Recently, alginates (ALG) characterized by high mannuronic content (M blocks) have been shown to undergo a reversible sol/gel transition during cooling in the presence of potassium salts. Cold gelling takes place at low temperatures, just below 0 °C for a KCl concentration of 0.3 mol/kg, but the aggregation process can be easily shifted to higher temperatures by increasing the salt concentration. In the present paper, we take advantage of this peculiar behavior to design a copolymer with schizophrenic gelling properties. For this purpose, side chains of poly(N-isopropylacrylamide) (PNIPAM), characterized by a Lower Critical Solution Temperature (LCST) in water, were grafted on the alginate backbone. Working in semidilute solutions, we show by coupling DSC and viscoelastic measurements that ALG-g-PNIPAM solutions are able to form gels either by cooling or heating depending on the ionic environment. As the aggregation process of ALG and PNIPAM depends mainly and respectively on the nature of the cations and anions, the choice of the salt is then critical to control the self-assembly behavior and the gel properties. Moreover, as the gelation process of alginates driven by the aggregation of mannuronic sequences is characterized by a large hysteresis of 20–30 °C between gelling and melting, both ALG and ALG-g-PNIPAM polymers offer a large versatility not only in terms of salt (nature and concentration) but also in preparation history as different states (sol or gel) can be obtained at room temperature.

中文翻译：

---

海藻酸钠接枝-PNIPAM的冷热胶凝：钾盐诱导的精神分裂症行为

最近，以高甘露糖醛酸酯含量（M嵌段）为特征的藻酸盐（ALG）已显示出在钾盐存在下冷却过程中经历了可逆的溶胶/凝胶转变。对于0.3 mol / kg的KCl浓度，冷胶凝在低温下进行，温度略低于0°C，但是通过增加盐浓度，可以很容易地将聚集过程转移到更高的温度。在本文中，我们利用这种独特的行为来设计具有精神分裂性胶凝特性的共聚物。为此，将聚（N-异丙基丙烯酰胺）（PNIPAM）的侧链接枝到藻酸盐骨架上，该侧链的特征在于在水中的临界溶液温度较低（LCST）。在半稀释溶液中工作，我们通过结合DSC和粘弹性测量结果表明ALG- g-PNIPAM溶液能够根据离子环境通过冷却或加热来形成凝胶。由于ALG和PNIPAM的聚集过程主要且分别取决于阳离子和阴离子的性质，因此盐的选择对于控制自组装行为和凝胶性质至关重要。此外，由于甘露糖醛酸序列的聚集所驱动的藻酸盐的胶凝过程的特征是胶凝和熔化之间存在20–30°C的较大滞后，因此ALG和ALG - g - PNIPAM聚合物不仅在以下方面提供了广泛的通用性在室温下可以获得盐（性质和浓度）以及制备过程中的不同状态（溶胶或凝胶）。