Correlations between chemorheology, printing parameters, and print quality in 3D direct-ink-writing

Amir Azimi Yancheshme

doi:10.17918/00011223

Direct Ink Writing (DIW) has emerged as a versatile additive manufacturing technique for producing large-format, high performance polymeric structures. However, the shape fidelity and mechanical integrity of printed parts are often compromised by uncontrolled relaxation of deposited filaments, commonly referred to as spontaneous spreading. As a result, DIW components frequently exhibit reduced dimensional accuracy and inferior mechanical performance compared to traditionally manufactured counterparts. Low-viscosity inks spread excessively, causing slump, while highly viscous inks resist coalescence, leading to voids and poor interlayer adhesion. These defects stem from inadequate control over filament shape and spreading dynamics. To address this limitation, the present work establishes correlations between fluid properties, processing parameters, and filament spreading behavior, enabling predictive control of deposition in DIW. This dissertation investigates the morphology of single and multiple printed beads across three representative material classes: Newtonian fluids, non-Newtonian systems including polymer solutions and colloidal suspensions, and photo-curable resins. The influence of resin properties, shear-thinning and thixotropic behavior, and photocuring kinetics on filament shape and spreading dynamics is elucidated, respectively. For Newtonian fluids, the fundamental physics of spontaneous spreading are resolved for both droplets and cylindrical filaments. Spreading is shown to be universally described by a viscous timescale ([tau][mu]), Bond number (Bo), and static advancing contact angle ([theta]s), yielding master curves that capture both transient dynamics and equilibrium shapes. Building upon this foundation, reactive photo-curable resins are investigated to capture the interplay between spreading and in situ polymerization. A predictive model is introduced that integrates Newtonian spreading theory with resin chemorheology, defined by an effective viscosity and gelation time, enabling accurate prediction of cured bead dimensions without extensive simulations. The analysis then extends to complex non-Newtonian fluids. For dilute polymer solutions, a generalized dynamic wetting framework is introduced in which an average viscosity, derived from constitutive rheology, collapses diverse shear-thinning fluids onto a master curve, providing the first generalized scaling law for dilute polymer droplet spreading. Colloidal suspensions present an additional challenge due to thixotropy and shear-history-dependent recovery. A dynamic spreading model is developed that incorporates relaxation spectra and a novel offset time formulation to encode nozzle shear history into post-deposition spreading. This model quantitatively predicts the sensitivity of spreading to concentration and deposition conditions, directly linking colloidal rheology, processing history, and spreading dynamics. Finally, the collective behavior of multiple adjacent filaments is examined, where uncontrolled spreading leads to voids that compromise structural integrity. Experiments with photocurable colloidal suspensions reveal correlations between filament spreading, line spacing, and defect morphology. Optimal deposition strategies are identified, demonstrating that void-free, dimensionally accurate structures can be achieved when line spacing is tuned relative to the steady-state shape of preceding filaments and adjusted dynamically with the number of deposited rows. Extending this strategy across multiple layers further improves structural uniformity and dimensional fidelity. Collectively, this dissertation develops a unified framework linking fluid properties, rheological response, and processing parameters to spreading dynamics across complex fluid systems. The resulting models establish predictive control over filament shape and inter-filament coalescence, laying the foundation for high-fidelity, defect-free DIW printing. Beyond additive manufacturing, the generalized insights into dynamic wetting extend to broader applications, including coatings, functional surfaces, and soft material processing.

Correlations between chemorheology, printing parameters, and print quality in 3D direct-ink-writing

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Correlations between chemorheology, printing parameters, and print quality in 3D direct-ink-writing

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