title: Multiple patterns of polymer gels in microspheres due to the interplay among phase separation, wetting, and gelation.
abstract: We report the spontaneous patterning of polymer microgels by confining a polymer blend within microspheres. A poly(ethylene glycol) (PEG) and gelatin solution was confined inside water-in-oil (W/O) microdroplets coated with a layer of zwitterionic lipids: dioleoylphosphatidylethanolamine (PE) and dioleoylphosphatidylcholine (PC). The droplet confinement affected the kinetics of the phase separation, wetting, and gelation after a temperature quench, which determined the final microgel pattern. The gelatin-rich phase completely wetted to the PE membrane and formed a hollow microcapsule as a stable state in the PE droplets. Gelation during phase separation varied the relation between the droplet size and thickness of the capsule wall. In the case of the PC droplets, phase separation was completed only for the smaller droplets, wherein the microgel partially wetted the PC membrane and had a hemisphere shape. In addition, the temperature decrease below the gelation point increased the interfacial tension between the PEG/gelatin phases and triggered a dewetting transition. Interestingly, the accompanying shape deformation to minimize the interfacial area was only observed for the smaller PC droplets. The critical size decreased as the gelatin concentration increased, indicating the role of the gel elasticity as an inhibitor of the deformation. Furthermore, variously patterned microgels with spherically asymmetric shapes, such as discs and stars, were produced as kinetically trapped states by regulating the incubation time, polymer composition, and droplet size. These findings demonstrate a way to regulate the complex shapes of microgels using the interplay among phase separation, wetting, and gelation of confined polymer blends in microdroplets.
authors.affiliation: Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan; Department of Applied Physics, Faculty of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan; and myanagi@cc.tuat.ac.jp.
authors.forename: Miho
authors.initials: M
authors.lastname: Yanagisawa
authors.affiliation: Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan;
authors.forename: Shinpei
authors.initials: S
authors.lastname: Nigorikawa
authors.affiliation: Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan;
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sakaue
authors.affiliation: Department of Biosciences and Informatics, Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Fujiwara
authors.affiliation: Department of Physics, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan;
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tokita
mesh_terms: D007700:Kinetics; D008567:Membranes, Artificial; D008863:Microspheres; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D011092:Polyethylene Glycols / Q000737:chemistry*; D017155:Wettability
chemical_list: D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C094877:dioleoyl phosphatidylethanolamine; D011092:Polyethylene Glycols; C017251:1,2-oleoylphosphatidylcholine
keywords: aqueous two-phase systems; emulsions; hydrogels; microgels; sol–gel phase separation