The osmotic energy existing in fluids is recognized as a promising “blue” energy source that can help solve the global issues of energy shortage and environmental pollution. Recently, nanofluidic channels have shown great potential for capturing this worldwide energy because of their novel transport properties contributed by nanoconfinement. However, with respect to membrane-scale porous systems, high resistance and undesirable ion selectivity remain bottlenecks, impeding their applications. The development of thinner, low-resistance membranes, meanwhile promoting their ion selectivity, is a necessity. Here, we engineered ultrathin and ion-selective Janus membranes prepared via the phase separation of two block copolymers, which enable osmotic energy conversion with power densities of approximately 2.04 W/m2 by mixing natural seawater and river water. Both experiments and continuum simulation help us to understand the mechanism for how membrane thickness and channel structure dominate the ion transport process and overall device performance, which can serve as a general guiding principle for the future design of nanochannel membranes for high-energy concentration cells.

Linear viscoelastic and dielectric measurements were conducted for a model associating polymer system, n-butyl acrylate (PnBA)-based copolymers containing 2-ureido-4[1H]-pyrimidinone (UPy) groups as stickers. The number of stickers per chain was varied from less than one to more than two, which covered a sol-to-gel transition region. Fitting the linear viscoelasticity (LVE) to an analytical model developed in our previous study, we found necessity of distinguishing the intra- and interchain association in the model, with only the latter contributing to the gel formation. For the PnBA-Upy sample slightly above the gel point, the relaxation processes due to the Rouse motion and the sticker dissociation were commonly detected in the same range of T covering from 20 to 60 °C. This feature enabled us to make the time–temperature superposition separately for respective relaxation processes, and two sets of shift factors, reflecting the temperature dependence of the Rouse time τ0 and dissociation time τs, were obtained accordingly. The T dependence of the ratio of these shift factors, being identical to the dependence of τs/τ0, enabled determination of activation energy of the sticker dissociation. This activation energy was found to be consistent with that determined from the model fitting of the LVE data. The dielectric measurements detected both segmental α relaxation and an ionic α2 relaxation processes. The α2 relaxation time was found to be shorter than τs, and this result was discussed in relation to a difference between fluctuation and dissociation of ionic pairs.

Post-cleavable block copolymers are crucially important for the fabrication of nanoporous structures from the self-assembly of block copolymers by the selective etching of one block. Here, we present a facile and inexpensive approach to synthesize block copolymers bearing an acid-cleavable junction. A difunctional inifer containing an acetal group is synthesized for the sequential reversible addition–fragmentation transfer (RAFT) polymerization of tert-butyl methacrylate and atom transfer radical polymerization (ATRP) of styrene. Moreover, the polymerization sequence of the monomers can be altered. The acetal junctions in the resulting block copolymers can be readily cleaved by acid under ambient conditions. Aldehyde or monoglyceride end groups are left at the ends of the PS residues, which can be used as binding sites for future applications.

Nanoporous structures derived from self-assembled block copolymers (BCP) are a facile template for nanofabrications. In order to enhance the stability of the nanoporous structures toward collapse, which is of crucial importance for practical applications, cross-linking the matrix is an essential process. Most of the BCP precursors undergo separated processes of degradation and cross-linking. Here, we provided one-step fabrication of a stable nanoporous film from a BCP precursor by UV treatment, eliminating multistep processing. The BCP contains an ortho-nitrobenzyl (ONB) group as a UV degradable juncture and a coumarin group as the UV cross-linkable component. After UV exposure, the ordered nanoporous thin film was achieved, with carboxyl groups in situ generated. The tolerance to solvents was highly enhanced. This facile strategy provides promising applications in stable nanoporous scaffolds.

pH-sensitive wettability of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) self assembled films, exhibiting superoleophobicity under water and hydrophilicity at low pH value, and oleophobicity under water and hydrophobicity at neutral condition, has been realized. The wettability properties resulted from the surface topological and chemical transition, which were confirmed by in situ AFM measurements under water at different pH. At low pH, P4VP chains, which were confined in the hexagonal-packed nanodomains, got protonated into a swollen state, while at high pH, P4VP chains were deprotonated into a collapsed state. The reversible protonation/deprotonation procedure on the molecular scale leads to surface topological and chemical transition, thereby pH-sensitive wettability.

The actuation of microscale liquid droplets is a key point in the lab-on-chip field. Marangoni force actuation resulting from a temperature gradient has remarkable advantages. However, high hysteresis between the droplet and the surface is an obstacle to this motion. Here, we take advantage of the temperature-responsive wettability of a surface made of a block copolymer (BCP) to show the temperature-controlled directional spreading of water droplets. By applying a temperature gradient on the BCP surface, both the topologies and chemical components in the nanodomains could be changed gradually. As a result, a wettability gradient force would form with the same direction as the Marangoni force, which could also be formed due to the same temperature gradient, and the collaborative effect of these forces could help overcome the high hysteresis. This was confirmed theoretically by calculating the total force acting on the droplet. The liquid droplet was observed to move by forces of non-mechanical origin in experiments conducted using a thermal gradient on the BCP films. Furthermore, two water droplets were observed to merge into one when they were placed in a V-shaped temperature field. These results help us understand the motion of droplets on a surface with high hysteresis and provide potential applications in microfluidic devices.

Linear-brush poly(styrene)-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PS-b-POEGMA) block copolymer incorporating a UV-crosslinkable coumarin group in a PS block, self-assembled into a cylindrical structure with POEGMA cylinders perpendicular to the film surface, which exhibit excellent CO2 separation properties. The block copolymer was successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and click chemistry. The molecular characterization of the diblock copolymer was performed with 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The cylindrical phase structure was confirmed by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The POEGMA amorphous phase was confirmed by differential scanning calorimeter (DSC). Gas permeation properties of CO2, N2 and He were determined around room temperature. Compared to the linear BCP, the total gas selectivity and especially CO2 permeation flux increased dramatically. The functional block units and self-assembled microphase structures synergetically played key roles in the high performance of the membrane.

We report photo-controlled water gathering on bio-inspired fibers. We have designed a bio-inspired fiber using azobenzene (Azo) polymer materials, with roughness and a curvature similar to the spindle-knots of wetted spider silk. We demonstrate that the cooperation between roughness and curvature and the photo-responsive wettability play a key role in water gathering after Vis or UV irradiation, which regulate effectively the separation of water droplets away from the spindle-knots or the coalescence towards the spindle-knots, respectively. This study offers an insight into the design of novel gradient surfaces that may drive tiny droplets to move in as-desired directions, which could potentially be extended to the realms of fluid-control in micro-scale engines, sub-micron masks, heat transfer, water-collecting devices and systems.

Inspired by the birch bark, which has multilayered structures, we fabricated layer-by-layer (LbL) assembled montmorillonite (MMT) and poly(p-aminostyrene) (PPAS) nanocomposites on cotton fiber curved surfaces to provide protection from atomic oxygen (AO) erosion. The multilayer coated fibers had high flexibility, uniformity, defect free, ease of preparation and low cost. The AO erosion durability has been dramatically enhanced which was evidenced by testing in the ground-based AO effects simulation facility. And the dimension and surface morphologies of the fibers observed by SEM had few changes, indicating excellent AO erosion resistant ability of the coatings. These results provide us a new method to design fibrous materials exposed directly in low earth orbit environment.

A polyethylene oxide-b-polystyrene (PEO-b-PS) block copolymer incorporating UV-crosslinkable coumarin groups in the PS block self-assembled into a cylindrical structure with PEO cylinders perpendicular to the film surface, which exhibited excellent CO2 separation properties. The block copolymer was successfully synthesized by atom transfer radical polymerization (ATRP). The molecular characterization of the diblock copolymer was performed with 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The UV-crosslinking of the film was monitored by UV-vis absorption spectroscopy. The cylindrical phase structure was confirmed by transmission electron microscopy (TEM). Gas permeation properties of CO2, N2 and He were determined at different temperatures varying from 20 °C to 70 °C. Both the CO2 permeation flux and total gas selectivity increased with increasing temperature. The maximum of CO2 permeance at 70 °C was 20400 × 10−6 cm3 cm−2 s−1 cmHg−1, and gas selectivity over He and N2 was 20.1 and 27.7, respectively. It was concluded that the functional block units and self-assembled microphase structures synergetically played key roles in the high performance of the membrane.

Linear-brush poly(styrene)-b-poly[oligo(ethylene glycol) methyl ether methacrylate] (PS-b-POEGMA) block copolymer incorporating a UV-crosslinkable coumarin group in a PS block, self-assembled into a cylindrical structure with POEGMA cylinders perpendicular to the film surface, which exhibit excellent CO2 separation properties. The block copolymer was successfully synthesized by a combination of atom transfer radical polymerization (ATRP) and click chemistry. The molecular characterization of the diblock copolymer was performed with 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The cylindrical phase structure was confirmed by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The POEGMA amorphous phase was confirmed by differential scanning calorimeter (DSC). Gas permeation properties of CO2, N2 and He were determined around room temperature. Compared to the linear BCP, the total gas selectivity and especially CO2 permeation flux increased dramatically. The functional block units and self-assembled microphase structures synergetically played key roles in the high performance of the membrane.

A polyethylene oxide-b-polystyrene (PEO-b-PS) block copolymer incorporating UV-crosslinkable coumarin groups in the PS block self-assembled into a cylindrical structure with PEO cylinders perpendicular to the film surface, which exhibited excellent CO2 separation properties. The block copolymer was successfully synthesized by atom transfer radical polymerization (ATRP). The molecular characterization of the diblock copolymer was performed with 1H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). The UV-crosslinking of the film was monitored by UV-vis absorption spectroscopy. The cylindrical phase structure was confirmed by transmission electron microscopy (TEM). Gas permeation properties of CO2, N2 and He were determined at different temperatures varying from 20 °C to 70 °C. Both the CO2 permeation flux and total gas selectivity increased with increasing temperature. The maximum of CO2 permeance at 70 °C was 20400 × 10−6 cm3 cm−2 s−1 cmHg−1, and gas selectivity over He and N2 was 20.1 and 27.7, respectively. It was concluded that the functional block units and self-assembled microphase structures synergetically played key roles in the high performance of the membrane.