New Frontiers in Materials Science for Art Conservation: Responsive Gels and Beyond

Abstract

The works of art and artifacts that constitute our cultural heritage are subject to deterioration, both from internal and from external factors. Surfaces that interact with the environment are the most prone to aging and decay; accordingly, soiling is a prime factor in the degradation of surfaces and the attendant disfigurement of a piece. Coatings that were originally intended to protect or contribute aesthetically to an artwork should be removed if they begin to have a destructive impact on its appearance or surface chemistry. Since the mid-19th century, organic solvents have been the method of choice for cleaning painted surfaces and removing degraded coatings. Care must be taken to choose a solvent mixture that minimizes swelling of or leaching from the original paint films, which would damage and compromise the physical integrity of all the layers of paint. The use of gels and poultices, first advocated in the 1980s, helps by localizing the solvent and, in some cases, by reducing solvent permeation into underlying paint layers. Unfortunately, it is not always easy to remove gels and their residues from a paint surface. In this Account, we address the removal problem by examining the properties of three classes of innovative gels for use on artwork--rheoreversible gels, magnetic gels, and "peelable" gels. Their rheological properties and efficacies for treating the surfaces of works have been studied, demonstrating uniquely useful characteristics in each class: (1) Rheoreversible gels become free-flowing on application of a chemical or thermal "switch". For art conservation, a chemical trigger is preferred. Stable gels formed by bubbling CO(2) through solutions of polyallylamine or polyethylenimines (thereby producing ammonium carbamates, which act as chain cross-links) can be prepared with a wide range of solvent mixtures. After solubilization of varnish and dirt, addition of a weak acid (mineral or organic) displaces the CO(2), and the resulting free-flowing liquid can be removed gently. (2) Incorporation of magnetic, coated-ferrite nanoparticles into polyacrylamide gels adds functionality to a versatile system comprising oil-in-water microemulsions, aqueous micellar solutions, or xerogels that act as sponges. The ferrite particles allow the use of magnets both to place the gels precisely on a surface and to lift them from it after cleaning. (3) Novel formulations of poly(vinyl alcohol)-borate gels, which accept a range of organic cosolvents, show promise for swelling and dissolving organic coatings. This family of gels can be quite stiff but can be spread. They are non-sticky and have sufficient strength to be removed by peeling or lifting them from a sensitive surface. These three classes of gels are potentially very important soft materials to augment and improve the range of options available for conserving cultural heritage, and their interesting chemical-physical properties open a rich area for future scientific investigation.

Gellan hydrogel as a powerful tool in paper cleaning process: A detailed study

“…At the same time, gel residues can induce dangerous microbial growth [8,9]. To overcome this drawbacks, highly rigid and film forming hydrogels may represent a useful alternative [3,5,7,10], as they can be completely and easily removed in one operation after their application, thus minimizing the side effects already presented. In this contest, a new wet cleaning technique based on the use of a rigid hydrogel of Gellan gum has been recently developed [3,6,11].…”

The Use of Solvent-Gel Systems for the Cleaning of PMMA

“…Gels could offer this, through their assumed potential to limit free solvent penetration into cracks and pores of the surface, while minimizing the risk of dissolution of the material [10,11]. As the use of gels on plastic surfaces has not been studied in depth to date, it is imperative to adopt a systematic approach to evaluate their effect on pristine acrylic surfaces, without dirt, to use as a reference point for further studies.…”

Influence of Functionalization Degree on the Rheological Properties of Isocyanate-Functionalized Chitin- and Chitosan-Based Chemical Oleogels for Lubricant Applications

“…Organogels are generating great interest and expectation in a wide spectrum of applications such as medical and pharmaceutical [1][2][3][4], development of new materials with specific optical and mechanical properties [5][6][7], matrixes for food systems [8,9], art conservation [10,11], etc. The term organogel refers to a variety of soft materials, from viscoelastic liquid-like to solid-like, comprised of an organic liquid and some molecules, i.e., organogelators, which are able to produce self-assembling and structure the organic medium [12].…”