Interfacial interactions betweenconjugated polymers and carbonnanotubes are pivotal in determining the device performance of nanotube-basedpolymer electronic devices. Here, we report on interfacial structuresand crystallization kinetics of poly(3-hexylthiophene) (P3HT) in thepresence of single-walled carbon nanotubes (SWNTs) in anisole by meansof transmission electron microscope (TEM) and ultraviolet–visible(UV–vis) absorption spectroscopy. Confined on SWNT surfaces,the P3HT forms nanofibril crystals perpendicular to the long axisof SWNTs. The equilibrium dissolution temperature of the P3HT crystalsin anisole is determined to be 381 ± 10 K according to the Hoffman–Weeksextrapolation approach. Upon cooling, the polymer solution spontaneouslyundergoes a time-dependent chromism. Various kinetics factors suchas crystallization temperature, concentration, and SWNT loading havebeen investigated. It is found that the growth rate (G) of the crystals scales with concentration (C)as G∝ C1.70±0.16. The Avrami model is utilized to analyze the nucleation mechanismand the Avrami exponents vary between 1.0 and 1.3. The Lauritzen–Hoffmantheory is applied to study the chain-folding process. The fold surfacefree energy is calculated to be (5.28–11.9) × 10–2J m–2. It is evident that the addition of 0.30wt % SWNTs reduces the fold surface free energy by 55.6%. [ABSTRACT FROM AUTHOR]