Smart mechanically tunable surfaces with shape memory behavior and wetting-programmable topography

TL;DR

This paper introduces a novel fabrication of high-aspect-ratio, shape-memory polymer surfaces with tunable wetting properties controlled by temperature and thermal history, enabling smart microfluidic device applications.

Contribution

It reports the first fabrication and investigation of lamellar surfaces with high aspect ratio and shape-memory behavior for tunable wetting properties influenced by thermal stimuli.

Findings

Wetting properties depend on temperature and thermal treatment.

High aspect ratio allows geometry tuning by droplets and temperature.

Polymer can switch between hard and soft states based on thermal pre-history.

Abstract

This contribution reports for the first time on fabrication and investigation of wetting properties of structured surfaces containing lamellae with an exceptionally high aspect ratio - height/width ratio demonstrated of 57:1. The lamellar surface was made using a polymer with tunable mechanical properties, and shape-memory behavior. It was found that wetting properties of such structured surfaces depend on temperature and thermal treatment history - lamellae are wetted easier at elevated temperature or after cooling to room temperature when the polymer is soft because of the easier deformability of lamellae. The shape of lamellae deformed by droplets can be temporarily fixed at low temperature and remains fixed upon heating to room temperature. Heating above the transition temperature of the shape-memory polymer restores the orginal shape. The high aspect ratio allows tuning of geometry not only manually, as it is done in most works reported previously, but can also be made by a liquid droplet and is controlled by temperature. The liquid in combination with thermoresponsive topography present a new kind of wetting behavior. Moreover, the mechanical properties can be controlled - the polymer can either be hard or soft at room temperature depending on thermal pre-history. This behavior opens new opportunities for the design of novel smart elements for microfluidic devices such as smart valves, whose state and behavior can be switched by thermal stimuli: valves can or cannot be opened, are able to close or can be fixed in an open or closed states.