Self-assembly In The Microchannel And Emulsification Behavior Of Amphiphilic Copolymer

In this paper, two amphiphilic random copolymers, Poly(Styrene-co-acrylicacid)(P(St-co-AA) and P(styrene-co-ethyl methacrylate)(P(St-co-DM)), were prepared throughfree radical copolymerization with acrylic acid (AA), styrene(St), ethyl methacrylate(DM) asco-monomers, respectively. These polymers were characterized by Spectroscopic(FTIR),Differential Scanning Calorimetry(DSC), Nuclear Magnetic Resonance Spectrometer(1HNMR) and Gel Permeation Chromatography(GPC).The copolymer could self-assemble into micelles in the selective solvent. In this paper, AY-shape microchannel is used to assist the formation of polymeric micelles throughnanoprecipitation which is triggered by a solvent exchange process when organic solutions ofthe polymer mixed with a non-solvent. The microchannel has many advantages, such asmixing in small scale, accurately controlling the self-assembly process. The morphologies andproperties of the products obtained by microchannel are much more stable. The critical watercontent (CWC) and the Zeta potential of self-assembled particles were measured respectivelyby UV Spectrophotometer and Zetasizer. The morphologies and the sizes of micelles werealso characterized respectively by means of Transmission Electron Microscope (TEM) andDynamic laser light scattering (DLS). The results show that the micelles size increased as theflow rates increased, and a narrower size distribution was observed within a givenmicrochannel dimension; Micelles size increased with the length of the microchannel. Themicelles size decreased when the microchannel width reduced and the micelle sizehomogeneity was improved under the identical fluidic conditions.Due to amphiphilicity of the P(St-co-AA) and P(St-co-DM) micelles, they can be used asemulsifier. We compared emulsification properties of P(St-co-AA) and P(St-co-DM) micellesprepared in the microchannel with different flow rates and in the bulk. The results show thatthe P(St-co-AA) and P(St-co-DM) micelles prepared in the bulk has the same emulsificationproperties as prepared in the microchannel.Due to the higher content of hydrophilic group in P(St47-co-DM141), the P(St47-co-DM141)micelles are not to be easily self-assembled and unstable. In the self-assembly processes ofP(St47-co-DM141), the addition of hydrophobic homopolymer PS was useful to improve thestability of P(St47-co-DM141)/PS micelles. The properties of P(St47-co-DM141)/PS micelleswere effected by the pH, the micelles solution concentration and the salt concentration. Theresults show that the stability of emulsions improved as the micelles solution concentrationincreasing at lower pH. The emulsification properties was less influenced by saltconcentration when salt concentration is below1mol·L-1. When the salt concentration isabove1mol·L-1, the micelle solution has no emulsification.