Kripotou Sotiria, Zafeiris Konstantinos, Culebras-Martínez Maria, Gallego Ferrer Gloria, Kyritsis Apostolos
National Technical University of Athens, Physics Department, Iroon Polytechneiou 9, Zografou Campus, 15780, Athens, Greece.
Centre for Biomaterials and Tissue Engineering (CBIT), Universitat Politècnica de València, Camino de vera s/n, 46022, Valencia, Spain.
Eur Phys J E Soft Matter. 2019 Aug 27;42(8):109. doi: 10.1140/epje/i2019-11871-2.
We employed broadband dielectric spectroscopy (BDS), for the investigation of the water dynamics in partially hydrated hyaluronic acid (HA), and gelatin (Gel), enzymatically crosslinked hydrogels, in the water fraction ranges [Formula: see text]. Our results indicate that at low hydrations ([Formula: see text]), where the dielectric response of the hydrogels is identical during cooling and heating, water plasticizes strongly the polymeric matrix and is organized in clusters giving rise to [Formula: see text]-process, secondary water relaxation and to an additional slower relaxation process. This later process has been found to be related with the dc charge conductivity and can be described in terms of the conduction current relaxation mechanism. At slightly higher hydrations, however, always below the hydration level where ice is formed during cooling, we have recorded in HA hydrogel a strong water dielectric relaxation process, [Formula: see text], which has Arrhenius-like temperature dependence and large time scale resembling relaxation processes recorded in bulk low density amorphous solid water structures. This relaxation process shows a strong-to-fragile transition at [Formula: see text]C and our data suggest that the VTF-like process recorded at [Formula: see text]C is controlled by the same molecular process like long range charge transport. In addition, our data imply that the crossover temperature is related with the onset of structural rearrangements (increase in configurational entropy) of the macromolecules. In partially crystallized hydrogels ([Formula: see text]) HA exhibits at low temperatures the ice dielectric process consistent with the bulk hexagonal ice, whereas Gel hydrogel exhibits as main low temperature process a slow relaxation process that refers to open tetrahedral structures of water similar to low density amorphous ice structures and to bulk cubic ice. Regarding the water secondary relaxation processes, we have shown that the [Formula: see text]-process and the [Formula: see text] process are activated in water hydrogen bond networks with different structures.
我们采用宽带介电谱（BDS）来研究部分水合的透明质酸（HA）和明胶（Gel）酶交联水凝胶在水含量范围[公式：见原文]内的水动力学。我们的结果表明，在低水合度（[公式：见原文]）下，水凝胶在冷却和加热过程中的介电响应相同，水强烈地使聚合物基质增塑，并以簇的形式组织起来，产生[公式：见原文]过程、二级水弛豫以及另一个较慢的弛豫过程。已发现后一过程与直流电荷传导率有关，并且可以用传导电流弛豫机制来描述。然而，在稍高的水合度下，始终低于冷却过程中形成冰的水合水平，我们在HA水凝胶中记录到一个强烈的水介电弛豫过程，[公式：见原文]，其具有类似阿仑尼乌斯的温度依赖性和较大的时间尺度，类似于在块状低密度非晶态固体水结构中记录到的弛豫过程。这个弛豫过程在[公式：见原文]°C时表现出从强到弱的转变，我们的数据表明在[公式：见原文]°C记录到的类似VTF的过程受与长程电荷传输相同的分子过程控制。此外，我们的数据表明交叉温度与大分子结构重排的开始（构型熵增加）有关。在部分结晶的水凝胶（[公式：见原文]）中，HA在低温下表现出与块状六方冰一致的冰介电过程，而Gel水凝胶在低温下表现出的主要过程是一个缓慢的弛豫过程，该过程涉及类似于低密度非晶态冰结构和块状立方冰的开放四面体水结构。关于水的二级弛豫过程，我们已经表明[公式：见原文]过程和[公式：见原文]过程在具有不同结构的水氢键网络中被激活。
