Dissipative disassembly of colloidal microgel crystals driven by a coupled cyclic reaction network.

A plethora of natural systems rely on the consumption of chemical fuel or input of external energy to control the assembly and disassembly of functional structures on demand. While dissipative assembly has been demonstrated, the control of structural breakdown using a dissipative cycle remains almost unexplored. Here, we propose and realize a dissipative disassembly process using two coupled cyclic reactions, in which protons mediate the interaction between the cycles. We show how an ordered colloidal crystal, can cyclically transform into a disordered state by addition of energy to a chemical cycle, reversibly activating a photoacid. This cycle is coupled to the colloidal assembly cycle via the exchange of protons, which in turn trigger charging of the particles. This system is an experimental realization of a cyclic reaction-assembly network and its principle can be extended to other types of structure formation.

Programmable Phase Transitions in a Photonic Microgel System: Linking Soft Interactions to a Temporal pH Gradient.

Soft amphoteric microgel systems exhibit a rich phase behavior. Crystalline phases of these material systems are of interest because they exhibit photonic stop-gaps, giving rise to iridescent color. Such microgel systems are promising for applications in soft, switchable, and programmable photonic filters and devices. We here report a composite microgel system consisting of a hard and fluorescently labeled core and a soft, amphoteric microgel shell. At pH above the isoelectric point (IEP), these colloids easily crystallize into three-dimensional colloidal assemblies. By adding a cyclic lactone to the system, the temporal pH profile can be controlled, and the microgels can be programmed to melt, while they lose charge. When the microgels gain the opposite charge, they recrystallize into assemblies of even higher order. We provide a model system to study the dynamic phase behavior of soft particles and their switchable and programmable photonic effects.

Deep-Blue Fluorescent Particles via Microwave Heating of Polyacrylonitrile Dispersions.

This study presents a new method to produce fluorescent particles. Established methods are based on the incorporation of conjugated dye molecules into dielectric polymer matrices or preparation of colloids, which are composed of fluorescent conjugated polymer. By contrast, this study presents a method where dielectric polyacrylonitrile is exposed to microwave radiation leading to an intramolecular cyclization reaction producing π-conjugated segments, which fluoresce blue. During this conversion, the particles shrink in diameter but as an ensemble they retain their monodispersity. This work investigates the optimal reaction conditions and characterizes the optical properties.

Social Self-Sorting of Colloidal Families in Co-Assembling Microgel Systems.

Colloids are valuable model systems to understand the structure and dynamics of matter, explore new self-assembly concepts, and realize advanced materials. Herein, we demonstrate social self-sorting of co-assembled families of colloids by orthogonal host/guest recognition using cyclodextrins. We show that mixtures of four partners self-sort into their respective families without mutual interference. Additionally, the self-assemblies and their interactions are switchable using orthogonal triggers. This study goes beyond previous features of molecular self-sorting, and opens the design space for future self-sorting colloidal systems via rationally designed molecular recognition.

Programmable co-assembly of oppositely charged microgels.

Here we report the development of an aqueous, self-assembling system of oppositely charged colloids leading towards particle arrangements with controlled order. The colloidal system consists of two types of particles, each consisting of refractive index matched colloidal core-shell microgel particles, which are either negatively charged or amphoteric. By slowly decreasing the pH of our system below the isoelectric point of the amphoteric particles, changing their net charge from negative to positive, the co-assembly of the colloids is induced. By using different buffer concentrations, we gain temporal and kinetic control over the acidification process and thus the ability to program the co-assembly of the two particles species.

Switchable Supracolloidal Coassembly of Microgels Mediated by Host/Guest Interactions.

Supramolecular engineering of multibody colloidal systems provides flexible ways of manipulating superstructures and material properties. We investigate a coassembling microgel (MG) system, in which host- and guest-modified MG partners coassemble by molecular recognition, and show in detail how electrostatic repulsion needs to be balanced for the supramolecular recognition to take place. We observe a gradual change from repellent MGs to stable clusters and ordered flocculates upon decreasing electrostatic repulsion. The adaptive nature of the multivalent interactions embedded in the soft MG shell leads to kinetically trapped scenarios and fibril formation from spherical building blocks.

Bio-degradable highly fluorescent conjugated polymer nanoparticles for bio-medical imaging applications.

Conjugated polymer nanoparticles exhibit strong fluorescence and have been applied for biological fluorescence imaging in cell culture and in small animals. However, conjugated polymer particles are hydrophobic and often chemically inert materials with diameters ranging from below 50 nm to several microns. As such, conjugated polymer nanoparticles cannot be excreted through the renal system. This drawback has prevented their application for clinical bio-medical imaging. Here, we present fully conjugated polymer nanoparticles based on imidazole units. These nanoparticles can be bio-degraded by activated macrophages. Reactive oxygen species induce scission of the conjugated polymer backbone at the imidazole unit, leading to complete decomposition of the particles into soluble low molecular weight fragments. Furthermore, the nanoparticles can be surface functionalized for directed targeting. The approach opens a wide range of opportunities for conjugated polymer particles in the fields of medical imaging, drug-delivery, and theranostics.Conjugated polymer nanoparticles have been applied for biological fluorescence imaging in cell culture and in small animals, but cannot readily be excreted through the renal system. Here the authors show fully conjugated polymer nanoparticles based on imidazole units that can be bio-degraded by activated macrophages.

Microfluidic colloid filtration.

Filtration of natural and colloidal matter is an essential process in today's water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a "cake layer"--often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.

Laser Carbonization of PAN-Nanofiber Mats with Enhanced Surface Area and Porosity.

Here we present a novel laser process to generate carbon nanofiber nonwovens from polyacrylonitrile. We produce carbon nanofabrics via electrospinning followed by infrared laser-induced carbonization, facilitating high surface area and well-controlled hierarchical porosity. The process allows precise control of the carbonization conditions and provides high nanoscale porosity. In comparison with classical thermal carbonization, the laser process produces much higher surface areas and smaller pores. Furthermore, we investigate the carbonization performance and the morphology of polyacrylonitrile nanofibers compounded with graphene nanoplatelet fillers.

Water-soluble dopamine-based polymers for photoacoustic imaging.

Here we present a facile synthetic method yielding a linear form of polydopamine via Kumada-coupling, which can be converted into water-soluble melanin, generating high contrast in photoacoustic imaging.

Novel variant of dual left anterior descending coronary artery.

A 29-year-old African American man presented with atypical chest pain. Coronary computed tomographic angiography (64-slice) showed a previously not described variant of dual (duplicated) left anterior descending artery (LAD). Duplication of LAD is a rare anomaly and has been categorized into 4 angiographic subtypes based on the origin, course, and termination of the short and long LAD. Our case is unique in that, unlike previous subtypes, the short LAD originates independently from the left coronary sinus and that the long LAD arises from the right coronary sinus and has an intramyocardial course before reaching the distal interventricular groove. It can be, thus, considered a new variant of dual LAD (type V).