Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the borax concentration Cborax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of borax can crosslink the PVA chains to form a reversible network. At low Cborax = 2.5 mM, the network strands are larger than the precursor chains. The stress relaxation is governed by the effective breakup, and the time temperature superposition (tTs) fails only slightly. In contrast, at high Cborx ≥ 4.0 mM, the network strands are dense and each chain is divided averagely into several network strands. For this case, the stress relaxation is governed by chain relaxation activated by continuous ion dissociations, where tTs fails significantly. Analysis of the thermorheological behavior provides rich information on the temperature-dependent structural evolution. Particularly, analyzing the high frequency data attributed to the ion dissociation process indicates that the failure of tTs is owing to a reduction of the degree of gelation with increasing T, which leads to an acceleration of the chain relaxation with respect to the ion dissociation.

中文翻译：

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聚乙烯醇/硼砂水溶液的热流变复杂性

检测了聚乙烯醇 (PVA) 和硼砂水溶液的热流变行为。PVA 含量固定为缠结浓度的大约四倍，硼砂浓度 Cborax 在 0-10.4 mM 的范围内变化。在该系统中，硼砂水解产生的硼酸盐离子可以交联 PVA 链，形成可逆网络。在低 Cborax = 2.5 mM 时，网络链大于前体链。应力松弛由有效破裂控制，时间温度叠加 (tTs) 仅轻微失效。相比之下，在高 Cborx ≥ 4.0 mM 时，网络链很密集，每条链平均分为几个网络链。对于这种情况，应力松弛由连续离子解离激活的链松弛控制，其中 tTs 显着失败。热流变行为的分析提供了关于温度依赖性结构演化的丰富信息。特别是，分析归因于离子解离过程的高频数据表明，tTs 的失败是由于随着 T 的增加凝胶化程度的降低，这导致链松弛相对于离子解离的加速。