The present study demonstrates the creation of a stable, superhydrophobic surface using the nanoscale roughness inherent in a vertically aligned carbon nanotube forest together with a thin, conformal hydrophobic poly(tetrafluoroethylene) (PTFE) coating on the surface of the nanotubes. Superhydrophobicity is achieved down to the microscopic level where essentially spherical, micrometer-sized water droplets can be suspended on top of the nanotube forest.

A versatile method to produce superhydrophobic fabrics by combining electrospinning and initiated chemical vapor deposition (iCVD) is reported. In this study, poly(caprolactone) (PCL) was first electrospun and then coated with a thin layer of hydrophobic polymerized perfluoroalkyl ethyl methacrylate (PPFEMA) by iCVD. The hierarchical surface roughness inherent in the PCL electrospun mats and the extremely low surface free energy of the coating layer obtained by iCVD yields stable superhydrophobicity with a contact angle of 175° and a threshold sliding angle less than 2.5° for a 20 mg droplet. This PPFEMA-coated PCL mat was also shown to exhibit at least “grade 8” oleophobicity. Hydrophobicity was demonstrated to increase monotonically with a reduction in diameter among bead-free fibers and with the introduction of a high density of relatively small diameter beads. The systematic effect of fiber morphology on superhydrophobicity was also investigated theoretically and experimentally using both beaded and bead-free fibers with diameters ranging from 600 to 2200 nm.

In a two-part investigation, an experimental study and a kinetic model analysis of the initiated chemical vapor deposition (iCVD) of alkyl acrylate polymers are described. In this first part, an experimental study was performed to look at the effect of process parameters on iCVD polymerization. A homologous series of alkyl acrylates, from ethyl up to hexyl acrylate, were iCVD polymerized. The resulting polymers matched well spectroscopically with those from liquid-phase polymerization, demonstrating that stoichiometric polymers with no observable cross-linking can be achieved in a chemical vapor deposition environment. Deposition rate and molecular weight increased by a factor of over 300 and 60, respectively, when monomer saturated vapor pressure, P sat, was reduced from 42.6 to 0.584 Torr at equal gas pressures, P M. Over three times increase in deposition rate was observed for ethyl acrylate when substrate temperature was reduced from 29 to 17 °C. These trends are attributed to an increase in P M/P sat or, equivalently, monomer surface concentration in Henry's law limit at low P M/P sat. Evidence for adsorption-limited iCVD kinetics came from an apparent negative activation energy of −79.4 kJ/mol obtained experimentally that agreed well with a mathematically derived activation energy of −81.8 kJ/mol equal to twice the heat of desorption in the negative sense. Adsorption measurements found Henry's law limit to be valid and, when fitted to a BET equation, allowed the heat of desorption to be calculated. On the basis of this experimental study, process guidelines were made to define the appropriate parameter space for future iCVD polymerization, with P M/P sat in the range of 0.4−0.7 recommended as an optimal iCVD window.

Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

We demonstrate a polymer-free carbon-based photovoltaic device that relies on exciton dissociation at the SWNT/C(60) interface, as shown in the figure. Through the construction of a carbon-based photovoltaic completely free of polymeric active or transport layers, we show both the feasibility of this novel device as well as inform the mechanisms for inefficiencies in SWNTs and carbon based solar cells.

The techniques of initiated chemical vapor deposition (iCVD) and oxidative chemical vapor deposition (oCVD) enable the fabrication of chemically well‐defined thin polymeric films on complex objects with micro‐ and nano‐scale features. By depositing polymers from the vapor phase, many wetting and solution effects are avoided, and conformal films can be created. In iCVD, a variant of hot filament CVD, the deposition rate is enhanced and chemical functionalities of the polymers' constituents are maintained by including a thermally labile initiator in the feed stream. Due to the low energy required when using an initiator, delicate substrates can be coated. In oCVD, infusible, electrically conductive films are formed directly on the substrate of interest as the oxidant and monomer are introduced into the reactor simultaneously. This Feature Article provides an overview of the work that has been done to develop iCVD and oCVD into platform technologies. Relevant background, fundamentals, and applications will be discussed.

Systematic variation in the electrical conductivity of poly(3,4-ethylenedioxythiophene) (PEDOT) was achieved by oxidative chemical vapor deposition (oCVD). For oCVD, both the oxidant, Fe(III)Cl3, and 3,4-ethylenedioxythiophene (EDOT) monomer are introduced in the vapor phase. A heated crucible allows for sublimation of the oxidant directly into the reactor chamber operating at 150 mTorr. Spontaneous reaction of the oxidant with the monomer introduced though a feedback-controlled mass flow system results in the rapid (>200 nm thick film in 30 min) formation of π-conjugated PEDOT thin films directly onto a temperature-controlled substrate. As the substrate temperature is increased from 15 to 110 °C, increasing conjugation length, doping level, and electrical conductivity of the PEDOT chains are observed by UV−vis absorption spectroscopy (UV−vis), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. Concomitantly, the measured electrical conductivity of the PEDOT films increases systematically with an apparent activation energy of 28.2 ± 1.1 kcal/mol.

Superhydrophobicity, water repellency, and self-cleaning properties of materials have recently attracted tremendous attention. [1][2][3] Superhydrophobic surfaces exhibit extraordinarily high water contact angles, by convention greater than 150°, and extraordinarily low contact-angle hysteresis (i.e., a low difference between advancing and receding contact angles), typically less than 5°-10°. Studies of superhydrophobicity realized by insects [4] and many plants, [5,6] particularly the lotus leaf, [6] show that these biological superhydrophobic surfaces not only have a low surface energy, but also a hierarchical surface roughness on at least two different (i.e., micro-and nanometer) length scales. Inspired by Nature, researchers have designed numerous synthetic superhydrophobic surfaces by creating nanometer-scale features on micrometer-scale roughened surfaces. [7][8][9][10][11] For example, Ming et al. [10] reported that a film containing raspberry-like particles (made by grafting 70 nm silica particles onto 0.7 lm silica particles) had a higher contact angle and lower contact-angle hysteresis than films composed solely of small (70 nm) or large (0.7 lm) particles with the same surface chemistry. Gao et al. [11] recently reported a significant increase in superhydrophobicity for hydrophobized surfaces containing micrometer-scale staggered rhombic posts, after imparting a second (nanoscale) topography onto the originally smooth surfaces of the posts with a solution reaction using methyltrichlorosilane. In this Communication, we describe two different strategies to make hierarchically roughened superhydrophobic surfaces, particularly in the form of electrospun nonwoven mats, by decorating micrometer-scale (ca. 1 lm) fibers with nanometer-scale (ca. 100 nm) pores or particles. These length scales are 1-2 orders of magnitude smaller than those exhibited by conventional woven textiles, including some composed of microfibers.[12]Electrospinning has become a popular method to generate continuous ultrathin fibers with micrometer and sub-micrometer diameters from a variety of polymeric materials. [13][14][15][16][17][18][19][20] Electrospun fibers intrinsically provide at least one length scale of roughness for superhydrophobicity because of the small fiber size. [21][22][23][24][25][26][27][28][29] For example, we previously showed that fiber mats composed solely of uniform fibers could be obtained by electrospinning a hydrophobic material (i.e., poly(styrene-blockdimethylsiloxane) block copolymer) blended with homopolymer polystyrene (PS).[23] The roughness of the nonwoven mat, resulting from the small diameters of the fibers (150-400 nm), combined with the enrichment of the dimethylsiloxane component at the fiber surfaces was sufficient to yield materials with a contact angle of 163°and a hysteresis value of 15°. Prior to that, Jiang et al. [21] reported a contact angle of 160.4°for a membrane consisting of micrometer-sized PS particles embedded within a fibrous PS matrix. Similarly, Acatay et al. [22] reported compa...