Research topics in Laboratory of Physics of Nanostructures
Characterization of properties of individual nanostructures
Properties of nanomaterials can be significantly different form macroscopic objects. For example, tensile strength of nanostructure can be several times or even orders of magnitude higher. Sometimes new and unique properties occur in nanoscale materials, which can depend on the dimensions and size of the structure. The situation is even more complicated due to the fact that classical laws of physics don’t always apply when describing individual nanostructures/systems. Therefore it is imperative to measure and analyze separately different parameters of individual nanostructure to better understand, control and apply unique properties of nanostructured materials. At the same time, manipulation and characterization of individual nano-sized structures is a difficult and a complex challenge despite the apparent simplicity.
Current project investigates mechanical, tribological and electrical properties of individual nanostructures. Measurements are conducted inside a scanning electron microscope using manipulation and force measurement systems that were developed and built in our laboratory. Experiments are complimented by modelling and simulations.
Bending of silica coated silver nanowire.
Glass with electrically tunable transparency
Glass with electrically tunable transparency has been developed in cooperation with Andrese Klaasi AS since 2009. The material is a type of liquid crystal dispersion (a so-called gel-glass dispersed liquid crystal (GDLC)) prepared as a ~20µm thick composite film consisting of organically modified silica or mixed oxide matrix and microscopic liquid crystal droplets. This material exhibits interesting electro-optical properties. Namely, the light scattering properties of GDLC material can be reversibly changed by applying an electric field. In the rest state, i.e. when the electric filed is not applied the material strongly scatters light due to mismatch of the refractive index of the oxide matrix and the effective refractive index of liquid crystal and thus the material is not transparent. When electric field of sufficient strength is applied the material turns from opaque scattering state to transparent non-scattering state and thus is potentially applicable as a “smart” window material. Method of preparation of large area GDLC films has been developed that exhibit 82% change in transmittance as electric field is applied, being sufficient for practical applications.
Electric field is switched off.
Electric field is switched on.
Nanostructured oil additives
There is a lasting need for new lubricants to reduce the energy losses due to friction and wear of materials. The lubricant performance of base oil is usually enhanced by various additives that improve its chemical durability, viscosity, lubricating efficiency and contaminant binding ability.
The aim of present project is to investigate the applicability of nanoparticles/ionic liquid composites as novel protective lubricant for metal wear parts. Either nanoparticles or ionic liquids independently have been shown to exhibit exceptional lubricating qualities. Ionic liquids have remarkable lubrication and anti-wear capabilities as compared with lubrication oils in general use and their thermo-oxidative stability and nonflammability is also very eligible. There is a very wide range of different ionic liquids and their properties can be modified by selection of suitable cation and anion. The new lubricant provides a significant decrease in the friction coefficient and in the wear rate compared to oil analogues, while being able to sustain harsh conditions like high temperatures, pressures and friction forces. The new lubricant additive forms a protective layer to prevent wear in lubricated contacts.
Wear scar when using synthetic base oil PAO
Wear scar when using synthetic base oil PAO with
Structural coatings can be done with sol-gel phase separation method. Size of these round silica surface features can be varied from few hundred nanometers to few micrometers and it is possible to cover comparatively large surfaces with spraying technique. Multifunctional micro- and nanoscale glass bumps can be used to mimic nature (i.e. lotus leaves) to achieve non-wetting and self-cleaning. Also, each round surface feature acts as a miniature lens resulting in matte or non-reflective coatings on glass.
Scanning electron microscope image of glass bumps.
Already in the last decade of the previous century laser radiation was used in Estonia and all over the world to influence the course of different skin diseases. Effect of low level red and infrared lasers on treatment turned out to be modest. Turnaround in treatment outcome took place at the turn of the century when scientists of Institute of Physics (University of Tartu) in cooperation with laser company Estla developed a relatively powerful (1 – 3 W) copper vapor laser system for medical application. Laser produces powerful short (20 ns) and high frequency (16 kHz) impulses of green (at 511 nm) and yellow (578 nm) laser light.
Laser therapy can be used to correct different cosmetic skin defects without surgical interference. Pigmentation marks with different genesis, telangiectasias, tattoos etc. can be removed without damaging the skin. In addition, laser therapy can be successfully used for treatment of inflammatory processes (arthritis, radiculitis, dental inflammation, herpes, sporting injuries). Laser complex has shown as an effective treatment method for skin diseases and injuries of small animals. Positive effect of laser radiation on the organism is based on three properties: activation of the immune system, analgesic and antibacterial effect.
Post-surgical inflammation hasn’t reduced in a month. After 3 laser treatments during 10 days normal use of the knee is restored.