Longcheng Gao

Temperature Controlled Water/Oil Wettability of a Surface Fabricated by a Block Copolymer: Application as a Dual Water/Oil On–Off Switch

A temperature controlled dual water/oil on-off switch is achieved by using a PMMA-b-PNIPAAm block-copolymer coated mesh, determined by the conformational change of the PNIPAAm chain around the lower critical solution temperature (LCST) and also the cooperation between PNIPAAm and PMMA. Water can permeate through the BCP-coated mesh, and oil cannot below the LCST, whereas oil can and water cannot above the LCST.

Temperature-triggered directional motion of tiny water droplets on bioinspired fibers in humidity

We designed a kind of smart bioinspired fiber using the N-isopropylacrylamide (NIPAAm) polymer, with roughness and curvature features similar to those of wetted spider silk. The motion of tiny water droplets can be manipulated reversibly in directions by the effective cooperation of multi-gradients such as roughness, curvature and temperature-responsive wettability.

Olfactory Sensory Neuron-Mimetic CO2 Activated Nanofluidic Diode with Fast Response Rate

DOI: 10.1002/adma.201405564 The CO 2 -activated nanofl uidic devices were constructed on an ion-track-etched [ 12 ] conically shaped nanopores (Figure S1, Supporting Information) in poly(ethylene terephthalate) (PET) membranes through a “grafting-from” method (More details in the Supporting Information). Atom transfer radical polymerization (ATRP) initiator was immobilized covalently with carboxylic groups on the nanopores surface. Then, imidazolecontaining monomer, 1-(4-vinylbenzyl)-1H-imidazole (VBI), was graft-polymerized through ATRP method ( Figure 2 a, some details in the Supporting Information). X-ray photoelectron spectroscopy (XPS) technique was applied to monitor the modifi cation. As shown in Figure S2 (Supporting Information), the XPS spectrum of primary PET exhibits only O1s and C1s signals. When grafted with poly[1-(4-vinylbenzyl)-1H-imidazole] (PVBI), the N1s signal appears, indicating successful PVBIgrafting (Figure S3, Supporting Information). The membrane surface properties before and after modifi cation were studied by contact angle (CA) measurements. The results show that obvious changes of the surface wettability occur. The water CA of the primary membrane is ≈35°, and increases to ≈90° after PVBI modifi cation (Figure 2 b). The ion current through the nanopores was measured in KCl solution (0.1 M ) under a scanning transmembrane electrical potential from −2 to +2 V. [ 13 ] The experiments were carried out at room temperature in fresh air (ca. 400 ppm). Ion current is ca. 61.14 nA at 2 V, ca. −108.29 nA at −2 V. When immobilized with PVBI, ion current decreases obviously to 3.10 nA at 2 V, ca. −3.15 nA at −2 V (Figure 2 c). The nanochannels turn to be a closed state. The I – V curves testify that PVBI is successfully incorporated on the nanochannels surface, as we will discuss later. The imidazole group in the PVBI can be protonated in CO 2 solution. [ 14 ] The major variation occurs in the narrow part of the pore, where the effects of the surface charge are higher, increasing the ionic transport property and the ion current. Therefore, the closed state of PVBI-grafted nanochannels is to be opened by CO 2 . After bubbling CO 2 in the solution, the transmembrane ion current increases to 300 nA ( Figure 3 a). Meanwhile, CO 2 induces surface charge change from neutral to positive and the anions pass preferentially from the tip to the base of the nanochannels due to the asymmetric conical shape, while cations are rejected, which show their ionic transport preference in one direction and determine the direction of the ion rectifi cation. Thereby, the current prefers to fl ow from the base to the tip, which is opposite to the direction of anions (Figure S4, Supporting Information). The nanochannels rectifi es the current, and the ion rectifi cation ratio (the ratio of absolute values of currents at a given voltage 2 vs −2 V) reaches as high as ≈23 (Figure 3 b). Meanwhile, the ions are not free to transport through the nanochannels with anion selectivity. The CO 2 is an important environmental stimulus that regulates many organisms’ behaviors, e.g., fi nding mates, seeking food or hosts, and avoiding predators. [ 1 ] A subset of olfactory sensory neurons (OSNs) is considered to be specialized for sensing CO 2 [ 2 ] The CO 2 response threshold of OSNs in mice is at nearatmospheric concentration of ≈0.066%. [ 3 ] This ability enables the mice to run away from the high concentration CO 2 places, avoiding unconsciousness or even death. [ 4 ] Ion channels, embedded in the cell membranes of OSNs, play crucial roles in the CO 2 -activated signaling transduction. CO 2 is fi rstly enzymecatalyzed into bicarbonate ions by carbonic anhydrase II (CAII). Then the product bicarbonate ions directly activates guanylyl cyclase-D and cyclic nucleotide-gated ion channels are opened to allow cation infl ux into the cells, resulting in neuronal depolarization to fi re bursts of action potentials. [ 3 ]

Layer by layer assembly of heparin/layered double hydroxide completely renewable ultrathin films with enhanced strength and blood compatibility

Renewable nacre-like heparin (HEP)/layered double hydroxide (LDH) ultrathin films were first fabricated via a bottom-up layer by layer (LBL) deposition technique, which simultaneously showed largely enhanced mechanical properties and good blood compatibility. The results of UV-vis, FTIR, XRD and SEM analysis indicate that the HEP/LDH ultrathin films stacked densely together to form a well-defined brick-and-mortar structure. A strong electrostatic and hydrogen bond network at the organic–inorganic interface allowed the modulus of the film reach ca. 23 GPa, which was remarkably enhanced compared to previously reported polymer–LDH hybrid films. Due to the interlamellar heparin, the (HEP/LDH)n film may prove to be beneficial for new medical applications or as a replacement for conventional petroleum based plastics.

CO2-selective free-standing membrane by self-assembly of a UV-crosslinkable diblock copolymer

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.

Photo-controlled water gathering on bio-inspired fibers

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.

Nacre-inspired green artificial bionanocomposite films from the layerby-layer assembly of montmorillonite and chitosan

The simple LBL technique was introduced to fabricate green nacre-like chatosan/montmorillonite (CHI/MMT) films. The results of SEM and XRD analysis demonstrate that the produced CHI/MMT composites films stacked densely together to bring out well-defined nacre-like brick-mortar structure. The nanoindentation technique is used to characterize the mechanical properties of the layered nanocomposite films, which show enhanced mechanical modulus (up to ∼6.64 GPa) compared with the pure chitosan.

pH-Sensitive Wettability Induced by Topological and Chemical Transition on the Self Assembled Surface of Block Copolymer

AbstractpH-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.

High flux CO2 transporting nanochannel fabricated by the self-assembly of a linear-brush block copolymer

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 facile strategy for the synthesis of block copolymers bearing an acid-cleavable junction

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.