10 research outputs found

    Effects of Annealing Solvents on the Morphology of Block Copolymer-Based Supramolecular Thin Films

    No full text
    We report a strategy that combines supramolecular assembly and solvent annealing to manipulate the microdomain orientation in block copolymer thin films. In supramolecular thin films formed by polystyrene-<i>b</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP) with 3-pentadecylphenol (PDP) hydrogen-bonded onto P4VP blocks, where PS blocks phase-separate into cylindrical microdomains, we found that the orientation of PS cylinders can be controlled by using different types of solvents to anneal the films. As films are annealed under the vapors of solvents bearing no oxygen atoms, such as chloroform, PS cylinders are perpendicular to the surface, while under those of solvents bearing oxygen, such as THF, PS cylinders are parallel to the surface. Furthermore, the orientation is switchable upon the alternate use of different types of solvents. The <sup>1</sup>H NMR measurements showed that the strengths of hydrogen bonds between PDP and P4VP are greatly weakened in oxygen-bearing solvents due to the competition of the highly electronegative oxygen atoms. We thus suggest that the binding capability of PDP onto P4VP is the key to determine whether the supramolecules can be assembled in the vapors of different types of solvents, which in turn, regulates the orientation of PS cylinders

    Biological Hydrogels Formed by Swollen Multilamellar Liposomes

    No full text
    The self-assembly of lecithin-bile salt mixtures in solutions has long been an important research topic, not only because they are both biosurfactants closely relevant to physiological functions but also for the potential biomedical applications. In this paper, we report an unusual biological hydrogel formed by mixing bile salts and lecithin at low bile salt/lecithin molar ratios (<i>B</i><sub>0</sub>) in water. The gel can be prepared at a total lipid concentration as low as ∌15 wt %, and the solidlike property of the solutions was confirmed by dynamic rheological measurements. We used cryo-TEM and SAXS/SANS techniques to probe the self-assembled structure and clearly evidence that the gel is made up of jammed swollen multilamellar vesicles (liposomes), instead of typical fibrous networks found in conventional gels. A mechanism-based on the strong repulsion between bilayers due to the incorporation of negatively charged bile salts is proposed to explain the swelling of the liposomes. In addition to gel, a series of phases, including viscoelastic, gel-like, and low-viscosity fluids, can be created by increasing <i>B</i><sub>0</sub>. Such a variety of phase behaviors are caused by the transformation of bilayers into cylindrical and spheroidal micelles upon the change of the effective molecular geometry with <i>B</i><sub>0</sub>

    Nonvolatile Organic Field-Effect Transistors Memory Devices Using Supramolecular Block Copolymer/Functional Small Molecule Nanocomposite Electret

    No full text
    Organic field-effect transistors (OFETs) memory devices based on hybrid nanocomposite electret were fabricated by cooperative supramolecular polystyrene-<i>block</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP) with two different block compositions (asymmetric L1 and symmetric L2) that contain hydroxyl-functionalized ferrocene small molecules (FMs). Because of the selective hydrogen interaction between the hydroxyl groups of FM and pyridine groups in P4VP block, the small FMs can preferentially disperse in the P4VP nanodomain, which can be used as nanostructured charge-trapping nanocomposite electret (L1-FMX and L2-FMX) under solvent-annealing process. The charge-storage functionalities can be easily tailored by morphologies of the hybrid nanocomposite thin film and spatial distribution of the FM molecules in which the relative molecular mass of block copolymers and the FM loading ratio can further control both of them. These block copolymer nanocomposite thin film electrets with charge-controlling guest FM for OFETs memory devices exhibit significant features including the ternary bits storage, high-density trapping sites, charge-carrier trapping of both polarities (ambipolar trapping), and solution processing that can make important progress for future advanced storage and memory technology

    Mixtures of Lecithin and Bile Salt Can Form Highly Viscous Wormlike Micellar Solutions in Water

    No full text
    The self-assembly of biological surfactants in water is an important topic for study because of its relevance to physiological processes. Two common types of biosurfactants are lecithin (phosphatidylcholine) and bile salts, which are both present in bile and involved in digestion. Previous studies on lecithin–bile salt mixtures have reported the formation of short, rodlike micelles. Here, we show that lecithin–bile salt micelles can be further induced to grow into long, flexible wormlike structures. The formation of long worms and their resultant entanglement into transient networks is reflected in the rheology: the fluids become viscoelastic and exhibit Maxwellian behavior, and their zero-shear viscosity can be up to a 1000-fold higher than that of water. The presence of worms is further confirmed by data from small-angle neutron and X-ray scattering and from cryo-transmission electron microscopy (cryo-TEM). We find that micellar growth peaks at a specific molar ratio (near equimolar) of bile salt:lecithin, which suggests a strong binding interaction between the two species. In addition, micellar growth also requires a sufficient concentration of background electrolyte such as NaCl or sodium citrate that serves to screen the electrostatic repulsion of the amphiphiles and to “salt out” the amphiphiles. We postulate a mechanism based on changes in the molecular geometry caused by bile salts and electrolytes to explain the micellar growth

    Molecular Interactions between Lecithin and Bile Salts/Acids in Oils and Their Effects on Reverse Micellization

    No full text
    It has been known that the addition of bile salts to lecithin organosols induces the formation of reverse wormlike micelles and that the worms are similar to long polymer chains that entangle each other to form viscoelastic solutions. In this study, we further investigated the effects of different bile salts and bile acids on the growth of lecithin reverse worms in cyclohexane and <i>n</i>-decane. We utilized rheological and small-angle scattering techniques to analyze the properties and structures of the reverse micelles. All of the bile salts can transform the originally spherical lecithin reverse micelles into wormlike micelles and their rheological behaviors can be described by the single-relaxation-time Maxwell model. However, their efficiencies to induce the worms are different. In contrast, before phase separation, bile acids can induce only short cylindrical micelles that are not long enough to impart viscoelasticity. We used Fourier transform infrared spectroscopy to investigate the interactions between lecithin and bile salts/acids and found that different bile salts/acids employ different functional groups to form hydrogen bonds with lecithin. Such effects determine the relative positions of the bile salts/acids in the headgroups of lecithin, thus resulting in varying efficiencies to alter the effective critical packing parameter for the formation of wormlike micelles. This work highlights the importance of intermolecular interactions in molecular self-assembly

    Phase Behavior and Structure of Supramolecules Formed by Poly(4-vinylpyridine) and Fanlike Benzoic Acid Derivative with Long Hydrophobic Tails

    No full text
    We investigated the self-assembly behaviors of supramolecules formed by poly­(4-vinylpyridine) (P4VP) and a fanlike small molecule, 3,4,5-tris­(hexadecyloxy)­benzoic acid (THBA), via hydrogen bonding interactions. Different from other commonly studied small molecules, THBA bears three particularly long hydrophobic tails and tends to form stable crystals by itself, which gives rise to unusual phase behaviors and structures. We used FTIR to investigate the degree of complexation and find that it is not monotonically increased to a plateau with increasing THBA but reaches a maximum and then decreased. This is attributed to the crystallization of excess THBA that induces a debonding of the originally associated THBA. The crystallization-induced dissociation and macrophase separation are further evidenced by DSC and X-ray scattering analyses. Below the order–disorder transition temperature, a coexistence of lamellae and hexagonally packed cylinders is found in melted P4VP­(THBA) supramolecules. After the associated THBA crystallizes, the complexes exclusively form hexagonally packed cylinders due to the bulky tails of THBA, in the absence of the lamellar structure generally seen in other polymer-based supramolecules

    Synthesis, Morphology, and Sensory Applications of Multifunctional Rod–Coil–Coil Triblock Copolymers and Their Electrospun Nanofibers

    No full text
    We report the synthesis, morphology, and applications of conjugated rod–coil–coil triblock copolymers, polyfluorene<i>-block-</i>poly­(<i>N</i>-isopropylacrylamide)<i>-block</i>-poly­(N-methylolacrylamide) (<b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><i><b>-b-</b></i><b>PNMA</b>), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-<i>b</i>-PNIPAAm-<i>b</i>-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the <b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><b>-</b><i><b>b</b></i><b>-</b><b>PNMA</b> along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod–coil block copolymers would have potential applications for multifunctional sensory devices

    Tunable Thermoelectric Performance of the Nanocomposites Formed by Diketopyrrolopyrrole/Isoindigo-Based Donor–Acceptor Random Conjugated Copolymers and Carbon Nanotubes

    No full text
    This paper presents the development of thermoelectric properties in nanocomposites comprising donor–acceptor random conjugated copolymers and single-walled carbon nanotubes (SWCNTs). The composition of the conjugated polymers, specifically the ratio of diketopyrrolopyrrole (DPP) to isoindigo (IID), is manipulated to design a series of random conjugated copolymers (DPP0, DPP5, DPP10, DPP30, DPP50, DPP90, DPP95, and DPP100). The objective is to improve the dispersion of SWCNTs into smaller bundles, leading to enhanced thermoelectric properties of the polymer/SWCNT nanocomposite. This dispersion strategy promotes an interconnected conducting network, which plays a critical role in optimizing the thermoelectric performance. Accordingly, the effects of morphologies on the thermoelectric properties of the nanocomposites are systematically investigated. The DPP95/SWCNT nanocomposite exhibits the strongest interaction, resulting in the highest power factor (PF) of 711.1 ÎŒW m–1 K–2, derived from the high electrical conductivity of 1690 S cm–1 and Seebeck coefficient of 64.8 ÎŒV K–1. The prototype flexible thermoelectric generators assembled with a DPP95/SWCNT film achieve a maximum power output of 20.4 ÎŒW m–2 at a temperature difference of 29.3 K. These findings highlight the potential of manipulating the composition of random conjugated copolymers and incorporating SWCNTs to efficiently harvest low-grade waste heat in wearable thermoelectric devices

    Using a Single Electrospun Polymer Nanofiber to Enhance Carrier Mobility in Organic Field-Effect Transistors toward Nonvolatile Memory

    No full text
    In this work, a single electrospun polymer nanofiber was employed as an additional dielectric in organic field-effect transistors where the active channel was a layer of pentacene. A high field-effect mobility (>1.50 cm<sup>2</sup>/(V·s)) and a high ON/OFF current ratio (>10<sup>6</sup>) could be achieved by the use of such a nanofiber. Probing by electron microscopy, atomic force microscopy, and scattering techniques, we found that the geometry of the fiber is key to induce a pentacene morphology with large and oriented grains that facilitates the charge transport in pentacene layer along the fiber. The feasibility of nonvolatile memory based on this new type of transistor has been explored and the devices showed a fairly high memory window and reliable memory characteristics. In addition to pure polymers, the effects of composite nanofibers with dispersed [6,6]-phenyl-C<sub>61</sub>-butyric acid methyl ester were also investigated, and the electrical properties and memory characteristics of the transistors were found to be further improved. This study highlights the importance of dielectric geometry to pentacene morphology that is decisive for the performances of organic field-effect transistors

    Effects of Alkali Cations and Halide Anions on the Self-Assembly of Phosphatidylcholine in Oils

    No full text
    The interactions between ions and phospholipids are closely associated with the structures and functions of cell membrane. Instead of conventional aqueous systems, we systematically investigated the effects of inorganic ions on the self-assembly of lecithin, a zwitterionic phosphatidylcholine, in cyclohexane. Previous studies have shown that addition of inorganic salts with specific divalent and trivalent cations can transform lecithin organosols into organogels. In this study, we focused on the effect of monovalent alkali halides. Fourier transform infrared spectroscopy was used to demonstrate that the binding strength of the alkali cations with the phosphate of lecithin is in the order Li<sup>+</sup> > Na<sup>+</sup> > K<sup>+</sup>. More importantly, the cation–phosphate interaction is affected by the paired halide anions, and the effect follows the series I<sup>–</sup> > Br<sup>–</sup> > Cl<sup>–</sup>. The salts of stronger interactions with lecithin, including LiCl, LiBr, LiI, and NaI, were found to induce cylindrical micelles sufficiently long to form organogels, while others remain organosols. A mechanism based on the charge density of ions and the enthalpy change of the ion exchange between alkali halides and lecithin headgroup is provided to explain the contrasting interactions and the effectiveness of the salts to induce organogelation
    corecore