Topological molecular architectures play a crucial role in many physico-chemical properties of materials and biological processes. Herein we synthesized a series of molecularly-defined cyclic oligomers, cyclic-TPEn+1 (n = 1–6), containing tetraphenylethylene (TPE) segments in the main chain by a stepwise chain-growth strategy. The cyclic structure endows the cyclic-TPEn+1 with a higher glass transition temperature (Tg) and quantum yields of aggregation induced emission (AIE) for n = 1 and 2 due to the constraints imposed by the cyclic topology itself. Importantly, the cyclic topology induces odd–even effects on both Tg and photoluminescence quantum yield, arising from the alternation of intermolecular interactions. Hopefully, this work will advance our understanding on the glass transition and AIE mechanism, and finally pave the way for the development of luminogens with a wide variety of functions.

We develop a solvent-assisted room temperature nanoimprint lithography (SART-NIL) technique to fabricate an ideal active layer consisting of poly(3-hexylthiophene) nanopillar arrays surrounded by [6,6]-phenyl-C61-butyric acid methyl ester. Characterization by scanning electron microscopy, two-dimensional grazing incidence wide angle X-rays diffraction, and conducting atomic force microscopy reveals that the SART-NIL technique can precisely control the size of P3HT nanopillar arrays. With the decrease in diameters of P3HT nanopillar arrays, the P3HT nanopillar arrays exhibit a more preferable face-on molecular orientation, enhanced UV-vis absorption and higher conducting ability along the direction perpendicular to the substrate. The ordered bulk heterojunction film consisting of P3HT nanopillar arrays with a diameter of ∼45 nm (OBHJ-45) gives face-on orientation, a high interfacial area of 2.87, a high conducting ability of ∼130 pA and efficient exciton diffusion and dissociation. The polymer solar cell (PSC) based on an OBHJ-45 film exhibits a significantly improved device performance compared with those of PSCs based on the P3HT nanoapillar arrays with diameters ∼100 nm and ∼60 nm. We believe that the SART-NIL technique is a powerful tool for fabricating an ideal active layer for high performance PSCs.

Smart stimuli-responsive superhydrophobic surfaces with reversibly switchable wettability have received considerable attention due to their various potential applications. We demonstrate here a new but versatile approach for preparing photoresponsive superhydrophobic surfaces. Fluorinated azobenzene derivatives or polymers are immobilized onto silica surface by taking advantage of the remarkable adhesive ability of polydopamine. By simply spin coating the silica particles onto silicon wafer, superhydrophobic surfaces can be obtained with a water contact angle greater than 150° and low contact angle hysteresis (<10°). In addition, reversible change water contact angles on the surfaces can occur upon irradiation with alternate UV and visible light.

We firstly report a novel strategy for the preparation of rapid and reversible photo-driven actuators consisting of an active linear azobenzene polymer layer and a passive silk fibroin substrate, avoiding the need for oriented azobenzene liquid crystalline elastomers (LCEs) that have been used until now, just through depositing linear azobenzene polymer on the top of silk fibroin film. The unimorph actuators can show uniquely different bending properties. Moreover, the response speed of the unimorph actuator is on the level of a few hundreds of milliseconds. The bending angle can be well controlled either by changing the UV light intensity or by altering the thickness ratio of the two composed layers. Additionally, complex and attractive arm-like movements are successfully achieved. We believe that the proposed unimorph actuators will pave the way for designing complicated and programmed artificial muscles.

Nanopillars of ferroelectric polymers are of strong interest for the fabrication of low-cost nanoscale actuators and memories of high density. However, a limiting factor of polymers compared to inorganic ferroelectric materials is their low ferro- to paraelectric Curie transition, a problem compounded by the possible further decrease of the Curie temperature in nanostructures as was suggested by previous studies. Here we develop a methodology based on piezoresponse force microscopy to study the thermal stability of data stored in free-standing poled and annealed nanopillars of ferroelectric poly(vinylidene fluoride-ran-trifluoroethylene), P(VDF-TrFE), and thereby demonstrate that the Curie transition of a properly processed strongly confined ferroelectric polymer is not significantly modified compared to the bulk material, at least down to a mass as small as ca. 560 attograms corresponding to ca. 1500 chains only.

The ferroelectric properties of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) thin films mainly depend on the crystal orientation and crystallinity. We demonstrate here the thermal history and thickness dependent crystal orientation in P(VDF-TrFE) ultrathin films, and its correlation with local polarization reversal. Upon annealing in the paraelectric phase after spin-cast, the lamellar crystals grow preferentially along the crystallographic a axis, with the c axis (chain axis) parallel to the substrate. In contrast, when crystallized in the paraelectric phase from melt, the lamellar crystals take a flat-on orientation with the crystallographic c-axis normal to the substrate. In addition, local measurement by piezoresponse force microscopy indicates that the flat-on crystals do not display any polarization switching, whereas the edge-on crystals exhibit proper switching upon application of a vertical electric field. Importantly, the coercive field measured from the piezoresponse hysteresis loops does not change with the film thickness in the edge-on oriented lamellar crystals.

Silk fibers featuring exceptional mechanical strength and high extensibility are composed of fibril bundles with diameters in the range of 20–150 nm. Regeneration of silk fibers with similar superstrong mechanical properties from reconstituted silk protein remains a challenge because controlled self-assembly of macromolecular components on the nanoscale is required. The self-assembly of silk protein in nanoconfined geometry and the mechanical properties are investigated in this study. Using a template-filling method, cylindrical nanofibers of silk protein are fabricated for different diameters within nanopores (50–120 nm) of anodic alumina oxide. By exposing to organic solvent, e.g. methanol, the proteins self-assemble to β-sheet crystals in which the c-axis is aligned normal to the fiber axis, in stacking contrast to the natural silk fibers in which the c-axis is aligned along the fiber axis. Such highly ordered structures contribute to the enhanced mechanical property which reaches the theoretical mechanical level. In addition, the Young’s modulus of the nanofibers linearly increases with decreasing the diameter of the nanofibers. This is important, on the one hand, to understand the self-assembly of macromolecules under spatial confinement and, on the other hand, to understand the structure–property relationships of nanomaterials and to fabricate soft nanostructures with controllable properties.

•Patterning of silk fibroin films.•The influence of topography on HUVEC cell behavior.•HUVEC cells are aligned by topographic grooves and ridges.•The primary growth direction of filopodia is altered by pattern ridges.Silk fibroin is an ideal blood vessel substitute due to its advantageous qualities including variable size, good suture retention, low thrombogenicity, non-toxicity, non-immunogenicity, biocompatibility, and controllable biodegradation. In this study, silk fibroin films with a variety of surface patterns (e.g. square wells, round wells plus square pillars, square pillars, and gratings) were prepared for in vitro characterization of human umbilical vein endothelial cell's (HUVEC) response. The affects of biomimetic length-scale topographic cues on the cell orientation/elongation, proliferation, and cell-substrate interactions have been investigated. The density of cells is significantly decreased in response to the grating patterns (70 ± 3 nm depth, 600 ± 8 nm pitch) and the square pillars (333 ± 42 nm gap). Most notably, we observed the contact guidance response of filopodia of cells cultured on the surface of round wells plus square pillars. Overall, our data demonstrates that the patterned silk fibroin films have an impact on the behaviors of human umbilical vein endothelial cells.

The physical properties of polymers strongly depend on the molecular or supermolecular order and orientation. Here we demonstrate the preferential orientation of lamellar crystals and the enhancement of ferro/piezoelectric properties in individual poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanowires fabricated from anodic alumina oxide (AAO) templates. The crystallographic a axis of P(VDF-TrFE) was found to be aligned along the long axis of nanowires due to geometrical confinement and grapho-expitaxial crystals growth. The alignment of lamellar crystals in P(VDF-TrFE) nanowires and enhancement of crystallization translated into improved ferro/piezoelectric properties such as lower coercive field and higher piezoelectric coefficient, testified by piezoresponse force microscopy images and piezoresponse hysteresis loops.

Nanoimprinting has been well explored to create nanostructures and to induce molecular orientation in conjugated polymer thin films. We demonstrate here that large area poly(3-hexylthiophene) (P3HT) nanopillar arrays can be fabricated by a simple, cost-effective nanoimprinting method in a solvent-swollen plasticized state at room temperature. In addition, the solvent-assistant room-temperature nanoimprinting induces face-on chain alignment in the P3HT nanopillars; i.e., the π–π stacking of P3HT is aligned normal to the substrate, favorable for organic photovoltaic cell applications. The face-on chain alignment solely depends on the diameters of nanopores defined in the nanoimprinting mold, rather than on the initial chain orientation in unprocessed thin films. Furthermore, a critical dimension of ca. 85 nm in diameter is found to be essentially needed to induce the face-on chain alignment within the nanopillars.

Nanoimprint lithography (NIL) was used to shape thin films of a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene (PVDF-TRFE), using a variety of molding shapes and imprinting conditions. The morphology of the layers was characterized by atomic force microscopy (AFM), and preferential orientation of the crystallographic axes was monitored by infrared microspectroscopy; in addition, the local ferroelectric properties were obtained by piezoresponse force microscopy (PFM). When the sample is imprinted in its paraelectric phase in conditions leading to complete confinement, in cavities of size lower than the natural lamellar length observed in a continuous thin film, the crystallographic a axis aligns preferentially parallel to the substrate, and the crystalline lamellae are of significantly reduced length. These characteristics translate in a strongly decreased coercive field and accelerated ferroelectric switching, which is in part ascribed to the improved coupling between the electric field and the properly oriented dipole moments. When decreasing the confinement either by leaving a residual film connecting the nanopillars, or by increasing the lateral size of the nanopillars above the natural lamellar length, or by using line molds where confinement only exists in one direction, or by using continuous films, the preferential orientation becomes less visible and the lamellar length increases, resulting in increased coercive and switching fields. Interestingly, the average length of the crystalline lamellae tends to correlate with the value of the coercive field. Finally, if the sample is imprinted in the melt, a flat-on setting of the crystalline lamellae ensues, with a vertical chain axis which is unfavorable for ferroelectric properties probed with a vertical electric field.

Confined crystallization of the micromolded poly(butadiene)-block-poly(ε-caprolactone) (PB-b-PCL) diblock copolymer thin film was studied in this work. The long-range regular ordering of the PCL crystal with crystallographic b-axis parallel to the long-axis of the channel was detected, as indicated by the electron diffraction and grazing-incidence X-ray diffraction experimental results. This preferential crystallographic orientation is mainly because that PCL block crystallization was readily influenced by the geometric effect, then, the fast-growth direction (crystallographic b-axis) was forced to extend along the long-axis of the channel to grow long. Moreover, the substrate induced ordering of the block copolymer restricted the “in-plane” molecular diffusion in the residual layer, and cross-channel crystallization was precluded. Hence, micromolding seems to be a promising method for tailoring the nanoscale crystallization of block copolymer in thin films.