Aggregation Behaviour And Encapsulation Of Organic Dyes

Organic dye molecules tend to form random or well-organized aggregates via self-assembly in solution or in adsorbed states.The formation of well-organized dye aggregates is desired because they exhibit diverse optical or electro-optical properties with potential applications in novel devices.In addition,due to aggregate behavior,dye molecules can be encapsulated into inorganic or polymer matrixes using various techniques to stabilize the tailored supramolecular dye aggregates and the better photophysical or photochemical properties can be obtained.In this study,the self-assembly behavior of Rhodamine B in binary solvents and the stability of the formed aggregates were investigated.Using miniemulsion and water-in-oil-in-water(w/o/w)double miniemulsion polymerization techniques,oil-soluble and water-soluble dyes were encapsulated polystyrene(PS)matrixes to fabricate composite "nanocolorants".The contents what is detailed concerned in this dissertation are shown as follows:(1) Rhodamine B aggregates with well-organized architecture at comparatively high concentration were fabricated by binary solvents-induced method.Using water as good solvent and THF as a poor one for RB dye,the self-assembly behavior,spectroscopic properties and stability of RB aggregates were investigated.Tuning the volume ratio of THF to H₂O to obtain RB nanorod structures at high concentration(1×10^-2M).TEM,SEM observation and selected-area electron diffraction patterns revealed that rod-like RB nanocrystals could be formed at 6:1 THF/H₂O.To stabilize the formed organic nanostructure,it was further encapsulated within silica using a sol-gel process.TEM, Zeta-potential measurement and selected-area electron diffraction patterns indicated that RB nanorods were successfully encapsulated within a silica layer using a sol-gel process.These silica-coated RB nanorods exhibited increased fluorescent intensity,non-leachability in polar solvents and RB photostability.(2) Using miniemulsion polymerization technique,oil soluble dye,Sudan black B(SDB) was encapsulated into polystyrene(PS)latex particles in the presence of methyl isobutyl ketone(MIBK).Effects of the weight ratio of MIBK/styrene(St)and the SDB load on the morphology of latex particles and encapsulation efficiency were studied.It was found that the encapsulation efficiency of SDB with PS increased as the weight ratio of MIBK/St rose. The prepared PS/SDB latex particles have a perfect core-shell structure and as high as more than 90%of encapsulation efficiency at 1:1 of MIBK/St and SDB load is as high as 50wt%. UV irradiation experiments and dynamic light scattering tests indicated that the obtained PS/SDB latexes exhibited excellent photostability and storage stability.(3) Hydrophilic dyes,reactive brilliant red K-2BP(C.I.reactive red 24),acid fuchsin(C.I. Acid violet 19)and cationic brilliant red 5GN(C.I.Basic red 14),were encapsulated into hydrophobic polystyrene(PS)latex particles using double miniemulsion technique in which water droplets containing dyes were first suspended in octane/styrene phase using lipophilic emulisifiers to form a primary miniemulsion and subsequently the primary miniemulsion was dispersed in water.It was found that the nature of water-soluble dyes,concentration of lipophilic emulsifiers and the ultrasonication time for formation of double miniemulsion are extremely critical to fabricate dye/PS core/shell colorants.TEM observation indicated that dye/PS latexes with core-shell structure can be prepared and the size of dye-loaded PS increased dramatically comparing with empty PS particles.Encapsulation efficiency as high as around 80%was reached for all three dyes.All the obtained dye/PS composite nanocolorants exhibited excellent water-fastness and photostability.