Relaxation dynamics of polymer thin films
under solvent annealing process
Hiroyuki Aoki (J-PARC Center, Japan Atomic Energy Agency)
1. Introduction
Polymer thin films have been widely used in various fields in our daily life.

A spincoating method has been often used to fabricate a polymer thin film with a thickness lessthan micrometers. In a spin coating process, a polymer solution flows on a spinning substrate
and the solvent evaporates rapidly. Therefore, an as-spun thin film is in an un-equilibrium
state. To reach an equilibrium state of a polymer thin film, an annealing method in vapor of agood solvent has been often used. Many research groups has extensively studied the relaxation
dynamics of polymer materials at the surface and interface under a thermal annealing condition;
however, little is known about the relaxation process in the solvent annealing. Therefore, in thecurrent study, the polymer dynamics in a thin film under solvent annealing conditions will be
examined by neutron reflectometry.
2. Experiment
The layered polymer thin film sample as shown
dPMMAin Figure 1 was prepared by hydrogenated and20 nm
deuterated poly(methyl methacrylate) (hPMMA

hPMMA
dPMMA

100 nmand dPMMA, respectively). A toluene solution ofhPMMA

hPMMA was spin-coated on a glass plate to form

dPMMA

a 20-nm-thick PMMA film and it was floated on aSi wafer

water surface. The hPMMA on water is scoopedby a Si wafer covered with a 20-nm-thick film of Figure 1: Structure of the 5-layer stacked
dPMMA. By repeating the deposition of dPMMA

film of dPMMA and hPMMA.

and hPMMA films, 5-layered stacked films of dPMMA and hPMMA with a total thickness of
100 nm were obtained. A 100-nm-thick film of dPMMA was also prepared.
The NR measurement was carried out at BL16 in MLF, J-PARC. The in situ measurement
in an annealing process was conducted using a neutron beam with a wavelength of 0.24 – 17.6
nm (double-frame mode) and at an incident angle of 1.2◦ . The data acquisition was started
immediately after the sample film and chloroform (0.5 mL) was sealed in an aluminum chamberwith a volume of ∼100 cm2 .
3. Results
Figure 2 shows the time evolution of the NR spectrum for a 100-nm-thick dPMMA filmin the solvent annealing process in chloroform vapor. It can be seen that the reflectivity andthe fringe gap decreased with the increase of time. The scattering length densities (SLDs) for0.4

1.010 3

1.2
10 4020406080

Time / min100120Figure 2: Time evolution of NR spectrum for a
100-nm-thick dPMMA film in chloroform vapor.

10 10.6

q / nmReflectivity

10 20.8

1000.410 10.6

q / nm0.2

100Reflectivity

0.2

10 20.8
1.0

10 3

1.2

10 4020406080

Time / min100120

Figure 3: Time evolution of NR spectrum for a
5-layered stacked film of dPMMA and hPMMA
in chloroform vapor.

dPMMA and chloroform are 6.88 × 10−4 and 2.38 × 10−4 nm−2 , respectively. The absorptionof chloroform molecules from vapor lowers the neutron refractive index contrast between the air
and the dPMMA film, resulting in the decrease of the reflectivity. The decrease of the fringe
gap indicates the increase of the film thickness. Thus, it was found that the PMMA film absorbs
the chloroform molecules from the vapor phase and that the thickness increased by swelling of
PMMA with chloroform.
The time evolution of the NR spectrum for the 5-layered dPMMA/hPMMA film is shown inFigure 3. At the initial state, the peaks at 0.55 and 0.80 nm−1 are found in the NR spectrum,
which are assigned to the correlation of the thickness of the 20-nm-thick layers of dPMMA andhPMMA. Moreover, a narrow fringe pattern attributed to the total thickness is also observed.
After the annealing time of 18 min, the peaks for the dPMMA/hPMMA layer disappeared andonly the correlation signal from the total thickness is seen in the NR spectrum. This indicatesthat the layered structure of dPMMA and hPMMA collapsed by the inter-diﬀusion of the PMMAchains.
4. Conclusion
The in situ NR measurement revealed that the structure relaxation of a PMMA thin films inan solvent annealing process in chloroform vapor completed in 20 min by the inter-diﬀusion of thepolymer chain. The quantitative relaxation dynamics will be discussed from the time evolutionof the SLD distribution for each component by the detailed analysis of the NR spectra.