Time-Dependent ATR-FTIR Spectroscopic Studies on Solvent Diffusion and Film Swelling in Oil Paint Model Systems

Abstract

In the restoration of paintings, solvent diffusion and swelling of polymeric oil paint binding media are important factors to consider. Common cleaning methods with organic solvents or aqueous solutions could lead to undesirable physicochemical changes in the paint in the long term, though the extent of this effect is not yet clear. We used tailored nonporous model systems for aged oil paint to measure paint swelling and solvent diffusion for a wide range of relevant solvents. Using dynamic mechanical analysis (DMA), the glass transition temperature of our model systems was found to be close to room temperature. Subsequently, with a custom sample cell and time-dependent attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, we were able to accurately track swelling and diffusion processes in the polymer films. To quantify the spectroscopic data, we developed a model that completely describes the solvent migration process, including significant film swelling and non-Fickian solvent diffusion. The relation between solvent properties, the diffusion coefficient, and the swelling capacity proved to be rather complex and could not be explained using a single solvent parameter. However, it was found that strongly swelling solvents generally diffuse faster than weakly swelling solvents and that pigmentation does not significantly influence solvent diffusion. These results contribute to a better understanding of transport phenomena in paintings and support the development of improved paint restoration strategies.

The concentration and origins of carboxylic acid groups in oil paint

“…22 Potentiometric titration of COOH groups 23 proved to be time consuming and inaccurate since polymerised LO is extremely insoluble and the diffusion of water is very slow. 24 Methods based on derivatization with uoride transfer reagents 25,26 showed the existence of acid groups but did not give a reproducible conversion when applied to our polymeric materials. Swollen-state 13 C NMR spectroscopy also enabled the detection of acid groups but was not used in a quantitative manner.…”

Quantifying solvent action in oil paint using portable laser speckle imaging

“…What exactly defines the impact of solvent action on paint is a complex interplay between many different chemical and physical phenomena. After the application of solvent, solvent swelling [24][25][26] , -diffusion 27 , -evaporation 28,29 , -leaching (extraction) [9][10][11][12][13][14] and chemical reactions 15,16 occur simultaneously. It is not possible to quantitatively measure the total physicochemical influence of these combined processes during cleaning practice, and conservators often assume that minimal exposure to water or solvents limits the risks associated with cleaning.…”

Nano- to microscale three-dimensional morphology relevant to transport properties in reactive porous composite paint films

“…Because the X-ray attenuation is similar for the pores and the oil phase at the tens of nm scale, empty pores cannot be differentiated from spaces occupied by the oil phase in these experiments. Nevertheless, studies in model paint systems have proposed that the transport of water, organic solvents and other species may also take place in the oil phase 8 , 9 .…”