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Metal soap formation is one of the most wide-spread degradation mechanisms observed in historical oil paintings, affecting works of art from museum collections worldwide. Metal soaps develop from a chemical reaction between metal ions present in the pigments and saturated fatty acids, which are released by the oil binder. The presence of large metal soap crystals inside paint layers or at the paint surface can be detrimental for the visual appearance of artworks. Moreover, metal soaps can possibly trigger mechanical damage, ultimately resulting in flaking of the paint. This paper departs from a recently proposed computational model to predict chemo-mechanical degradation in historical oil paint- ings, as presented in Eumelen et al. (J Mech Phys Solids 132:103683, 2019). The model describes metal soap formation and growth, which are phenomena that are driven by the diffusion of saturated fatty acids and proceed by a nucleation process from a crystalline nucleus of small size. This results into a chemically-induced strain in the paint, which may pro- mote crack nucleation and propagation. The proposed model is here used to investigate the effects of saturated fatty acid concentration and initial nucleus geometry on the amount of chemo-mechanical damage generated. Numerical simulations show that both factors have a marginal influence on the growth rate of the metal soap crystal, but play a significant role on the extent of fracture induced in the paint.

Metal soap formation is one of the most wide-spread degradation mechanisms observed in historical oil paintings, affecting works of art from museum collections worldwide. Metal soaps develop from a chemical reaction between metal ions present in the pigments and saturated fatty acids, which are released by the oil binder. The presence of large metal soap crystals inside paint layers or at the paint surface can be detrimental for the visual appearance of artworks. Moreover, metal soaps can possibly trigger mechanical damage, ultimately resulting in flaking of the paint. This paper departs from a recently proposed computational model to predict chemo-mechanical degradation in historical oil paint- ings, as presented in Eumelen et al. (J Mech Phys Solids 132:103683, 2019). The model describes metal soap formation and growth, which are phenomena that are driven by the diffusion of saturated fatty acids and proceed by a nucleation process from a crystalline nucleus of small size. This results into a chemically-induced strain in the paint, which may pro- mote crack nucleation and propagation. The proposed model is here used to investigate the effects of saturated fatty acid concentration and initial nucleus geometry on the amount of chemo-mechanical damage generated. Numerical simulations show that both factors have a marginal influence on the growth rate of the metal soap crystal, but play a significant role on the extent of fracture induced in the paint.

Natural rubber (NR) merely usage in the rubber compounds due to high viscosity is difficult. To overcome the problem or even to make possible the mixing, at first, the viscosity level has to be decreased enough by so called mastication. This process was initially just in the mechanical form but since the NR broken chains joined to each other from their free ends, yielding undesirable branched chains and hence didn't have the high elastic properties of NR, a chemical peptizer has been used. To this point, we conclude that to use NR peptizer, a special mixing part is necessary for the material and natural rubber both and also because of cutting the long valuable NR chains the final properties of the compound will be decreased, such as dynamic properties, HBU and elasticity., Natural rubber (NR) merely usage in the rubber compounds due to high viscosity is difficult. To overcome the problem or even to make possible the mixing, at first, the viscosity level has to be decreased enough by so called mastication. This process was initially just in the mechanical form but since the NR broken chains joined to each other from their free ends, yielding undesirable branched chains and hence didn't have the high elastic properties of NR, a chemical peptizer has been used. To this point, we conclude that to use NR peptizer, a special mixing part is necessary for the material and natural rubber both and also because of cutting the long valuable NR chains the final properties of the compound will be decreased, such as dynamic properties, HBU and elasticity.

Lanthanide(III) hexanoate 1,10-phenanthroline complexes crystallise in the space group P21/n. The compounds consist of dimers, whereby two lanthanide ions are held together by two bidentate bridging and two tridentate bridging carboxylate groups. The first coordination sphere of the lanthanide ions is completed by one bidentate chelating carboxylate group and by one bidentate 1,10-phenanthroline molecule, resulting in the coordination number 9. The dimers have a spherical form, which has important consequences for the thermal properties of complexes. The basic idea behind the preparation of this type of compounds is the stabilisation of the ionic lanthanide layer, so that the smaller lanthanide ions (from which the normal alkanoates do not show mesomorphism because they are too small) show liquid crystallinity. The stabilisation of the ionic layer was successful, expressed by the high melting temperatures, but mesomorphism is not observed. The absence of mesomorphism is related to the isotropic structure of the compounds. A lower symmetry is obtained when a hexanoate group is replaced by a nitrate group. Thulium(III) dihexanoate nitrate 1,10-phenanthroline crystallises in the space group P1̄. However, this compound also shows a spherical dimeric structure, but no mesomorphism.