Matching the organic functional group on the silicon atom to the type of resin polymer to be combined can guide which silane coupling agent is used in a particular application. The organic group on the silane can be a reactive organic group (such as an organic functional group) or a non-reactive organic group. These groups can be hydrophobic or hydrophilic, or have a variety of thermally stable properties. Because of different organic structures, the solubility parameters of the groups are different; to a certain extent, this will affect the mutual penetration between the polymer system and the silicone system used for surface treatment. The choice of silane should include matching chemical reactivity, solubility, structural characteristics, and even the thermal stability of organosilanes with the same parameters in the polymer structure.
The number of reactive sites per unit specific surface area of the treated object (substrate) and the thickness of the surface covered by the silane coupling agent are the key factors that determine the amount of coupling agent required for the siliconization of the substrate surface. In order to obtain a monolayer coverage, the Si-OH content of the substrate needs to be determined first. It is known that the Si-OH content of most siliceous substrates is 4-12 pieces / µ㎡, so when uniformly distributed, 1 mol of silane coupling agent can cover about 7500 m2 of substrate. Due to the self-condensation reaction of silane coupling agents with multiple hydrolyzable groups, the accuracy of the calculation will be affected to some extent. If you use Y3SiX to treat the substrate, you can get a single molecular layer coverage that is consistent with the calculated value. However, Y3SiX is not practical because it is expensive and has poor hydrolysis resistance. In addition, the number of Si-OH on the surface of the substrate also changes depending on the heating conditions.
For example, under normal conditions, the number of Si-OH is 5.3 pieces / µ㎡. After heating at 400 ° C or 800 ° C, the Si-OH value can be reduced to 2.6 pieces / µ㎡ or <1 piece / µ. ㎡. Conversely, when the substrate is treated with hot and humid hydrochloric acid, a high Si-OH content can be obtained; when the surface of the substrate is treated with an alkaline detergent, a silanol anion can be formed. The wettable area (WS) of a silane coupling agent refers to the area (㎡ / g) that can be covered by a solution of 1g of silane coupling agent. If it is related to the surface area value (㎡ / g) of the silicon-containing substrate, the amount of silane coupling agent required for monolayer coverage can be calculated. Taking the filler as an example, the silane coupling agent W (g) required to form a monolayer on the surface of the filler is proportional to the surface area S (㎡ / g) of the filler and its mass, and it is proportional to the wettable area WS ( ㎡ / g). According to this, the formula for calculating the amount of silane coupling agent is as follows: The amount of silane (g) = the surface (S) value of some common fillers.