Abstract:
How does water behave when it is con ned to slits and pores of the order
of its own molecular size?? This question has been asked and debated for
decades. The present thesis is a body of work towards the development of a
novel technique to answer the above question. We use a quartz tuning fork
as a force sensor as it can detect forces as weak as a pico-Newton. We attach
a bre along the length of one of the arms of the tuning fork such that the
sharp tip of the bre protrudes beyond the length of the arm. The other arm
of the fork is xed to a piezo actuator. The bre tip is then immersed into
water in a liquid cell, and is brought close to the bottom surface of the cell,
which is atomically smooth freshly cleaved mica. Water is con ned between
the tip and mica surface as the tip is brought within a few nanometres of
the surface. With the help of the actuator piezo the tuning fork is oscillated
and a shear force is applied to the con ned water column. By recording the
change in amplitude and phase of the tuning fork, we get the shear response
of the liquid column. Viscoelastic behaviour was observed followed by shear
thinning as we approached towards the surface. It is also seen that the range
at which these behaviours are observed depends upon the shear frequency and
the shear rate applied. This behaviour closely resembles to liquids near their
critical points. Further work is being done to verify this analogy between
con ned liquid and liquid near its critical temperature. If veri ed this will
consolidate all the data so far in the literature and explain the seemingly
contradicting results.
