Ould Ehssein C, Serfaty S, Griesmar P, Le Huerou J Y, Martinez L, Caplain E, Wilkie-Chancellier N, Gindre M, Gouedard G, Figuiere P
Equipe Circuits, Instrumentation et Modélisation Electronique, Université de Cergy, Neuville sur Oise, 95031 Cergy Pontoise Cedex, France.
Ultrasonics. 2006 Dec 22;44 Suppl 1:e881-5. doi: 10.1016/j.ultras.2006.05.035. Epub 2006 Jun 5.
The last decades have seen the development of sol-gel (SG) process currently used to develop new materials in a wide range of scientific applications. The SG process leads to an oxide macromolecular network through a sol (liquid phase) to gel transition. To optimize this process, the control of the kinetic of the chemical reaction is required. This kinetic can be deduced from the temporal evolution of the viscoelastic parameters. Upto date no complete investigation during the SG formation can be achieved by a unique non-destructive technique. In this paper, we present an ultrasonic technique to measure the viscoelastic parameters (storage G' and loss G'' shear moduli) of the gel material during its formation. By using a suitable model which takes into account the mass loading on the surface, the viscoelastic parameters of these materials are accurately deduced. In order to study the efficiency of this technique, silica gels transition is monitored at various formation temperatures and for different initial hydrolysis molar ratio (h). In addition, the monitoring is performed at different oscillatory shear measurements in the 6-54 MHz frequency range to determine a new characteristic time t(vs) corresponding to the moment when the material is no more a newtonian liquid. This characteristic time is then compared to the gelation time t(g) determined by rheological or acoustic audible range methods. Thus the new characteristic time is also a good criterion to characterize earlier the SG matrix transition. Our AT-cut quartz technique using our model can also be used as a high frequency rheometer for the sol-gel materials.
在过去几十年里，溶胶 - 凝胶（SG）工艺得到了发展，目前该工艺被用于众多科学应用领域中新型材料的研发。SG工艺通过溶胶（液相）到凝胶的转变形成氧化物大分子网络。为了优化这一工艺，需要控制化学反应动力学。这种动力学可以从粘弹性参数的时间演变中推导出来。到目前为止，在SG形成过程中还无法通过一种独特的无损技术进行全面研究。在本文中，我们提出了一种超声技术，用于测量凝胶材料在形成过程中的粘弹性参数（储能模量G'和损耗模量G''）。通过使用一个考虑了表面质量负载的合适模型，可以准确推导出这些材料的粘弹性参数。为了研究该技术的有效性，在不同的形成温度和不同的初始水解摩尔比（h）下监测硅胶的转变。此外，在6 - 54 MHz频率范围内的不同振荡剪切测量条件下进行监测，以确定一个新的特征时间t(vs)，该时间对应于材料不再是牛顿流体的时刻。然后将这个特征时间与通过流变学或声学可听范围方法确定的凝胶化时间t(g)进行比较。因此，这个新的特征时间也是更早地表征SG基质转变的一个良好标准。我们使用该模型的AT切石英技术也可以用作溶胶 - 凝胶材料的高频流变仪。
