Plasticization by Water Governs the Hydration–Adhesion Relationship of Cellulose Mucilage

Hydration modulates the adhesion of cellulosic plant-seed mucilage to substrates. Using coarse-grained many-body dissipative particle dynamics (MDPD), we show the synergistic adhesion of hydrated cellulose; the adhesion of the water–cellulose mixture is stronger than the weighted average of the two components. At low to moderate hydration, water plasticizes the stiff cellulose chains, making them more flexible and better able to adapt to the substrate during retraction. We show this by artificially modifying dry cellulose so that its flexibility matches that of hydrated cellulose. Thus, softened dry cellulose has the same pull-off force as the unchanged, but hydrated cellulose. More support for the softening mechanism being responsible for increased adhesion is that it can also be brought about by small molecules other than water: Mixing in cellulose monomers or dimers improves adhesion, but the admixture of longer oligomers does not. For comparison, we also investigated pectin mucilages, pectin being the other important component of seed mucilage. Here, there is no synergy between water and pectin, with the effect being additive at best. Blending cellulose with pectin increases adhesion because pectin is inherently more flexible and has a higher baseline stickiness, yet the effect remains additive.

水分可调控纤维素基植物种子黏液与基底间的黏附性能。本研究采用粗粒化多体耗散粒子动力学（coarse-grained many-body dissipative particle dynamics, MDPD）方法，揭示了水合纤维素的协同黏附效应：水-纤维素混合物的黏附强度高于两种组分单独作用的加权平均值。在低至中等含水量条件下，水分可对刚性纤维素链产生增塑作用，使其柔韧性提升，进而在回缩过程中更好地适配基底表面。我们通过人工改性干燥纤维素，使其柔韧性与水合纤维素一致，由此验证了该机制。经软化处理的干燥纤维素，其剥离力与未改性的水合纤维素相当。进一步支持增塑机制是黏附强度提升的原因的证据在于：除水之外的小分子也可实现该效果——向体系中掺入纤维素单体或二聚体可改善黏附性能，但掺入更长链的低聚物则无法提升黏附性能。为进行对照实验，本研究还探究了果胶黏液，果胶是种子黏液的另一重要组成成分。在此体系中，水分与果胶之间未表现出协同效应，其作用至多为加和性。将纤维素与果胶共混可提升黏附强度，这是由于果胶本身柔韧性更强且本征黏附性更高，但该作用仍仅为加和性效应。