Laser-induced nanometer-nanosecond expansion and contraction dynamics of poly(methyl methacrylate) film studied by time-resolved interferometry

Masubuchi, T Furutani, H Fukumura, H Masuhara, H

T. Masubuchi et al., Laser-induced nanometer-nanosecond expansion and contraction dynamics of poly(methyl methacrylate) film studied by time-resolved interferometry, J PHYS CH B, 105(13), 2001, pp. 2518-2524

43

INGLESE

Article

Physical Chemistry/Chemical Physics

JOURNAL OF PHYSICAL CHEMISTRY B

1520-6106 → ACNP

105

13

2001

2518 - 2524

ISI

1520-6106(20010405)105:13<2518:LNEACD>2.0.ZU;2-1

The expansion and contraction behavior of a neat poly(methyl methacrylate) film is induced by 248 nm excimer laser exitation and directly measured by nanosecond interferometry. Above the ablation threshold (1400 mJ/cm(2)), th e film expands during the excitation laser pulse, and after 25% expansion o f the thickness, it undergoes fragmentation. Below the threshold, the expan sion rate is still high (a few nm/ns), and permanent swelling is observed a fter transient expansion and succeeding contraction. By decreasing the lase r fluence below 800 mJ/cm(2), permanent swelling was not observed, and at a few tens of mJ/cm(2), novel oscillatory expansion and contraction behavior was successfully detected. The expansion amplitude as a function of laser fluence indicates that the polymer film undergoes phase transition from gla ss to rubber upon excitation with a fluence higher than 450 mJ/cm(2). In th e glass state, the interpenetrating structure of the polymer film and assoc iated free volume distribution may be changed upon irradiation and photoche mical degradation should be involved. A dynamic view of these polymer prope rties explains well the unique expansion and contraction behavior. Furtherm ore, these laser-induced morphological changes are compared with those of p olymer films doped with aromatic molecules and considered in general.