Sources and control of instrumental drift in the surface forces apparatus

Instrumental drift in the surface forces apparatus (SFA) has been carefully scrutinized. A diversity of different contributions with different charact eristic time constants could be distinguished. The face seal of the functio nal attachment was identified as a potential weak point in the mechanical l oop of the instrument. We compared drift in three different design variants and found that the drift rate may vary over four orders of magnitude. We b elieve that the presented results are applicable to a number of different S FA types. (C) 2000 American Institute of Physics. [S0034- 6748(00)01112-6].