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Hoar and Schulman were the first (in 1943) to describe the transparent water-in-oil dispersion. They noted that a certain combination of water, oil, surfactant and alcohol cosurfactant would produce a clear homogeneous "solution", which Schulman in 1959 termed microemulsion. Schulman’s model of the inverse submicroscopic micelle is shown in Fig. 1. The IUPAC definitiondescribes microemulsion as a dispersion made of water, oil, and surfactant(s), which is an isotropic and thermodynamically stable system with dispersed domain diameter varying approximately from 1 to 100 nm, usually 10 to 50 nm. Water-in-oil microemulsions are important for the synthesis of various inorganic materials. In contrast to inverse micelle, water-in-oil micro-emulsion aggregates have mobile or free water in the core of the aggregate (Fig. 2). Reactions take place in a small volume of water inside a microdroplet, which results in improved properties of the products in terms of purity and particle size distribution. Microdroplet size can be controlled by suitable choice and mixing ratio of surfactant and cosurfactant (Fig. 3) and by the chemical composition of the oil and water phases. Microemulsions may have complex phase behaviour, commonly displayed in a phase diagram (Fig. 5 and Fig. 12). Surfactants are amphiphile molecules with hydrophilic head and lypophilic tail, thus bringing them affinity both to water and oil. Their main characteristics are adsorption at the interface and self-organization into supramolecular structures. By forming the interface layer, surfactants decrease surface tension and stabilize the microemulsion. According to the character of the hydrophilic head, surfactants are divided into anionic, cationic, nonionic, and amphoteric. Chemical structures of typical representatives are given in Fig. 6. Microemulsion aggregates may have various shapes, e.g. spherical, ellipsoidal, cylindrical, worm-like or bilayer (Fig. 7). Bicontinuous phase also occurs in different forms, e.g. hexagonal, lamellar or cubic. The main parameters that determines the microstructure are curvature of the interface film. (Fig. 8) and critical packing parameter (Fig. 10). A microemulsion can be composed of microdroplets of oil in water, or microdroplets of water in oil, or it can be the so-called bicontinuous phase in which water and oil are continuously intermixed in a sponge-like structure (Fig. 9). The solubility of water in microemulsion (Fig. 12) as well as morphology of microemulsion aggregates (Fig. 7) are very important for the synthesis of nano particles using microemulsion technique.

U ovom pregledu prikazane su mikroemulzijske tehnike za sintezu metalnih, metal-oksidnih, sulfidnih i polimernih nanočestica. Sinteza se izvodi u mikroemulzijama voda-u-ulju, miješanjem dviju mikroemulzija, od kojih jedna sadrži kationski prekursor, a druga precipitacijski medij ili redukcijsko sredstvo. Nanočestice metala dobivaju se redukcijom metalnog kationa s jakim redukcijskim sredstvima uz oslobađanje vodika prikladnim redukcijskim sredstvom. Na sličan način mogu se pripraviti i nanočestice legura od soli različitih metala pod uvjetom da se metali međusobno miješaju. Mikroemulzijska tehnika veoma je pogodna i za nanošenje nanočestica na različite podloge. Na taj način mogu se dobiti visokoaktivni katalizatori od nanočestica Pt, Pd, Rh i drugih plemenitih metala. Metalni oksidi i hidroksidi pripravljaju se hidrolizom ili taloženjem u vodenoj jezgri mikroemulzije. Da se spriječi oksidacija nanočestica, osobito Fe, čestice se prevlače inertnim metalima, oksidima, različitim polimerima i dr. Prevlačenjem se može postići dodatna funkcionalnost; npr. prevlačenje zlatom omogućava naknadnu funkcionalizaciju organskim spojevima koji sadrže sumpor, zahvaljujući jakoj tiolnoj vezi Au–S. Polimerne prevlake smanjuju toksičnost nanočestica i povećavaju biokompatibilnost, a funkcionalne skupine na površini omogućavaju razne primjene u biomedicini. Reakcije polimerizacije ili umrežavanja mogu se inicirati u vodenim jezgrama mikroagregata kemijskim sredstvima ili npr. UV ili ionizirajućim zračenjem. Prednosti mikroemulzijske polimerizacije su velika brzina, jednolična veličina čestica, stabilnost te visoki stupanj polimerizacije. Nanočestice magnetita pobuđuju velik interes zbog primjene u biomedicini. Magnetit je biokompatibilni materijal, a može se pripremiti u obliku dobro dispergiranih nanočestica manjih od 4 nm, koje imunosni sustav ne prepoznaje. Prikazana je vlastita metoda mikroemulzijske sinteze nanočestica magnetita potpomognuta γ-zračenjem., Nanoparticles and nanomaterials have wide applications in electronics, physics, material design, being also utilized as sensors, catalysts, and more and more in biomedicine. Microemulsions are an exceptionally suitable medium for the synthesis of nanoparticles due to their thermodynamical stability, great solubility of both polar and nonpolar components, as well as their ability to control the size, dispersity and shape of the particles. This review presents microemulsion techniques for the synthesis of inorganic nanoparticles. It takes place in water-in-oil microemulsions by mixing one microemulsion with a cationic precursor, and the other with a precipitating or reducing agent, or by direct addition of reducing agents or gas (O2, NH3 ili CO2 ) into microemul sion (Fig. 1). Metal nanoparticles are used as catalysts, sensors, ferrofluids etc. They are produced by reducing the metal cation with a suitable reducing agent. In a similar way, one can prepare nanoparticles of alloys from the metal salts, provided that the metals are mutually soluble. The microemulsion technique is also suitable for depositing nanoparticles onto various surfaces. Highly active catalysts made from nanoparticles of Pt, Pd, Rh and other noble metals may be obtained in this way. Metal oxides and hydroxides may be prepared by hydrolysis or precipitation in the water core of microemulsion. Precipitation can be initiated by adding the base or precipitating agent into the microemulsion with water solution of metal ions. Similarly, nanoparticles may be prepared of sulphides, halogenides, cyanides, carbonates, sulphates and other insoluble metal salts. To prevent oxidation of nanoparticles, especially Fe, the particles are coated with inert metals, oxides, various polymers etc. Coating may provide additional functionality; e.g. coating with gold allows subsequent functionalization with organic compounds containing sulphur, due to the strong Au–S bond. Polymer coatings decrease toxicity of the nanoparticles and increase their biocompatibility, and the functional groups on the surface enable specific applications in biomedicine. Microemulsion synthesis is convenient both for organic and polymer particles. Polymerization or crosslinking reactions may be initiated in the water core of microaggregates by using chemicals, UV or ionizing radiation (Fig. 3). Microemulsion polymerization is advantageous due to fast reactions, uniform particle size, great stability and high polymerization degree. Magnetite nanoparticles induce great interest due to biomedical applications. Magnetite is a biocompatible material that may be prepared in the form of well-dispersed nanoparticles smaller than 4 nm, which are not recognized by the immune system. The authors’ own approach for the synthesis of magnetite nanoparticles using γ-irradiation assisted microemulsion technique is described (Figs. 5–10).

Factors that influence the precipitation of iron oxides from Fe(II) containing solutions were investigated by X-ray powder diffraction, (57)Fe Mossbauer and FT-IR spectroscopies, FE SEM and EDS techniques. Near spherical aggregates of spindle-shape goethite particles were obtained by oxidation of 0.1 mol dm(-3) FeSO(4) solution (suspension) with pure oxygen at 90 degrees C. Wide and thin goethite particles elongated along the crystallographic c-axis were formed in parallel. With the addition of tetramethylammonium hydroxide to 0.1 mol dm(-3) FeSO(4) solution (suspension) substoichiometric magnetite (Fe(3-x)O(4)) particles were additionally formed. They were dominant at pH > 12.5. Mossbauer spectroscopy was used to calculate the stoichiometries of Fe(3-x)O(4) particles. Very small magnetite particles (approximate to 20-100 nm) showed a tendency to aggregate. The twinning effect of octahedral magnetite particles (> 200 nm) was observed. A drastic effect on the properties of iron oxide precipitates was achieved by adding H(3)PO(4) to the precipitation system containing 0.1 mol dm(-3) FeSO(4) + 0.01 mol dm(-3) H(2)SO(4) solution at the start, In dependence on the concentration of the added H(3)PO(4). nanosize goethite particles about 15-25 nm in size, or poor crystalline ferrihydrite particles (two-line ferrihydrite) were obtained. The EDS analyses of the precipitates did not show any significant change in the sulphur content, whereas the phosphorous content gradually increased in the precipitates with an increase in the added H(3)PO(4). In high concentrations phosphates completely suppressed the formation of goethite under given experimental conditions, and phosphated ferrihydrite was formed instead.

U zadnje dvije dekade postoji snažan interes znanstvene zajednice kao i visoko-tehnološke industrije za materijalima koji u svojem nazivu imaju prefiks "nano", npr. nanoˇcesticama, nanokristalima, nanostrukturama. Nano ˇcestiˇcni materijali pokazuju veliko bogatstvo novih temeljnih fiziˇckih fenomena koji se gotovo u potpunosti razlikuju od onih u makroskopskim sistemima. Ciljana nanostrukturna istraživanja u Laboratoriju za molekulsku fiziku IRB-a poˇcinju vec poˇcetkom devedesetih godina istraživanjem nanostrukturnih defekata u amorfnom siliciju i galijevom arsenidu u suradnji s grupom T. E. Haynesa, SAD. Sredinom devedesetih istraživanja se proširuju na oksidne nanoˇcestice dobivene sol-gel metodom u suradnji s grupom Dr. S. Musi´ca i na nanoˇcestice CdxSe1-x u staklenoj matrici u suradnji s grupom Prof. W. Kiefera, Njemaˇcka. Trenutna istraživanja se još odvijaju u suradnji s talijanskim znanstvenicima na TiO2 nanoˇcesticama u kvarcnoj matrici dobivenih sol-gel metodom u suradnji s grupom prof. M. Montagne, Si - nanoˇcesticama u kvarcnoj matrici u suradnji s prof. L. Pavesijem i helijem induciranim nanostrukturama u siliciju u suradnji s prof. G. Mariottom. U okviru ovog rada biti ´ce prikazane osnove teorije Ramanovog raspršenja na nanoˇcesticama kao i zanimljiviji primjeri primjene Ramanove spektroskopije na nanostrukturama.

Titania, TiO2, is a technologically interesting material because of its catalytic and electronic properties. Its properties, however, change when it is doped with metal atoms or when prepared to have a very small crystallite size [R. J. H. Clarc, The Chemistry of Titanium and Vanadium, Elsevier Publ. Co., New York, 1968]. In this work we examined the influence of iron doping on structural properties of titania. Polycrystalline titania and Fe-doped titania samples containing 0.5, 1.1, 2.6, 8.1 and 18 at% Fe were prepared by a sol-gel technique. Ti(IV)-isopropoxide and Fe(III)-nitrate were used as precursors of titanium and iron. Synthesis was performed in a nitrogen inert atmosphere under alkaline conditions, which was accomplished by addition of NH3. As-synthesized samples were annealed at 500 °C for 2 hours. The samples were examined by X-ray powder diffraction at room temperature. Sample of pure titania was anatase (tetragonal, S. G. I41/amd). Sample with 0.5 at% Fe was an anatase-type solid solution. For Fe doping level higher than 0.5 at% Fe the samples contained two phases, that of anatase-type and of rutile-type (tetragonal, S. G. P42/mnm), respectively. Anatase phase was dominant for all the doped samples. The sample with 18 at% Fe contained impurity, namely ~5% Fe2TiO5. All the samples were nanocrystalline, with crystallite sizes in the range 10-20 nm. Diffraction line broadening increased with Fe doping level. Unit-cell parameters were determined using Si as an internal standard, and refined by the whole powder pattern fitting [WPPF program, H. Toraya, J. Appl. Cryst. 19 (1986) 440]. Iron doping increased slightly unit-cell parameters of both anatase- and rutile-type phases. The Rietveld method [H. M. Rietveld, J. Appl. Cryst. 2 (1969) 65] was performed to refine the crystal structure of obtained phases, and the real incorporation level of Fe into the anatase and rutile lattices was determined.