Uniform deposition of particles in large scale by drying of binary droplets

Abstract: The evaporation of liquid droplets often results in a ring-like deposition pattern of particles, presenting challenges for applications requiring highly uniform patterns. Despite extensive efforts to suppress the coffee ring effect, achieving a uniform particle distribution remains a great challenge due to the complex and non-equilibrium nature of the evaporation process. In this work, we introduce and demonstrate a one-step drying method for binary droplets (water and 2-methoxyethanol) that produces uniform deposition of nano- and micro-particles. By adjusting the initial water volume fraction, we effectively control the interplay between capillary and Marangoni flows, resulting in deposition patterns that vary from coffee ring to uniform and to volcano-like. Through both theoretical and experimental analyses, we determine the conditions necessary for achieving such high uniformity. This approach requires no special substrate treatment, particle modification, or controlled environments, and works for various particles, including silica and polystyrene. Our method provides a robust solution for fabricating uniform patterns that are crucial for many practical applications, ranging from printing to microelectronics to bio-pharmacy.