Nanomaterials have permeated numerous scientific and technological fields, and have gained growing importance over the past decades also in the preservation of Cultural Heritage. After a critical overview of the main nanomaterials adopted in art preservation, we provide new insights into some highly relevant gels, which constitute valuable tools to selectively remove dirt or other unwanted layers from the surface of works of art. In particular, the recent “twin-chain” gels, obtained by phase separation of two different PVAs and freeze-thawing, were considered as the most performing gel systems for the cleaning of Cultural Heritage. Three factors are crucial in determining the final gel properties, i.e., pore size, pore connectivity, and surface roughness, which belong to the micro/nanodomain. The pore size is affected by the molecular weight of the phase-separating PVA polymer, while pore connectivity and tortuosity likely depend on interconnections formed during gelation. Tortuosity greatly impacts on cleaning capability, as the removal of matter at the gel–target interface increases with the uploaded fluid's residence time at the interface (higher tortuosity produces longer residence). The gels’ surface roughness, adaptability and stickiness can also be controlled by modulating the porogen amount or adding different polymers to PVA. Finally, PVA can be partially replaced with different biopolymers yielding gels with enhanced sustainability and effective cleaning capability, where the selection of the biopolymer affects the gel porosity and effectiveness. These results shed new light on the effect of micro/nanoscale features on the cleaning performances of “twin-chain” and composite gels, opening new horizons for advanced and “green”/sustainable gel materials that can impact on fields even beyond art preservation, like drug-delivery, detergency, food industry, cosmetics and tissue engineering.

中文翻译：

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先进纳米材料用于文化遗产保护的新视野

纳米材料已经渗透到许多科学和技术领域，并且在过去几十年中在文化遗产保护方面也变得越来越重要。在对艺术品保存中采用的主要纳米材料进行批判性概述后，我们对一些高度相关的凝胶提供了新的见解，这些凝胶构成了选择性去除艺术品表面污垢或其他不需要的层的宝贵工具。特别是，最近通过两种不同 PVA 的相分离和冻融获得的“双链”凝胶被认为是用于文化遗产清洁的性能最佳的凝胶系统。决定最终凝胶性能的三个因素至关重要，即属于微/纳米域的孔径、孔连通性和表面粗糙度。孔径大小受相分离 PVA 聚合物分子量的影响，而孔连通性和弯曲度可能取决于凝胶化过程中形成的互连。弯曲度对清洁能力有很大影响，因为凝胶-目标界面处物质的去除随着上传流体在界面处的停留时间而增加（弯曲度越高，停留时间越长）。凝胶的表面粗糙度、适应性和粘性也可以通过调节致孔剂的量或在PVA中添加不同的聚合物来控制。最后，PVA 可以部分替换为不同的生物聚合物，产生的凝胶具有增强的可持续性和有效的清洁能力，其中生物聚合物的选择会影响凝胶的孔隙率和有效性。这些结果为微/纳米尺度特征对“双链”和复合凝胶清洁性能的影响提供了新的线索，为先进和“绿色”/可持续凝胶材料开辟了新视野，这些材料甚至可以影响艺术保存以外的领域，例如药物输送、洗涤剂、食品工业、化妆品和组织工程。