Polycarbonate (PC for short) is a polymer containing carbonate groups in the molecular chain, which can be divided into aliphatic, aromatic, aliphatic-aromatic and other types according to the structure of the ester group. Among them, the aliphatic and aliphatic-aromatic polycarbonate has low mechanical properties, thus limiting its application in engineering plastics.
For a liquid system with a certain composition, its surface tension is constant at a certain temperature and pressure. If the surface area △A is increased, the system energy increase value AE=yA A, where y is the surface tension of the liquid.
Surface tension is a kind of interfacial tension. When two phases coexist, if one phase is a liquid and the other is a gas, the interaction force between the two phases is very small and can be ignored. The interfacial tension is the surface tension of the liquid; if two different liquid phases coexist or If the liquid phase and the still phase coexist, the interaction force between the two phases cannot be ignored. The force is the interfacial tension between the liquid and the liquid or between the liquid and the solid.
Liquid surface tension and solid critical surface tension
The surface tension of the liquid can be measured by the ring lifting method, the lifting plate method, the drop method and the bubble maximum pressure method. Refer to ASTM 1331-56, ASTM D 3825-90, ISO304-8 and other standards.
It is difficult to directly measure the surface tension of solids. The measurable critical surface tension of solids is used to measure the surface tension of solids. The critical surface tension of a solid can also be called wetting tension. To determine the critical surface tension of a solid, a series of known liquids with different surface tensions can be dropped on the solid surface, and the contact angle can be measured, and the surface tension of each liquid is in contact with the corresponding Plot the angle cosine and extrapolate the curve to co sf/-1. The corresponding surface tension value is the critical surface tension of the solid. The ASTM D 2578 standard can also be used to determine the critical surface tension of plastics.
Table 8-1 lists the surface tensions of some solvents and film-forming polymers, and lists the critical surface tensions of some substrates. It can be seen from Table 8-1 that the surface tension of most solvents is less than the surface tension of the film-forming polymer. Therefore, in solvent-based coatings, the solvent plays a certain role in reducing the surface tension of the system. The surface tension of the polymer increases with the increase of the relative molecular mass, but after the relative molecular mass reaches 2000 to 3000, the change is small. When the paint is recoated, the original dry film is the coated substrate, and its surface tension is different from the original substrate.
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