Order−Order and Order−Disorder Transitions in Thin Films of an Amphiphilic Liquid Crystalline Diblock Copolymer

Bulk self-assembly and ionic conductivity of a block copolymer containing an azobenzene-based liquid crystalline polymer and a poly(ionic liquid)

A block copolymer containing a liquid crystalline polymer and a poly(ionic liquid) self-assembles and can be used as a solid electrolyte.

Live Templates of a Supramolecular Block Copolymer for the Synthesis of Ordered Nanostructured TiO2 Films via Guest Exchange

In this work, we introduce a facile method based on host-guest chemistry to synthesize a range of nanostructured TiO₂ materials using supramolecular templates of a dendron-jacketed block copolymer (DJBCP). The DJBCP is composed of amphiphilic dendrons (4'-(3,4,5-tridodecyloxybenzoyloxy)benzoic acid, TDB) selectively incorporated into a P4VP block of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) via hydrogen bonding. The PS-b-P4VP host acts as a structure-directing template, while the guest molecules (TDB) assist the self-assembly nanostructures and zone-axis alignment, resulting in the nanostructured template of vertically oriented cylinders formed via successive phase transformations from Im3̅m to R3̅m to P6mm upon thermal annealing in the doctor-blade-cast film. The guest molecules subsequently direct the titania precursors into the P4VP domains of the templates via supramolecular guest exchange during immersion of the film in a designated precursor solution containing a P4VP-selective solvent. The subsequent UV irradiation step leads to the formation of PS-b-P4VP/TiO₂ hybrids. Finally, removal of the host template by calcination leaves behind mesoporous channels and makes sacrifices to be a carbon source for carbon-doping TiO₂ materials. Various TiO₂ nanoarchitectures, namely, vertical and wiggly micrometer-length channels, inverse opals, fingerprint-like channels, heterogeneous multilayers, and nanotubes, have been fabricated by highly tunable DJBCP nanostructures.

Slowing the translocation of single-stranded DNA by using nano-cylindrical passage self-assembled by amphiphilic block copolymers

We report a novel approach to slow the translocation of single-stranded DNA (ssDNA) by employing polyethylene oxide (PEO) filled nano-cylindrical domains as transportation channels. DNA strands were demonstrated to electrophoretically translocate through PEO filled cylindrical domains with diameters of 2 and 9 nm, which were self-assembled by amphiphilic liquid crystalline block copolymers. The average translocation rate of ssDNA strands was effectively reduced to an order of 10 μs per nucleotide, which was 1-2 orders slower than that attained by utilizing conventional solid-state nanopore devices.

Probing the self-assembled nanostructures of functional polymers with synchrotron grazing incidence X-ray scattering

For advanced functional polymers such as biopolymers, biomimic polymers, brush polymers, star polymers, dendritic polymers, and block copolymers, information about their surface structures, morphologies, and atomic structures is essential for understanding their properties and investigating their potential applications. Grazing incidence X-ray scattering (GIXS) is established for the last 15 years as the most powerful, versatile, and nondestructive tool for determining these structural details when performed with the aid of an advanced third-generation synchrotron radiation source with high flux, high energy resolution, energy tunability, and small beam size. One particular merit of this technique is that GIXS data can be obtained facilely for material specimens of any size, type, or shape. However, GIXS data analysis requires an understanding of GIXS theory and of refraction and reflection effects, and for any given material specimen, the best methods for extracting the form factor and the structure factor from the data need to be established. GIXS theory is reviewed here from the perspective of practical GIXS measurements and quantitative data analysis. In addition, schemes are discussed for the detailed analysis of GIXS data for the various self-assembled nanostructures of functional homopolymers, brush, star, and dendritic polymers, and block copolymers. Moreover, enhancements to the GIXS technique are discussed that can significantly improve its structure analysis by using the new synchrotron radiation sources such as third-generation X-ray sources with picosecond pulses and partial coherence and fourth-generation X-ray laser sources with femtosecond pulses and full coherence.

Complex Self-Assembled Morphologies of Thin Films of an Asymmetric A3B3C3 Star Polymer

An asymmetric nine-arm star polymer, (polystyrene)₃-(poly(4-methoxystyrene))₃-(polyisoprene)₃ (PS₃-PMOS₃-PI₃) was synthesized, and the details of the structures of its thin films were successfully investigated for the first time by using in situ grazing incidence X-ray scattering (GIXS) with a synchrotron radiation source. Our quantitative GIXS analysis showed that thin films of the star polymer molecules have very complex but highly ordered and preferentially in-plane oriented hexagonal (HEX) structures consisting of truncated PS cylinders and PMOS triangular prisms in a PI matrix. This HEX structure undergoes a partial rotational transformation process at temperatures above 190 °C that produces a 30°-rotated HEX structure; this structural isomer forms with a volume fraction of 23% during heating up to 220 °C and persists during subsequent cooling. These interesting and complex self-assembled nanostructures are discussed in terms of phase separation, arm number, volume ratio, and confinement effects.

Tunable Film Morphologies of Brush-Linear Diblock Copolymer Bearing Difluorene Moieties Yield a Variety of Digital Memory Properties

An amphiphilic brush-linear diblock copolymer bearing a rigid difluorene moiety was synthesized, yielding a copolymer with a high thermal stability and excellent processability. The immiscibility of the blocks induced the formation of a variety of nanostructures, depending on the fabrication conditions, which differed significantly from the nanostructures observed among common diblock copolymers in similar composition. Interestingly, the orientations of the nanostructures could be controlled. The nanostructured polymer displayed a variety of tunable morphologies that yielded distinct electrical memory properties when incorporated as the active layer into a digital memory device. The memory devices could be operated under very low power consumption levels and displayed excellent unipolar switching properties.

Liquid-crystalline ordering helps block copolymer self-assembly

Interaction between liquid-crystalline elastic deformation and microphase separation in liquid-crystalline block copolymers enables them to supramolecularly assemble into ordered nanostructures with high regularity. With the help of liquid-crystalline alignment, parallel and perpendicular patterning of nanostructures is fabricated with excellent reproducibility and mass production, which provides nanotemplates and nanofabrication processes for preparing varieties of nanomaterials. Furthermore, nanoscale microphase separation improves the optical performance of block-copolymer fi lms by eliminating the scattering of visible light, leading to advanced applications in optical devices and actuators. Recent progress in liquid-crystalline block copolymers, including their phase diagram, structure-property relationship, nanostructure control and nanotemplate applications, is reviewed.

Well-defined DNA-mimic brush polymers bearing adenine moieties: synthesis, layer-by-layer self-assembly, and biocompatibility

Two new DNA-mimicking brush polymers were synthesized: poly[oxy(11-(3-(9-adeninyl)propionato)-undecanyl-1-thiomethyl)ethylene] (PECH-AP) and poly[oxy(11-(5-(9-adenylethyloxy)-4-oxopentanoato)undecanyl-1-thiomethyl)ethylene] (PECH-AS). These polymers were found to be thermally stable up to 220 °C and could be applied easily by conventional coating processes to produce good quality films. Interestingly, both brush polymers formed molecular multibilayer structures to provide an adenine-rich surface. Despite the structural similarities, PECH-AS surprisingly exhibited higher hydrophilicity and better water sorption properties than PECH-AP. These differences were attributed to the chemical structures in the bristles of the polymers. The adenine-rich surfaces of the polymer films demonstrated selective protein adsorption, suppressed bacterial adherence, facilitated HEp-2 cell adhesion, and exhibited good biocompatibility in mice. However, the high hydrophilicity and good water sorption characteristics of the PECH-AS film suggest that this brush polymer is better suited to applications requiring good biocompatibility and reduced chance of bacterial infection compared with the PECH-AP film.

Debye–Scherrer rings from block copolymer films with powder-like order

The powder-like orientation of lamellar domains in thin films of the diblock copolymer polystyrene-block-poly(methyl methacrylate) is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence small-angle neutron scattering (GISANS). Conventional monochromatic GISANS and GISAXS measurements are compared with neutron time-of-flight GISANS. For angles of incidence and exit larger than the critical angle of total external reflection of the polymer, Debye–Scherrer rings are observed. The position of the Debye–Scherrer rings is described quantitatively based on a reduced version of the distorted-wave Born approximation. A strong distortion of the ring shape is caused by refraction and reflections from the film interfaces. Close to the critical angle, the ring shape collapses into a banana shape.

pH-dependent structures of an i-motif DNA in solution

We have investigated for the first time the structure of i-motif DNA in solution at various pH conditions by using synchrotron small-angle X-ray scattering technique. To facilitate direct structural comparison between solution structures of i-motif DNA at various pH values, we created atomic coordinates of i-motif DNA from a fully folded to unfolded atomic model. Under mild acidic conditions, the conformations for i-motif DNA appeared to be similar to that of the partially unfolded i-motif atomic model in overall shape, rather than the fully folded i-motif atomic model. Collectively, our observations indicate that i-motif DNA molecule is structurally dynamic over a wide pH range, adopting multiple conformations ranging from the folded i-motif structure to a random coil conformation. As the i-motif structure has been used as an important component in nanomachines, we can therefore believe that the structural evidence presented herein will promote the development of future DNA-based molecular-actuator devices.