Binary mixtures of IPA with ethanol and t-butanol also produce nonuniform deposits, but a mixture of IPA with 2-butanol suppresses the CRE ( Fig. However, as we observe, ring stains persist with IPA-based 2D crystal inks ( Fig. It supports a metastable dispersion of the 2D crystal nanoflakes, and its low surface tension ensures good wetting of substrates ( 3). IPA is widely used as a solvent for graphics inks and, recently, for 2D crystal inks ( 3). We investigate isopropanol (IPA)–based alcohol mixtures in our ink formulation. In particular, CRE-induced nonuniform deposition for additive-free 2D crystal inks is considerable on uncoated and nonporous substrates such as polyethylene terephthalate (PET) and Si/SiO 2. Although various strategies have been developed to suppress the CRE ( 9, 10), none of these are generally applicable for 2D crystal inks due to problems of dispersion stability, postprocessing requirements, or the effect of ink additives on material functionality. Because of this fundamental drying mechanism, suppression of the CRE is currently a major challenge in ink formulations of 2D crystals.
Faster solvent evaporation at the contact line than at the apex enhances this capillary flow, which carries dispersed solutes to the contact line and deposits them there, leading to a ring-shaped stain. Note that capillary flow refers to Laplace pressure–driven flows of liquid arising from variations in the curvature of the liquid-air interface. Simple geometric considerations then result in radially outward capillary flow to replenish solvent evaporating near the contact line. 1I) ( 7, 8): first, that the contact line is pinned and, second, that the droplet adopts a spherical-cap shape to minimize its surface-free energy. The CRE in a drying droplet requires two essential conditions ( Fig. Although various approaches have been proposed to realize stable jetting and appropriate wetting (section S2), a strategy to suppress nonuniform deposition during drying of the deposited droplet, the coffee-ring effect (CRE), remains elusive. The three critical parameters behind this are suboptimal droplet jetting (section S2), poor control over substrate wetting (section S2), and drying of the inks ( Fig. However, this direct adaption without elaborate ink formulation through control over composition, rheology, and fluidic properties presents challenges in achieving uniformly deposited functional structures and, hence, device reproducibility and scalability. These stably suspended dispersions are then directly used for device fabrication, showing glimpses of their exciting potential in recent advances ( 4– 6). For this, the most common approach is to exfoliate their bulk crystals through chemical or ultrasonic assisted processes into mono- and few-layer flakes. In recent years, remarkable efforts have been devoted to adapting 2D crystals to functional printing toward their scalable and low-cost device fabrication ( 3). Engineering the 2D crystals also allows the fabrication of their hybrids and heterostructures, with an even more diverse set of properties for a substantially expanded application scope. The wide spectrum of distinct and yet complementary properties of two-dimensional (2D) crystals offers huge potentials for (opto)electronics, photonics, and sensor development ( 1, 2). Kelleher, Zhipei Sun, Xiao Huang, Meng Zhang, Colin D.
Guohua Hu, Lisong Yang, Zongyin Yang, Yubo Wang, Xinxin Jin, Jie Dai, Qing Wu, … Show All …, Shouhu Liu, Xiaoxi Zhu, Xiaoshan Wang, Tien-Chun Wu, Richard C.
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