RESUMO
As a step toward the bottom-up construction of magnonic systems, this paper demonstrates the use of a large-amplitude surface-pressure annealing technique to generate 2-D order in a Langmuir-Blodgett monolayer of magnetic soft spheres comprising a surfactant-encapsulated polyoxometalate. The films show a distorted square lattice interpreted as due to geometric frustration caused by 2-D confinement between soft walls, one being the air interface and the other the aqueous subphase. Hysteresis and relaxation phenomena in the 2-D layers are suggested to be due to folding and time-dependent interpenetration of surfactant chains.
RESUMO
We demonstrate the assembly of a compact, gel-like Langmuir-Blodgett film of rods formed by self-assembly of a ß-sheet-forming water-soluble peptide, Ac-IKHLSVN-NH2, at the surface of aqueous electrolytes. We characterize surface pressure hysteresis and demonstrate shear stiffening of the surface caused by area cycling, which we interpret as due to rearrangement and alignment of the rods. We show strong effects of the electrolyte on the assembly of the elementary rods, which can be related to the Hofmeister series and interpreted by effects on the interaction energies mediated by ions and water. Formation of ß-sheet structures and assembly of these into surface-segregated semicrystalline gels was strongly promoted by ammonium sulfate electrolyte. With ammonium sulfate electrolyte as subphase for Langmuir-Blodgett film deposition, shear stiffening by surface area cycling resulted in very compact films on transfer to a substrate.