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A simple strategy is provided to construct novel supramolecular hydrogels with both self-healing and shape memory properties. Starting from achieving self-healable hydrogel based on the dynamic interactions of phenylboronic acid modified sodium alginate (Alg-PBA) and poly(vinyl alcohol) (PVA), further formation of a complex of alginate with Ca(2+) renders this hydrogel with the capability of shape memory at the macro-/microscopic scales.

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Thermoresponsive hydrogel actuators have attracted tremendous interest due to their promising applications in artificial muscles, soft robotics, and flexible electronics. However, most of these materials are based on polymers with lower critical solution temperature (LCST), while those from upper critical solution temperature (UCST) are rare. Herein, we report a multiple-responsive UCST hydrogel actuator based on the complex of poly­(acrylic acid) (PAAc) and poly­(acrylamide) (PAAm). By applying a heterogeneous photopolymerization, a bilayer hydrogel was obtained, including a layer of the interpenetrating network (IPN) of PAAm/PAAc and a layer of a single network of PAAm. When cooled down below the UCST, the PAAm/PAAc layer contracted due to the hydrogen bonding of the two polymers while the PAAm layer stays in swelling state, driving the hydrogel to curl. By adjusting the composition of the two layers, the amplitude of actuation behavior could be regulated. By creating patterned IPN domains with photomasks, the hydrogel could deform into complex two-dimensional (2D) and three-dimensional (3D) shapes. An active motion was realized in both water and oil bath, thanks to the internal water exchange between the two layers. Interestingly, the hydrogel actuator is also responsive to urea and salts (Na2SO4, NaCl, NaSCN), due to that the strength of the hydrogen bonds in the IPN changes with the additives. Overall, the current study realized an anisotropic UCST transition by introducing asymmetrically distributed polymer–polymer hydrogen bonds, which would inspire new inventions of intelligent materials.

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In this work, we investigated the structure and morphology formation in crystalline–crystalline diblock copolymer of poly(l-lactide)-block-poly(ethylene glycol) (PLLA-b-PEG) on different length scales with optical microscopy (OM), atomic force microscopy (AFM), synchrotron time-resolved small-angle X-ray scattering (TR-SAXS) and wide-angle X-ray scattering (WAXS) methods. The PLLA-b-PEG copolymer with 5000 of number-average of molecular weight of PLLA and PEG blocks was used in this work. The structure and morphology of PLLA-b-PEG copolymers were formatted by a two-step crystallization process: i.e., the PLLA block crystallized fully at 110 °C in the first step, and then the PEG block crystallized fully at 30 °C in the second step. The OM, AFM, and SAXS results indicated that the PEG block crystallized in the multilength scales amorphous regions confined by PLLA crystals. The PEG block crystallized not only in the interlamellar regions of PLLA crystals, but also in the interfibrillar regions of PLLA. However, the subsequent crystallization of PEG block did not alter the foregoing spherulitic morphology of PLLA on the micrometer scale.

We have systematically investigated the effect of alcohols (ethanol, propanol, butanol, and pentanol) on the structure of the water/AOT/IPM system using conductivity, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) techniques. The results show that no percolation phenomenon is observed in the water/AOT/IPM system, whereas the addition of ethanol (propanol and butanol) induces apparently percolation. The threshold water content (W(p)) depends closely on the alcohol type and concentration. The effect of alcohols on the conductance behavior is discussed from the physical properties of alcohols, the interfacial flexibility, and the attractive interactions between droplets. The hydrodynamic diameter of droplets (d(H)) obtained from DLS increases markedly with the increase in water content (W(0)); however, it decreases gradually with increasing alcohol chain length and concentration. SAXS measurements display distinctly the shoulder, the low hump peaks, and the heavy tail phenomenon in the pair distance distribution function p(r) profile, which rely strongly on the alcohol species and its concentration. The gyration radius (R(g)) increases with increasing W(0), and decreases with the increase of alcohol chain length and concentration. Schematic diagram of the conductance mechanism of water/AOT/IPM/alcohol systems is primarily depicted. Three different phases of the discrete droplets, the oligomers, and the isolated ellipsoidal droplets existed in the different W(0) ranges correspond to three different stages in the conductivity-W(0) curve. Coupling the structure characteristics of reverse micelles obtained from DLS and SAXS techniques with conductivity could be greatly helpful to deeply understand the percolation mechanism of water/AOT/IPM/alcohols systems.

Poly(acrylic acid) is water soluble but can be converted into a thermoresponsive polymer possessing an upper critical solution temperature (UCST) by copolymerizing with acrylonitrile. The copolymers showed a UCST in water under ambient conditions, driven by the combined effect of hydrogen bonding between the carboxylic acid groups and hydrophobic interaction among the acrylonitrile moieties. The cloud point of the copolymers can be tuned by changing the copolymer composition, concentration, pH, and ionic strength of the solution. The dynamic light scattering results indicate that the amphiphilic copolymer chains are solubilized in the form of micelles through interchain hydrophobic interaction and the micelles may also form small aggregates through hydrogen bonding at temperatures below the UCST. This work demonstrates a new strategy for the design of thermoresponsive polymers from comonomers that are not known to produce thermoresponsive polymers but can be made into such polymers through the synergetic effect of different interactions that contribute to the enthalpic and entropic changes of mixing in the aqueous systems.