## 1 Introduction  
Microemulsions have largely attracted attention in cleaning for Cultural Heritage restoration, replacing conventional methods that are difficult to control. In particular, the commonly used organic solvents or gels are often toxic and high evaporation rates can represent a risk for the operators. Moreover, the aggressive nature of the organic solvents may cause partial swelling and solubilization of the original artwork materials [1]. On the other hand, microemulsions allow for better control of diffusion at the surface of the substrate and their formulations require fewer amounts of solventswith a significant reduction in toxicity and environmental impact. Restoration of the Renaissance paintings by [PERSON], [PERSON], and [PERSON] in the Brancacci Chapel in Florence (1984-1990) represents the first case study reporting the use of microemulsions for conservation purposes [2; 3]. Recently, amphiphile-based systems were intensively studied by [PERSON] to remove synthetic materials (acrylic and vinyl polymers) from painted surfaces [4]. These results show that the designed nanostructures improved the traditional methods while both minimizing the environmental impact and the optimizing cleaning performance [4]. Disadvantages for the use of colloidal systems are related to the high wettability of the treated surface and to spreading within the substrate porosity. Small traces of surfactant that remain on the artwork may cause deterioration and, in some cases, lead to the complete disfiguration of painted surfaces [5]. A fascinating resolution is freezing the microemulsion dynamics into a rigid nanocontainer in such a way as to simplify the removal of the whole cleaning system [6]. Among nanomaterials, hybrid systems prepared by a combination of mesoporous particles and sustainable polymers or surfactants are promising for several applications within materials science and biotechnology [1; 7; 8; 9; 10; 11; 12; 13; 14; 15]. Clay nanoparticles are promising as solid supports due to their sustainability and low cost [16; 17; 18; 19; 20]. Halosyite is an emerging hollow tubular clay which is naturally available worldwide and cheap compared to synthetic nanoparticles with similar morphology [16]. From a mineralogical viewpoint, halloysite is a 1:1 aluminosilicate (Al2 Si2O5(OH)4\(\bullet\)2H2O) that possesses two water molecules in the interlayer wall with a spacing of 10 A [21]. Similar to kaolinite, dehydrated halloysite presents a shorter interlayer wall periodicity (7.2 A) due to the loss of the water molecules. Typically, halloysite nanotubes (HNTs) are quite polydisperse in nature depending on the geological deposit [22]. Biological studies conducted both in vitro and in vivo show that halloysite is a biocompatible and low toxic nanoparticle that can be employed for numerous medical and pharmaceutical purposes [23; 24; 25; 26; 27; 28]. The hollow tubular shape and peculiar surface properties make HNTs suitable as catalytic supports for several reactions [29; 30; 31; 32; 33; 34] as well as adsorbent systems for wastewater decontamination [35; 36; 37; 38]. Filling polymeric matrices with halloysite presents as a successful strategy to obtain functional nanocomposite materials with excellent characteristics in terms of mechanical performance [39; 40], thermal stability [10; 41; 42], and vapor barrier properties [43]. The unique behavior of HNTs allows for selective modification with functional molecules; promising for the preparation of organic/inorganic composites [44; 45]. The opposite charges of the inside and outside surfaces allow for the selective adsorption of anionic or cationic surfactants presenting as an easy strategy to prepare new advanced hybrid materials [46; 47]. Furthermore, it was demonstrated that the anionic surfactant modification of the internal surface increases the net negative charge of the nanotubes enhancing the electrostatic repulsions and consequently the dispersion stability [16].