Reversible Magnetic Agglomeration: A Mechanism for Thermodynamic Control over Nanoparticle Size.

We present a method for the synthesis and precise size control of magnetic nanoparticles in a reversible magnetic agglomeration mechanism. In this approach, nanoparticles nucleate and grow until a critical susceptibility is reached, in which magnetic attraction overcomes dispersive forces, leading to agglomeration and precipitation. This phase change in the system arrests nanoparticle growth and gives true thermodynamic control over the size of nanoparticles. We then show that increasing the alkyl chain length of the surfactant, and hence increasing steric stabilization, allows nanoparticles to grow to larger sizes before agglomeration occurs. Therefore, simply by choosing the correct surfactant, the size and magnetic properties of iron nanoparticles can be tailored for a particular application. With the continuous addition of the precursor solution, we can repeat the steps of nucleation, growth, and magnetic agglomeration indefinitely, making the approach suitable for large scale syntheses.

Solvent programmable polymers based on restricted rotation.

Solvent programmable polymers (SPPs) were developed that can modulate their recognition properties by heating in different solvents. These highly cross-linked polymer gels were able to respond to differences in solvent polarity at elevated temperatures via rotation about a C(aryl)-N(imide) bond of a carboxylic acid monomer. When heated in polar solvents such as water, the number of solvent accessible carboxylic acids in the polymers increases. When heated in nonpolar solvents such as toluene, the number of solvent accessible carboxylic acids decreases. On cooling to rt, these changes are preserved and maintained even when the polymer is removed from the solvent imprinting environment. The solvent memory is due to the reestablishment of restricted rotation around that C(aryl)-N(imide) bond, which locks the carboxylic acid recognition groups into either a solvent accessible or inaccessible orientation. The solvent programmability was also shown to be reversible. The fidelity of the SPP switching process did not decrease after five cycles of heating in polar and nonpolar solvents.

A supramolecular switch with molecular memory.

A supramolecular switch is demonstrated that maintains a stable ON state even in the absence of guest at room temperature.

Rapid screening of a receptor with molecular memory.

[reaction: see text] Atropisomeric receptor 1 can change conformation and maintain the new conformation when heated and cooled in the presence of a guest molecule. This molecular memory can be used as a rapid method of screening potential guests. Heating atropisomeric diacid 1 with various hydrogen-bonding guests leads to a shift in the syn/anti ratio that could be easily monitored as it is stable at room temperature even in the absence of the guest molecules.

Conformationally imprinted receptors: atropisomers with "write", "save", and "erase" recognition properties.

[reaction: see text] An atropisomeric receptor with "write", "save", and "erase" recognition properties is presented. The receptor adopts a complementary conformation when heating in the presence of an ethyl adenine-9-acetate guest molecule. This complementary hydrogen bonding conformation is "saved" upon cooling to room temperature due to the reestablishment of restricted rotation and is stable even upon removal of the guest. Finally, the atropisomeric receptor can be "erased" by heating in the absence of the guest.

New multi-electron high capacity anodes based on nanoparticle vanadium phosphides.

Nanoscale vanadium phosphides can serve as new high capacity anodes in alkaline aqueous electrolytes. Competing corrosion reaction(s) are mitigated with the novel use of an anion exchange membrane providing for capacities as high as 2800 mAh g(-1) @ 100 mA g(-1) discharge rate.