Abstract
Highly monodisperse polystyrene/poly(N-isopropylmethacrylamide) (PS-PNIPMAM) core-shell composite microgels were synthesized and further nanoengineered in either ellipsoidal, faceted or bowl-shaped particles. Beside their anisotropy in shape, the microgel design enables an exquisite control of the particle conformation, size and interactions from swollen and hydrophilic to collapsed and hydrophobic using temperature as an external control variable. The post-processing procedures and the characterization of the different particles are first presented. Their potential as model systems for the investigation of the effects of anisotropic shape and interactions on the phase behavior is further demonstrated. Finally, the self-assembly of bowl-shaped composite microgel particles is discussed, where the temperature and an external AC electric field are employed to control the interactions from repulsive to attractive and from soft repulsive to dipolar, respectively.
Highlights
The average particle radius R ≈ 470 nm was determined from the half distance between the centers of the particles in the crystalline area, in good agreement with the value for the average hydrodynamic radius RH = 479 nm obtained from dynamic light scattering (DLS)
Particles are embedded into a high molecular weight polyvinyl alcohol (PVA) film and heated above the glass transition temperature, Tg, of the polystyrene core
Following the procedure described in our previous study,[46] the core–shell particles are embedded into a 100 000 g mol−1 PVA film
Summary
Microgel particles have received considerable attention over the years owing to their tunable and responsive nature.[25] In particular, crosslinked poly(N-isopropylacrylamide) (PNIPAM) microgels have been established as a versatile model system where the overall size, softness and hydrophobicity of the resulting particles can be controlled through a temperatureinduced volume phase transition Their conformation, size, effective volume fraction and interaction potential can be externally controlled and adjusted from repulsive to attractive.[26,27,28,29] They exhibit a rich phase behavior[26] and have been proven to be ideal building blocks for complex selfassembly.[30,31,32] Stimuli-responsive microgels have found a broad range of potential applications, such as switchable stabilizers for emulsions at oil/water interfaces[33,34,35,36,37,38] and lipid membranes[39] and as cell substrates[40] where the
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