Direct Observation of Transient Flow Kinematics of Environment-Friendly Silica-Based Alcogel at Instantaneous Gelation
Direct Observation of Transient Flow Kinematics of Environment-Friendly Silica-Based Alcogel at Instantaneous Gelation
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DOI：
10.3390/su151914460
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发表时间：
2023-10
期刊：
影响因子：
3.9
通讯作者：
Kenichi Kurumada;Hidenori Ue;Jun Sato
中科院分区：
文献类型：
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作者：
Kenichi Kurumada;Hidenori Ue;Jun Sato
这项研究旨在探索在硅酸盐齐聚物溶液中加入催化咪唑所引起的醇凝胶快速凝胶化的可能性。为此，对直接观察凝胶行为的实验可行性进行了实际检验。以正硅酸乙酯在酸性条件下(pH~5)水解制得的硅酸盐低聚物作为快速胶凝母液。由于其简单，当添加咪唑的催化溶液时，低聚物溶液仅在几秒钟内就能形成不可流动的物质的能力在稳定沙地表面方面是有希望的。从实用的角度来看，在选择合适的胶凝化学物质时，胶凝所需的时间是一个关键参数。因此，这项研究关注的是一种尽可能简单的实验方法，用于评估实际经历瞬时凝胶的凝胶体系的凝胶时间。硅酸盐低聚物溶液具有胶凝速度快、环境友好等优点，是一种较理想的材料。对于如此快速的凝胶化，流变学方法不适用于检测机械性能中的边界，该边界描述了“凝胶”的区域。在这项研究中，取而代之的是直接观察来捕捉凝胶化完成的短时间间隔。低聚硅酸盐凝胶溶液在0.2 S内就失去了流动性，因为它在5赫兹时从摇动的圆柱体底部脱落。为了更定量地估计，在高速电影中观察到了相同的凝胶溶液。高速运动画面可以清晰地捕捉到水流突然停止时的瞬间凝胶化。对凝胶化行为的亚毫秒直接观察表明，流动的瞬时终止的时间尺度在数量级上快至1ms。这种亚毫秒量级的瞬时凝胶化不能从我们肉眼观察到的从102ms到103ms的可观测的巨型凝胶化中预测出来。应注意肉眼观察到的凝胶的时间刻度与由高速电影确定的局部点的真实凝胶时间之间的显著差距，以避免过度搅拌，例如，在机械搅拌的强烈变形影响下，过度搅拌可能导致刚固化或已经固化的凝胶完全崩塌成凝胶碎片。
This study was intended to exploit the possibility of using the quick gelation of alcogel that is induced by adding catalytic imidazole into a silicate-oligomer-based solution. For this purpose, the experimental viability of the direct observation of the gelation behavior was actually examined. The silicate oligomer, derived from tetraethyl orthosilicate hydrolyzed under an acidic condition (pH ~ 5), was used as the quickly gelling mother solution. The capability of the oligomer solution to form a non-flowable matter in only a few seconds when triggered by the addition of the catalytic solution of imidazole is promising, for example, for stabilizing a sandy ground surface, due to its simplicity. From the practical viewpoint, how long the gelation could take (=gel time) is a crucial parameter when the choice of an appropriate gelling chemical species needs to be made. Thus, this study focused its interest on as simple an experimental method as possible for evaluating the gel time of the gelling systems that actually underwent instantaneous gelation. The silicate oligomer solution was an appropriate material both in its quick gelling behavior and environmental friendliness. For such quick gelation, rheological approaches are not applicable for detecting the boundary in the mechanical properties that delineate the regime of “gel”. In this study, instead, direct observation was employed to capture the short interval during which the gelation was completed. The silicate-oligomer-based gelling solution was observed to lose its flowability within only 0.2 s, as it was seen to come off the bottom of the shaken cylinder at 5 Hz. For a more quantitative estimation, the same gelling solution was observed by high-speed motion picture. The high-speed motion picture could clearly capture the instantaneous gelation as a sudden arrest of the flow. The sub-millisecond direct observation of the gelation behavior revealed that the timescale of the instantaneous termination of the flow was as quick as 1 ms in order of magnitude. Such instantaneous gelation in the sub-millisecond-order timescale could not be forecasted from the observable megascopic gelation, which appeared to last from 102 ms to 103 ms in our naked-eye observation. The noteworthy gap between the timescale of the naked-eye-observed gelation and that of the true gel time at a localized spot determined by the high-speed motion picture should be noted to avoid excess agitation, which can result in total collapse into gel fragments of the just solidifying or already solidified gel under strong deformational influence by mechanical agitation, for example.