Louis T. Germinario

Probing the temperature dependence of the mechanical properties of polymers at the nanoscale with band excitation thermal scanning probe microscopy

Understanding local mechanisms for temperature-induced phase transitions in polymers requires quantitative measurements of the thermomechanical behavior, including glass transition and melting temperatures as well as temperature dependent elastic and loss modulus and thermal expansion coefficients in nanoscale volumes. Here, we demonstrate an approach for probing local thermal phase transitions based on the combination of thermal field confinement by a heated SPM probe and multi-frequency thermomechanical detection. The local measurement of the glass transition temperature is demonstrated and the detection limits are established.

Local thermomechanical characterization of phase transitions using band excitation atomic force acoustic microscopy with heated probe

An approach for thermomechanical characterization of phase transitions in polymeric materials (polyethyleneterephthalate) by band excitation acoustic force microscopy is developed. This methodology allows the independent measurement of resonance frequency, Q factor, and oscillation amplitude of a tip-surface contact as a function of tip temperature, from which the thermal evolution of tip-surface spring constant and mechanical dissipation can be extracted. We demonstrate a heating protocol which keeps the contact area and contact force constant, thus allowing for reproducible measurements and quantitative extraction of material properties including temperature dependence of indentation-based elastic and loss moduli.

Fundamentals of hot-melt pressure-sensitive adhesive tapes: the effect of tackifier aromaticity

We revisit the effect of varying the tackifier aromaticity on adhesive performance in a styrenic block co-polymer (SBC)-based pressure-sensitive adhesive tape. Aromaticity strongly affects the compatibility between the tackifying resin and base polymer and is defined as the relative number of protons attached to an aromatic ring. Dynamic mechanical analysis, peel resistance, tack, shear resistance and atomic force microscopy were utilized to detect changes in adhesive performance due to resin aromaticity. The results indicate that increasing the aromaticity of the tackifier enhanced the compatibility between the tackifier and styrene domains. As a consequence, the high-temperature cohesive performance measured by the shear adhesion failure temperature decreased due to plasticization of the end-blocks by the aromatic resins. However, other properties of interest such as the glass transition of the rubbery matrix, tack, peel resistance and holding power were less affected by the resin aromaticity. We note that this paper is of limited scope because we have focused this research on styrene–isoprene–styrene, which is very compatible with a wide range of tackifiers. More significant differences would be expected in formulations based on styrene–butadiene–styrene or styrene–isoprene–butadiene–styrene polymers in which the compatibility between the resin and midblock would be more sensitive to the resin aromaticity. In addition to our results, we review the literature and some fundamentals of formulating SBC-based adhesives and PSA testing.

Development of Protocols Suitable for Atomic-Scale Imaging of Catalyst Clusters at Catalytic Temperatures

Louis T. Germinario* and Lawrence F. Allard** *Eastman Chemical Company, Kingsport, TN 37662 **Materials Science & Technology Div., Oak Ridge National Laboratory, Oak Ridge, TN 37831 Recent advances in aberration corrected electron microscopy (ACEM) are providing new tools and opportunities for studying chemical processes at gas-solid interfaces at atomic resolutions. In the area of heterogeneous catalysis, STEM-based high-angle annular dark-field imaging (HA-ADF) has provided the potential for direct observation of single heavy atoms and atom clusters. [1]. This approach has been used to study catalytic properties by directly probing structure development as a result of metal particle-substrate interactions, and used to explore the combined effects of temperature, promoters, and organic ligands on the evolution of catalyst structure [2-3]. Associated with this new tool is the potential for artifacts, such as electron beam-induced polymerization of organic components [4], and the influence of the electron beam on heavy atom diffusion and nanostructuring [5]. Experiments were conducted in order to develop sample preparation techniques and imaging protocols that are suitable for achieving sub-Angstrom resolutions at ambient temperatures. In-situ heating studies were also conduct using Aduro