Occurrence, shape, and dimensions of large surface hemimicelles made of semifluorinated alkanes. Elongated versus circular Hemimicelles. Pit- and tip-centered hemimicelles

The formation of large (approximately 20-35 nm) surface hemimicelles in monolayers of semifluorinated alkanes, C(n)F(2)(n)(+1)C(m)H(2)(m)(+1) (FnHm), observed after transfer onto silicon wafers, is a general phenomenon. F6H16 and F8H14 exclusively form highly monodisperse circular hemimicelles, organized in a hexagonal array. The other FnHm investigated form both circular and elongated hemimicelles. The longer FnHm is, the larger the area fraction of elongated micelles; both the hydrocarbon block (H-block) and the fluorocarbon block (F-block) affect this area fraction. The length of the elongated micelles increases with the total length of the diblocks. The diameter of the circular micelles increases with the length of the H-block but, unexpectedly, not with that of the F-block. Model calculations account for these observations. Close examination of the circular micelles showed that they generally present a pit or a tip at their center. The width of the elongated micelles is comparable to the radius of the circular micelles, suggesting that the latter arise from a partition of elongated micelles, followed by coalescence of the edges of the resulting fragments. The elongated micelles become shorter and fewer when surface pressure increases, further suggesting a conversion of elongated into circular micelles. This conversion is reversible. The surface pressure-molecular area isotherms do not present any feature that forebears the existence of hemimicelles. The obtaining of stable surface patterns from simple, "nonpolar" molecular fluorocarbon/hydrocarbon diblocks opens a new approach for producing featured nanostructures from organic templates.     

Effect of the molecular structure on the hierarchical self-assembly of semifluorinated alkanes at the air/water interface

Semifluorinated alkanes (C(n)F(2n+1)C(m)H(2m+1)), short FnHm display local phase separation of mutually incompatible hydrocarbon and fluorocarbon chain moieties, which has been utilized as a structure-forming motif in supramolecular architectures. The packing of semifluorinated alkanes, nominally based on dodecyl subunits, such as perfluoro(dodecyl)dodecane (F12H12) and perfluoro(dodecyl)eicosane (F12H20), as well as a core extended analogue, 1,4-dibromo-2-((perfluoroundecyl)methoxy)-5-(dodecyloxy)benzene) (F11H1-core-H12), was studied at the air/water interface. Langmuir monolayers were investigated by means of neutron reflectivity directly at the air/water interface and scanning force microscopy after transfer to silicon wafers. Narrowly disperse surface micelles formed in all three cases; however, they were found to bear different morphologies with respect to molecular orientation and assembly dimensionality, which gives rise to different hierarchical aggregate topologies. For F12H12, micelles of ca. 30 nm in diameter, composed of several circular or "spherical cap" substructures, were observed and a monolayer model with the fluorocarbon block oriented toward air is proposed. F12H20 molecules formed larger (ca. 50 nm diameter) hexagonally shaped surface micelles that were hexagonally, densely packed, besides more elongated but tightly interlocked wormlike structures. Conversely, F11H1-core-H12 films organized into linear rows of elongated surface micelles with comparable width, but an average length of ca. 400 nm, apparently formed by antiparallel molecular packing.     

Crystalline Phase Separation of Racemic and Nonracemic Zwitterionic α‐Amino Acid Amphiphiles in a Phospholipid Environment at the Air/Water Interface: A Grazing‐Incidence X‐Ray Diffraction Study

A grazing‐incidence X‐ray‐diffraction (GIXD) study of the self‐assembly, on water, of nonracemic γ‐stearyl glutamic acid (pure or as a mixture with racemic or (S)‐1,2‐dipalmitoyl‐glycero‐3‐phosphoethanolamine (DPPE)) demonstrated a phase separation of the α‐amino acid amphiphile into racemic and enantiomorphous two‐dimensional crystallites within the phospholipid domains. The packing arrangements of the two α‐amino acid crystalline phases were identical to those found in the absence of DPPE and have been determined, at almost atomic resolution, by X‐ray structure‐factor calculations. By contrast, racemic and nonracemic N^ε‐stearoyllysine spontaneously segregated into two‐dimensional enantiomorphous domains within the DPPE environment that induced a change in the tilt direction of the hydrocarbon chains of the α‐amino acid molecules. Phase separation of nonracemic amphiphiles, originating from preferred lateral homochiral or heterochiral intermolecular interactions, is in agreement with the formation of enantiomerically pure or enriched homochiral oligopeptides in overrepresented amounts in the polycondensation of activated nonracemic amphiphilic α‐amino acids on plain water or within phospholipid monolayers.     

(R)‐12‐Hydroxystearic Acid Hydrazides as Very Efficient Gelators: Diffusion,Partial Thixotropy,and Self‐Healing in Self‐Standing Gels

The gelation properties of derivatives of N‐alkylated (R)‐12‐hydroxystearic acid hydrazide (n‐HSAH, n=0, 2, 6, 10; n is the length of an n‐alkyl chain on the terminal nitrogen atom) in a wide variety of liquids is reported. The n‐HSAH compounds were derived from a naturally occurring alkanoic acid, (R)‐12‐hydroxystearic acid (R‐12HSA), and although they differ from the analogous N‐alkyl (R)‐12‐hydroxystearamides (n‐HSAA) only by the presence of one N?H group, their behavior as gelators is very different. For example, the parent molecule (0‐HSAH) is a supergelator in ethylene glycol, in which it forms self‐standing gels that are self‐healing, partially thixotropic, moldable, and load‐bearing; gels of 0‐HSAA are not self‐standing. 0‐HSAH is structurally the simplest molecular gelator of which we are aware that is capable of forming both self‐standing and partially thixotropic gels. Also, diffusion of the cationic dye erythrosine B and the anionic dye methylene blue in 0‐HSAH/ethylene glycol gel blocks is much slower than the self‐diffusion of ethylene glycol. Polarizing optical microscopy, X‐ray diffraction, and FTIR studies revealed that the self‐assembled fibrillar networks (SAFINs) of the gels are crystalline, and that 0‐HSAH molecules may be arranged in a triclinic subcell with bilayer stacking. The SAFINs are stabilized by strong hydrogen‐bonding interactions between the hydrazide groups of adjacent molecules and a perpendicular hydrogen‐bonding network between the pendent hydroxyl groups of 0‐HSAH. The other n‐HSAH (n=2, 6, 10) molecules appear to be arranged in orthorhombic subcells with monolayers and strong hydrogen‐bonding interactions between the hydrazide group of one gelator molecule and the hydroxyl group of a neighboring one. These results show how small structural modifications of structurally simple gelator molecules can be exploited to form gels with novel properties that can lead potentially to valuable applications, such as in drug delivery.     

Topological “interfacial” polymer chemistry: Dependency of polymer “shape” on surface morphology and stability of layer structures when heating organized molecular films of cyclic and linear block copolymers of n‐butyl acrylate‐ethylene oxide

The “topological polymer chemistry” of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB‐type diblock and ABA‐type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed‐phase temperature‐dependent behaviors were observed in surface pressure–area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA‐type triblock linear copolymers adopted a fiber‐like surface morphology via two‐dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature‐controlled out‐of‐plane X‐ray diffraction (XRD) analysis of Langmuir–Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat‐resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher‐order reflections (d₀₀₂, d₀₀₃) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 486–498     

C?H/π‐Interaction‐Guided Self‐Assembly in π‐Conjugated Oligomers

We report CH/π hydrogen‐bond‐driven self‐assembly in π‐conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single‐crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π‐stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single‐crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π‐ring (H‐bond acceptor) and alkyl C? H (H‐bond donor). The four important crystallographic parameters, d_c?x=3.79 Å, θ=21.49°, φ=150.25° and d_Hp?x=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close‐packing of mesogens in x–y planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid‐crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11 %. The orientation and translational ordering of mesogens in the liquid‐crystalline (LC) phases induced H‐ and J‐type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H‐ and J‐type molecular arrangements were found to emit a blue or yellowish/green colour. Time‐resolved fluorescence decay measurements confirmed longer lifetimes for H‐type smectic OPVs relative to that of loosely packed one‐dimensional nematic hydrocarbon‐tailed OPVs.     

Dimensional Control of Block Copolymer Nanofibers with a π‐Conjugated Core: Crystallization‐Driven Solution Self‐Assembly of Amphiphilic Poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine)

With the aim of accessing colloidally stable, fiberlike, π‐conjugated nanostructures of controlled length, we have studied the solution self‐assembly of two asymmetric crystalline–coil, regioregular poly(3‐hexylthiophene)‐b‐poly(2‐vinylpyridine) (P3HT‐b‐P2VP) diblock copolymers, P3HT₂₃‐b‐P2VP₁₁₅ (block ratio=1:5) and P3HT₄₄‐b‐P2VP₁₁₅ (block ratio=ca. 1:3). The self‐assembly studies were performed under a variety of solvent conditions that were selective for the P2VP block. The block copolymers were prepared by using Cu‐catalyzed azide–alkyne cycloaddition reactions of azide‐terminated P2VP and alkyne end‐functionalized P3HT homopolymers. When the block copolymers were self‐assembled in a solution of a 50 % (v/v) mixture of THF (a good solvent for both blocks) and an alcohol (a selective solvent for the P2VP block) by means of the slow evaporation of the common solvent; fiberlike micelles with a P3HT core and a P2VP corona were observed by transmission electron microscopy (TEM). The average lengths of the micelles were found to increase as the length of the hydrocarbon chain increased in the P2VP‐selective alcoholic solvent (MeOH<iPrOH<nBuOH). Very long (>3 μm) fiberlike micelles were prepared by the dialysis of solutions of the block copolymers in THF against iPrOH. Furthermore the widths of the fibers were dependent on the degree of polymerization of the chain‐extended P3HT blocks. The crystallinity and π‐conjugated nature of the P3HT core in the fiberlike micelles was confirmed by a combination of UV/Vis spectroscopy, photoluminescence (PL) measurements, and wide‐angle X‐ray scattering (WAXS). Intense sonication (iPrOH, 1 h, 0 °C) of the fiberlike micelles formed by P3HT₂₃‐b‐P2VP₁₁₅ resulted in small (ca. 25 nm long) stublike fragments that were subsequently used as initiators in seeded growth experiments. Addition of P3HT₂₃‐b‐P2VP₁₁₅ unimers to the seeds allowed the preparation of fiberlike micelles with narrow length distributions (L_w/L_n <1.11) and lengths from about 100‐300 nm, that were dependent on the unimer‐to‐seed micelle ratio.     

Amphiphilic Homochiral Oligopeptides Generated via Phase Separation of Nonracemic α‐Amino Acid Derivatives and Lattice‐Controlled Polycondensation in a Phospholipid Environment

Racemic S‐ethyl thioesters of N^ε‐stearoyllysine (= S‐ethyl (R,S)‐2‐amino‐6‐(stearoylamino)hexanethioate) and S‐ethyl thioesters of γ‐stearyl glutamic acid (=stearyl (R,S)‐4‐amino‐5‐(ethylsulfanyl)‐5‐oxopentanoate) self‐assemble as separated two‐dimensional crystalline monolayers within an achiral phospholipid environment of racemic 1,2‐dipalmitoylglycerol (DPG) and 1,2‐dipalmitoylglycero‐3‐phosphoethanolamine (DPPE), as demonstrated by grazing‐incidence X‐ray‐diffraction (GIXD) measurements performed on the surface of H₂O. Lattice‐controlled polycondensation within these crystallites with deuterium‐enantiolabeled monomers was initiated by injecting aqueous solutions of Ag⁺ or I₂/KI beneath the monolayers, which yielded mixtures of diastereoisomeric oligopeptides containing up to six to eight repeating units, as analyzed by MALDI‐TOF mass spectrometry. Analysis of the diastereoisomeric distribution showed an enhanced relative abundance of the oligopeptides with homochiral sequences containing three or more repeating units. Within the DPPE monolayers, the nucleophilic amino group of the phospholipid operates as an initiator of polymerization at the periphery of the monomer two‐dimensional crystallites. Enhanced relative abundance of enantiomerically enriched homochiral oligopeptides was obtained by the polycondensation of nonracemic monomers. This enhancement indicated a phase separation into racemic and enantiomorphous monomer crystallites within the phospholipid environment, although this separation could not be observed directly by GIXD. A possible role that might have been played by crystalline assemblies for the abiotic generation and amplification of oligopeptides with homochiral sequences is discussed.     

Exchange of Methyl‐ and Azobenzene‐Terminated Alkanethiols on Polycrystalline Gold Studied by Tip‐Enhanced Raman Mapping

Mixed thiol self‐assembled monolayers (SAMs) presenting methyl and azobenzene head groups were prepared by chemical substitution from the original single‐component n‐decanethiol or [4‐(phenylazo)phenoxy]hexane‐1‐thiol SAMs on polycrystalline gold substrates. Static contact‐angle measurements were carried out to confirm a change in the hydrophobicity of the functionalized surfaces following the exchange reaction. The mixed SAMs presented contact‐angle values between those of the more hydrophobic n‐decanethiol and the more hydrophilic [4‐(phenylazo)phenoxy]hexane‐1‐thiol single‐component SAMs. By means of tip‐enhanced Raman spectroscopy (TERS) mapping experiments, it was possible to highlight that molecular replacement takes place easily and first at grain boundaries: for two different mixed SAM compositions, TERS point‐by‐point maps with <50 nm step sizes showed different spectral signatures in correspondence to the grain boundaries. An example of the substitution extending beyond grain boundaries and affecting flat areas of the gold surface is also shown.     

New Linear and Star‐Shaped Thermogelling Poly([R]‐3‐hydroxybutyrate) Copolymers

The synthesis of multi‐arm poly([R]‐3‐hydroxybutyrate) (PHB)‐based triblock copolymers (poly([R]‐3‐hydroxybutyrate)‐b‐poly(N‐isopropylacrylamide)‐b‐[[poly(methyl ether methacrylate)‐g‐poly(ethylene glycol)]‐co‐[poly(methacrylate)‐g‐poly(propylene glycol)]], PHB‐b‐PNIPAAM‐b‐(PPEGMEMA‐co‐PPPGMA), and their subsequent self‐assembly into thermo‐responsive hydrogels is described. Atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide (NIPAAM) followed by poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(propylene glycol) methacrylate (PPGMA) was achieved from bromoesterified multi‐arm PHB macroinitiators. The composition of the resulting copolymers was investigated by ¹H and ¹³C J‐MOD NMR spectroscopy as well as size‐exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The copolymers featuring different architectures and distinct hydrophilic/hydrophobic contents were found to self‐assemble into thermo‐responsive gels in aqueous solution. Rheological studies indicated that the linear one‐arm PHB‐based copolymer tend to form a micellar solution, whereas the two‐ and four‐arm PHB‐based copolymers afforded gels with enhanced mechanical properties and solid‐like behavior. These investigations are the first to correlate the gelation properties to the arm number of a PHB‐based copolymer. All copolymers revealed a double thermo‐responsive behavior due to the NIPAAM and PPGMA blocks, thus allowing first the copolymer self‐assembly at room temperature, and then the delivery of a drug at body temperature (37 °C). The non‐significant toxic response of the gels, as assessed by the cell viability of the CCD‐112CoN human fibroblast cell line with different concentrations of the triblock copolymers ranging from 0.03 to 1 mg mL^?1, suggest that these PHB‐based thermo‐responsive gels are promising candidate biomaterials for drug‐delivery applications.     

A Simple Fabrication Method for Three‐Dimensional Gold Nanoparticle Electrodes and Their Application to the Study of the Direct Electrochemistry of Cytochrome c

A simple method for constructing gold nanoparticle‐modified electrodes with three‐dimensional nanostructures is demonstrated. The electrodes were prepared by casting citrate‐reduced AuNPs onto polycrystalline gold electrodes. The resultant electrodes had a large surface area‐to‐volume ratio, adequate for high protein loading and conferring high stability. The gold nanoparticle electrodes were covered with a self‐assembled monolayer of 11‐mercaptoundecanoic acid for electrostatic immobilization of cytochrome c (cyt c). At the electrode, direct, reversible electron transfer from cyt c was observed with remarkable stability. Moreover, an extremely high surface coverage of electrochemically active cyt c, 167 fully packed monolayers, was obtained through use of the electrode.     

Self‐assembled Monolayers of Alkylphosphonic Acids on Aluminum Oxide Surfaces – A Theoretical Study

Density‐functional based calculations were used to investigate self‐assembled monolayers of different alkylphosphonic acids on corundum α‐Al₂O₃ (0001), bayerite β‐Al(OH)₃ (001) and boehmite γ‐AlOOH (010) surface models. Mono‐, bi‐, and tridentate adsorption modes were considered. In addition, the organization of single adsorbed molecules was compared to the organization at full surface coverage. The height (thickness) of the self‐assembled monolayers is always shorter than the length of the phosphonic acid molecules due to tilting of the alkyl chains. Tilt angles at full surface coverage are very similar to the tilt angle of a single adsorbed molecule, which indicates that the density of the self‐assembled monolayers is limited by the density of adsorption sites. The lateral interactions between alkyl chains are evidenced by small torsions of the adsorbed molecules, which may serve to minimize the repulsion forces between interchain hydrogen atoms. Similar tilt angles were obtained for mono‐, bi‐, and tridentate adsorptions. Hence, the coordination mode cannot be characterized by the molecule tilting.     

Compression of Self‐Assembled Nano‐Objects: 2D/3D Transitions in Films of (Perfluoroalkyl)Alkanes—Persistence of an Organized Array of Surface Micelles

Understanding and controlling the molecular organization of amphiphilic molecules at interfaces is essential for materials and biological sciences. When spread on water, the model amphiphiles constituted by C_nF_2n+1C_mH_2m+1 (FnHm) diblocks spontaneously self‐assemble into surface hemimicelles. Therefore, compression of monolayers of FnHm diblocks is actually a compression of nanometric objects. Langmuir films of F8H16, F8H18, F8H20, and F10H16 can actually be compressed far beyond the “collapse” of their monolayers at ～30 Ų. For molecular areas A between 30 and 10 Ų, a partially reversible, 2D/3D transition occurs between a monolayer of surface micelles and a multilayer that coexist on a large plateau. For A<10 Ų, surface pressure increases again, reaching up to ～48 mN m^?1 before the film eventually collapses. Brewster angle microscopy and AFM indicate a several‐fold increase in film thickness when scanning through the 2D/3D coexistence plateau. Compression beyond the plateau leads to a further increase in film thickness and, eventually, to film disruption. Reversibility was assessed by using compression–expansion cycles. AFM of F8H20 films shows that the initial monolayer of micelles is progressively covered by one (and eventually two) bilayers, which leads to a hitherto unknown organized composite arrangement. Compression of films of the more rigid F10H16 results in crystalline‐like inflorescences. For both diblocks, a hexagonal array of surface micelles is consistently seen, even when the 3D structures eventually disrupt, which means that this monolayer persists throughout the compression experiments. Two examples of pressure‐driven transformations of films of self‐assembled objects are thus provided. These observations further illustrate the powerful self‐assembling capacity of perfluoroalkyl chains.     

Hydrogen‐bonded networks in trans‐3‐(3‐pyridyl)acrylic acid and rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride

The structure of trans‐3‐(3‐pyridyl)acrylic acid, C₈H₇NO₂, (I), possesses a two‐dimensional hydrogen‐bonded array of supramolecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring molecules [3.821 (1) Å] along the a axis. The crystal structure of the photoproduct, rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride, C₁₆H₁₆N₂O₄²⁺·2Cl⁻, (II), consists of a three‐dimensional hydrogen‐bonded network built from crosslinking of helical chains integrated by self‐assembly of dipyridinium cations and Cl⁻ anions via different O—H...Cl, C—H...Cl and N⁺—H...Cl hydrogen‐bond interactions.     

1‐[5‐(4,5‐Dimethyl‐1,3,2‐dioxaborolan‐2‐yl)thiophen‐2‐yl]ethanone and 4‐(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)benzaldehyde

In both title compounds, C₁₀H₁₃BO₃S, (I), and C₁₃H₁₇BO₃, (II), the molecules adopt nearly planar conformations. The crystal packing of (I) consists of a supramolecular two‐dimensional network with a herringbone‐like topology formed by self assembly of centrosymmetric pairs of molecules linked via dipole–dipole interactions. The crystal structure of (II) consists of a supramolecular two‐dimensional network built up from centrosymmetric pairs of molecules viaπ–π interactions. These pairs of molecules are self‐organized in an offset fashion related by a symmetry centre, generating supramolecular ribbons running along the [101] direction. Neighbouring ribbons are stacked via complementary van der Waals and hydrophobic methyl–methyl interactions.     

Highly Luminescent and Water‐Soluble Two‐Dimensional Supramolecular Organic Framework: All‐Organic Photosensitizer Template for Visible‐Light‐Driven Hydrogen Evolution from Water

A highly fluorescent (Φ_F=0.60) and water‐soluble two‐dimensional (2D) honeycomb‐shaped supramolecular organic framework (SOF) was successfully synthesized in pure aqueous solution via self‐assembly of novel cyanostilbene‐functionalized trilateral guest molecules and cucurbit[8]uril hosts. The size of this fluorescent 2D SOF was >500 nm in diameter, 1.7 nm in thickness, and 3.9 nm in the honeycomb pore diameter. This 2D SOF holds potential as a new all‐organic photosensitizer template for photocatalytic H₂ evolution from pure water.     

Hydrogel Formation Using New L‐Lysine‐Based Low‐Molecular‐Weight Compounds with Positively Charged Pendant Chains

Low‐molecular‐weight compounds based on L ‐lysine with alkylpyridinium or ‐imidazolium groups have been synthesized and studied for their gelation behavior in H₂O. Most compounds formed gels below a concentration of 2.5 weight‐%, the pyridinium bromide 2a and the 1‐methyl‐1H‐imidazolium bromide 3 even at 0.1 weight‐%. The minimum gel concentration (MGC) necessary for hydrogelation increased with increasing length of the Lys N^α‐alkanoyl chain, but the gelation ability concomitantly decreased. Electron‐microscopic images demonstrated that these hydrogelators create a three‐dimensional network in H₂O by entanglement of self‐assembled nanofibers. A fluorescence study with 8‐anilinonaphthalene‐1‐sulfonic acid (ANS) proved that some hydrophobic aggregates are formed at hydrogelator concentrations below an MGC of less than 50 μM (0.004%). FT‐IR, ¹H‐NMR, and Fluorescence studies indicated that the driving forces for the self‐assembly into nanofibers are mainly hydrophobic interactions and H‐bonding between amide groups.     

A facile route to regular and nonregular dot arrays by integrating nanoimprint lithography with sphere‐forming block copolymer directed self‐assembly

Nanoimprint lithography is used to create large‐area two‐dimensional prepatterns with tunable topographic heights in a resist layer. The resist prepatterns are applied to direct the self‐assembly of sphere‐forming polystyrene‐block‐polydimethylsiloxane block copolymers so as to form sparse nonregular nanodot arrays with flexible pattern layouts from high‐topography prepattern or dense regular nanodot arrays with a multiplicative pattern density from low‐topography prepattern. By precisely controlling the topographic height in substrate prepatterns, the origin of directed self‐assembly of block copolymer spheres using low‐topography prepattern is found to be topographic contrast. High‐fidelity pattern transfer from spherical block copolymer nanotemplates to functional materials indicates a promising route to ultrahigh density nanodevices. Bit‐patterned media over 1 teradot/in on a 2.5‐inch disk are fabricated, thus presenting future magnetic data storage media with great areal density growth potential. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 361–367     

A cadmium(II) coordination polymer with both polyrotaxane and polycatenane features constructed by a V‐shaped semi‐rigid ligand: synthesis and fluorescence properties

One of the most interesting phenomena in coordination polymers (CPs) is the co‐existence of different interlaced motifs. However, CPs having two different interlaced motifs at the same time are still rare. Colourless block‐shaped crystals of the two‐dimensional polymer poly[[aqua(μ₂‐naphthalene‐2,6‐dicarboxylato){μ₂‐4,4′‐[oxybis(4,1‐phenylene)]dipyridine}cadmium(II)] monohydrate], {[Cd(C₁₂H₆O₄)(C₂₂H₁₆N₂O)(H₂O)]·H₂O}_n , (I), was synthesized under hydrothermal conditions by the self‐assembly of 4,4′‐[oxybis(4,1‐phenylene)]dipyridine (OPY) with Cd^II in the presence of naphthalene‐2,6‐dicarboxylic acid (H₂ndc). Each Cd^II ion is six‐coordinated by two N atoms from the pyridine rings of two OPY ligands and by four O atoms, three of which are from two ndc²⁻ ligands and one of which is from a water molecule. In (I), every two identical two‐dimensional (2D) 6³ layers are interpenetrated in a parallel fashion, resulting in an interesting 2D→2D framework with both polyrotaxane and polycatenane characteristics. The extension of these sheets into a three‐dimensional supramolecular net is via O—H…O hydrogen bonds. The solid‐state photoluminescence properties of (I) are also discussed.     

Synthesis of Responsive Two‐Dimensional Polymers via Self‐Assembled DNA Networks

Despite a growing interest in two‐dimensional polymers, their rational synthesis remains a challenge. The solution‐phase synthesis of a two‐dimensional polymer is reported. A DNA‐based monomer self‐assembles into a supramolecular network, which is further converted into the covalently linked two‐dimensional polymer by anthracene dimerization. The polymers appear as uniform monolayers, as shown by AFM and TEM imaging. Furthermore, they exhibit a pronounced solvent responsivity. The results demonstrate the value of DNA‐controlled self‐assembly for the formation of two‐dimensional polymers in solution.