The surface topography of paper fibers is studied using atomic force microscopy (AFM), and thus the surface roughness power spectrum is obtained. Using AFM we have performed indentation experiments and measured the effective elastic modulus and the penetration hardness as a function of humidity. The influence of water capillary adhesion on the fiber-fiber binding strength is studied. Cellulose fibers can absorb a significant amount of water, resulting in swelling and a strong reduction in the elastic modulus and the penetration hardness. This will lead to closer contact between the fibers during the drying process (the capillary bridges pull the fibers into closer contact without storing up a lot of elastic energy at the contacting interface). In order for the contact to remain good in the dry state, plastic flow must occur (in the wet state) so that the dry surface profiles conform to each other (forming a key-and-lock type of contact).
In this article we present a comprehensive study of 11-mercaptoundecanoic acid self-assembled monolayer (SAM) formation on gold surfaces. The SAMs were prepared in ethanolic solution, utilizing two different substrates: Au(111)/mica and polycrystalline gold foils. Several experimental methods (X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and atomic force microscopy) reveal a well-defined SAM. The main focus of this work, however, was to test the stability of these SAMs by thermal desorption spectroscopy. The spectra show different desorption peaks indicating different adsorption states and/or decomposition products on the surface. The assumed monolayer peak, which can be attributed to desorption of the intact molecule, is detected at 550 K. Further desorption peaks can be found, which result, e.g., from cracking of the S-C bond on the surface, depending on the substrate quality and on the residence time under ambient conditions.
The process of ozone treatment of high kappa kraft pulp is studied using polarization modulated Fourier transform infrared spectroscopy and atomic force microscopy. The complementary information from the two methods enables a detailed analysis of reaction sites on the fibers, and gives a detailed view of the reaction mechanisms of delignification by ozone treatment. Furthermore we describe a simple method to measure the kappa number of paper sheets that can be used on-line.
A new and relatively simple polarization modulation technique is presented and tested that enables the whole spectral range to be detected between 400 and 4000 cm−1. This experiment is conventionally carried out using a photoelastic modulator that modulates incident plane polarized light through 90°. This suffers from the drawback that it enables spectra to be collected only over a relatively narrow spectral range. As an alternative, a polarizer is placed in the beam and oriented at 45° to the sample normal. This produces incident radiation fluxes with identical intensities for both s- and p-polarized light. A second polarizer is then modulated through 90° and the surface spectrum is then extracted in the usual manner from the difference between these signals, normalized to their sum. The method is demonstrated for a self-assembled monolayer of 11-mercapto-undecanoicacid (11-MUA) on gold on mica, and it is shown that, while the resulting spectra are extremely sensitive to optical alignment, the method yields spectra that are in excellent agreement with published data.
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