Droplet manipulation on a structured shape memory polymer surface

Abstract

While methods for dynamic tuning of surface wettability to manipulate water droplets have been widely explored for many applications including digital microfluidics, those based on dynamically changeable surface morphology have remained challenging to achieve. In this work, we present a structured shape memory polymer (SMP) surface which shows dynamically tunable surface wettability through changeable surface morphology in order to manipulate water droplets. The structured SMP surface involves a SMP pillar array consisting of nanotextured small and large pillars which can change its morphology between permanent and temporary shapes upon thermomechanical loading. Specifically, the structured SMP surface dynamically creates a surface morphological gradient and changes its surface wettability during thermally induced shape recovery of the SMP pillar array. Different wetting characteristics of the structured SMP surface between permanent and temporary shapes are theoretically predicted and experimentally verified. Based on these measured wetting characteristics, the structured SMP surface is designed to demonstrate that the morphological difference between two shapes under a water droplet overcomes contact angle hysteresis, resulting in driving a water droplet, when combined with the thermal Marangoni effect.iii ACKNOWLEDGMENTS

Smart Wetting Control on Shape Memory Polymer Surfaces

“…For example, Kim and Park realized the dynamic manipulationo fd roplets based on the SMP surface with gradient morphology. [12] They first prepared pillar arrays on the SMP,a nd found that deformed pillars, which wereo btained by applying an ormal pressure on the surface at at emperature higher than that of the T g (about 60 8C), had al ower apparent CA than that on the permanent pillars. By precisely controlling the pillar structures, ag radientm orphology can be obtained.…”

“…Reproducedw ith permission from ref. [12]. work, mushroom-like structures with re-entrant features were first prepared on the thiol-ene/acrylate-based thermoresponsive SMP surface, which had good toughness and impact resistance( T g = 60 8C).…”

Magnetically Responsive Elastomer–Silicon Hybrid Surfaces for Fluid and Light Manipulation

“…Fabrication of Black Silicon Surfaces: A black silicon surface was formed on the top silicon layer of a silicon on insulator (SOI) wafer (Ultrasil Corp.) by a three-step process ( Figure S2, Supporting Information). [29] This process (Oxford ICP RIE) started with a passivation of silicon (O 2 gas 10 sccm, RF 1 120 W, RF 2 200 W, 90 mTorr, 5 min), during which a thin oxide layer was formed. Next, the oxide layer was incompletely etched (CHF 3 gas 12 sccm, RF 1 300 W, RF 2 500 W, 90 mTorr, 2 min) to yield randomly scattered oxide islands.…”

Microfluidics for Biosynthesizing: from Droplets and Vesicles to Artificial Cells

“…Furthermore, based on the principles of mechanical [129][130][131][132][133][134][135] or thermal [136] forces, the manipulation of droplets based on mechanical and thermal forces can also be achieved by designing the structures of the microfluidic chip.…”