Naibo Lin

Crystal Networks in Silk Fibrous Materials: From Hierarchical Structure to Ultra Performance

This review provides a comprehensive survey of the structural characteristics of crystal networks of silk soft fibrous materials in correlation with the macroscopic properties/performance and the network formation mechanisms. The correlation between the hierarchical mesoscopic structures and the mechanical properties of silk soft fibrous materials including silk fibroin hydrogels and naturally spun silk fibers are addressed based on the hierarchical crystal network models. Namely, two types of hierarchical networks are identified: the weak nanofibril-nanofibril interaction case (i.e., silk fibroin hydrogels), and the strong nanofibril-nanofibril interaction case (i.e., silk fibers). The macroscopic properties, i.e., the rheological/mechanical properties, can be controlled in terms of tuning different levels of hierarchical network structures by ultrasonication-induced gelation, introducing the initial nucleation centers, etc. Such controls take effect by different mesoscale assembly pathways, which are found to occur via different routes of the nucleation and growth processes. Furthermore, the hierarchical network model of soft fibrous materials can be applied to explain the superior mechanical properties and the unique strain-hardening behaviors of spider silk fibers within the framework of hierarchical breaking mechanism. Obviously, a knowledge of crystal networks will allow the prediction of the performance and engineering strategy of silk fibrous materials in generals.

Thermally stable oxadiazole-containing polyacetylenes: Relationship between molecular structure and nonlinear optical properties

Two novel high molecular weight functional polyacetylenes bearing oxadiazole groups as pendants, poly(2-(4-decyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P1) and poly(2-(4-butyloxyphenyl)-5-(4-ethynylphenyl)-1, 3, 4-oxadiazole) (P2) were designed and synthesized by a multistep reaction route. The structures and properties were characterized and evaluated with FTIR, NMR, UV, TGA, GPC, optical-limiting (OL) and nonlinear optical (NLO) analyses. The incorporation of oxadiazole into polyacetylene significantly endows polyacetylenes with higher thermal stability and optical limiting property. The solubility, stereoregularity and optical properties of resultant polyacetylenes are obviously affected by flexible terminal alkoxy chain length. The cis olefinic structure content in polyacetylene backbone increases with increasing terminal alkoxy group length. The functional polyacetylene with the higher cis olefinic structure content shows higher thermal stability, better optical limiting property and larger third-order nonlinear optical performance. The optical limiting mechanism of resulting polymers was investigated, which is mainly originated from larger excitation state absorption cross-section of molecules to result in reverse saturable absorption.

Crosslinked waterborne polyurethane with high waterproof performance

A study on the cross-linking of fluorinated acrylate and siloxane waterborne polyurethanes was carried out in order to produce a material with improved waterproof property. Trimethylolpropane-tris-(β-N-aziridinyl) propionate was employed as a simple, fast curing and low cost crosslinking agent. It follows that the acquired polyurethane film had the lowest water absorption and highest water contact angles so far among this series of compounds, and has better mechanical/thermal properties once the fluoride acrylic monomer content reaches 8 wt% and polyether modified polydimethylsiloxane content is 10 wt%. Once the crosslinked structure is acquired, the overall performance of the polyurethane films are enhanced, i.e. the water absorption decreases to 3.48% and n-heptane swelling decreases to 1.02%, the hardness reaches 6H and the tensile strength also rises to 33.2 MPa. Such eco-friendly crosslinked polyurethane films with outstanding waterproof property can find various applications in corrosion protection and optoelectronic devices.

Two-photon fluorescent Bombyx mori silk by molecular recognition functionalization

Two-photon fluorescent (TPF) Bombyx mori silk fibers were acquired for bioimaging by molecular recognition functionalization. In this context, 2,7-bis((E)-4-((E)-4-nitrostyryl)styryl)-9,9-dioctyl-9H-fluorene (NF) was adopted to functionalize silkworm silk fibers. NF exhibits a large two-photon absorption cross section, but has a low TPF quantum yield in the solid form due to the side-by-side (π-π) molecular stacking. In terms of the molecular recognition between the nitro groups of NF and the amide groups of silk fibroin, the silk fibers acquire the two-photon fluorescent emission with a significant enhancement of 350% in TPF quantum yield of NF molecules, compared with the solid state. For comparison, two other molecules, 2,7-bis((E)-4-methylstyryl)-9,9-dioctyl-9H-fluorene (MF1) and 2,7-bis((E)-4-((E)-4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene (MF2), were selected for similar experiments. These molecules show little effect due to the lack of molecular recognition. The TPF silk scaffolds were obtained, and high quality imaging of NF in cell culture was finally achieved, which has extremely relevant implications for biomedical applications.

Preparation and properties of electron injecting molecular hybrid materials with high thermal performance

A series of oxadiazole-containing molecular hybrid materials with different structures (H1–H5) are controllably prepared by a hydrosilylation method based on the octahydridosilsesquioxane (POSS, T88HH). All these resultant hybrid materials are soluble in common organic solvents, such as chloroform, toluene, tetrahydrofuran, and 1,2-dichloroethane, and possess good film-forming properties. Their structure and properties are characterized and evaluated by FTIR, 1H NMR, 29Si NMR, GPC, TGA, DSC, UV-vis, PL, CV, and elemental analysis, respectively. It is found that the hydrosilylation reaction almost proceeds quantitatively when the feed ratio (molar number of organic monomer to molar number of POSS) is less than 4, at which the resultant hybrids can be controllably prepared by varying the feed ratio. These hybrids possess high thermal stability and good electron injecting properties and an intense blue emission was observed in these hybrids. Simultaneously, it is found that the hybrids (H3–H5) with a strong π electron conjugation effect between POSS and the oxadiazole moiety show higher thermal stability, better electron injecting properties and more intense blue emission than those (H1 and H2) without a π electron conjugation effect between POSS and the oxadiazole moiety.

Structural engineering of waterborne polyurethane for high performance waterproof coatings

A series of modified waterborne polyurethanes were synthesized using a self-emulsifying method for high performance waterproof coatings, such as fluoride polyurethane (FPU), siloxane modified waterborne polyurethane (SPU) and the polyurethane containing fluorine and siloxane (FSPU). The structures of waterborne polyurethane were designed from scratch, and the contents of fluoride acrylic monomer (FMA) and siloxane contents (HO-PDMS) segments in FSPU were adjusted for high performance waterproof. Its found that the sample has lowest water absorption, higher water contact angles, and better mechanical/thermal properties, when the FMA content is 20 wt% and HO-PDMS content is 3 wt%. The mechanisms of improvement of contact angles were investigated, due to the vinyl group crosslinking, higher temperature can significantly improve the hydrophobicity of the films in emulsion polymerization and film forming process. Optimized FSPU has a promising future as a kind of waterborne waterproof coatings.

Electrochromic performance of WO3 films: optimization by crystal network topology modification

In this study, we demonstrate the enhancement of the electrochromic performance of tungsten oxide (WO3) by crystal network topology modification. This is achieved by constructing various crystalline morphologies and patterns of the films. Different mesoscopic crystalline networks of WO3 were acquired on transparent conducting fluorine-doped tin oxide (FTO) by a crystal-seed-assisted hydrothermal process. The modification of the crystal network topology and crystal growth habit of WO3 films was achieved by adding different concentrations of oxalic acid and HCl, and controlling the growth time. The influence of the topological patterns on the corresponding electrochromic performance of WO3 films was examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and in situ reflectance spectroscopy. It follows that four different topological patterns of WO3 microstructures, namely random “rocks” of the seed layers, micro-urchin, small peony, and blooming peony were obtained by adding different concentrations of oxalic acid and hydrochloric acid. It is found that pH and oxalic acid are both the key modifying factors of the habit and topology of the crystal networks. Consequently, the urchin-like pattern gives rise to a high efficiency in optical modulation and coloration due to its similarity to micro-sized antennas, which may facilitate the emission and absorption of charged particles and electrochemical reactions at the WO3 surfaces.

Mesoscopic-Functionalization of Silk Fibroin with Gold Nanoclusters Mediated by Keratin and Bioinspired Silk Synapse

Silk fibroin (SF) offers great opportunities in manufacturing biocompatible/partially biodegradable devices with environmental benignity and biomedical applications. To obtain active SF devices of next generation, this work is to demonstrate a new functionalization strategy of the mesoscopic functionalization for soft materials. Unlike the atomic functionalization of solid materials, the meso-functionalization is to incorporate meso-dopants, i.e., functional molecules or nanomaterials, quantum dots, into the mesoscopic networks of soft materials. In this work, wool keratin (WK) molecules were adopted as mediating molecules to incorporate gold nanoclusters (AuNCs), into the mesoscopic networks of SF. It follows from our analyses that the β-crystallites between WK and SF molecules establish the binding between WK@AuNCs and the SF networks. The incorporated WK@AuNCs are electron rich and serve as electronically charged nano particles to bridge the growth of Ag filaments in bio-degradable WK@AuNCs-SF memristors. The meso-functionalization can greatly enhance the performance of SF materials and endows them with new functionalities. This can be highlighted by biocompatible/partly degradable WK@AuNCs functionalized SF resistive random-access memories, having the enhanced resistive switching memory performance, and the unique synapse characteristics and the capability of synapse learning compared with neat SF devices, and of great importance in nonvolatile memory, analog circuits, and neuromorphic applications.

Ultrastable, highly luminescent quantum dot composites based on advanced surface manipulation strategy for flexible lighting-emitting

Although quantum dots (QDs) have remarkable potential application in flexible light emitting diodes (LED), the loss of solvent-protected QDs leads to low quantum yield (QY) and poor stability, severely restricting the development. Flexible QD LEDs (Q-LEDs) with three primary colors were fabricated by mixing CdS/ZnS, CdSe@ZnS/ZnS, and CdSe/CdS QDs with polydimethylsiloxane (PDMS) by in situ hydrosilylation based surface manipulation strategy, which endows the device with highly ultrastable and luminescent performance. The surface manipulation strategy mainly includes the control of solvent dosage, purification times of QDs, concentration of QDs in PDMS, and oxidation on the preparation process of the QDs and PDMS composites. The highest QY of CdSe@ZnS/ZnS-PDMS composite is 82.03%, higher than the QY (80%) of the QD solution. After UV bleaching, organic solvents (acetone, ethanol and water), and heating treatment, the QYs of the QDs and PDMS maintain a high value, manifesting their good stability. Q-LED hybrid light-emitting devices were further fabricated by a molding technique demonstrating satisfied current and thermal stability. Flexible Q-LEDs can be expended to other shapes, such as fibers and blocks, indicating the huge potential of QD-polymer composites for light sources and displays etc.

Polyfluorenylacetylene for near-infrared laser protection: polymer synthesis, optical limiting mechanism and relationship between molecular structure and properties

A series of functional polyacetylenes bearing the fluorene moiety with different conjugated lengths and terminal substituents, poly[2-ethynyl-7-(4-nitrostyryl)-9,9-dioctyl-9H-fluorene] (P1), poly[2-ethynyl-7-(4-(4-nitrostyryl)styryl)-9,9-dioctyl-9H-fluorene] (P2), poly[2-ethynyl-7-(4-(4-methoxystyryl)styryl)-9,9-dioctyl-9H-fluorene] (P3), poly[2-ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-dioctyl-9H-fluorene] (P4), and poly[2-ethynyl-7-(4-(4-methylstyryl)styryl)-9,9-didodecyl-9H-fluorene] (P5), were designed and prepared using [Rh(nbd)Cl]2 as the catalyst. Their structures and properties were characterized and evaluated by FTIR, NMR, UV, FL, GPC and TGA analyses. The optical limiting properties were investigated using 450 fs laser pulses at 780 nm. These results show that the incorporation of styryl/stilbene functionalized polyfluorenylacetylenes has endowed resultant polyacetylenes with novel near-infrared laser protection properties and enhanced thermal stability. The optical limiting mechanism for laser protection was studied. It was found that the optical limiting properties mainly originated from two-photon absorption (TPA) of molecules in the resulting polyacetylenes. Additionally, it was also found that the functionalized polyacetylene with a longer fluorene-based conjugated chromophore and a stronger terminal electron acceptor group exhibits better optical limiting properties because of the larger π-electron delocalization and dipolar effect.