Recently, Chinese researchers developed a new way to improve liquid transport efficiency and designed a bionic self-siphon device that takes inspiration from the slippery behaviour of the pitcher plant’s peristome surface. This study, published online in Proceedings of the National Academy of Sciences of the United States of America, PNAS, was conducted by DONG Zhichao’s team at Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences. 

Dating back to the Ming dynasty, Chinese craftsman invented a porcelain cup, justice cup, for drinking. Inside the cup, there is a waterline. When liquid level is below this line, the cup is a normal container. In contrast, if liquid surpasses this line, it will leak from the bottom of the cup. This phenomenon is caused by siphon effect. Nowadays, various devices use siphon effect to achieve liquid transport, such as espresso machine, hand wash sink, and toilet. Similar to the porcelain cup, the siphon effect only works when the liquid level is above a threshold line, which is troublesome for liquid transport in tubes. For example, while using siphon effect changing the water in fish tank, we usually need to fill the siphon first and then put it in the tank to drain water out or take a deep sip to achieve water draining. These problems will be easily solved if self-siphon effect is realized. 

Figure 1. The justice cup uses siphon effect to drain water out of the cup when the water level is above the threshold waterline. 

Inspired by the phenomenon that water transports continuously on the peristome surface of Nepenthes alata, Chinese scientists demonstrated the use of peristome-mimetic structure and curvature to control capillary rise and siphon behaviours. Through three-dimensional (3D) printing techniques, they fabricated self-siphon tubes and made it possible to actuate liquid to transfer spontaneously and continuously in an antigravity direction without complex accessories, such as pumps or valves. 

Figure 2. The self-siphon device. Although a small amount of water deposits into the tank, the peristome-mimetic tube can elevate water to fill the tube spontaneously in a high speed and drain water out of the tank without retention. 

Self-siphon tube is different from justice cup that cups or tubes need to be filled first to trigger siphon effect. Simply bending it into a Candy cane shape and placing on the sidewall of cup, even a small quantity of water can spontaneously fill the tube under enhanced capillary rising effect and leave the tube from the other side. This self-siphon effect relies on inner wall structure that enhances capillary rising in the tube, which enables high flux and overcoming gravity liquid continuous transport without external energy input.  

Due to its excellent properties, peristome-mimetic tube holds great promise for use in microfluidic chips, dental suction products and medical injection devices.  

https://doi.org/10.1073/pnas.1821493116 

Email: dongzhichao@iccas.ac.cn.