Microscale, pick-and-place assembly is a non-lithographic assembly method poised to impact diverse fields including flexible electronics, microfluidics and robotics. However, a major technological challenge is the need to deterministically control adhesion between parts. Here, switchable adhesion involving 3D-printed, self-complementary surfaces is demonstrated. Mechanical properties of metasurfaces pressed against flat, rigid substrates are modeled using finite element methods. A series of flat slabs and metastructured slabs with 2D sinusoidal surfaces are printed using two-photon polymerization (2PP) of a shape-memory resin. The surface frequency of featured slabs was varied between 3.3̅ mm-1 and 26.6̅ mm-1 with similar amplitudes. Adhesion between printed metasurfaces and glass and between printed, self-complementary metasurfaces is studied above and below the cured resin's glass transition temperature (∼45 °C). Simple heating of adhering surfaces to above 60 °C lowers adhesion, and compression of surfaces while above the glass transition temperature followed by cooling to room temperature elevates adhesion. The nominal adhesive strength between printed, self-complementary surfaces, as determined by the maximum observable pull-off stress, exceeds 3 MPa. Further tailoring complementary surfaces for adhesion control may facilitate microscale disassembly for recovery of components or precious metals.

The selective reflection and circular polarization characteristics of cholesteric liquid crystals (CLCs) arise from their self-assembly into helicoidal structures, producing photonic stopbands typically 50-100 nm wide. Here, we demonstrate that thermal annealing of enantiomeric cholesteric glassy liquid crystals (ChGLCs)-differing only in stereochemistry-can generate pitch profiles that broaden the photonic stopband across the full visible spectrum. The resulting structures are permanently fixed by vitrification into the glassy state. When adjacent ChGLC layers share the same handedness, enantiomer diffusion follows Fickian-like behavior, enabling predictable gradient formation. In contrast, when layers of opposite handedness are annealed, molecular diffusion is strongly suppressed, and no stopband broadening is observed. These results clarify how chirality influences molecular mobility in chiral liquid crystalline media and establish a robust approach for engineering broadband optical films with tunable reflection properties. This strategy provides a platform for designing next-generation photonic materials, including broadband reflectors, polarization optics, and reconfigurable coatings.

Two-photon printing is accomplished using a photobase generator, 2-(2-nitrophenyl)-propyloxycarbony tetramethyl guanidine, to locally catalyze thiol-ene coupling between multifunctional monomers while mitigating chain-growth polymerization with free radical scavengers. Microstructures printed from base-catalyzed resins exhibit higher resolution (linewidths < 400 nm) and lower print error (<3%) than analogous microstructures printed using a photosensitive, free radical initiator. Further, Raman spectroscopy reveals that resins polymerized using the photobase generator in the presence of free radical scavengers exhibit higher selectivity of thiol-ene coupling over radical polymerization, resulting in stiffer, more uniform polymer networks. The base-catalyzed resins are capable of producing 3D microstructures printed with high accuracy and minimal post-processing defects. A direct comparison between free radical and base-initiated resins highlights the need for mindful consideration of how chemical reaction pathway influences printability and network end-properties when designing resins.

Since 2001, 3D microfabrication based on two-photon polymerization (TPP) has drawn extensive attention and interest in biology, optics, photonics, material science, and high-energy physics. The in-volume fabrication capability due to the threshold behavior of two-photon absorption enables TPP higher flexibility compared with other nanofabrication techniques. However, as determined by the in-volume fabrication feature as well as various reaction dynamics, the writing characteristics of TPP, such as throughput, accuracy, surface quality, and fabrication capability, are still limited. Herein, a comprehensive study is performed on the spatiotemporal behavior of reaction dynamics during TPP fabrication, mainly focusing on spatiotemporal characteristics of radical diffusion, photothermal effect, microscale mechanics, and voxel stacking process. Based on the study, a nonsequential fabrication method is established to simultaneously improve key writing characteristics of TPP and realize sharp features, high speeds, large overhang structure, and smooth surfaces. The method established in this work can be applied to improve the performance of functional devices for various fields. In this study, radical diffusion, structural mechanics, thermal accumulation, and the formation of surface morphology during the two-photon polymerization (TPP) process are investigated. A nonsequential scanting strategy is established to enhance the writing resolution, structural limit, surface smoothness, and throughput of the TPP process. Scale bar:3 mu m. image

Mesomorphic ceramic films comprising uniaxially oriented short nanorods with a modest aspect ratio are desired for a wide range of applications, including waveplates requiring optical transparency and optoelectronics benefiting from enhanced surface area. Fabrication of such films remains challenging but can, in principle, be facilitated by coassembly with relatively large companion nanorods. This idea is successfully demonstrated for 30 nm long TiO2 nanorods with an aspect ratio of 5 assisted by 200 nm long cellulose nanocrystals (CNCs) with an average aspect ratio of 20 in an aqueous suspension. Blade-coating is exploited as a cost-effective, scalable method for shear alignment to fabricate centimeter-scale, transparent thin films. The resulting dried, composite films contain over 50 wt % TiO2. Upon calcination, 260 nm thick mesomorphic ceramic coatings emerge with an optical birefringence at 0.09 and a transparency over 90% from 420 to 1690 nm. This simple method to align small nanorods through coassembly with CNCs could be generalized to fabricate a variety of transparent composite and inorganic thin film optical retarders.

Glassy liquid crystals are a unique class of materials that can preserve their spontaneously ordered liquid crystalline state upon cooling through the glass-transition temperature. Cholesteric glassy liquid crystals (ChGLCs), in particular, are attractive for their selective reflection and circular polarization properties, and core-pendent ChGLCs display high morphological stability and exclusive mesomorphism over a broad temperature range. An enantiomeric pair of core-pendent ChGLCs was prepared following a deterministic synthesis route, allowing for both enantiomers to be scaled up and purified at the gram-level. The ability to process these compounds into well-ordered, nm- and μm-thick films with glassy, monodomain cholesteric structures is demonstrated. Processed films exhibit a photonic band gap structure that splits unpolarized incident light into circularly polarized transmitted light of one handedness and circularly polarized reflected light of the opposite handedness. Mixing enantiomers at different stoichiometric ratios alters the cholesteric structure, thereby tuning the wavelength of reflection from the near-UV to the mid-IR. Moreover, glass transition temperatures and clearing temperatures of enantiomeric mixtures are independent of the mixing ratio, enabling the design and fabrication of durable circular polarizers, notch filters, and polarization control devices across different spectral regions.

Chiral nanomaterials possess unique electronic, magnetic, and optical properties that are relevant to a wide range of applications including photocatalysis, chiral photonics, and biosensing. A simple, bottom-up method to create chiral, inorganic structures is introduced that involves the co-assembly of TiO2 nanorods with cellulose nanocrystals (CNCs) in water. To guide experimental efforts, a phase diagram was constructed to describe how phase behavior depends on the CNCs/TiO2/H2O composition. A lyotropic cholesteric mesophase was observed to extend over a wide composition range as high as 50 wt % TiO2 nanorods, far exceeding other examples of inorganic nanorods/CNCs co-assembly. Such a high loading enables the fabrication of inorganic, free-standing chiral films through removal of water and calcination. Distinct from the traditional templating method using CNCs, this new approach separates sol-gel synthesis from particle self-assembly using low-cost nanorods.

Robust, transparent, and birefringent inorganic films are demanded for polarization control of high‐power lasers. While single crystals or films obtained via glancing angle deposition exhibit desirable optical properties and laser damage resistance, these methods are limited by cost and scalability. Mesomorphic ceramics as inorganic solids with liquid crystalline superstructure offer appealing transparency and birefringence but lack mechanical robustness due to their high porosity. Here, the effect of sintering on optical and mechanical properties of mesomorphic ceramics is evaluated. Films prepared by blade coating are sintered under varying conditions. Constrained sintering accomplished crystallite growth, densification, and morphological changes including necking as well as cracking while preserving the crystallographic orientation. The extent of sintering as a function of thermal treatment is quantified by morphology, surface area loss, and crystallite growth. Moreover, activation energies for surface diffusion and grain growth are estimated by surface area analysis and X‐ray diffraction peak narrowing, respectively. After sintering, birefringence decreases while Young's modulus and hardness improve as the film densifies. Upon partial sintering, mesomorphic ceramics retain transparency, high birefringence, and enhanced modulus. Laser‐induced damage threshold is measured as well. The reported results represent an important step toward the assembly and sintering of robust waveplates with high laser damage resistance.

Fabrication of three-dimensional (3D) carbon-based structures at micro/nanoscale, mainly by pyrolysis of photocured resins, has recently drawn attention in battery development, material engineering, and catalysts. Upon pyrolysis, photocured 3D polymer structures undergo thermal decomposition and eventually carbonize while maintaining their 3D features. Herein, we systemically investigate the physical and chemical reactions that occur during the pyrolysis of methacrylate-based resin structures, yielding fundamental knowledge and an improved understanding of the pyrolysis processes. Based on our results, the pyrolysis process can be divided into three stages: monomer evaporation, chemical decomposition, and carbonization, in which the volume shrinkage mainly occurs in the first and third stages. The three stages have different effects on the mechanical properties of the pyrolyzed structures, with monomer evaporation and carbonization enhancing the Young's modulus while decomposition reduces the Young's modulus. Additionally, the surface smoothness of the photocured structures can be improved during pyrolysis due to the shrinkage of the polymer resins, which provides a potential approach to generating ultrasmooth carbon surfaces.

Mesomorphic ceramics include inorganic solids with liquid crystalline superstructures and show great promise as waveplates for high-power lasers. Waveplates require sufficiently thick, birefringent, and uniform films, and mesomorphic ceramics made from shear-assembly of zinc oxide nanorods can offer both transparency and uniform birefringence over large areas. However, cracking occurs during processing of mesomorphic ceramics with a thickness beyond a micrometer. Crack formation impairs optical performance and is attributed to excess in-plane tensile stress generated during film processing. To reduce cracks, mesomorphic ceramic zinc oxide films were prepared using three different methods: (I) A single, sintered blade-coated layer was treated with inorganic precursors. (II) Multiple, thin layers were successively blade-coated and sintered. (III) Multiple coatings were combined for precursor treatment. A 2-mu m-thick film with a birefringence of 0.09 and a transparency of >92% was achieved by Method III, and the film behaved as a quarter-waveplate at wavelengths between 700 and 725 nm. This reported method repairs cracks in anisotropic nanoparticle assemblies and enables the fabrication of large aperture optical devices such as ceramic waveplates. Such a processing methodology also benefits diverse applications including thin-film transistors, optoelectronics, and photocatalysis.

Mesomorphic ceramic films are fabricated over large areas by blade coating of a lyotropic nematic sol of zinc oxide nanorods. Upon calcination to remove organics, continuous monodomain films with a uniform thickness result as transparent ceramics, exhibiting uniform birefringence over centimeter dimensions. At low blade-coating velocities, the dry film thickness varies inversely with the coating velocity, whereas at high coating velocities, it increases with increasing velocity as prescribed by the Landau-Levich theory. The thickness-velocity scaling in the Landau-Levich regime depends on the shear-thinning behavior of the lyotropic nematic sol. The optimization of the coating process for the minimization of optical defects leads to transparent monodomain films that exhibit a uniform in-plane birefringence of 0.032 +/- 0.002 from 580 to 1690 nm. After calcination, the resulting mesomorphic ceramic films span large areas (3.5 cm x 2.5 cm), are optically transparent with uniform thickness (0.60 +/- 0.03 mu m), and exhibit smooth surface finish with an average surface roughness of 20 nm. The alignment of zinc oxide crystallites along the coating direction within mesomorphic ceramics is confirmed by X-ray diffraction texture analysis and scanning electron microscopy imaging. As explained by the effective medium theory, the measured in-plane birefringence of 0.118 +/- 0.003 is primarily contributed by form birefringence over intrinsic birefringence of zinc oxide in mesomorphic ceramics. The reported approach to highly ordered mesomorphic ceramics directly from lyotropic nematic sols, avoiding the gel state, could be generally applicable to other mineral liquid crystals, thereby benefiting the manufacture of optics for high-power lasers.

Shape‐memory resists capable of high‐resolution curing into arbitrarily designed structures are increasingly demanded for soft robotics, optical sensors, microscale manufacturing, and biomedicine. Amorphous, shape‐memory thiol‐vinyl networks are printed using two‐photon polymerization (2PP) curing of a simple resin formulated with commercially available reagents. The ability to print high‐resolution feature sizes down to 200 nm is attributed to the use of radical‐mediated, thiol‐vinyl step‐growth polymerization that quickly cross‐links the resin, limiting diffusive transport. The thermomechanical behavior of the 2PP‐cured material analyzed in compression, tension, and three‐point bending is similar to the behavior of the UV‐polymerized samples. To demonstrate the ability to design, field, and test 4D responsive microstructures, an array of nine springs with coil diameters of 330 µm is printed. Following compressive shape‐fixing, printed arrays can release 11 µJ of stored elastic strain energy when reheated. Further, a new concept of dichroic‐memory of a metamaterial device is demonstrated by printing a twisted woodpile structure with circular dichroism as characterized by Mueller Matrix ellipsometry. The results of this study demonstrate how combining high‐resolution 2PP curing with stimuli‐responsive molecular architectures can further the engineering of responsive microstructures and metamaterials.

Semicrystalline shape-memory elastomers are molded into deformable geometrical features to control adhesive interactions between elastomers and a glass substrate. By mechanically and thermally controlling the deformation and phase-behavior of molded features, we can control the interfacial contact area and the interfacial adhesive force. Results indicate that elastic energy is stored in the semicrystalline state of deformed features and can be released to break attractive interfacial forces, automatically separating the glass substrate from the elastomer. Our findings suggest that the shape-memory elastomers can be applied in various contact printing applications to control adhesive forces and delamination mechanics during ink pickup and transfer.

Cross-linked semicrystalline shape-memory networks are capable of storing large amounts of elastic energy with negligible plastic deformation; however, thermosets are not easily melt-processed or recycled. Here, we demonstrate a shape-memory polymer that is melt-recyclable with high processability and little performance loss. Catalyst-free isocyanate chemistry is used to prepare two linear poly(caprolactone)s with bisurea hydrogen-bonding groups periodically positioned along the main chain. Compared to an entangled poly(caprolactone) homopolymer of similar molecular weight, the segmented poly(bisurea)s exhibit minimal stress relaxation when elastically strained at identical conditions. Furthermore, the materials’ single relaxation times combined with small-angle X-ray scattering results indicate that stress relaxation is limited more by disentanglement kinetics rather than by phase segregation of hard domains. The polymers show excellent shape fixity and recovery before and after shredding, melt-pressing, and annealing into a reprocessed film. Together with thermomechanical cycling, creep experiments provide insight into the relationship between stress relaxation and shape-memory training.

Mesomorphic ceramics are broadly defined as solid systems with morphologies intermediate between isotropic materials and single crystals. To illustrate this materials concept, a class of mesomorphi...

Crystallization of polymer strands within elastically strained cross-linked networks can lower tension, leading to stabilization of mechanically deformed states. This process, referred to as shape-fixing, is sensitive to thermomechanical path because both mechanical strain and thermal undercooling affect crystallization kinetics. In the present study, shape-fixing of a well-defined poly(caprolactone) network is examined at fixed strains ranging from 25 to 100%. Isothermal crystallization kinetics were studied using wide angle X-ray scattering while simultaneously monitoring tension loss. Plots of tensile stress versus degree of crystallization show that significant stress reduction occurs at only a few percent crystallinity (<0.05). The development of Young's modulus under identical conditions was evaluated, and results are combined to estimate the shape-fixity at different crystallization conditions and times. This study contributes to understanding the interrelationship between crystallization, stress reduction, and material stiffening to support further development of semicrystalline shape-memory networks.