[Show abstract][Hide abstract] ABSTRACT: Poly(N-(1-hexylheptyl)-N′-(12-oxydodecyl)perylene-3,4,9,10-tetracarboxyldiimide acrylate) (PAcPDI), a perylene diimide (PDI) containing brush polymer, is synthesized, revealing good solubility in organic solvents, excellent thermal stability up to around 340 °C, and two melting transitions over 130−220 °C. The self-assembly and n-type memory characteristics of PAcPDI in nanoscale thin films are quantitatively investigated. As-cast films of PAcPDI are completely amorphous and the PDI units nevertheless formed π–π stacks favorably. However, the PAcPDI molecules can self-assemble via thermal annealing, developing a well-ordered horizontal lamellar structure with monomorphic or polymorphic monoclinic PDI crystals. The formation of monomorphic or polymorphic monoclinic crystals is attributed to various π–π stack modes of the PDI units, and is shown to be dependent on the film thickness. The differences in the thin film morphologies are directly reflected into the electrical memory behavior. The thermally annealed films demonstrate high-performance n-type unipolar volatile memory behavior within the thickness range of 12−31 nm. The as-cast films show n-type unipolar nonvolatile or volatile memory behavior in the range of 12−53 nm. The memory mode of PAcPDI films can be tuned by changing either the morphology or the film thickness.
[Show abstract][Hide abstract] ABSTRACT: Two series of crystalline−crystalline miktoarm star polymers were prepared and their thin film morphologies were investigated in detail by synchrotron grazing incidence X-ray scattering (GIXS): poly(n-hexyl isocyanate)(5000)−poly(ε-caprolactone) 1−3 (17000) (PHIC(5k)−PCL 1−3 (17k)) and poly(n-hexyl isocyanate)(10000)−poly(ε-caprolactone) 1−3 (10000) (PHIC(10k)−PCL 1−3 (10k)). In addition, their thermal properties were examined. All miktoarm star polymers revealed a two-step thermal degradation behavior where the PHIC arm was degraded first, followed by the PCL arm underwent degradation. Interestingly, all miktoarms were found to show a highly enhanced thermal stability, regardless of their molecular weight over 3k to 17k, which might be attributed to their one-end group capped with the counterpart arm(s) via arm-joint formation. Surprisingly, all miktoarm star polymers always developed only lamellar structure in toluene-and chloroform-annealed films via phase-separation, regardless of the length of PHIC arm as well as the length and number of PCL arm. Despite having highly imbalanced volume fractions, lamellar structure was constructed in the films of miktoarm star polymers through the override of volume fraction rule based on the rigid chain properties, self-assembling characteristics, conformational asymmetry, and compressibilities of PHIC and PCL arms. Furthermore, the orientation of such lamellar structures was controlled by the selection of either toluene or chloroform in the solvent-annealing process. The PHIC arm phases in the lamellar structures favorably formed a mixture of edge-on and face-on structures with fully extended backbone and bristle conformations even under the confined lamellar geometry and arm-joint. The PCL arm phases still crystallized, forming fringed-micelle like structures in which orthorhombic crystals were laterally grown along the in-plane direction of lamellae although their crystallization was somewhat suppressed by the confined lamellar geometry and arm-joint. Overall, crystalline−crystalline PHIC−PCL 1−3 miktoarm polymers demonstrated very interesting but unusual, very complex hierarchical structures in the solvent-annealed thin films.
[Show abstract][Hide abstract] ABSTRACT: A new approach for synthesizing well-defined hollow nanochanneled-silica nanosphere particles is demonstrated and the structural details of these particles are described for the first time. Positively charged styrene copolymer nanospheres with a clean, smooth surface and a very narrow size distribution are synthesized by surfactant-free emulsion copolymerization and used as a thermally sacrificial core template for the production of coreshell nanoparticles. A surfactant/silica composite shell with a uniform thickness is successfully produced and deposited onto the polymeric core template by charge density matching between the polymer nanosphere template surface and the negatively charged silica precursors and then followed by selective thermal decomposition of the polymeric core and the surfactant cylinder domains in the shell, producing the hollow nanochanneled-silica nanosphere. Comprehensive, quantitative structural analyses collectively confirm that the obtained nanoparticles are structurally well defined with a hollow core and a shell composed of cylindrical nanochannels that provide facile accessibility to the hollow interior space. Overall, the hollow nanochanneled-silica nanoparticles have great potential for applications in various fields.
[Show abstract][Hide abstract] ABSTRACT: Covalent incorporations into polymers of fullerene were achieved via the Cu(I)-catalyzed azide–alkyne click polymerizations of a fullerene derivative monomer functionalized with 5-(trimethylsilyl)pent-4-yn-1-yl groups and a comonomer functionalized with azidomethyl groups, producing the novel fullerene polymers P1-C60 and P2-C60. Despite their extremely high fullerene loading levels, the polymers were soluble in common organic solvents and exhibited no aggregation of fullerene units in films. Moreover, devices containing these fullerene polymers were easily fabricated with common coating processes that exhibit excellent unipolar and bipolar flash memory characteristics as well as unipolar permanent memory characteristics, with high ON/OFF current ratios, long retention times, and low power consumption. These electrical switching behaviors were favorably operated by electron injection. Overall, these devices are the first n-type bipolar and unipolar digital polymer memory devices which can be operated in flash and write-once-read-many-times modes.
[Show abstract][Hide abstract] ABSTRACT: The electrical memory mechanism of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoroisopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal, optical, and electrochemical properties of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. Devices with the polymers and aluminum top and bottom electrodes were fabricated and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was governed by trap-limited space-charge limited conduction and ohmic conduction. The memory characteristics were found to originate from the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the PI backbone is not conjugated, the present results collectively indicate that the electrical memory behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.
[Show abstract][Hide abstract] ABSTRACT: A series of miktoarm star polymers, [poly(n-hexyl isocyanate)(12K)]–[poly(ε-caprolactone)1–3(5K)] (PHIC–PCL1–3) (composed of a rigid self-assembling PHIC arm and one to three flexible crystallizable PCL arms), were investigated to examine the polymers’ thermal properties and nanoscale thin film morphologies. The miktoarm polymers were stable up to 180 °C. The PHIC and PCL arm components underwent phase separation during the solution casting, drying, and post toluene-annealing processes, forming interesting but very complex thin film morphologies. The resulting thin film morphologies were examined in detail for the first time using synchrotron grazing incidence X-ray scattering (GIXS) measurements and quantitative data analysis. All of the miktoarm star polymer films formed vertically well-oriented lamellar structures, regardless of the number and length of PCL arms. These structures were quite different from the cylindrical structures commonly observed in conventional flexible diblock copolymer films having comparable volume fractions. The individual PHIC and PCL lamellar domains self-assembled to form their own respective morphological structures. The PHIC lamellae consisted of a mixture of horizontal and vertical multibilayer structure domains, as observed in the PHIC homopolymer film. The PCL lamellae formed fringed micelle-like crystals and/or highly imperfect folded crystals that differed significantly from the structures found in a PCL homopolymer film composed of typical folded lamellar crystals. These PCL crystals were formed with a mixture of vertical and horizontal orthorhombic lattices. Overall, the GIXS analysis revealed that the parameters that characterized the hierarchical structures in the thin films depended significantly on the number and length of the PCL arm and its crystallization characteristics as well as the chain rigidity and multibilayer structure formation characteristics of the PHIC arm.
[Show abstract][Hide abstract] ABSTRACT: Self-assembly characteristics of a well-defined brush polymer, poly(oxy(n-dodecyl-thiomethyl)ethylene) were in detail investigated at the air-water interface with surface–area isotherm, X-ray reflectivity, and infrared spectroscopy analyses. The brush polymer self-assembled
at the air-water interface as a fully-extended chain via favorable lateral packing of the bristles in a fully extended conformation, forming highly ordered, oriented Langmuir monolayer. This well-ordered monolayer was produced via a five-regime structure formation with varying surface pressure.
A Langmuir monolayer film with ≤1.92 nm thick was formed in the low surface pressure regime ≤18 mN/m and then converted to a highly dense, ordered monolayer with 3.65 nm thick in the high surface pressure regime ≥35 mN/m through monolayer-to-bilayer transition and bilayer-to-monolayer
inversion. These Langmuir film formations and their ordering and orientation might be driven by the well-defined chemical architecture and the lateral orderings of the polymer backbones and the bristles in fully extended conformations.
[Show abstract][Hide abstract] ABSTRACT: The structural features of nanoscale thin films composed of a miktoarm (polystyrene)2-(polyisoprene)2 (PS2-PI2) star polymer were studied for the first time using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray reflectivity
(XR) analyses. The acetone-annealed thin films formed a horizontally oriented lamellar structure via phase separation. The lamellar structure displayed interesting and unique features not present in the corresponding diblock copolymer thin films. The thick interfacial layers formed by the
PS and PI arm components were three times the thicknesses of the corresponding layers in the diblock copolymer films. The interfacial layers further displayed a relatively high degree of thermal expansion. The overall lamellar structure was thermally stable up to temperatures approaching the
degradation temperature. These unique structural features could be understood in terms of the rigidity and bulkiness of the confined crowded environment surrounding the arm-jointer.
[Show abstract][Hide abstract] ABSTRACT: The nanoscale thin film morphologies of a series of interesting miktoarm star polymers composed of a highly rigid and crystallizable poly(n-hexyl isocyanate) (PHIC) arm and one to three flexible and crystallizable poly(ε-caprolactone) (PCL) arms were investigated
using synchrotron grazing incidence X-ray scattering methods. Nanoscale thin films of a PHIC and a PCL homopolymer were also characterized for comparison. The PCL homopolymer and star polymers formed horizontally oriented lamellar structures in toluene-annealed films. The horizontal lamellar
structures formed in the miktoarm star polymer films were quite different from those observed in common flexible block copolymer specimens. Interestingly, the structural parameters associated with the star polymer films were significantly influenced by the exceptional rigidity of the PHIC
arm chain and by the number and length of the PCL arms. This study demonstrated that a miktoarm star polymer system consisting of rigid and crystallizable arms could form thin films with a morphology that is suitable for specific target applications.
[Show abstract][Hide abstract] ABSTRACT: In-situ synchrotron small-angle X-ray scattering measurements and quantitative data analysis were used to investigate isothermal self-assembly in a series of high-performance poly(1,4-cyclohexyldimethylene-co-ethylene terephthalate)s (PCETs) enriched with 1,4-cyclohexanedimethanol
(CHDM). Interestingly, the bulky CHDM units, which assumed a kinked chair conformation, formed lamellar crystals. The self-assembly process was governed by a nucleation and growth mechanism that depended on the degree of supercooling. Isothermal self-assembly occurred through a four-regime
process. The structural evolution was driven mainly by a primary crystallization process, which contributed to crystal layer thickening, and in part by a secondary crystallization process during the later stages, which did not contribute to crystal layer thickness, to produce a lamellar structure.
In addition to the primary crystals, highly imperfect small secondary crystals distinct from the lamellar crystals were observed to form. The secondary crystals formed only in the amorphous phases, including in the amorphous layer of the lamellar structure. Surprisingly, the minor ethylene
glycol (EG) units tended to be excluded from the primary lamellar crystals.
[Show abstract][Hide abstract] ABSTRACT: The self-assembly characteristics in nanoscale thin films and digital memory behaviors of poly(5-phenyl-1,3,4oxadiazol-2-yl-[1,1 -biphenyl]carboxyloxy-n-nonyl acrylate), a well-defined brush polymer bearing oxadiazole moieties, were investigated. The synchrotron grazing incidence
X-ray scattering analysis found that the brush polymer molecules in thin films always formed a multibilayer structure consisting of fully extended backbone and bristle conformations. In the structure, the bristles were interdigitated in part; In particular, the oxadiazole containing mesogens
were fully interdigitated via the – interaction of the biphenyl linkers. The multibilayer structured film undergoes three phase transitions (glass, melting, and liquid crystal-to-isotropic transitions) below the degradation temperature of 350 °C. The film's overall crystallinity,
as well as the orientation of the multibilayer structure was found to depend on the film formation process conditions. While the as-cast films had a relatively low crystallinity and formed a vertical multibilayer structure with a broad orientation distribution, the thermally annealed films
had a high crystallinity and formed an almost perfect horizontally oriented multibilayer structure. These different morphologies led different digital memory modes in devices; the as-cast films revealed volatile memory behavior, whereas the thermally annealed films showed permanent memory
characteristics. These memory modes originated from the oxadiazole moieties in the two different film morphologies. The memory modes were demonstrated for the polymer films in the thickness range 5–50 nm.
[Show abstract][Hide abstract] ABSTRACT: The three-dimensional structures of the wild-type Pseudomonas putida ketosteroid isomerase (KSI-WT) and its single mutant KSI-Y57S were studied in solution for the first time using synchrotron X-ray scattering methods. The protein solutions were further analyzed using pulse field
gradient nuclear magnetic resonance spectroscopy and ultracentrifugation analysis. The X-ray scattering profiles were extracted from the atomic crystal structures and analyzed. The KSI-WT solution structure differed in size and shape from the structure observed in the crystal form. In solution,
the KSI-WT structure included an open cavity around the active site. This feature might be essential for the catalytic performance. The structure of KSI-WT changed upon introduction of a single mutation (the Tyr57 of KSI-WT was replaced with a serine residue). This single mutation was found
to reduce the size and shape of the KSI-WT structure. However, the open cavity around the active site was abnormally enlarged in the presence of the single mutation. The changes in the size and shape might directly correlate with the large decrease in the catalytic performance of KSI-Y57S.
[Show abstract][Hide abstract] ABSTRACT: Linear-brush diblock copolymers bearing carbazole moieties in the brush block were synthesized. Various phase-separated nanostructures were found to develop in nanoscale thin films of the copolymers, depending on the fabrication conditions including selective solvent-annealing. This variety of morphologies and orientations means that these block copolymers exhibit digital memory versatility in their devices. Overall, the relationship between the morphology and digital memory performance of these copolymers has several important features. In particular, the carbazole moieties in the vertical cylinder phase with a radius of 8 nm or less can trap charges and also form local hopping paths for charge transport, which opens the mass production of advanced digital memory devices with ultrahigh memory density. Charges can be transported through the layer when the dielectric linear block phase has a thickness of 10.6 nm; however, charge transport is not possible for a dielectric phase with a thickness of 15.9 nm. All the observed memory behaviors are governed by the trap-limited space-charge-limited conduction mechanism and local hopping path (i.e., filament) formation.
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The fully pi-conjugated donor-acceptor hybrid polymers Fl-TPA, Fl-TPA-TCNE, and Fl-TPA-TCNQ, which are composed of fluorene (Fl), triphenylamine (TPA), dimethylphenylamine, alkyne, alkyne-tetracyanoethylene (TCNE) adduct, and alkyne-7,7,8,8-tetracyanoquinodimethane (TCNQ) adduct, were synthesized. These polymers are completely amorphous in the solid film state and thermally stable up to 291-409 deg.C. Their molecular orbital levels and band gaps vary with their compositions. The TCNE and TCNQ units, despite their electron acceptor characteristics, were found to enhance the pi-conjugation lengths of Fl-TPA-TCNE and Fl-TPA-TCNQ, i.e. to produce red shifts in their absorption spectra and significant reductions in band gap. These changes are reflected in the electrical digital memory behaviors of the polymers. Moreover, the TCNE and TCNQ units were found to diversify the digital memory modes and to widen the active polymer layer thickness window. In devices with aluminum top and bottom electrodes, the Fl-TPA polymer exhibits stable unipolar permanent memory behavior with high reliability. The Fl-TPA-TCNE and Fl-TPA-TCNQ devices exhibit stable unipolar permanent memory behavior as well as dynamic random access memory behavior with excellent reliability. These polymer devices were found to operate by either hole injection or hole injection along with electron injection, depending on the polymer compositions. Overall, this study demonstrated that the incorporation of -conjugated cyano moieties, which control both the pi-conjugation length and electron-accepting power, is a sound approach to the design and synthesis of high performance digital memory polymers. The TCNE and TCNQ polymers synthesized in this study are highly suitable active materials for the low-cost mass production of high performance, polarity-free, programmable, volatile, and permanent memory devices that can be operated with very low power consumption, high ON/OFF current ratios, and high reliability.
[Show abstract][Hide abstract] ABSTRACT: A series of diblock copolypeptides with various compositions (PBLGm-b-PBCLn) was synthesized through the living ring-opening polymerizations of γ-benzyl-L-glutamate and ε-(benzyloxycarbonyl)-L-lysine N-carboxyanhydrides with the aid of a nickel catalyst system. They were found to be stable up to around 150 °C and easily processable. Their chain conformations and morphologies in nanoscale thin films were characterized in detail by using infrared spectroscopy, atomic force microscopy, and in situ synchrotron grazing incidence X-ray scattering. In particular, quantitative X-ray scattering analysis was used to provide for the first time the morphological structures and orientation details of the diblock copolypeptides in thin films. Fibrils are present in the thin films of the copolypeptides; interestingly, the films are composed of two different rotationally isomeric hexagonally (HEX) packed cylinder structures that are preferentially oriented in the film plane. Further, the HEX structures consist of two substructural block units: one consisting of PBLG block chain cylinders and the other consisting of PBCL block chain cylinders. The block chains in the substructural units were found to interdigitate partially via the side groups. Thus the cylinders' interdigitation takes place selectively between block chains of the same kind rather than between different kinds of block chains. It was also confirmed that this high interdigitation selectivity occurs in the blend films of the homopolypeptides. These results show that in diblock copolypeptide films such selective interdigitation can override any thermodynamic penalties associated with the high chain rigidity due to the α-helical conformation and the effects of confinement in the connected diblock architecture, which leads to phase separation and the formation of well-defined, integrated HEX cylinder structures. These cooperatively and selectively formed HEX cylinder structures were found to be stable up to the degradation temperature. Molecular structure models are presented for the copolypeptide thin films as well as for the homopolypeptide blend films.
[Show abstract][Hide abstract] ABSTRACT: The structural characteristics of aqueous micelles composed of amphiphilic cyclic poly(n-butyl acrylate-b-ethylene oxide) (cyclic PBA-b-PEO) or a linear analogue (i.e., linear poly(n-butyl acrylate-b-ethylene oxide-b-n-butyl acrylate) (linear PBA-b-PEO-b-PBA)) were examined for the first time using synchrotron X-ray scattering techniques and quantitative data analysis. The scattering data were analyzed using a variety of methodologies in a comprehensive complementary manner. These analyses provided details of the structural information about the micelles. Both micelles were found to consist of a core and a fuzzy shell; however, the cyclic block copolymer had a strong tendency to form micelles with core and shell parts that were more compact and dense than the corresponding parts of the linear block copolymer micelles. The PBA block of the cyclic copolymer was found to form a hydrophobic core with a density that exceeded the density of the homopolymer in the bulk state. The structural differences originated primarily from the topological difference between the cyclic and linear block copolymers. The elimination of the chain end groups (which introduced entropy and increased the excess excluded volume) from the amphiphilic block copolymer yielded more stable dense micelles in solution.
[Show abstract][Hide abstract] ABSTRACT: Time-resolved small-angle X-ray scattering (SAXS) analysis was performed on a series of poly(ethyleneco-1,4-cyclohexyldimethylene terephthalate)s (PECT copolymers) containing 1.6, 5.3, and 9.8 mol% 1,4-cyclohexyldimethylene (CHDM) units during isothermal crystallization and subsequent melting processes. The measured SAXS data were quantitatively analyzed to yield detailed information (scattering invariant quantity, Q; long period, L p ; lamellar crystal layer thickness, d c ; and amorphous layer thickness, d a ) about the crystal structure evolution and melting devolution behaviors. The Q value was found to be a very sensitive powerful probe for monitoring the crystallization and crystal melting processes. The structural evolution of the copolymers was dominated by the primary crystallization transition. The secondary crystallization effects contributed little to the structural evolution. The few secondary crystals present most likely formed fringed micelle structures that were very small and included a high degree of imperfections. The poor secondary crystal formation was attributed to the presence of bulky, kinked CHDM units, which introduced a high degree of steric hindrance. The high steric hindrance of the CHDM units resulted in their exclusion from the lamellar crystal layers and secondary crystals, and in their insertion into amorphous regions and layers. Overall, the CHDM comonomer units strongly perturbed the crystallization process and the morphological structure of the PECT copolymer. The effects of CHDM as a chemical modifier of poly(ethylene terephthalate)-based polymers may potentially be optimized in an effort to enhance the properties and processability of the polymer.
Macromolecular Research 02/2014; 22(2). DOI:10.1007/s13233-014-2020-2 · 1.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A series of well-defined poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene-ran-oxy(n-dodecylthiomethyl)ethylene) (PECH-PCm: m = 0-100 mol% phosphorylcholine (PC)) polymers were used to prepare nanoscale thin films that were characterized by synchrotron X-ray reflectivity (XR) analysis. The quantitative XR analysis provided structural insights into the PECH-PCm thin films. The PECH-PC0 polymer film formed a well-ordered in-plane oriented molecular multibilayer structure, whose individual layers consisted of two sublayers. One sublayer was composed of the fully extended backbones and inner part of the bristles, exhibiting a relatively low electron density, whereas the other sublayer was composed of a bilayer of the outer parts of the bristles without interdigitation. The PECH-PC100 polymer film also formed a well-ordered in-plane oriented molecular multibilayer structure, the individual layers of which were composed of four sublayers rather than two. The bristles in the layer were interdigitated in part via the zwitterionic interactions of the PC end groups. Surprisingly, regardless of the copolymer composition, the PECH-PCm random copolymer molecules in the thin films self-assembled to form a multilayered structure that resembled the structure formed by the PECH-PC100 polymer. These properties have not been observed in other conventional random brush copolymer films. The remarkable multibilayer structures originated from the zwitterionic PC end groups and their favorable interactions and interdigitated structures, which overcame any negative contributions caused by the heterogeneity of the bristles. The unique self-assembly properties of the PECH-PCm polymers always provide a PC-rich surface. The PECH-PCm random copolymers successfully mimicked the molecular bilayer structures formed by natural lipids.