Oscillations of aqueous PEDOT:PSS fluid droplets and the properties of complex fluids in drop-on-demand inkjet printing

Abstract

a b s t r a c tShear-thinning aqueous poly(3,4-ethylenedioxythiophene): poly(styrene sulphonate) (PEDOT:PSS) fluids were studied under the conditions of drop-on-demand inkjet printing. Ligament retraction caused oscillation of the resulting drops, from which values of surface tension and viscosity were derived. Effective viscosities of <4 mPa s at drop oscillation frequencies of 13-33 kHz were consistent with conventional high-frequency rheometry, with only a small possible contribution from viscoelasticity with a relaxation time of about 6 ls. Strong evidence was found that the viscosity, reduced by shear-thinning in the printhead nozzle, recovered as the drop formed. The low viscosity values measured for the drops in flight were associated with the strong oscillation induced by ligament retraction, while for a weakly perturbed drop the viscosity remained high. Surface tension values in the presence of surfactant were significantly higher than the equilibrium values, and consistent with the surface age of the drops.

Surface Tensions of Picoliter Droplets with Sub-Millisecond Surface Age

“…12 In this paper, we describe an approach to resolve the surface tension of 10-25 μm radius picoliter droplets with surface age <1 ms by reproducible droplet ejection from a microdroplet dispenser. The novel aspect relative to previously reported approaches [33][34][35][36][37][38] is that we explore a much larger parameter space, investigating a wider range of particle size, oscillation time, and chemical composition than previous studies. In addition, we examine in detail measurement-tomeasurement reproducibility across all parameters, with an aim to develop this approach into a robust platform to investigate the dynamic surface tension of fresh droplet surfaces across a wide size range.…”

Unraveling the Modified PEDOT:PSS Thin Films Based Near‐Infrared Solar‐Heat Shields by Using Broadband Transmittance and Raman Scattering Spectrometers

“…The three sprayed materials (PEDOT:PSS) were prepared with the different volume ratios of methanol/water (0/1, 1/1 and 2/1), which have the different viscosities. The viscosities of PEDOT:PSS (1:2.5 wt%) solution and methanol are about 63 and 0.53 mPas at room temperature, respectively. A viscometer (DV‐III Ultra Rheometer, Brookfield) was used to determine the viscosities of the PEDOT:PSS solution mixed with methanol.…”

A simple levitated-drop tensiometer

“…In fact, equations 4 and 6 have been used in the past to determine both the viscosity and the surface tension of drops undergoing oscillations following jetting from a inkjet printing nozzle [10,15]. In the scheme presented here, the oscillation frequency Ω 2 of levitated liquid droplets can be optically detected.…”

“…A recently developed method to measure liquid properties during inkjet processes consists of analysing the oscillation of ink droplets during the jetting and flight stages of printing via high speed imaging [9,10]. This method was designed to work under normal printing operational conditions, where drop sizes are of the order of 50 µm in diameter at shear rates of 10 5 s −1 .…”

“…shear rates and speeds) relevant to the jetting process for further ink formulation and development. However, most printers (or droplet generators) require several millilitres of ink to operate [10,15], and therefore the technique is not appropriate for applications where the available liquid volume is limited. In addition, this method is inherently expensive as it requires high-priced microscopes/lenses, high speed cameras, and cumbersome illumination systems.…”