Effect of a binary solvent mixture of methyl and ethyl myristate on colour hysteresis in a microencapsulated leuco dye thermochromic system

Pogorelc, Eva (author), Klanjšek Gunde, Marta (author), Panák, Ondrej (author), Urbas, Raša (author)

Microencapsulated reversible thermochromic systems based on leuco dyes often exhibit broad colour hysteresis between the coloured and decoloured states, which can reduce the reliability of printed temperature indicators. In this study, we investigated whether a binary fatty acid ester solvent mixture near the eutectic composition could narrow this hysteresis and mitigate the effect of microencapsulation on solvent crystallisation. Methyl myristate (MeM) and ethyl myristate (EtM) were used as model ester solvents, while crystal violet lactone and benzyl 4-hydroxybenzoate served as the leuco dye and developer, respectively. Differential scanning calorimetry of bulk MeM/EtM mixtures identified the mixture containing 40 mol% MeM as exhibiting the clearest eutectic-like behaviour. This mixture was therefore selected and compared with the corresponding pure ester systems before and after microencapsulation in a melamine-formaldehyde shell. Scanning electron microscopy and laser diffraction confirmed the formation of spherical, well-separated microcapsules with comparable bimodal particle size distributions. All prepared systems showed reversible thermochromic behaviour. The 40 mol% MeM system exhibited the narrowest colour hysteresis in both bulk and microencapsulated forms. Upon microencapsulation, the downward shift in crystallisation onset temperature was less pronounced for the binary thermochromic system than for the corresponding pure ester systems, and a similarly smaller shift was observed for the onset of colouration. Comparison of thermal and colourimetric measurements showed that colouration was closely associated with solvent crystallisation, whereas decolouration began below the DSC melting onset. These results indicate that, in the investigated MeM/EtM system, a binary ester solvent mixture exhibiting eutectic-like behaviour can limit the confinement-induced shift in crystallisation and colouration towards lower temperatures, resulting in a narrower colour hysteresis after microencapsulation.

• Language: English
• Keywords: leuco dye, thermochromism, colour hysteresis, microencapsulation, fatty acid esters, temperature indicator
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2027
• Number of pages: 15 str.
• Numbering: Vol. 257, pt. 2, art. 114297
• PID: 20.500.12556/RUL-190029
• UDC: 535.6
• ISSN on article: 0143-7208
• DOI: 10.1016/j.dyepig.2026.114297
• COBISS.SI-ID: 301665795
• Publication date in RUL: 23.10.2026

Record is a part of a journal

• Title: Dyes and pigments
• Shortened title: Dyes pigm.
• Publisher: Elsevier
• ISSN: 0143-7208
• COBISS.SI-ID: 25357056

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: leuko barvilo, termokromizem, barvna histereza, mikroenkapsulacija, estri maščobnih kislin, temperaturni indikator

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0450-2024
• Name: Inovativna grafična tehnologija