Overview

Two things should be accentuated once more in detail: questions of definitions in order to ensure a clearly marked scientific declaration of the effects as well as possible developments in the future.

The terms thermochromic and thermotropic, used for a verbal description of macroscopic visible effects, are unfortunately sometimes used incorrectly. This is the point of origin for misunderstandings and misinterpretations. Even published papers are not accurate [1 4].

In [4] the headline describes thermotropic colour-changing nanoparticles. In this connection a change of colour from deep blue at room temperature to a much lighter pastel blue as the temperature is increased above the LCST is discussed. However, no colour change - no changes of the wavelength maximum - takes place. A pure thermotropic effect leads to a variation of the translucence of the system. It is not correct to use the term colour change in this context.

An electro- and thermochromic hydrogel as a full-colour indicator is presented in [2]. A common electrolysis of an aqueous medium, which is accompanied by changes of the pH-value is called electrochromism. The use of the term electrochromism in this content seems to be incorrect. The term electrochromism is clearly defined. An electrochromic material is characterised by its ability to sustain reversible and persistent changes of optical properties when a voltage is applied to it [5, 6].

In [1] the preparation and characterisation of thermochromic fibres are reported. The detection of the thermochromic effect of the fibres obtained is described only by DSC measurements.