  PublisherOA PDFDOI

• Full-field strain measurements at the nanoscale

  Journal of Intelligent Material Systems and Structures · 2025-06-28

  article1st authorCorresponding

  A summary of advances in nanomechanical characterization of materials by utilizing high-spatial resolution Atomic Force Microscopy (AFM) for full-field strain measurements is presented along with perspectives for fast and accurate AFM imaging for nanoscale strain mapping. The combination of in situ AFM, and more broadly Scanning Probe Microscopy (SPM), specimen imaging during mechanical testing, with Digital Image Correlation (DIC) based strain calculations has provided full-field nanoscale deformation data in heterogeneous materials, which have enabled the investigation of microstructural effects on local deformation and fracture processes at the nanoscale. However, the inherent line-by-line scanning principle of an AFM requires long image acquisition times, thus prohibiting its application to viscoelastic materials while also increasing the susceptibility of AFM images to noise and thermal drift. Advances in control electronics, photodetectors, and cantilever microfabrication and excitation methods have opened new possibilities to reduce the acquisition time for high-resolution AFM images by 1–2 orders of magnitude, hence making the AFM/DIC experimental methodology an effective tool for nanomechanical studies.

  PublisherDOI

• An integrated experimental-computational investigation of the mechanical behavior of random nanofiber networks

  Soft Matter · 2025-01-01

  articleOpen accessSenior authorCorresponding

  near-field electrospinning. The structure of the same networks served as input to a computational model to obtain predictions of the macroscopic mechanical response. This methodology provides consistency in fabricating, testing and simulating nominally identical random fiber networks. Specimens with 500 to 5000 nanofibers were subjected to uniaxial tension and compared to modeling predictions for the network mechanical behavior. The predictions by the computational model, with inputs from the experimental network structure, the measured single PEO nanofiber properties, and the fiber crimp parameter, agreed with the experimental results both quantitatively and with respect to the dependence of the measured quantities on the network parameters. The network stiffness and strength followed a power-law scaling with the network density, with exponents 2.78 ± 0.15 and 1.59 ± 0.04, respectively, while the network stretch at failure gradually decreased with increasing network fiber density. Finally, the experimentally determined network toughness demonstrated a rather weak power-law dependence on the network fiber density (exponent of 1.18 ± 0.12).

  PublisherOA PDFDOI

• The nonlinear elastic deformation of liquid inclusions embedded in elastomers

  arXiv (Cornell University) · 2024-11-25

  preprintOpen access

  Elastomers filled with liquid inclusions -- as opposed to conventional solid fillers -- are a recent trend in the soft matter community because of their unique range of mechanical and physical properties. Such properties stem, in part, from the very large deformations that the underlying liquid inclusions are capable of undergoing. With the objective of advancing the understanding of the mechanics of this emerging class of materials, this paper presents a combined experimental/theoretical study of the nonlinear elastic deformation of initially spherical liquid inclusions embedded in elastomers that are subjected to quasistatic mechanical loads. The focus is on two fundamental problems, both within the limit regime when elasto-capillarity effects are negligible: ($i$) the problem of an isolated inclusion and ($ii$) that of a pair of closely interacting inclusions. Experimentally, specimens made of a polydimethylsiloxane (PDMS) elastomer filled with either isolated or pairs of initially spherical liquid glycerol inclusions are subjected to uniaxial tension. For the specimens with pairs of inclusions, three orientations of the two inclusions with respect to the direction of the applied macroscopic tensile load are considered, $0^\circ$, $45^\circ$, and $90^\circ$. The liquid glycerol is stained with a fluorescent dye that permits to measure the local deformation of the inclusions \emph{in situ} via confocal laser scanning fluorescent microscopy. Theoretically, a recently developed framework -- wherein the elastomer is considered to be a nonlinear elastic solid, the liquid comprising the inclusions is considered to be a nonlinear elastic fluid, and the interfaces separating the elastomer from the liquid inclusions can feature their own nonlinear elastic behavior (e.g., surface tension) -- is utilized to carry out full-field simulations of the experiments.

  PublisherOA PDFDOI

• Local electrical conductivity of carbon black/PDMS nanocomposites subjected to large deformations

  Journal of Composite Materials · 2023-02-01 · 5 citations

  articleSenior author

  The full-field microscale electrical behavior of polydimethylsiloxane (PDMS) matrix composites with 12 wt% (below the electrical percolation threshold) and 20 wt% (above the electrical percolation threshold) carbon black (CB) nanoparticles was obtained with the aid of Conductive Atomic Force Microscopy (C-AFM) as a function of uniaxial tensile strain. A comparison between the macroscale and the microscale 2D strain fields showed that 25 × 25 μm 2 specimen domains can serve as a representative surface element (RSE) to describe the macroscale mechanical response under finite deformations. The same surface domain size was shown to serve as RSE for the local electrical behavior of CB/PDMS nanocomposites at small and large strains. The transverse specimen contraction due to the Poisson’s effect increased the through-thickness conductivity of 12 wt% CB specimens, with a rapid increase in the total electric current measured at the scale of the RSE taking place above 23% uniaxial true strain. The locally dominant tunneling conductance in the undeformed specimen state transitioned to a combination of Ohmic (linear local current-voltage (I–V) characteristics) and tunneling (parabolic local I–V characteristics) at 35% uniaxial true strain. In comparison, the local I–V characteristics of undeformed PDMS composites with 20 wt% CB were a combination of Ohmic (contributing the majority of the total current) and tunneling. Upon application of 35% uniaxial true strain the vast majority of local conduction sites became Ohmic, while the total electric current at the scale of the RSE increased relatively linearly with applied strain.

  PublisherDOI

• Durable and impact-resistant thermoset polymers for the extreme environment of low Earth orbit

  Extreme Mechanics Letters · 2023-10-11 · 4 citations

  articleCorresponding
  PublisherDOI

• Strain rate induced toughening of individual collagen fibrils

  Applied Physics Letters · 2022-03-14 · 9 citations

  articleOpen accessSenior authorCorresponding

  The nonlinear mechanical behavior of individual nanoscale collagen fibrils is governed by molecular stretching and sliding that result in a viscous response, which is still not fully understood. Toward this goal, the in vitro mechanical behavior of individual reconstituted mammalian collagen fibrils was quantified in a broad range of strain-rates, spanning roughly six orders of magnitude, from 10−4 to 35 s−1. It is shown that the nonlinear mechanical response is strain rate sensitive with the tangent modulus in the linear deformation regime increasing monotonically from 214 ± 8 to 358 ± 11 MPa. More pronounced is the effect of the strain rate on the ultimate tensile strength that is found to increase monotonically by a factor of four, from 42 ± 6 to 160 ± 14 MPa. Importantly, fibril strengthening takes place without a reduction in ductility, which results in equivalently large increase in toughness with the increasing strain rate. This experimental strain rate dependent mechanical response is captured well by a structural constitutive model that incorporates the salient features of the collagen microstructure via a process of gradual recruitment of kinked tropocollagen molecules, thus giving rise to the initial “toe-heel” mechanical behavior, followed by molecular stretching and sustained intermolecular slip that is initiated at a strain rate dependent stress threshold. The model shows that the fraction of tropocollagen molecules undergoing straightening increases continuously during loading, whereas molecular sliding is initiated after a small fibril strain (1%–2%) and progressively increases with applied strain.

  PublisherOA PDFDOI

• Nonlinear time-dependent mechanical behavior of mammalian collagen fibrils

  Acta Biomaterialia · 2022-03-05 · 20 citations

  articleOpen accessSenior authorCorresponding
  PublisherOA PDFDOI

• Microscale creep and stress relaxation experiments with individual collagen fibrils

  Optics and Lasers in Engineering · 2021 · 16 citations

  Senior authorCorresponding
  • Materials science
  • Composite material
  • Biophysics
  PublisherOA PDFDOI

Recent grants

• NIRT: Novel Experiments and Models for the Nanomechanics of Polymeric and Biological Nanofibers

  NSF · $1.1M · 2005–2009

• Investigation of the Deformation, Fatigue and Fracture Properties of Amorphous Diamond-like Carbon Films

  NSF · $188k · 2005–2007

• Collaborative Research: An Integrated Experimental/Computational Study of the Mechanics of Nanofiber Networks

  NSF · $333k · 2016–2020

• Experiments and Models on Room Temperature Creep of Nanocrystalline Metallic Films

  NSF · $399k · 2009–2013

• PECASE: Nanoscale Confinement in Polymers: Integrated Research and Education in Nanoscale Experimental Mechanics

  NSF · $406k · 2008–2014

Frequent coauthors

• Mohammad Naraghi

  Texas A&M University

  19 shared

• Krishna N. Jonnalagadda

  17 shared

• Debashish Das

  14 shared

• John Lambros

  University of Illinois Urbana-Champaign

  14 shared

• Nikhil Karanjgaokar

  Worcester Polytechnic Institute

  12 shared

• Tanil Ozkan

  Medical Components (United States)

  12 shared

• W. G. Knauss

  California Institute of Technology

  11 shared

• Ronald G. Polcawich

  DEVCOM Army Research Laboratory

  10 shared

Awards & honors

• Fellow of the Society for Experimental Mechanics (2020)
• Fellow of the American Society for Mechanical Engineers (201…
• A.J. Durelli Award from the Society for Experimental Mechani…
• Hetenyi Best Paper Award in Journal Experimental Mechanics (…
• ASME Thomas J.R. Hughes Young Investigator Award (2011)