胶粘剂/胶黏剂为什么能粘接的胶接理论之吸附理论

胶接理论之吸附理论

一切原子或分子之间都存在着相互作用的力，这种作用力可分为强作用力（即主价力或化学键）和弱作用力（即范德华力或偶极力）。而吸附分为物理吸附和化学吸附。物理吸附是分子间力的吸附，即范德华力作用的结果；化学吸附是发生在化学反应形成的化学键的吸附。

吸附理论认为，胶接产生的黏附力主要来源于胶与被粘物之间界面上两种分子之间相互作用的结果，所有的液体-固体分子之间都存在这种作用力，这些作用力包括化学键力、范德华力和氢键力。胶黏剂分子与被胶接材料表面分子的相互作用过程有两个阶段，首先是液体胶黏剂分子由布朗运动向被胶接材料表面移动，使二者所有的极性基团或链节相互靠近，在此过程中可采用升温、施加压力、降低胶黏剂液体黏度等措施，都有助于布朗运动的加强。其次是吸附力的产生，当胶黏剂的表面分子与被胶接材料的表面分子间距离小于0.5nm时，分子间便产生吸附作用，就产生了范德华力或氢键力的结合，并使分子间距进一步缩短达到能处于最大稳定状态的距离，完成胶接作用。根据吸附理论，如果胶分子中极性基团的极性越大，数量越多，则对极性被粘物的胶接强度就越高，但胶黏剂的极性过高，有时会严重妨碍润湿过程的进行；极性胶黏剂与非极性被粘物或非极性胶与极性被粘物粘接，由于分子间排斥，不利于分子的接近，不能产生足够的分子间力，所以粘接力很差；而非极性胶与非极性被粘物结合，由色散力产生的粘接强度较小。

吸附理论把胶接主要归结于胶黏剂与被粘物分子间力的作用，但它不能充分解释胶与被粘物之间的粘接力有时大于胶黏剂本身这一事实；也不能很好解释有的胶极性大，而粘接力差，有的胶极性小，却粘接力大的现象等，这不仅说明这一理论的局限性，而且它所能解释的现象中，也有例外的情况。

Adsorption theory of bonding theory

All atoms or molecules interact with each other, which can be divided into strong force (i.e. principal valence force or chemical bond) and weak force (i.e. van der Waals force or couple force). Adsorption can be divided into physical adsorption and chemical adsorption. Physical adsorption is the result of van der Waals force; Chemisorption is the adsorption of chemical bonds formed in chemical reactions.

According to the adsorption theory, the adhesive force is mainly derived from the interaction between two molecules on the interface between the adhesive and the adherent. All liquid solid molecules have such forces, including chemical bond force, van der Waals force and hydrogen bond force. There are two stages in the process of the interaction between adhesive molecules and the surface molecules of the bonded material. The first stage is that the liquid adhesive molecules move from Brownian motion to the surface of the bonded material, so that all the polar groups or chain links of the two molecules are close to each other. In this process, heating, applying pressure, reducing the viscosity of the adhesive liquid and other measures can help to strengthen the Brownian motion. The second is the generation of adsorption force. When the distance between the surface molecules of the adhesive and the surface molecules of the bonded material is less than 0.5nm, there will be adsorption between the molecules, resulting in the combination of van der Waals force or hydrogen bonding force, and further shorten the molecular distance to reach the maximum stable state to complete the bonding. According to the adsorption theory, if the polarity of polar groups in the adhesive molecule is larger and the number of polar groups is more, the bonding strength of the polar adherent will be higher. However, if the polarity of the adhesive is too high, sometimes it will seriously hinder the wetting process; The adhesion between polar adhesive and non-polar adhesive or between non-polar adhesive and polar adhesive is very poor due to intermolecular repulsion, which is not conducive to the approach of molecules and can not produce enough intermolecular force; The bonding strength produced by dispersion force is smaller when nonpolar adhesive is combined with nonpolar adhesive.

According to the adsorption theory, the bonding is mainly attributed to the intermolecular force between the adhesive and the adherent, but it can not fully explain the fact that the adhesive force between the adhesive and the adherent is sometimes greater than the adhesive itself; It also can't explain the phenomenon that some glue polarity is big, but adhesive force is bad, some glue polarity is small, but adhesive force is big, etc. this not only shows the limitation of this theory, but also there are exceptions in the phenomena that it can explain.