Ever Smarter Materials

Introduction

The first symposium to unify two Québec strategic research groups, the CSACS (Centre for Self-Assembled Chemical Structures) and the CQMF (Centre québécois sur les matériaux fonctionnels), was held on May 3 and 4, 2016, at the École de technologie supérieure (ÉTS), in Montréal. At this symposium, researchers from strategic CSACS and CQMF groups presented their perspectives on the following research areas:

1. Self-assembled supermolecular structures
2. Polymers
3. Biointerfaces
4. Nanoscience and nanotechnologies
5. Energy
6. Biomedical
7. Environmental and sustainable development
8. Smart materials

This article presents an overview of the research axis on smart materials, presented by Fiorenzo Vetrone, Professor at the Energy Materials Telecommunications Research Centre (EMT), Institut national de la recherché scientifique (INRS).

Smart Materials

A smart material is described as a material having one or more properties that may be substantially modified, in a controlled manner, by external stimulation such as mechanical stress, temperature, moisture, pH, light, electric or magnetic fields, etc. [1]. It is for this reason that smart materials are also known as materials sensitive to stimuli.

Smart materials can be found in various applications (biology and nano-medicine, sensors, aerospace, robotics, transportation, energy, environment, electronics, etc.). These application areas are interrelated since they all share certain characteristics, this being only a partial list.

Examples of Applications

Stimuli-Sensitive Polymers

With the application of a stimulus (mechanical, thermal, chemical, light, etc.), these polymers undergo a change of chemical origin, which leads to a change in their physical properties [2].

Shape Memory Alloys

Shape memory alloys (SMA) are materials with a special property called shape memory. These materials can be made of metals, polymers, ceramics, composites, etc. Just like the stimuli-sensitive polymers, their scope of application is extensive.

At the ÉTS, the Shape Memory Alloys and Intelligent Systems Laboratory (LAMSI) promotes the design and development of components in shape memory alloys for various industrial applications.

The following video shows the shape memory process of a nickel titanium alloy (also known as nitinol) under a thermal stimulus.

Bio-inspired materials

Bio-inspired materials are essentially a class of materials for which some properties are inspired by living organisms, to take advantage of solutions and inventions produced by nature. Among the most popular are:

• The hydrophobic property of the lotus leaf, due to its nano-scale roughness, which makes it a self-cleaning surface;

• The hydrophobic property of gerridae legs (an insect commonly known as a water strider), which allows the insect to use the surface tension to move on water;

• The bonding mechanism of the slats under the feet of the gecko (a small reptile), enabling it to attach to virtually any type of surface, at any tilt angles.

Materials for Tissue Engineering and Regenerative Medicine

These nano-materials are often biocompatible polymers and metals with physicochemical properties, which enable them to mimic, create, replace, restore, maintain, or improve certain aspects of cells or tissues.

Photochromic Materials

The best example of a photochromic material is the photochromic lenses that adapt their coloring to ultraviolet rays (UV), depending on the amount of exposure: as the UV exposure increases, the tint of the glasses becomes more opaque, and the reverse occurs when the UV exposure decreases. This phenomenon, called photochromism, comes from a reversible reaction between two forms of a chemical compound [3].

Photochromic glass partially exposed to sunlight (the other part is hidden from the sun by a sheet of paper)

Smart Textiles

Forbes magazine presented a very interesting article on smart textiles where they are classified into two categories [4]:

1. Aesthetic (fashion): textiles becoming brighter or changing color;

2. Performance Enhancing (for top athletes as well as military personnel): controlling body temperature, lowering wind resistance, etc.

Future Research

Professor Vetrone proposed some topics for future research to the CQMF / CSACS strategic group in the field of smart materials:

• Development of hybrid materials: combining different types of materials, adding certain properties/features to existing materials to make them smarter;
• Development of adaptive systems that can respond to external stimuli in smart ways;
• In the longer term, development of a new generation of smart materials that could interact with the environment without any external stimulus.