ABSTRACT
We studied the dependence of solid deposit shape obtained by free drying of sessile drops on particle concentration and Derjaguin-Landau-Verwey-Overbeek (DLVO) particle/substrate interaction. In contrast to previous contributions using pH as a control parameter of interactions, we investigated an unprecedentedly wide range of concentrations and particle/substrate DLVO forces by modifying the nature of the substrate and particles as well as their size and surface chemistry, whereas long-distance repulsive interactions between particles were maintained for most of the drying time. Our main result is that the different shapes of deposits obtained by modifying the particle concentration are the same in the different regimes of concentration regardless of particle/substrate interaction in the studied range of DLVO forces and particle concentrations. The second result is that, contrary to expectations, the dominant morphology of dry patterns at low particle concentration always shows a dotlike pattern for all the studied systems.
ABSTRACT
We studied the morphology of linear particle deposits obtained by inkjet printing of a silica nanoparticle suspension in drying conditions where contact line depinning occurs. We show that this evaporation mode can be obtained by adjusting the particle concentration in different solvents. For isolated drops, deposited manually or by inkjet printing, drying induces the formation of two concentric rings in which particles self-assemble into a monolayer. For fused drops, our main result is that stable rivulets could be formed by drop overlap leading, after drying, to the formation of three parallel lines composed of a self-assembled particle monolayer. The three lines are of homogeneous thickness with two very thin outer lines (â¼1 µm width) and a wider central line (â¼20 µm width). We reveal how the width of the resulting lines is influenced by drop spacing in a predictable manner for a large experimental window knowing the drop size.
ABSTRACT
We studied the assembly of nanoparticles (NPs) with oppositely charged linear and periodic copolymers (CPs), alternating ionic and polar sequences, in the dilute range of polymer concentration. For the first time, we considered CPs displaying a contour length much higher than the gold NP (AuNP) perimeter. We assumed that such CPs will enable the collection of a finite number of NPs into linear nanostructures with a gain of colloidal stability and a better structural control compared to electrostatic complexes obtained with homopolyelectrolytes. As a case study, we synthesized anionic AuNPs and CPs consisting of alternated cationic poly-l-lysine (PLL) blocks and polar sequences of poly(ethylene glycol) (PEG). We showed that complexation of AuNPs with CPs is quite similar to that observed with homo PLL. In that respect, finite size nanometric clusters, of less than 30 NPs, are formed outside the electroneutrality domain and a fast phase separation occurs at the electroneutrality. Nevertheless, the presence of PEG blocks allowed us to highlight some specific effects. First, the global charge of the positively charged clusters was found to be always lower for CP-based clusters than for homo PLL with a dependence of the charge with the number and the mass of the PEG blocks. Second, in spite of this effect which should have promoted the formation of a dense structure, the fractal dimension characterizing the structure of the clusters in bulk was found to be always below 1.8. Finally, we showed that PEG blocks influence the interparticle distance by disfavoring plasmon delocalization when the clusters are dispersed in water and collapse around the NPs when the clusters are deposited on the substrate.
