Immobilization of optical sensors on selected plastic surfaces

Cilj ovog rada bio je pripremiti optički senzorski sloj u kanalu mikroreaktora. Mikroreaktor i pločice proizvedeni su 3D-ispisom. Senzorski sloj prvo je ispitan na pločicama kako bi se utvrdilo koji senzorski sloj će dati najbolje rezultate te se može koristiti za prevlačenje kanala. Krajnji cilj je dobiti funkcionalan film na površini cijevi mikroreaktora. Dva načina pripreme koktela ispitana su u ovome radu. Prvi način je sol-gel metoda u kojoj je kiselo kataliziranom hidrolizom i kondenzacijom tetraetoksisilana i feniltrimetoksisilana dobiveno šest filmova od kojih su tri filma s pojedinačnim indikatorom, a tri filma smjese dvaju indikatora. Redom to su indikatori: metil crveno, brom timol plavo i brom krezol zeleno (BCG) i njihove smjese metil crveno i brom timol plavo, metil crveno i brom krezol zeleno i smjesa brom timol plavog i brom krezol zelenog. Drugi set koji sadrži šest pločica s istim pojedinačnim i smjesom senzora dobiven je otapanjem cikličkog olefinskog kopolimera (COC) u toluenu pri povišenoj temperaturi uz miješanje i dodatak bis(2-etilheksil) sebacata kao plastifikatora. Na zadnjih šest pločica nanesen je film s jednakim indikatorima kao i kod prvih 12, uz razliku da je kao otapalo korišten tetrahidrofuran (THF) te poli(vinil-klorid) kao matrica za film uz dodatak istog plastifikatora kao i kod prethodnog filma. Filmovi dobiveni otapanjem PVC-a u THF-u pokazali su se najlošijim jer nisu prošli nijedan od preliminarnih testova: otpornost na grebanje i testiranje senzorskih svojstava jer su se svi filmovi vrlo lako izgrebli pincetom te nijedan nije zadržao senzorska svojstva, već je samo došlo do istjecanja indikatora u otopinu. Sol-gel metoda pokazala se najboljom od svih koje su korištene. Najveći broj filmova otpornih na grebanje dolazi iz ove skupine pločica te je i najveći broj filmova zadržao senzorska svojstva. Problem prilikom nanošenja indikatora je što je nanesen metodom ubacivanja u otopinu te je iz tog razloga film velike debljine i vrijeme odaziva najboljeg filma je nešto više od 20 minuta. Mikroreaktor prevučen filmom TEOS-FTMS-BCG dao je odziv za 90 sekundi, čime je pokazao da je moguće uspješno prevuči površinu kanala, no još uvijek postoji problem nereverzibilnosti procesa jer kada brom krezol zeleno pređe u deprotonirano stanje, nije moguće provesti mjerenja u zakiseljenim otopinama jer odziva više nema tj. indikator ne prelazi ponovno u protonirano stanje.The goal of this study was to prepare an optical sensory film in the channel of the microreactor. The microreactor and the little plates were manufactured with 3D-printing technology. The sensory film was preliminary tested on the little plates to determine which coating will yield the best result. The film which yielded best results is then later tested in the microreactor channel. The utmost goal is to obtain functional film on the microreactor channel surface. Two methods of preparing the coating cocktail were studied. The first studied method was a sol-gel method in which we use acidly catalysed hydrolysis and condensation of precursors: tetraethoxysilane and trimethoxyphenylsilane to make six films. Three of the six films are made with single indicator and other three were mixtures of previous indicators. Those indicators are: methyl red, bromothymol blue, bromocresol green (BCG) and their mixtures methyl red with bromothymol blue, methyl red with bromocresol green and bromotyhmol blue with bromocresol green. The second set containing six little plates was made with the same single indicator and indicator mixtures as previously. The solution is made by dissolving cyclic olefin copolymer (COC) in toluene with heating and mixing and addition of bis(2-ethylhexyl) sebacate as a plasticizer. Third set of plates was made with same indicators as previous twelve with the only difference that the solution was made by dissolving polyvinyl chloride (PVC) in tetrahydro furane (THF) with the same plasticizer as before. The films made with PVC and THF yielded worst results because they did not pass any of the preliminary tests: scratch test or retention of the sensory properties test. All films were scratched easily with the pincers and none of them had the sensory properties, instead only leaching of indicator in solution was observed. The sol-gel method proved to be best of two methods used in this study. The most films that are scratch resistant come from this group of the little plates and the greatest number of the films kept sensory properties. The biggest problem of these films was the method of coating used which is drop coating in which we are unable to control the thickness of film and response time of the film is more than 20 minutes. The microreactor coated with the TEOSFTMS-BCG film changed the colour in 90 seconds. That shows us that it is possible to successfully coat the channel of the microreactor. One problem still lingers, the process is still irreversible because when bromocresol green goes into the deprotonated state, it is impossible to conduct the analysis in acidic solutions because the indicator does not go back to the protonated state