TY  - JOUR
AU  - Liu, Fei
AU  - de Beer, Sissi
AU  - van den Ende, Dirk
AU  - Mugele, Frieder
TI  - Atomic force microscopy of confined liquids using the thermal bending fluctuations of the cantilever
JO  - Physical review / E
VL  - 87
IS  - 6
SN  - 1539-3755
CY  - College Park, Md.
PB  - APS
M1  - FZJ-2013-04327
SP  - 062406
PY  - 2013
AB  - We use atomic force microscopy to measure the distance-dependent solvation forces and the dissipation across liquid films of octamethylcyclotetrasiloxane (OMCTS) confined between a silicon tip and a highly oriented pyrolytic graphite substrate without active excitation of the cantilever. By analyzing the thermal bending fluctuations, we minimize possible nonlinearities of the tip-substrate interaction due to finite excitation amplitudes because these fluctuations are smaller than the typical 1 Å, which is much smaller than the characteristic interaction length. Moreover, we avoid the need to determine the phase lag between cantilever excitation and response, which suffers from complications due to hydrodynamic coupling between cantilever and fluid. Consistent results, and especially high-quality dissipation data, are obtained by analyzing the power spectrum and the time autocorrelation of the force fluctuations. We validate our approach by determining the bulk viscosity of OMCTS using tips with a radius of approximately 1 μm at tip-substrate separations >5 nm. For sharp tips we consistently find an exponentially decaying oscillatory tip-substrate interaction stiffness as well as a clearly nonmonotonic variation of the dissipation for tip-substrate distances up to 8 and 6 nm, respectively. Both observations are in line with the results of recent simulations which relate them to distance-dependent transitions of the molecular structure in the liquid.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000320771000002
DO  - DOI:10.1103/PhysRevE.87.062406
UR  - https://juser.fz-juelich.de/record/138059
ER  -