Collaborative Research: Water Mediated Transport of Ions and Molecules in Ionomeric Paint Films: An Integrated Multi-Technique Investigation

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Non-technical AbstractIrreplaceable masterworks of art dating from the 14th century through the 20th century are slowly deteriorating due to chemical reactions among the paint components. One step believed to be important in this complex process is the movement of ions and molecules through the paint. In this project, the dynamics and transport of materials such as water and solvents in paint films are examined to determine (1) the nature of the process, and (2) what factors affect this process. Paint films are complex materials, and they must be studied with multiple techniques to characterize the processes as completely as possible. With the support from the Solid State and Materials Chemistry program in the Division of Materials Research and the Chemical Measurement and Imaging program in the Division of Chemistry, the ongoing collaboration between the University of Delaware and The Metropolitan Museum of Art to address the deterioration of paintings with modern technologies is expanded by the involvement of scientists at Brookhaven National Laboratory and Pacific Northwest National Laboratory to provide additional unique analyses of materials prepared at The Metropolitan Museum of Art and the University of Delaware and of microscopic samples removed works of art affected, to provide answers to questions like "Why and how does this process occur?" and "What types of actions can be taken to minimize or eliminate these processes that ultimately destroy priceless art objects?" The project, through outreach carried out by The Metropolitan Museum of Art and the University of Delaware, provides the public with a tangible connection between scientific discovery and the elements of culture and history, at the same time as it develops an understanding of complex chemical processes that affect more than just paintings. Technical AbstractThe reaction of heavy-metal-containing pigments with fatty acids in oil paintings, derived from the oil paint binders, produces metal carboxylates also called soaps. These soaps may produce disfiguring inclusions, surface crusts and/or increased transparency of the paints, resulting in unwanted and ultimately deleterious effects. Most oil paintings suffer from this process to some degree. From a scientific perspective, the process consists of a series of steps: (1) production of free fatty acids by hydrolysis of the oil; (2) migration of acids and pigment-derived ions; (3) the reactive event; and (4) agglomeration of the products to produce soap aggregates or migration to the paint film surface to produce crusts. Each step is important and complex, in part due to the heterogeneity of the material. This project focuses on the dynamics of materials in the paint films, predominantly characterizing step 2, but the dynamics are also important as materials like water and solvents, sometimes from restoration interventions, and environmental effects may be involved in steps 1 and 4. Additionally, because these materials are heterogeneous, one must simultaneously consider the effects of properties such as pigment particle size and shape, and porosity of the paint in understanding the nature of these process. This can only be achieved by a multi-pronged approach to characterize samples treated in different ways. By combining the strengths of the Metropolitan Museum, the University of Delaware together with expertise at Brookhaven National Laboratory and Pacific Northwest Laboratory, several sophisticated technologies are directed towards understanding the process. The novel strategy proposed to study a complex heterogeneous multilayered system is applicable to the characterization of analogous problems in the field of soft matter science.