Sagar, Kaushal Shashikant

Blokcopolymerers evne til at selvorganisere kan udnyttes i forbindelse med fabrikationen af nanostrukturerede materialer. Det er netop hvad vi har gjort i det arbejde som præsenteres her: nanoporøse materialer (NP) med porediameter af ca. 10 nm er skabt udefra en 1,2-polybutadien-bpolydimethylsiloxan (1,2-PB-b-PDMS) blokcopolymer. Nanoporøsiteten er induceret ved først at krydsbinde 1,2-PB blokken og derefter kemisk fjerne PDMS blokken fra PB-b-PDMS copolymeren, som fra polymersyntesestadiet er designet til at have gyroid struktur. Vi udnytternanoporøsiteten i polymeren samt dens kemiske komposition til at fremstille en ny type bølgeledere med en blandet fast-flydende kerne, som potentielt kan bruges i en række optofluidiske applikationer. Det opnås ved at fremskaffe hydrofile mønstre på de oprindelige hydrofobe NP vha. to typer fotokemiske modifikationer. Brydningsindeks kontrast genereres ved at vand spontant fylder de veldefinerede hydrofile områder af polymeren mens den omkringliggende hydrofobe NP forbliver tør og dermed har en lavere effektiv brydningsindeks.Således vil lys under total refleksion propagere indenfor de hydrofile mønstre. Bølgelederen med blandet kerne viser potentielt samme høj følsomhed overfor små prøvevolumener som de mere traditionelle flydende kerne bølgeledere; dog, den vigtige nye funktion af in situ prøvefiltrering gør den nye type bølgeleder særlig velegnet til at analysere komplekse væsker som blod og mælk. Den første mode at inducere hydrofilicitet på i den iboende hydrofobe nanoporøse polymer er via UV foto-oxidering af 1,2-PB, hvor ilt fra luften fotokemisk fikseres på porernes grænseflade i form af hydrofile grupper som hydroxyl og carboxylsyregrupper. En detaljeret kvantitativ og kvalitativ karakterisering af foto-oxidations reaktionsprodukter udføres ved at kombinere gravimetriske målinger, titrering og spektrometriske analyser, såsom infrarød spektroskopi og faststof 13C kerne magnetisk resonans. De fleste af foto produkterne viser sig at være placeret på en subnanometer tynd lag ved den meget udstrakte polymer-luft grænseflade. Fordelingen af iltholdige kemiske grupper langs prøvens dybde kortlægges vha. energi dispersive x-ray spektroskopi. Analysen viser en meget heterogen fordeling af foto-oxidations produkterne med 4-5 gange højere ilt koncentration på prøvens overflade vendt mod UV kilden end i områder somligger dybere end 100 μm ind i prøven. Optisk karakterisering af bølgeledere fremstillet ved UV foto-oxidation er udført for at måle forskellige tab der opstår under lys propagering i bølgelederne.For den anden type hydrofile modificering af den stor nanoporøse polymers overflade udnytter vi de meget effektive thiol-ene fotokemiske ’klik’ reaktioner. Dette gøres ved at lade grænsefladens vinyl dobbeltbindingerne i 1,2-PB (ene funktionalitet) fotokemisk reagere med udvalgte hydrofile thiol forbindelser i forvejen bragt ind i porerne. Reaktionen er overvåget vha. spektroskopi (UVVis, FT-IR) samt gravimetriske og kontakt vinkel målinger. Kvanteudbyttet af de anvendte fotokemiske reaktioner er også estimeret. Thiol-ene reaktionstiden er en faktor 50-300 kortere endfoto-oxidations reaktionstiden. Thiol-ene reaktionen tillader en høj grad af kontrol overfor typen og mængden af de introducerede hydrofile grupper, meget homogen fordeling af grupperne i hele pore grænsefladen samt en intakt materiale mekaniske styrke. Know-how af thiol-ene reaktionens kemiske aspekter bliver anvendt til at fabrikere fast-flydende kerne bølgeledere. Fabrikationen sker ved hjælp af standard mikrofabrikations renrums teknikker og UV-litografi. Bølgelederne fabrikeret vha. thiol-ene modifikation viser betydelige mindre optiske tab end tilsvarendebølgeledere lavet vha. UV foto-oxidering.Immobilisering af et antistof binding fragment (FAB) inde i porerne af thiol-ene modificeretnanoporøse grænseflade er demonstreret. Dette er et første skridt i at undersøge brugen af voresbølgeledere indenfor biosensor applikationer.Block copolymers are known for their self-assembling ability utilized for bottom-up nanostructure fabrication. It is particularly capitalized in the context of present work where nanoporous scaffolds are created from a 1,2-polybutadiene-b-polydimethylsiloxane (1,2-PB-b-PDMS) block copolymer precursor material. Upon attaining thermodynamically stable gyroid phase segregation, nanoporosity is induced by chemically removing PDMS, the so-called sacrificial block. The isotropic nanoporosity in the polymer is utilized in fabricating a novel type of waveguides for opto-fluidic applications, which we call solid-liquid core waveguides, shortly SLCW. The high refractive index core of a SLCW consists of nanoporous polymer (solid) rendered hydrophilic and filled with water (liquid), while the low refractive index cladding consists of air-filled hydrophobic nanoporous polymer. Under conditions of total internal reflection, light is confined within the solid-liquid core. Controlled regions of the originally hydrophobic nanoporous 1,2-PB arerendered hydrophilic by photochemical modification of the polymer in the presence of photolithographic masks. In contact with water the hydrophilic regions are spontaneously filled with water by capillary suction, forming the core, while the unmodified hydrophobic regions remain dry, forming the clad. Two types of photo-modification reactions are presented in this thesis: photo-oxidation and thiol-ene photo-clicking.The hydrophilicity is firstly induced by surface photochemistry via UV photo-oxidation of nanoporous 1,2-PB. Detailed quantitative and qualitative analysis of photo-oxidation in the presence of air is carried out by gravimetry, titrimetry and spectrometry. Distribution study of the hydrophilic photo-products relative to the polymer-air interface shows high concentration at the nanoporous interface. Thus, the majority of cross-linked PB matrix remains unmodified.Distribution of the hydrophilic groups along the depth is carried out by energy dispersive x-ray spectroscopy. It shows a highly heterogeneous photo-oxidation reaction with most of the oxygen fixed close to the surface facing the UV source. Optical characterization of UV photo-oxidation based devices is performed to report various losses occurring during light guiding experiments. Thiol-ene click reactions are also used for the hydrophilization of the internal surface area of nanoporous polymer. This is done by photochemical reaction of the vinyl unsaturations of 1,2-PB at the interface (ene functionality) with hydrophilic thiols in the presence of a photoinitiator. The reaction is monitored by UV-Vis, FT-IR and contact angle measurements. Quantum yields of the photochemical reactions are estimated. Kinetic aspects of the photo grafting reaction on thenanoporous wall are studied using gravimetry. The fabrication of solid-liquid core waveguides is done by adapting the know-how on thiol-ene photochemistry to standard microfabrication cleanroom setup and UV lithography. Contrast curves for thiol-ene systems are reported to comment on the homogeneity of the polymer modification by the reaction. Finally optical characterization of devices is carried out to report propagation loss values.The UV photo-oxidation of nanoporous 1,2-PB is found to be a simple but heterogeneous surface modification technique compared to thiol-ene photo-modofication. Reaction times for photooxidation are longer by factors of 50-300 than thiol-ene reaction times. Compared to the oxidation, the thiol-ene reaction imparts better control, homogeneity and results in about half propagation loss in the fabricated waveguides.The fabricated waveguides are also tested in few preliminary biosensing experiments. Antibody fragments, Fab that quench fluorescence from the fluorescein dye are introduced into the nanopores. The distribution of Fab fragments in the hydrophilic core is mapped by confocal microscopy. The study of their ability to quench the fluorescence from the dye is work under progress

Online Research Database In Technology

Polymer Design and Processing for Liquid-Core waveguides

http://orbit.dtu.dk/ws/files/9608294/Kaushal%20Sagar.pdf

Polymer Design and Processing for Liquid-Core waveguides

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Online Research Database In Technology