Lamellar Structure by SAXS

SAXS probes X-rays scattered by electron density contrasts between the crystalline and amorphous layers that form the lamellar stacks in semi-crystalline polymers. The resulting scattering pattern typically exhibits sharp long-period peaks or oscillations that reflect the periodicity of these alternating domains.

Furthermore, when data are analyzed in real space using the electron density auto-correlation function, SAXS provides access to quantitative lamellar parameters [1], including:

• Long period (L), corresponding to the average repeat distance of the lamellar stack
• Crystalline layer thickness, related to the crystalline domain within each period
• Amorphous layer thickness, obtained from the full periodic profile

Figure 1. Auto-correlation function extracted from SAXS data of a semi-crystalline polymer, illustrating the long and short periods associated with the lamellar stack (processed with the XSACT Pro software).

Because SAXS integrates the signal from large material volumes, the resulting parameters represent statistically meaningful, bulk-averaged structural information, highly relevant for polymers where morphology depends sensitively on processing history.

Lamellar spacing analysis by SAXS applies to a broad variety of semi-crystalline and self-assembled polymer systems.

Typical materials include:

• Semi-crystalline polymers such as PE, PP, PA, PEEK, PEKK, PET, and bio-based polymers
• Block copolymers exhibiting lamellar microphase separation
• Polymer blends and nanocomposites where lamellae form or reorganize during processing
• Films, fibers, molded components, or powder materials
• Samples under processing conditions, including heating, cooling, stretching, or flow

Moreover, because SAXS is non-destructive and requires little to no preparation, lamellar structures can be studied in situ, following crystallization, melting, annealing, cold-crystallization, or structural rearrangement in real time.

SAXS provides a direct, quantitative view of the layered organization that defines semi-crystalline polymer morphology. Its strengths include:

Together, these features make SAXS an essential tool for linking polymer processing conditions, lamellar morphology, and final material performance.