Formation of CO2 bubbles in epoxy resin coatings: A DFT study.

The epoxy resin coating is a fundamental species with epoxy resins used as main components to form the final film. Unexpectedly, bulky CO2 bubbles that occasionally appeared during the curing process of epoxy resin coatings might destroy the final film properties. With an attempt to thoroughly understand the formation mechanism of CO2 bubbles and further propose countermeasures to control them, Density Function Theory (DFT) in this paper was employed to calculate the absorption process, the curing reaction and the formation mechanism of CO2 bubbles. The gas phase basicity (GB) values and pKa values of common amine curing agents were calculated. The total Gibbs free energies difference of the curing reactions between polluted curing agents and epoxy resins were calculated according to a thermodynamic cycle. Whether in gas phase or resin phase, the energetically negative ΔGsolv indicated that the curing reactions might occur spontaneously and CO2 molecules would be separated and released from amine molecules. The total Gibbs free energy calculations also revealed that the re-absorption of CO2 by the curing system was energetically unfavorable. Thus, the formation mechanism of CO2 bubbles of epoxy resin coatings could be summarize in three steps: (1) Carbon dioxide pollutes accidentally the curing agents. (2) CO2 molecules are gradually released as the curing process occurs. (3) CO2 molecules are collected to form big bubbles which can lead to seriously surface and/or internal defects. Finally, based on practical experiences three tips were proposed to control CO2 bubbles. The present results not only evidenced the nature of the unexpected bubbles of epoxy resin coatings, but also additionally paved to the way to full utilization of the formation mechanism to improve the epoxy coatings' properties.

A novel ratiometric fluorescent sensor for Ag+ based on two fluorophores.

A novel ratiometric fluorescent probe BCB was reported for the first time for the sensitive and selective analysis of Ag+ based on two Boradiazaindacene (BODIPY) as both the reference fluorophore and recognition part. Upon the addition of Ag+ ions, a strong fluorescence emission at 570 nm from recognition BODIPY would be appeared, whereas the fluorescence of the other BODIPY at 535 nm would be a constant reference fluorescence signal. As a result, the ratio of fluorescence intensity (λ570/λ535) was changed from 0.16 to 1.0. And the selectivity of BCB towards Ag+ over other metal ion was excellent. Other metal ions, such as Cd2+, Cu2+, Fe3+, Hg2+, Mg2+, Ni2+, Pb2+ and Zn2+ showed negligible changes in the both absorption and fluorescence spectra of BCB.

Aggregation of two carboxylic derivatives of porphyrin and their affinity to bovine serum albumin.

Aggregation of two porphyrin derivatives with carboxylic groups, 4-oxo-4-((4-(10,15,20-triphenyl-21H,23H-porphin-5-yl)phenyl)amino)butanoic acid (MAC) and 4,4',4'',4'''-[21H,23H-porphine-5,10,15,20-tetrayltetrakis(4,1-phenyleneimino)]tetrakis(4-oxo-butanoic acid) (TA4C), and their affinity to bovine serum albumin were investigated via absorption spectrometry, (1)H NMR and fluorescence spectrometry. MAC and its complexes with beta-cyclodextrin could form aggregates in an aqueous solution while TA4C was self-associated loosely. From the absorbance profiles of MAC in the titration of bovine serum albumin, hypochromicity was observed without any shift of the maximum absorbance wavelength. In both absorption spectra of TA4C in aqueous solutions and in solid state, three Q bands appeared in the visible region. In the measurements of absorption and fluorescence spectra upon titration of BSA, some spectral changes of TA4C were observed. The whole procedure of titration could be divided into three successive stages. The three-banded profiles of TA4C might be explained according to a loose dimer model.