No abstract

Core/shell microcapsules with low‐permeability membranes and controlled morphology are crucial for the delivery and controlled release of fragrance molecules, pharmaceuticals, inks, or vitamins. Design criteria for next generation microcapsules must include chemical and mechanical stability, and also provide enhanced substrate interactions to improve deposition onto relevant complex surfaces. Here, a coupled approach is presented to synthesize core/shell delivery systems by interfacial polymerization to enhance both the microcapsule–substrate interactions and the mechanical properties of the capsules to induce a burst‐type release. By combining membrane synthesis, nonlinear mechanics, interfacial rheology, analysis of mass transfer, and capsule morphology generated during interfacial polymerization, large permanent deformations into the capsule geometry are programmed, resulting in chemically stable, yet mechanically rupturing microcapsules with anisotropic geometry. To promote interactions and capsule adhesion onto complex substrates, the capsule contact area is controlled to form prominent “suction cup” shaped rims. These capsules have favorable, far‐reaching electrostatic interactions with oppositely charged substrates such as glass, hair, skin, or fabric. By modulating membrane mechanical properties and morphology during synthesis, formulation‐independent physical criteria are used to improve the overall performance of a functional delivery system while expanding knowledge of the key parameters influencing the interfacial polymerization process and membrane formation.

Moringa oleifera (Moringa) seeds contain a natural cationic protein (MOCP) that can be used as an antimicrobial flocculant for water clarification. Currently, the main barrier to using Moringa seeds for producing potable water is that the seeds release other water-soluble proteins and organic matter, which increase the concentration of dissolved organic matter (DOM) in the water. The presence of this DOM supports the regrowth of pathogens in treated water, preventing its storage and later use. A new strategy has been established for retaining the MOCP protein and its ability to clarify and disinfect water while removing the excess organic matter. The MOCP is first adsorbed and immobilized onto sand granules, followed by a rinsing step wherein the excess organic matter is removed, thereby preventing later growth of bacteria in the purified water. Our hypotheses are that the protein remains adsorbed onto the sand after the functionalization treatment, and that the ability of the antimicrobial functionalized sand (f-sand) to clarify turbidity and kill bacteria, as MOCP does in bulk solution, is maintained. The data support these hypotheses, indicating that the f-sand removes silica microspheres and pathogens from water, renders adhered Escherichia coli bacteria nonviable, and reduces turbidity of a kaolin suspension. The antimicrobial properties of f-sand were assessed using fluorescent (live-dead) staining of bacteria on the surface of the f-sand. The DOM that can contribute to bacterial regrowth was shown to be significantly reduced in solution, by measuring biochemical oxygen demand (BOD). Overall, these results open the possibility that immobilization of the MOCP protein onto sand can provide a simple, locally sustainable process for producing storable drinking water.

We report a novel approach to directly measure the interactions and deposition behavior of functional capsule delivery systems on glass substrates versus the concentration of an anionic surfactant sodium lauryl ether sulfate (SLES) and a cationic acrylamide-acrylamidopropyltrimonium copolymer (AAC). Analyses of three-dimensional optical microscopy trajectories were used to quantify lateral diffusive dynamics, deposition lifetimes, and potentials of mean force for different solution conditions. In the absence of additives, negatively charged capsule surfaces yield electrostatic repulsion with the negatively charged substrate, which inhibits deposition. With an increasing SLES concentration below the critical micelle concentration (CMC), capsule-substrate electrostatic repulsion is mediated by the charged surfactant solution that decreases the Debye length. Above the SLES CMC, depletion attraction causes enhanced deposition until eventually depletion repulsion inhibits deposition at concentrations ∼10 wt %. Addition of an ACC causes deposition via capsule-substrate bridging at all concentrations; the weakest deposition occurs at intermediate AAC concentrations from a competition of steric repulsion and attraction via a few extended bridges. The novel measurements and models of capsule interactions and deposition on substrates in this work provide a basis to fundamentally understand and rationally design complex rinse-off cleansing formulations with optimal characteristics.

Total internal reflection microscopy (TIRM) is used to directly, sensitively, and simultaneously measure colloidal interactions, dynamics, and deposition for a broad range of polymer–surfactant compositions. A deposition state diagram containing comprehensive information about particle interactions, trajectories, and deposition behavior is obtained for polymer–surfactant compositions covering four decades in both polymer and surfactant concentrations. Bulk polymer–surfactant phase behavior and surface properties are characterized to provide additional information to interpret mechanisms. Materials investigated include cationic acrylamide–acrylamidopropyltrimonium copolymer (AAC), sodium lauryl ether sulfate (SLES) surfactant, silica colloids, and glass microscope slides. Measured colloid–substrate interaction potentials and deposition behavior show nonmonotonic trends vs polymer–surfactant composition and appear to be synergistic in the sense that they are not easily explained as the superposition of single-component-mediated interactions. Broad findings show that at some compositions polymer–surfactant complexes mediate bridging and depletion attractions that promote colloidal deposition, whereas other compositions produce electrosteric repulsion that deters colloidal deposition. These findings illustrate mechanisms underlying colloid–surface interactions in polymer–surfactant mixtures, which are important to controlling selective colloidal deposition in multicomponent formulation applications.