We mundanely observe cellulose (kitchen) sponges swell while absorbing water. Fluid flows in deformable porous media, such as soils and hydrogels, are classically described on the basis of the theories of Darcy and poroelasticity, where the expansion of media arises due to increased pore pressure. However, the situation is qualitatively different in cellulosic porous materials like sponges because the pore expansion is driven by wetting of the surrounding cellulose walls rather than by increase of the internal pore pressure. We address a seemingly so simple but hitherto unanswered question of how fast water wicks into the swelling sponge. Our experiments uncover a power law of the wicking height versus time distinct from that for nonswelling materials. The observation using environmental scanning electron microscopy reveals the coalescence of microscale wall pores with wetting, which allows us to build a mathematical model for pore size evolution and the consequent wicking dynamics. Our study sheds light on the physics of water absorption in hygroscopically responsive multiscale porous materials, which have far more implications than everyday activities (for example, cleaning, writing, and painting) carried out with cellulosic materials (paper and sponge), including absorbent hygiene products, biomedical cell cultures, building safety, and cooking.

中文翻译：

---

纤维素海绵的多孔弹性毛细管芯吸。

我们平时观察到纤维素（厨房）海绵在吸水时会膨胀。在达西理论和多孔弹性理论的基础上，经典地描述了可变形多孔介质（例如土壤和水凝胶）中的流体流动，其中，介质的膨胀是由于孔隙压力的增加而引起的。但是，纤维素多孔材料（如海绵）的情况在质量上有所不同，因为孔的膨胀是由周围纤维素壁的润湿而不是内部孔压的增加来驱动的。我们解决了一个看似如此简单但迄今尚未解决的问题，即水如何迅速吸进膨胀的海绵中。我们的实验揭示了芯吸高度与时间的幂率定律与非膨胀材料的幂定律不同。使用环境扫描电子显微镜进行的观察揭示了微尺度壁孔与润湿的结合，这使我们能够为孔尺寸演变和随后的芯吸动力学建立数学模型。我们的研究揭示了对吸湿性多尺度多孔材料的吸水物理特性，其影响远大于使用纤维素材料（纸和海绵）进行的日常活动（例如，清洁，书写和绘画），包括吸收性卫生产品，生物医学细胞培养，建筑物安全和烹饪。