Adhesion and friction becomes more important when the lateral size of objects decreases. This is due to the increased surface to volume ratio. At the micro and nanoscale the gravitational interaction is usually negligible compared to the van der Waals interaction and electrostatic interactions, or forces due to the formation of small (nanometer) capillary bridges. Problems related to adhesion and friction (and wear) are the most severe problems to be overcomed in the development of many useful micro or nanoscale mechanical systems, e.g., micromotors.
In this presentation I will describe a new theory of contact mechanics for solids with randomly rough surfaces. I consider the elastic contact between solids both without and with adhesion. As an illustration I will discuss in detail biological adhesion systems used for locomotion, and show how natural selection in some cases has optimized the adhesive systems from the (macroscopic) size of the adhesion pads (typically of order ~ 1 mm) to the nanoscale. As a second application of the theory I will briefly describe rubber friction on rough substrates. Finally, I will briefly discuss molecular dynamics resuls for the friction between solids consisting of (alkane) hydrocarbon chains with 20, 60, 100, 140 and 1400 carbon atoms, and describe some basic results relating to the friction on ice and snow.
Enkapsling har vært brukt i stor utstrekning til å sperre inn flere typer kjemikalier i partikulære materialer. Typiske anvendelser finnes i biovitenskap, matvareindustri, kosmetikk, kjemisk og farmasøytisk industri.
Størrelsen til kapsler er vanligvis fra 1 µm til flere mm. Dette representerer en viktig hindring for å kunne anvende kapsler i belegg og maling.
Nanomedisin, definert som nanoteknologi anvendt på helse, er et raskt voksende nytt forskningsområde. Nanopartikler og nanokapsler vil være helt sentralt ved utviklingen av morgendagens medisiner.
Denne presentasjonen tar utgangspunkt i kompetanse innen nanoteknologi som SINTEF har bygget på gjennom flere år. Spesielt har nye materialer i form av nanopartikler og nanokapsler blitt utviklet for kontrollert frigivelse av molekyler eller kjemikalier. Flere typer eksterne stimuli så som temperatur, pH eller lys er benyttet til å slippe ut aktive komponenter. Ultra-tynne belegg og overflatemodifisering har satt oss i stand til å funksjonalisere overflater. Flere eksempler vil vises frem som illustrasjon av det store potensialet som ligger i anvendelsen av slike materialer innen biomedisin og korrosjonsmotstand.
Water soluble and amphiphilic polymers may respond to various stimuli in aqueous solutions. Changes in the dimensions or the degree of aggregation may find use in several applications.
Thermally responsive polymers like poly(N-isopropylacrylamide), PNIPAM, poly(vinylcaprolactam), PVCL, and poly(vinylmethylether), PVME, have been extensively investigated during the last decade. These polymers dissolve in cold water but phase separate upon increasing temperature at a certain critical temperature. Polymers either precipitate or, in very dilute solutions, form colloidally stable particles. Crosslinked polymers (gels) collapse upon heating at the critical temperature but reswell upon cooling. PVCL microgel particles, for example, may find use as drug carriers and in controlled drug release. For this application it is beneficial to stabilise the particles against coagulation.
Polyelectrolytes respond to changes of pH and ionic strength. As an example, the synthesis and properties of amphiphilic star diblock copolymers will be described. In these stars, the outer block of the arm is a polyelectrolyte whereas the inner one is hydrophobic. Aggregation and self assembling of these polymers is affected by the number of arms, as well as by changes in the solvent composition.
A traditional skiwax should give sufficient kick and glide on a specific snow-surface. This means a balance between static and kinetic friction. The meteorological conditions will vary within large limits, creating everything from tiny, sharp crystals at very low sub-freezing temperatures to a melting coarse-grained substance at several degrees above melting. A discussion of the problems caused by the conditions around freezing, also called the critical temperature of ski-waxing. What type of raw-materials are used to match such large differences in surface conditions ? How do the blends interact with the snow surface? As the name of the products indicate, waxes are important, but not all “ski-waxes” contain wax. A discussion on waxes, resins and additives used to-day. Application and interaction with the UHMW-PE in the ski-bases.
The tribological system of a ski sliding on snow consists of four elements, the slider, the snow surface, the interface and the surrounding atmosphere. All four have an important influence on the glide performance of the slider. The slider base is prepared to meet the different conditions of the snow surface both with respect to base material, base structure and surface treatment. The condition of the second element, snow, is determined by the atmospheric conditions before the time of contact. Important meteorological parameters include air and snow temperature, relative humidity and net radiation. The dominating friction mechanism at the interface is determined by the conditions of the base, the snow surface and the atmosphere. Since snow, at the temperatures at which skiing is performed, constantly is changing its properties different preparations are needed in order to meet the prevailing conditions. The paper discusses the important parameters of each element in order to decrease the friction between slider and snow.
Siden oppdatert 20.3.2007