Er-Qiang Chen

Giant surfactants provide a versatile platform for sub-10-nm nanostructure engineering

The engineering of structures across different length scales is central to the design of novel materials with controlled macroscopic properties. Herein, we introduce a unique class of self-assembling materials, which are built upon shape- and volume-persistent molecular nanoparticles and other structural motifs, such as polymers, and can be viewed as a size-amplified version of the corresponding small-molecule counterparts. Among them, “giant surfactants” with precise molecular structures have been synthesized by “clicking” compact and polar molecular nanoparticles to flexible polymer tails of various composition and architecture at specific sites. Capturing the structural features of small-molecule surfactants but possessing much larger sizes, giant surfactants bridge the gap between small-molecule surfactants and block copolymers and demonstrate a duality of both materials in terms of their self-assembly behaviors. The controlled structural variations of these giant surfactants through precision synthesis further reveal that their self-assemblies are remarkably sensitive to primary chemical structures, leading to highly diverse, thermodynamically stable nanostructures with feature sizes around 10 nm or smaller in the bulk, thin-film, and solution states, as dictated by the collective physical interactions and geometric constraints. The results suggest that this class of materials provides a versatile platform for engineering nanostructures with sub-10-nm feature sizes. These findings are not only scientifically intriguing in understanding the chemical and physical principles of the self-assembly, but also technologically relevant, such as in nanopatterning technology and microelectronics.

High efficiency luminescent liquid crystal: aggregation-induced emission strategy and biaxially oriented mesomorphic structure

Rational combination of aggregation-induced emission active luminogens and mesogens generates high solid-state efficiency luminescent liquid crystals, thus resolving the problem of aggregation-caused quenching normally occurs in the fabrication of luminescent mesomorphic films.

Mesogen jacketed liquid crystalline polyacetylene containing triphenylene discogen: synthesis and phase structure

Triphenylene-containing acetylenes with one or three methylene units as spacers and the corresponding mesogen-jacketed liquid crystalline polyacetylenes (MJLCPAs) were designed and synthesized, the mesomorphic properties and phase behaviors of the monomers and novel side-chain liquid crystalline polymers were investigated. The monomers [HCC(CH2)mC18H6(OC6H13)5; m = 1, 3] are prepared by consecutive etherization, coupling, and etherization reactions, and the chemical structures were confirmed by mass spectroscopy and 1H/13C-NMR. The phase behaviors of the monomers were investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD). The results show that both of the monomers form a hexagonal columnar liquid crystal phase at room temperature. The monomers are polymerized using [Rh(nbd)Cl]2 as catalyst and producing soluble polymers in the yields of 55% and 52%, respectively. The chemical structures and phase behaviors of the two polymers are characterized and evaluated by IR, NMR, TGA, DSC, and WAXD analyses. Both of the two polymers show enhanced thermal and chemical stability with thermal decomposition temperatures up to higher than 340 °C due to the protection of the “jacketed effect” of the side-chain triphenylenes wrapped around the rigid polyacetylene main-chain. The polymers adopt a columnar shaped structure and self-organized into hexagonally packed columnar phase. The relative electron density maps of the columnar structure are also reconstructed.

Fluorinated polyhedral oligomeric silsesquioxane-based shape amphiphiles: molecular design, topological variation, and facile synthesis

This paper reports the design and synthesis of fluoroalkyl-functionalized polyhedral oligomeric silsesquioxane (FPOSS)-based shape amphiphiles with two distinct topologies: (i) mono-tethered FPOSS-poly(e-caprolactone) (PCL) and (ii) FPOSS tethered with two polymer chains possessing different compositions, namely, polystyrene (PS) and PCL, denoted as PS–(FPOSS)–PCL. The synthetic strategy features an efficient “growing-from” and “click-functionalization” approach. From a monohydroxyl-functionalized heptavinyl POSS, a PCL chain was grown via ring opening polymerization (ROP) of e-caprolactone; subsequent thiol–ene “click” chemistry with 1H,1H,2H,2H-perfluoro-1-decanethiol allowed the facile introduction of seven perfluorinated alkyl chains onto the POSS head. Similarly, PS–(FPOSS)–PCL was synthesized from a PS precursor bearing both hydroxyl group and heptavinyl POSS at the ω-end, which was prepared by living anionic polymerization and hydrosilylation. The compounds were fully characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography. The introduction of perfluorinated molecular cluster into polymers is expected to make them surface-active while the interplay between crystallization and fluorophobic/fluorophilic bulk phase separation in these shape amphiphiles shall lead to intriguing self-assembly behavior and novel hierarchical structures. This study has demonstrated FPOSS as a versatile building block in the construction of shape amphiphiles and established a general and efficient method to introduce such fluorous molecular clusters into polymers.

In situ observation of low molecular weight poly(ethylene oxide) crystal melting, recrystallization

A low-molecular-weight poly(ethylene oxide) (PEO) fraction with a number-average molecular weight of 4250 g/mol was used to study the melting and recrystallization behaviors during heating. After complete crystallization at 46 8C, the PEO possessed almost exclusively once-folded chain ½IFðn ¼ 1Þ� crystals and very few extended chain IFðn ¼ 0Þ crystals. Comparing differential scanning calorimetry heating experiments of the PEO bulk samples after crystallized at 46 8C with those further step-annealed at temperatures ðTasÞ in the melting range of the IFðn ¼ 1Þ crystals showed that the crystal melting and recrystallization occur to form the IFðn ¼ 0Þ crystals. In situ melting and recrystallization of the PEO crystals after crystallized at 46 8C were also investigated using both small angle X-ray scattering (SAXS) experiments in reciprocal space and atomic force microscopy (AFM) coupled with a hot stage in real space. It was found that in the SAXS measurements, the lamellar long period shifted from the IFðn ¼ 1Þ crystals towards the IFðn ¼ 0Þ crystals. This transformation process involved melting and recrystallization. During this process, more than one lamellar long period could exist. At Ta ¼ 58 8C; the long period reached the thickness of the IFðn ¼ 0Þ crystals. In the in situ AFM observations, the IFðn ¼ 1Þ crystals was melted starting from inner parts of the surface lamellae, whereas the lamellar edges were quickly transformed to the IFðn ¼ 0Þ crystals with higher thermodynamic stability. The remaining lamellar edges serve as nucleation sites of the PEO recrystallization. The IFðn ¼ 0Þ crystal growth rate measured by the in situ AFM was slower than that measured in the single crystals of the isothermal crystallization at the same temperature. The fast overall recrystallization of the IFðn ¼ 0Þ crystals was mainly deduced by the fact that the high nucleation density provided by the survived nucleation sits such as the lamellar edges. q 2003 Published by Elsevier Ltd.

Supramolecular [60]Fullerene Liquid Crystals Formed By Self-Organized Two-Dimensional Crystals†

Fullerene-based liquid crystalline materials have both the excellent optical and electrical properties of fullerene and the self-organization and external-field-responsive properties of liquid crystals (LCs). Herein, we demonstrate a new family of thermotropic [60]fullerene supramolecular LCs with hierarchical structures. The [60]fullerene dyads undergo self-organization driven by π-π interactions to form triple-layer two-dimensional (2D) fullerene crystals sandwiched between layers of alkyl chains. The lamellar packing of 2D crystals gives rise to the formation of supramolecular LCs. This design strategy should be applicable to other molecules and lead to an enlarged family of 2D crystals and supramolecular liquid crystals.

Primary Nucleation in Polymer Crystallization

Isothermal crystallization of a low- molecular- weight polyethylene oxide) from both isotropic and structured melts at low undercoolings has been investigated via simultaneous measurements of small angle and wide angle X ray scatterings (SAXS and WAXS). An evolution of the SAXS pattern was observed prior to the appearance of crystallinity determined through WAXS. A possible interpretation of the experimental observation is provisted through the nucleation concept: primary nuclei exist in the melt due to localized large- amplitude density fluctuations in the isotropic medium.

Thermoplastic High Strain Multishape Memory Polymer: Side-Chain Polynorbornene with Columnar Liquid Crystalline Phase

A thermoplastic high strain multishape memory polymer can be fabricated using a hemiphasmid side-chain polynorbornene (P1) with hexagonal columnar liquid crystalline (ΦH ) phase. Without any chemical crosslinks, P1 can memorize multiple temporary shapes with high strain and exhibit excellent shape fixity and shape recovery. As the building blocks of ΦH , the multichain columns in P1 act as robust physical crosslinks.

Synthesis, crystal structure, enhanced photoluminescence properties and fluoride detection ability of S-heterocyclic annulated perylene diimide-polyhedral oligosilsesquioxane dye

A novel S-heterocyclic annulated perylene diimide (SPDI) derivative connected to two polyhedral oligosilsesquioxane (POSS) nanoparticles was designed and synthesized to reveal the effect of bulky substituent groups on its self-assembly behavior and photoluminescence properties. This featured organic–inorganic hybrid can easily self-assemble into crystalline microbelts with a length of several hundred micrometers. The phase behavior and crystal structure of the compound was then elucidated via a combination of different experimental techniques such as differential scanning calorimetry (DSC), one- and two-dimensional (1D and 2D) X-ray diffraction (XRD), UV/Vis and fluorescence spectra, and tandem mass spectrometry with traveling wave ion mobility separation. The experimental results reveal that the compound has a strong propensity to form a dimer in solution and possesses unique molecular packing of discrete dimeric motifs in the solid state. Moreover, due to this discrete molecular packing behavior, the compound exhibits enhanced photoluminescence properties both in solution and in the solid state compared to the reference compound SPDI without a pendant POSS cage. In addition, based on the dual reactions of electron transfer and fluoride-triggered Si–O bond cleavage, the POSS containing SPDI exhibits higher selectivity and sensitivity to fluoride anions, and a quicker response against the reference SPDI without a pendant POSS cage. The enhanced luminescence properties, and the ability to form ultralong crystalline microbelts, in combination with the rapid selective response for F− make this compound a promising material for the fabrication of luminescent devices and colorimetric chemosensors.

Synthesis and self-organization of azobenzene containing hemiphasmidic side-chain liquid-crystalline polymers with different spacer lengths

A series of new hemiphasmidic side-chain liquid crystalline (LC) polymers (P-n, where n is the number of methylene units in the spacer, n = 2, 6, 10, 14) were synthesized. The azobenzene containing hemiphasmidic mesogens are linked to a polymethacrylate main-chain through flexible spacers. The chemical structures of the monomers and polymers were confirmed by various characterization techniques. All of the P-ns exhibit enantiotropic LC phase behavior, which is influenced greatly by varying the spacer length. Specifically, P-2 and P-6 exhibit a hexagonal columnar (ΦH) phase. As longer spacers are introduced, P-10 and P-14 can form a centered rectangular columnar (ΦR) phase at low temperatures, which will change into the ΦH phase upon heating. The lattice dimensions of the columnar (Φ) phases are pretty large, approaching 9 nm when n increases to 14. This indicates that the column of the Φ phase of P-n is constructed from several chains laterally assembled together. For P-10 and P-14, the transition of ΦH–ΦR may be associated with the change in chain numbers of the supramolecular column. As the transition temperature is close to the glass transition temperature, the kinetics of the ΦH-to-ΦR transition of P-10 becomes very slow.