Debuisson Damien, Merlen Alain, Senez Vincent, Arscott Steve
Institut d'Electronique, de Microélectronique et de Nanotechnologie (IEMN), CNRS UMR 8520, The University of Lille , Cité Scientifique, Avenue Poincaré, 59652 Villeneuve d'Ascq, France.
Langmuir. 2016 Mar 22;32(11):2679-86. doi: 10.1021/acs.langmuir.6b00070. Epub 2016 Mar 11.
We present an experimental study of stick-jump (SJ) evaporation of strongly pinned nanoliter volume sessile water droplets drying on micropatterned surfaces. The evaporation is studied on surfaces composed of photolithographically micropatterned negative photoresist (SU-8). The micropatterning of the SU-8 enables circular, smooth, trough-like features to be formed which causes a very strong pinning of the three phase (liquid-vapor-solid) contact line of an evaporating droplet. This is ideal for studying SJ evaporation as it contains sequential constant contact radius (CCR) evaporation phases during droplet evaporation. The evaporation was studied in nonconfined conditions, and forced convection was not used. Micropatterned concentric circles were defined having an initial radius of 1000 μm decreasing by a spacing ranging from 500 to 50 μm. The droplet evaporates, successively pinning and depinning from circle to circle. For each pinning radius, the droplet contact angle and volume are observed to decrease quasi-linearly with time. The experimental average evaporation rates were found to decrease with decreasing pining radii. In contrast, the experimental average evaporation flux is found to increase with decreasing droplet radii. The data also demonstrate the influence of the initial contact angle on evaporation rate and flux. The data indicate that the total evaporation time of a droplet depends on the specific micropattern spacing and that the total evaporation time on micropatterned surfaces is always less than on flat, homogeneous surfaces. Although the surface patterning is observed to have little effect on the average droplet flux-indicating that the underlying evaporation physics is not significantly changed by the patterning-the total evaporation time is considerably modified by patterning, up to a factor or almost 2 compared to evaporation on a flat, homogeneous surface. The closely spaced concentric circle pinning maintains a large droplet radius and small contact angle from jump to jump; the result is a large evaporation rate leading to faster evaporation.
我们展示了一项关于强钉扎纳米升体积的静态水滴在微图案表面上进行粘滞跳跃（SJ）蒸发的实验研究。该蒸发过程是在由光刻微图案化的负性光刻胶（SU - 8）构成的表面上进行研究的。SU - 8的微图案化能够形成圆形、光滑、槽状特征，这会导致蒸发液滴的三相（液 - 气 - 固）接触线产生非常强的钉扎作用。这对于研究SJ蒸发非常理想，因为在液滴蒸发过程中它包含连续的恒定接触半径（CCR）蒸发阶段。蒸发过程是在无限制条件下进行研究的，且未使用强制对流。定义了初始半径为1000μm的微图案同心圆，其半径以500至50μm的间距递减。液滴蒸发时，依次在各个圆上钉扎和脱钉。对于每个钉扎半径，观察到液滴接触角和体积随时间准线性减小。实验发现平均蒸发速率随钉扎半径减小而降低。相反，实验平均蒸发通量随液滴半径减小而增加。数据还表明了初始接触角对蒸发速率和通量的影响。数据表明液滴的总蒸发时间取决于特定的微图案间距，并且在微图案表面上的总蒸发时间总是小于在平坦、均匀表面上的总蒸发时间。尽管观察到表面图案化对平均液滴通量影响很小——这表明图案化并未显著改变潜在的蒸发物理过程——但总蒸发时间却因图案化而有相当大的改变，与在平坦、均匀表面上的蒸发相比，最多可达近2倍。紧密间隔的同心圆钉扎使得液滴在每次跳跃时都保持较大的半径和较小的接触角；结果是蒸发速率较大，导致蒸发更快。
