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 characteristic time constants could be distinguished. The face seal of the functional attachment was identified as a potential weak point in the mechanical loop 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 believe that the presented results are applicable to a number of different SFA types. (C) 2000 American Institute of Physics. [S0034- 6748(00)01112-6].