Reversible aggregation of responsive polymer-stabilized colloids and the pH-dependent formation of porous scaffolds

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Entry by Pichet Adstamongkonkul, AP 225, Fall 2011

Work in progress


Title: Reversible aggregation of responsive polymer-stabilized colloids and the pH-dependent formation of porous scaffolds

Authors: Robert T. Woodward, Christopher Hight, Ufuk Yildiz, Nicolas Schaeffer, Esther M. Valliant, Julian R. Jones, Molly M. Stevens, and Jonathan V. M. Weaver

Journal: Soft Matter, 2011, Vol. 7, No. 16

Keyword: colloid, emulsion, surfactant, steric stabilization, electrosteric stabilization, disassembly, assembly


Fine tuning interactions of colloids, such as switching the properties in response to stimuli and on-demand disassembly, is a very interesting aspect in the field and can have many applications. An alternative strategy of polymeric particles synthesis, in contrast with the in situ syntheses in poor solvent or self-assembly, is the isolation of pre-formed polymer within localized microscopic domains and template removal of solvent to form colloids, the so-called emulsion-solvent-evaporation (ESE) process. In this process, surfactant molecules play an important part in stabilizing the initial emulsion templates. In this study, the authors synthesized a pH-responsive, branched, amphiphilic copolymers of hydrophilic poly(ethylene glycol) methacrylate (PEGMA) and poly(methacrylic acid) (PMA), and 1-dodecanethiol-derived (DDT) hydrophobic chain ends, to be used as a surfactant. It has been shown that the resulting oil in water emulsion is stable at basic pH by both steric and electrostatic stabilization of both PEGMA and MA residues. However, at acidic pH, these colloids assemble as hydrogen bonds form between MA and EG repeat units, not only on the same droplets, but also between droplets. The research also demonstrated the reversible transition between the dispersed and aggregated states, only by the change in pH, without significant deformation or degradation. The fabrication of compacted monolith out of a collection of colloid additionally showed that one can control the macroporosity of such scaffold by the method of drying. This may be suitable for medical applications.


Polymeric particles are good as building blocks since they can be prepared with controllable sizes and properties, such as functional groups, encapsulation and release profile. On the other hand, amphiphilic copolymers are convenient surfactants, with many advantage points: interfacial adsorption, self-assembly, encapsulation capability, low toxicity, tunable properties, greater functionality, and highly stabilize emulsions. The branched amphiphilic copolymers have been shown to be extremely efficient emulsifiers, in that the emulsions can have excellent long term stabilities.

Results and Discussion