Volume 48 Issue 4, April 2016

Nature-inspired material design concepts and recent progress on anti-fouling polymer materials are reviewed, and our recent researches on anti-fouling studies with polymer brushes are summarized. Zwitterionic polyelectrolyte brush immobilized surfaces represent significant anti-fouling for bio-macromolecules, oil foulants, marine fouling organisms and pipeline foulants. The anti-fouling mechanism was considered on the basis of the wetting, lubrication, hydrated chain dimension and hydrogen-bonding structure of hydrated water in the polyelectrolyte brushes.

Various cross-linkable poly(styrene-random-methyl methacrylate) (P(S-r-MMA)) that can neutralize substrates are reviewed. Four efficient cross-linkable random copolymers incorporated with benzocyclobutene (BCB), glycidyl methacrylate (GMA), azide and ketene functional groups can be used to prepare a thin, cross-linked neutral layer. On this cross-linked layer, polystyrene-block-poly(methyl methacrylate) (P(S-b-MMA)), thin films produce microdomains oriented perpendicular to the substrate, confirming the effective neutralization of the substrate to both PS and PMMA blocks.

This focused review describes how surface properties can be manipulated by combining surface-initiated atom transfer radical polymerization (SI ATRP) and the very-large-scale integration (VLSI) lithography process. These fabricated surfaces with solvent-responsive or bio-inert/bioactive are applied to VOC sensors and non-biofouling/cell-growing surfaces. We also discussed the functionalization of renewable resources and how SI ATRP is extended to the applications of high-performance adsorbents.

Three approaches for directly reacting chemical agents and polymer chains with multi-walled CNTs (MWCNTs) are presented, including (i) sequential atom transfer radical addition/polymerization to MWCNTs; (ii) ozone-mediated addition reaction to MWCNTs; and (iii) Diels–Alder reaction-mediated MWCNT functionalization. On the basis of the reaction routes, the scopes and functions of MWCNT-based nanohybrids and nanocomposites have been extended.

The recent advances of AIE polymers, including structural design, synthetic approaches and practical applications have been summarized. A series of functional nonconjugated or conjugated AIE linear polymers with AIEgens on the side chains or main chains, and star-shaped or hyperbranched AIE polymers with AIEgens on the core or terminal parts are introduced. Their performances in a series of practical applications such as fluorescent sensors, stimuli-responsive materials, biological applications, porous materials and circularly polarized luminescence are updated.

This review tests you for survival in modern science and technology.Q1: Can we operate molecular machines by our hands?Ans: YES (Hand-Operating Nanotechnology)!Q2: Can we mechanically control life and bio-events?Ans: YES (Mechanobiology)!Q3: What comes after nanotechnology?Ans: It is definitely Nanoarchitectonics.

A mixture of the micellar dispersions of linear PLLA–PEO–PLLA and linear PDLA–PEO–PDLA block copolymers formed a gel upon heating, whereas a mixture of the cyclic counterparts did not undergo this phase transition. These results suggest that the gelation behavior is directed by the topology of the polymer components. Furthermore, cyclic PLLA–PEO and cyclic PDLA–PEO block copolymers incorporating photocleavable o-nitrobenzyl units were synthesized. A mixture of the micellar dispersions of these block copolymers formed a gel upon ultraviolet (UV) irradiation via the ‘topological conversion’.

The orientation behavior and domain spacing relaxation of the phase-separated structure of poly(methyl methacrylate-b-n-butyl acrylate) thin films were investigated by grazing-incidence small-angle X-ray scattering (GISAXS). Moreover, low-energy GISAXS was performed for the in-depth profiling of the lamellar structure. The domain spacing (D_||) relaxation took longer than the orientation of the lamellae. Furthermore, the D_|| in the vicinity of the surface was greater than inside the film, which indicates that the D_|| near the surface relaxed faster than inside due to the higher mobility of the polymer chain.

Three types of bottom surface layers (BSLs-A, B, C) with different surface properties and a top-coat (TC-A) were applied to investigate perpendicular orientation control of PMMA-b-PMAPOSS domains in the thin films with thermal annealing. The combination of BSL-A and TC-A yielded perpendicular cylinders after annealing at 180 °C for 60 min, whereas the other combinations produced parallel cylinders. Water contact angles and surface free energies (SFEs) of the BSLs were evaluated for the perpendicular orientation. It was found that the SFEs were more effectual indicators than the water contact angles.

The interfacial dynamics of the segment of poly(methyl methacrylate) (PMMA) terminated with elemental blocks containing polyhedral oligomeric silsesquioxane (POSS), namely PPMP (PMAPOSS-b-PMMA-b-PMAPOSS), was much slower than that of the conventional PMMA. The number of platelets adhered to the PPMP film was dependent on the pre-immersion time in phosphate-buffered saline before the platelet seeding, and these results could be explained in terms of the aggregation states of water at the interface.

The wrapping abilities of comb-like polymers with pendant conjugated fluorine moieties and their tunable electrical properties of SWNTs were discussed. It is found that longer side-chain-conjugated fluorene segments in homopolymer (P(St-Fl)₃₀₀, 7) can strongly bind to the SWNTs surfaces through π–π interaction and its copolymer (P2VP₇₉-co-P(St-Fl)₃₄₇, 5a) lead to predominant dispersion of SWNTs due to the flexibility of P2VP for further increasing the solubility. Thus, SWNTs wrapped by 5a after thermal annealing can be selected as a gate electrode, whereas the spin-coated SWNTs wrapped by 7 can be as a semiconductor for the FET channel, resulting in a mobility of 0.82 cm² V⁻¹s⁻¹, a threshold voltage of 0.35 V and an ON/OFF ratio of 2.8 × 10⁴.

We synthesized a series of poly(N-isopropylacrylamide)-based ionic hydrogels with dicationic ionic liquid crosslinking structures. The obtained ionic hydrogels showed typical feature of poly(ionic liquid) in aqueous solutions, of which the quaternized imidazolium moieties could interfacially interact with anionic dyes, such as methyl orange (MO), methyl blue (MB), congo red (CR), orange G (OG), thymol blue (TB) and bromothymol blue (BTB), which were strongly dependent on the chemical structures of the dyes.

The chemosensor-filter based on novel multifunctional fluorescent electrospun (ES) nanofibers exhibiting high sensitivity for various metal ions were prepared from binary blends poly(HEMA-co-NMA) and bpy-F-bpy by using a single-capillary spinneret. It shows apparent color change from blue (blank) to green, to blue-green and to be fluorescence quenching when detecting Zn²⁺, Hg²⁺ and Cu²⁺, respectively, and high reversibility. A microfluidics system study indicated that these nanofibers can be used as ‘naked eye’ sensors for sensing various metal ions and as efficient multifunctional chemosensor-filtering devices.

Distribution of end of polymer in the filler-filled material is simulated using self-consistent field method. In our simulation results, the segregation of ends of polymer can be found at the interface of filler, though the depletion region of ends is also existed around the region in the distance of Rg from filler. Sizes and shape of filler are affected to the segregation of ends of polymer, and in the cases of smaller or spherical fillers, the density of ends of polymer near the interface of filler increases. These results can be explained by the entropic effect of polymer chain ends. The segregation of ends contributes to the stabilization of interface of filler adding the entropic part of free energy.

Pore formation on the liposome resulted from the photo-cross-linking reaction between DC_8,9PCs, which is a photo-polymerizable lipid, is only observed when the saturated lipids comprise of the hosting matrix. To understand the influence of the hosting matrix, the Langmuir monolayer is employed because the system is capable of precisely controlling the packing state and the compositions of the film. The kinetics of reaction is found to strongly depend on the packing state of the film, and the cross-distance between DC_8,9PCs plays a key role for the polymerization reaction to proceed.

A unique methodology to control the morphology and ion transport properties of block copolymer electrolytes by the inclusion of functional terminal groups.

Surfaces of cyclo-olefin polymers (COP) are photoactivated by vacuum ultraviolet (VUV) light and can be bonded with a practical bonding strength at low temperatures below T_g. We investigated the mechanism of the low-temperature bonding of COP by nanofractography using high-resolution scanning electron microscopy. It was indicated that the interfaces were fractured via pull out of the polymer chains connected at the interface by hydrogen bonding.

We demonstrate that nonvolatile memory devices can be prepared using layer-by-layer-assembled nanocomposite films, and additionally that their memory performance can be easily enhanced by an additional insertion of charge trap elements (that is, graphene oxide nanosheets) within the films. These devices exhibited memory performance with a high ON/OFF current ratio of ~10⁴.

The poly(pentafluorophenyl acrylate) thin film provides a reactive surface platform through facile post-modification with primary alkyl amines. We report the effect of the most important parameters in this reaction, molecular weight of the reactive polymers and the aliphatic chain length of primary amines, on the degree of exchange of the thin films. The studies with neutron reflectivity and quartz crystal microbalance offer physical backgrounds for developing versatile functional thin films based on this chemistry, in terms of penetration and exchange kinetics as a function of molecular weight of reactive ester polymers and primary amines.

Cross-linked nanocellular polymer films: water- and oil-repellent anti-reflection coating. We applied the block copolymer template assisted with supercritical carbon dioxide method to poly(methyl methacrylate-r-glycidylmethacrylate)-b-poly(perfluorooctylethyl methacrylate) (PMGMA-PFMA) to fabricate cross-linkable nanocellular thin films. The nanocellular thin films showed a very low refractive index, low reflection as an AR coating as well as good chemical robustness by chemical cross-linkage of the glycidyl groups. In addition, the film surface provides water- and oil-repellent properties due to hydrophobic and oleophobic fluorine-containing PFMA.

Autophobic dewetting of polymer melts was characterized by well-defined polystyrene (PS) melt droplets that dewetted chemically identical brushes upon thermal annealing. The contact angle (θ) of PS droplets on the brushes and interfacial tension (γ_m/b) between the PS melts and brushes significantly increased as the chain length of PS brushes decreased and grafting density increased. The super autophobicity of the PS melt at the extremely short and dense PS brush was evaluated when the γ_m/b increasingly converges on the maximum interfacial tension (γ*_m/b).

We demonstrated the controlled incorporation of Au nanoparticle grafted with polystyrene (PS) molecules in the helical microdomains of ABC-type linear triblock terpolymers composed of PS, polyisoprene (PI) and poly(methyl methacrylate) (PMMA). The Au nanoparticles grafted with three PSs with different molecular weights were synthesized and incorporated into the terpolymer films. The morphologies of composite films and localization of Au nanoparticles were three-dimensionally characterized with transmission electron microtomography observation. By varying the molecular weights of grafted PS molecules on Au nanoparticles, their assemblies were successfully controlled in the double-helical microdomains.

A series of n-type D–A terpolymers (P(NDI2HD-T-S)) with various thiophene (T) and selenophene (S) compositions (T/S=100/0, 80/20, 50/50, 20/80 and 0/100) was successfully synthesized. To understand the effects of the T/S ratios, we studied their influence on the optical, electrical and structural properties. The insertion of more S content in the polymer backbone induced the enhanced structural ordering and electron mobility. Therefore, the all-polymer solar cells based on PTB7:P(NDI2HD-T-S) blend had greatly improved efficiency as the S content increased.

We prepared bisphenol A (BPA)-imprinted polypeptide gel layers by chemical cross-linking of β-cyclodextrin-modified poly(L-lysine) (CD-PLL) on quartz crystal microbalance (QCM) sensor chips and investigated their molecular recognition behaviors using QCM. This paper focuses on the preparation and molecular recognition capacity of the BPA-imprinted CD-PLL gel layers on QCM sensor chips with polyterthiophene film formed via electropolymerization.

Interface manipulation to pursue unusual nanostructures was performed using a strategically designed triblock terpolymer with a short middle segment, poly(styrene-b-methyl methacrylate-b-2,2,2-trifluoroethyl methacrylate). A short middle segment of poly(methyl methacrylate) (PMMA) that does not form any distinct domains was found to play an important role in manipulating the interface between the polystyrene (PS) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) domains and forming unconventional partially continuous oblate cylinders with an oblique lattice, as confirmed by small angle X-ray scattering (SAXS) and dual-axis transmission electron microtomography (TEMT).

Artificial sheet-like nanocelluloses composed of cellulose oligomers with the cellulose II allomorph were synthesized by phosphorylase-catalyzed enzymatic reactions, and their hydrolytic activities against ester substrates were characterized. The as-prepared nanocelluloses exhibited relatively low hydrolytic activities. However, distorted and smaller nanocelluloses with larger surface areas, which were prepared by sonication-based mechanical treatment of the as-prepared nanocelluloses, exhibited significantly greater hydrolytic activities.

Drug loading and release abilities of freestanding films made of polyion complexes of chondroitin sulfate C and chitosan were examined using dye molecules such as methylene blue and carboxyfluorescein. The dye-loading films were prepared using pre- and post-loading methods. Microscopic film morphologies were not affected by the dye loadings. The mechanical strengths of the dye-loaded films were almost identical to those of the unloaded films. The dye release behaviors of the films in various aqueous solutions were examined, and the results demonstrated that the films exhibited media-responsive dye release abilities.

A series of poly(ethylene glycol) methyl ether methacrylate (PEGMA) hydrogels have been prepared. The smaller the monomer molecular weight, the higher the crosslinking degree, the lower the hydration. Protein adsorption and bacteria/blood cell attachment tests unveil that PEGMA₅₀₀ hydrogel presents a suitable structure to minimize biofouling. A higher molecular weight of monomers is associated to a higher hydrophilicity, but excess of free water facilitates foulant diffusion. Low molecular weight of monomer does not permit to achieve hydration level good enough to form a protective layer against fouling.