Flow‐Induced Polymer Degradation During Ink‐Jet Printing

Abstract

We report for the first time evidence of flow-induced polymer degradation during inkjet printing for both poly(methyl methacrylate) (PMMA) and polystyrene (PS) in good solvent. This has significance for the deposition of functional and biological materials. Polymers having Mw either less than 100 kDa or greater than approximately 1,000 kDa show no evidence of molecular weight degradation. The lower boundary condition is a consequence of low Deborah Number De imposed by the printhead geometry and the upper boundary condition due to visco-elastic damping. For intermediate molecular weights the effect is greatest at high elongational strain rate and low solution concentration with higher polydispersity polymers being most sensitive to molecular weight degradation. For low polydispersity samples, PDi ≤ 1.3, chain breakage is essentially centro-symmetric induced either by turbulance or overstretching when the strain rate increases well beyond a critical value, that is the stretching rate is high enough to exceed the rate of relaxation. For higher polydispersity samples chain breakage is consistent with almost random scission along the chain, inferring that the forces required to break the chain are additionally transmitted either by valence bonds, i.e. network chains and junctions or discrete entanglements rather than solely by hydrodynamic interaction.

Jetting behavior of polymer solutions in drop-on-demand inkjet printing

“…We have used an average extension rate here rather than a local value, and the emerging jet tip speed is 2-3 times higher than the final drop speed. However, the agreement between the scaling predictions of the model and the experimental data from de and A-Alamry et al (2011), including both transitions, and with the trend of the experimental data from the present work within regime III, suggest that the model is well-founded. Morrison and Harlen (2010) reported numerical simulations of the jetting of viscoelastic fluids which also showed the same scaling law as that predicted for regime III.…”

“…However, the observed scaling behavior appears closer to regime II. We note that A-Alamry et al (2011) found that polymer chain scission occurred within the DMP nozzle which would reduce s Z and consequently the value of Wi in the fluid ligament.…”

Drop-on-demand drop formation of polyethylene oxide solutions

“…This odd result may be associated with chain scission occurring during either solution preparation or jetting. 45,46 The discrepancy between the results for 1000 kg/mol PEO and the lower molecular weight PEO was slightly more than a factor of 4. Since k eff varies with molecular weight raised to a power of 2.07, chain scission at the chain midpoint may be responsible.…”

“…Since k eff varies with molecular weight raised to a power of 2.07, chain scission at the chain midpoint may be responsible. A-Alamry et al 46 have reported evidence of flow-induced polymer degradation during inkjet printing for both poly(methylmethacrylate) and polystyrene in good solvents. Bossard et al 45 studied the rheological properties of PEO (Sigma-Aldrich) solutions as a function of concentration and molecular weight for two dispersion processes: stirring and shaking.…”

Experimental study of atomization patterns produced by the oblique collision of two viscoelastic liquid jets

“…We note that Tirtaatmadja et al [14] suggested using a surface tension reduction agent (2-butanol) to provide a constant equilibrium surface tension for PEO solutions over 10 2 -10 4 ms timescales, but use of such an additive was not considered to be necessary for the shorter timescales accessed by the present experiments. The poly-dispersity index for the PEO samples was unknown but a recent study [15] of the dispersion of high molecular weight PEO in aqueous solution quotes a PDI = 3.33 for PEO from the same supplier, while Tirtaatmadja et al [14] quote PDI ∼ 1.8 for PEO 1 M as a typical value, although the effective PDI may be affected by different methods of PEO solution preparation [15] or even be altered during jetting [16,17].…”