pH-responsive cotton can be used as a flexible sensor because it changes colour with pH. However, the safety of some synthetic pH-responsive dyes is uncertain, so the application of pH-responsive cotton to wounds is limited. Herein, natural madder dye was selected to explore the dyeing conditions and produce safe, pH-responsive cotton. Based on experimental data and computational calculations, the variation in the conjugation of the molecule was responsible for the colour change of the cotton dyed with madder. When the pH of the madder solution increases, the phenolic hydroxyl group of the alizarin, which is its main component, is ionised, and the colour changes from yellow to purple. The effect of the dye concentration was studied, and the results showed that the higher the dye concentration, the more obvious the colour change of the cotton. The reversibility of cotton dyed with madder was investigated, and the results showed that there was a good reversible transformation with changing pH. The reversibility time of the colour change was less than 20 seconds.

中文翻译：

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天然茜草染料染色的 pH 响应棉纤维

pH 响应棉可用作柔性传感器，因为它会随着 pH 值改变颜色。然而，一些合成的pH响应染料的安全性不确定，因此pH响应棉在伤口上的应用受到限制。在此，选择天然茜草染料来探索染色条件并生产安全、pH 敏感的棉花。基于实验数据和计算计算，分子共轭的变化是茜草染棉颜色变化的原因。当茜草溶液的pH值升高时，其主要成分茜素的酚羟基被电离，颜色由黄色变为紫色。研究了染料浓度的影响，结果表明染料浓度越高，棉花的颜色变化越明显。对茜草染棉的可逆性进行了研究，结果表明随着pH的变化存在良好的可逆转化。颜色变化的可逆时间小于20秒。