Yiyang Lin

A facile route to design pH-responsive viscoelastic wormlike micelles : Smart use of hydrotropes

A simple and effective route to design pH-responsive viscoelastic wormlike micelles based on commercial compounds is reported. According to this route, pH-sensitive viscoelastic fluids can be easily obtained by introducing a pH-responsive hydrotrope into a surfactant solution. In this paper, the mixed system of cetyltrimethylammonium bromide (CTAB) and potassium phthalic acid (PPA) was studied in detail. This pH-sensitive fluid can be switched between a gellike state and a waterlike state within a narrow pH change. Rheology and DLS results revealed that the pH-sensitive flowing behavior was attributed to the microstructure transition between wormlike micelles and short cylindrical micelles. Combined with fluorescence anisotropy, NMR, and UV-vis, it was demonstrated that the pH response of viscoelastic fluid originated from the different binding abilities of hydrotrope to surfactant as pH varies. Furthermore, different kinds of hydrotropes can be utilized to prepare pH-responsive viscoelastic fluids in the desired pH areas.

Metal-Driven Hierarchical Self-Assembled One-Dimensional Nanohelices

Sophisticated helical structure has been an attractive subject due to its significance in understanding of biological self-assembly and appealing application in nanoscience. In this work, a facile route toward one-dimensional helical nanostructure is presented based on metal-cholate supramolecular self-assembly. Well-defined right-handed helical nanoribbons in calcium-cholate systems are systematically investigated and a series of metal ions are exploited to drive metal-cholate supramolecular helix. It is anticipated that the incorporation of metal ions may endow versatile functionalities and merits to the self-assembled nanohelices. Particularly helical inorganic nanomaterials (i.e., SiO(2) and ZnS) have been prepared based on metal-cholate supramolecular nanohelix via two distinct templating strategies.

Effects of Inorganic and Organic Salts on Aggregation Behavior of Cationic Gemini Surfactants

All salts studied effectively reduce critical micelle concentration (CMC) values of the cationic gemini surfactants. The ability to promote the surfactant aggregation decreases in the order of C(6)H(5)COONa > p-C(6)H(4)(COONa)(2) > Na(2)SO(4)> NaCl. Moreover, only C(6)H(5)COONa distinctly reduces both the CMC values and the surface tension at CMC. For 12-4-12 solution, the penetration of C(6)H(5)COO(-) anions and charge neutralization induce a morphology change from micelles to vesicles, whereas the other salts only slightly increase the sizes of micelles. The 12-4(OH)(2)-12 solution changes from the micelle/vesicle coexistence to vesicles with the addition of C(6)H(5)COONa, whereas the other salts transfer the 12-4(OH)(2)-12 solution from the micelle/vesicle coexistence to micelles. As compared with 12-4-12, the two hydroxyls in the spacer of 12-4(OH)(2)-12 promote the micellization of 12-4(OH)(2)-12 and reduce the amounts of C(6)H(5)COONa required to induce the micelle-to-vesicle transition.

Creation of photo-modulated multi-state and multi-scale molecular assemblies via binary-state molecular switch

The creation of photo-modulated multi-state and multi-scale molecular self-assemblies was realized by the ingenuous utilization of a binary-state molecular switch, sodium (4-phenylazo-phenoxy)-acetate (AzoNa). Depending on the irradiation time, the binary state of the azobenzene group (i.e. trans/cis isomerization) can be exploited to generate multi-state nanostructures (including wormlike micelle, vesicle, lamellar structure, small micelle) by the coupling of conventional surfactant CTAB. Meanwhile, the conformation transition of azobenzene at molecular scale (∼A), stimulated by light input can be amplified to regulate molecular architectures at mesoscopic scale (from nanometer to micrometer), leading to significant changes in solution property at macroscopic scale (naked-eye visible scale). By exposing to UV or visible light, the multi-state and multi-scale molecular self-assemblies can be reversibly controlled. It is proposed that light-triggered structural changes in the dipole moment and geometry of azobenzene group, which impart a significant effect upon molecular packing of surfactant aggregates, were responsible for this peculiar phenomenon.

Thermo-responsive viscoelastic wormlike micelle to elastic hydrogel transition in dual-component systems

In this work, we report a thermo-responsive phase transition from a viscoelastic wormlike micelle solution to an elastic hydrogel in a mixture of an imidazole-type surfactant, 1-hexadecyl-3-methylimidazolium bromide (C16MIMBr), and sodium salicylate (NaSal). Above the critical temperature Tgel, the sample exhibits characteristic wormlike micelle features with strong viscoelastic properties. As the temperature was lowered below the Tgel, the viscoelastic solution transforms into an elastic hydrogel with a remarkable elastic modulus increase. Polarization microscopy, SEM, and XRD were employed to reveal the morphology and molecular arrangement of the organized microstructures in the hydrogel. The unexpected phase transition from viscoelastic solution to hydrogel can be attributed to the crystallization of wormlike micelles, which is related to the strong synergic interaction between the surfactant and hydrotrope.

Lanthanide-Containing Photoluminescent Materials: From Hybrid Hydrogel to Inorganic Nanotubes

Functional photoluminescent materials are emerging as a fascinating subject with versatile applicability. In this work, luminescent organic-inorganic hybrid hydrogels are facilely designed through supramolecular self-assembly of sodium cholate, and lanthanide ions such as Eu(3+), Tb(3+), and Eu(3+)/Tb(3+). Fluorescence microscopy and TEM visualization demonstrates the existence of spontaneously self-assembled nanofibers and 3D networks in hybrid hydrogel. Photoluminescence enhancement of lanthanide ions is realized through coordination with cholate and co-assembly into 1D nanofibers, which can successfully shield the Eu(3+) from being quenched by water. The photoluminescence emission intensity of a hybrid hydrogel exhibits strong dependence on europium/cholate molar ratio, with maximum emission appearing at a stoichiometry of 1:3. Furthermore, the emission color of a lanthanide-cholate hydrogel can be tuned by utilizing different lanthanide ions or co-doping ions. Moreover, photoluminescent lanthanide oxysulfide inorganic nanotubes are synthesized by means of a self-templating approach based on lanthanide-cholate supramolecular hydrogels. To the best of our knowledge, this is the first time that the lanthanide oxysulfide inorganic nanotubes are prepared in solution under mild conditions.

Controllable self-assembled laminated nanoribbons from dipeptide-amphiphile bearing azobenzene moiety

Artificial peptide self-assembly is an appealing research subject which has been demonstrated to be a reliable approach to create hierarchical nanostructures and biomaterials. In this paper, a dipeptide-amphiphile incorporated with an azobenzene moiety is synthesized, which are found to self-assemble into well-defined laminated nanoribbons as well as macroscopic hydrogel. The nanoribbons are formed by nanofibers aligning in nearly lamellar arrays. The driving force of dipeptide self-assembly is proposed to be a synergic effect of hydrophobic interaction, aromatic packing, and hydrogen bond. The addition of NaCl is found to promote hydrogelation and nanoribbon formation. Finally photoisomerization of the azobenzene group is utilized to rationally control dipeptide self-assembly and hydrogel formation by remote light input.

Construction and application of tunable one-dimensional soft supramolecular assemblies

Self-assembly of small molecules into one-dimensional soft nanostructures offers many advantages in understanding biological process and fabrication of electronically active materials. In recent decades, various one-dimensional soft nanostructures have been fabricated. The present review focuses on the following content: (1) frequently occurring forces in one-dimensional molecular self-assembly; (2) how these forces are used to construct this type of nanostructures; (3) fine-tuning one-dimensional self-assemblies by employing tools such as photo, pH, temperature, additives, and concentration; (4) some examples of the applications of one-dimensional self-assemblies in fabrication of one-dimensional hard materials are described.

Self-assembled laminated nanoribbon-directed synthesis of noble metallic nanoparticle-decorated silica nanotubes and their catalytic applications

Substrate-supported noble metallic nanoparticles have received intense attention owing to their great potential in various applications. In this work, silica nanotube-supported metallic nanoparticles (i.e., Au, Ag, and Pd) are synthesized by in situ reducing metal ions into nanoparticles on the nanotube surface. The silica nanotubes are prepared through the traditional sol–gel approach using laminated nanoribbons as soft templates, which are self-assembled from dipeptide-amphiphiles. The surface of silica nanotubes is functionalized to display amino groups, which serve as active sites to host metallic particles. By changing the preparation conditions, the wall thickness of silica nanotubes is adjusted and the density of metallic nanoparticles on silica surface is facilely tuned. Finally the metallic nanoparticle-coated silica nanotubes are proven to be applicable in recyclable catalysis of 4-nitrophenol (4-NP) reduction.

Microstructures and rheological dynamics of viscoelastic solutions in a catanionic surfactant system

Viscoelastic solutions formed in a catanionic surfactant system of dodecyltriethylammonium bromide (DTEAB)/sodium dodecylsulfate (SDS) at the molar ratio of 27/73 were systematically studied using a combination of rheology and dynamic light scattering (DLS). Wormlike micelles began to form above the total surfactant concentration (C(total)) of 120 mM by the growth of small cylindrical micelles. Subsequently the system was found to exhibit linear viscoelasticity with characteristic of a Maxwell fluid in the intermediate concentration range of 170-210 mM, which arose from a 3D entangled network of wormlike micelles. At higher surfactant concentrations, a transition from linear micelles to branched structures probably took place. Finally and significantly, the effect of the surfactant headgroup on the rheological property of catanionic surfactant mixtures was discussed.