Fabrication of Thermo-responsive Polymer/Rhodamine films for intelligent packaging applications

Abstract

This research, the synthesis and properties of rhodamine B derivatives for use as an easy-to-use optical temperature indicator label were studied. A series of macrocyclic compounds, methyl-N-benzylhexahomotriazacalix[3]arene (MeAC3), p-chloro-N-benzylhexahomo-triazacalix[3]arene (ClAC3), α-cyclodexdrin (α-CD), β-cyclodexdrin (β-CD), p-tert-cutylthiacalix[4]arene (TC4), calix[4]arene (C4), and resorcin[4]arene (RC4) were synthesized. Among these macrocyclic compounds, RC4 was determined to be the most appropriate candidate to replace BPA as the developer material used in thermochromic dyes. In tests of prepared thermochromic dyes, RC4 had results similar to those of BPA, achieving the best protonation/deprotonation equilibria and providing a dark contrast with the thermochromic dye. The density functional theory (DFT) calculations also showed stable complexes between RC4 and crystal violet lactone (CVL) via hydrogen-bond interactions. The color change of the rhodamine solution, filter paper dipped in rhodamine solution and rhodamine/polymer blend film were tested. It was found that the solution and the filter paper changed from colorless to pink after heat treatment. For the polymer/rhodamine blend films, it was also found that all films exhibited a colorless to pink color change when taken from room temperature to 80 °C. Moreover, the films turned orange when observing the color change under UV light. FT-IR (fourier transform infrared spectroscopy) and UV-Vis spectroscopy were used to study the color change mechanism. The FT-IR spectra of Open and closed structures of rhodamine B showed broadband at 3450-3250 cm-1 which was attributed to O-H stretching of the carboxylic group of open structure of Rhodamine B and a sharp band at 1725 cm-1 was attributed to C=O stretching of the carbonyl group. A strong peak appearing at 1067 cm-1 was attributed to C-O stretching and C-O stretching at 1067 cm-1 slightly shifted to 1066 cm-1 after synthesis. In addition, it was observed that FT-IR spectra of two structures of rhodamine were different, indicating that the structure has been changed in which open structure has completed the change to a closed structure. The UV-Vis spectroscopy results showed the absorbance at a wavelength of 530-580 nm in which the open structure Rhodamine B had higher absorbance intensity than the closed structure. From the experimental results, it can be concluded that polymer/rhodamine B blend film can be developed and applied as an optical temperature indicator label material.