Evaporation-controlled dripping-onto-substrate (DoS) extensional rheology of viscoelastic polymer solutions

Abstract

Extensional flow properties of polymer solutions in volatile solvents govern many industrially-relevant coating processes, but existing instrumentation lacks the environment necessary to control evaporation. To mitigate evaporation during dripping-onto-substrate (DoS) extensional rheology measurements, we developed a chamber to enclose the sample in an environment saturated with solvent vapor. We validated the evaporation-controlled DoS device by measuring a model high molecular weight polyethylene oxide (PEO) in various organic solvents both inside and outside of the chamber. Evaporation substantially increased the extensional relaxation time $$\lambda _{E}$$ λ E for PEO in volatile solvents like dichloromethane and chloroform. PEO/chloroform solutions displayed an over 20-fold increase in $$\lambda _{E}$$ λ E due to the formation of an evaporation-induced surface film; evaporation studies confirmed surface features and skin formation reminiscent of buckling instabilities commonly observed in drying polymer solutions. Finally, the relaxation times of semi-dilute PEO/chloroform solutions were measured with environmental control, where $$\lambda _{E}$$ λ E scaled with concentration by the exponent $$m=0.62$$ m = 0.62 . These measurements validate the evaporation-controlled DoS environment, and confirm that chloroform is a good solvent for PEO, with a Flory exponent of $$\nu =0.54$$ ν = 0.54 . Our results are the first to control evaporation during DoS extensional rheology, and provide guidelines establishing when environmental control is necessary to obtain accurate rheological parameters.

Temperature-controlled dripping-onto-substrate (DoS) extensional rheometry of polymer micelle solutions

“…Additionally, the measurement cell is not well-sealed, as shown recently in measurements of volatile polymer solutions. 23…”

“…Recently introduced by Dinic and Sharma, 16 dripping-ontosubstrate (DoS) extensional rheometry has addressed some shortcomings of the CaBER technique, enabling the characterization of low-viscosity (Z 0 o 20 mPa s), low-elasticity (l E o 1 ms), and low surface tension (s o 30 mN m À1 ) fluids such as dilute polymer solutions and protein solutions. 16,23,24 In DoS rheometry, a single droplet is slowly extruded from the end of a nozzle. The droplet then contacts a substrate, forming a liquid bridge that undergoes capillary-driven thinning and breakup.…”

“…As the DoS technique was pioneered less than one decade ago, one major limitation is that DoS measurements are limited to ambient temperatures. Recently, researchers have created closed chambers 28 or chambers with solvent reservoirs 23 to enable DoS measurements in volatile solvents. However, a temperature control chamber has yet to be incorporated into DoS rheometry, whereas heated CaBER has been developed both commercially and via custom design.…”

“…Additionally, the measurement cell is not well-sealed, as shown recently in measurements of volatile polymer solutions. 23 Custom CaBER instruments have made advances in temperature-controlled capillary thinning measurements. To measure the extensional rheology of polycarbonate melts, Sur et al 29 constructed a high-temperature CaBER wherein the sample environment was enclosed in an oven that could reach temperatures up to 400 1C.…”

Polysorbate identity and quantity dictate the extensional flow properties of protein‐excipient solutions

“…The liquid bridge is illuminated with a light behind a diffusing screen, and the evolution of the liquid bridge radius in time is captured with a high-speed camera, which can detect spatial features down to $5 μm. 57 As the drop is stationary prior to slowly moving the substrate upwards to form the liquid bridge, the surface tension for each trial can also be determined prior to capillarydriven thinning of the bridge. Fluids measured via DoS in this work reach extension rates of order 10 4 (SI.3), in the range for clinically relevant injection flows.…”