Department of Chemistry, Materials Science, and Chemical Engineering (CMIC), Politecnico di Milano, Edificio 6, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
J Chem Phys. 2022 Nov 7;157(17):174901. doi: 10.1063/5.0086533.
We investigate the rheo-mechanical properties of Mebiol Gel®, a thermosensitive gel-forming polymer extensively used as a medium for cellular culture, using passive microrheology made either by standard dynamic light scattering or by photon correlation imaging. In the dilute limit, Mebiol displays a Newtonian behavior with an effective viscosity that decreases with temperature, consistent with a peculiar aggregation mechanism characterized by an increase of the molecular weight with a simultaneous reduction of the aggregate size. By increasing concentration and approaching gelation, both the storage and loss moduli show a nonmonotonic dependence with temperature, with a pronounced maximum around T ≃ 28-30 °C, the value above which, in the dilute limit, the individual Mebiol chains are fully compacted. Such a distinctive trend of the elastic and viscous properties persists within the gel, which, therefore, becomes "softer" above T. Although when temperature changes are performed adiabatically, the transition from the fluid to the gel phase takes place without any apparent discontinuity, a rapid T-jump leads to the formation of a hard gel at a concentration where a low heating rate conversely yields a fluid phase. This is a visible manifestation of the nonequilibrium nature of these physical gels.
我们采用标准动态光散射或光子相关成像被动微流变学的方法研究了 Mebiol Gel®（一种广泛用作细胞培养介质的温敏凝胶形成聚合物）的流变性和力学性能。在稀溶液中，Mebiol 表现出牛顿行为，其有效粘度随温度降低而降低，这与一种特殊的聚集机制一致，该机制的特征是分子量增加，同时聚集尺寸减小。随着浓度的增加并接近凝胶化，储能模量和损耗模量均表现出与温度的非单调依赖性，在 T ≃ 28-30°C 左右出现明显的最大值，在这个温度以上，在稀溶液中，单个 Mebiol 链完全压缩。这种弹性和粘性特性的独特趋势在凝胶中持续存在，因此在 T 以上凝胶变得“更软”。尽管在进行绝热温度变化时，从流体相到凝胶相的转变没有任何明显的不连续性，但快速的 T 跳跃会导致在浓度下形成硬凝胶，而相反，较低的加热速率会产生流体相。这是这些物理凝胶非平衡性质的明显表现。
