Adsorption Races of Binary Colloids with Different Softness at the Air/Water Interface of Sessile Droplets

Abstract

drying phenomena are ubiquitous not only in the laboratory environment, but also in our daily lives.So far, substantial theoretical and experimental effort has been devoted to controlling the drying behavior of colloidal dispersions. For instance, the formation of coffee-ring stains can be suppressed by using various additives or anisotropic particles, as well as by modifying substrates, [3c,4] which leads to various applications including surface coating, ink-jet printing, and chemical/biological sensors. [5] Despite being able to suppress inhomogeneous structures after drying, it remains challenging to control the micropatterns acquired during evaporation of water from sessile droplets that contain colloidal particles.

Relationship between π–A isotherms and single microgel/microgel array structures revealed via the direct visualization of microgels at the air/water interface

“…In this context, our group has investigated the selforganization of microgels and soft deformable particles during the evaporation of water from sessile droplets. [40][41][42][43][44][45][46] Microgels spontaneously adsorb and gradually order at the air/water interface of a dilute dispersion droplet, whereby the center-to-center distances of the microgels decrease due to the decrease in the interfacial area. 40 Furthermore, the ordered structures of the microgel monolayers that are formed at the air/water interface remain on a solid substrate after evaporation.…”

Triple-line dynamics of a soft colloid-laden drop on a hydrophobic surface

“…Soft microgel particles based on poly(Nisopropylacrylamide) (p-NIPAM) are known to adsorb onto air/ water interfaces of drops. [15][16][17] Moreover, polyelectrolyte microgels, 18 binary mixture of soft and softer microgels 19 and rodshaped microgels 20 are also found to adsorb onto the air/water interface. Unlike a pure water drop or a drop dispersed with hard colloidal particles, a soft microgel particle laden drop stays pinned even on a hydrophobic surface for almost the entire duration of evaporation.…”

The compression of deformed microgels at an air/water interface

“…11 To date, a considerable amount of research has been dedicated to understanding phenomena related to the deformation of microgels at fluid interfaces. 11,12 In our group, we have investigated the drying behavior of sessile droplets that contain various soft particles, including microgels, 13 and found that deformed microgels at the air/water interface become more regularly arranged over time, whereby the center-to-center distances of the microgels decrease. 11 b ,13 c This process results in the compression of the deformed microgels at the air/water interfaces, and thus the microgels are further deformed at the interface as the surface area of the sessile droplets decreases.…”