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HYPOTHESIS: Colloidal surface morphology determines suspension properties and applications. While existing methods are effective at generating specific features on spherical particles, an approach extending this to non-spherical particles is currently missing. Synthesizing un-crosslinked polymer microspheres with controlled chemical patchiness would allow subsequent thermomechanical stretching to translate surface topographical features to ellipsoidal particles. EXPERIMENTS: A systematic study using seeded emulsion polymerization to create polystyrene (PS) microspheres with controlled surface patches of poly(tert-butyl acrylate) (PtBA) was performed with different polymerization parameters such as concentration of tBA monomer, co-swelling agent, and initiator. Thermomechanical stretching converted seed spheres to microellipsoids. Acid catalyzed hydrolysis (ACH) was performed to remove the patch domains. Roughness was characterized before and after ACH using atomic force microscopy. FINDINGS: PS spheres with controlled chemical patchiness were synthesized. A balance between two factors, domain coalescence from reduced viscosity and domain growth via monomer absorption, dictates the final PtBA) patch features. ACH mediated removal of patch domains produced either golf ball-like porous particles or multicavity particles, depending on the size of the precursor patches. Patchy microspheres were successfully stretched into microellipsoids while retaining their surface characteristics. Particle roughness is governed by the patch geometry and increases after ACH. Overall, this study provides a facile yet controllable platform for creating colloids with highly adjustable surface patterns.

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Anisotropic particles pinned at fluid interfaces tend toward disordered multiparticle configurations due to large, orientationally dependent, capillary forces, which is a significant barrier to exploiting these particles to create functional self-assembled materials. Therefore, current interfacial assembly methods typically focus on isotropic spheres, which have minimal capillary attraction and no dependence on orientation in the plane of the interface. In order to create long-range ordered structures with complex configurations via interfacially trapped anisotropic particles, control over the interparticle interaction energy via external fields and/or particle engineering is necessary. Here, we synthesize colloidal ellipsoids with nanoscale porosity and show that their interparticle capillary attraction at a water-air interface is reduced by an order of magnitude compared to their smooth counterparts. This is accomplished by comparing the behavior of smooth, rough, and porous ellipsoids at a water-air interface. By monitoring the dynamics of two particles approaching one another, we show that the porous particles exhibit a much shorter-range capillary interaction potential, with scaling intriguingly different than theory describing the behavior of smooth ellipsoids. Further, interferometry measurements of the fluid deformation surrounding a single particle shows that the interface around porous ellipsoids does not possess the characteristic quadrupolar symmetry of smooth ellipsoids, and quantitatively confirms the decrease in capillary interaction energy. By engineering nanostructured surface features in this fashion, the interfacial capillary interactions between particles may be controlled, informing an approach for the self-assembly of complex two-dimensional microstructures composed of anisotropic particles.

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A one-step dispersion copolymerization technique is demonstrated to fabricate biphasic particles as an approach to streamline the production of particles with complex morphology. The model system studies a monomer feed of hydrophobic styrene and hydrophilic, zwitterionic sulfobetaine methacrylate (SBMA) in a water/isopropanol cosolvent mixture. The resulting particles have a core-shell morphology that can be transformed, simply by washing the particles with water, into particles with a single surface opening connected to an interior cavity. Results indicate that particle morphology is dependent on the presence of nanoscopic SBMA-rich aggregates in the initial reaction mixture to act as nucleation sites, forming an SBMA-rich core encased in a styrene-rich shell. Systematic study of the morphology evolution reveals that the difference in monomer solubility profile can be exploited to control compositional drift of the particle composition during copolymerization yielding copolymer with sufficiently different composition to form phase-separated particle morphology. When SBMA is replaced with various ionic comonomers, the cavity-forming morphology is observed when reaction conditions result in low solubility of the comonomer in the cosolvent mixture. Based on these results, design guidelines are developed that may be applied to a variety of systems requiring complex and responsive particles made from chemically distinct comonomer pairings.

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We report the first use of NiO, Fe3O4, TiO2, and Co3O4 nanoparticles as surfaces for surface-assisted laser desorption/ionization (SALDI) mass spectrometry of asphaltenes. Higher signal-to-noise ratios (S/Ns) for asphaltene species were observed using NiO and Fe3O4 nanoparticles for SALDI as compared to LDI, where both surfaces consistently provided 2- to 3-fold improved S/Ns. The new SALDI detection method showed reliable adsorption data measuring supernatant solutions after 24 hour asphaltene adsorption on NiO, Fe3O4, and Co3O4. These results indicated that NiO has a higher adsorption affinity than Fe3O4 and Co3O4 for asphaltene molecules, corroborating reported asphaltene adsorption on metal oxide nanoparticles.