Abstract: [Background] Block copolymers can spontaneously self-assemble into various micro-scale morphologies under the various external fields, which have an extensive potential on the application of the electronics, information, chemistry and biology, etc. However, the self-assembly process is still a "black box", the understanding is still limited to the evolution of morphology during the varying external conditions.[Purpose] This study aims to investigate the self-assembly behavior of Poly(styrene)-block-poly (acrylic acid) (PS-b-PAA) in the temperature field by using in-situ synchrotron radiation small-angle X-ray scattering (SAXS).[Methods] SAXS experiments were performed on the BL16B1 beamline of Shanghai Synchrotron Radiation Facility (SSRF). Energy was selected as 10 keV and the wave length is 0.124 nm. 2D SAXS patterns were recorded by Mar165 CCD with pixel size of 79 μm×79 μm. A sample-to-detector distance of 1946 mm was chosen. The temperatures of the specimens were monitored by using a Linkam thermal stage THMS600 (Linkam scientific instruments). One-dimensional integrated intensity curves were obtained from 2D SAXS patterns by self-developed software. PS-b-PAAs (PS:PAA=3000:5000) were used directly as purchased from Sigma-Aldrich Inc.[Results] The in-situ SAXS experiment shows that the center of scattering peak was shifted with increasing temperature from q≈0.73 nm^-1 to q≈0.39 nm^-1, which was also accompanied by the varying of full width of half maximum, integral area, and maximum value of SAXS peak. A phase transition temperature was estimated as T_c=128℃ and the temperature width of transition is 5℃. Pair distance distribution function was used for the analysis of SAXS data.[Conclusion] With increasing temperature, the length of particle decreased gradually and body perforated, A rod-like shape with an undulating surface exists before the phase transition. At the temperature higher than T_c, the particle was degraded from the rod-like shape changes to a near-spherical shape still contains hole residue. The particles grow and gradually condense into a larger sphere with a diameter of~30 nm at the later stage.

Key words: Block copolymer, Self-assembly, SAXS, Synchrotron radiation