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Membrane technology has been proven to be highly valuable in extensive applications, such as separation and purification, surface engineering, packaging, and electronics. Controllable surface wetting behavior is pivotal in determining the practical applications of membranes in various scenarios. In this study, a superhydrophobic nanofibrous membrane with diverse adhesion was prepared by a novel in-situ fibrillation of polytetrafluoroethylene (PTFE). The fibrous structures can be facilely manipulated by the processing temperatures, and a hierarchical structure of micro-/nano-scale PTFE fibrils simultaneously achieves superhydrophobicity with high adhesion. In contrast, a superhydrophobic surface with extremely low adhesion was fabricated by in-situ introducing SiO 2 microspheres into membrane. Therefore, the distinct adhesion of the membranes enables multifunctional applications that require different liquid wettability, such as the manipulation of tiny droplets, self-cleaning, and anti-icing properties. Furtherly, the nanofibrous membranes demonstrated outstanding oil/water separation performance with great efficiency over 99.5% and flux as high as 5303 L·m−2·h−1. The fabricated nanofibrous PTFE membrane, exhibiting either a "petal effect" or "lotus effect", along with their flexible fabrication methodology, offer a promising approach to meet the demand for chemical, environment, and biomedicine area. [Display omitted] • Novel nanofibrous polytetrafluoroethylene (PTFE) and composite membranes are presented that exhibit superhydrophobicity. • Diverse droplet adhesion of "petal effect" and "lotus effect" are achieve by NF-PTFE and NF-PTFE/SiO 2 membranes respectively. • The prepared superhydrophobic surfaces shows excellent chemical-resistance in micro droplet transfer, self-cleaning and anti-icing applications. • The prepared superhydrophobic membranes have outstanding oil/water separation property with high flux and separation efficiency. [ABSTRACT FROM AUTHOR]

[Display omitted] • A lattice-patterned tactile sensing skin is introduced for large-area pressure mapping applications. • The lattice structure is made of a piezoresistive silicone composite and is embedded into a silicone substrate. • Electrical impedance tomography (EIT) enables spatial mapping of pressure sans any internal wiring. • The entire surface of the sensing skin offers high sensitivity and spatial resolution in both flat and non-planar configurations. • The lattice pattern can be tailored to suit different applications in health monitoring and robotics. Spatially distributed sensing has gained significant value in diverse domains, with wearables as a notable application. In this work, a flexible skin-like sensor was developed for distributed pressure sensing. The sensing skin comprised a carbon black/silicone composite lattice structure embedded in a silicone sheet. The lattice-patterned structure is a distinct departure from conventional uniform sensing skins. Electrical impedance tomography (EIT) was employed to reconstruct electrical resistance over the sensing area, which was then mapped into pressure distribution based on the principle of piezoresistivity. EIT offers continuity and design simplicity as it eliminates the need for internal wiring, making it a promising technique in the wearable industry. The lattice sensing skin offered favorable sensing attributes, including quick response and recovery (75 ms and 84 ms at 85 kPa), a linear response with sensitivity as high as 0.119 kPa−1, a full-scale range of at least 100 kPa, and high repeatability (∼0.5% drop in maximum relative resistance over 300 cycles). The sensing skin was responsive over its entire area in both flat and non-planar conditions and was able to detect both single- and multi-point touch. The sensitivity and tactile area detectability varied depending on the position of applied pressure over the sensing area. Future studies will examine other lattice patterns and conductive composite fillers with the intention to develop a framework for optimizing the lattice sensing skin for tailored accuracy and resolution. [ABSTRACT FROM AUTHOR]

We studied poly(lactic acid)’s strain-induced crystallization behavior during a tandem extrusion process using visualization techniques. Our visualization results showed that, despite its inherently slow crystallization kinetics in the quiescent condition, PLA crystallites were quickly formed inside the die at a temperature even above the melting temperature (T m ), as the melt temperature was decreased. Their rapid formation at a high temperature above the T m peak, was due to the strain-induced crystallization. We also studied how the strain rate and the use of supercritical CO 2 affected PLA crystallization. A significant increase in the PLA crystallization kinetics was caused by a sudden increase in the screw speeds of the extruders with a fixed barrel temperature. The crystallization enhancement, which was caused by the increased flow rate, became more pronounced at lower temperatures due to the higher degree of molecular orientation. Adding the CO 2 shifted the crystallization temperature to a lower processing temperature due to its plasticization effect, but it accelerated the crystallization kinetics as well. We also observed a correlation between the content of the induced crystallites inside the extruder and the cellular structure of the extruded foams. This clearly explained the decrease in the optimal processing temperature for foaming with an increased CO 2 content. [ABSTRACT FROM AUTHOR]

Since the introduction of triboelectric nanogenerators (TENGs), a variety of dielectric and electrode materials have been developed to improve the TENGs output performance. However, due to their inherent shortcomings, including mechanical deficiencies, insufficient contact area, and limited breathability, the development of TENGs with diverse features and multi functionalities has been limited. To address these challenges, various porous materials and structural designs have been explored in the last decade for development of dielectrics and electrodes. Porous materials include hydrogels, aerogels, foams, and fibrous media, which due to their unique interconnected porous network, high surface area, and tunable pore size distribution, have been shown to be effective in improving the performance and versatility of TENGs. Alternatively, structural designs have also been introduced in the form of textiles and yarns to further expand the functionalities of TENGs. Compared to the first approach, such designs provide larger pores, which can be implemented as air gap in TENG designs. Therefore, these can provide the opportunity for the fabrication of all-in-one TENGs. Given the importance of the above strategies in improving the performance of TENGs and expanding their functionalities, this work aims to summarize, categorize, and highlight the recent advancements in the field of porous materials and structural designs. Representative applications of porous TENGs, including human-machine interfaces, smart wearables, and self-powered sensors with respect to the pore size, are reviewed. The current challenges and future perspectives for integrating porous materials and structures into TENGs are also discussed. [Display omitted] • Porous materials and structures are studied for the TENG dielectrics and electrodes. • Porous materials include hydrogels, aerogels, foams, and fibrous media. • Porous structure assembly includes textile-based and yarn designs. • Pore size of the porous TENG systems varies in the range of nano to macro meter. • The benefits and challenges of porous systems for the TENG application are reported. [ABSTRACT FROM AUTHOR]

This study investigates the influence of material properties and foaming temperature on the cellular structure of foams produced by batch foaming of linear, branched and nucleated polylactide (PLA), using supercritical nitrogen. Higher viscosities, corresponding to low foaming temperatures, resulted in smaller cell sizes within the investigated foaming temperature range of 140–180 °C, whereas higher foaming temperatures favoured larger volume expansion ratio ( VER ). In the presence of branching the PLAs exhibited strain hardening, which served to stabilize the foams and resulted in a finer cellular structure and improved VER s. Formulations containing boron nitride (BN) nucleating agent could not foam at the lowest temperature of 140 °C, because of crystallization taking place at this temperature. A combination of branching and nucleation achieved by reactive modification of PLA using peroxide and coagent crosslinking agents yielded the best results. The cell densities of foams made out of this formulation were significantly higher compared to the rest of the formulations, of the order of 10 11 cells/cm 3 . Very fine, sub-micron sized foams were obtained when this material was foamed at 140 °C, which is close to its exothermic crystallization temperature. This work provides guidelines of the ranges of material property values that are more conducive to achieve micro- and sub-micron sized foams. [ABSTRACT FROM AUTHOR]

Microelectronic is developing towards high frequency (GHz) and high speed (Gpbs), putting forward high requirements for low dielectric materials. The most efficient method for fabricating low dielectric materials is the incorporation of air into matrix via supercritical CO 2 foaming. Herein, a low dielectric thermoplastic perfluorinated polymer is selected to be the matrix and another low dielectric perfluorinated polymer which is capable to form in-situ nanofibrils is selected to regulate the matrix viscoelasticity. Supercritical CO 2 foaming method is then applied to introduce a large amount of low dielectric air into nanofibrill modified perfluorinated polymer. Owing to supercritical CO 2 as a residue-free foaming agent (residue impurities in matrix originated from foaming agent would increase dielectric loss significantly at GHz) and its strong interaction with perfluorinated polymer (ensure large expansion ratio of the obtained foams to introduce a large amount of low dielectric air in matrix), the lowest dielectric loss of 0.00015 (among the existing polymeric materials) is then obtained by supercritical CO 2 foaming of in-situ nanofibril modified perfluorinated polymer. Furthermore, the hydrophobic and oilphobic properties of the perfluorinated polymer were enhanced by supercritical CO 2 foaming to form a cellular structure; simultaneously, the corrosion resistance to strong alkali and V0 flame retarding properties of the ultra-low dielectric foam were maintained resulted from the perfluorinated cell walls. Therefore, such superior comprehensive performance of this ultra-low dielectric perfluorinated foam made from supercritical CO 2 foaming enables it the best alternative for the next-generation high-frequency (GHz to THz) and high-speed (sub Tbps) signal transmission substrate in electronics. [Display omitted] • Supercritical CO 2 foaming for ultra-low dielectric loss. • Lowest dielectric loss of 0.00015 among existing polymeric material. • Ultra-low dielectric material withstands harsh environment frequently encountered for PCB substrate. [ABSTRACT FROM AUTHOR]

The present work adopts the one-step batch foaming technique to develop microcellular foams from polysulfone (PSU) and polyethersulfone (PES) using supercritical carbon dioxide (CO 2) as a physical blowing agent. The results illustrates that the high temperature polymers can successfully generate highly uniform cellular structures with CO 2, exhibiting cell densities in the order of 1010 cells/cm3 but limited volume expansion ratios of up to 4 times. The cell densities of both systems, PSU/CO 2 and PES/CO 2 , were observed to be highly affected by the foaming pressure, showing significant enhancement of over 5 orders of magnitude with an increase in pressure from 3.4 to 13.8 MPa. On the other hand, the expansion ratio showed a strong dependence on the foaming temperature. Especially, the foams produced at pressures below 13.8 MPa exhibited a unique double peak behavior consisting of two maximum expansion ratios obtained at two different temperatures. In the temperature range of the first expansion peak, nanostructures were observed on the cell walls of the foams. The surficial features appeared in the form of a nanofibril network and gradually disappeared as the temperature approached the region of the second peak. Based on the observation, the unique double peak behavior may be correlated to the presence of the nanostructures. The work also encompassed measurement of CO 2 solubility and high pressure thermal analysis of the two polymers, which were incorporated in the discussion of the distinctive foaming behavior. • Experimental and theoretical determination of carbon dioxide (CO 2) solubility in sulfone polymers: polysulfone (PSU), and polyethersulfone (PES). • Depression of glass transition temperatures of PSU and PES as a function of the dissolved CO 2 content. • Unique expansion behaviors of PSU and PES showing two expansion ratio maxima with respect to the processing temperature. • Observation of nanostructures on the cell walls of the PSU and PES foams. [ABSTRACT FROM AUTHOR]

A class of microcellular polymer nanocomposites of multi-walled carbon nanotubes (MWCNT) is reported that exhibits a stable and significantly high dielectric permittivity coupled with a stable and low dielectric loss in a wide range of frequency. Polypropylene (PP)-MWCNT nanocomposites with a cellular structure were prepared by melt mixing followed by physical foaming in an injection molding process. The generation of a cellular structure inside the nanocomposites provides a unique planar-like arrangement of the MWCNTs around the cells. This enhances the dielectric permittivity of nanocomposites up to an order of magnitude. Therefore, microcellular PP-1.25 vol% MWCNT presents a dielectric permittivity of ε ′ = 57.2 and a dielectric loss of tan δ =0.05 at 0.1 MHz, highly superior to the best values of the solid nanocomposites prepared by regular compression molding ( ε ′ = 14.1 and tan δ =0.39) and by injection molding ( ε ′ = 17.8 and tan δ =0.04). Also, microcellular PP-1.66 vol% MWCNT exhibits ε ′ = 95.6 and tan δ =0.14, which surpasses the dielectric performances reported in the literature. Hence, these nanocomposites with a cellular structure provide a novel and general approach to develop microscopically tailored structures for dielectric applications using facile methods. Such dielectrics can be used for energy storage in modern electronics and electrical power systems. [ABSTRACT FROM AUTHOR]