A device composed of a poly (N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgel layer sandwiched between two thin Au layers (all on a glass support) was used as a novel platform for controlled and triggered small molecule delivery. Tris (4-(dimethylamino)phenyl)methylium chloride (Crystal Violet, CV), which is positively charged, was loaded into the microgel layer of the device and released in a pH dependent fashion, at a rate that could be controlled by the thickness of the Au layer coating the microgels. Specifically, at pH 6.5 (above the pKa for AAc) the microgels were negatively charged, promoting the strong interaction between the CV and the microgels, hindering its release from the layer. At pH 3.0 the microgel's AAc groups are protonated making the microgel mostly neutral, allowing CV to be released from the microgel layer at a rate that depends on the thickness of the Au covering the microgels. Specifically, devices with thin Au overlayers on the microgel layer allow CV to be released from the device faster than devices with thick Au overlayers. The ability to tune the release rate with pH and Au layer thickness is advantageous for developing implantable devices that are capable of releasing small molecule drugs in a triggered and controlled fashion.

The main elementary processes were identified during simultaneous crystallization of NaCl and KCl from aqueous solutions by the batchwise evaporative method using NaCl seeds. In the early stages of the batch operation, when only NaCl crystallizes, the main elementary processes are molecular crystal growth, agglomeration, and secondary nucleation. When the eutonic condition is exceeded, a KCl primary nucleation event takes place in solution. Subsequently, part of the resulting KCl particles agglomerate with the NaCl particles. Besides, epitaxial growth of KCl upon NaCl crystals takes place. Consequently, the product is comprised of mixed composition polycrystalline particles and single crystals of each salt. The elementary phenomena just described were sensitive to crystallization conditions such as evaporation rate, seed size, and seed content, suggesting the possibility of controlling the morphological features of the particulate product as well as the chemical composition of its size fractions. Such knowledge is important in the context of wastewater treatment, where the particulate product should be suitable either for disposal as a residue or for further processing in easily separable size fractions for exploitation of valuable components.

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To meet contemporary industry needs, saline wastewater treatment with zero liquid discharge goals is gaining increasing attention. In this context, evaporative crystallization has been applied to simultaneously remove all dissolved compounds as a solid residue. By conducting simultaneous crystallization in a way that the components crystallize as single particles, their downstream separation as products is made simple, so that no solid waste is generated. We have recently identified the main phenomena that control particle morphology for batchwise simultaneous crystallization in the NaCl–KCl–H2O model system seeded with NaCl. In this work, a process strategy is proposed, wherein crystallization elementary phenomena are tuned by seeding with KCl particles. Formation of multicomponent particles was inhibited with a small seed surface area, because the epitaxial growth of NaCl upon the KCl seeds was hampered. By a proper choice of seeding policy, the product may be classified into large particles rich in KCl (purity higher than 90 wt %) and smaller particles rich in NaCl (∼75 wt %). Secondary nucleation and epitaxial growth of NaCl on KCl were the main hindrances to the formation of pure populations of each compound.

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