Walter Caseri

Bio: Walter Caseri is an academic researcher from ETH Zurich. The author has contributed to research in topics: Adsorption & Platinum. The author has an hindex of 38, co-authored 180 publications receiving 5164 citations. Previous affiliations of Walter Caseri include Max Planck Society & University of Fribourg.

Nanocomposites of polymers and metals or semiconductors: Historical background and optical properties

Abstract: Upon transmission of visible light through composites comprising of a transparent polymer matrix with embedded particles, the intensity loss by scattering is substantially reduced for particle diameters below 50-100 nm (nanoparticles, nanosized particles). As a consequence, related materials (nanocomposites) have found particular interest in optical studies. The first part of this article deals with a historical survey on nano-particles and nanocomposites and the importance of small particle sizes on their optical properties. The second part focuses on results from our laboratory concerning nanocomposites with extremely high or low refractive indices and dichroic nanocomposites and their application in bicolored liquid crystal displays (LCD). The inorganic colloids required for these studies (lead sulfide, iron sulfides, gold, and silver) were prepared in situ in presence of a polymer or isolated as redispersable metal colloids modified at the surface with a self-assembled monolayer (SAM) of an alkanethiol. The nanocomposites themselves were finally obtained by coprecipitation, spin coating, solvent casting or melt extrusion, with poly(ethylene oxide), gelatin, poly(vinyl alcohol) and polyethylene as matrix polymers.

Polymer-TiO2 Nanocomposites: A Route Towards Visually Transparent Broadband UV Filters and High Refractive Index Materials

Abstract: Colloids of TiO2, where rutile was the only crystal modification which could be detected, with ca. 2.5 nm average particle diameter were synthesized by hydrolysis of TiCl4 in acidic solutions. The as-prepared particles were incorporated in polymers such as poly(vinyl alcohol) (PVAL), partially hydrolyzed poly(vinyl acetate) (PVAC88), polyvinylpyrrolidone, and poly(4-vinylpyridine). Nanocomposites transparent in the visible range were obtained. The highest TiO2 contents in such materials were achieved with PVAL and PVAC88, with TiO2 contents of ca. 35 wt.-% (i.e. 10.5 vol.-%). In particular, the nanocomposites with TiO2 contents above 24 wt.-% acted as efficient UV filters for radiation up to ca. 360 nm. At very low TiO2 contents, an absorption maximum of the embedded TiO2 particles was observed at 225 nm with an extinction coefficient of 140 000 cm−1 and a full width at half maximum of 45 nm, i.e. not only the absorption at the maximum at 225 nm but also at the flank of this band contributed significantly to the broadband UV absorption in the nanocomposites at higher TiO2 fractions. The incorporation of TiO2 enhanced the refractive index of the nanocomposites: for instance a refractive index of 1.609 was measured for a nanocomposite comprising 10.5 vol.-% TiO2 in PVAL, compared with 1.521 for the pristine polymer. TEM image of a section of a nanocomposite of poly(vinyl alcohol) and 11 wt.-% TiO2 (appearing dark).

Nanocomposites of polymers and inorganic particles: preparation, structure and properties

Abstract: Although composites with, e.g.nanosized SiO2, TiO2, carbon black or gold are known for a long time, an increasing number of polymer composites comprising inorganic nanoparticles have been described only in the last 15 years. Frequently employed inorganic materials include metals (e.g. gold, silver or copper), semiconductors (e.g. PbS or CdS) or clay minerals (e.g.montmorillonite or vermiculite). In most cases, nanocomposites with spheric or plate like particles have been prepared so far but materials with nanorods (rod like particles, including nanotubes) also attracted attention. The structure of nanocomposites is essentially established by the arrangement of the particles in the polymer matrix. The particles may be dispersed as individual primary particles or as agglomerated particles (secondary particles), and the primary or secondary particles can be arranged randomly or in an ordered or oriented state, depending on the method of nanocomposite preparation and processing (including, e.g. coprec...

Preparation and characterization of cationic nanofibrillated cellulose from etherification and high-shear disintegration processes

Abstract: Oat straw cellulose pulp was cationized in an etherification reaction with chlorocholine chloride. The cationized cellulose pulp was then mechanically disintegrated in two process steps to obtain trimethylammonium-modified nanofibrillated cellulose (TMA-NFC). The materials thus obtained were analyzed by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and other techniques. A higher nitrogen content of TMA-NFC samples was found by XPS analysis than by elemental analysis, which indicates that the modification occurred mainly on the surface of cellulose fibrils. XPS also confirmed the existence of ammonium groups in the samples. SEM provided images of very fine network structures of TMA-NFC, which affirmed the positive effect of ionic charge on mechanical disintegration process. According to XRD and SEM results, no severe degradation of the cellulose occurred, even at high reaction temperatures. Because of the different properties of the cationic NFC compared to negatively charged native cellulose fibers, TMA-NFC may find broad applications in technical areas, for instance in combination with anionic species, such as fillers or dyes. Indeed, TMA-NFC seems to improve the distribution of clay fillers in NFC matrix.

Handbook of Chemistry and Physics

Abstract: There is a special reason for reviewing this book at this time: it is the 50th edition of a compendium that is known and used frequently in most chemical and physical laboratories in many parts of the world. Surely, a publication that has been published for 56 years, withstanding the vagaries of science in this century, must have had something to offer. There is another reason: while the book is a standard fixture in most chemical and physical laboratories, including those in medical centers, it is not as frequently seen in the laboratories of physician's offices (those either in solo or group practice). I believe that the Handbook can be useful in those laboratories. One of the reasons, among others, is that the various basic items of information it offers may be helpful in new tests, either physical or chemical, which are continuously being published. The basic information may relate

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

Polymer/Silica Nanocomposites: Preparation, Characterization, Properties, and Applications

Abstract: 5. In Situ Polymerization 3907 5.1. General Polymerization 3907 5.2. Photopolymerization 3910 5.3. Surface-Initiated Polymerization 3912 5.4. Other Methods 3913 6. Colloidal Nanocomposites 3913 6.1. Sol-Gel Process 3914 6.2. In Situ Polymerization 3916 6.2.1. Emulsion Polymerization 3917 6.2.2. Emulsifier-Free Emulsion Polymerization 3919 6.2.3. Miniemulsion Polymerization 3920 6.2.4. Dispersion Polymerization 3921 6.2.5. Other Polymerization Methods 3923 6.2.6. Conducting Nanocomposites 3924 6.3. Self Assembly 3926 7. Other Preparative Methods 3926 8. Characterization and Properties 3928 8.1. Chemical Structure 3928 8.2. Microstructure and Morphology 3929 8.3. Mechanical Properties 3933 8.3.1. Tensile, Impact, and Flexural Properties 3933 8.3.2. Hardness 3936 8.3.3. Fracture Toughness 3937 8.3.4. Friction and Wear Properties 3937 8.4. Thermal Properties 3938 8.5. Flame-Retardant Properties 3941 8.6. Optical Properties 3942 8.7. Gas Transport Properties 3943 8.8. Rheological Properties 3945 8.9. Electrical Properties 3945 8.10. Other Characterization Techniques 3946 9. Applications 3947 9.1. Coatings 3947 9.2. Proton Exchange Membranes 3948 9.3. Pervaporation Membranes 3948 9.4. Encapsulation of Organic Light-Emitting Devices 3948