## 3 Results
### In Situ FTIR  
FTIR allows for the determination of the chemical and physical structure of material via interpretation of the spectrum of characteristic bands that is produced by the excitation vibrations of molecular bonds following absorption of IR photons in the material [20]. FTIR is particularly powerful in the analysis of the polymeric systems under different environmental conditions. The chemical identity of the chains is achieved by detecting the chemical groups present in the polymer, the monomer sequences, and the stereoregularity. Additionally, one can observe the local conformation of individual chains as well as conformational change when macroscopic fields such as temperature, pressure, and relative humidity are applied to the sample. Due to these advantages, a combination of FTIR and SANS represents an outstanding investigation approach for understanding the detailed mechanism of structure formation and structural changes in multiphase polymeric systems such as semi-crystalline polymers, copolymers, or polymer composites: the conformational change of the molecules that make up such a complex system can be monitored by FTIR, while the hierarchy of morphologies occurring in different phases can be qualitatively and quantitatively characterized by SANS with contrast variation. Polymeric materials are very sensitive to slight variations of external conditions; therefore, it is more useful to apply the combination of these techniques in a simultaneous approach, when in situ or time-resolved analyses of rapid structural changes or irreversible processes can be performed. We previously conducted pioneering work in developing a simultaneous SANS and FTIR spectroscopy measuring system using the KWS-2 diffractometer in 2014. Using this approach we studied the structure of a d-sPS co-crystalline film with various guest molecules [10]: higher-order crystalline structures were characterized by SANS while the local molecular configuration and molecular packing were characterized by FTIR. We demonstrated that the FTIR data were useful for interpreting and analyzing SANS profiles when larger molecules are included in the sPS films [21]. To extend the measurable Q-range for wide-angle neutron scattering (WANS), we used this approach on the time-of-flight SANS instrument TAIKAN installed at the Material and Life Science Experimental Facility (MLF), Japan Proton Accelerator Research Complex (J-PARC, Tokai, Japan) [22; 23]. The old measurement system tested with the KWS-2 consisted of a portable FTIR spectrometer Perkin-Elmer Spectrum Two (PerkinElmer, Rodgau, Germany) and an optical system made up of six mirrors. For an easier optical path adjustment, higher light utilization efficiency, and proper use of the available space on the sample stage of the KWS-2, and for the installation of a device for the measurement of polarization-dependent infrared absorption and a more complex sample environment, the optical system including the FTIR spectrometer was redesigned, using the experience accumulated in [22]. A new FTIR spectrometer (JASCO VIR-200, JASCO Deutschland GmbH, Pfungstadt, Germany) is currently in regular use for conducting FTIR measurements in transmission geometry, with the IR beam going through the sample coaxially with the neutron beam (Figure 1): the two optical ports in the same lateral face, the outlet port for emitting parallel light and the inlet port for the incoming light, enable a great flexibility in designing the optical system and accommodating special sample environments (Figure 1b,c). At the same time, this geometry is paving the way for the installation of an in situ ATR-FTIR option that can be used simultaneously with SANS in the near future for an optimal investigation of liquid samples. In the current geometry, only the two Al-coated quartz plates (LASER COMPONENTS GmbH, Olching, Germany) are left (elements 3 and 4 in the scheme of Figure 1a).