Investigation into the Formation and Adhesion of Cyclopentane Hydrates on Mechanically Robust Vapor-Deposited Polymeric Coatings

Blockage of pipelines by formation and accumulation of clathrate hydrates of natural gases (also called gas hydrates) can compromise project safety and economics in oil and gas operations, particularly at high pressures and low temperatures such as those found in subsea or arctic environments. Cyclopentane (CyC5) hydrate has attracted interest as a model system for studying natural gas hydrates, because CyC5, like typical natural gas hydrate formers, is almost fully immiscible in water; and thus CyC5 hydrate formation is governed not only by thermodynamic phase considerations but also kinetic factors such as the hydrocarbon/water interfacial area, as well as mass and heat transfer constraints, as for natural gas hydrates. We present a macroscale investigation of the formation and adhesion strength of CyC5 hydrate deposits on bilayer polymer coatings with a range of wettabilities. The polymeric bilayer coatings are developed using initiated chemical vapor deposition (iCVD) of a mechanically robust and densely cross-linked polymeric base layer (polydivinylbenzene or pDVB) that is capped with a covalently attached thin hydrate-phobic fluorine-rich top layer (poly(perfluorodecyl acrylate) or pPFDA). The CyC5 hydrates are formed from CyC5-in-water emulsions, and differential scanning calorimetry (DSC) is used to confirm the thermal dissociation properties of the solid hydrate deposits. We also investigate the adhesion of the CyC5 hydrate deposits on bare and bilayer polymer-coated silicon and steel substrates. Goniometric measurements with drops of CyC5-in-water emulsions on the coated steel substrates exhibit advancing contact angles of 148.3 ± 4.5° and receding contact angles of 142.5 ± 9.8°, indicating the strongly emulsion-repelling nature of the iCVD coatings. The adhesion strength of the CyC5 hydrate deposits is reduced from 220 ± 45 kPa on rough steel substrates to 20 ± 17 kPa on the polymer-coated steel substrates. The measured strength of CyC5 hydrate adhesion is found to correlate very well with the work of adhesion between the emulsion droplets used to form the CyC5 hydrate and the underlying substrates

Tunable Photoluminescence via Thermally Evaporated ZnS Ultra Thin Films

ZnS thin films have been deposited by thermal evaporation at various deposition rates. By controlling the deposition rate, the position of the maximum in the photoluminescence spectra could be easily tuned from 2.9 to 2.0 eV, which produced a corresponding change in the emission color. The optical and morphological characteristics of the ZnS thin films were measured. The photoluminescence spectra had broad peaks, suggesting a distribution of ZnS nanocrystallites dimensions. Nanocrystallites dimensions were in the range of 1 nm to 3 nm via TEM analyses. The changes in optical properties were potentially attributable to the lattice defects of ZnS crystals, including Schottky defects and the substation of sulfur atoms by oxygen atoms. The color of the resulting light emission was obtained by controlling the deposition rate of ZnS

Conformal single-layer encapsulation of PEDOT at low substrate temperature

In this work, we demonstrate a single-layer encapsulation method for poly(3,4-ethylenedioxythiophene) (PEDOT). This method is achieved by initiated chemical vapor deposition (iCVD) process, which is scalable and employs solvent-free and low-substrate temperature conditions. The encapsulant used, poly(divinylbenzene-co-maleic anhydride) (PDVB-MA), was first time synthesized via vapor phase process. This cross-linked iCVD polymer can be rapidly deposited (40 nm min−1) with uniform and conformal morphology. In the test of PEDOT degradation, the encapsulation extended the halflife of PEDOT to 900 h at 30 °C in air, which is more than 10 times of the counterpart without encapsulation.Eni S.p.A. (Firm) (Eni-MIT Solar Frontiers Alliance

Super-Hydrophobic and Oloephobic Crystalline Coatings by Initiated Chemical Vapor Deposition

Preferred crystallographic orientation (texture) in thin films frequently has a strong effect on the properties of the materials and it is important for stable surface properties. Organized molecular films of poly-perfluorodecylacrylate p(PFDA) were deposited by initiated Chemical Vapor Deposition (iCVD). The high tendency of p(PFDA) to crystallize has been fully retained in the polymers prepared by iCVD. The degree of crystallinity and the preferred orientation of the perfluoro side chains, either parallel or perpendicular to the surface, were controlled by tuning the CVD process parameters (i.e. initiator to monomer flow rate ratio, filament temperature, and substrate temperature). Super- hydrophobicity (advancing water contact angle, WCA, of 160°, low hysteresis of 5°), and oleophobicity (advancing CA with mineral oil of 120°) were achieved. Low hysteresis was associated with high crystallinity, particularly when the orientation of the crystallites resulted in the perfluoro side groups being oriented parallel to the surface. The latter texture resulted in smoother film (RMS roughness < 30 nm) than the texture with the chains oriented perpendicularly to the surface. This can be very advantageous for applications that require smooth but still crystalline films.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract DAAD-19-02D-0002

Mechanics of Graded Wrinkling

The properties and behavior of a surface as well as its interaction with surrounding media depend on the inherent material constituency and the surface topography. Structured surface topography can be achieved via surface wrinkling. Through the buckling of a thin film of stiff material bonded to a substrate of a softer material, wrinkled patterns can be created by inducing compressive stress states in the thin film. Using this same principle, we show the ability to create wrinkled topologies consisting of a highly structured gradient in amplitude and wavelength, and one which can be actively tuned. The mechanics of graded wrinkling are revealed through analytical modeling and finite element analysis, and further demonstrated with experiments.Center for Clean Water and Clean Energy at MIT and KFUP

Desalination by Membrane Distillation using Electrospun Polyamide Fiber Membranes with Surface Fluorination by Chemical Vapor Deposition

Fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were fabricated by electrospinning and rendered hydrophobic by applying a conformal coating of poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) using initiated chemical vapor deposition (iCVD). A set of iCVD-treated electrospun PA6(3)T fiber membranes with fiber diameters ranging from 0.25 to 1.8 μm were tested for desalination using the air gap membrane distillation configuration. Permeate fluxes of 2–11 kg/m²/h were observed for temperature differentials of 20–45 °C between the feed stream and condenser plate, with rejections in excess of 99.98%. The liquid entry pressure was observed to increase dramatically, from 15 to 373 kPa with reduction in fiber diameter. Contrary to expectation, for a given feed temperature the permeate flux was observed to increase for membranes of decreasing fiber diameter. The results for permeate flux and salt rejection show that it is possible to construct membranes for membrane distillation even from intrinsically hydrophilic materials after surface modification by iCVD and that the fiber diameter is shown to play an important role on the membrane distillation performance in terms of permeate flux, salt rejection, and liquid entry pressure

Ultrathin high-resolution flexographic printing using nanoporous stamps

Since its invention in ancient times, relief printing, commonly called flexography, has been used to mass-produce artifacts ranging from decorative graphics to printed media. Now, higher-resolution flexography is essential to manufacturing low-cost, large-area printed electronics. However, because of contact-mediated liquid instabilities and spreading, the resolution of flexographic printing using elastomeric stamps is limited to tens of micrometers. We introduce engineered nanoporous microstructures, comprising polymer-coated aligned carbon nanotubes (CNTs), as a next-generation stamp material. We design and engineer the highly porous microstructures to be wetted by colloidal inks and to transfer a thin layer to a target substrate upon brief contact. We demonstrate printing of diverse micrometer-scale patterns of a variety of functional nanoparticle inks, including Ag, ZnO, WO[subscript 3], and CdSe/ZnS, onto both rigid and compliant substrates. The printed patterns have highly uniform nanoscale thickness (5 to 50 nm) and match the stamp features with high fidelity (edge roughness, ~0.2 μm). We derive conditions for uniform printing based on nanoscale contact mechanics, characterize printed Ag lines and transparent conductors, and achieve continuous printing at a speed of 0.2 m/s. The latter represents a combination of resolution and throughput that far surpasses industrial printing technologies.Massachusetts Institute of Technology. Department of Mechanical EngineeringNational Science Foundation (U.S.) (Grant CMMI-1463181)United States. Air Force Office of Scientific Research. Young Investigator Program (Grant FA9550-11-1-0089)National Institutes of Health (U.S.) (Grant 1R21HL114011-01A1

Controlled formation of Schottky diodes on n-doped ZnO layers by deposition of p-conductive polymer layers with oxidative chemical vapor deposition

We report the controlled formation of organic/inorganic Schottky diodes by depositing poly(3,4- ethylenedioxythiophene) (PEDOT) on n-doped ZnO layers using oxidative chemical vapor deposition (oCVD). Current-voltage measurements reveal the formation of Schottky diodes that show good thermal and temporal stability with rectification ratios of 10 7 and ideality factors of ∼1.2. In the frame of a Schottky model, we identify a mean barrier height at the hybrid inorganic-organic interface of 1.28 eV, which is consistent with the difference between the work function of PEDOT and the electron affinity of ZnO. The findings highlight the strength of oCVD to design high-quality hybrid PEDOT/ ZnO heterojunctions with possible applications in electronic and optoelectronic devices

The effects of iCVD film thickness and conformality on the permeability and wetting of MD membranes

Membranes possessing high permeability to water vapor and high liquid entry pressure (LEP) are necessary for efficient membrane distillation (MD) desalination. A common technique to prepare specialized MD membranes consists of coating a hydrophilic or hydrophobic base membrane with a low surface-energy material. This increases its liquid entry pressure, making the membrane suitable for MD. However, in addition to increasing LEP, the surface-coating may also decrease permeability of the membrane by reducing its average pore size. In this study, we quantify the effects of initiated chemical vapor deposition (iCVD) polymer coatings on membrane permeability and LEP. We consider whether the iCVD films should have minimized thickness or maximized non-conformality, in order to maximize the permeability achieved for a given value of LEP. We determined theoretically that permeability of a single pore is maximized with a highly non-conformal iCVD coating. However, the overall permeability of a membrane consisting of many pores is maximized when iCVD film thickness is minimized. We applied the findings experimentally, preparing an iCVD-treated track-etched polycarbonate (PCTE) membrane and testing it in a permeate gap membrane distillation (PCMD) system. This study focuses on membranes with clearly defined, cylindrical pores. However, we believe that the principles we discuss will extend to membranes with more complex pore architectures. Overall, this work indicates that the focus of surface-coating development should be on minimizing film thickness, not on increasing their non-conformality.MIT & Masdar Institute Cooperative Program (02/MI/MI/CP/11/07633/GEN/G/00)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-13-d-0001