A fast (30 s) thermoresponse and rapid (30 min) self-healing were achieved by noncovalently incorporating a small fraction of poly(N-isopropylacrylamide) (PNI-PAM) nanogels (≤0.18 wt %) into a benzyl methacrylate-cooctadecyl methacrylate-co-methacrylic acid (BOMA-16) polymer matrix. The PNIPAM serves as the thermoresponsive component while the BOMA-16 provides self-healing via hydrophobic associations. The PNIPAM/BOMA-16 composite showed tunable lower critical solution temperature and up to 95% more visible light modulation (ΔT) than the same concentration of PNIPAM by itself. Conversely, the PNIPAM nanogels (≤0.18 wt %) served as reinforcements and increased the storage modulus of the PNIPAM/BOMA-16 hydrogel by up to 2.7 times relative to a BOMA-16 hydrogel. Using different analytical techniques, we show that the synergistic thermoresponsive light modulation is due to a hydrophilic−hydrophobic phase transition and clustering of the PNIPAM nanogels facilitated by the BOMA-16. The synergistic optical effect is also observed for mixtures of PNIPAM and other polyelectrolytes.

Self-healing hydrogels are attractive for a variety of applications including wound dressings and coatings. This paper describes the facile preparation and characterization of an autonomous self-healing hydrogel system comprising surfactant-free hydrophobic associations. The hydrogel comprised a copolymer of benzyl methacrylate (B), octadecyl methacrylate (O), and methacrylic acid (MA). The hydrogels were prepared via a controlled dehydration procedure to achieve the formation of strong intermolecular hydrophobic associations of the octadecyl groups above a critical polymer concentration. Fractured hydrogels healed within 30 min without any external intervention. Increasing hydrogel polymer content from 31 wt % to 39 wt % resulted in a threefold increase in the shear modulus and 50% reduction of the relaxation time. Addition of 4 mM NaCl to a hydrogel of 31 wt % polymer content resulted in 2.5 times longer relaxation time and 24% decrease in shear modulus. The hydrogels swelled up water by up to four times its weight, which corroborates the robustness of the hydrophobic association crosslinks. The bulk properties of the hydrogels are discussed in terms of the hydrophobic associations of the O-groups and the electrostatic interaction of the MA-groups in the polymer chains.

Processing of a high glass transition (Tg) polymer such as polyethersulfone (PES; Tg = 225°C) poses a challenge as it requires high processing temperatures or sometimes toxic solvents. In this work, we report of a facile process using superheated water (shH2O) and supercritical carbon dioxide (scCO2) co‐media. PES solids were foamed in the scCO2/shH2O co‐media or scCO2 alone in a batch process at different temperatures. The scCO2/shH2O produced a synergistic effect and achieved PES foams even at processing temperatures as low as 85°C below the nominal Tg; whereas, scCO2 alone required higher processing temperatures. Moreover, the scCO2/shH2O co‐media produced highly porous PES foams that were at least 23% higher in porosity than what was obtained using scCO2 alone. In addition, the scCO2/shH2O produced open cell foams at some processing conditions; whereas, scCO2 produced closed cell morphologies. Since both CO2 and H2O are innocuous, this approach has potential for use in the preparation of ultrafiltration membranes, which currently require the use of toxic solvents for their fabrication by way of the phase inversion process. Moreover, the use of scCO2/shH2O is a cost‐effective approach for the processing of high Tg polymers at significantly lower temperatures. POLYM. ENG. SCI., 58:1108–1114, 2018. © 2017 Society of Plastics Engineers

Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to study the dynamic layer-by-layer (LBL) growth of a sodium polyacrylate (NaPA)/poly(diallydimethylammonium) chloride (PDADMAC) multilayer on TiO2 particles. Molecular weights (Mw) used were 30 and 60 kDa for NaPA and 8.5 and 150 kDa for PDADMAC. IR spectra were recorded in situ as a function of time and were used to obtain the dynamic mass adsorbed and bound fraction of the polymers during each deposition step. For 30 kDa NaPA layers, the dynamics of adsorption show an initial rapid rise in mass followed by a slow increase toward a plateau value upon LBL with 150 kDa PDADMAC. In contrast, the 60 kDa NaPA layers achieve a plateau quickly and do not show a slow increase toward a plateau. In the case of LBL with 150 kDa PDADMAC, the dynamics of the bound fraction of polymer per layer suggest that polymer diffusion and conformational rearrangement occur for the layers of 30 kDa NaPA but not for the 60 kDa NaPA layers. Furthermore, PDADMAC adsorption profiles show that there is no diffusion of the PDADMAC layers and that PDADMAC flattens onto the underlying layer. A linear growth in the mass adsorbed per layer was observed for 150 kDa PDADMAC with both molecular weights of NaPA. In the case of 8.5 kDa PDADMAC, smaller growth increments and the desorption of underlying layers were observed. This work demonstrates the use of ATR-IR in obtaining the dynamics of LBL multilayer formation. Furthermore, it provides an example in which polymer diffusion during LBL film formation does not lead to exponential growth.

The effect of a calcium stearate (CaSt2) additive on the melt processability and flame retardancy of polyethersulfone (PES) was studied. Measurements of the viscosity of PES and its composites showed a marked decrease in viscosity with increase in the fraction of CaSt2 additive. About 40% reduction in viscosity of PES was achieved with addition of 5 wt % CaSt2. By decreasing the viscosity, the CaSt2 additive enabled the melt extrusion of PES at lower temperatures up to 90 °C below that of conventional melt processing. The flammability was also investigated using a Pyrolysis Combustion Flow Calorimeter (PCFC). The CaSt2 additive resulted in tremendous improvement in the flame retardancy of PES as evident in the reduction of the heat release capacity (HRC) of the composites by up to 37%. Moreover, the peak of heat release rate (pHRR) of PES in the composites was up to 84% lower than in the neat polymer. The remarkable improvement in flame retardancy of PES was demonstrated to be related to the rapid charring of the composites and the in situ formation of calcium carbonate/calcium oxide upon decomposition of CaSt2. The CaSt2 additive was also found to enhance the flame retardancy of thermoplastics including polyamide‐6 and polypropylene (PP). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43525.

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Unique and random wrinkle features are desired for applications, especially in anticounterfeiting. Multifunctional wrinkled materials as well as simple wrinkling methods are desired for more applications. In this study, free-standing wrinkle-patterned porous polymer films were prepared using a modified supercritical CO 2 foaming strategy. Spontaneous wrinkling was generated by applying moderate normal stress to the polymer films while foaming in situ. The wrinkle characteristics (wavelength and amplitude) were shown to be governed by the film thickness and the magnitude of the applied stress. Excessive (>5000 N) or no stress produced no obvious wrinkling or foaming whatsoever. Moreover, different morphologies of the wrinkles such as brain coral and herringbone patterns were achieved depending upon the shape of the mold used to apply the stress. Thus, the patterns show unique features for each batch process. Notwithstanding, geometric shape of the foamed wrinkle area is customizable. The reported wrinkling strategy offers the complementary advantage of patterning a foam in a polymer film and templating a PDMS stamp for different applications such as "mask-less" soft lithography, anticounterfeiting, pattern transfer, flexographic printing, and displays.

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