共軛導電高分子Poly(3,4-ethylenedioxythiophene) (PEDOT) 為一疏水性材料，在與poly(styrene sulfonate) (PSS) 混摻後可得均勻之水溶液。本研究以X光散射工具觀察兩種混摻比例下PEDOT:PSS系統中導電高分子的聚集(aggregation)情況，藉由比較PSS/PEDOT重量比例 r = 2.5以及r = 6之PEDOT:PSS膠體溶液與薄膜內部結構之差異，進而了解PSS混摻比例對系統穩定性的影響，並以實驗結果建立PEDOT:PSS系統在此兩種混摻比例下的結構模型。本研究所使用的X光散射工具包含小角度X光散射(small-angle X-ray scattering, SAXS)、掠角小角度X光散射(grazing-incident small-angle X-ray scattering, GISAXS) 以及X光反射 (X-ray reflectivity, XRR)。研究之樣品溶液固含量分別為1.2 wt%, 0.8 wt%, 0.4 wt%與0.2 wt%，並以旋轉塗布方式在矽基材上形成約90奈米之薄膜樣品，藉由降低溶液固含量，得以放大水對PEDOT聚集的作用。SAXS實驗結果顯示PEDOT:PSS膠體溶液由粒徑約5奈米之圓柱狀顆粒組成，並有尺寸約200奈米之碎形結構，r = 2.5的溶液中PEDOT傾向於形成較大型的聚集，聚集的結構也更緻密。GISAXS與XRR實驗結果顯示PEDOT:PSS薄膜內部為長橢球所組成之碎形結構，橢球之長軸約45奈米，隨著溶液固含量的降低，橢球之聚集更明顯，其中，又以r = 2.5的薄膜內部PEDOT聚集情況更嚴重。薄膜表面結構分析顯示r = 6的薄膜表面附近結構較鬆散、具有一個粗糙的表面，而r = 2.5的薄膜整體較為緻密。總和各實驗結果，相對較高的PSS混摻比例將可避免PEDOT:PSS系統中PEDOT的聚集，使導電高分子均勻分布。

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an inherently conductive polymer, and usually doped with poly(styrene sulfonate) (PSS) in order to be well-dispersed in its aqueous solution, since PEDOT itself is hydrophobic. In this work, we aim to show the effect caused by PSS on the stability of PEDOT:PSS system by comparing PEDOT:PSS systems of PSS/PEDOT mass ratio r = 2.5 vs. 6. For both the colloidal dispersion and the solid thin film, structural models of PEDOT:PSS systems were constructed to facilitate analysis of synchrotron-based small-angle X-ray scattering (SAXS), grazing-incident small-angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR) data. Colloidal dispersions with solid contents ranging from 1.2 to 0.2 wt% and the corresponding spin-cast films were observed in the attempt to emphasis the stability strength of PSS in severe condition, in which water is much more than PEDOT in its amount. According to SAXS results, PEDOT:PSS dispersion generally comprises colloidal particles (of a PEDOT-rich core ca. 5 nm in size) as well as their fractal aggregates up to ca. 200 nm in diameter. It was observed that the colloidal particles tend to aggregate with decreasing PSS content. As for structural characterization of PEDOT:PSS thin film, results from GISAXS analysis reveal a fractal structure composed of prolate particles (~45 nm) in the film, along with some degree of particle aggregation, which is more severe at r = 2.5. GISAXS analysis also suggests that, there is no significant structural differences between bulk layer and surface layer in the case of r = 2.5 whereas the surface layer of high-PSS-ratio system appears to be less compact in its structure than the bulk layer in the case of r = 6. Meanwhile, XRR result provides in-depth composition analysis of the thin film, and indicates higher surface roughness in films with high PSS ratio. Integrating all experimental observations, it is concluded that an adequately high PSS content in PEDOT:PSS greatly decreased the aggregation of PEDOT particles in both the aqueous dispersion and thin-film states.

1. Introduction
1.1.1 Background
1.1.1 Investigation on PEDOT:PSS colloids in aqueous dispersion
1.1.2 Investigation on PEDOT:PSS thin film
1.2 Objective and approach
2.Experimental details
2.1 Material and specimen preparation
2.2 Instruments
3. Data analysis
3.1 Small-angle X-ray scattering data analysis
3.2 Grazing-incident small-angle X-ray scattering data analysis
4. Results and discussion
4.1 Structural characterization of PEDOT:PSS colloidal dispersion
4.1.1 Small particles and inter-particle relationship
4.1.2 Fractal aggregates
4.1.3 Dependence of PEDOT aggregation on PSS/PEDOT ratio
4.2 Structural characterization of PEDOT:PSS thin film
4.2.1 Fractal structure and some aggregates
4.2.2 Structural difference between bulk layer and surface layer
4.2.3 Surface roughness
5. Conclusions
References
Appendix A. SAXS profiles described by form factor, structure factor and power law
Appendix B. SAXS profile fitting results by different form factors
Appendix C. GISAXS 2D patterns
Appendix D. GISAXS profile fitting results: aggregates in PEDOT:PSS thin film

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