Colloidal crystallization in the quasi-two-dimensional induced by electrolyte gradients

We investigated driven crystal formation events in thin layers of sedimented colloidal particles under low salt conditions. Using optical microscopy, we observe particles in a thermodynamically stable colloidal fluid to move radially converging towards cation exchange resin fragments acting as seed particles. When the local particle concentration has become sufficiently large, subsequently crystallization occurs. Brownian dynamics simulations of a 2D system of purely repulsive point-like particles exposed to an attractive potential, yield strikingly similar scenarios, and kinetics of accumulation and micro-structure formation. This offers the possibility of flexibly designing and manufacturing thin colloidal crystals at controlled positions and thus to obtain specific micro-structures not accessible by conventional approaches. We further demonstrate that particle motion is correlated with the existence of a gradient in electrolyte concentration due to the release of electrolyte by the seeds.

Re-entrant melting as a design principle for DNA-coated colloids

Colloids functionalized with DNA hold great promise as building blocks for complex self-assembling structures. However, the practical use of DNA-coated colloids (DNACCs) has been limited by the narrowness of the temperature window where the target structures are both thermodynamically stable and kinetically accessible1, 2, 3, 4, 5. Here we propose a strategy to design DNACCs, whereby the colloidal suspensions crystallize on cooling and then melt on further cooling. In a phase diagram with such a re-entrant melting, kinetic trapping of the system in non-target structures should be strongly suppressed. We present model calculations and simulations that show that real DNA sequences exist that should bestow this unusual phase behaviour on suitably functionalized colloidal suspensions. We present our results for binary systems, but the concepts that we develop apply to multicomponent systems and should therefore open the way towards the design of truly complex self-assembling colloidal structures.

Paper-Based, Capacitive Touch Pads

Metallized paper is patterned to create touch pads of arrayed buttons that are sensitive to contact with both bare and gloved fingers. The paper-based keypad detects the change in capacitance associated with the touch of a finger to one of its buttons. Mounted on an alarmed cardboard box, the keypad requires the appropriate sequence of touches to disarm the system.

 

Rapidly in situ forming polyphosphoester-based hydrogels for injectable drug delivery carriers

In situ forming hydrogels allow the modulation of physicochemical properties and are providing new opportunities for biomedical applications. Here, the preparation and characterization of a series of rapidly in situ forming and pH-responsive hydrogels with different crosslinking degrees are reported, which were achieved by accelerated free radical copolymerization of polyphosphoester-based macrocrosslinker and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer. The hydrogel formation can be completed very quickly under mild conditions, ranging from several to tens of minutes with varying concentrations of components. The polyphosphoester-based macrocrosslinker was synthesized via a combination of ring-opening polymerization and post-polymerization modification, and it was characterized by 1H NMR, 31P NMR, and GPC measurements. The sol–gel transition was monitored by dynamic time sweep rheological analysis. Moreover, the swelling kinetics, interior morphology, pH-responsive property, in vitro cytotoxicity and drug release of these hydrogels were characterized. The results indicate that these hydrogels show great potential as injectable drug delivery system.

Biotemplated Synthesis of Perovskite Nanomaterials for Solar Energy Conversion

 
A synthetic method of using genetically engineered M13 virus to mineralize perovskite nanomaterials, particularly strontium titanate (STO) and bismuth ferrite (BFO), is presented. Genetically engineered viruses provide effective templates for perovskite nanomaterials. The virus-templated nanocrystals are small in size, highly crystalline, and show photocatalytic and photovoltaic properties.

Pattern Formation in Nature: Physical Constraints and Self-Organising Characteristics

Pattern formations are apparent in natural systems ranging from clouds to animal markings, and from sand dunes to shells of microscopic marine organisms. Despite the astonishing range and variety of such structures, many have comparable features. In this article, Philip Ball reviews some of the common patterns found in nature. He explains how they are typically formed through simple, local interactions between many components of a system – a form of physical computation that gives rise to self-organisation and emergent structures and behaviours.

Design to Self-Assembly

The increasing power of design software, the widespread availability of digital fabrication and growing complexity of our built environment are in stark contrast to the inefficient techniques that currently plague the construction industry. Today's processes of assembly can be fundamentally re-imagined by looking at biological systems that are building structures with far more complexity, information capacity and assembly instructions than even the most advanced structures possible with current technologies. Skylar Tibbits explains that the key ingredient embedded within these natural systems is self-assembly. He outlines four principles for designing systems that build themselves, and shows a number of projects that demonstrate first steps towards this new mode of architectural production.