BOUNDARY LUBRICATION AND SHEAR PROPERTIES OF THIN SOLID FILMS OF DIOCTADECYL DIMETHYL AMMONIUM-CHLORIDE (TA100)

The friction and shear strength behaviour of thin films of a surfactant dioctadecyl dimethyl ammonium chloride (TA100) has been extensively studied. These films were of different types, such as Langmuir-Blodgett (LB), hexane-retracted, self-assembly and 'melt'; they were deposited on clean soda-lime glass and sapphire flats. The frictional force required to slide spheres of soda-lime glass and sapphire on these-flats was measured. The parameters investigated were (i) the contact pressure (in the range of 100-1900 MPa) between the sliding sphere and the flat, (ii) the number of friction cycles (up to 10(4)), (iii) the substrate temperature (range: 290-380 K), and (iv) the sliding velocity (range: 0.01-0.3 mm s-1). It was found that even a single monolayer of LB film of this material causes a dramatic reduction of the friction between a glass slider and a coated glass flat: for a clean glass sphere sliding on a clean glass slide, the coefficient of dynamic friction was 0.9, whereas it dropped to a low value of 0.05-0.06 when there was a single monolayer on it. On the glass, films of TA100 have been shown to be considerably more durable and tenacious than those of stearic acid; even after 10000 to-and-fro friction cycles on a single track, the coefficient of dynamic friction remained at a low value of approximately 0.06. The various results obtained by varying different parameters have been satisfactorily explained using Eyring's shear flow model.