【作者】 储鸿；

【导师】 崔正刚； 殷福珊；

【作者基本信息】 江南大学 ， 应用化学， 2005， 硕士

【摘要】 本文研究了用薄板毛细渗透技术表征表面改性导致的粉体表面能及其各成分的变化的可能性。所研究的粉体包括硅胶、氧化铝、氢氧化镁和改性氢氧化镁。首先研究了用毛细渗透技术测定液体在粉体表面的接触角和表面能的成分,发现对粉体材料要区分其是否带有次级微孔,从而使用不同的理论公式。对于带次级微孔的粉体材料如薄层色谱分析用的商品硅胶,在与挥发性烷烃的蒸汽预接触过程中会发生明显的毛细凝聚效应。对这类粉体材料应用毛细渗透技术测定接触角或表面能的成分,必须定量校正毛细凝聚效应,方法是独立测定渗透液体蒸汽的饱和吸附量,计算出所谓的曲折度参数,并使用修正的Washburn方程。对商品硅胶板应用毛细渗透技术和修订的Washburn方程得到,无论是否预接触,正构烷烃及乙二醇显示零接触角,而1-溴代萘、二碘甲烷、甲酰胺和水显示非零接触角。基于毛细渗透获得的动态前进角和动态后退角相差很小,近似地取两者的平均值作为静态平衡接触角或Young接触角。由此测得的1-溴代萘和二碘甲烷在硅胶板上的接触角分别为16.5°和35.8°,与文献值十分吻合。相应地求得硅胶表面能的非极性成分分别为42.7和41.7mN/m,两者较为一致。基于甲酰胺-水、乙二醇-水和甲酰胺-乙二醇三对探针液体的毛细渗透求得的硅胶表面能的极性成分分别为7.03,7.04,和7.30 mN/m,彼此完全一致。吸附试验表明,氧化铝和氢氧化镁颗粒不具有次级微孔,其毛细渗透可以应用经典的Washburn方程。通过测定不同探针液体的接触角,进而求出的氧化铝和氢氧化镁的总表面能和表面能的组成彼此分别完全一致。氢氧化镁经用硬脂酸钠改性后表面能大大减小,致使常用的极性探针液体在其表面上的接触角变得大于90°,自发毛细渗透不能进行。依据1-溴代萘的毛细渗透结果计算出改性使氢氧化镁表面能的非极性成分从改性前的31.3mN/m下降到22.5mN/m。通过选用低表面张力的极性探针液体甲醇,乙醇以及辛醇进行毛细渗透试验,成功地计算出改性导致的氢氧化镁粉体表面能非极性成分的变化。当改性剂用量为0.5%时,非极性成分从改性前的5.88mN/m下降到1.08mN/m,其中γ+s趋向于零(0.012mN/m),而γ?s有更多还原

【Abstract】 The possibility of characterisation of particle surface energy and surface energy componentchanges due to surface modification by thin layer wicking technique is studied. The particlesconcerned include silica gel, aluminium oxide, and magnesium hydroxide with or withoutsurface modification. The contact angle of liquids on the particles is first studied and it isfound that the differentiation of particles with or without sub-pores is very important. Forparticles with sub-pores like silica gel capillary condensation takes place during pre-contactof the particle with volatile liquids, which strongly affects wicking velocity and need to beindependently corrected before calculating contact angle by typical Washburn equation. Thecapillary condensation effect can be quantitatively corrected by introducing a parameter,tortuosity, into typical Washburn equation, which can be calculated based on the saturatedadsorption of wicking liquid vapour on the particles. With commercial silicagel plate for TLC analysis by using wicking technique andapplying modified Washburn equation it is obtained that n-alkanes and ethylene glycol showzero contact angles, while 1-bromonaphthalene, diiodomethane, formamide and water shownon-zero contact angles. The difference between dynamic advancing and receding angles isfound to be so small that their average could be taken as the equilibrium or Young’s contactangle. With this approximation the measured contact angles of 1-bromonaphthalene anddiiodomethane on the silicagel plate are 16.1° and 35.8 ° respectively, well agreeing withliterature reported, and closed nonpolar component of the surface tension, 42.7 and41.7mN/m, are calculated correspondingly. The polar component of the surface tensionobtained based on the wicking of three pair of probe liquids, formamide-water, ethyleneglycol-water and formamide-ethylene glycol, are 7.03, 7.04, and 7.30mN/m, respectively,quite in good agreement with each other.The adsorption tests showed that, both aluminium oxide and magnesium hydroxide haveno sub-pores and their wicking can be deal with by typical Washburn equation. The totalsurface tension and the surface tension components of aluminium oxide magnesiumhydroxide obtained by wicking with different probe liquid are in good agreement with eachother, respectively.The surface energy of magnesium hydroxide decreases by modification with 0.5% stearicacid so greatly that the spontaneous wicking of typical polar probe liquids become impossible,or the contact angle of these liquid on the surface is higher than 90°. The wicking of1-bromonaphthalene is still possible and the nonpolar component of the surface free energy iscalculated to be 22.5mN/m, greatly reduced compared with that without surface modification.By wicking with methanol and ethanol the total polar component are successfully calculatedto be 1.08mN/m, also decreases compared to the 5.88mN/m before surface modification, andit is found that the γ +s tendts to be zero(0.012mN/m),while γ ?s increases. Increasingstearic acid amount to 1% leads to a very small further decrease of both nonpolar and polarsurface tension component and is not suggested.Compared with other methods such as wet adsorption and dispersing, wicking techniquecan provide not only the reliable results but also the detail change of surface tensioncomponents, which is significant for the selection of modifying agents and their addingconcentration and for the characterisation of their adsorption styles on particle surface.In addition,the surface tension components of n-butanol is calculated based on thewicking technique, but the accuracy is waiting for further confirming with other systems.更多还原