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Mikroemulzije se sve češće koriste kao metode priprave nanočestica, a posebno nanosfera, zbog svojih svojstava kao što su termodinamička stabilnost, optička prozirnost i niska viskoznost. Mikrosfere su sferične čestice veličine od 1 do 1000 μm, a odlikuju se velikom specifičnom površinom te su biorazgradljive što ih čini dobrim potencijalnim nosačima za lijekove te kontrolirano otpuštanje lijekova u manjim količinama. Mikrosfere se mogu pripremiti raznim postupcima, a u ovom je radu opisan postupak priprave mikrosfera na temelju kitozana metodom emulzije, odnosno mikroemulzije. Kao vodena (dispergirana) faza je korištena otopina kitozana, prirodnog polimera, uz dodatak bakrovih (II) iona (Cu2+) kao fizikalnog umreživala (otopina kompleksa CHT‒Cu). Kao uljna (kontinuirana) faza su korišteni izooktan, odnosno smjesa lakog i teškog parafina, uz dodatak emulgatora SPAN 85. Ispitivan je utjecaj različitih uljnih faza, omjer vodene i uljne faze te vrsta reaktora na sastav, izgled, morfologiju i veličinu dobivenih čestica. FTIR analiza je pokazala da su dobivene mikročestice kitozanske, a budući da nije detektirana pojava novih apsorpcijskih vrpci, interakcije funkcionalnih skupina polimera s bakrovim ionima su elektrostatske prirode. SEM analizom je utvrđeno da su dobivene mikročestice neporozne i glatke površine za sustav dobiven primjenom aparature s reaktorom ravnog dna, uz omjer vodene i uljne faze 1/5 te izooktanom kao uljnom fazom. Također, taj sustav je pokazao i najužu raspodjelu veličinu čestica. Čestice koje su nastale u emulziji sa smjesom lakog i teškog parafina kao uljnom fazom bile su nepravilnog oblika. Microemulsions are increasingly being used as methods of preparation of nanoparticles, especially nanospheres, due to their properties such as thermodynamic stability, optical transparency and low viscosity. Microspheres are spherical particles ranging in size from 1 to 1000 μm, characterized by a large specific surface area and biodegradability, which makes them suitable drug carriers for controlled release of drugs in smaller dosages. Microspheres can be prepared by various methods, and this work describes the preparation of chitosan-based microspheres using the emulsion, specifically the microemulsion method. A solution of chitosan, a natural polymer, was used as aqueous (dispersed) phase with the addition of copper (II) ions (Cu2+) as a physical crosslinker (solution of the CHT‒Cu complex). Isooctane and a mixture of viscous and highly liquid paraffin were used as the oil (continuous) phase, with the addition of the SPAN 85 as an emulsifier. The influence of different oil phases, the water-to-oil phase ratio and type of a reactor were examined on the composition, appearance, morphology and size of the particles. FTIR analysis showed that the obtained particles are chitosan-based, and the absence of new absorption bands indicated electrostatic nature of the interactions between chitosans’ functional groups and copper. SEM analysis showed that the obtained particles are non-porous and have smooth surface when prepared using the flat bottom reactor, with the ratio of water-to-oil phase of 1/5 and isooctane as the oil phase. Also, that system showed the narrowest particle size distribution. The particles formed in the emulsion with a mixture of viscous and highly liquid paraffin as the oil phase were irregular in shape.

U ovom radu proveden je postupak optimiranja pripreme mikroemulzija ulje u vodi i ulje i vodenom ekstraktu mente u mikroprotočnom sustavu uz emulgator polietilen glikol (PEG1500, 6000 i 20000). Ispitan je utjecaj količine emulgatora, količine ulja i ukupnih protoka na stabilnost mikroemulzija koja je izražena zeta potencijalom i Feretovim promjerom te su određeni optimalni procesni uvjeti za 6 sustava pripreme mikroemulzija. Na temelju dobivenih vrijednosti zeta potencijala kao najstabilnije su se pokazale emulzije pripremljene s vodom kao kontinuiranom fazom i emulgatorom PEG1500 te je uočeno da vrijednost zeta potencijala opada porastom molekulske mase upotrijebljenog emulgatora. Nadalje izabrani emulgatori ne osiguravaju zadovoljavajuću stabilnost emulzija ako se kao kontinuirana faza upotrijebi vodeni ekstrakt mente. Umjetne neuronske mreže pokazale su se pouzdanima u predviđanju Feretovog promjera kapljica emulzija ulje u vodi za sve analizirane sustave. In this work, optimisation of oil in water and oil in peppermint extract microemulsion preparation in microfluidic system using polyethylene glycol as emulsifier (PEG 1500, 6000 and 20000) was performed. The effect of the emulsifier amount, oil amount and total flow rate on the microemulsion stability expressed as zeta potential and Feret diameter was analysed. Optimal process conditions for microemulsion preparations were estimated for all 6 analysed systems. Based on the zeta potential, the most stable emulsions were prepared with water as continuous phase and using PEG 1500 as emulsifier. It was observed that with the increase of emulsifier molecular weight value of zeta potential decreases. Furthermore, the selected emulsifiers did not ensure satisfactorily stability for emulsions when the aqueous extract of mint was used as the continuous phase. Artificial neural networks (ANNs) were shown reliable for prediction of Feret diameter of droplets in oil in water emulsions for all analysed systems.

Eterična ulja prisutna su u topikalnoj primjeni zbog svojih antimikrobnih, antioksidacijskih, protuupalnih i drugih pozitivnih učinaka. Posebno je ineresantna njihova primjena kao promotora penetracije. Upotrebom nanotehnoloških nosača, kao što su nanoemulzije, mikroemulzije, nanogelovi i nanočestice, omogućuje se primjena nestabilnih i teško topljivih djelatnih tvari, poboljšava se dermalna raspoloživost i omogućava kontrolirano oslobađanje djelatnih tvari. Primjenom eteričnih ulja u nanotehnološkim pripravcima s uklopljenom djelatnom tvari, dobivaju se sustavi jedinstvenih svojstava. Eterična ulja dodatno poboljšavaju fizičku stabilnost uklopljene djelatne tvari, njenu permeaciju i raspodjelu u koži, a posljedično i biološku aktivnost djelatne tvari. Upotrebom eteričnih ulja moguće je pripremiti nanotehnološke nosače s boljim kapacitetom uklapanja za određene djelatne tvari. Nadalje, eterična ulja u nanotehnološkim pripravcima zadržavaju svoja farmakološka svojstva i djelujući sinergistički poboljšavaju učinak uklopljene djelatne tvari. Brojna su in vitro ispitivanja pokazala sigurnost i učinkovitost nanotehnoloških formulacija s uklopljenim eteričnim uljima i djelatnim tvarima. Stoga, takve formulacije predstavljaju veliki potencijal za daljnje istraživanje. Prije svega, potrebno je utvrditi njihovu sigurnost i učinkovitost u kliničkoj primjeni. Essential oils are used for topical application because of their antimicrobial, antioxidant, anti-inflammatory, and other beneficial effects. Their use as penetration enhancers is particularly interesting. Nanotechnological carriers, such as nanoemulsions, microemulsions, nanogels and nanoparticles, enable application of unstable and poorly soluble active ingredients, improve dermal availability and enable sustained release of active ingredients. Use of essential oils in nanotechnological carriers with encapsulated active ingredients enables production of formulations with unique properties. Essential oils further improve active ingredient physical stability, improve active ingredient permeation and skin distribution, and consequently its biological activity. Using essential oils, it is possible to prepare nanotechnological carriers with better encapsulation efficiency for some active ingredients. Furthermore, essential oils in nanotechnological carriers retain their pharmacological properties and acting synergistically, improve the effect of encapsulated active ingredient. Numerous in vitro researches show nanotechnological formulations with encapsulated essential oils safety and efficiency. Therefore, there is a huge potential for further research of such formulations. Especially, their safety and efficiency in clinical trials should be determined.

Mikroemulzije su se u proteklih nekoliko godina pojavile kao novi dozirni oblik kojim se omogućuje povećanje apsorpcije djelatne tvari u organizam. To su termodinamički stabilni, optički izotropni sustavi sastavljeni od ulja, vode, surfaktanata i kosurfaktanata. Zbog postojanja hidrofilnih i lipofilnih domena pokazuju poboljšanu topljivost djelatne tvari. Prema strukturi dijele se na mikroemulzije ulja u vodi, mikroemulzije vode u ulju te bikontinuirane strukture. U eksperimentalnom su istraživanju formirane samoorganizirajuće mikroemulzije s uklopljenim dronedaron-hidrokloridom. Dronedaron-hidroklorid otopljen je u etanolu koji je uklonjen isparavanjem u rotacijskom isparivaču i vakuumskom sušioniku. Korištena su dva stabilizatora, Kolliphor EL i Kolliphor RH40. In vitro metodom ispitana je brzina oslobađanja dronedaron-hidroklorida iz mikroemulzija. Promjena koncentracije dronedarona određena je pomoću UV/Vis spektrofotometra mjerenjem apsorbancije te su dobiveni profili oslobađanja dronedaron-hidroklorida. Mikrografijama je potvrđeno da dodatkom pripremljenog sustava u fosfatni pufer nastaju mikroemulzije. In vitro metoda ispitivanja pokazala je izuzetno brzo oslobađanje dronedaron-hidroklorida iz mikroemulzija, već 90 % nakon 10 minuta. In last few years, microemulsions have been recognized as new alternative dosage form which allows increase in the absorption of active substance. They are thermodynamically stable, optically isotropic systems of oil, water, surfactants and cosurfactants. Due to the existence of hydrophilic and lipophilic domains better solubility of active substances is possible. Structurally, they are divided into oil in water, water in oil and bicontinuous microemulsions. Self-microemulsifying drug delivery systems containing dronedarone hidrochloride were prepared in this study. Dronedarone hydrochloride was dissolved in ethanol and then removed by evaporation in rotational evaporator and vacuum dryer. Two stabilizers were used, Kolliphor EL i Kolliphor RH40. In vitro method was used to determine the release rate of dronedarone hydrochloride from microemulsions. The change of dronedarone concentration was determined measuring the absorbance by UV/Vis spectrophotometer. Also, dronedarone hydrochloride dissolution profiles were obtained. Micrographs confirmed self-formation of microemulsions when prepared mixtures were added into phosphate buffer. In vitro method showed instant release of dronedarone hydrochloride from microemulsions, 90% after 10 minutes.

Maslinovo ulje je jedna od najvažnijih namirnica u čovjekovoj svakodnevnoj prehrani zbog visoko vrijednih sastojaka koji potpomažu u očuvanju ljudskog zdravlja zbog uravnoteženog sastava masnih kiselina. Također, maslinovo ulje ima visok sadržaj vitamina E i polifenola koji imaju zaštitnu i antioksidacijsku ulogu. Riblje ulje je u posljednje vrijeme vrlo korištena namirnica zbog visokog sadržaja nezasićenih masnih kiselina, no ono je isto kao i maslinovo ulje podložno oksidaciji. Skvalen je polunezasićeni ugljikovodik koji ima značajan antioksidacijski učinak i mnoga biološka djelovanja, te zaštitno djeluje na nekoliko vrsta tumora. U ovom završnom radu se istraživao utjecaj dodatka skvalena na oksidacijsku stabilnost ribljeg i maslinovog ulja. Rezultati su potvrdili da skvalen nema utjecaj na produljenje oksidacijske stabilnosti ekstra djevičanskog maslinovog ulja niti ribljeg ulja. S druge strane, korištenje emulzijskog sustava može povećati utjecaj skvalena na produljenje oksidacijske stabilnosti. Olive oil is one of the most important foods in human daily diet because of high-value ingredients that affect the preservation of human health due to a balanced fat composition. Also, olive oil has a high vitamin E precentage that has a protective and antioxidant role. Fish oil has been a very useful food for the last time due to the high content of unsaturated fatty acids, but it is like olive oil an inadequate oxidation. Squalen is a semi-saturated hydrocarbon having a significant antioxidant effect and many biological effects, and protects against several types of tumors. In this final paper, the effect of squalene on the oxidative stability of fish and olive oil was investigated. Results showed that squalene had no effect on the prolongation of the oxidative stability of olive oil and fish oil. On the other hand, the use of emulsions system with incorporated squalene showed the prolongation of the olive oil and fish oil oxidative stability.

Nanoemulzije zbog svojih su svojstava zanimljive kao formulacije namijenjene oftalmičkoj primjeni. Mogu biti izrađene niskoenergetskim i visokoenergetskim metodama. Za potrebe ovog rada korištene su dvije visokoenergetske metode, visokotlačna homogenizacija i mikrofluidizacija. Nanoemulzije su pripremljene tako da se najprije izradila primarna emulzija, koja je zatim prošla kroz jedan, tri i pet ciklusa visokotlačne homogenizacije, odnosno mikrofluidizacije. Veličina kapljica, PDI i zeta-potencijal određeni su nakon izrade i dva tjedna nakon izrade kako bi se mogla procijeniti stabilnost nanoemulzija. Dobivene nanoemulzije bile su mliječno bijele boje i nisu pokazale odvajanje faza tijekom dva tjedna. Općenito su pri većem tlaku i pri većem broju ciklusa izmjerene najmanje veličine kapljica, dok je najmanja veličina kapljica izmjerena za nanoemulziju izrađenu nakon pet ciklusa mikrofluidizacije pri tlaku od 1300 bara. PDI nijednom nije bio manji od 0,1. Zeta-potencijal bio je približno sličan kod svakog uređaja, pri svakom tlaku i broju ciklusa. Bitno je naglasiti da su izmjerene vrijednosti (~4 mV) daleko od očekivanih vrijednosti (~30 mV). Nijedna formulacija nije pokazala željena svojstva. Nanoemulsions are interesting as pharmaceutical formulations for ophthalmic use because of their specific properties. They can be made with low-energy and high-energy methods. High-pressure homogenization and microfluidization were two high-energy methods used in this research. Nanoemulsions were prepared as follows: firstly, the primary emulsion was made, which was then passed through one, three and five cycles of high-pressure homogenization or microfluidization. Droplet size, PDI and zeta-potential were measured one day after preparation and two weeks after preparation to assess the stability of nanoemulsions. Prepared nanoemulsions were milky white and phase separation did not occur in two weeks. In general, using higher pressure and greater number of cycles resulted with smaller droplet size, with the smallest droplet size measured for nanoemulsion produced after five microfluidization cycles at 1300 bar. PDI was never less than 0.1. The zeta-potential was approximately the same in nanoemulsions prepared using both devices, regardless of pressure and number of cycles. It is important to note that the measured values (~ 4 mV) are far from the expected values (~ 30 mV). None of the formulations showed the desired properties.

Tinkture su alkoholne ili hidroalkoholne otopine pripremljene od biljnih ili kemijskih tvari. Tinkture su veoma korisne u industriji parfema , jer sadrže etanol koji je dobro otapalo mirisnih spojeva. U ovom istraživanju titracijskom metodom je određeno monofazno područje u trokomponentnom sustavu citral - etanol-voda . Stabilnost mikroemulzijskih agregata ispitana je mjerenjem zeta - potencijala . Tinctures are alcoholic or hydroalcoholic solutions prepared from vegetable or chemical substances. Tinctures are very useful in the perfume industry, because they contain ethanol, which is a good solvent of aromatic compounds. In this study titration method is used for the determination of single-phase area in three-component system citral - a water-ethanol. The stability of the microemulsion of aggregates was tested by measuring the zeta – potential.

Nanočestice zlata (AuNČ) sintetizirane su u mikroemulzijskom sustavu Triton X-100/voda/cikloheksan/1-pentanol pri čemu su kod sinteze mijenjani redukcijski uvjeti u mikroemulziji. Istraživane su tri mikroemulzijske sinteze; (i) sinteza AuNČ u mikroemulziji kod jakih redukcijskih uvjeta (dodatak NaBH4), (ii) sinteza AuNČ u mikroemulziji γ-zračenjem (radiolitička sinteza uz umjereno jake redukcijske uvjete) i (iii) sinteza AuNČ u mikroemulziji kod oksidacijskih uvjeta (dodatak vodene otopine NaOH). Sve sinteze odvijale su se na sobnoj temperaturi. Postupak sinteze započinje pripravom dviju mikroemulzija, A i B, od kojih Mikroemulzija A sadrži ione zlata (Au3+), dok Mikroemulzija B sadrži redukcijsko ili oksidacijsko sredstvo. Kada se Mikroemulzije A i B pomiješaju nastaje Mikroemulzija AB gdje dolazi do reakcije između mikroemulzijskih agregata, a time i do redukcije Au3+ iona u Au0 i nastajanja nanočestica zlata. Kada je u mikroemulziji B korišteno jako redukcijsko sredstvo NaBH4, prosječna veličina kristala zlata iznosi 11,7 nm što je utvrđeno iz proširenja difrakcijskih maksimuma. Prosječna veličina čestica na rubovima čestičnih agregata za isti uzorak mjerena elektronskom mikroskopijom iznosila je 7 ± 2 nm. Kod radiolitičke sinteze Au3+ ioni u mikroemulziji bili su reducirani γ-zračenjem. Redukcijska svojstva γ-zračenja bila su podešena propuhivanjem mikroemulzije plinovitim dušikom. Mikroemulzije koje nisu bile propuhane dušikom sadržavale su otopljeni kisik, a time i slabije redukcijske uvjete. γ-zračenjem mikroemulzija zasićenih kisikom dobivene su relativno veće nanočestice zlata (~12 nm) u odnosu na iste uvjete kod dušikom zasićenih mikroemulzija gdje su dobivene nanočestice prosječne veličine čestica 7-10 nm koje su nakon centrifugiranja djelomično agregirale u velike nanočestice promjera oko 150 nm. Dobivene velike nanočestice zlata posjeduju tiksotropna svojstva. Kod mikroemulzijske sinteze na sobnoj temperaturi kod oksidacijskih uvjeta u kiselom području (pH 7, jači oksidacijski uvjeti), nastaju dobro dispergirane nanočestice zlata promjera oko 12 nm. Sinteza nanočestica zlata u mikroemulziji kod alkalnog pH, ali ne i kod kiselog pH, može se objasniti oksidacijom alkoholnih skupina (-C-OH) u karbonilne skupine (>C=O) uz pomoć katalitičkog djelovanja hidroksilnih iona i zlata. Paralelno s katalitičkom oksidacijom alkoholnih skupina u mikroemulziji, ioni zlata (Au3+) reduciraju se u elementarno zlato (Au0) uz nastajanje nanočestica zlata. The gold nanoparticles (AuNPs) were synthesized in a microemulsion Triton X-100/water/cyclohexane/1-pentanol using various reducing agents. Basically, three microemulsion syntheses were studied; (i) the microemulsion synthesis of AuNPs using strong chemical reducing agent (NaBH4), (ii) the microemulsion synthesis of AuNPs using γ-irradiation (radiolytical synthesis at moderate reducing conditions) and (iii) the microemulsion synthesis of AuNPs at oxidising conditions (with the addition of NaOH aqueous solution). The syntheses were performed at room temperature. As the first step, Microemulsion A containing Au3+ ions and Microemulsion B containing reducing or oxidising agent were prepared separately. Then, the Microemulsion B was rapidly poured into Microemulsion A. While obtaining Microemulsion AB, a collision, coalescence and exchange of content between the microemulsion aggregates occurred. As a consequence the Au3+ ions were reduced to Au0 and the gold nanoparticles formed. When the strong chemical reducing agent NaBH4 was used in the microemulsion, the gold nanoparticles of 11,7 nm in size were obtained as determined on the basis of XRD line broadening. The mean particle size at the edges of aggregates for the same sample as measured by electron microscopy was 7 ± 2 nm. In the next experiments the aureate (Au3+) ions in microemulsions were reduced using γ-irradiation. The reducing power of γ-irradiation was tuned by bubbling microemulsions with nitrogen gas. The microemulsions that were not bubbled contained dissolved oxygen and thus more oxidizing conditions in comparison to the nitrogen saturated microemulsions. Basically, the γ-irradiated oxygen-saturated microemulsions produced relatively larger gold nanoparticles (~12 nm) in comparison to the γ-irradiated nitrogen-saturated microemulsions (7-10 nm), which under isolation by centrifugation aggregated in huge nanoparticles of about 150 nm in size. These gold nanoparticles possessed thixotropic properties. In addition, the microemulsion synthesis of gold nanoparticles under oxidising condition was investigated. The microemulsion stirred at room temperature and at pH < 7 containing no added reducing agent did not produce gold nanoparticles. At the identical experimental conditions and at pH >7 (oxidising conditions) the well-dispersed gold nanoparticles of 12 nm in size as measured using TEM were formed. Microemulsion synthesis of gold nanoparticles in the alkaline range, but not at an acidic pH, could be explained by the oxidation of alcoholic groups (-C-OH) into carboxylic groups (>C=O) due to the catalytic action of hydroxyl ions and gold. In parallel with the catalytic oxidation of alcohol groups in microemulsion, the Au3+ ions reduced to Au0 with subsequently formation of gold nanoparticles.

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).

U pregledu su prikazane glavne karakteristike mikroemulzija i njihove primjene. Mikroemulzije su termodinamički stabilni i optički izotropni sustavi koji se sastoje od ulja, vode i amfifilnih molekula koje nazivamo surfaktantima i kosurfaktantima. Mikroemulzija može biti sastavljena od mikrokapljica ulja u vodi ili od mikrokapljica vode u ulju, ili može biti tzv. bikontinuirana faza u kojoj se voda i ulje kontinuirano isprepliću u strukturi nalik spužvi. Mikroemulzije su samoorganizirajući sustavi i nastaju bez utroška energije. Mikroemulzije voda-u-ulju važne su za sintezu raznih anorganskih materijala. Reakcije se zbivaju u malom obujmu vode unutar mikrokapljice i zbog toga produkti često imaju poboljšane karakteristike u pogledu čistoće i raspodjele čestica po veličini. Veličinu mikrokapljica moguće je kontrolirati vrstom i omjerom surfaktanta i kosurfaktanta te kemijskim sastavom uljne i vodene faze. Mikroemulzije mogu imati složeno fazno ponašanje, koje se obično prikazuje faznim dijagramom. Osim spomenutih čistih strukturnih tipova, u mikroemulziji može biti zastupljeno i više njih odjednom. Surfaktanti su amfifilne molekule građene od hidrofilne glave i lipofilnog repa, zbog čega imaju afinitet i prema vodi i prema ulju. Njihova glavna svojstva su adsorpcija na međupovršini i samoorganizacija u supramolekulske strukture. Stvaranjem sloja na granici faza surfaktanti smanjuju površinsku napetost i stabiliziraju mikroemulziju. Prema vrsti hidrofilnog dijela surfaktanti se dijele u anionske, kationske, neionske i amfoterne. U pregledu su prikazane kemijske strukture njihovih tipičnih predstavnika. Mikroemulzijski agregati mogu imati različit oblik, kao npr. sferičan, elipsoidan, cilindričan, crvolik ili dvoslojni. Bikontinuirana faza također se javlja u više različitih oblika, npr. u heksagonskom, lamelnom ili kubičnom. Glavni parametri koji određuju mikrostrukturu su zakrivljenost međupovršinskog filma i kritični parametar pakiranja., 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 definition describes 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.