Photon Factory Activity Report 2014 #32 (2015) B

BL-15A2 and BL-10C/2014G115

Nanostructure Evaluation of Block Copolymer Photonic Filmsby Ultra-Small Angle X-ray Scattering
Atsushi Noro* and Yusuke Tomita
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
1 Introduction
Photonic crystals are periodic structures composed ofcomponents with different refractive indices. An
alternating layer stack with multiple refractivecomponents reflects the light with a specific wavelength
depending on the layer thicknesses and refractive indicesof components. Lamellar nanophase-separated structuresof block copolymers (BCPs) can be applied as such one
dimensional photonic crystals; however, large molecularweight (Mn > 300 kg/mol) BCPs are normally required toreflect visible light with a wavelength larger than 400 nm,
which are not easy to synthesize. Here we report
preparation of BCP photonic films swollen with anonvolatile ionic liquid (IL), where the molecular weightof the BCP used for photonic film preparation is less than
100 kg/mol. [1]2 Experiments
Thin films of neat polystyre-b-poly(2-vinyl pyridine)(PS-P2VP, Mn = 78k, PS = 0.5) were prepared on glass or
polyimide substrates by spin-coating of the polymer
solutions, which were followed by solvent vapor
annealing. Photonic films reflecting blue visible light(wavelength ~ 400 nm) were prepared by depositing
several drops of IL onto the neat PS-P2VP films.
Nanostructures of the films were observed bytransmission electron microscopy (TEM), small-angle Xray scattering (SAXS), and ultra-small angle X-ray
scattering (U-SAXS).
3 Results and Discussion
An TEM image of the cross-sections of a neat PSP2VP film was shown in Fig 1a, where symmetriclamellar nanophase-separated structure with domain
periodicity (D) of approx. 33 nm was seen. On the otherhand, asymmetric lamellar structure with D of approx.
106 nm was observed in a TEM image of an IL-deposited
PS-P2VP film (Fig 1b), suggesting swelling of the filmwith the IL occurred at the nanoscopic scale.
To estimate D of the IL-deposited PS-P2VP film morequantitatively, both conventional SAXS and U-SAXS
were measured at Photon Factory. The beamlines usedfor SAXS and U-SAXS were BL-10C and BL-15A2,respectively. SAXS provided multiple peaks on theprofile (bottom profile in Fig 1c), but the first order peak
was not observed in the SAXS profile. On the other hand,
U-SAXS profile (top profile in Fig 1c) showed multiple
integer order peaks including the first order peak. D wasdetermined to be 135 nm from the relationship of D =2/(qn/n), where qn is the scattering vector of the nthorder peak and n is the integer number of the relative q
value of the peak.
In summary, U-SAXS was found to be very useful andeffective for measuring nanostructures with D of over 100
nm, which is usually difficult to measure by SAXS.

Fig 1. (a) TEM image of neat PS-P2VP. (b) TEM imageof IL-deposited PS-P2VP. (c) U-SAXS (top) and SAXS
(bottom) profiles of IL-deposited PS-P2VP.
Acknowledgement
Use of synchrotron X-ray source was supported byPhoton Factory, KEK, Japan (no. 2014G115 (A.N.)). The
authors thank Prof. N. Shimizu and Prof. N. Igarashi at
Photon Factory, KEK for their kind assistance in USAXS measurements. This work was financially
supported through KAKENHI grant no. 24685035 (A.N.)
and no. 25620172 (A.N) by JSPS, Japan.
References[1] A. Noro, Y. Tomita, Y. Shinohara, Y. Sageshima, J. J.
Walish, Y. Matsushita, E. L. Thomas, Macromolecules
47, 4103-4109 (2014)
Research Achievements
1. Patent (WO/2014/185426) pending.
2. The research about block copolymer photonic films
was featured in the Chemical Daily newspaper (20June-2015 issue), “Scientific News” of Kobunshi(Sep-2014 issue), “Topics” of Ceramics Japan (Nov2014 issue).
*noro@nagoya-u.jp