[c0mrade]

Hello, dear members of the forum, I am far from chemistry, so I came to you for advice. There is a need for a window film that will darken from the current supply, after searching, I came to the conclusion that liquid crystals are best suited for this. But the question is, mainly under the influence of current, magnetic field, etc., an ordered structure is formed, which allows light to pass through. Is it possible vice versa, for the structure to be disturbed from the supply of current and the film to darken, and when the power is turned off, the structure is restored? Maybe there are some other chemicals. substances that change their optical properties (reversibly) from the supply of current?

p.s
Sorry, English is not my native language, so i may have many mistakes. But i hope, that my message is clear

[Borek]

Read more about liquid crystals, you are on the right track in general - the phase changes (between forms that block/pass the light) are reversible.

Whether liquid crystals are applicable to a large scale objects like windows is another question.

[Enthalpy]

Many types of liquid crystals exist, some darken by current, others get transparent. It's often a mere question of relative orientation of the optical polariser vs analyser, turn one by 90° and the behaviour reverses.

Big surfaces are technically possible. I ignore possible cost limitations. The limit at computer screens is the reaction time which increases with the square or the smallest dimension, hence 16:9 screens replaced 4:3.  So 0.35m becoming 1.4m would be 16* slower, seems acceptable for a window.

You need also electrodes. A thin metal grid should help Ito.

The transparency may be limited. If the liquid crystal needs polarised light to operate, you lose half the power.

Liquid crystals tend to degrade under sunlight.

==========

Alternatives exist to liquid crystals. Electrolytic deposition of a metal from a thin film between glass panels was published, around 1989. I don't have references about that, but got inspired by the windows to invent a display using such cells
https://patents.google.com/patent/EP0564012A1/en
This process is fast because already 100nm metal are opaque, so the electrolyte too (can be solid or immobilized) can be thin.

Beware I never developed the idea and can't tell how many times this work, but I suspect operating over many cycles is non-trivial. In the display, I needed no reversibility. Secondary batteries tend to live for 10³ cycles only.