Rheology of Thin Organic Films

This paper deals with the effects of contact pressure and temperature on the shear strength of thin organic films. The experimental method involves depositing the material as thin films (ca. 3 nm to 500 nm) on smooth glass surfaces. The film is sheared by sliding over it indenters of fired glass. By varying the indenter radius from 4 μm to 2.5 mm and the load from 10 mg to 20 g, the contact pressure may be varied from 107 Pa (1.4 × 103 P.s.i.) to 8 × 109 Pa (12 × 105 p.s.i.). The temperature dependence of the shear strength is also studied. Two types of organic materials have been investigated. These range from simple low molecular weight compounds such as stearates, to more complex high molecular weight polymers, for example P.M.M.A. The shear strength of these films has been compared with the bulk shear properties and consideration has been given to the molecular processes occurring during shear.