We report the formation of poly(acrylic acid) (sodium salt) (PAA) and poly(allylamine hydrochloride) (PAH) multilayers on polystyrene (PS) and melamine formaldehyde (MF) colloid particles by the layer-by-layer (LbL) assembly technique. The use of different solution processing conditions (e.g., pH and ionic strength) was found to have a pronounced effect on film growth, with the degree of dissociation of both polyelectrolytes (PEs) playing an important role for regular PAA/PAH multilayer growth. To retain colloidal stability during the sequential adsorption of PEs, it was essential to deposit the PE layers from adsorption solutions where the PEs are in a highly charged state, the degree of which was regulated by varying the pH. Thicker PAA/PAH coatings were obtained when the pH value of the PAA deposition solution was close to the pK a value of PAA in solution. The presence of salt in the deposition and rinsing solutions also promoted the formation of thicker PAA/PAH coatings. The ζ-potential of the particles, measured at different pH values, allowed estimation of the isoelectric point (pI) of the adsorbed layers. The pI values of the coatings showed a dependence on the nature of the underlying layers and particle surface, particularly when PAA formed the outermost layer. A pI of 5.5 was observed for PAA adsorbed on bare MF particles, compared with a pI of 2.5 for (PAA/PAH) 2-coated PS spheres. The formation of hollow PAA/PAH capsules, achieved by removal of the core from the PAA/PAH-coated colloids, further confirmed the deposition of PAA and PAH multilayers. The techniques of microelectrophoresis, fluorescence spectroscopy, and transmission electron microscopy were used to characterize the layer buildup and film morphology. The formation of PAA/PAH multilayers on colloids highlights the potential of weak PEs for exploitation in colloid surface modification and encapsulation technologies.

The formation of weak polyelectrolyte films on planar and spherical supports has recently evoked major interest, as such coatings allow novel material properties to be tunable by pH and salt adjustment of the polyelectrolyte deposition conditions. We report on the build up of multilayers of the weak polyelectrolytes poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) on submicrometer‐sized polystyrene (PS) and silica colloid spheres (∼ 500 nm) with the aid of copper ion templating. The copper ions complex to the carboxylate groups of PAA, facilitating the formation of PAA/PAH multilayers on the particles. Regular growth of the layers on the colloid spheres with each polyelectrolyte deposition step was confirmed by microelectrophoresis, single‐particle light scattering (SPLS), and transmission electron microscopy (TEM), with an average bilayer thickness of ∼ 3 nm. The polyelectrolyte multilayer‐coated particles formed stable colloidal dispersions, with ζ‐potentials ranging from 30 mV (PAH outer layer) and –50 mV (PAA outer layer). Complementary quartz‐crystal microbalance and UV‐vis spectrophotometry studies on PAA/PAH multilayers formed on planar supports were performed to examine the film formation and the role of copper ion binding to the layers. PAA/PAH multilayers formed on colloid particles were also chemically crosslinked by using the activator 1‐ethyl‐3‐(3‐dimethylaminopropyl) carbodiimide (EDC). The degree of film crosslinking could be readily controlled by varying the concentration of EDC employed. Following solvent decomposition of the template particles coated with crosslinked PAA/PAH multilayers, intact hollow polymer capsules were obtained. These capsules were found to be impenetrable to polystyrene.

We report on the formation of nanostructured, ultrathin films of a new class of fluorescent nanoparticles (NPs) within the same size range as quantum dots, but with a different kind of fluorescence, by using the layer-by-layer (LbL) technique. The fluorescence of these rare-earth-doped lanthanum phosphate (LaPO4) NPs is due to the bulk properties of the material and is therefore independent of their size. Additionally, different colors are available due to variation of the dopants used in their synthesis (e.g., Ce, Tb, Eu, and Dy). These NPs were electrostatically assembled to form thin films on planar quartz supports as well as on polystyrene (PS) microspheres with the aid of oppositely charged polyelectrolyte interlayers. Regular growth of the multilayers was observed on both quartz and PS substrates, providing control over the composition and, in turn, the fluorescence intensity of the planar films and composite spheres. The resulting films exhibit the same UV and fluorescence characteristics as the corresponding aqueous NP dispersions. NPs with different fluorescence characteristics (i.e., colors) retain their individual optical properties when premixed and assembled into thin films and can be detected individually using only a single excitation wavelength. Biofunctionalization of LaPO4 NP-tagged PS spheres and of the individual LaPO4 NPs is expected to yield versatile labels that could be exploited in various biological applications.

We study both experimentally and theoretically the self-assembly of binary polycaprolactonepolyethyleneoxide (PCL-PEO) block copolymers in dilute solution, where self-assembly is triggered by changing the solvent from the common good solvent THF to the selective solvent water, and where the two species on their own in water form vesicles and spherical micelles respectively. We find that in water the inter-micellar exchange of these block copolymers is extremely slow so that the resultant selfassembled structures are in local but not global equilibrium (i.e., they are non-ergodic). This opens up the possibility of controlling micelle morphology both thermodynamically and kinetically. Specifically, when the two species are first molecularly dissolved in THF before mixing and self-assembly ('premixing') by dilution with water, the morphology of the formed structures is found to depend on the mixing ratio of the two species, going gradually on a route of decreasing surface curvature from vesicles via an intermediate regime of micelles in the shape of 'bulbed' rods, rings, Y-junctions finally to spherical micelles as we increase the proportion of the "sphere formers". On the other hand, if the two species are first partially self-assembled (by partial exchange of the solvent with water) before mixing and further self-assembly ('intermediate mixing'), novel metastable structures, including nanoscopic 'pouches', emerge. These experimental results are corroborated by self-consistent field theory

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