Paper Number
AM1                         My Program 

Session
Additive and Advanced Manufacturing

Title
Printability and rheology of colloidal inks under high-frequency pulsed strain histories

Presentation Date and Time
October 21, 2025 (Tuesday) 1:30

Track / Room
Track 5 / O’Keeffe + Milagro

Authors (Click on name to view author profile)

  1. Kroo, Laurel (University of Massachusetts at Amherst)
  2. Rishabh, More (Monash University, Department of Chemical and Biological Engineering)
  3. Tuladhar, Tri (TriJet Limited)
  4. McKinley, Gareth H. (Massachusetts Institute of Technology, Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Laurel Kroo1, More Rishabh1, Tri Tuladhar2 and Gareth H. McKinley1
1Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; 2TriJet Limited, Cambridge, United Kingdom

Speaker / Presenter 
Kroo, Laurel

Keywords
experimental methods; colloids; methods; non-Newtonian fluids; particualte systems; polymer solutions; rheometry; techniques

Text of Abstract
Complex time-varying strain histories are commonly used in industrial inkjet printing and paint-deposition technologies to facilitate droplet ejection, but the physical mechanisms that underpin "optimal" waveforms for ejection efficiency (especially in the presence of viscoelasticity) remain elusive. In this study, we investigate the transient rheological response of particle-laden viscoelastic fluids using a piezo-electric high-frequency rheometer (TriJet Limited). Specifically, we study a "model paint" formulated from polyisobutylene, polyalphaolefin and colloidal particulates (carbon black), suspended in a paraffinic oil-based solvent. The high-frequency compressional rheometer squeezes a thin disk of this fluid between two parallel plates at exceptionally high-frequencies (under sinusoidal oscillations up to 10,000 Hz), while simultaneously measuring the dynamic response of the system.? Using a lumped-parameter model of the squeeze flow rheometer, we begin by isolating the response of the fluid from the "plant", while the fluid is subjected to rapid trains of step-pulses (parameterized through the duty cycle, ramp time, period, and number of pulses). From the rheological characterization at high frequency, we find that this category of highly-filled colloidal fluid is well-represented with a fractional Kelvin-Voigt constitutive model. Using this model as a "virtual" fluid with a relaxation spectra representative of real, industrially relevant printing inks/paints— we systematically study the linear system response to a variety of waveform parameters. Finally, we explore the question of rheologically-meaningful objective functions for identifying an optimal waveform that maximizes droplet ejection performance. We compare this with observations on a range of fluids that vary in concentration of carbon black from 2% to 10% wt. and connect to potential mechanisms that affect printability.