Correlation between Roughness of Nanowires and Polymer Backbone Conformation

Interactions of Single Particle with Organic Matters: A Facile Bottom-Up Approach to Low Dimensional Nanostructures

A particle induces a pack of chemical reactions in nanospace: chemical reactions confined into extremely small space provide an ultimate technique for the nanofabrication of organic matter with a variety of functions. Since the discovery of particle accelerators, an extremely high energy density can be deposited, even by a single isolated particle with MeV-ordered kinetic energy. However, this was considered to cause severe damages to organic molecules due to its relatively small bond energies, and lack of ability to control the reactions precisely to form the structures while retaining physico-chemical molecular functionalities. Practically, the severely damaged area along a particle trajectory: a core of a particle track has been simply visualized for the detection/dosimetry of an incident particle to the matters, or been removed to lead nanopores and functionalized by refilling/grafting of fresh organic/inorganic materials. The use of intra-track reactions in the so-called “penumbra” or “halo” area of functional organic materials has been realized and provided us with novel and facile protocols to provide low dimensional nano-materials with perfect size controllability in the 21st century. These protocols are now referred to as single particle nanofabrication technique (SPNT) and/or single particle triggered linear polymerization technique (STLiP), paving the way towards a new approach for nanomaterials with desired functionalities from original molecules. Herein, we report on the extremely wide applicability of SPNT/STLiP protocols for the future development of materials for opto-electronic, catalytic, and biological applications among others.

Unraveling the Solution-State Supramolecular Structures of Donor-Acceptor Polymers and their Influence on Solid-State Morphology and Charge-Transport Properties

Polymer self-assembly in solution prior to film fabrication makes solution-state structures critical for their solid-state packing and optoelectronic properties. However, unraveling the solution-state supramolecular structures is challenging, not to mention establishing a clear relationship between the solution-state structure and the charge-transport properties in field-effect transistors. Here, for the first time, it is revealed that the thin-film morphology of a conjugated polymer inherits the features of its solution-state supramolecular structures. A "solution-state supramolecular structure control" strategy is proposed to increase the electron mobility of a benzodifurandione-based oligo(p-phenylene vinylene) (BDOPV)-based polymer. It is shown that the solution-state structures of the BDOPV-based conjugated polymer can be tuned such that it forms a 1D rod-like structure in good solvent and a 2D lamellar structure in poor solvent. By tuning the solution-state structure, films with high crystallinity and good interdomain connectivity are obtained. The electron mobility significantly increases from the original value of 1.8 to 3.2 cm² V^-1 s^-1 . This work demonstrates that "solution-state supramolecular structure" control is critical for understanding and optimization of the thin-film morphology and charge-transport properties of conjugated polymers.

Fabrication of Thermoresponsive Nanoactinia Tentacles by a Single Particle Nanofabrication Technique

Nanowires that are retractable by external stimulus are the key to fabrication of nanomachines that mimick actinia tentacles in nature. A single particle nanofabrication technique (SPNT) was applied over a large area to the fabrication of retractable nanowires (nanoactinia tentacles) composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(vinylpyrrolidone) (PVP), which are thermoresponsive and hydrophilic polymers. The nanowires were transformed with increasing temperature from rod-like- to globule-forms with gyration radii of ∼1.5 and ∼0.7 μm, respectively. The transformation of the nanowires was reversible and reproducible under repeated cycles of heating and cooling. The reversible transformation was driven by hydration and dehydration of PNIPAM, the thermoresponsive segments, resulting in coil-to-globule transformation of the segments. The nanoactinia tentacle systems trapped the nanoparticles as a model of living cells under thermal stimulation, and the trapping was controlled by temperature. We present herein a unique nanomachine system which can be applicable to nanoparticle filtering/sensing systems and expandable to large-area functionalization and demonstrate polymer-based nanoactuators via scaling of molecular level coil-to-globule transformation into micron-sizes.

Temperature-responsive one-dimensional nanogels formed by the cross-linker-aided single particle nanofabrication technique

A single particle nanofabrication technique was successfully applied to the fabrication of homogeneous poly(N-isopropylacrylamide) (PNIPAAm) 1D nanogels over a large area, using N,N'-methylene-bis-acrylamide (MBAAm) as a cross-linker. The PNIPAAm 1D nanogels with high aspect ratio over 130 were formed uniformly on the substrate, and the mechanical strength and the length of the 1D nanogels can be easily controlled by adjusting the MBAAm content. The 1D nanogels were transformed from the non-aggregated to aggregated forms over a lower critical solution temperature (LCST) of approximately 32 °C in water. Precise trace of the temperature induced change in the size of the 1D nanogel was well interpreted by the coil-to-globule transition of PNIPAAm, which was clearly visualized in the present study. This is the first report of uniform shape change for a 1D nanogel by external stimulus over a large area.