This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact epubs@purdue.edu for additional information.Strus, Mark C.; Cano, Camilo I.; Pipes, R. Byron; Nguyen, Cattien V.; and Raman, Arvind, "Interfacial energy between carbon nanotubes and polymers measured from nanoscale peel tests in the atomic force microscope" (2009 b s t r a c tThe future development of polymer composite materials with nanotubes or nanoscale fibers requires the ability to understand and improve the interfacial bonding at the nanotube-polymer matrix interface. In recent work [Strus MC, Zalamea L, Raman A, Pipes RB, Nguyen CV, Stach EA. Peeling force spectroscopy: exposing the adhesive nanomechanics of one-dimensional nanostructures. Nano Lett 2008;8(2):544-50], it has been shown that a new mode in the Atomic Force Microscope (AFM), peeling force spectroscopy, can be used to understand the adhesive mechanics of carbon nanotubes peeled from a surface. In the present work, we demonstrate how AFM peeling force spectroscopy can be used to distinguish between elastic and interfacial components during a nanoscale peel test, thus enabling the direct measurement of interfacial energy between an individual nanotube or nanofiber and a given material surface. The proposed method provides a convenient experimental framework to quickly screen different combinations of polymers and functionalized nanotubes for optimal interfacial strength.Published by Elsevier Ltd.

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Solid poly(amic acid) (PAA) precursor is used for foaming into microspheres or foams depending on whether the powder particles are free or confined inside a mold. Solid-state foaming of powder precursors is studied by examining concurrent and competitive phenomena that determine the morphology and physical properties of the foam unit cell. Simultaneous analysis through thermo gravimetric analysis (TGA) and modulated differential scanning calorimetry (MDSC) is proposed for the characterization of important transitions during the blowing process. Effects of particle size and shape on bubble growth will be addressed.

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Morphological characteristics of polyimide microstructures obtained by solid-state powder foaming determine the geometric properties of the unit cell, in polyimide foams prepared by this process. Morphological analysis of precursor particles has shown that particle size and shape, as well as the presence of embedded microvoids, exert a strong influence on the final microstructure morphology. Of equal importance in the morphological development are processing conditions such as heating rate and primary blowing agent content in the particles, prior to thermal treatment.In the present paper, the first of two numerical schemes is presented. A numerical model has been developed to study the preliminary stages that lead to particle inflation. Based on this model, a parametric analysis is performed for pertinent governing parameters, with the purpose of determining their effect on the onset of particle inflation and the potential morphological characteristics of polyimide microstructures. It has been found that precursor particle morphology and nuclei density are the key parameters in determining the potential morphology of the microstructures, by limiting the number of bubbles that grow within each particle.

The morphological development of cellular polyimide microstructures from poly(amic acid) powders has been shown to depend on the processing conditions throughout the inflation process and the morphological characteristics of the precursor particles. In an earlier publication the authors presented a numerical study of the preliminary stages prior to particle inflation when the processing temperature is below the glass transition temperature, Tg. In the present article, a second numerical scheme is presented for behavior above Tg in which bubble growth is modeled to account for the effect of multiple phenomena in the final stages of morphological development. The bubble growth kinematics and subsequent cessation of growth are predicted as a function of process parameters and material properties. Morphological characteristics of the precursor particles have also been shown to influence the kinematics of inflation. These results provide a clearer understanding of the solid‐state foaming processes for polyimide cellular materials. POLYM. ENG. SCI., 47:572–581, 2007. © 2007 Society of Plastics Engineers.

Several concurrent phenomena occur during the thermal inflation of poly(amic acid) precursor particles leading to polyimide foams as part of the solid-state powder foaming process. The precursor experiences bubble growth from within while volatiles desorb and the polymer itself increases its molecular weight and changes its backbone structure. These changes affect the transport properties of the material by modifying significantly the effective glass transition temperature, T g . By studying the chemical transformations that take place during the inflation process (amidation and imidization reactions), a complete understanding of the material's molecular changes can be obtained and corresponding property changes can be followed. This article is the third of a series where the inflation of precursor materials for polyimide foams has been studied. The two previous articles in the series present numerical models that simulate the inflation process from first principles. In this article, the authors discuss the experimental and analytical methodologies employed to accurately characterize and incorporate the changes in material and transport properties as a function of the glass transition temperature. POLYM. ENG. SCI.,