Research

Chinese Brushes: Controllable Liquid Transfer

    A research team led by Huan Liu has recently revealed the most fundamental of the Chinese brush: why must the freshly emergent animal hairs. The controllable liquid transfer of a Chinese brush is attributable to the unique anisotropic multi-scale structures of the freshly emergent hairs. Inspired by this, a device is developed with parallel hairs that allows for direct writing micro-lines.
     In nature, various biological organisms composed of fibrous systems exhibit a unique dynamic wetting process, which has shown many advantages in inhabiting local environments. However, controlling liquid transfer by an open fibrous system is still poorly understood.


    The Chinese brush, made of a bundle of freshly emergent animal hairs in quasi-parallel arrangement, allows manipulation of low-viscosity ink liquid in a controlled manner: high-mass ink loading and steady, uniform, and continuous ink transfer onto the substrate. Therefore, with oriental civilization development over the past 5000 years, it has been widely used by Eastern artists to deposit ink on paper with certain characters and figures that express their feelings and emotions or convey knowledge and information from one generation to another.
    Here, we revealed the most fundamental of the Chinese brush: why must the freshly emergent animal hairs. We demonstrated that the unique anisotropic multi-scale structure of the freshly emergent hairs, featured by the tapered architecture with conical tip enveloped by micro-meter scaled ratcheted squamae, is responsible for the liquid manipulation of Chinese brush. Large mass of low viscosity liquid could be dynamically balanced within the Chinese brush as a cooperative effect among forces of Laplace pressure difference (generated by the conical structure), the asymmetrical retention force (aroused from oriented squamae), and the gravity. Upon deforming the tips of Chinese brush, the steady, continuous and uniform liquid delivery can be realized in a controlled manner.
    Inspired by these findings, we developed model devices with double- parallel freshly emergent hairs that allows for direct writing functional microlines with 10mm resolution and nanometer-thick, respectively, with well defined profile and uniform distribution on diverse substrates. We envision that the smart liquid transfer of Chinese brush will shed light on the novel template-free printing of organic composite functional materials devices.

References
(1) Q. Wang, B. Su, H. Liu*, L. Jiang*, Adv. Mater. 2014, 26, 4889-4894.