The fabrication of complex colloidal particles with anisotropic "patchy" e.g. Januslike, morphology will be studied. Known approaches towards "Janus particles" focus mostly on the micron-sized domain, with common fabrication routes based on monolayer modification or microfluidic production (restricts scale-up). We operate in the submicron regime (typically 100-500 nm) and use scalable emulsion polymerization strategies, in combination with entropic phase separation of swollen cross-linked latex particles and living radical polymerization, i.e. SET-LRP, to prepare our "patchy" amphiphilic particles. In this research, various Cross-linked densities (typically from 1 - 8wt%) poly(styrene) latexes (typically 100-500 nm) functionalized with tert-bromine functional groups, by batch or shot addition of (2-methacryloxyethyl -2- bromoisobutyrate) made via soap-free emulsion polymerization used as the precursor particles. Two synthetic pathways were investigated to make the targeted hairy Janus Particles. Approach one: in which we carried out the domain formation step prior to the fabrication of the polymer brushes, We found out that the effective synthetic way to make Janus hairy dumbbell particles in a reproducible manner is to start the synthesis with light cross-linked density of (1.9 to 3.0 wt% DVB) precursor poly(styrene) latex particles (150-250 nm diameter) made by shot addition method. The direct entropic phase separation from these latex particles leads to the formation of only one new domain with dumbbell shape morphology, when the swelling ratio used between monomer and latex is between 2.0 and 4.0, and with low DVB concentration in the swelling monomer (between 0.15-1.0wt%) using AIBN as initiator. Formation of hydrophilic polymer brushes by SET-LRP resulted in targeted hairy Janus particles with sub-micrometer diameter, in a reproducible manner. The length of the polymer brushes can be controlled by addition of water soluble ATRP initiator to produce shorter polymer brushes. The rate of SET-LRP was ultrafast and the rate can be reduced by addition of deactivator CuBr2. The second approach: water-soluble polymer brushes were grafted onto the surface of latex particles by SET-LRP. These “hairy” cross-linked colloids were swollen with additional monomers and initiator. Elevation of temperature causes entropic phase separation inducing new domains, which were polymerized. This approach leads to mainly popcorn and raspberry particles with some limited cases that are able to make hairy Janus Particles with non reproducible manner. The obtained complex particles show some interesting application such as a stabilization agent for Carbon Nanotubes (CNTs) in aqueous medium, Pickering emulsion stabilizer, and they self assembled upon addition of dilute electrolyte solution.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560118 |
| Date | January 2011 |
| Creators | Alzhrani, Attyah |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/46004/ |
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