Coffee-ring effect

Soltman D, Subramanian VS. (2008) Inkjet printed line morphologies and temperature control of the coffee ring effect. Langmuir in press. 

A capiUaiy flow is generated towards the contact line by an evaporation rate gradient at the air-solvent interface close to the contact line. It is noteworthy that the first step is often referred to as the coffee-ring effect proposed by Deegan in 1997 [1]. However, the entire four-step process is more accurately described as such with this merely being the first part in an essentially iterative process throughout the duration of evaporation. 

Yunker, P.J., Still, T., Lohr, M.A., Yodh, A.G. Suppression of the coffee-ring effect by shape-dependent capillary interactions. Nature 476, 308-311 (2011)... 

Anyfantakis, M., Baigl, D. Dynamic photocontrol of the coffee-ring effect with optically tunable particle stickiness. Angew. Chem. Int. Ed. 126, 14301-14305 (2014)... 

To fabricate OPVs by this printing system, the ink formulation needs to be modified to control the droplet volume and meniscus of the solution. In addition, the inkjet printing process should allow good film morphology without the coffee ring effect, as shown in Figure 13.5. 

In the following sections, the effect on the impression that polymer solutions leave on a substrate as a variation of printing height and molar mass will be discussed. Moreover, the coffee ring effect, which is often observed when handling liquids that contain solute materials, will be explained in detail. 

Hu H, Larson RG. (2006) Marangoni effect reverses coffee-ring depositions. / Phys Chem B 110 7090-7094. 

Caffeine (1.10), found in coffee (Coffea arabica), was introduced to Europe through Constantinople (modem Istanbul) in the 1500s (Figure 1.5). The stimulant effects of coffee were widely acknowledged, but coffee was recognized as a useful diuretic. Caffeine was first synthesized by Emil Fischer in 1882. Two related compounds, theobromine (1.11) and theophylline (1.12), found in cacao seeds (Theobroma cacao) and tea (Camellia sinensi), respectively, are more potent diuretics than caffeine.1 All three compounds are based on the purine ring system (1.13). 

While the effects of caffeine vary from person to person, a dose of 1,000 mg or more will generally produce adverse effects such as insomnia, restlessness, excitement, trembling, rapid heart beat with extra heart beats, increased breathing, desire to urinate, ringing in the ears, and heartburn. A fatal dose of caffeine appears to be more than 10 g or 170 mg/kg of body weight—about 80 to 100 cups of coffee in one sitting. 

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