Controlling Coffee Ring Formation during Drying of Inkjet Printed 2D Inks

Abstract

There have been several reports of the deposition of graphene dispersions and other 2D materials using inkjet printing. [12,[14][15][16][17][18] Generally, 2D material inks show similar drying behavior to inks made from nanoparticles or nanotubes, i.e. under appropriate drying conditions they show a clear coffee ring with the 2D flakes or 1D tubes arranged at the contact line forming a characteristic ringlike structure. [14,15] Ring formation can be suppressed, for example, by using two solvents [16,17] or adding surfactant and a high boiling point solvent. Recent work by Kim et al. identified both an effect of size and an effect of temperature on the transition to a coffee ring during the drying of suspensions of graphene oxide (GO), [19] with higher drying temperatures suppressing coffee ring formation and a slightly lower critical temperature for ring suppression with inks containing larger GO flakes.Here, we further study the influence of flake size, substrate temperature, and drop size on the morphology of dried droplets of a GO ink. GO is an appropriate model ink because of its ease of dispersal in water and that it is possible to make inks with a wide range of flake sizes showing a common mean flake thickness with little variance. [20] The critical flake size for ring/no ring transition decreases as the substrate (drying) temperature increases. A decrease in the critical flake size also occurs when smaller drop diameters were used. We show that this behavior is governed by hysteresis between the advancing and receding contact angle caused by contact line pinning from heterogeneities in the surface energy or profile (roughness). [21,22] At the onset of drying, the diameter of the drop does not change but the contact angle reduces. The contact line becomes pinned if there is sufficient deposition of solute at the contact line to prevent detachment once the receding contact angle for the substrate is reached. [23] The onset of a coffee ring during drying drops of GO inks is consistent with a model for contact line pinning that compares characteristic time constants for flake aggregation and for the transition from the equilibrium to the receding contact angle.Inkjet printing was used to provide single sessile drops on Si/SiO 2 substrates from aqueous inks containing GO flakes of different sizes. Figure 1 shows the particle size distribution for the eight inks (GO-0-GO-7) used in this study; the mean particle size ranges from 0.68 to 35.9 µm. Sample scanning electron microscopy (SEM) images of the flakes and atomic force microscopy (AFM) height profiles are presented in the Supporting Information showing that the majority of the flakes The morphology of drops of graphene oxide (GO) inks produced by inkjet printing shows a distinctive coffee ring after drying when the mean diameter of the GO is below a critical size. Inks with larger diameter flakes do not show a coffee ring and the transition mean flake diameter decreases as the substrate temperature increases and when the printed drop size decreases. This be...

Advances in Ink‐Jet Printing of MnO2‐Nanosheet Based Pseudocapacitors

“…Copyright 2011, Springer Nature; h) Width of the “coffee‐ring” (w) normalized by droplet radius (R) as a function of lateral size of GO flakes. Reproduced with permission . Copyright 2017, Wiley‐VCH; i) Optical images of printed lines at varying droplet spacing.…”

“…Copyright 2018, Elsevier; j) Droplet morphology map of drying droplets defined by substrate temperature and mean flake size. Reproduced with permission . Copyright 2017, Wiley‐VCH; k) Optical micrograph of inkjet printed graphene droplet on O 2 plasma‐cleaned (left), pristine (middle) and HMDS‐coated (right) Si/SiO 2 substrate, and l) AFM images of printed graphene stripes on pristine (left), O 2 plasma‐cleaned (middle), and HMDS‐coated (right) Si/SiO 2 substrate.…”

“…It has also been shown that the morphology of printed graphene oxide (GO) droplets is influenced by the flake size . As shown in Figure h, the width of the coffee‐ring normalized by the droplet radius as a measure of the mean diameter of GO shows a gradual transition from the coffee‐ring structure to uniform deposition.…”

Interfacial Self‐Assembly of Colloidal Nanoparticles in Dual‐Droplet Inkjet Printing

“…For applications in printed electronics, this nonuniform deposition is particularly detrimental to the device performance. The complex multibody interactions, e.g., droplet–substrate interaction, particle–substrate interaction, and droplet–environment interaction, ultimately determine the final deposition and morphology of patterns . Various approaches have been explored to modify these interactions in order to control the contact line dynamics and/or to induce Marangoni flow driven by the surface tension gradient on the air–droplet interface, including tuning substrate wettability, application of surfactant additives and cosolvent systems to the droplet, vapor absorption of low‐surface tension solvents to the droplet, etc.…”

Compound redistribution due to droplet evaporation on a thin polymeric film: Theory

“…The formation of the dark rings of deposit is a result of the material being transported by internal flows inside the droplet caused by differences in the evaporation rate across the surface. Apart from a fundamental scientific interest, understanding the deposition of solids and being able to predict the topology of the resulting stain is of importance in applications such as inkjet printing 3,4 , semiconductor device manufacturing [5][6][7] and the creation of colloidal photonic crystals 8 . The redistribution and deposition of material due to the evaporation of a droplet are therefore studied extensively, both experimentally 1,2,[9][10][11][12] and theoretically 1,2,11,[13][14][15][16] .…”