Advances in Photo-Active Materials

Dear Colleagues,

The direct conversion of light energy into mechanical work is a very important field of scientific and technological research. Just to give a few examples: On the one hand, in solar energy harvesting, direct conversion of light into mechanical work would in principle allow to overcome energy-expensive steps such as storage and distribution of light/solar energy, increasing its efficiency in the exploitation of that energy resource; on the other hand, by allowing remote control of micro-switches/actuators from optical/photonic signals, it opens up new perspectives in opto- and micro- electronics. It is achievable using many different types of materials: from nanotubes to graphene, polymers/elastomers, liquid crystals, plasmonic materials, etc.

The best known materials that exploit such a conversion are photomobile polymers, which—two decades after their first realization—are recently experiencing further enormous scientific and technological development. They are mainly based on azobenzene liquid crystals, while, more recently, there has been a new development in the field due to the use of bilayered systems in which each layer is characterized by a different expansion coefficient under illumination, leading to a deformation of the system under light. Treating the topic from another point of view, the light-induced Marangoni effect is the basis of the controlled movement of macro-/micro-objects on the surface of liquids (placed at the interface of two fluids), and consists of highly absorbent materials. From this point of view, optical/photonic manipulation of materials at the nano-, micro-, and macroscale can also be considered as a part of the described field of research, when focusing on the material side.

Thus, the ability to generate and control the movement of objects from the molecular scale to the macro is achieved in many different ways, involving phenomena at different levels. The topic concerns interdisciplinary connections—and involves many fields of applications—in materials science, from chemistry, physics, physical chemistry/chemical physics, to micro- and opto-electronics, to energy harvesting. The tremendous progress in the field is underlined by a large number of studies, articles in international peer-review journals, and international projects.

This Issue aims to focus on the theoretical and application aspects of the conversion of light into mechanical work with particular regard to the materials involved in the field.

I have the pleasure to invite all my colleagues in the field to submit a full paper, communication, or a review for the realization of this issue.

Dr. Riccardo Castagna
Guest Editor

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• photomobile polymers
• azobenzene liquid crystals
• photo-actuators
• solar energy harvesting
• marangoni effect