Papers by Keyword: Thermochromism

Abstract: The aim of presented paper was to prepare and characterise multifunctional thermochromic-fluorescent pigments with potential application in anti-counterfeiting patterns in security printing. Pigments were prepared by microencapsulation of chosen thermochromic system into melamine formaldehyde resin and the resin was modified with Uranine and Acid Red 52 fluorescent dyes, respectively. The fluorescence at low and high temperature was measured by spectrofluorometer. The concentration of 2.3 × 10^–5 grams of fluorescent dye per one gram of polymer is sufficient for detection of fluorescence of modified polymeric shell. The dynamic colour change of prepared pigments was analysed in terms of cumulative colour difference obtained from reflectance measurements. Resulting multifunctional pigments exhibit much lower colour contrast and wider temperature sensitive interval in comparison with the bulk thermochromic system. However, the concept of two levels of verification based on two types of colour change embodied in one pigment has been approved.

Abstract: Three new coordination compounds of iron (II), [Fe (HC(Pz)₃)₂](C₈H₅O₄)₂^.C₈H₆O₄ (I), [Fe (HC(Pz)₃)₂](C₁₀H₇SO₃)₂^.2H₂O (II) and Fe (HC(Pz)₃)₂](C₁₂H₂₅SO₄)₂ (III), where HC(Pz)₃ is the tridentate chelator tris(pyrazol-1-yl) methane, have been synthesized and investigated by X-ray structure analysis, electronic and IR spectroscopy, static magnetic susceptibility method. The magnetochemical study of complexes I–III in the interval from 300 to 500 K showed that they possessed the high-temperature spin crossover ¹A₁ ↔ ⁵T₂ accompanied by thermochromism (the pink ↔ white color change).

Abstract: Nanocrystalline vanadium oxide thin films have been deposited by reactive DC magnetron sputtering onto glass substrates under different processing conditions. Structural analysis and phase identification have been carried out by means of X-ray diffractometry (XRD). The surface morphologies of the different films have been examined by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD results revealed single and multiple phase oxides such as VO2(B), VO2(M), V2O5, etc. with considerable differences concerning to surface morphologies, as observed by SEM and AFM. The effects the O2/Ar flow ratio, DC current, and working pressure on the phases formed and growth rates is discussed. Moreover, VO2(M) films exhibited different morphologies concerning to grain size and shape as well as dissimilar preference in crystal orientation, as a result of the processing conditions. The optical/thermochromic response of the VO2(M) specimens deposited under different growth rate conditions was evaluated by optical spectrophotometry and related to the respective structural characteristics.

Abstract: Thermochromic glazing is a type of intelligent glazing; one where the properties of the glazing change according to some external stimulus. More particularly a thermochromic window is a device that changes its transmission and reflectance properties at a critical temperature (Tc). Atthis specific temperature the material undergoes a semi-conductor to metal transition. At temperatures lower than Tc the window lets all of the solar energy that hits it through. At emperatures above Tc the window reflects the infra-red portion of solar energy. In such a way thermochromic windows may help reduce air conditioning and heating costs leading to more energy efficient buildings. This review details the nature of the semi-conductor to metal transition and indicates how substitutional doping within a crystal lattice can be used to manipulate and fine tune the critical temperature. Also detailed is the underlying science and methodologies so far employed in the production of thermochromic thin films.

Abstract: This paper focuses on the structural change and the thermochromism of the phase transition of the hybrid (C12H25NH3)2FeCl4. The temperature and the structures of the phase transition is investigated by a thermal gravimetry (TG) and differential scanning calorimetry (DSC), an infrared spectra (IR) and X-ray diffraction (XRD) patterns. The UV adsorption spectra account for the thermochromism. The results suggest that the reversible phase transition arises from the structural changes of the organic chains. The thermochromism is presumably due to the electrons redistribution on the levels and to the energy transition to translational and rotational motions of the organic chains.