Sequential surface chemical reactions of poly(acrylic acid-co-N-isopropylacrylamide) [poly(AAc-co-NIPAAm)] with AAc contents of 5, 10, and 15 mol %, of which carboxyl groups were previously activated by 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDC), plus poly(vinylamine hydrochloride) through amide linkages produced ultrathin films on a solid substrate. Assembly processes were quantitatively monitored by a quartz crystal microbalance as substrates. Assembled amounts increased with decreasing both AAc and EDC amounts. Subsequent immersion of ultrathin films into aqueous media resulted in the thickness increases, producing ultrathin hydrogels. Swelling ratios were estimated by percent increases in the thickness and increased with increasing AAc and EDC amounts. Swelling ratios were regularly changed by varying the ionic strength and pH of aqueous media. Swelling properties were interpreted on the basis of structural information on ultrathin hydrogels. Cyclic voltammetries using potassium ferricyanide revealed that ions permeated ultrathin hydrogels, and permeabilities were clearly suppressed above a lower critical solution temperature (LCST) of polyNIPAAm. Reversible on−off changes in permeabilities below and above a LCST were potentially observed. Not only structural control but also stimuli responsive functions of ultrathin hydrogels were realized within the present study.

We demonstrate the successful preparation of stable liquid marbles from various liquids. This is accomplished by using low-surface-energy poly[2-(perfluorooctyl)ethyl acrylate] (PFA-C(8)) as microparticles. The PFA-C(8) microparticles were prepared by the spontaneous self-organized microparticulation of PFA-C(8). The physical properties remained intact in the polymer morphology as confirmed by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) measurements. The extremely low surface energy of PFA-C(8) provides a high solid-liquid spreading coefficient (S(S/L)) value for various combinations of liquids. As a result, liquid marbles were obtained from various liquids, unlike the case with other fluorine polymer particles such as poly(tetrafluoroethylene) (PTFE) and poly(vinilydene fluoride) (PVDF). These results suggest that the technique is widely applicable for preparing novel functional materials.

Adhesives composed of synthetic and low-cost molecules that are based on simple chemical principles are attractive because of their versatility. In this article, we report adhesion between two planar substrates coated with layer-by-layer (LbL) assembled films of cationic poly(diallyldimethylammonium chloride) (PDDA) and anionic poly(sodium styrenesulfonate) (PSS) and perform lap shear measurements of the adhered substrates. Films prepared on the substrates functioned as adhesives when one substrate coated with the PDDA-surface film contacted the other surface coated with the PSS-surface film under adequate pressure in the presence of water droplets, suggesting that two films adhered on the basis of polyion complex formation. Observations suggested that the adhesives failed at the substrate-film interface rather than at the bulk films. The adhesion was compared between film-coated substrates and noncoated ones. Confocal laser scanning microscopic observation of adhesives composed of fluorescently labeled poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) revealed that the labeled PAH assembled on one substrate was well dispersed, even in a nonlabeled film assembled on another substrate. It was therefore confirmed that after adhesion in the presence of the water component, the polyelectrolytes became intermixed between the glassy films, resulting in changes in the adhesive structure at the substrate-film interface.

To develop stimuli-responsive ultrathin polymer films on a solid substrate, a novel photo-cross-linkable polymer with both temperature- and pH-responsive properties was prepared. The photoreactive 4-aminobenzophenone (BP) was introduced onto the side groups of poly(N-isopropylaclylamide-co-2-carboxyisopropylaclylamide) [poly(NIPAAm-co-CIPAAm)]. This copolymer was designed for highly random sequences of comonomers. After the formation of spin-coated polymer films on a solid substrate, UV-light irradiation started the cross-linking reaction. The spin-coating processes and stability of the polymer films were quantitatively monitored by a quartz crystal microbalance (QCM), and the thickness was estimated using an atomic force microscope (AFM). These measurements confirmed the formation of a very plain polymer film, and the film thickness was precisely controlled by the concentration of the polymer solution used for spin coating. Moreover, the obtained films showed a high stability due to the cross-liking reaction and UV irradiation. Cyclic voltammetry using potassium ferricyanide revealed that the ions could permeate the photo-cross-linked ultrathin polymer films. The permeability of the ultrathin hydrogel films was dramatically changed by varying the pH and temperature of the aqueous media. These observations suggest that the preparation of isopropylacrylamide-based stimuli-responsive ultrathin hydrogel films is possible.

In this paper, we describe here the first room temperature π‐conjugated liquid based on N‐heteroacene framework showing a fluorescent property. This π‐conjugated liquid N‐heteroacene molecule is composed of branched‐long alkoxy chains and thiophene moieties. Also, N‐heteroacene‐based liquid itself can function as a stimuli‐responsive photofunctional material unlike room temperature π‐conjugated liquids reported previously. When a coated film prepared from this liquid was exposed to HCl vapor, an adsorption of HCl molecules occurred accompanied to the change in color of film from yellow to deep yellow. Moreover, emission colors of a coated film markedly changed from blue to yellow. This result indicates that this π‐conjugated liquid N‐heteroacene can function as stimuli‐responsive functional material.

A novel stimuli-responsive room-temperature photoluminescent liquid 1 based on the N-heteroacene framework is developed and analyzed by several experiments such as differential scanning calorimetry, X-ray diffraction, dynamic viscoelasticity measurement, in situ observation by optical and polarized optical microscopes, UV–vis absorption and fluorescence spectroscopy, and by theoretical methods such as ab initio calculation and molecular dynamics (MD) computer simulation techniques. In contrast to stimuli-responsive solid materials reported previously, liquid 1 in response to HCl vapor as a single stimulus can involve dramatically multiple changes in physical properties such as rheological behavior, morphology, as well as photoluminescence. The present ab initio calculation and microsecond-timescale MD simulations reveal that the complexation of 1 and HCl molecules induces a large dipole moment, leading to the formation of stacking structures because of their dipole–dipole interaction. Upon exposure to HCl vapor, in situ microscopic observation of the stimuli-responsive liquid elucidates a self-assembling process involving the formation of the wrinkle structure in a micrometer scale, indicating disorder–order phase transition. Further exposure of 1 to HCl vapor from seconds to hours has an influence on the macroscopic physical properties such as viscosity, viscoelasticity, and photoluminescent colors. The synergy between the experimental and theoretical investigations opens a new strategy to develop a novel class of stimuli-responsive materials showing multiple changes in physical properties.

A liquid marble was prepared from bio-based poly(lactic acid) [PLA] microparticles and water droplets.Solvent vapor exposure to the liquid marble changed the morphology of the granular PLA microparticle shell layer to a film-like shell layer even though the spherical shape of the liquid marble is retained. The morphological changes suppressed the evaporation of the water within the liquid marble by a factor of six compared with a liquid marble without the solvent vapor treatment. The compression test revealed that the mechanical stability of the solvent-treated liquid marble was changed due to the increased rigidity of the shell structure. Solvent vapor exposure is a simple but effective way to fabricate a robust liquid marble with long-term stability.

Construction of the interpenetrating polymer network (IPN) in hydrogels has received increased attention because it not only improves their mechanical properties but also mimics the extracellular matrix, which can be used as cell culturing scaffolds for tissue engineering. Usually, IPN gels are prepared using separated procedures, in which primal networks, followed by other networks, are formed by adding chemical reagents or subjecting to external stimuli. Herein, we designed a one-pot and in situ gelation system, which involved strategic selection of precursors for constructing IPN gels by simply mixing them. This design involved two types of gelation processes: RADA16 peptide self-assembling and covalent bond formation between chitosan (CH) and N-hydroxysuccinimide ester-terminated poly­(ethylene glycol) (NHS–PEG–NHS). The gelation kinetics suggested that RADA16 peptide networks were formed independently, followed by the formation of CH/PEG networks in the mixture containing the three components. Culturing chondrocytes in CH/PEG/RADA16 demonstrated that construction of the IPN structure promoted the embedded chondrocyte properties for the formation of the articular cartilage. Moreover, lower inflammation and higher protein production were observed in mice implanted with CH/PEG/RADA16-containing chondrocytes than in those with clinically used atelocollagen gel, appealing the feasibility of the proposed IPN hydrogel design for use as cell culturing scaffolds in tissue regeneration.