Material Characterization and Modeling of Single-Wall Carbon Nanotube/Polyelectrolyte Multilayer Nanocomposites

Strong single-wall carbon nanotubes (SWNTs) possess very high stiffness and strength. They have potential for use to tailor the material design to reach desired mechanical properties through SWNT nanocomposites. Layer-by-layer (LBL) assembly technique is an effective method to fabricate SWNT/polyelectrolyte nanocomposite films. To determine the relationship between the constituents of the SWNT/polymer nanocomposites made by LBL technique, a method has been developed to extend the recent work by Liu and Chen (Mech. Mater., 35, pp. 69-81, 2003) for the calculation of the effective Young's modulus. The work by Liu and Chen on the mixture model is evaluated by finite element analysis of nanocomposites with SWNT volume fraction between 0% and 5%. An equivalent length coefficient is introduced and determined from finite element analysis. A formula is presented using this coefficient to determine the effective Young's modulus. It is identified that the current work can be applied to SWNT loadings between 0% and 5%, while Liu and Chen's approach is appropriate for relatively high SWNT volume fractions, close to 5%, but is not appropriate for relatively low SWNT volume fractions. The results obtained from this method are used to determine the effective Young's modulus of SWNT/ polyelectrolyte nanocomposite with 4.7% SWNT loading. The material properties are characterized using both nanoindentation and tensile tests. Nanoindentation results indicate that both the in-plane relaxation modulus and the through-thickness relaxation modulus of SWNT nanocomposites are very close to each other despite the orientation preference of the SWNTs in the nanocomposites. The steady state in-plane Young's relaxation modulus compares well with the tensile modulus, and measurement results are compared with Young's modulus determined from the method presented.