Switchable Isotropic/Anisotropic Wettability and Programmable Droplet Transportation on a Shape-Memory Honeycomb

Abstract

Programmable droplet transportation is required urgently but is still challenging. In this work, breath figure was employed to fabricate shape-memory poly­(lactic acid) (PLLA) honeycombs in which tiny crystals and an amorphous network act as the shape-fixed phase and recovery phase, respectively. Upon uniaxial tension, circle pores from the breath figure were deformed to elliptical pores, producing contact angle differences and anisotropic wetting behaviors in two directions. Both pore geometry and anisotropic wettability can be tailored via the draw ratio. On the PLLA honeycomb surface with a lower draw ratio, the contact angle difference is too small to induce droplet transportation along the desired direction. In the case of a higher draw ratio, however, the movement of water droplets has been controlled absolutely along the tension direction. The transition between them can be achieved reversibly during uniaxial tension and recovery processes based on the shape-memory effect. The enhanced flow control, which can be attributed to the synergism between optimal hydrophobicity and enlarged anisotropic wetting behaviors, endows water droplets with the ability to turn a corner spontaneously on a V-shaped surface including two regions exhibiting different oriented directions.

Programmable Transition between Adhesive/Anti-Adhesive Performances on Porous PVDF Spheres Supported by Shape Memory PLLA

“…In this work, the crystallinity of PLLA is 3.6% (determined by DSC, data not shown here). The shape memory effect endows PLLA with the ability to be deformed at high temperatures and be fixed by cooling down, which has been investigated in detail in our previous work [ 31 , 32 , 33 ]. The glass transition temperature of PLLA (63.4 °C, determined by means of dynamical mechanical analysis, Figure S3 ) acts as the switching temperature of the shape memory effect.…”

Gradient monolayered porous membrane for liquid manipulation: from fabrication to application

“…The breath gure (BF) method has been widely used to prepare a monolayered porous membrane. 37,[66][67][68][69][70] Our group prepared polystyrene membrane coated copper by the breath gure method. 67 Without a voltage, the PS membrane can retain an oil droplet under water.…”

“…For the preparation of the honeycomb-like polylactic acid (PLLA), You's group employed the BF method, which uses tiny crystalline and amorphous networks to represent the shape-fixed phases and recovery phases. 69 Ma's group employed star-shaped polyhedral oligomeric silsesquioxane (POSS)-fluorinated polyacrylates to prepare porous membranes with hydrophobicity and tunable surface morphology through the BF method. 70 …”

Smart Bionic Surfaces with Switchable Wettability and Applications

“…In addition to the control of static wetting, the surface wettability transition also exhibits in the dynamic wettability by the droplet sliding property. Programmable droplet transportation is usually caused by changes in dynamic wettability under external stimuli, showing the difference in contact angle and anisotropic wetting behavior in two directions, which can be applied in various fields, such as biomedicine for non-powered micro-drug delivery, controllable self-lubricating transfer in mechanical engineering, controllable microfluidics system and long-distance water delivery for agricultural drip irrigation etc [145][146][147][148] . Inspired by the microstructure of stomata distributed on plants, Zhao et al prepared a surface with programmable wettability arrays by using microfluidic emulsification templates, achieving the printing with mask integration because of the property of controllable droplet sliding on programmable wettability pathways and effective droplet transfer (Fig.…”