The ability to control the dispersion, aggregation, and assembly of colloidal systems is important for a number of applications, for instance, Pickering emulsions, drug and gene delivery, control of fluid rheology, and the formation of colloidal crystal arrays. We generated a responsive colloidal system based on polymer-brush-grafted silica nanoparticles and demonstrated that such a colloidal system can be used to produce stable oil-in-water Pickering emulsions. Cationic poly(2-(methacryloyloxy)-ethyl-trimethyl-ammonium chloride) (PMETAC) brushes were grown from silica nanoparticles (diameter ∼320 nm) through surface-initiated atom-transfer radical polymerization (ATRP). PMETAC brushes are attractive coatings for controlling the behavior of colloidal systems, owing to their ion-specific collapse resulting in the switching of surface hydrophilicity. Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta-potential measurements indicated the successful grafting of PMETAC brushes on nanoparticles. The resulting colloidal dispersion was shown to be responsive to perchlorate ions (ClO 4 -), which triggered particle aggregation and enabled the generation of Pickering emulsions. The onset of aggregation depended on the polymer chain length. Aggregation was not affected by the initiator density and brush conformational changes. Further studies suggested that particle aggregation and the formation of stable Pickering emulsions were not simply due to brush collapse but also were due to a gradual shielding of electrostatic repulsion. Finally, the stability and homogeneity of the resulting Pickering emulsions were studied

The functionalisation and patterning of polymer brushes via thiol–ene chemistry is studied via ellipsometry, XPS and AFM.

The intricacy of the different parameters involved in cell adhesion to biomaterials and fate decision (e.g. proliferation, differentiation, apoptosis) makes the decoupling of the respective effects of surface properties, extra-cellular matrix protein adsorption and ultimately cell behaviour difficult. This work presents a micro-patterned polymer brush platform to control the adsorption of extra-cellular matrix (ECM) proteins to well defined micron-size areas and consequently control cell adhesion, spreading and shape independently of other chemical and physical surface properties. Protein patterns can be readily generated with brushes presenting a range of hydrophilicity and surface charge density. The surface properties of the selected brushes are fully characterised using a combination of FTIR, XPS, ellipsometry, atomic force microscopy, water contact goniometry, dynamic light scattering and ζ-potential measurements. Interactions of proteins relevant to cell patterning and culture with these brushes are studied by surface plasmon resonance, dynamic light scattering, ellipsometry and immuno-fluorescence microscopy. Finally this platform is used in an assay investigating the relative contributions of matrix geometry and surface chemistry on epidermal stem cell differentiation. It is found that moderate hydrophobicity does not impact stem cell commitment, whereas strongly negative surface potential increases the incidence of differentiation. This correlates with a marked decrease in the formation of focal adhesions (but not cell spreading).

By using molecular self-assembly and polymer brush chemistry, adhesion of water droplets at solid/oil interfaces could be achieved and modulated by external triggers. Silicon wafers were hydrophobically modified with binary mixed self-assembled layers consisting of fluorinated silanes and atom transfer radical polymerisation (ATRP) initiator silanes, and subsequently grafted with responsive polymers via surface-initiated ATRP. Temperature-and pH-responsive adhesion of water in oil droplets occurred on surfaces coated with phase-separated self-assembled layers and grafted with short polymer chains. Experimental section Materials Di(ethylene glycol) methyl ether methacrylate (MEO 2 MA), poly (ethylene glycol) methyl ether methacrylate (average M n z 300)

We have demonstrated capture and release of underwater-oil droplets based on fouling-resistant surfaces coated with pH-responsive polymer brushes. In response to the change of environmental pH, oil droplets were captured on the polymer brush-modified surfaces in the high adhesion state. As the droplet volume increased upon coalescence with other oil droplets in the aqueous phase, the captured droplets eventually self-released from the surfaces under the influence of buoyancy and rose to the air-water interface. The fact that the polymer brush surfaces were partially oil-wettable (high oil-in-water contact angles) enabled the adhesion but not the spreading of oil droplets. This allowed buoyancy release of oil droplets and led to fouling-resistant surfaces that could be reused for capture-release of more oil droplets. The practicality and versatility of this oil droplet capture-release system was demonstrated using monodisperse and polydisperse hydrocarbon oil compositions in purified water, tap water, and brines in which the salt concentration was as high as that of seawater.