Self-Assembling Behavior of Amphiphilic Dendron Coils in the Bulk Crystalline and Liquid Crystalline States

Effect of architectural asymmetry of hyperbranched block copolymers on their phase boundaries

Asymmetric architecture of AB-type block copolymers can induce additional spontaneous curvature to the A/B interface, accordingly deflecting the phase boundaries. However, it is often difficult to determine or compare the asymmetric effects of different asymmetric architectures. In this work, we proposed to use the equivalent arm number nequ, which was originally defined as nequ = n/iĐ for ABn with unequal B-arms and iĐ being the intramolecular polydispersity of these B-arms, to quantify the asymmetric effect of various linear-hyperbranched copolymers. For each linear-hyperbranched copolymer, nequ is estimated by matching its phase boundaries on the side with expanded spherical phase region with those of ABn with unequal B-arms but tunable iĐ. Our results suggest that the addition of B-blocks at the further location from the A-B joint point has less influence on nequ, i.e. the asymmetric effect, because these B-blocks can access more space. For the linear-dendrimer copolymers, nequ changes from 2 to about 3.8 when the overall generation number of the copolymer increases from 2 to 5. In other words, the asymmetric effect of these linear-dendrimer copolymers is intermediate between those of AB2 and AB4 miktoarm star copolymers. In brief, nequ can effectively describe the asymmetric effect on the interfacial curvature of complex asymmetric architectures.

Unprecedented Cubic Mesomorphic Behaviour of Crown-Ether Functionalized Amphiphilic Cyclodextrins

Amphiphilic supramolecular materials based on biodegradable cyclodextrins (CDs) have been known to self-assemble into different types of thermotropic liquid crystals, including smectic and hexagonal columnar mesophases. Previous studies on amphiphilic CDs bearing 14 aliphatic chains at the secondary face and 7 oligoethylene glycol (OEG) chains at the primary face showed that the stability of the mesophase can be rationally tuned through implementation of terminal functional groups to the OEG chains. Here, we report the syntheses of first examples of crown ether-functionalized amphiphilic cyclodextrins that unexpectedly form thermotropic bicontinuous cubic phases. This constitutes the first reported examples of cyclodextrins forming such phases, which are potentially capable of 3D ion transport. Lithium composites were made to assess lithium conduction in the material. XRD revealed the added lithium salt destabilizes the cubic phase in favour of the smectic phase. Solid-state NMR studies showed that these materials conduct lithium ions with a very low activation energy.

Molecular Weight-Dependent, Flexible Phase Behaviors of Amphiphilic Block Copolymer/Additive Complexes in Aqueous Solution

Pluronic amphiphilic block copolymers, well known to have a phase behavior can be controlled by external conditions, have a wide range of potential for applications such as nanotemplates or nanobuilding blocks. However, the phase behaviors of Pluronic block copolymer/additive complexes with highly ordered phases have not been fully investigated. Here, we report the unusual molecular weight-dependent self-assembly of Pluronic block copolymer/additive complexes. Depending on the temperature and additive, Pluronic P65 block copolymer with a lower molecular weight showed the closed loop-like (CLL) phase behavior with the disorder-order-disorder-order phase transition in aqueous solution, whereas Pluronic P105 and P85 block copolymers with higher molecular weights underwent highly ordered continuous phase transitions with face centered cubic (FCC), hexagonal, and lamellar phases. It is expected that the specific phase behavior of the block copolymer/additive complex can be applied in optical devices such as nanotemplates or optical sensors for a highly ordered superlattice. Furthermore, this study provides a new route to control the phase behavior of the block copolymers without a complicated process.

Bicontinuous Cubic and Hexagonal Columnar Liquid Crystalline Ion-Conductors at Room Temperature in Ion-Doped Dendritic Amphiphiles

A bicontinuous cubic (Cubbi) liquid crystalline (LC) phase consisting of three dimensional (3D) conducting networks is a promising structural platform for ion-conductors. For practical applications using this fascinating LC structure, it is necessary to suppress crystallization at room temperature (RT). Herein, we report the Cubbi structure at RT and the morphology–dependent conduction behavior in ionic samples of a non-crystallizable dendritic amphiphile. In the molecular design, branched alkyl chains were used as an ionophobic part instead of crystallizable linear alkyl chains. Two ionic samples with Cubbi and hexagonal columnar (Colhex) LC phases at RT were prepared by adding different amounts of lithium salt to the amphiphile. Impedance analysis demonstrated that the Cubbi phase contributed to the faster ion-conduction to a larger extent than the Colhex phase due to the 3D ionic networks of the Cubbi phase. In addition, the temperature–dependent impedance and electric modulus data provided information regarding the phase transition from microphase-separated phase to molecularly mixed liquid phase.

Alkyl-bis(imidazolium) salts: a new amphiphile platform that forms thermotropic and non-aqueous lyotropic bicontinuous cubic phases

New ionic amphiphiles with a hexyl-bridged bis(imidazolium) headgroup; Br(-), BF4(-), or Tf2N(-) anions; and a long n-alkyl tail can form thermotropic bicontinuous cubic liquid crystal phases in neat form and/or lyotropic bicontinuous cubic phases with several non-aqueous solvents or water.

Supramolecular transformation from ordered columnar to disordered columnar to tetragonal micellar structures in clicked dodeca-alkylated discotic triphenylene liquid crystals

We prepared three discotic liquid crystals (DLCs) based on a triphenylene (TP) disc functionalized with twelve alkyl peripheries. The synthesis of the discogens was performed by a click reaction using Cu(OAc)2 as the catalyst, with six triazolyl groups connecting the TP core with twelve alkyl chains. According to thermal data from differential scanning calorimetry (DSC), discogen , which has the shortest hexyl peripheries, exhibited two LC phases, and and , with decyl and tetradecyl peripheries, respectively, displayed three LC phases as a function of the temperature. Structural analyses using small- and wide-angle X-ray scattering (SAXS and WAXS) techniques revealed ordered and disordered hexagonal columnar LC phases in all the discogens. On the other hand, an unconventional micellar phase with P42/mnm symmetry consisting of thirty micelles was found only in and , when the temperature increased. The thermally induced transformation from the columnar to the micellar phase can be explained by increased chain entropy at higher temperatures. The complex micellar packing in the noncubic phase is attributed to the softness of the DLC micelles because the micellar corona consists of flexible alkyl chains. The discogen design concept in this study (i.e., the introduction of multibranched alkyl peripheries to the discotic mesogens via click chemistry) resulted in unconventional columnar-to-micellar transformation in conventional TP DLCs.

Functionality- and Size-Dependent Target-Differentiation of Nanoporous Carboxylated Polystyrenes in Polar Protic Solvents

In this study, we investigated the functionality- and size-dependent differentiation capability of bulk nanoporous polystyrene (PS) materials in aqueous environments. A three-arm star block copolymer (consisting of dibranched PS and linear polylactide (PLA) blocks) was employed to prepare PS nanochannels with the average pore diameter of 14.2 nm. Due to the ester group at the junction of the PS and PLA blocks, a negatively charged carboxylate group could be placed as the wall functional group automatically after the PLA etching. Based on specific electrostatic interactions, the bulk PS channels with the carboxylated wall could selectively capture a water-soluble cationic dye (rhodamine 6G) in the aqueous and methanolic solutions. Furthermore, the well-defined porous PS displayed excellent size-dependent selectivity, which was proved by a fluorescence quenching experiment using differently sized gold nanoparticles (AuNPs). Rhodamine 6G dyes on the pore wall were effectively quenched by 2 nm AuNPs. In contrast, the 16 nm AuNPs (larger than the pore diameter) did not affect the brightness of the rhodamine 6G-loaded PS.

Direct synthesis of polymerizable surfactant-stabilized nanoparticles: the macromolecular monomers for fabricating nanoparticle-polymer composites

Incorporation of inorganic nanoparticles (NPs) into polymers is the current means for enhancing the performance of polymer materials, the key to which is the increase of compatibility between NPs and polymer media. In this paper, the polymerizable surfactant octadecyl-p-vinylbenzyldimethylammonium chloride (OVDAC) is synthesized and used as a capping agent for direct synthesis of various metal NPs, for instance Au, Ag, Pd, and Pt, and semiconductor NPs, for instance ZnS, CdS, and PbS. The preformed OVDAC-stabilized NPs are lipophilic and act as macromolecular monomers in the copolymerization with lipophilic monomers.

Dendritic effect on supramolecular self-assembly: organogels with strong fluorescence emission induced by aggregation

A novel class of dumbbell-shaped dendritic molecules with a p-terphenylene core was synthesized, and their self-assembling properties were investigated. The incorporation of bulky dendritic wedges to the central stiff aromatic scaffolds could finely tune their solubility in many organic solvents. Unlike the self-assembly behavior of p-terphenylen-1,4"-ylenebis(dodecanamide), the p-terphenylene cored different generation dendritic molecules could form gels in several kinds of organic solvents through a cooperative effect of the pi-pi stacking, hydrogen-bonding, and van der Waals forces. Interestingly, significant fluorescence enhancement was observed after gelation. Extensive investigations with atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), theological measurements, UV-vis absorption spectroscopy, FT-IR spectroscopy, 1H NMR, and X-ray powder diffraction (XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels.