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We demonstrate the potential of thermoresponsive poly N‐(isopropylacrylamide) (PNIPAM) based surfaces in achieving a low‐energy approach to modulate surface wetting for applications such as fog harvesting and anti‐fogging. Alternative to grafting methods, we use a two‐step approach for tuning the response amplitude. First, we blend PNIPAM with a chemically non‐reactive poly (vinylidene fluoride), PVDF (1/3, 1/1, 3/1 by weight). Second, thermal nanoimprint lithography is used to create micro (3, 5, 10, and 20 μm) and nano‐scale (100 and 200 nm) pillars. Nano‐patterned surfaces show a response amplitude of ~30°–50° compared to ~15°–30°, observed for the micro‐patterned surface. X‐ray photo‐electron spectroscopy and energy dispersive X‐ray analysis confirms the reduction of polyvinylidene fluoride phase domains and enrichment of PNIPAM on the nano‐patterned surface. A real‐time dynamic mist condensation study showed that the nano‐patterned blend exhibited a lower temperature range (34/41°C) for on/off (wetting/drying) state compared to an unpatterned blend (37/50°C). [ABSTRACT FROM AUTHOR]

Isoporous membranes consist of well‐defined micro and nanoscale pore architecture comprising uniform pore sizes with straight pore channels. In contrast to traditional random porous membranes with tortuous flow paths, isoporous membranes offer the opportunity to achieve a high degree of membrane customization and low pressure drop. Here, a physics‐based machine learning methodology that enables the predictive design of a single‐layer isoporous membrane in terms of the pressure drop is reported. In short, the methodology consists of a hybrid approach that includes experimental data on the variability of the pore architecture and the resulting pressure drop, training of a neural network with data from validated physics‐based simulations of laminar flow through the membrane, and Monte Carlo simulation (MCS) to stochastically account for the inherent variabilities of the pore architecture of fabricated isoporous membranes. Overall, the neural network and MCS predict the range of Δp for a given single‐layer membrane well. Experimental values fall within 90% of the minimum and maximum predicted Δp values. In addition, a sensitivity analysis with MCS is carried out to quantify how design and operating parameters affect the overall pressure drop. The methodology can be extended to membranes comprising multiple layers and to account for filtration efficiency. [ABSTRACT FROM AUTHOR]

Photonic building blocks fabricated using two‐photon polymerization laser lithography are reported. 3D polymer structures are fabricated using a direct laser writing process with nonlinear two‐photon absorption in photosensitive material. The 3D photonic structures include 3D photonic waveguides, Bragg gratings, and resonators. In particular, high‐quality spiral and air‐bridge waveguides providing 3D light guiding beyond a single plane are demonstrated. Sub‐micrometer features as well as unique coupling interfaces with 1.6 dB coupling losses and large 3 dB bandwidth are also demonstrated. Experimental characterization reveals the good transmission performance of the fabricated photonic devices. In addition, the waveguides are demonstrated to support 30 Gb s−1 NRZ (nonreturn to zero) and 56 Gb s−1 PAM4 (pulse amplitude modulation 4) high‐speed data. Small power penalties of 0.7 dB for NRZ (BER = 10−12) and 1.5 dB for PAM4 (BER = 10−6) are obtained. [ABSTRACT FROM AUTHOR]

Byline: Hong Yee Low This paper presents an overview on three major fabrication techniques developed in our laboratory for achieving complex polymeric structures using nanoimprint lithography (NIL), namely reversal imprinting, combinatorial-mould imprinting and sequential imprinting. The key strategy employed by all three techniques is the use of conventional two-dimensional (2D) molds to achieve greater degrees of complexity than are ordinarily achievable with conventional imprinting techniques. For example, reversal imprinting combined with colloidal self-assembly allows for structures that have variations with depth as well as scale. Combinatorial-mould imprinting enables the fabrication of three-dimensional (3D) structures that have variations in length, width as well as depth. Sequential imprinting enables hierarchical structures that have scale-dependent variations and complexity. 3D structures, hierarchical structures, and combinations thereof are obtained in fewer processing steps and without the use of a sacrificial component or process.

Safety of lithium‐ion batteries (LIBs) has persistently plagued their development, despite widespread commercialization and usage. Thermal runaway is a notorious event where the overheating of the LIB results in a chain of events leading to the catastrophic failure of the device. Here, an in situ safety mechanism that shutdowns the LIB at critical temperatures before the onset of thermal runaway is developed. This is achieved by the deposition of thermal responsive polyethylene (PE) microspheres coated with multiwalled carbon nanotubes (CNTs) on electrodes via 3D printing. Rapid shutdown of LIB full cells under 60 s with ≈1 mg of additive is demonstrated. The mechanism of the shutdown is investigated through post‐mortem analysis of the heat‐treated cells that provides evidence of the formation of an insulating PE film that prevents ionic flow, disabling the LIB. Further, galvanostatic cycling of CNT‐coated PE‐loaded cells is used to demonstrate the advantages of the approach, where the precise and low loading of the conductive additive exhibits no impact on the full cell normal operation. Safety first: The safety of lithium‐ion batteries (LIBs) has plagued their development, despite their widespread commercialization and usage. Thermal runaway is a notorious event where the overheating of the LIB results in a chain of events leading to the catastrophic failure of the device. An in situ safety mechanism that shutdowns the LIB at critical temperatures before the onset of thermal runaway is achieved by depositing thermal responsive polyethylene (PE) microspheres coated with multiwalled carbon nanotubes (CNTs) on electrodes via 3D printing. [ABSTRACT FROM AUTHOR]

ABSTRACT The super hydrophobic, self-cleaning properties of natural species derive from the fine hierarchical topography evolved on their surfaces. Hierarchical architectures which are function-mimetic of the lotus leaf are here described and created from multi-scale hierarchical assembled templates. The first level of hierarchy was a micromachined dome structure template and the second level of hierarchy was added by layering a thin nanoporous membrane such as porous anodized alumina or an ion track etch membrane. The assembled templates were nanoimprinted by a single step process on thermoplastic films. The wetting angle of the surfaces reached a value of 160° and the self-cleaning behavior was observed. The superhydrophobic behavior remained over 1 year after fabrication, which demonstrates the stability of these polymeric self-cleaning topographies. © 2014 Wiley Periodicals, Inc. J. Polym. Sci. Part B. Polym. Phys. 2014, 52, 603-609 [ABSTRACT FROM AUTHOR]

With the aim to gain a wider understanding on the design rules of bioinspired adhesives for application in the medical field, the adhesion of fibrillar structures on soft and stiff polymers was determined in bench top studies on surfaces with variable roughness and in ex-vivo wet tissue tests. The adhesion strength of stiff fibrillar structures was found to be dependent on the roughness of the adherent surface. For a given fibril width and density, the optimal adhesion was seen when the length of the fibrils was of the same range as that of the roughness of the surface it was tested against. Over this limit, the adherence decreased. In the case of soft adhesive structures, the same trend was observed where an optimum adhesion was seen when the size of the pillars matched that of the adherent surface roughness. This observation was attributed to an increase in surface contact. The adhesion of fibrillar structures on tissue samples in ex-vivo tests showed a similar trend with enhanced fibrillar interpenetration favoring a larger number of contacts and a stronger capillary force expected to account for the adhesion enhancement. [ABSTRACT FROM PUBLISHER]

Hydrogen bonding in a series of alkyl-substituted benzoxazine dimers in the solid state was investigated using fast magic-angle spinning and double-quantum 1H nuclear magnetic resonance spectroscopy. Experimental results revealed significant shifts to low field of the chemical shifts of the hydrogen-bonded protons as well as the predominance of an alternative linear arrangement of hydrogen-bonded dimers for the ethyl and n-propyl dimer. On the other hand, pairs of hydrogen-bonded dimers exist for the methyl dimer.

Patterned arrays of light-responsive microchambers are suggested as candidates for site-specific release of chemicals in small and precisely defined quantities on demand. A composite film is made of poly(allylammonium)-poly(styrene sulfonate) multilayers and gold nanoparticles incorporated between subsequent stacks of polyelectrolytes. The film shaped as microchambers is loaded with colloid particles or oil-soluble molecules. The microchambers are sealed onto a glass slide precoated with an adhesive poly(diallyldimethylammonium)-poly(styrene sulfonate) multilayer film. A focused laser beam is used for remote addressing the individual microchambers and site-specific release of the loaded cargo. [ABSTRACT FROM AUTHOR]

Using nanoimprint lithography, arrays of highly ordered patterns of polyelectrolyte multilayer microcapsules consisting of alternating layers of poly(allylamine hydrochloride) and poly(sodium 4-styrene sulfonate) have been achieved. Anchoring the capsules on a pre-patterned substrate facilitates the utilization of their various capabilities in lab-on-a chip devices. In this paper we have demonstrated a very effective method to entrap soft capsules into surface cavities. Supported microcapsules were applied as the depots for loading and storage of macromolecular cargo (glucose oxidase and peroxidase) and as preserved microvessels for the cascade of enzymatic reactions. The loading of capsules was achieved under a pre-determined pH environment. This development is potentially useful for the realization of novel multianalytical systems for catalytic, bio-affinity and pH detection with protected sensing molecules. [ABSTRACT FROM AUTHOR]