Shuang Yang

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-πu2005interactions to form triple-layer two-dimensional (2D) fullerene crystals sandwiched between layers of alkyl chains. The lamellar packing of 2Du2005crystals gives rise to the formation of supramolecular LCs. This design strategy should be applicable to other molecules and lead to an enlarged family of 2Du2005crystals and supramolecular liquid crystals.

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 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.

Self organization of main-chain/side-chain liquid crystalline polymer based on “jacketing” effect with different lengths of spacer: from smectic to hierarchically ordered structure

A series of combined main-chain/side-chain liquid crystalline polymers (MCSCLCP) based on “jacketing” effect, poly{(2,5-bis[n-(4-butoxy-4′-oxybiphenyl)n-alkyl]oxycarbonyl}styrene) with different lengths of alkyl spacers (denoted as Pn, n represents the number of carbon atoms in the alkyl spacers, n = 2–10) have been successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structures of Pns and the corresponding monomers were characterized using combined techniques with satisfactory analysis data. The phase structures and transitions of Pn were investigated using differential scanning calorimetry (DSC), polarized optical microscope (POM), and one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD). It has been identified that P2 and P4 with short alkyl spacers form typical smectic phase. For n ≥ 6, Pns exhibit similar hierarchical ordered structure at low temperatures, bearing double orderings on the nanometer and sub-nanometer scales. In the hierarchical structure, the main-chains based on “jacketing” effect form a 2D centered rectangular scaffold, and the side-chain biphenyl mesogens within the scaffold pack into a smectic E-like structure. The a dimension of rectangular lattice enlarges with n. When the temperature is increased, different from P6, P8 and P10 present the same phase behavior, forming smectic B-like packing of side chains and maintaining their main-chain scaffold until isotropization.

Shear Effects on Stability of DNA Complexes in Presence of Serum

The behavior of nanocarriers, even though they are well-defined at equilibrium conditions, is unpredictable in living system. Using the complexes formed by plasmid DNA (pDNA) and K20 (K: lysine), protamine, or polylysine (PLL) as models, we studied the dynamic behavior of gene carriers in the presence of fetal bovine serum (FBS) and under different shear rates, a condition mimicking the internal physical environment of blood vessels. Without shear, all the positively charged complexes bind to the negatively charged proteins in FBS, leading to the formation of large aggregates and even precipitates. The behaviors are quite different under shear. The shear generates two effects: a mechanical force to break down the complex into smaller size particles above a critical shear rate and a stirring effect leading to secondary aggregation of complexes below the critical shear rate. In the studied shear rate from 100 to 3000 s-1, the mechanical force plays a key role in K20/pDNA and protamine/pDNA, while the stirring effect is dominant in PLL/pDNA. A model study shows that the interfacial tension, the chain density, and the elasticity of the complexes determine their responsiveness to shear force. This study is helpful to understand the fate of drug/gene carriers under physiological conditions. It also gains insight in designing drug/gene carriers with desirable properties for in vivo applications.