Eduard Gilli

Adhesion of cellulose fibers in paper

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).

A Study on the Formation and Thermal Stability of 11-MUA SAMs on Au(111)/Mica and on Polycrystalline Gold Foils

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.

A New Method for Performing Polarization Modulation Infrared Reflection-Adsorption Spectroscopy of Surfaces

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.

Analysis of lignin precipitates on ozone treated kraft pulp by FTIR and AFM

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.

An Optical Model for Polarization Microscopy Analysis of Pulp Fibre-to-Fibre Bonds

Pulp fibre-to-fibre bonds were studied using polarization microscopy and microtome cuts. The experiments showed considerable discrepancies between these two experimental methods. While microtome cuts clearly show if a bond between two fibres has formed, polarization microscopy cannot unambiguously discern between crossed unbonded fibres and bonded fibres; also certain bonds cannot be detected with this method. To examine these shortcomings, a physical model of polarization microscopy of bonded and unbonded pulp fibers was built. Experimental validation of the model gave good agreement between calculations and reflectance measurements. Calculations based on this model clearly demonstrate that only bonded fibres resembling a plane parallel plate show as bonds. However, crossings of unbonded fibers also appear as bonds if the two fibres are flat and plane parallel to each other. The model provides a consistent interpretation for polarization microscopy imaging of pulp fibre bonds, an important topic in research of mechanical and optical properties of fibrous composites like paper.

Determination of Noise-Free Optical Constants in the Infrared by Kramers–Kronig Transformation of the Reflectance Ratio in s - and p -Polarization

A method for Kramers–Kronig transformation of the reflectance ratio of s- and p-polarized light is discussed. The method is well suited for the determination of the optical constants of isotropic samples such as pellets prepared from powders. An algorithm is given that performs the transformation, including extrapolation at the data margins and an automated data fitting routine, that can handle very complex spectra of, e.g., biomacromolecules such as cellulose to obtain noise free spectra. Criteria for evaluation of the quality of the obtained data are given, and experimental data for cellulose II and xylane are presented.

Optical biosensor system with integrated microfluidic sample preparation and TIRF based detection

There is a steadily growing demand for miniaturized bioanalytical devices allowing for on-site or point-of-care detection of biomolecules or pathogens in applications like diagnostics, food testing, or environmental monitoring. These, so called labs-on-a-chip or micro-total analysis systems (μ-TAS) should ideally enable convenient sample-in – result-out type operation. Therefore, the entire process from sample preparation, metering, reagent incubation, etc. to detection should be performed on a single disposable device (on-chip). In the early days such devices were mainly fabricated using glass or silicon substrates and adapting established fabrication technologies from the electronics and semiconductor industry. More recently, the development focuses on the use of thermoplastic polymers as they allow for low-cost high volume fabrication of disposables. One of the most promising materials for the development of plastic based lab-on-achip systems are cyclic olefin polymers and copolymers (COP/COC) due to their excellent optical properties (high transparency and low autofluorescence) and ease of processing. We present a bioanalytical system for whole blood samples comprising a disposable plastic chip based on TIRF (total internal reflection fluorescence) optical detection. The chips were fabricated by compression moulding of COP and microfluidic channels were structured by hot embossing. These microfluidic structures integrate several sample pretreatment steps. These are the separation of erythrocytes, metering of sample volume using passive valves, and reagent incubation for competitive bioassays. The surface of the following optical detection zone is functionalized with specific capture probes in an array format. The plastic chips comprise dedicated structures for simple and effective coupling of excitation light from low-cost laser diodes. This enables TIRF excitation of fluorescently labeled probes selectively bound to detection spots at the microchannel surface. The fluorescence of these detection arrays is imaged using a simple set-up based on a digital consumer camera. Image processing for spot detection and intensity calculation is accomplished using customized software. Using this combined TIRF excitation and imaging based detection approach allowes for effective suppression of background fluorescence from the sample, multiplexed detection in an array format, as well as internal calibration and background correction.

Diagnostic Lab-on-a-Chip System Based on Fluorescence Imaging and Integrating Sample Preparation.

In this contribution we describe a microfluidic chip combining plasma separation, sample metering, dissolution/incubation with reagents stored on-chip and optical detection. The system allows defining the incubation time and works under constant externally applied pressure using only passive valves for actuation. This allowed the realization of a bioanalytical device for whole blood samples comprising a disposable plastic chip using TIRF (total internal reflection fluorescence) based optical detection of biochemical binding events.

Imaging ellipsometry based method and algorithm for the analysis of fiber–fiber bonds in a paper network

The measurement of the bonded area of pulp fibers has been an unsolved issue in paper science for more than 40 years. By the use of an established pulp fiber model, and a 4 × 4 transfer matrix formalism we simulated the optical behavior of pulp fibers in a modified imaging ellipsometer, and we demonstrate that there are rather strong symmetries in the ellipsometric angles Ψ and Δ when comparing single fibers, unbonded fiber crossings, and fiber-fiber bonds. Based on these symmetries we propose and test an algorithm that allows to distinguish the three cases (single fibers, unbonded fiber crossings, and fiber-fiber bonds) in the analysis of ellipsometric data.