The crystallization behaviors of n-hexacontane (C60H122)/Stöber silica (SiO2) composites with various compositions were investigated by a combination of differential scanning calorimetry (DSC), solid-state 13C nuclear magnetic resonance (solid-state 13C NMR), and proton NMR relaxation experiments. By means of DSC, C60H122 molecules in C60H122/silica composites were observed to be involved in the interfacial freezing not present in the free bulk C60H122. The orientation of C60H122 molecules, being preferentially normal to silica surface, was confirmed by grazing incidence X-ray diffraction experiments on thin n-hexacontane film adsorbed on the silicon wafer with a native SiO2 layer. Inferred from the solid 13C NMR data, the interfacial monolayer is in orthorhombic phase with certain chain disorders. It is speculated that the “interfacial freezing” of C60H122 formed in the presence of silica particles is driven by the combination of the strong attraction between the molecules and the enhanced number of interfacial molecules on the silica surface.

ABSTRACTThe confinement effects introduced by nanoparticles have been reported to influence the phase behaviors thus the properties of polymer nanocomposites. In this study, molecular dynamics and crystallization behaviors of polyethylene (PE) composited with three types of silica (SiO2) nanoparticles, namely unmodified SiO2, hydrophobically modified SiO2, SiO2-APTES (3-aminopropyltriethoxysilane) and SiO2-PTES (n-propyltriethoxysilane), were systematically investigated via a combination of DSC, XRD and 1H solid-state NMR measurements. The suppressions in crystallization and chain mobilities of PE rank in the order of unmodified SiO2 < SiO2-APTES < SiO2-PTES due to the increasing interfacial interactions between PE and SiO2 nanoparticles. Additionally, independent of polymer–nanoparticle interactions, a silica network forms for all three kinds of nanocomposites when SiO2 content reaches 83 wt %. The mobilities of polymer chains are severely restricted by such a percolated network structure, leading to a turning point in the crystallization ability of nanocomposites and a new crystallization peak at 45 °C lower than that of pure PE. The synergetic effects of interfacial interactions and filler network on polymer crystallization have been thoroughly studied in this work, which will provide guidance on modifying and designing nanocomposites with controlled properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 498–505

•HA nanoparticles were in situ synthesized via electrophoresis method.•Bilayered hydrogels were obtained by controlling the time of the electrophoresis process.•The bilayered hydrogels showed gradient mechanical strength.•The two regions of the bilayered hydrogels showed different osteoblast cell adhesion properties.Bilayered poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogels with anisotropic and gradient mechanical properties were prepared by the combination of directional freezing-thawing (DFT) and electrophoresis method. Firstly, PVA hydrogels with aligned channel structure were prepared by the DFT method. Then, HA nanoparticles were in situ synthesized within the PVA hydrogels via electrophoresis. By controlling the time of the electrophoresis process, a bilayered gradient hydrogel containing HA particles in only half of the gel region was obtained. The PVA/HA composite hydrogel exhibited gradient mechanical strength depending on the distance to the cathode. The gradient initial tensile modulus ranging from 0.18 MPa to 0.27 MPa and the gradient initial compressive modulus from 0.33 MPa to 0.51 MPa were achieved. The binding strength of the two regions was relatively high and no apparent internal stress or defect was observed at the boundary. The two regions of the bilayered hydrogel also showed different osteoblast cell adhesion properties.

•Mechanical properties of native thermoresponsive PNIPAM hydrogels are discussed.•Strategies to improve the mechanical properties are comprehensively appraised.•These include interpenetrating polymer network, nanocomposite and copolymerization.•Few applications of enhanced strength PNIMPAM based hydrogels are highlighted.•Future areas of research in PNIPAM hydrogel are mentioned.Materials which adjust their properties in response to environmental factors such as temperature, pH and ionic strength are rapidly evolving and known as smart materials. Hydrogels formed by smart polymers have various applications. Among the smart polymers, thermoresponsive polymer poly(N-isopropylacrylamide)(PNIPAM) is very important because of its well defined structure and property specially its temperature response is closed to human body and can be finetuned as well. Mechanical properties are critical for the performance of stimuli responsive hydrogels in diverse applications. However, native PNIPAM hydrogels are very fragile and hardly useful for any practical purpose. Intense researches have been done in recent decade to enhance the mechanical features of PNIPAM hydrogel. In this review, several strategies including interpenetrating polymer network (IPN), double network (DN), nanocomposite (NC) and slide ring (SR) hydrogels are discussed in the context of PNIPAM hydrogel.

The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state 13C nuclear magnetic resonance (VT solid-state 13C NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C18 molecules involve two phase transitions unknown from the bulk C18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles’ surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WAXD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C18.

•A semi-interpenetrating network hydrogel based on a natural polymer and synthetic polymer is prepared by a simple one-pot method.•The hydrogels show excellent self-healing ability at ambient temperature without the need for any stimulus or healing agent.•The healed gels exhibit high tensile strengths and high elongations.A novel self-healing semi-interpenetrating network hydrogel based on a natural polymer (konjac glucomannan, KGM) and synthetic polymer (polyacrylamide, PAAm) is prepared by a simple one-pot synthesis method. The hydrogels show excellent self-healing ability at ambient temperature without the need for any stimulus or healing agent and high recovery degrees (up to 73% tensile strength) can be achieved at a prolonged healing time. The healed gels exhibit high tensile strength (up to 66 kPa) and high elongation (up to 1200%). And the effect of the NH3·H2O content, the ratio of KGM to acrylamide (AAm) and the cross-linker content on the self-healing efficiency have been investigated. The combination of structural transition of PAAm and the intermolecular hydrogen bonding is essential for self-healing property of the hydrogels.

A novel physically linked double-network (DN) hydrogel based on natural polymer konjac glucomannan (KGM) and synthetic polymer polyacrylamide (PAAm) has been successfully developed. Polyvinyl alcohol (PVA) was used as a macro-crosslinker to prepare the PVA–KGM first network hydrogel by a cycle freezing and thawing method for the first time. Subsequent introduction of a secondary PAAm network resulted in super-tough DN hydrogels. The resulting PVA–KGM/PAAm DN hydrogels exhibited unique ability to be freely shaped, cell adhesion properties and excellent mechanical properties, which do not fracture upon loading up to 65 MPa and a strain above 0.98. The mechanical strength and microstructure of the DN hydrogels were investigated as functions of acrylamide (AAm) content and freezing and thawing times. A unique embedded micro-network structure was observed in the PVA–KGM/PAAm DN gels and accounted for the significant improvement in toughness. The fracture mechanism is discussed based on the yielding behaviour of these physically linked hydrogels.

Motivated by the interest in an interfacial effect on crystallization behaviors and material properties of polymer nanocomposites, phase behaviors of a novel model system for polymer nanocomposite, 1-octadecanol/silica nanosphere composites (C18OH/SiO2), were studied by means of thermal analysis and wide-angle X-ray diffraction. Although a huge specific surface area of silica nanoparticles enlarges the surface–volume ratio of C18OH molecules, surface freezing phenomenon is not observed by DSC in the C18OH/SiO2 composites. While pure C18OH exhibits rotator RIV phase with molecules tilted with respect to the layer normal, the silica network favors and enhances untitled RII phase by disturbing the layering arrangement. Moreover, the confined C18OH shows a polycrystalline mixture of orthorhombic β form and monoclinic γ form. It is demonstrated that the interfacial interaction between the C18OH molecules and the silica surface contributes to the peculiar phase transition behaviors of C18OH/SiO2 composites. The investigation of the model system of long-chain alcohol/nano-SiO2 composites may help us to understand the complicated interfacial effect on phase behaviors and material properties of polymer nanocomposite systems.

Hydroxyapatite [HAp, Ca10 (PO4)6 (OH)2] crystals were successfully prepared by the electrophoresis approach and an ion diffusion method using a template of polyacrylamide (PAAm) hydrogel. Flower-like porous hollow HAp spheres were both obtained in the PAAm hydrogel by the two methods. The diameters of the HAp spheres could be controlled in the range of 500 nm to 28 μm. The formation of flower-like porous hollow HAp crystals is believed to be the combined result of the three-dimensional hydrogel template and electrostatic interaction.

The confined phase behaviors of microencapsulated normal hexadecane/octadecane mixtures (abbreviated as m-C16/C18) have been investigated by combination of differential scanning calorimetry and in situ wide-angle X-ray scattering. The binary alkane mixtures confined in three-dimensional geometrical space demonstrate two novel crystallization features. The surface freezing is significantly enhanced after C16/C18 mixtures being encapsulated, and the surface monolayer formed is proved to be an ideal solid solution composed by C16 and C18. Furthermore, m-C16/C18 mixtures are trapped into a stabilized rotator phase below the crystallization temperatures, whereas C16/C18 mixtures with certain compositions form the low-temperature crystalline structure directly. These confined crystallization features originate from the jointed effects of spatial confinement and chain mixing of the components. Moreover, the phase diagram of the confined binary alkane mixtures (m-C16/C18) is successfully established for the first time, which enlightens the crystallization features of other spatially confined soft-matter binary systems.

Mechanically strong hydrogel–HAp composites have been successfully fabricated through in situ formation of hydroxyapatite (HAp) in a tough polyacrylamide (PAAm) hydrogel with a modified electrophoretic mineralization method. The pre-swelling of the PAAm hydrogels in CaCl2 buffer solutions makes the electrophoresis method able to produce large area (10 × 8 cm2) hydrogel–HAp composites. At the same time the CaCl2 solution with different concentrations could control the HAp contents. The obtained hydrogel–HAp composites exhibit enhanced mechanical properties, namely higher extensibility (>2000%), tensile strength (0.1–1.0 MPa) and compressive strength (up to 35 MPa), in comparison to the as-synthesized PAAm hydrogels. FTIR and Raman characterizations indicate the formation of strong interactions between PAAm chains and HAp particles, which are thought to be the main reason for the enhanced mechanical properties. The hydrogel–HAp composite also shows excellent osteoblast cell adhesion properties. These composite materials may find more applications in biomedical areas, e.g. as a matrix for tissue repair especially for orthopedic applications and bone tissue engineering.

Calcite rhombohedron with stepped indentation on its (104) face attached onto the air–solution interface was easily fabricated by using a non-ionic peptide type block copolymer poly (ethylene glycol)-b-poly (L-leucine) as the structure-directing agent. The balance of gravity and pulling force coming from the surface tension of the solution in combination with the limited Ca2+ and CO32− ion transport from the mineralization solution together played a significant role in modifying the crystal morphologies. Based on the calcite particle morphologies at different aging times, the mechanism for the formation of stepped calcite in the presence of polymer was proposed. This study provides an example that it is possible to access morphogenesis of calcium carbonate by a non-ionic copolymer which may shed new light on the controlled morphogenesis of other inorganic materials.

Crystallization and phase transition behaviors of n-hexadecane (n-C16H34, abbreviated as C16) confined in microcapsules and n-alkane/SiO2 nanosphere composites have been investigated by the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). As evident from the DSC measurement, the surface freezing phenomenon of C16 is enhanced in both the microcapsules and SiO2 nanosphere composites because the surface-to-volume ratio is dramatically enlarged in both kinds of confinement. It is revealed from the XRD results that the novel solid–solid phase transition is observed only in the microencapsulated C16, which crystallizes into a stable triclinic phase via a mestastable rotator phase (RI). For the C16/SiO2 composite, however, no novel rotator phase emerges during the cooling process, and C16 crystallizes into a stable triclinic phase directly from the liquid state. Heterogeneous nucleation induced by the surface freezing phase is dominant in the microencapsulated sample and contributes to the emergence of the novel rotator phase, whereas heterogeneous nucleation induced by foreign crystallization nuclei dominates the C16/SiO2 composite, leading to phase transition behaviors similar to those of bulk C16.

The phase behaviors of binary consecutive even normal alkane (n-alkane) mixtures (n-CnH2n+2/n-Cn+2H2n+6, with mass ratios of 90/10 and 10/90) with different average carbon numbers n̅ both in the bulk state (abbreviated as Cn/Cn+2) and in nearly monodisperse microcapsules (abbreviated as m-Cn/Cn+2), have been investigated by the combination of differential scanning calorimetry and temperature-dependent X-ray diffraction. The phase behavior of n-alkane mixtures gradually shifts from complete phase separation, partial miscibility to total miscibility in both bulk and microcapsules with the increase of average carbon numbers n̅. There are critical points for average carbon numbers of Cn/Cn+2, where the corresponding mixtures exhibit coexistence of a triclinic phase (formed by alkane with a longer chain) and an orthorhombic ordered phase (formed by the two components of mixtures). Due to the confinement from hard shells of microcapsules, the critical points of m-Cn/Cn+2 are smaller than those of Cn/Cn+2. Such a phase behavior originates from the delicate combined action of confinement and repulsion energy for the encapsulated n-alkane mixtures with different average carbon numbers n̅. When n̅ is less than the critical point, the repulsion energy between the two kinds of molecules exceeds the suppression effect of confinement, and phase separation occurs in microcapsules. It is believed that the average carbon number is another important factor that exerts strong negative influence on the phase separation of m-Cn/Cn+2 systems.

Isotactic polypropylene (iPP) fiber, the surface of which is hydrophobic, can modulate the crystallization polymorphs of calcium carbonate (CaCO3) at the air/solution interface under mild conditions. The present results provide a novel perspective on controlling the crystallization of biominerals by an insoluble matrix, and they can shed new light on understanding the biomineralization process of CaCO3 as it occurs in nature.

The crystallization behaviors of binary normal alkane (n-alkane) mixtures with a series of carbon number difference (denoted as Δn), both in the bulk state and in nearly monodisperse microcapsules, have been investigated by the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). As revealed by the DSC data, the surface freezing temperature (denoted as Ts) of spatially confined binary n-alkane mixtures with large Δn is lower than the calculated value due to the enrichment of shorter component in the surface freezing phase. More alkane molecules with shorter carbon chain are located on the interface between the inner shell of microcapsules and the bulk mixture, thus leading to the decrease of the average chain length of the surface freezing phase and corresponding lower Ts. Furthermore, XRD results have proved that the enhanced surface freezing phenomenon can contribute to the stabilization of the rotator phases in n-alkane mixtures and even induce the crossover of some certain rotator phase (RII) from transient to metastable. However, the decisive reason for such stabilization or crossover is attributed to the suppression of the orienting movement of alkane molecules toward their next-nearest neighbors within the layer of rotator phases.

Calcium oxalate particles with different morphologies and phase structures were prepared by a facile precipitation reaction of sodium oxalate with calcium chloride in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) at different temperatures. The as-prepared products were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the variations in the concentration of surfactants and temperatures significantly influenced the crystal structure, morphology, and particle size of the products. Cationic surfactant CTAB did not affect the crystal phase: calcium oxalate monohydrate (COM) was the only hydrate formed. Anionic surfactant SDS, however, not only changed the crystal shape, but also induced the formation of metastable calcium oxalate dihydrate (COD) with increasing surfactant concentration. High temperature favored the formation of COM. This work may provide new insights into the morphological control of calcium oxalate particles.Graphical abstractHighlights► Crystallization experiments were carried out at different temperatures. ► Calcium oxalate crystals with many interesting morphologies were synthesized in cationic and anionic surfactant systems. ► Surfactants affect the crystallization of calcium oxalate depending on their headgroup charge and state of aggregation.

The present work reports the confined crystallization behaviours of binary even–even normal alkane (n-alkane) mixtures of n-octadecane (n-C18H38) and n-eicosane (n-C20H42), which are microencapsulated in monodisperse microcapsules, using the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). A new metastable rotator phase (RII) absent in the bulk state, has been detected for the n-alkane mixture in confined geometry under all the investigated compositions. Such a crossover is attributed to the lower interfacial energy due to the same in-planar hexagonal structure of the surface monolayer and RII, as well as the weakened intermolecular interaction in alkane mixtures. This is the first time that RII is found in such a binary even–even n-alkane mixture that neither of the components contains RII phase in the crystallization process. Furthermore, based on the variation of alkane molecule conformation and in-planar structure with temperature, the correlations between the phase transition temperature and composition have been discussed.

In the present investigation, the crystallization and phase transition behaviours of normal alkane (n-docosane) in microcapsules with a mean diameter of 3.6 μm were studied by the combination of differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD) and variable-temperature solid-state nuclear magnetic resonance (VT solid-state 13C NMR). The DSC and VT solid-state 13C NMR results reveal that a surface freezing monolayer is formed prior to the bulk crystallization of the microencapsulated n-docosane. More interestingly, it is confirmed that after the bulk crystallization, the ordered triclinic phase coexists with the rotator phase I (RI) for the microencapsulated n-docosane. We argue that the reduction of the free energy difference between the two phases, resulting from the microencapsulation process, leads to the coexistence of the ordered triclinic and rotator phases of the normal alkanes.

In the present work, in situ polymerization method was used to prepare nearly monodispersed microcapsules with long chain normal alkanes as core and melamine–formaldehyde (M–F) resin as shell at reaction temperature both above and below the cloud point of nonionic surfactant. A previously neglected point has been clarified, i.e., changing the reaction temperature is proved to be an effective way to tune the microcapsule size, surface pore size and density. Nano-scaled pores (from 5 to 200 nm) on the microcapsule surface were formed by the self-assembly template of nonionic surfactant micelles at different reaction temperatures. The dynamic morphological evolution in the encapsulation process was illustrated, for the first time, by scanning electron microscopy (SEM) at different reaction time. It is the alteration of the hydrophilic–lipophilic balance of crosslinked M–F preploymer in the polymerization process that leads the micelle droplets to migrate inside out, and consequently forms nano- or submicron-pores on the microcapsule surface. The prepared microcapsules have close inner space, providing a good 3-dimensional environment for the confined crystallization of alkanes within the polymeric shell. This methodology is versatile and effective for the synthesis of other porous microspheres, which can be applied potentially for encapsulating lipophilic functional materials.Graphical abstractHighlights► We examine the temperature effect on the size of surface pores and microcapsules. ► We investigate the morphological evolution during the encapsulation at different reaction time. ► The alteration of the hydrophilic–lipophilic balance of crosslinked preploymer plays an important role in the formation of the surface pores. ► Aggregation of micelles plays an important role for the formation of porous microcapsules.

The crystallization behaviors of binary even−even normal alkane (n-alkane) mixtures (n-C18H38/n-C20H42, abbreviated as C18/C20) with different compositions, both in the bulk state and in nearly monodisperse microcapsules, have been investigated by the combination of differential scanning calorimetry and temperature-dependent X-ray diffraction. The solid−solid phase separation, usually observed during the cooling process of bulk samples, is greatly suppressed and even eliminated after being microencapsulated, with the orthorhombic-ordered phase dominating in the low-temperature crystal. Such a crystallization transition is attributed to the special interaction between the two even n-alkanes and the confined environment in microcapsules. The triclinic ordered phase, solely formed by the single even n-alkanes (C18 or C20), becomes less stable due to the weakening of the layered structure and the suppression of the terminal methyl−methyl interactions in the confined geometry, which favors the miscibility of the two components. Furthermore, besides the chain-length difference and the composition, the confined environment is proved to be another important factor to exert strong positive influence on suppressing the solid−solid phase separation of C18/C20 binary system.

The crystallization behavior of n-C19H40/SiO2 nanosphere composites was investigated by a combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). Three kinds of confined alkanes with different solid−solid phase transition supercoolings and a surface (or interface) freezing monolayer of n-C19H40 at the bulk liquid/SiO2 interface were found in the composites at high SiO2 loading. The surface freezing monolayer induces the chain packing of bulk alkanes by forming a 2D close-packed arrangement without long-range positional ordering in 3D space. A homogeneous nucleation and growth mechanism is found for the solid−solid transition in confined geometry, in which the supercooling of the transition is sensitive to the confined size.

The crystallization of binary n-alkane solid solution n-C18H38/n-C19H40 = 90/10 (molar ratio) (abbreviated as C18/C19 = 90/10) and the microencapsulated counterpart (abbreviated as m-C18/C19 = 90/10) has been investigated by a combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). The solid−solid phase separation was obviously detected in C18/C19 = 90/10 by XRD, which is absent in m-C18/C19 = 90/10. The XRD data also show that the chain packing of m-C18/C19 = 90/10 is different from that of bulk C18/C19 = 90/10. The packing mode of m-C18/C19 = 90/10 molecular chains is unique; i.e., the n-alkane chains pack along the longitudinal direction and the neighboring layers interdigitate with each other, subsequently resulting in the deconstruction of lamellar ordering. The extinction of phase separation in m-C18/C19 = 90/10 can be understood in terms of the suppression of longitudinal chain diffusion caused by the special three-dimensional confinement effect provided by microcapsules.

Mechanically strong hydrogel–HAp composites have been successfully fabricated through in situ formation of hydroxyapatite (HAp) in a tough polyacrylamide (PAAm) hydrogel with a modified electrophoretic mineralization method. The pre-swelling of the PAAm hydrogels in CaCl2 buffer solutions makes the electrophoresis method able to produce large area (10 × 8 cm2) hydrogel–HAp composites. At the same time the CaCl2 solution with different concentrations could control the HAp contents. The obtained hydrogel–HAp composites exhibit enhanced mechanical properties, namely higher extensibility (>2000%), tensile strength (0.1–1.0 MPa) and compressive strength (up to 35 MPa), in comparison to the as-synthesized PAAm hydrogels. FTIR and Raman characterizations indicate the formation of strong interactions between PAAm chains and HAp particles, which are thought to be the main reason for the enhanced mechanical properties. The hydrogel–HAp composite also shows excellent osteoblast cell adhesion properties. These composite materials may find more applications in biomedical areas, e.g. as a matrix for tissue repair especially for orthopedic applications and bone tissue engineering.

The present work reports the confined crystallization behaviours of binary even–even normal alkane (n-alkane) mixtures of n-octadecane (n-C18H38) and n-eicosane (n-C20H42), which are microencapsulated in monodisperse microcapsules, using the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). A new metastable rotator phase (RII) absent in the bulk state, has been detected for the n-alkane mixture in confined geometry under all the investigated compositions. Such a crossover is attributed to the lower interfacial energy due to the same in-planar hexagonal structure of the surface monolayer and RII, as well as the weakened intermolecular interaction in alkane mixtures. This is the first time that RII is found in such a binary even–even n-alkane mixture that neither of the components contains RII phase in the crystallization process. Furthermore, based on the variation of alkane molecule conformation and in-planar structure with temperature, the correlations between the phase transition temperature and composition have been discussed.

In the present investigation, the crystallization and phase transition behaviours of normal alkane (n-docosane) in microcapsules with a mean diameter of 3.6 μm were studied by the combination of differential scanning calorimetry (DSC), temperature-dependent X-ray diffraction (XRD) and variable-temperature solid-state nuclear magnetic resonance (VT solid-state 13C NMR). The DSC and VT solid-state 13C NMR results reveal that a surface freezing monolayer is formed prior to the bulk crystallization of the microencapsulated n-docosane. More interestingly, it is confirmed that after the bulk crystallization, the ordered triclinic phase coexists with the rotator phase I (RI) for the microencapsulated n-docosane. We argue that the reduction of the free energy difference between the two phases, resulting from the microencapsulation process, leads to the coexistence of the ordered triclinic and rotator phases of the normal alkanes.

A novel physically linked double-network (DN) hydrogel based on natural polymer konjac glucomannan (KGM) and synthetic polymer polyacrylamide (PAAm) has been successfully developed. Polyvinyl alcohol (PVA) was used as a macro-crosslinker to prepare the PVA–KGM first network hydrogel by a cycle freezing and thawing method for the first time. Subsequent introduction of a secondary PAAm network resulted in super-tough DN hydrogels. The resulting PVA–KGM/PAAm DN hydrogels exhibited unique ability to be freely shaped, cell adhesion properties and excellent mechanical properties, which do not fracture upon loading up to 65 MPa and a strain above 0.98. The mechanical strength and microstructure of the DN hydrogels were investigated as functions of acrylamide (AAm) content and freezing and thawing times. A unique embedded micro-network structure was observed in the PVA–KGM/PAAm DN gels and accounted for the significant improvement in toughness. The fracture mechanism is discussed based on the yielding behaviour of these physically linked hydrogels.