Surface Plasmons and Visible Light Iniferter Initiated Polymerization for Nanolocal Functionalization of Mesoporous Separation Layers

Although the technological relevance of mesoporous ceramic polymer hybrid materials is well accepted, missing functionalization concepts enabling 3D nanoscale local control of polymer placement into mesoporous materials, including thin films, and ideally using controlled polymerization techniques limit the application potential. Here, nanolocal functionalization of mesoporous separation layers using controlled, visible light iniferter initiated polymerization allowing responsive polymer functionalization locally limited to the irradiated spot is introduced. Thereby, two visible light sensitive iniferters, s-p-trimethoxysilylbenzyl-S´-dodecyltrithiocarbonate and 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, are developed for polymer functionalization of mesoporous films in a grafting from and a grafting through approach. 3D nanolocal polymer placement close to the proximity of the plasmonic field source is demonstrated by combining these visible light iniferter initiated polymerizations with optical near field modes, such as localized surface plasmon resonance (LSPR). As the location of the LSPR in mesoporous films can be controlled by placing metal alloy nanoparticles into these films and film thicknesses can be adjusted, this strategy is applied for precise positioning of polymers into mesoporous films with nanolocal control in three dimensions and thus reduces the gap in precision of functional group positioning between technological and biological nanopores.     

From Membrane to Skin: Aqueous Permeation Control Through Light‐Responsive Amphiphilic Polymer Co‐Networks

The functionalization of amphiphilic polymer co‐networks with light‐responsive spiropyran and spirooxazine derivatives leads to a new type of light‐responsive materials. The material consisting of hydrophilic nanochannels shows desirable properties such as light‐responsive permeability changes of aqueous caffeine solutions, an exceptional repeatability of the photochromism, and tunable basic permeability rates. The versatility of the system is demonstrated by using different functionalization routes such as copolymerization of light‐responsive monomers or crosslinker as well as postmodification of the preformed amphiphilic network. Moreover, light‐responsive spirobenzopyran and novel spirooxazine derivatives are synthesized, which changes the properties of the light‐responsive membranes after inclusion into the amphiphilic co‐networks. Finally, the permeability of the delivery membrane can be tailored to match the properties of porcine skin, an in vitro model of human neonatal skin. One possible application might be the use of the light‐responsive membranes as key‐unit of a transdermal caffeine‐delivery system for preterm neonates.     

Controlling Polymorphism in Poly(3‐Hexylthiophene) through Addition of Ferrocene for Enhanced Charge Mobilities in Thin‐Film Transistors

Crystalline organic molecules often exhibit the ability to assemble into multiple crystal structures depending on the processing conditions. Exploiting this polymorphism to optimize molecular orbital overlap between adjacent molecules in the unit lattice is an effective method for improving charge transport within the material. In this study, grazing incident X‐ray diffraction was employed to demonstrate the formation of tighter π‐π stacking poly(3‐hexylthiophene‐2,5‐diyl) polymorphs in films spin coated from ferrocene‐containing solutions. As a result, the addition of ferrocene to casting solutions yields thin‐film transistors which exhibit approximately three times higher source‐drain currents and charge mobilities than neat polymer devices. Nevertheless, XPS depth profiling and NMR analyses of the active layer reveal that all ferrocene is removed during the spin coating process, which may be an essential factor to achieve high mobilities. Such insights gleaned from ferrocene/poly(3‐hexylthiophene‐2,5‐diyl) mixtures can serve as a template for selection and optimization of other small molecule/polymer systems with greater baseline charge mobilities.     

Protein/Polymer‐Based Dual‐Responsive Gold Nanoparticles with pH‐Dependent Thermal Sensitivity

This article presents the synthesis and physicochemical behavior of dual‐responsive plasmonic nanoparticles with reversible optical properties based on protein‐coated gold nanoparticles grafted with thermosensitive polymer brushes by means of surface‐initiated atom transfer radical polymerization (SI‐ATRP) that exhibit pH‐dependent thermo‐responsive behavior. Spherical gold NPs of two different sizes (15 nm and 60 nm) and with different stabilizing agents (citrate and cetyltrimethylammonium bromide (CTAB), respectively) were first capped with bovine serum albumin (BSA). The resulting BSA‐capped NPs (Au@BSA NPs) exhibited not only extremely high colloidal stability under physiological conditions, but also a reversible U‐shaped pH‐responsive behavior, similar to pure BSA. The ?‐amine of the L‐lysine in the protein coating was then used to covalently bind an ATRP‐initiator, allowing for the SI‐ATRP of thermosensitive polymer brushes of oligo(ethylene glycol) methacrylates with an LCST of 42 °C in pure water and around 37 °C under physiological conditions. Such protein coated nanoparticles grafted with thermosensitive polymers exhibit a smart pH‐dependent thermosensitive behavior.     

pH‐Responsive Nanoporous Silica Colloidal Membranes

Free‐standing colloidal membranes (nanofrits) with varied thickness and nanopore size are fabricated and modified with pH‐responsive poly(2‐(dimethylamino)ethyl methacrylate) brushes. The polymer‐modified nanofrits demonstrate excellent gating behavior for molecular diffusion: in the presence of acid, the diffusion rate of positively charged species significantly decreases. Increasing the polymer length and membrane thickness and decreasing the nanopore size leads to the complete acid‐controlled gating of the membranes.     

Electrochemically Triggered Selective Adsorption of Biotemplated Nanoparticles on Self‐Assembled Organometallic Diblock Copolymer Thin Films

The controlled adsorption of the iron‐containing cage protein ferritin at the nanoscale using stimuli‐responsive self‐assembled diblock copolymer thin‐film templates is reported. The diblock copolymer used study consists of a cylinder‐forming polystyrene‐block‐polyferrocenylsilane (PS‐b‐PFS), with PFS as the minor block, and shows reversible redox properties. To prevent any spontaneous protein adsorption on either block, the electrolyte pH is selected to leave the ferritin negatively charged, and the protein concentration and solution ionic strength are carefully tuned. Selective adsorption of ferritin on the PFS domains of the self‐assembled thin films is then triggered in situ by applying a positive potential, simultaneously oxidizing the PFS and attracting the ferritin electrostatically.     

Noncovalent Polymer‐Gatekeeper in Mesoporous Silica Nanoparticles as a Targeted Drug Delivery Platform

Selective targeting of tumor cells and release of drug molecules inside the tumor microenvironment can reduce the adverse side effects of traditional chemotherapeutics because of the lower dosages required. This can be achieved by using stimuli‐responsive targeted drug delivery systems. In the present work, a robust and simple one‐pot route is developed to synthesize polymer‐gatekeeper mesoporous silica nanoparticles by noncovalent capping of the pores of drug‐loaded nanocontainers with disulfide cross‐linkable polymers. The method offers very high loading efficiency because chemical modification of the mesoporous nanoparticles is not required; thus, the large empty pore volume of pristine mesoporous silica nanoparticles is entirely available to encapsulate drug molecules. Furthermore, the polymer shell can be easily decorated with a targeting ligand for selective delivery to specific cancer cells by subsequent addition of the thiol‐containing ligand molecule. The drug molecules loaded in the nanocontainers can be released by the degradation of the polymer shell in the intracellular reducing microenvironment, which consequentially induces cell death.     

Colorimetric Logic Gates Based on Poly(2‐alkyl‐2‐oxazoline)‐Coated Gold Nanoparticles

A straightforward end‐capping strategy is applied to synthesize xanthate‐functional poly(2‐alkyl‐2‐oxazoline)s (PAOx) that enable gold nanoparticle functionalization by a direct “grafting to” approach with citrate‐stabilized gold nanoparticles (AuNPs). Owing to the presence of remaining citrate groups, the obtained PAOx@AuNPs exhibit dual stabilization by repulsive electrostatic and steric interactions giving access to water soluble molecular AND logic gates, wherein environmental temperature and ionic strength constitute the input signals, and the solution color the output signal. The temperature input value could be tuned by variation of the PAOx polymer composition, from 22 °C for poly(2‐ⁿpropyl‐2‐oxazoline)@AuNPs to 85 °C for poly(2‐ethyl‐2‐oxazoline)@AuNPs. Besides, advancing the fascinating field of molecular logic gates, the present research offers a facile strategy for the synthesis of PAOx@AuNPs of interest in fields spanning nanotechnology and biomedical sciences. In addition, the functionalization of PAOx with xanthate offers straightforward access to thiol‐functional PAOx of high interest in polymer science.     

Selenium‐Containing Polymer@Metal‐Organic Frameworks Nanocomposites as an Efficient Multiresponsive Drug Delivery System

The development of efficient multiresponsive drug delivery systems (DDSs) to control drug release has been widely explored. Herein, a facile strategy is reported that enables the micelles of the selenium‐containing polymer with the drug to be encapsulated in metal‐organic frameworks (MOFs), which serves as multiresponsive drug release by employing the selenium‐containing polymers with redox‐triggered property and the MOFs with pH‐triggered property in DDS. In this case, the micelles of selenium‐containing polymers, as core easily disassembles in the presence of redox agents, can then release the drug in MOFs matrixes. The ZIF‐8 (one type of MOFs) crystal frameworks serving as shell can collapse only under low pH conditions, and the drug can be further released. In the presence of external redox agents as well as the pH stimuli, the prepared nanocomposite (P@ZIF‐8) drug system exhibits the capability of multiresponsive release of the doxorubicin (DOX) and possesses good selectivity in releasing the DOX under low pH conditions instead of normal pH conditions. In addition, the merits of P@ZIF‐8 such as good biocompatibility, multiresponsive release properties, and especially the selective release properties under different pH conditions make the materials highly promising candidates for the realization of controlled drug delivery in tumor tissue systems.     

Switching Light Transmittance by Responsive Organometallic Poly(ionic liquid)s: Control by Cross Talk of Thermal and Redox Stimuli

A novel organometallic poly(ionic liquid) with both redox‐ and thermoresponsive properties is synthesized from a poly(ferrocenylsilane) (PFS) via a one‐step Strecker sulfite alkylation reaction by using tetraalkylphosphonium sulfite as an effective and versatile nucleophile. This dual‐responsive polymer is composed of a PFS backbone and quaternary phosphonium sulfonate side groups and exhibits a concentration‐dependent lower critical solution temperature (LCST)‐type phase transition in aqueous solution. Furthermore, the LCST‐type phase behavior of the polymer can be switched between the “off” state and “on” state by chemical or electrochemical oxidation and reduction on the ferrocene units in the polymer main chain. As a consequence, a classical LCST‐type phase transition, as well as an “isothermal” redox‐triggered phase transition can be induced by using thermal and electrochemical triggers without changing the composition of the system. On the basis of this dual responsiveness, a “smart window” device is fabricated. The optical characteristics of this device are completely unaltered after 100 thermal and/or redox cycles.     

Synthesis and Applications of Stimuli‐Responsive DNA‐Based Nano‐ and Micro‐Sized Capsules

Stimuli‐responsive, drug‐loaded, DNA‐based nano‐ and micro‐capsules attract scientific interest as signal‐triggered carriers for controlled drug release. The methods to construct the nano‐/micro‐capsules involve i) the layer‐by‐layer deposition of signal‐reconfigurable DNA shells on drug‐loaded microparticles acting as templates, followed by dissolution of the core templates; ii) the assembly of three‐dimensional capsules composed of reconfigurable DNA origami units; and iii) the synthesis of stimuli‐responsive drug‐loaded capsules stabilized by DNA?polymer hydrogels. Triggers to unlock the nano‐/micro‐capsules include enzymes, pH, light, aptamer?ligand complexes, and redox agents. The capsules are loaded with fluorescent polymers, metal nanoparticles, proteins or semiconductor quantum dots as drug models, with anti‐cancer drugs, e.g., doxorubicin, or with antibodies inhibiting cellular networks or enzymes over‐expressed in cancer cells. The mechanisms for unlocking the nano‐/micro‐capsules and releasing the drugs are discussed, and the applications of the stimuli‐responsive nano‐/micro‐capsules as sense‐and‐treat systems are addressed. The scientific challenges and future perspectives of nano‐capsules and micro‐capsules in nanomedicine are highlighted.     

Halogen Bonding versus Hydrogen Bonding in Driving Self‐Assembly and Performance of Light‐Responsive Supramolecular Polymers

Halogen bonding is arguably the least exploited among the many non‐covalent interactions used in dictating molecular self‐assembly. However, its directionality renders it unique compared to ubiquitous hydrogen bonding. Here, the role of this directionality in controlling the performance of light‐responsive supramolecular polymers is highlighted. In particular, it is shown that light‐induced surface patterning, a unique phenomenon occurring in azobenzene‐containing polymers, is more efficient in halogen‐bonded polymer–azobenzene complexes than in the analogous hydrogen‐bonded complexes. A systematic study is performed on a series of azo dyes containing different halogen or hydrogen bonding donor moieties, complexed to poly(4‐vinylpyridine) backbone. Through single‐atom substitution of the bond‐donor, control of both the strength and the nature of the noncovalent interaction between the azobenzene units and the polymer backbone is achieved. Importantly, such substitution does not significantly alter the electronic properties of the azobenzene units, hence providing us with unique tools in studying the structure–performance relationships in the light‐induced surface deformation process. The results represent the first demonstration of light‐responsive halogen‐bonded polymer systems and also highlight the remarkable potential of halogen bonding in fundamental studies of photoresponsive azobenzene‐containing polymers.     

Functional Polymer Brushes on Diamond as a Platform for Immobilization and Electrical Wiring of Biomolecules

For the biofunctionalization of electronic devices, polymer brushes can provide a route which allows combining the advantages of other commonly used approaches, such as immobilization of functional biomolecules via self assembled monolayers or coated polymer matrices: high stability and loading capacity, efficient electron transport, and excellent biocompatibility. In the work presented here, poly(methacrylic acid) brushes are prepared by self‐initiated photografting and photopolymerization on diamond electrodes. In this straightforward process no prior grafting of initiators is required since the initiation of the polymerization can be conveniently controlled by the hydrogen or oxygen termination of the diamond surface. Boron doped nanocrystalline diamond as an electrode material provides extreme chemical inertness and stability, inherent biocompatibility, and superior electrochemical properties, such as the large accessible potential window and low background currents. As a proof of concept we demonstrate the amperometric detection of glucose by polymer brushes covalently modified with the redox enzyme glucose oxidase and aminomethyl ferrocene as electron mediator. Characterization by X‐ray photoelectron spectroscopy and atomic force microscopy both indicate a high loading of the ferrocene mediator. Consistently, electrochemical cyclic voltammetry shows a multilayer equivalent loading of ferrocene and highly efficient electron transfer throughout the polymer film. Overall, functionalized polymer brushes can provide a promising platform for the immobilization and electrical wiring of biomolecules for bioelectronic and biosensing applications.     

Surface Imprinting in Layer‐by‐Layer Nanostructured Films

In this Full Paper, we develop a novel approach for the generation of stable molecularly imprinted sites in polymeric films by combining the layer‐by‐layer (LbL) technique and photochemical crosslinking of the layered structure. After photo‐crosslinking, the imprinted films show high reproducibility and rapid loading and unloading of imprinted sites by the template molecules. Moreover, the competitive adsorption of template molecules and redox labels into the imprinted film using electrochemical methods indicates that the imprinted film has higher affinity for template molecules. We believe this approach may have some advantages over traditional ways of preparing imprinted sites in polymer matrices and it may open a new avenue for the functionalization of LbL films.     

Alkoxy‐Functionalized Thienyl‐Vinylene Polymers for Field‐Effect Transistors and All‐Polymer Solar Cells

π‐conjugated polymers based on the electron‐neutral alkoxy‐functionalized thienyl‐vinylene (TVTOEt) building‐block co‐polymerized, with either BDT (benzodithiophene) or T2 (dithiophene) donor blocks, or NDI (naphthalenediimide) as an acceptor block, are synthesized and characterized. The effect of BDT and NDI substituents (alkyl vs alkoxy or linear vs branched) on the polymer performance in organic thin film transistors (OTFTs) and all‐polymer organic photovoltaic (OPV) cells is reported. Co‐monomer selection and backbone functionalization substantially modifies the polymer MO energies, thin film morphology, and charge transport properties, as indicated by electrochemistry, optical spectroscopy, X‐ray diffraction, AFM, DFT calculations, and TFT response. When polymer P7 is used as an OPV acceptor with PTB7 as a donor, the corresponding blend yields TFTs with ambipolar mobilities of μ_e = 5.1 × 10^?3 cm² V^–1 s^–1 and μ_h = 3.9 × 10^?3 cm² V^–1 s^–1 in ambient, among the highest mobilities reported to date for all‐polymer bulk heterojunction TFTs, and all‐polymer solar cells with a power conversion efficiency (PCE) of 1.70%, the highest reported PCE to date for an NDI‐polymer acceptor system. The stable transport characteristics in ambient and promising solar cell performance make NDI‐type materials promising acceptors for all‐polymer solar cell applications.     

Self‐Assembled Dense Colloidal Cu2Te Nanodisk Networks in P3HT Thin Films with Enhanced Photocurrent

The integration of colloidal nanocrystals with polymers adds optoelectronic functionalities to flexible and mechanically robust organic films. In particular, self‐assembled structures of nanocrystals in polymers can act as functional components enhancing, for instance, transport or optical properties of the hybrid material. This study presents Cu₂Te hexagonal nanodisks that assemble into ribbons with a face‐to‐face configuration in poly(3‐hexylthiophene‐2,5‐diyl) through a controlled solvent evaporation process. The ribbons form weaving patterns that create 3D networks fully embedded in the thin polymer film at high nanodisk concentration. The photoresponse of these composite films measured in a layered vertical geometry demonstrates increased photocurrent with increasing nanocrystal loading. This study attributes this behavior to the presence of networks of Cu₂Te nanodisks that form a bulk heterojunction with the semiconducting polymer, which improves exciton dissociation and the overall photoelectric response.     

Highly Scalable,Closed‐Loop Synthesis of Drug‐Loaded,Layer‐by‐Layer Nanoparticles

Layer‐by‐layer (LbL) self‐assembly is a versatile technique from which multi­component and stimuli‐responsive nanoscale drug‐carriers can be constructed. Despite the benefits of LbL assembly, the conventional synthetic approach for fabricating LbL nanoparticles requires numerous purification steps that limit scale, yield, efficiency, and potential for clinical translation. In this report, a generalizable method for increasing throughput with LbL assembly is described by using highly scalable, closed‐loop diafiltration to manage intermediate purification steps. This method facilitates highly controlled fabrication of diverse nanoscale LbL formulations smaller than 150 nm composed from solid‐polymer, mesoporous silica, and liposomal vesicles. The technique allows for the deposition of a broad range of polyelectrolytes that included native polysaccharides, linear polypeptides, and synthetic polymers. The cytotoxicity, shelf life, and long‐term storage of LbL nanoparticles produced using this approach are explored. It is found that LbL coated systems can be reliably and rapidly produced: specifically, LbL‐modified liposomes could be lyophilized, stored at room temperature, and reconstituted without compromising drug encapsulation or particle stability, thereby facilitating large scale applications. Overall, this report describes an accessible approach that significantly improves the throughput of nanoscale LbL drug‐carriers that show low toxicity and are amenable to clinically relevant storage conditions.     

Systematic Control of Nucleation Density in Poly(3‐Hexylthiophene) Thin Films

While molecular ordering via crystallization is responsible for many of the impressive optoelectronic properties of thin‐film semiconducting polymer devices, crystalline morphology and its crucial influence on performance remains poorly controlled and is usually studied as a passive result of the conditions imposed by film deposition parameters. A method for systematic control over crystalline morphology in conjugated polymer thin films by very precise control of nucleation density and crystal growth conditions is presented. A precast poly(3‐hexylthiophene) film is first swollen into a solution‐like state in well‐defined vapor pressures of a good solvent, while the physical state of the polymer chains is monitored using in situ UV–vis spectroscopy and ellipsometry. Nucleation density is selected by a controlled deswelling of the film or by a self‐seeding approach using undissolved crystalline aggregates that remain in the swollen film. Nucleation densities ranging successively over many orders of magnitude are achieved, extending into the regime of spherulitic domains 10 to 100 μm in diameter, a length scale highly relevant for typical probes of macroscopic charge transport such as field‐effect transistors. This method is presented as a tool for future systematic study of the structure‐function relation in semicrystalline semiconducting polymers in a broad range of applications.     

Combinatorial Study of Temperature‐Dependent Nanostructure and Electrical Conduction of Polymer Semiconductors: Even Bimodal Orientation Can Enhance 3D Charge Transport

Temperature‐dependent (80–350 K) charge transport in polymer semiconductor thin films is studied in parallel with in situ X‐ray structural characterization at equivalent temperatures. The study is conducted on a pair of isoindigo‐based polymers containing the same π‐conjugated backbone with different side chains: one with siloxane‐terminated side chains (PII2T‐Si) and the other with branched alkyl‐terminated side chains (PII2T‐Ref). The different chemical moiety in the side chain results in a completely different film morphology. PII2T‐Si films show domains of both edge‐on and face‐on orientations (bimodal orientation) while PII2T‐Ref films show domains of edge‐on orientation (unimodal orientation). Electrical transport properties of this pair of polymers are also distinctive, especially at high temperatures (>230 K). Smaller activation energy (E _A) and larger pre‐exponential factor (μ ₀) in the mobility‐temperature Arrhenius relation are obtained for PII2T‐Si films when compared to those for PII2T‐Ref films. The results indicate that the more effective transport pathway is formed for PII2T‐Si films than for the other, despite the bimodally oriented film structure. The closer π–π packing distance, the longer coherence length of the molecular ordering, and the smaller disorder of the transport energy states for PII2T‐Si films altogether support the conduction to occur more effectively through a system with both edge‐on and face on orientations of the conjugated molecules. Reminding the 3D nature of conduction in polymer semiconductor, our results suggest that the engineering rules for advanced polymer semiconductors should not simply focus on obtaining films with conjugated backbone in edge‐on orientation only. Instead, the engineering should also encounter the contribution of the inevitable off‐directional transport process to attain effective transport from polymer thin films.     

Chain Extension of Stimuli‐Responsive Polymer Brushes: A General Strategy to Overcome the Drawbacks of the “Grafting‐To” Approach

Stimuli‐responsive polymer brushes are smart materials for the design of bio‐interactive and responsive interfaces. The “grafting‐to” approach is a convenient preparation procedure that allows the modification of surfaces with preformed and most notably well‐defined functionalized macromolecules. However, the shortcoming of this approach is an intrinsic limitation of the grafting density, which in turn affects the stimuli‐responsive properties of the brush system. Here, a general strategy to overcome this limitation and to simultaneously improve the switching behavior of a temperature‐responsive poly(N‐isopropylacrylamide) (PNiPAAm) brush is reported. A technically simple processing step is used in combination with the thermal azide–alkyne cycloaddition to perform the chain extension of alkyne‐functionalized PNiPAAm brushes with azide‐functionalized PNiPAAm molecules.