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pH-regulated release of antibiotics is achieved by conjugation with the hydrogel matrix through the reversible imine bond.

Stress-induced ion transport through three-layered hydrogels with different stiffnesses and ion selectivities enabled the efficient conversion of low-frequency mechanical vibrations into electricity.

열방성 고분자를 이용한 스마트 윈도우는 수용액 내에서의 상전이에 따른 광산란을 통해 태양광의 투광도를 조절할 수 있다. 주로 활용되었던 폴리(N-이소프로필아크릴아미드) 계열의 열방성 고분자는 고정된 상전이 온도(32 ℃)로 인해, 다양한 기후에 적용할 수 없다는 한계가 있다. 본 연구에서는 N-이소프로필 아크릴아마이드와 친수성 혹은 소수성 단량체와의 공중합을 통해 고분자의 화학적 조성과 상전이 온도와의 상관관계가 규명되었다. 소수성인 N,N"-디에틸아크릴아미드와의 공중합은 고분자와 용매인 물과의 상호작용을 약화시켜 상전이 온도를 낮추는 결과를 보였다. 반대로 친수성의 N-바이닐피롤리돈과의 공중합을 통해 강화된 고분자-용매의 상호작용은 상전이 온도를 상승시켰다. 상전이 온도는 공중합체의 조성에 따라 24-48 ℃ 구간 내에서 조절할 수 있었다. 합성된 공중합체를 이용하여 제작된 스마트 윈도우는 다양한 지역의 기후에 따라 맞춤형 작동이 가능함을 확인하였다.

Ionogels are crosslinked polymeric networks swollen in ionic liquids (ILs) with coupled cation–anion structures. Notably, ionogels are promising candidates for a wide range of applications owing to their biocompatibility, high electrical conductivity, mechanical durability, and chemical stability. The thermal behavior of ionogels can be tuned based on the chemical structure of the polymer network. However, the modification of the swelling behavior and thermo-responsiveness depending on the properties of the IL for a given polymer network has been rarely reported. To better understand the thermal behavior of ionogels based on the chemical structure of the ILs, in this study, a series of poly(N-isopropylacrylamide-co-N,N′-diethylacrylamide) ionogels were prepared and swollen in various ILs and their mixtures. By measuring the temperature-dependent swelling ratio change of the prepared ionogels, it was revealed that the chemical structure of the IL is the major factor governing their swelling and thermal behavior. Variations in the cationic and/or anionic structures led to changes in the transition temperature range and degree of volume change upon heating; this was owing to variations in the interactions between the IL and the polymer network. Furthermore, the volume phase transition of the ionogels could be finely tuned by adjusting the composition of the medium, which was controlled by the mixing of ILs.

Emerging organic solar cells based on a ternary strategy is one of the most effective methods for improving the blend film morphology, absorption ability, and device performances. On the other hand, this strategy has had very limited success in all-polymer solar cells (all-PSCs) because of the scarcity of new polymers and the challenges faced during third component optimization. Herein, highly efficient ternary all-PSCs were developed from siloxane-functionalized side chains with a wide-band-gap (

The development of stretchable strain sensors having high linearity and sensitivity, low hysteresis, and fast response to reliably monitor fast human motions is challenging. In this study, hydrogel-based strain sensors in the form of microfibers comprising tough double-network hydrogels or organogels and multi-walled carbon nanotubes (CNTs) are fabricated using aqueous microfluidic devices. Owing to the shear thinning effect on the microchannel, the CNTs can be aligned parallel to the flow direction, which increases the linearity of the sensor up to a strain of 400% and provides high durability over 50,000 strain cycles at 300% elongation. Owing to the negligible hysteresis, high resolution of 0.1%, and low response time of ∼30 ms, the strain sensors enable the quantitative conversion of the measured resistance change to the extent of stimulus and the simple detection of the motion. The developed sensors can be stably used to detect human motions in real time in both air and water. Furthermore, the developed material system demonstrates the potential for use in the fabrication of pressure sensors.

Antimicrobial function of Ag nanoparticles (NPs) has a strong correlation with the released Ag+ cations that are produced by oxidation of Ag NPs in a solution state under ambient condition. Therefore, in order to develop anti-infective materials for biomedical applications, one needs to include Ag NPs inside biocompatible materials, which can allow slow release of Ag+ cations. Hydrogels of natural polymers could be an ideal choice for the purpose because (a) the physicochemical properties of hydrogels resemble with biological tissue, and (b) the inclusion of Ag NPs inside hydrogels prevents the direct release of Ag NPs, while allowing the release of Ag+ cations out of the hydrogels. In this regard, we present a simple strategy for producing Ag NPs-containing hydrogel based on natural alginate polymers. The chemical modification of alginate, blending with Ag NPs, gelation by photo-crosslinking process have been discussed in connection with antimicrobial reaction on model bacterium.

End group engineering on the side chain of π-conjugated donor polymers is explored as an effective way to develop efficient photovoltaic devices. In this work, we designed and synthesized three new π-conjugated polymers (PBDT-BZ-1, PBDT-S-BZ, and PBDT-BZ-F) with terminal aryl end groups on the side chain of chlorine-substituted benzo[1,2

When the intensity of the incident light increases, the photocurrents of organic photodiodes (OPDs) exhibit relatively early saturation, due to which OPDs cannot easily detect objects against strong backlights, such as sunlight. In this study, this problem is addressed by introducing a light-intensity-dependent transition of the operation mode, such that the operation mode of the OPD autonomously changes to overcome early photocurrent saturation as the incident light intensity passes the threshold intensity. The photoactive layer is doped with a strategically designed and synthesized molecular switch, 1,2-bis-(2-methyl-5-(4-cyanobiphenyl)-3-thienyl)tetrafluorobenzene (DAB). The proposed OPD exhibits a typical OPD performance with an external quantum efficiency (EQE) of100% and a photomultiplication behavior with an EQE of100% under low-intensity and high-intensity light illuminations, respectively, thereby resulting in an extension of the photoresponse linearity to a light intensity of 434 mW cm

High-resolution 3D-printable hydrogels with high mechanical strength and biocompatibility are in great demand because of their potential applications in numerous fields. In this study, a material system comprising Pluronic F-127 dimethacrylate (FDMA) is developed to function as a direct ink writing (DIW) hydrogel for 3D printing. FDMA is a triblock copolymer that transforms into micelles at elevated temperatures. The transformation increases the viscosity of FDMA and preserves its structure during DIW 3D printing, whereupon the printed structure is solidified through photopolymerization. Because of this viscosity shift, various functionalities can be incorporated through the addition of other materials in the solution state. Acrylic acid is incorporated into the pregel solution to enhance the mechanical strength, because the carboxylate group of poly(acrylic acid) ionically crosslinks with Fe3+ , increasing the toughness of the DIW hydrogel 37 times to 2.46 MJ m-3 . Tough conductive hydrogels are also 3D printed by homogenizing poly(3,4-ethylenedioxythiophene) polystyrene sulfonate into the pregel solution. Furthermore, the FDMA platform developed herein uses DIW, which facilitates multicartridges 3D printing, and because all the materials included are biocompatible, the platform may be used to fabricate complex structures for biological applications.

High efficiency and nonhalogenated solvent processing are important issues for commercial application of all-polymer solar cells (all-PSCs). In this regard, we increased the photovoltaic performance of all-PSCs to a benchmark power conversion efficiency (PCE) of 11.66% by manipulating the pre-aggregation of a new π-conjugated polymer donor (Nap-SiBTz) using toluene as a solvent. This use of Nap-SiBTz enhanced the absorption coefficient (λmax = 9.30 × 104 cm-1), increased charge carrier mobility, suppressed trap-assisted recombination, improved bulk heterojunction morphology, and resulted in high PCEs of all-PSCs with an active layer thickness of 200 nm. To overcome severe charge recombination and energy losses, a 1-phenylnapthalene additive was used to achieve a well-ordered microstructure and molecular packing that inherently improved the device performances. The resulting encapsulation-free devices exhibited good ambient and thermal stabilities. The results of this study augur well for the future of the roll-to-roll production of all-PSCs.

For white light-emitting diode (LED) applications, semiconductor quantum dots (QDs) have been widely utilized as efficient down-converters to change the blue color of the light source into different emission colors. Because QDs offer spectral tunability over the entire visible light range, as well as improved color purity, they have rapidly replaced conventional phosphor-based white LEDs. However, for the sustainable growth of QD-mediated LEDs, the amount of QDs required must be reduced by enhancing the color-conversion efficiency. For this purpose, we prepared poly(lauryl methacrylate) (PLMA) composite films by the photo-crosslinking polymerization of lauryl methacrylate monomers in the presence of Au@Ag@SiO2 nanoparticles (NPs) and InP@ZnS QDs. In the PLMA composites, the Au@Ag NPs not only amplified the blue light source but also modified the relaxation of the excited QDs via localized surface plasmon resonance. This resulted in a maximum 12.9-fold enhancement in the QD fluorescence. Because the blue light source in this study can be easily replaced by blue LEDs, the enhanced efficiency of QD emissions via the plasmonic effect could potentially increase the performance of QDs for display applications.

Plasmonic superstructures composed of multiple metal nanoparticles (NPs) may represent an elegant example for hot-spot mediated surface-enhanced Raman scattering (SERS) enhancement. For sufficient SERS activity in the superstructures, the gap distance between adjacent NPs has to be engineered to be as small as possible, and often a sub-5 nm gap distance is necessary to create intensive hot spots. However, despite the recent advances in synthesis, the preparation of such plasmonic superstructures still requires laborious assembly, purification, and separation steps. In addition, the resulting plasmonic assemblies often undergo agglomeration and conformational change, which deteriorates the uniformity of the gap distance as well as SERS reproducibility. To overcome these issues, we utilized the self-segregating behavior of block copolymer micelles, and concomitantly functionalized the core and corona of micelles with different kinds of metal NPs. The prepared micellar NP assemblies structurally resembled colloidal core–satellite NP assemblies and exhibited strong SERS activity. However, unlike the initial expectation, the plasmonic coupling between dissimilar NPs was blocked in the micellar structure. Alternatively, we discovered that the local field inside the micellar NP assembly could be enormously amplified by multiple scattering processes, which significantly increased the path length of incident photons for SERS enhancement.

The development of multifunctional hydrogels with excellent stretchability and toughness is one of the most fascinating subjects in soft matter research. Numerous research efforts have focused on the design of new hydrogel systems with superior mechanical properties because of their potential applications in diverse fields. In this Minireview, we consider the most up-to-date mechanically strong hydrogels and summarize their design strategies based on the formation of double networks and dual physical crosslinking. Based on the synthetic approaches and different toughening mechanisms, double-network hydrogels can be further classified into three different categories, namely chemically crosslinked, hybrid physically-chemically crosslinked, and fully physically crosslinked. In addition to the above-mentioned methods, we also discuss few uniquely designed hydrogels with the intention of guiding the future development of these fascinating materials for superior mechanical performance.

The development of multifunctional hydrogels with high strength and stretchability is one of the most important topics in soft-matter research owing to their potential applications in various fields. In this work, a dual physically cross-linked network was designed for the fabrication of ultrastretchable tough hydrogels. The hydrogels were prepared through

Although substantial progress has been made at increasing power conversion efficiencies (PCEs) the field of ternary organic solar cells (TOSCs) during the past few years, choice of π-conjugated polymers that exhibit strong complementary spectra and achieve high photovoltaic parameters (open-circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), and PCE) simultaneously is limited. In this paper, TOSCs demonstrated a high PCE of 17.09% based on a π-conjugated polymer (named SiCl-BDT, bandgap ≈ 1.84 eV) as a third component (15 wt%) to the host binary system consisting of a PM7:Y7. The third component was used to achieve enhanced absorption coefficient (λmax = 5.5 × 104 cm−1) and more balanced charge carrier transport, frontier molecular orbital (FMO) energy levels, and blend miscibility, contributed to an improved FF of 70.38% and yielded an impressive Jsc of 27.37 mA/cm2 and Voc of 0.84 V. The PCE was higher than the host PM7:Y7 (15.13%) binary device. In addition, we found the photovoltaic performance of TOSCs could be further increased to a benchmark PCE of 17.40% using an interface engineering strategy. Thus, enables efficient charge transfer in TOSCs compared with that of without interlayer TOSCs, leading to high Jsc, Voc. The resulting encapsulation-free TOSCs showed excellent ambient and thermal stability. Accordingly, this work suggests that the use of a passivated electron transporting layer (ETL) and a π-conjugated polymer as a third component offers a promising means of overcoming the lower PCEs of OSCs.

Soft strain sensors have received considerable attention because of their promising applications in human motion detection, soft robotics, and smart clothing. Mechanically strong and highly conductive strain sensors with a wide working range, high linearity, and fast response are in high demand. To fulfill these requirements, in this study, we prepared mechanically tough and stretchable elastomer microfibers comprising natural rubber, poly (3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS), and multi-walled carbon nanotubes (CNTs) using a microfluidic device composed of coaxially aligned micro-capillaries. The strain sensors fabricated with these elastomer microfibers demonstrated high stretchability with a wide sensing range up to an elongation of 1275% and a high linearity of 1000%, with a very low response time of ~63 ms and a high resolution of 0.05%. The PEDOT:PSS functions as “bridges” to connect the CNTs, leading to the improved conductivity and linearity of the sensor. Furthermore, the strain sensor could be readily sewn on fabric and demonstrated excellent real-time detection of various human motions such as finger or elbow bending, walking, jumping, and phonation.

Photo-polymerization has been intensively studied for the preparation of hydrogels because of several attractive features, including independent spatial control with photomasks, mild reaction conditions, and a simple procedure. Benzophenone (BP) and its derivatives are representative photoactive materials for the crosslinking of polymer chains; however, the incorporation of BP in a polymer chain results in low solubility in water, low swelling ratio, and slow swelling kinetics of the hydrogels. In this work, we have synthesized photo-crosslinkable copolymers of grafted PNIPAm and a benzophenone moiety. We could fabricate the hydrogels by UV illumination of the synthesized copolymers, and found that the fabricated hydrogels showed enhanced swelling kinetics through free chains of comb-type copolymers. We also demonstrated volume changes of the 3D hydrogel triggered by temperature, suggesting that the prepared copolymers can be applied to the fabrication of stimuli-responsive and fast responding origami patterns, actuators, and so on.

To utilize water-responsive hydrogels in biomedical devices and soft robotics, hydrogels with high response speed and good mechanical properties are required. However, fabrication of such hydrogels remains challenging. In this study, a facile method for producing a one-dimensional (1D) hydrogel with water-responsive programmable deformations was developed. A tough hydrogel fiber with an interpenetrating polymer network based on a biopolymer was synthesized using a template-directed method. A 1D hydrogel that shrinks quickly in contact with water was fabricated by simply stretching and drying the hydrogel fiber under ambient conditions. The fabricated 1D hydrogel exhibited excellent mechanical properties, accurately controlled and programmable deformations, and an extraordinarily high degree of deformation with dimensional changes greater than 300%. Based on such 1D hydrogels, one-way soft actuators, which can be bent or can lift a weight when exposed to water, and a chemical sensing platform, which can detect ethanol in a water–ethanol mixture, were developed.

Ionogels are good candidates for flexible electronics owing to their excellent mechanical and electrical properties, including stretchability, high conductivity, and stability. In this study, conducting ionogels comprising a double network (DN) of poly(N-isopropylacrylamide-co-N,N'-diethylacrylamide)/chitosan which are further reinforced by the ionic and covalent crosslinking of the chitosan network by tripolyphosphate and glutaraldehyde, respectively, are prepared. Based on their excellent mechanical properties and high conductivity, the developed DN ionogels are envisioned as stretchable ionic conductors for extremely stretchable alternating-current electroluminescent (ACEL) devices. The ACEL device fabricated with the developed ionogel exhibits stable working operation under an ultrahigh elongation of over 1200% as well as severe mechanical deformations such as bending, rolling, and twisting. Furthermore, the developed ACEL devices also display stable luminescence over 1000 stretch/release cycles or at temperatures as harsh as 200 °C.

In order to achieve a hydrogel capable of programmable volume change, poly(N-isopropylacrylamide)-graft-methylcellulose hydrogel (PNIPAm-g-MC) was prepared through the grafting of PNIPAm onto a MC backbone and simultaneous cross-linking of the chains. PNIPAm-g-MC exhibited large thermal hysteresis in its volume change, which results from the stable hydrophobic junctions between the MC strands formed during heating. By combining photothermal magnetite nanoparticles as a heat transducer with the prepared hydrogel, programmable volume phase transition between the shrunken and swollen state could be triggered by visible light irradiation and excessive cooling, respectively. Based on this programmable feature, a bilayer actuator capable of static bending was fabricated. The developed programmable hydrogels are expected to provide a platform for the next generation of origami, microvalves, and drug delivery systems.

Hydrogels in the shape of double-walled microtubes possess great potential for development into artificial human blood vessels. In this work, we have prepared temperature-responsive tubular hydrogels with selectively controllable wall diameters, by using alginate templated photopolymerization in a triple channel microfluidic device. These tubular hydrogels mimic human blood vessels because of the separate thermally active inner and passive outer walls. The different behavior of each wall leads to the expansion of the hollow center volume with increasing temperature. This temperature-based control of the hollow center volume cannot be achieved in the case of conventional hydrogel microtubes. Furthermore, through this method, the hydrogels can be modified to achieve a controllable outer diameter while maintaining the hollow center dimensions simply by changing the position of the hydrogel walls. The ability to change the layer properties of the developed system indicates that the preparation of hydrogels with various monomers is possible.

Active switching glazings driven by electrical energy have been widely used for the on-demand control of the optical transmittance of smart windows; however, continuous electrical energy consumption is necessary to maintain the optical state. In this work, to minimize the energy consumption during operation of switchable windows, we have developed an optically bistable switching glazing based on the memory function in the volume change of the hydrogels. By grafting a multicomponent copolymer that has a chemical composition gradient of three different monomers onto the methyl cellulose backbone, the prepared hydrogel exhibits a smooth transition during heating and a large thermal hysteresis in the swelling behavior during cooling. On the basis of the novel thermal behavior of the triangular shape in volume phase transitions, an optically bistable window capable of retaining a switched state as well as stepwise activation, depending on the applied current, can be prepared. The developed bistable glazing is expected to provide energy-saving devices for on-demand solar control and variation in visibility.

The stress relaxation of ultrahigh molecular weight polyethylene (UHMWPE) gels in a broad composition range ( 0.025≤ϕP≤1.0) was studied within the framework of the reptation model. The molecular weight distribution (MWD) was determined at an optimum gel concentration ( ϕP=0.365) by regularization analysis of the stress relaxation data. The calculated relaxation moduli [ G(t)] by using MWD evaluated at a certain composition (UHMWPE gels, ϕP=0.365) were consistent with the experimental G(t) of other compositions in a broad range ( 0.218≤ϕP≤1.0). That is, the MWD (regularization method) was self-consistent within the framework of the reptation model. The composition dependence of the monomeric friction factor ( ζeff) of the UHMWPE gels was examined by use of the double reptation (DR) model with the determined MWD. The Ferry's free volume model of the molecular weight dependence of ζeff can be extended to the composition dependence of ζeff. In the low-concentration gels ( 0.025≤ϕP≤0.17), the experimental G(t)...

We fabricated transparent conductive gas barrier films by reducing graphene oxide (GO) coatings on polyethylene terephthalate (PET) films. GO solutions were cast on pure PET films, and the film surfaces were chemically reduced in a hydrazine hydrate solution. By measurement of the electrical conductivity of the films, the chemical reduction kinetics at the surface were examined as a function of reduction time, reductant concentration, and temperature. Based on these measurements, we determined the activation energy, 16 kcal mol−1, which corresponds to the barrier for the anchoring of the hydrazine either opposite to an epoxide ring or at a top site adjacent to a surface OH group. When the GO film was reduced to a carbon-to-oxygen (C/O) atomic ratio of 4.7, the electrical conductivity was 2.0 × 103 S m−1, with a light transmittance of 67% at 550 nm. We also revealed that the oxygen permeability of the film is a single exponential function of C/O atomic ratio. The reduced GO (rGO)/PET films exhibited an oxygen permeability of 7.97 × 10−8 Barrer (1 Barrer = 10−10 cm3 cm cm−2 s−1 cm Hg−1), providing optically transparent and electrically conductive polymer films for gas barrier applications.

Superstructures composed of diblock copolymer micelles and inorganic nanoparticles are quite interesting because the specific arrangement of inorganic nanoparticles within the micellar structure can reveal interesting opportunities in many field of science. In this perspective, we report a simple method to produce clustered assembly of Au nanoparticles in the micelles in attempt to induce plasmonic coupling among multiple Au nanoparticles in the assembled structures. Here, we utilized polystyrene-block-poly(acrylic acid), PS-PAA, micelles containing single Au nanoparticle in the core (Au@PS-PAA micelles) as building materials to initiate next-level assembling process. In particular, the addition of HCl to the solution of Au@PS-PAA micelles affected the overall equilibrium condition as well as kinetic process in the micellar solution. As a result, individual Au@PS-PAA micelles could be merged together to form more large micelles with inclusion of multiple nanoparticles in the core, the process of which was accompanied with plasmonic coupling of Au nanoparticles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44693.

Targeted drug delivery has long been extensively researched since drug delivery and release at the diseased site with minimum dosage realizes the effective therapy without adverse side effects. In this work, to achieve enhanced intracellular uptake of anticancer drug carriers for efficient chemo-therapy, we have designed targeted multifunctional anticancer drug carrier hydrogels. Temperature-responsive poly(N-isopropylacrylamide) (PNIPAm) hydrogel core containing superparamagnetic magnetite nanoparticles (MNP) were prepared using precipitation polymerization, and further polymerized with amine-functionalized copolymer shell to facilitate the conjugation of targeting ligand. Then, folic acid, specific targeting ligand for cervical cancer cell line (HeLa), was conjugated on the hydrogel surface, yielding the ligand conjugated hybrid hydrogels. We revealed that enhanced intracellular uptake by HeLa cells in vitro was enabled by both magnetic attraction and receptor-mediated endocytosis, which were contributed by MNP and folic acid, respectively. Furthermore, site-specific uptake of the developed carrier was confirmed by incubating with several other cell lines. Based on synergistically enhanced intracellular uptake, efficient cytotoxicity and apoptotic activity of HeLa cells incubated with anticancer drug loaded hybrid hydrogels were successfully achieved. The developed dual-targeted hybrid hydrogels are expected to provide a platform for the next generation intelligent drug delivery systems.