Liquid crystal elastomers (LCEs) are broadly recognized as programmable actuating materials that are responsive to external stimuli, typically heat or light. Yet, soft LCEs that respond to changes in environmental humidity are not reported, except a few examples based on rigid liquid crystal networks with limited processing. Herein, a new class of highly deformable hygroscopic LCE actuators that can be prepared by versatile processing methods, including surface alignment as well as 3D printing is presented. The dimethylamino‐functionalized LCE is prepared by the aza‐Michael addition reaction between a reactive LC monomer and N,N′‐dimethylethylenediamine as a chain extender, followed by photopolymerization. The humidity‐responsive properties are introduced by activating one of the LCE surfaces with an acidic solution, which generates cations on the surface and provides asymmetric hydrophilicity to the LCE. The resulting humidity‐responsive LCE undergoes programmed and reversible hygroscopic actuation, and its shape transformation can be directed by the cut angle with respect to a nematic director or by localizing activation regions in the LCE. Most importantly, various hygroscopic LCE actuators, including (porous) bilayers, a flower, a concentric square array, and a soft gripper, are successfully fabricated by using LC inks in UV‐assisted direct‐ink‐writing‐based 3D printing.

Effects of silica nanoparticles with different natures (hydrophilicity and hydrophobicity) on (80/20) PP/PS blends were investigated via linear and nonlinear rheological properties. The hydrophilic silica nanoparticle was fumed silica OX50 while the two hydrophobic ones were precipitated silica D17 and fumed silica R202. SEM images revealed that hydrophilic OX50 could not improve morphological properties of the blends. On the other hand, the two hydrophobic silica nanoparticles (R202 and D17) improved morphological properties. TEM examination showed that OX50 silica nanoparticles aggregated inside PS droplets, thereby making breakup of PS (dispersed) phase into smaller sizes more difficult. D17 and R202 improved morphological properties regardless of the different droplet size reduction mechanisms, and rheological properties improved as a result. Both linear rheological properties from SAOS (small-amplitude oscillatory shear) tests and nonlinear rheological properties from LAOS (large-amplitude oscillatory shear) tests were obtained. The nonlinear−linear viscoelastic ratio (NLR ≡ normalized nonlinear rheological properties/normalized linear rheological properties) was used to quantify the degree of droplet dispersion and distinguish the effects of silica particles on the morphology of PP/PS blends. Previous research has observed an inverse correlation between NLR and droplet size. PP/PS/OX50 blends with no alteration of droplet size showed constant NLR values (≅1) with increasing concentration of OX50 (hydrophilic silica). However, NLR values of PP/PS blends with hydrophobic silica nanoparticles (D17 and R202) were much larger than 1 (NLR > 1) and increased with silica concentration, which is consistent with morphological evolution, i.e., reducing droplet size. However, NLR values of PP/PS/R202 blends were relatively larger than those of PP/PS/D17 blends despite smaller droplet sizes. This can be attributed to a different morphology microstructure, i.e., R202 located in PP matrix phase and D17 at interface between PP and PS. Therefore, the NLR value of PP/PS/silica blend could be due to the combined effects of the interface between droplets (PP/PS blend) and particle−polymer interactions (PP/silica nanocomposites). Especially, R202 showed larger NLR values due to PP/R202 nanocomposites. Based on these findings, relative NLR (= NLR PP/PS/silica /NLR PP/silica ) is proposed as an effective measurement of droplet size information in PP/PS blends by eliminating the effects of PP/silica nanocomposites. Relative NLR matched well with droplet size evolution from the SEM results.

The effects of various Cloisite nanoparticulate clays with different hydrophobicities on (80/20) polypropylene/polystyrene (PP/PS) blends were investigated using their linear and nonlinear rheological properties. In descending order of hydrophobicity the four Cloisite clays examined were C20A > C10A > C30B > CNa+. Clays with a wetting coefficient ω a of between 1 and −1, that is C20A and C10A, located at PP/PS polymer interfaces and suppressed coalescence, while clays with a ω a of >1, that is C30B and CNa+, accumulated inside the PS droplets and increased viscosity ratios. As a result, C20A and C10A caused PS droplet size reductions while C30B and CNa+ did not change morphology of the PP/PS blend. Linear rheological properties as determined by SAOS (small amplitude oscillatory shear) test and nonlinear rheological properties determined by LAOS (large amplitude oscillatory shear) test revealed C20A and C10A increased mechanical properties of PP/PS blends. Rheological properties from SAOS and LAOS tests decreased in the same order as clay hydrophobicities at same concentration. The nonlinear–linear viscoelastic ratio (NLR is defined as normalized nonlinear viscoelastic properties/normalized linear viscoelastic properties) was used to quantify degrees of PS droplet dispersion and to determine the compatibilizing effects of the four clays on PP/PS blends. PP/PS blends filled with hydrophilic clays (C30B and CNa+) exhibited constant NLR values (NLR ≅ 1) with increasing clay concentration. However, NLR values of PP/PS blends containing C20A and C10A were much larger than 1 (NLR > 1) and increased with clay concentration, which concurred with reductions in droplet sizes. Interestingly, NLR values and droplet size changes exhibited inverse relationships with clay hydrophobicity. In addition, PS droplet sizes in PP/PS/C20A blends in the medium amplitude oscillatory shear (MAOS) flow region (Q 0 zone) were observed to check NLR validation. It was found that droplet sizes did not change in the MAOS region where NLR values are calculated and that thus NLR values corresponded with droplet sizes. Finally, inverse composition (20/80) PP/PS/C20A blends were studied, and a good correlation was obtained between PP droplet sizes and NLR values.

Characterizing dispersion quality of polymer nanocomposite (PNC) is as important as dispersing nanosized fillers in the polymer matrix. In this study, to quantify the dispersion quality of PNCs, we used rheological properties, that is, linear viscoelasticities determined by small-amplitude oscillatory shear tests and nonlinear viscoelasticities determined by large-amplitude oscillatory shear tests. Nonlinear viscoelasticities were analyzed with Fourier transform (FT)-rheology. Two different disperse-controlled PNCs were investigated. One is a polypropylene (PP)/clay nanocomposite system compatibilized using maleic anhydride-grafted polypropylene (MAPP), and the other is a PP/silica nanocomposite system containing four different types of silica (two hydrophilic and two hydrophobic silicas). Rheological measurements and transmission electron microscopy (TEM) findings for both PNCs, and X-ray diffraction (XRD) findings for PP/MAPP/clay were used to investigate morphological evolutions. In the case of PP/MAPP/clay nanocomposites, dispersion qualities, as characterized by linear and nonlinear rheological properties, were consistent with each other and well matched TEM and XRD observations. In contrast, in the case of PP/silica nanocomposites, dispersion qualities as characterized by linear and nonlinear rheological properties were inconsistent with each other. In this study, dispersion states of PNCs predicted by nonlinear rheological properties corresponded with TEM observations, whereas linear rheological properties did not. Especially, NLR (nonlinear–linear viscoelastic ratio ≡ normalized nonlinear viscoelasticity as determined by FT-rheology/normalized linear viscoelasticity) parameter well predicted dispersion degrees of PP/MAPP/clay nanocomposites and PP/silica nanocomposites.

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