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Friday, 17 May 2019

A new step in the development of self-shaping materials

Researchers from the ICN2 Supramolecular NanoChemistry and Materials Group, led by ICREA Prof. Daniel Maspoch, have developed a procedure to obtain films that can adopt programmed shapes. Published in Advanced Materials, the method is based on the use of flexible submicrometric crystals that increase in size when humidified. The resulting films could serve as autonomous mechanical devices, having potential applications in micromanipulation, automation, and robotics.

Living systems have the ability to change their own shape in response to environmental stimuli (e.g., changes in moisture, pH, temperature, or light). The phenomenon has caught the attention of scientists, who are developing materials mimicking this responsive behaviour.

The simplest way to achieve a similar artificial product is via assembly of bilayers built from components that differ in their swelling properties: if, in the same conditions, one layer tends to contract and the other to expand, you can get self-rolling structures such as tubes and scrolls. However, the two layers will tend to separate if the process is performed repeatedly.

A more convenient approach to design custom self-shaping 3D objects is to fabricate monolayer materials and control the distribution of swellable and nonswellable (or less swellable) domains. For instance, you can produce composite films through embedding of swellable materials into a nonresponsive polymer matrix.

Following this approach, Dr Javier Troyano, Dr Arnau Carné-Sánchez, and Group Leader ICREA Prof. Daniel Maspoch, from the ICN2 Supramolecular NanoChemistry and Materials Group, have extended this concept to develop multiaxial films that can undergo programmable and well-defined 2D-to-3D transformations. That is, applying these materials in the right place you can produce a paper origami for different purposes with nanotechnology. Their results have been published in Advanced Materials.

 

The method is based on the use of flexible submicrometric crystals that increase in size when humidified. Firstly, the crystals are uniformly embedded in the film. Secondly, some of them are conveniently removed from specific locations through a chemical etching method. When moistened, by adsorbing the environmental humidity or soaking it into water, the obtained heterogeneous film adopts a new shape.

The work takes advantage of a molecular interaction on the nanoscale to create an effect on the macroscale. This effect, which is basically folding, may be used for the material to acquire movement or a certain mechanical function, such as grabbing an object. In addition, it also works backwards: the initial shape of the material is restored by irradiating it with ultraviolet or visible light which triggers a desorption process.

This method provides a simple, fast, and low-cost approach to design self-shaping objects with complex geometries and diverse responsive characteristics. The resulting composite films, in addition to delight origami makers, could serve as autonomous soft mechanical devices, having potential applications in micromanipulation, automation, and robotics.

Article reference
Javier Troyano, Arnau Carné-Sánchez, and Daniel Maspoch. Programmable Self-Assembling 3D Architectures Generated by Patterning of Swellable MOF-Based Composite Films. Adv. Mater. 2019, 1808235. DOI: 10.1002/adma.201808235
https://doi.org/10.1002/adma.201808235