Capillary flow as the cause of ring stains from dried liquid drops

Abstract

The mean acoustic intensity, m, in the quiet Sun seems to increase with depth, as shown in Fig. 3. The depth dependence of m may be related to the variation of acoustic absorption with depth and the fraction of the acoustic spatiotemporal spectrum that is detected in viewing different depths. (5) The spatial resolution of constructed images decreases with depth. The time-distance relations flatten with increasing depth, so the phase gradient over the observing annulus decreases. The difference in phases used to image adjacent spatial points becomes small, and a point in space is imaged with a broad point-spread function. Another cause is that shorter-wavelength modes cannot be detected in viewing a deeper region.Finally, we mention some important questions that call for further study. What is the degree of cancellation of signals from points other than the target point in this phased detection? What are the horizontal and vertical spatial resolutions corresponding to this 'computational acoustic lens'? What is the correct interpretation of the mean intensity, m, and its apparent variation with depth? Can this method reconstruct the complex index of refraction of acoustic waves at each target point, using the phase information in addition to the intensity? Finally, could one use this method to detect active regions before they emerge, or active regions at the other side of the Sun?Ⅺ

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

“…This avoided the typical coffee ring effect seen upon evaporation of the ink, when depositing low quantities of 90 catalysts. 10 The catalyst layers deposited via VFC were found to be significantly more reproducible with respect to morphology, thickness and size than we were able to achieve with the evaporation techniques such as the catalyst coated membrane (CCM) technique. A 60 % Pt on carbon support catalyst was 95 chosen to reduce the amount of carbon in the catalyst layer, allowing for thinner layers with equivalent catalyst loading.…”

“…Sun et al 3 applied this strategy to study the HOR on a RDE with catalyst probably caused by capillary effects of the solvent in the catalyst ink, pulling catalyst to the edges of the drop as it dries. 10 Therefore, they reduced catalyst loadings by adding uncatalyzed carbon, creating a thicker layer of equivalent thickness to a higher catalyst loading. 5 Measuring the catalytic activity within a PEFC would be the most appropriate method.…”

Nanocrystal Diffusion in a Liquid Thin Film Observed by in Situ Transmission Electron Microscopy

“…When a liquid that contains colloidal nanoparticles evaporates from a surface, a variety of intricate patterns can form 1,2 . In a controlled drying process 3,4 large-scale arrays of highly organized patterns of nanoparticles can be generated.…”

Ordered Two-Dimensional Superstructures of Colloidal Octapod-Shaped Nanocrystals on Flat Substrates

“…First, chains of interlocked octapods were found all over the substrate where the solution had been deposited, even though they were predominant at the "coffee stain" region ( Figure 1a). 33 This represents a stripe of accumulated material, including nanocrystals and often also excess organics, that was generated during the evaporation of the solvent and that delimited the whole region of the substrate where the original droplet was sitting. It is very likely that the chains of interlocked octapods were already present in the solution prior to deposition, as shown by us in our previous work.…”