Confined liquids: Solvation forces in liquid alcohols between solid surfaces

The force profile between a silicon nitride tip and solid substrates in short linear alcohols (CnH2n+O-2, n = 2-8) has been measured with an atomic force microscope. On a hydrophilic substrate like mica the profile was oscillatory. The period was longer than the length of a single molecule and increased proportional to the chain length. This indicates that the molecules are in a roughly upright position and may form a double-layer. On a hydrophobic substrate the force profiles showed two distinct jumps that are independent of the chain length of the alcohols, indicating that the molecules lie flat on a hydrophobic substrate.