  This study has numerically investigated the effect of surface wettability on
two-phase immiscible flow and dynamics of droplet pinch-off in a T-junction
microchannel using finite element method. A conservative level set method
(CLSM) has been adopted to capture the interface topology in squeezing regime
($Ca_c <10^{-2}$) for wide flow rate ratio ($1/10 \leq Q_r \leq 10$) and
contact angle ($120^{\circ} \leq \theta \leq 180^{\circ}$). Based on the
instantaneous phase profiles, droplet formation stages are classified as
initial, filling, squeezing, pinch-off and stable droplet. Wettability effects
are insignificant in filling stage. However, hydrophobic effects are more
visible in squeezing and pinch-off stages. Engineering parameters have
generally shown complex dependence on dimensionless parameters ($Ca_c$, $Q_r$,
$\theta$). Capturing the instantaneous interface evolution has revealed droplet
shape senstivity with the contact angle. Interface profiles transform from
convex into concave immediately for hydrophobic ($120^{\circ} \leq \theta \leq
135^{\circ}$) whereas slowly for super hydrophobic ($150^{\circ} \leq \theta
\leq 180^{\circ}$) conditions. In contrast to the literature, pressure in
dispersed phase is not constant, but it is an anti-phase with pressure in
continuous phase. Comparing the filling and pinch-off time based on the
pressure and phase profiles has brought new insights that the droplet pinch-off
mechanism can be elucidated by installing the pressure sensors even without the
flow visualization and phase profiles. The interface curvature adopts a
flattened to a more concave shape when the Laplace pressure varies from a
smaller to a higher value. The interface neck width (2r) shows an increasing
trend up to a threshold value and then decreases linearly with the contact
angle.
