On the photoluminescence changes induced by ageing processes on zinc white paints

Recent research is focusing on the study of interaction mechanisms between pigments and binders, as they are crucial for understanding paint ageing and conservation issues. In this work, we investigate these mechanisms and follow the changes induced by ageing on zinc white paint by employing Fourier Transform Infrared (FTIR) and Time-Resolved Photoluminescence (TRPL) spectroscopies. The two techniques, applied on thermally aged mock-up samples and on a 19th oil painting, provide complementary information on the effect of the binder on the ZnO pigment particles. The characterization of the infrared absorption spectra confirms the well-known tendency of amorphous metal carboxylate formation in zinc white paint following ageing. At the same time, the ageing of paint film produces significant changes in the photoluminescence emission from defect centres of ZnO. The emission that is mostly affected by the changes of the micro-environment is the blue band (430 nm) – associated with surface defects – whereas the green emission (530 nm) is stable. The results demonstrate that the evolution of the pigment-binder system has detectable consequences on the crystalline structure of the pigment particles and we speculate that the main cause of these modifications is the functionalization of the pigment particle surfaces. The possibility to follow crystal structure changes with time-resolved photoluminescence can thus support chemical studies on metal carboxylate formation and paint deterioration by providing information about pigment-binder interactions

Exploring a Graph Complement in Quadratic Congruence

In this work, we investigate essential definitions, defining G as a simple graph with vertices in Zn and subgraphs Γu and Γq as unit residue and quadratic residue graphs modulo n, respectively. The investigation extends to the degree of G, Γu, and Γq, illuminating the properties of these subgraphs in the context of quadratic congruences

Characterization and functional properties of some natural Acacia gums

Authentic representative gum exudate samples from Acacia species namely Acacia senegal var. senegal (ASG), Acacia mellifera (AMF), Acacia seyal var. seyal (ASY), and Acacia tortilis var. raddiana (ATR), were physicochemically analyzed. The moisture, ash, nitrogen and protein content, pH, specific optical rotation, and number average molecular weight were found to be ranging from 9.76% to 8.35%, 3.40% to 2.05%, 0.243% to 1.549%, 1.610% to 10.378%, 4.45 to 4.94, −48.25 to +86.75 and 0.24 × 106 to 2.95 × 106 respectively. The 13C and 1H NMR spectra of gum samples showed similarity in individual sugar components, but characteristic patterns of each gum, were observed. FTIR spectra of the studied gums show the presence of the same functional groups in the four gums. DSC and TGA thermograms were characteristic for each gum. Evaluation of the functional properties of the four gums indicated that ATR gum bears the best emulsification characteristics in terms of emulsion’s stability and emulsification power. Keywords: Acacia gums, NMR, ATR–FTIR, Thermal analysis, DSC, TG