The monomeric unit of the PMMA polymer is shown here. Each atom or group of atoms represents a coarse-grained bead in the simulation. Norrish type I correspond to a break in the bond, whereas Norrish type II is a break in the C–CO bond.
Chemical reactions taking place in the substrate upon laser induced bond breaks.
(Color online) Snapshots from simulations for the three different cases: (a) heating (at ), (b) Norrish type I reactions (at ), and (c) Norrish type II reactions (at ). The fluence is and the pulse width is . The gray circles correspond to coarse-grained beads in original polymer molecules, the yellow circles represent radicals and beads with thermally broken bonds, the green circles represent small gas molecules, and the blue circles represent double bonded carbon atoms. The associated xy plot shows full density (red) and contribution to density from thermally broken bonds, radicals, and gaseous particles, including monomer and polymer fragments (blue) as a function of distance from the initial surface.
(Color online) Contour plot of pressure (in gigapascal) as a function of depth from surface and time at the fluence of for (a) heating, , (b) heating, ; (c) Norrish type I, ; and (d) Norrish type II, .
(Color online) Contour plot of fraction of beads with thermally broken bonds per layer as a function of depth from surface and time at the fluence of for (a) heating, and (b) heating, .
The total number of broken bonds, , vs time for fluences of (squares) and (diamonds) along with their least squares fits (solid lines). Also shown along the right and top axes are the derivatives , for the fluence, computed from the numerical differentiation of raw data (circles), from the differentiation of polynomial fit to (dashed line), and from the optimized fit to the polynomial’s derivative (solid line).
(Color online) Contour plot of the fraction of beads representing the transformed substrate per layer as a function of depth from surface and time at the fluence of and for (a) Norrish type I and (b) Norrish type II.
The evolution of the total number of transformed beads, , for Norrish type I (squares) and for Norrish type II (triangles) cases at fluence. The corresponding least squares fits are shown with solid lines.
(Color online) Chemical composition of the ablation plumes at fluence of and for heating (blue), Norrish type I (red), and Norrish type II (green) reaction cases. Only clusters in the mass range of are shown.
Ablation yields (and average sizes) expressed in number of equivalent MMA units ejected.
Article metrics loading...
Full text loading...