Madis Paalo

Pinching of alkoxide jets—a route for preparing nanometre level sharp oxide fibres

The pinching phenomenon is used to shape jets of Sn(OBu)4 based viscous oligomeric melts into nanometre range sharp oxide needles. The influence of viscosity of the liquid, humidity of surrounding environment and pulling speed on formation of the needles is investigated. Optimal conditions enable reproducible preparation of needles that have tip radii down to 15–25 nm, i.e. in the range that is of considerable interest for many nanotechnological applications.

Alkoxide-based precursors for direct drawing of metal oxide micro- and nanofibres

Abstract The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol–gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.

Fibroblast growth on micro- and nanopatterned surfaces prepared by a novel sol–gel phase separation method

Physical characteristics of the growth substrate including nano- and microstructure play crucial role in determining the behaviour of the cells in a given biological context. To test the effect of varying the supporting surface structure on cell growth we applied a novel sol–gel phase separation-based method to prepare micro- and nanopatterned surfaces with round surface structure features. Variation in the size of structural elements was achieved by solvent variation and adjustment of sol concentration. Growth characteristics and morphology of primary human dermal fibroblasts were found to be significantly modulated by the microstructure of the substrate. The increase in the size of the structural elements, lead to increased inhibition of cell growth, altered morphology (increased cytoplasmic volume), enlarged cell shape, decrease in the number of filopodia) and enhancement of cell senescence. These effects are likely mediated by the decreased contact between the cell membrane and the growth substrate. However, in the case of large surface structural elements other factors like changes in the 3D topology of the cell’s cytoplasm might also play a role.

Structure and Rheological Behavior of Alkoxide-Based Precursors for Drawing of Metal Oxide Micro- and Nanofibres

The aim of this study is investigation of the influence of the method of metal alkoxy precursors preparation on their rheological characteristics and spinability for metal oxide fibre drawing. The precursor samples were obtained from tin 1-butoxide Sn(OBu)4 as a result of aqueous (AQ) and non-aqueous (NAQ) (thermolysis) treatment. Small angle X-ray scattering (SAXS) data of precursors in the range of scattering vector modulus 0.07–5.3 nm-1 were recorded on a slit collimation camera KRM-1 by using Cu Kα radiation and NaI:Tl scintillation detector. Program system ATSAS [1] was used for calculation of the radius of gyration Rg and for 3D modeling of the cluster shape. The rheological characterization of samples was conducted with a help of a rotational rheometer Mars II (Haake, Karlsruhe, Germany) equipped with plate-and-plate test geometry (plate diameter 20 mm). The precursors studied in this work consist of the elongated particles of 3 – 5 nm in length and 2 nm in diameter for both AQ and NAQ prepared precursors. Rheological tests have proved that the solvent free precursors are typical non-Newtonian fluids. Precursors obtained with the help of NAQ treatment are more elastic as compared to those prepared with AQ procedure. Surface tension (ST) measurements show that the coefficient of ST of NAQ prepared precursor is 45% lower than that of AQ prepared one. Fibres with aspect ratio up to 10000 and diameter of 200 nm were directly drawn from the NAQ precursors at room temperature in standard lab atmosphere. AQ prepared precursor allows obtaining of the fibers of minimum 500 nm in diameter with maximal aspect ratio 1000.

Preparation and Characterization of CNT/TiO2 Based Transparent Fiber Electrodes

In the present work, it is shown that carbon nanotube-doped transition metal oxides are potential candidates for use as ceramic transparent electrode materials. Electrodes in shape of fibers are obtained via inexpensive and low temperature sol-gel method. Fiber electrodes are characterised by SEM-FIB and rheological analizes. Due to extraordinary electrical and optical properties of CNT-s and good chemical and physical stability of metal oxide ceramics, resulting composites could be an interesting subject for industry.

Preparation and Characterization of Transparent Electrodes Based on CNT-s Doped Metal Oxides

In the present work, it is shown that carbon nanotube-doped transition metal oxides are potential candidates for use as ceramic transparent electrode materials. Used carbon nanotubes (CNT-s) are synthesized by using chemical vapor deposition (CVD) method. Electrodes in shape of fibers are obtained via inexpensive and low temperature sol-gel method. Due to extraordinary electrical and optical properties of CNT-s and good chemical and physical stability of metal oxide ceramics, resulting composites could be an interesting subject for industry.

Sol-Gel Derived SnO2 Nanometric Fibers

The applicability of Sn(OBu)4 based viscous oligomeric concentrates in fabrication of thin oxide fibers and needles is demonstrated. Influence of several crucial parameters like viscosity of the concentrate, humidity of surrounding atmosphere and pulling speed on formation of the structures is discussed. We show that the method enables to obtain fibers less than a micron in diameter and needles with tip radii down to 15 nm, i.e. in range that is of considerable interest for many nanotechnological applications.