Glass and window: the last frontier in the integration of smart and functional materials

Senentxu Lanceros-Méndez 

Between me and life is a faint glass.
No matter how sharply
I see and 
understand life, I cannot touch it.

Fernando Pessoa


With the turn of the new century and the strong focus on energy resources and environmental issues, new paradigms are determining our everyday life. Furthermore, the strong emergence of new technologies based, among others, on nanotechnology approaches and the rapid evolution of the so-called “internet of things” provide widespread tools for a more interactive and efficient way of living.

Words such as sustainability, interaction and smartness are increasingly applied to our daily life, leading to a paradigm shift that can be considered more a revolution rather than an actual evolution, as it involves the modification of all aspects of human activity, including communication, organization, mobility, housing, and so on.

One of the key playgrounds of this technological revolution/evolution will be at the level of buildings, including housing, work, culture and entertainment. Stronger energy efficiency requirements and interactivity will require our buildings to be shaped with new materials and solutions.

Among building materials, glass is taking on a dominant role in our living and working environment: the increasing architectural value of glass is already recognized, as it is applied not only in its classical role as windows, but has also established its presence in larger parts of the entire structure of the building, as well as in its interior, as an essential part of decoration and innovative features.

Thus, glass as a structural and base material for energy management and interactive technologies will take advantage of many new technologies, adding value to this classical material.

In this context, many novel materials and technologies are being and will be increasingly used in combination with glass. Together with strong efforts to improve glass itself, allowing for its weight, mechanical and thermal properties to be tailored, novel coatings and printing and other technologies allow for the introduction of new features, which will certainly shape the future technological and commercial possibilities of glass.

Glass thus functionalized will allow for the thermal, luminous and acoustic environment to be tailored both passively and actively, using specific coatings and printed materials with controllable and/or switchable properties. Further, it can be modified to introduce novel interactive functionalities through display, sensor and actuator capabilities for an enriched environmental experience.

Glass and windows will thus also become a key element in the concept of the “internet of things”, aiming at complete interaction and multifunctionality.

Most of the materials that will allow for these implementations are so-called smart materials, which can be generally grouped into property changing and energy exchanging. Some of the materials are ready for implementation, while others are still being improved in terms of transparency, stability and commercial applicability, and other properties. In any case, proofs of concept and demonstrations already exist based on smart materials and their effects, which will certainly be increasingly implemented in the near future. Some representative examples include:

[1] color and optically changing materials, including photochromic, thermochromic and electrochromic materials, which change their optical properties or color under light, thermal or electrical stimuli, respectively, enabling control of color and/or optical transparency;

[2] materials with shape memory and shape changing properties, triggered by different stimuli, such as thermal, electrical and magnetic variations, allowing for the implementation of specific switches and the modification of shape for specific features;

[3] adhesion changing materials, which are able to reversibly change the attraction forces of adsorption or absorption of specific components in response to a stimulus, including light, temperature, an electrical field or a liquid and/or biological component, enabling the implementation of self-cleaning features, among many other possibilities;

[4] photoluminescent smart materials, including fluorescence and phosphorescence, and electroluminescent materials, including (organic) light-emitting diodes, polymers and small molecules, enabling specific lighting possibilities for decoration and safety;

[5] photoelectric and thermoelectric materials, which will enable the implementation of energy generation, storage and management systems;

[6] piezoelectric and magnetoelectric materials, which will enable the implementation of sensor and actuator capabilities, as well as energy harvesting from mechanical vibration;

[7] heat, water and gas storage materials, which will contribute to energy efficiency management, air cleaning and safety.


Other effects based on the use of smart and functional materials can be similarly presented. Functions can be implemented that react to light, temperature, pressure, electric and magnetic fields as well as to the chemical environment, opening the way to smart glass and smart window concepts.

Smart glasses can be defined as systems including interactivity or switchable properties, mainly based on the effects presented above.
It is noteworthy that this concept applies both to glasses placed in the exterior of buildings (windows) and to ones for interior decoration and/or multifunctional applications, including displays, sensing and interactive modules.

Some interesting examples of already implemented solutions or solutions that are close to being implemented include:

[1] optical transmittance that can be actively or passively modified, resulting in variations in light transmittance in the visible spectrum in order to manage incident solar radiation, privacy or decorative issues. Associated with this, switchable materials will enable control of view both to and from the exterior and in interior partitions, as well as reflection control;

[2] similarly, thermal transmittance can be managed by passive or active control of wavelengths up to the infrared region of the electromagnetic spectrum. Further, materials can allow thermal absorption control to tune heat flow. The proper control of radiation transmission and thermal absorption will enable the implementation of energy saving strategies relating to heating and cooling of buildings, and other features;

[3] active or passive control of hydrophobicity of the surface, enabling the implementation of self-cleaning glasses;

[4] finally, the last frontier will be the implementation of sensor, actuator and display capabilities based on the greatly improving “transparent electronics” materials and concepts that enable the highest levels of interactivity.

It is important to note that many of the novel active properties of glass are electronically stimulated, or require the implementation of a readout and communication electronic system. In this area, a critical role is also played by the framework around the window systems, where electronics and specific active systems should be placed efficiently, with minimal visual impact and cost effective industrialization and maintenance.

Thus, multifunctional approaches should be combined, integrating electronics and mechanical parts, as well as modular and flexible production with artwork finishing, for a complete integration of the systems.

Finally, it is always relevant to note that real impact and success can only be achieved through the active involvement of companies and universities/research centres by promoting the necessary creative and technical conditions enabling rapid technology transfer and implementation.

In particular, companies, being at the center of the identification of specific needs and trends while also being responsible for the implementation of the solutions, should play a proactive and leading role in promoting the integration of new materials and solutions that, in the end, will contribute to higher competitive standards.

Thus, new materials and concepts will combine with one of the most traditional ones, glass, in order to achieve higher architectural levels, together with a more interactive and energy efficient experience, both in the outer skin and inside our buildings…and in our lives.