Bioinspired Dual Stimuli-Responsive Membranous System with Multiple On-Off Gates

Polymerization within Nanoporous Anodized Alumina Oxide Templates (AAO): A Critical Survey

In the last few years, the polymerization of monomers within the nanocavities of porous materials has been thoroughly studied and developed, allowing for the synthesis of polymers with tailored morphologies, chemical architectures and functionalities. This is thus a subject of paramount scientific and technological relevance, which, however, has not previously been analyzed from a general perspective. The present overview reports the state of the art on polymerization reactions in spatial confinement within porous materials, focusing on the use of anodized aluminum oxide (AAO) templates. It includes the description of the AAO templates used as nanoreactors. The polymerization reactions are categorized based on the polymerization mechanism. Amongst others, this includes electrochemical polymerization, free radical polymerization, step polymerization and atom transfer radical polymerization (ATRP). For each polymerization mechanism, a further subdivision is made based on the nature of the monomer used. Other aspects of "in situ" polymerization reactions in restricted AAO geometries include: conversion monitoring, kinetic studies, modeling and polymer characterization. In addition to the description of the polymerization process itself, the use of polymer materials derived from polymerization in AAO templates in nanotechnology applications, is also highlighted. Finally, the review is concluded with a general discussion outlining the challenges that remain in the field.

The toolbox of porous anodic aluminum oxide–based nanocomposites: from preparation to application

Anodic aluminum oxide (AAO) templates have been intensively investigated during the past decades and have meanwhile been widely applied through both sacrificial and non-sacrificial pathways. In numerous non-sacrificial applications, the AAO membrane is maintained as part of the obtained composite materials; hence, the template structure and topography determine to a great extent the potential applications. Through-hole isotropic AAO features nanochannels that promote transfer of matter, while anisotropic AAO with barrier layer exhibits nanocavities suitable as independent and homogenous containers. By combining the two kinds of AAO membranes with diverse organic and inorganic materials through physical interactions or chemical bonds, AAO composites are designed and applied in versatile fields such as catalysis, drug release platform, separation membrane, optical appliances, sensors, cell culture, energy, and electronic devices. Therefore, within this review, a perspective on exhilarating prospect for complementary advancement on AAO composites both in preparation and application is provided.

100th Anniversary of Macromolecular Science Viewpoint: Integrated Membrane Systems

Membranes fabricated from self-assembled materials are one recent example of how polymer science has been leveraged to advance membrane technology. Due to their well-defined nanostructures, the performance of membranes made from these materials is pushing the boundaries of size-selective filtration. Still, there remains a need for higher performance and more selective membranes. The advent of functional membrane platforms that rely on mechanisms beyond steric hindrance (e.g., charge-selective membranes and membrane sorbents) is one approach to realize improved solute-solute selectivity and further advance membrane technology. To date, the lab-scale demonstration of these platforms has often relied on fabrication schemes that require extended processing times. However, in order to translate lab-scale demonstrations to larger-scale implementation, it is critical that the rate of the functionalization scheme is reconciled with membrane manufacturing rates. In this viewpoint, it is postulated that substrates lined by reactive moieties that are amenable to postfabrication modification would enable the production of membranes with controlled nanostructures while providing access to a diverse array of pore wall chemistries. A comparison of reaction and manufacturing rates suggests that mechanisms that exhibit second-order reaction rate constants of at least 1 M^-1 s^-1 are needed for roll-to-roll processing. Furthermore, for mechanisms that exhibit rate constants greater than 300 M^-1 s^-1, it may be possible to integrate multiple functional domains over the membrane surface such that useful properties emerge. These multifunctional systems can expand the capabilities of membranes when the patterned chemistries interact at the heterojunctions between domains (e.g., Janus and charge-patterned mosaic membranes) or if they exhibit cooperative responses to external operating conditions (e.g., membrane pumps).

A monolithic anti-freezing hydro/organo Janus actuator with sensitivity to the polarity of solvents

A monolithic anti-freezing hydro/organo Janus actuator which was synthesized by a one-step interfacial copolymerization shows various deformation patterns with solvent polarity.

Ferrocene-Modified Block Copolymers for the Preparation of Smart Porous Membranes

The design of artificially generated channels featuring distinct remote-switchable functionalities is of critical importance for separation, transport control, and water filtration applications. Here, we focus on the preparation of block copolymers (BCPs) consisting of polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) having molar masses in the range of 91 to 124 kg mol-1 with a PHEMA content of 13 to 21 mol %. The BCPs can be conveniently functionalized with redox-active ferrocene moieties by a postmodification protocol for the hydrophilic PHEMA segments. Up to 66 mol % of the hydroxyl functionalities can be efficiently modified with the reversibly redox-responsive units. For the first time, the ferrocene-containing BCPs are shown to form nanoporous integral asymmetric membranes by self-assembly and application of the non-solvent-induced phase separation (SNIPS) process. Open porous structures are evidenced by scanning electron microscopy (SEM) and water flux measurements, while efficient redox-switching capabilities are investigated after chemical oxidation of the ferrocene moieties. As a result, the porous membranes reveal a tremendously increased polarity after oxidation as reflected by contact angle measurements. Additionally, the initial water flux of the ferrocene-containing membranes decreased after oxidizing the ferrocene moieties because of oxidation-induced pore swelling of the membrane.

Facile Fabrication of Composite Membranes with Dual Thermo- and pH-Responsive Characteristics

Facile fabrication of novel functional membranes with excellent dual thermo- and pH-responsive characteristics has been achieved by simply designing dual-layer composite membranes. pH-Responsive poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers and polystyrene blended with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) nanogels are respectively used to construct the top layer and bottom layer of composite membranes. The stretching/coiling conformation changes of the P4VP chains around the pK_a (∼3.5-4.5) provide the composite membranes with extraordinary pH-responsive characteristics, and the volume phase transitions of PNIPAM nanogels at the pore/matrix interfaces in the bottom layer around the volume phase transition temperature (VPTT, ∼33 °C) provide the composite membranes with great thermoresponsive characteristics. The microstructures, permeability performances, and dual stimuli-responsive characteristics can be well tuned by adjusting the content of PNIPAM nanogels and the thickness of the PS-b-P4VP top layer. The water fluxes of the composite membranes can be changed in order of magnitude by changing the environment temperature and pH, and the dual thermo- and pH-responsive permeation performances of the composite membranes are satisfactorily reversible and reproducible. The membrane fabrication strategy in this work provides valuable guidance for further development of dual stimuli-responsive membranes or even multi stimuli-responsive membranes.

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ever increasing set of computational and simulation tools that allow understanding and predictions of these surface-grafted polymer architectures. The aim of this contribution is to provide a comprehensive review that critically assesses recent advances in the field and highlights the opportunities and challenges for future work.

Functional micelles formed from glucose-, thermo- and pH-triple responsive copolymers for controlled release

Spherical micelles self-assembled from the block copolymer PPBDEMA-b-PDMAEMA presented glucose, thermo- and pH-triple responsive properties.