Flexible, Elastic, and Superhydrophobic/Superoleophilic Adhesive for Reusable and Durable Water/Oil Separation Coating.

This study investigates a highly flexible/stretchable and mechanically durable superhydrophobic/superoleophilic coating for efficient oil/water separation and oil absorption. The coating is applied via a simple immersion process using a mixed solution of a biocompatible adhesive (ethyl cyanoacrylate, ECA), a highly stretchable polymer (polycaprolactone, PCL), and superhydrophobic/superoleophilic nanoparticles (fluorine-coated silica nanoparticles, F-SiO2 NPs) in a solvent, followed by solvent evaporation and ECA polymerization. Polymerized ECA (poly-ECA) in the coating material strongly adheres the F-SiO2 NPs to the substrate surface, while PCL bestows the rigid poly-ECA with high flexibility. A coated polyurethane sponge exhibits superhydrophobicity (water contact angle of >150°), while retaining robust mechanical stability and flexibility/elasticity. This provides an efficient means of cleaning oil spills with high selectivity, even after mechanical abrasion (>99% separation efficiency is retained after 120 tape test cycles and 50 rubbing test cycles), with excellent reusability.

A strategy for preparing controllable, superhydrophobic, strongly sticky surfaces using SiO2@PVDF raspberry core-shell particles.

In nature, wetting by water droplets on superhydrophobic materials is governed by the Cassie-Baxter or Wenzel models. Moreover, sticky properties, derived from these types of wettings, are required for a wide range of applications involving superhydrophobic materials. As a facile new strategy, a method employing a gaseous fluorine precursor to fabricate core-shell particles, comprising perfectly shaped fluorine shells with adjustable adhesive strength, is described in this paper. Silica was used as the hydrophilic core, while polyvinylidene fluoride (PVDF) was used for the hydrophobic shell coating, forming a raspberry-like shape. In addition, controlling the amount of PVDF coated on the silica surface enabled the water droplets to come into contact with both the PVDF of the shell and the silica of the core, thereby controlling both the superhydrophobicity and the adhesive strength. Thus, the synthesized particles formed a structured coating with controllable stickiness and contact angles of 131-165°. Furthermore, on surfaces with high adhesivity, the water droplets remained stable at tilt angles of 90° and 180° even under a strong centrifugal force, whereas on surfaces with low adhesivity, the water droplets slid off when the substrate was tilted at 4°.

Perfluoropolyether-benzophenone as a highly durable, broadband anti-reflection, and anti-contamination coating.

Anti-reflection and anti-contamination coatings prepared from fluorinated polymers have widespread and important applications, ranging from protective films for corrosion resistance to high-tech microelectronics and medical devices due to their transparency, low refractive index, stain resistance, and antifouling properties. However, the application of existing coatings is hindered by low surface adhesion to the target substrate and weakness when exposed to mechanical stress or damage, resulting in significant limitations to their practical applications. Herein, we incorporate perfluoropolyether (PFPE) with benzophenone (BP) to develop an efficient coating material (PFPE-BP) possessing broadband anti-reflectivity, anti-contamination properties, excellent abrasion resistance, and stability under elevated temperatures and relative humidity. The presence of BP allows the coating materials to be homogeneously mixed with a commercial hard coating solution to uniformly coat the target substrate. Furthermore, UV light irradiation on the coating surface results in excellent adhesion between BP groups of PFPE-BP and the hard coating matrix.

Fluorinated Titania Nanoparticle-Induced Piezoelectric Phase Transition of Poly(vinylidene fluoride).

We prepared F-coated rutile titanium dioxide nanoparticles (r-TiO2 NPs) via simple thermal annealing of titania NPs in poly(vinylidene fluoride) (PVDF) and demonstrated that the F-coated r-TiO2 NP-doped composite film could efficiently induce piezoelectric phase transition of non-electroactive PVDF due to highly electronegative F bonds on the surface of these NPs. In the case of a 2.0 wt % composite film, 99.20% of the non-electroactive PVDF was transformed into the electroactive phase. Additionally, utilizing the F-coated r-TiO2 NPs for a piezoelectric device led to an enhancement of the piezoelectric performance. With the 5.0 wt % composite film, the resulting piezoelectric device exhibited voltage generation of 355 mV, whereas a device with the innate r-TiO2 NPs exhibited voltage generation of only 137 mV. Furthermore, because of optical inactivity of F-coated r-TiO2 NPs, the piezoelectric films exhibited high stability under 64 h of photoirradiation at an intensity of 0.1 W/cm2. These results indicate that the F-coated r-TiO2 NP-doped composite films could be useful for various applications, including outdoor energy-harvesting, self-powered wearable devices, and portable sensors.

Preparation and electroactive phase adjustment of Ag-doped poly(vinylidene fluoride) (PVDF) films.

The crystallinities of Ag-doped poly(vinylidene fluoride) (PVDF) films were modified by removing Ag+ using a novel washing process, which allowed control of the ratio of γ- and ß-phases. The polarity of the composite film without Ag+ removal through the washing process reached 98%, and the ß-phase content in the total electroactive phase was increased to 61%, according to Fourier-transform infrared spectroscopy. When Ag+ were removed through a process involving several cycles of washing, filtering, drying, and re-dissolving, the highest ratio of the γ-phase was increased to 67%, 28% higher than that before washing. This showed that Ag+ induced ß-phase formation while Ag nanoparticles induced γ-phase formation, and that the ratio of γ- and ß-phases in PVDF composite films can be controlled to suit specific applications by this washing process.

High-Performance Magnetorheological Suspensions of Pickering-Emulsion-Polymerized Polystyrene/Fe3O4 Particles with Enhanced Stability.

The magnetorheological (MR) performance of suspensions based on core-shell-structured foamed polystyrene (PSF)/Fe3O4 particles was investigated by using a vibrating sample magnetometer and a rotational rheometer. Core-shell-structured polystyrene (PS)/Fe3O4 was synthesized by using the Pickering-emulsion polymerization method in which Fe3O4 nanoparticles were added as a solid surfactant. Foaming the PS core in PS/Fe3O4 particles was carried out by using a supercritical carbon dioxide (scCO2) fluid. The density was measured by a pycnometer. The densities of PS/Fe3O4 and PSF/Fe3O4 particles were significantly lowered from that of the pure Fe3O4 particle after Pickering-emulsion polymerization and foaming treatment. All tested suspensions displayed similar MR behaviors but different yield strengths. The important parameter that determined the MR performance was not the particle density but rather the surface density of Fe3O4 on the PS core surface. The morphology was observed by scanning electron microscopy and transmission electron microscopy. Most Fe3O4 particles stayed on the surface of PS/Fe3O4 particles, making the surface topology bumpy and rough, which decreased the particle sedimentation velocity. Finally, Turbiscan apparatus was used to examine the sedimentation properties of different particle suspensions. The suspensions of PS/Fe3O4 and PSF/Fe3O4 showed remarkably improved stability against sedimentation, much better than the bare Fe3O4 particle suspension because of the reduced density mismatch between the nanoparticles and the carrier medium as well as the surface topology change.

Tuning Surface Properties of Poly(methyl methacrylate) Film Using Poly(perfluoromethyl methacrylate)s with Short Perfluorinated Side Chains.

To control the surface properties of a commonly used polymer, poly(methyl methacrylate) (PMMA), poly(perfluoromethyl methacrylate)s (PFMMAs) with short perfluorinated side groups (i.e., -CF3, -CF2CF3, -(CF3)2, -CF2CF2CF3) were used as blend components because of their good solubility in organic solvents, low surface energies, and high optical transmittance. The surface energies of the blend films of PFMMA with the -CF3 group and PMMA increased continuously with increasing PMMA contents from 17.6 to 26.0 mN/m, whereas those of the other polymer blend films remained at very low levels (10.2-12.6 mN/m), similar to those of pure PFMMAs, even when the blends contained 90 wt %PMMA. Surface morphology and composition measurements revealed that this result originated from the different blend structures, such as lateral and vertical phase separations. We expect that these PFMMAs will be useful in widening the applicable window of PMMA.

Neurally Encoding Time for Olfactory Navigation.

Accurately encoding time is one of the fundamental challenges faced by the nervous system in mediating behavior. We recently reported that some animals have a specialized population of rhythmically active neurons in their olfactory organs with the potential to peripherally encode temporal information about odor encounters. If these neurons do indeed encode the timing of odor arrivals, it should be possible to demonstrate that this capacity has some functional significance. Here we show how this sensory input can profoundly influence an animal's ability to locate the source of odor cues in realistic turbulent environments-a common task faced by species that rely on olfactory cues for navigation. Using detailed data from a turbulent plume created in the laboratory, we reconstruct the spatiotemporal behavior of a real odor field. We use recurrence theory to show that information about position relative to the source of the odor plume is embedded in the timing between odor pulses. Then, using a parameterized computational model, we show how an animal can use populations of rhythmically active neurons to capture and encode this temporal information in real time, and use it to efficiently navigate to an odor source. Our results demonstrate that the capacity to accurately encode temporal information about sensory cues may be crucial for efficient olfactory navigation. More generally, our results suggest a mechanism for extracting and encoding temporal information from the sensory environment that could have broad utility for neural information processing.

Quantifying bursting neuron activity from calcium signals using blind deconvolution.

Advances in calcium imaging have enabled studies of the dynamic activity of both individual neurons and neuronal assemblies. However, challenges, such as unknown nonlinearities in the spike-calcium relationship, noise, and the often relatively low temporal resolution of the calcium signal compared to the time-scale of spike generation, restrict the accurate estimation of action potentials from the calcium signal. Complex neuronal discharge, such as the activity demonstrated by bursting and rhythmically active neurons, represents an even greater challenge for reconstructing spike trains based on calcium signals. We propose a method using blind calcium signal deconvolution based on an information-theoretic approach. This model is meant to maximise the output entropy of a nonlinear filter where the nonlinearity is defined by the cumulative distribution function of the spike signal. We tested our maximum entropy (ME) algorithm using bursting olfactory receptor neurons (bORNs) of the lobster olfactory organ. The advantage of the ME algorithm is that the filter can be trained online based only on the statistics of the spike signal, without any assumptions regarding the unknown transfer function characterizing the relation between the spike and calcium signal. We show that the ME method is able to more accurately reconstruct the timing of the first and last spikes of a burst compared to other methods and that it improves the temporal precision fivefold compared to direct timing resolution of calcium signal.

Organic electrochemical transistor based immunosensor for prostate specific antigen (PSA) detection using gold nanoparticles for signal amplification.

We demonstrated a highly sensitive organic electrochemical transistor (OECT) based immunosensor with a low detection limit for prostate specific antigen/alpha1-antichymotrypsin (PSA-ACT) complex. The poly(styrenesulfonate) doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) based OECT with secondary antibody conjugated gold nanoparticles (AuNPs) provided a detection limit of the PSA-ACT complex as low as 1pg/ml, as well as improved sensitivity and a dynamic range, due to the role of AuNPs in the signal amplification. The sensor performances were particularly improved in the lower concentration range where the detection is clinically important for the preoperative diagnosis and screening of prostate cancer. This result shows that the OECT-based immunosensor can be used as a transducer platform acceptable to the point-of-care (POC) diagnostic systems and demonstrates adaptability of organic electronics to clinical applications.

Synthesis and Surface Property of Aqueous Fluorine-Containing Polyurethane.

A novel aqueous fluorine-containing polyurethane was prepared with a hydrophobic macromonomer of a perfluoroalkyl group. Two representative properties of the polyurethane, initial particle diameter dispersed in water and surface free energy of coating films, were investigated. The macromonomer was synthesized by radical copolymerization of perfluoroalkylethyl acrylate and methyl methacrylate with a diol of chain-transfer agent in order to attenuate solubility and hydrophobic property. Anionic aqueous polyurethane was obtained with a good hydrophobic film property by one-step condensation polymerization of the macromonomer with hydrophilic comonomers and successive ionization. The polyurethane showed an initial average diameter of less than 1100 nm in water and surface free energies of less than 19 dyn/cm. The water dispersion property and hydrophobic surface property of the polyurethane can be controlled by controlling the content and hydrophobic property of the macromonomer. The incorporation of the macromonomer in the polyurethane backbone did not show a significant effect on the glass transition temperature, or the softness, of the polyurethane. Copyright 2001 Academic Press.