THESIS
2016
xv, 49 pages : illustrations (some color) ; 30 cm
Abstract
The behavior of Pt-coated Janus particle in an aqueous solution of hydrogen peroxide is studied
using atomic force microscopy (AFM). The catalytic chemical reaction between the platinum and
hydrogen peroxide generates a propulsion force to propel the Janus particle in the liquid. To characterize
the self-propelling nature of the Janus particle, we designed and assembled a new AFM
probe with a Janus particle glued on the free end of the hanging fiber. The self-propulsion force
generated by the Janus particle is then measured by recording and analyzing the capillary-force-versus-travel-distance curve and the power spectrum ∣z(w)∣
2 of the modified hanging fiber probe at
an optimal immersion depth of the liquid-air interface. Meanwhile, theoretical attempts were made
to determine th...[
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The behavior of Pt-coated Janus particle in an aqueous solution of hydrogen peroxide is studied
using atomic force microscopy (AFM). The catalytic chemical reaction between the platinum and
hydrogen peroxide generates a propulsion force to propel the Janus particle in the liquid. To characterize
the self-propelling nature of the Janus particle, we designed and assembled a new AFM
probe with a Janus particle glued on the free end of the hanging fiber. The self-propulsion force
generated by the Janus particle is then measured by recording and analyzing the capillary-force-versus-travel-distance curve and the power spectrum ∣z(w)∣
2 of the modified hanging fiber probe at
an optimal immersion depth of the liquid-air interface. Meanwhile, theoretical attempts were made
to determine the physical origin of the propulsion force. A new propulsion peak was found in the
measured power spectrum ∣z(w)∣
2 in the low frequency range of 100 - 300 Hz. The concentration
dependence of the propulsion peak location and height were analyzed to find the catalytic chemical
reaction rates between Pt and hydrogen peroxide and the height fluctuation of the contact line near
the Janus particle equator. The obtained values of the production rate k
1 of the intermediate product Pt(H
2O
2) and the production rate k
2 of the solute molecule O
2 for the catalytic reaction are
found in reasonable agreement with those obtained from previous experiments by particle tracking.
The fluctuating height h of the contact line is analyzed theoretically. Compared to the traditional
method of particle tracking, the AFM measurement is faster and more accurate, and provides a new
reliable way of determining the chemical reaction rate. The newly developed AFM method will
become a useful tool for the study of dynamic properties of various micro- or nano-scale systems.
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