On variations of the interphase thickness and the slope of strengthening by clay addition in exfoliated polymer-clay nanocomposites

- The concept of interphase region in PCNs is explained by an “algae explanation”.
- Structural impact of interphase thickness on macroscopic modulus is formulated.
- Thickness of interphase can be calculated based on macroscopic elastic modulus.
- A series of parametric finite element simulations are implemented.
- The interphase thickness lay in the range of 2.5-7 nm for PA6-MMT system.

Polymer-clay nanocomposites (PCNs) have received intensive attention in recent years because of their wide domain of applications. The present report provides an approach to calculate the thickness of nanometric interphase region in exfoliated PCNs based on the information about their macroscopic modulus and their nanoclay content. First, the concept of interphase region in PCNs is explained with an “algae explanation”. Then, a series of parametric finite element simulations together with analytical equations are employed to derive an explicit relationship between the interphase thickness and the PCN macroscopic modulus. The obtained analytical model considers the structural impact of the nanometric interphase thickness on the macroscopic behavior. Results show that the model predictions for interphase thickness lay in the range of 2.5-7 nm for PA6-MMT system which is in accordance with the measured interphase thicknesses for this system in literature. Moreover, a graphical map is provided to facilitate predicting the interphase thicknesses at a given macroscopic modulus. Finally, it is shown that the reason of slope variations in strengthening by nanoclay addition can be solely a structural effect attributed to the predicted variations of the interphase thickness by increasing clay content even if no agglomeration of nanoclay flakes take place in process.