Polymers Going Rigid, Thick, and Laterally Infinite

This short review article provides insight into the impact organic chemistry can have on state-of-the-art materials creation. Three cases were selected from the authors' laboratory, the first being 'Suzuki polycondensation', a powerful method with which innovative organic chemistry was successfully transferred to polymer synthesis and which meanwhile has even found technical scale application. The second describes the decoration of linear polymers with a dense layer of regular branch work. Though seemingly a rather esoteric enterprise, these decorations resulted in considerable property changes as compared to other linear polymers and, additionally, led to the discovery of novel properties. Consequently, this area which is commonly referred to as 'dendronized polymers' in a world-wide activity has been developed into a ripe research field, presently under exploration for possible technical application. Finally, an example still very much in its first tumbling steps was selected to give yet another perspective of the role of organic chemistry in a materials-oriented chemistry. It aims at the generation of ultrathin, yet internally strictly defined, sheet-like macromolecules for which a great future is foreseen, e.g. as a 2D platform for the systematic construction of 3D matter

a new level of hierarchical structure control by use of supramolecular self-assembled dendronized block copolymers

Complexation of dendronized block copolymers with sulfate alkyl tails forms unprecedented hierarchically ordered bulk structures, including rectangular-in-lamellar, tetragonal-in-lamellar, hexagonal-in-lamellar and lamellar-in-lamellar. These novel liquid-crystalline morphologies, which can be designed at low length scales in these systems, are expected to provide final materials with not only unprecedented structural complexity, but also tunable physical properties

Liquid crystalline period variations in self-assembled block copolypeptides-surfactant ionic complexes

We investigate the complexation of ampholytic poly(N-isopropylacylamide)-block-poly- (L-glutamic acid)-block-poly(L-lysine) (PNiPAM-b-PLG-b-PLLys) triblock copolymers and PNiPAM-block-(PLG-co-PLLys) diblock copolymers with counter charged anionic and cationic surfactants. Both triblock and diblock copolymers are able to selectively form complexes through either L-glutamic acid-cationic surfactant or L-lysine-anionic surfactant ionic pairs, depending on the protonated or deprotonated states of the ampholytic peptide units. The complexes show ordering at multiple length scales: i) the block copolymer length scale (10¹ nm), ii) the liquid crystalline length scale (10⁰ nm), and, iii) the peptidic secondary structures length scale (10⁰ nm). We show that the liquid crystalline period can be tuned by varying the random/block copolypeptide architectures and the composition of the ampholytic amino acid species

Dual-Responsive Supramolecular Chiral Assemblies from Amphiphilic Dendronized Tetraphenylethylenes

Supramolecular assembly of amphiphilic molecules in aqueous solutions to form stimuli-responsive entities is attractive for developing intelligent supramolecular materials for bioapplications. Here we report on the supramolecular chiral assembly of amphiphilic dendronized tetraphenylethylenes (TPEs) in aqueous solutions. Hydrophobic TPE moieties were connected to the hydrophilic three-fold dendritic oligoethylene glycols (OEGs) through a tripeptide proline–hydroxyproline–glycol (POG) to afford the characteristic topological structural effects of dendritic OEGs and the peptide linker. Both ethoxyl- and methoxyl-terminated dendritic OEGs were used to modulate the overall hydrophilicity of the dendronized TPEs. Their supramolecular aggregates exhibited thermoresponsive behavior that originated from the dehydration and collapse of the dendritic OEGs, and their cloud point temperatures (Tcps) were tailored by solution pH conditions. Furthermore, aggregation-induced fluorescent emission (AIE) from TPE moieties was used as an indicator to follow the assembly, which was reversibly tuned by temperature variation at different pH conditions. Supramolecular assemblies from these dendronized amphiphiles exhibited enhanced supramolecular chirality, which was dominated mainly by the interaction balance between TPE with dendritic OEG and TPE with POG moieties and was modulated through different solvation by changing solution temperature or pH conditions. More interestingly, ethoxyl-terminated dendritic OEG provided a much stronger shielding effect than its methoxyl-terminated counterpart to prevent amino groups within the peptide from protonation, even in strong acidic conditions, resulting in different responsive behavior to the solution temperature and pH conditions for these supramolecular aggregates

Dendronized Gelatin-Mediated Synthesis of Gold Nanoparticles

Thermoresponsive dendronized gelatins (GelG1) or gelatin methacrylates (GelG1MA) were used as precursors to modulate the efficient reduction of Au(III) to form stable gold nanoparticles (AuNPs) through UV irradiation. These dendronized gelatins were obtained through the amidation of gelatin or gelatin methacrylates with dendritic oligoethylene glycols (OEGs). Crowded OEG dendrons along the gelatin backbones create a hydrophobic microenvironment, which promotes the reduction of Au(III). Gelatin backbones act as ligands through the electron-rich groups to facilitate the reduction, while the dendritic OEGs provide shielding effects through crowding to form a hydrophobic microenvironment, which not only enhances the reduction but also stabilize the formed AuNPs through encapsulation. The effects of dendron coverage on the dendronized biomacromolecules and their thermoresponsiveness on the reduction kinetics were examined. Dendronized gelatin/AuNPs hydrogels were further prepared through the in situ photo-crosslinking of GelG1MA. The modification of natural macromolecules through dendronization presented in this report facilitates a novel platform for the environmentally friendly synthesis of noble metal nanoparticles, which may form a new strategy for developing smart nano-biosensors and nano-devices

Comparison of bioimpedance equations and dual-energy X-ray for assessment of fat free mass in a Chinese dialysis population

AbstractPurpose Bioelectrical impedance analysis (BIA) is simple, noninvasive, inexpensive and frequently used for estimating fat free mass (FFM). The aims of this study were to evaluate the applicability of different BIA equations on FFM in Chinese subjects, and to compare the difference in hemodialysis and peritoneal dialysis patients with healthy controls respectively.Methods Dialysis patients and healthy adults were enrolled in this study, and the subjects were matched by age, gender, and the minimum sample size in each group was calculated using PASS. FFM estimated by BIA was calculated using equations of Kyle, Sun SS and Segal, and TBW/0.73. Dual-energy X-ray absorptiometry (DXA) method was set as reference method. Pearson’s correlation and Bland-Altman analysis were used to test the validity of the BIA equations.Results 50 hemodialysis (HD) patients, 52 peritoneal dialysis (PD) patients and 30 healthy adults aged 22–67 y were included in this study. Age, height, weight, BMI and gender did not differ significantly among HD, PD patients, and healthy controls (p > 0.05), but BIA parameters were quite different (p＜0.01). Bland-Altman analysis showed that in healthy volunteers, all equations showed good agreement with DXA measured. For dialysis patients, the FFM predictions of different equations showed differences between HD and PD patients, and the equations seemed more applicable for HD patients.Conclusion The equations developed by healthy subjects might be not appropriate for dialysis patients, especially peritoneal dialysis patients. It is recommended to develop a specific BIA equation from dialysis population

Controlling hierarchical self-assembly in supramolecular tailed-dendron systems

We study the self-assembly of a dendritic macromolecular system formed by a second-generation dendron with pH-responsive end groups and with a polymer chain emanating from its focal point, typically referred to as dendron-coil system. We use supramolecular ionic interactions to attach to the periphery of the dendrons sulfate-terminated alkyl tails of various lengths. The resulting ionic complexes have a molecular architecture similar to a four-arm dendritic pitchfork with varying arms and holder lengths. The bulk morphologies observed by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) show thermodynamically stable, hierarchical “inverted” hexagonal or lamellar structures. In addition, for a specific range of volume fractions, we show order-to-order transitions associated with the melting of the crystalline alkyl tails. The structural models for the molecular packing emerging from TEM and SAXS analysis are benchmarked to available self-consistent field theories (SCFTs) developed for identical systems and experiments and theoretical predictions are found in perfect agreement. With respect to our previous work on inverted dendron and dendrimer-surfactant self-assembled morphologies (Mezzenga et al. Soft Matter. 2009, 5, 92−97), the present findings show that keeping the same dendritic molecular architecture but adding a polymer chain emanating from the focal point enables the scale up of the structural organization from the liquid crystalline length scale (100 nm) to the block copolymer length scale (101 nm) while preserving the inverted unconventional morphologies. Because the length of the holder and the arms of the dendritic pitchfork can be finely tuned, these systems offer new possibilities in the design of nanostructured organic materials and their use in templating applications

Numerical Simulation and Parameter Optimization of a New Reed–Nylon Net Combined Sand Fence

This paper introduces a kind of double-row reed–nylon net combined sand barrier. Using the computational fluid dynamics (CFD) method and the Euler–Euler double-fluid model, the new sand fences’ windproof effect and airflow features are simulated under different porosities and spacings, and the optimal configuration parameters are selected. The new sand fence has better windproof performance and practical significance than double-row reed and double-row nylon net fences. The new sand fences with a porosity of 0.3–0.4 and spacing of 28 H provide a longer protection range and a better wind protection effect. Considering the serious sand damage in China’s Taklamakan Desert, the new fences’ impact on sand buildup is examined. The combined sand fences have powerful sand blocking and accumulation effects, even though there is only a small quantity of sand accumulation on the leeward side of the second row. The sand particles primarily settle between sand fences in the center and rear areas. The combination of sand fences made of different materials combines the advantages of both, improves the construction efficiency and service life, and provides a more economical and efficient sand barrier arrangement for the arrangement of wind and sand-blocking facilities around railroads and highways in desert areas

Light-Controlled Shrinkage of Large-Area Gold Nanoparticle Monolayer Film for Tunable SERS Activity

The two-dimensional (2D) monolayer gold nanoparticle (Au NP) film is of significant interest and importance in both fundamental and practical applications including optoelectronic devices, sensing, catalysis, and surface-enhanced Raman spectroscopy (SERS). Because of the weak physical interaction, the conventional monolayer Au NP film fabricated at the oil-water interface was unstable, easily breakable, and difficultly transferred. In the present work, we report on a simple and effective chemical cross-linking strategy at the air-water interface to achieve a large-scale monolayer gold nanoparticle film with intelligently tunable size of nanogaps, and excellent free-standing and easily transferable properties. In our strategy, acrylamide, a polymerizable molecule, was first modified on the surface of Au NPs for subsequent self-assembly into a monolayer film at the liquid-liquid interface. Through photopolymerization of acrylamide, a chemically cross-linked film was formed with closely packed nanoparticles, highly macroscopic uniformity, and excellent free-standing property, which allowed it to be easily transferred from the air water interface onto various solid substrates while maintaining its integrity. It is interesting to find that the macroscopic film underwent an in situ shrinkage under irradiation of UV-light, and its area shrinkage ratio is close to 55% (equal to 2.2 times) of that from non-cross-linked counterparts. More importantly, UV-light-controlled in situ shrinkage of the Au NP film would lead to intelligently, precisely tuned nanogaps less than 0.5 nm between neighboring Au NPs for maximal amplification of SERS signals, and the macroscopic uniformity of the films ensured the reproducible performance of SERS signals, providing an ideal candidate for SERS applications