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Keywords:

  • chemical vapor deposition;
  • polymers;
  • scale-up;
  • surface chemistry;
  • thin films

Abstract

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

Chemical vapor deposition (CVD) methods are a powerful technology for engineering surfaces. When CVD is combined with the richness of organic chemistry, the resulting polymeric coatings, deposited without solvents, represent an enabling technology in many different fields of application. This article focuses on initiated chemical vapor deposition (iCVD), a new technique that utilizes benign reaction conditions to yield conformal and functional polymer thin films. The latest achievements in coating surfaces and 3D substrates with functional materials, and the use of the technique for biotechnology and selective permeation applications are reviewed, and future directions for iCVD technology are discussed.


1. Introduction

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

Designing polymer surfaces has become a very common approach to tune surface properties for addressing the needs of specific applications. Indeed, wet chemical methods have long been used to achieve this goal.1, 2 Solvent-free processing extends the realms in which polymeric surface modification can be used. First, chemical vapor deposition (CVD) provides a means of synthesizing polymer thin films that are insoluble or infusible. Additionally, eliminating solvent usage avoids the potential for damage or unwanted modification, such as swelling, of the object to be coated. Since CVD builds the polymeric layer from the surface, use of such techniques can produce covalent chemical bonds between the film and substrate, resulting in adhesive grafted layers. CVD provides precise control over film thickness and yields so-called “conformal coatings” that uniformly cover diverse geometric features, including trenches, microparticles, and nanotubes.3–5 Finally, CVD polymer films contain no entrained solvent. Consequently, a curing step is not typically needed after the film is formed and leaching of residual solvent is not a concern for achieving biocompatibility.6

The optimal CVD method for fabricating solvent-free polymeric layers depends on the reaction mechanism, reaction rate, and volatility of the starting monomer(s). In hot-wire chemical vapor deposition (HWCVD), a monomer is delivered as a gaseous precursor, which is thermally decomposed over resistively heated filaments. The resulting reactive species undergo polymerization by adsorption on a cooled surface. This technique is commonly used to create fluorocarbon and organosilicon films7 and has attracted significant attention due to the high quality of the films and scalability of the process.8 Vapor-deposition polymerization (VDP) avoids the use of heated filaments by coevaporating two or more reactive monomers and is often utilized for step-growth polymers. For example, Chen et al.9 showed that diamines and dianhydrides yield poly(amic acid) films, which, after thermal curing, form polyimides and polybenzoxazoles. In addition, adjusting the incident molar flux and the ratio of components during VDP allows for control of surface crystallization of the monomers.10 Plasma-enhanced chemical vapor deposition (PECVD) is compatible with a wide variety of monomers, including many that use a chain polymerization mechanism. Additionally, PECVD often operates at low surface temperatures. As a consequence, the numerous reactive functional groups that are retained in the polymer film make this technique suitable for biomedical applications.11 Contrary to the previous methods, initiated chemical vapor deposition (iCVD) employs an initiator, such as a peroxide, to kick off the polymerization. The initiator is introduced as a vapor-phase reactant and is thermally decomposed to form radicals. These radicals and vinyl monomer(s) adsorb on the surface and free-radical polymerization occurs. iCVD thin films have been exploited for wettability, sensing, microelectronics, and protein adsorption control applications.12–15 The iCVD method is unique in that it requires low energy input and operates at low surface temperatures, yet yields high deposition rates. iCVD also enables conformal coating, and the benign reaction conditions used during deposition ensure that chemical functionality is preserved.16, 17 A similar method, oxidative chemical vapor deposition (oCVD), employs an oxidant molecule, which acts as an initiator and dopant for step-growth polymerization of conducting and semiconducting polymers. Due to their electrical properties, these films have been integrated into organic photovoltaic cells18–20 and biosensors.21, 22 Here, we focus on the iCVD process and highlight the capability of this method to modify physical properties on surfaces and to create new interfaces. The implementation of iCVD films in biotechnology applications and the selective permeation properties of these materials are discussed. Finally, we briefly outline future directions and perspectives for solvent-free methods.

2. Tailored Surfaces and Interfaces

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

Optimal physical and chemical surface properties are sought when depositing an organic thin film. Thus, the interaction between the polymer and its surroundings – either the substrate or the external environment – determines the viability of a material for a specific application. For instance, for thin films in photovoltaic cells, enhancing the degree of crystallinity increases the number of charge carriers.23 In contrast, a high degree of crystallinity is undesirable in some biomaterials because it results in a loss of mechanical properties.24 Coclite et al.25 reported that the degree of crystallinity in poly(perfluorodecyl acrylate) (pPFDA) thin films can be controlled by tuning iCVD process parameters (filament temperature, substrate temperature, and the ratio of initiator and monomer flow rates). In addition, the perfluoro side chain can be oriented parallel or perpendicular to the surface modifying the wettability and roughness of the film. A second study26 revealed that grafting of PFDA polymer chains enhances the crystalline order of the coating, resulting in fiber-like structures. The grafted films exhibit superhydrophobic and oleophobic properties. Grafting is achieved by covalently bonding trichlorovinylsilane to a plasma-treated silicon wafer. During the iCVD process, the vinyl groups of the silane react with radical initiators to yield alkyl radicals. These radicals are the starting point for synthesizing grafted polymer films (Figure 1a). Trichlorovinylsilane has also been used as an adhesion promoter between polydimethyldisiloxane (PDMS) and poly(ethylene glycol diacrylate) (pEGDA) films deposited by iCVD. This system is buckled to construct highly ordered herringbone patterns through a new sequential wrinkling strategy (Figure 1b).27 In a similar approach, Yang et al.28 modified the amine groups present in RO membranes with maleic anhydride (MA) to facilitate covalent grafting of a zwitterionic polymer coating. Without MA grafting, the zwitterionic films delaminated from the membrane when placed in water. The grafted membranes exhibited antifouling properties and salt rejection remained unimpaired. Surface adhesion can also be achieved by covalent bonding of two iCVD films. A nanoadhesive iCVD-bonding technique has been used to fabricate non-PDMS-based devices for oxygen-free flow lithography.29 iCVD poly(glycidyl methacrylate) (pGMA) and poly(4-ami-nostyrene) (pAS) films were deposited on the top and bottom, respectively, of ultraviolet-curable Norland Optical Adhesive (NOA) channels. To finish the construction of the two-layer NOA device, the top channel was placed over the bottom channel and the device was fully cured under vacuum at 90 °C for 24 h (Figure 1c). The ring-opening curing reaction of the epoxy and amine groups formed strong covalent bonds between the two channels. In addition to covalent bonds, other types of interactions can be used to induce adhesion on surfaces. For example, Chen et al.30 showed how capillary forces can be used to collapse pillars into microstructures using water as the solvent. Hydrophilic iCVD polymer coatings were deposited onto elastomeric pillars. When submerged in water, the pillars self-assembled into clusters and the formation of solvent bonds helped to stabilize these microstructures (Figure 1d).

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Figure 1. a) Grafting procedure to covalently bond PFDA chains to silicon wafers through an adhesion promoter; the resulting films exhibit superhydrophobic and oleophobic properties. Adapted with permission.26 Copyright 2012, Wiley-VCH. b) 3D pattern obtained via buckling of iCVD pEGDA films grafted to a PDMS substrate. The grafting prevents film delamination. Reproduced with permission.27 Copyright 2012, Wiley-VCH. c) Nanoadhesive iCVD-bonding technique used for the creation of non-PDMS-based devices for oxygen-free flow lithography. pGMA and pAS films were deposited on the top and bottom of NOA channels; the ring-opening curing reaction of epoxy and amine groups forms covalent bonds between the two channels. Reproduced with permission.29 Copyright 2012, Nature Publishing Group. d) Close-up view of stable microstructures formed by coating 54 μm tall pillars with 250 nm of hydrophilic poly(methyl methacrylate) (PMAA) and submerging them in solvent. Reproduced with permission.30 Copyright 2011, American Chemical Society. e) Paper PV array produced by oCVD and encapsulated by iCVD continues to operate during submersion in water. Reproduced with permission.19 Copyright 2011, Wiley-VCH. f) Scheme depicting encapsulation of IL droplets during polymerization in an iCVD reactor. Reproduced with permission.38 Copyright 2012, American Chemical Society.

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Polymer CVD methods also facilitate the development of novel microelectronic devices. The ability to obtain organic conducting films enables integration of electronics into a wide range of non-conventional surfaces. Bakker et al.31 reported the first production of poly- or oligoacetylene by iCVD. Upon doping with I2 vapors, the thin film conductivities are comparable to those of solution-processed polymers. The most promising technique to yield conducting organic films, however, is oCVD. By using vapor-printed oCVD polymer device layers, high-voltage, flexible, paper-thin photovoltaic (PV) arrays are monolithically fabricated directly onto conventional substrates (glass and plastics) and ubiquitous, yet unconventional substrates (paper). The fabrication steps used are identical, regardless of the substrate. The paper PV arrays produce >50 V, power common electronic displays in ambient indoor lighting, and can be tortuously flexed and folded without loss of function. Additionally, a thin-film vapor-deposited encapsulation layer extends lifetime, even allowing for operation during submersion in water (Figure 1e).19

As described above, CVD methods are compatible with a large variety of surfaces. Furthermore, several studies have been performed using more complex substrates, including three-dimensional nonplanar surfaces. Recently, Bose et al.32 employed iCVD to encapsulate microparticles of a highly water-soluble crop protection compound (CPC). Controlled release of the CPC was monitored on the basis of the hydrophilic character of the monomer, coating thickness, and cross-linking density. A method for patterning polymeric features on curved substrates has also been developed using iCVD.33 A conformal coating of poly(4-vinylpyridine) (p4VP) is deposited on curved surfaces and functionalized with a photoactive diacetylene. A mask is applied and the surface is exposed to UV light (λ = 254 nm), which photopolymerizes the diacetylene. Development in ethanol selectively solvates the masked regions creating a pattern. This method has also been used to pattern bifunctional organic surfaces and metal microstructures on planar and curved substrates. In addition, patterning of three-dimensional porous substrates has been demonstrated by Haller et al.34 Further studied carried out by Kwong et al.35 demonstrated a general method to control the location of polymer deposition onto three-dimensional porous substrates using metal salt inhibitors. These materials will enable the production of next-generation, multifunctional, paper-based microfluidic devices, polymeric photonic crystals, and filtration membranes.

Important advancements have also been made in the development of complex surface coatings and creation of new interfaces. Gupta and co-workers36 have achieved impressive results regarding vapor-phase polymerization on ionic liquids (IL). Initial work by this group demonstrated that polymerization can occur either at the vapor–IL interface or within the IL, depending on the reaction conditions. Additionally, it has been shown that the deposition of poly(2-hydroxyethyl methacrylate) (pHEMA) and poly(N-isopropylacrylamide) (pNIPAAm) on silicone oil results in the formation of polymer particles, whereas deposition onto an IL results in continuous polymer skin. This difference in polymer morphology was obtained when both the silicone oil and IL were patterned onto a common substrate.37 Moreover, IL droplets have been encapsulated within robust polymer shells; this was accomplished by incorporating polytetrafluoroethylene (PTFE) particles to facilitate polymerization over the entire surface of the droplet (Figure 1f).38 These results will enable the design of new polymer-IL composite materials for use in fuel cell and battery applications, as well as for in vivo biomedical research.

3. Functional, Responsive Surfaces for Biotechnology

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

The development and modification of functional surfaces for biotechnological applications have garnered considerable interest. Surfaces exhibiting modulating properties are particularly promising; the properties of these surfaces can be reversibly switched – on demand – in response to external stimuli such as light, temperature, and pH. Dynamic remodeling of macroscopic surface properties is a widely observed phenomenon in nature, and the possibility to mimic this process with synthetic systems is an important requirement for numerous biomedical applications, including cell culture, tissue engineering, biosensors, biofouling, and microfluidics. Use of a vapor-phase deposition process to create responsive surfaces facilitates their integration into novel devices and improves scalability via roll-to-roll processing. In particular, the iCVD process offers the additional benefits of exacting control over film thickness and conformality, excellent retention of chemical functionality, and fast deposition speed.

Coaxial nanofilms with hydrogel cores and shape memory shells were successfully fabricated by iCVD and used as temperature-activated nanotubes for controlled release.39 To fabricate these devices, the pores of anodized aluminum oxide membranes were sequentially coated with conformal layers of shape memory polymer and a hydrogel core. Hydrogel materials, such as pHEMA, swell in response to external stimuli, including heat and pH. As shown in Figure 2a, a fluorescent dye was encapsulated and adsorbed by the swollen hydrogel layer when the system was maintained at a high temperature. After the nanotube is loaded, the temperature is lowered and the dye remains fixed in the hydrogel. Increasing the temperature of the system a second time stimulates the recovery mechanism of the shape memory polymer; the outer layer shrinks to its initial dimensions, which subsequently pushes the swollen inner layer and results in a burst release of the dye. In addition, the mesh size of the hydrogel can be tuned by systematically altering its cross-linking density – this enables selective diffusion of species through the polymer network.40 For example, fluorescein, which molecular size is about 1 nm, was released from a hydrogel layer with a mesh size of 2 nm, as indicated by the presence of the fluorescein emission peak at 490 nm in the UV–vis spectrum (Figure 2b). Conversely, no release of fluorescein was observed for a hydrogel sample with a mesh size of 0.5 nm. iCVD was also used to synthesize thick, free-standing films of pHEMA hydrogel with low, non-specific protein adsorption. The films were capable of supporting excellent cell adhesion and proliferation without the need for cross-linking.41, 42 In addition, an iCVD pHEMA coating was used to increase the response of an impedance biosensor.43 The rapid and reversible swelling of the hydrogel in solution allowed the passage of the analyte, altering the impedance of the device.

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Figure 2. a) Coaxial nanofilms with an iCVD hydrogel cores and iCVD shape memory polymer (SMP) shells are used as temperature-activated nanotubes for controlled release. A fluorescent dye (FTSC) is encapsulated and adsorbed by the swollen hydrogel layer when the temperature (T) is maintained above the glass-transition temperature (Tg). The dye remains fixed in the tube at ambient temperature. Reheating the nanotube enables the recovery mechanism of the shape-memory polymer; the outer layer shrinks toward its initial diameter, which pushes the swollen inner layer and results in a burst release of the dye. Reproduced with permission.39 Copyright 2011, The Royal Society of Chemistry. b) Release of fluorescein from a hydrogel layer with a mesh size of 2 nm is evidenced by an emission peak at 490 nm; no release is observed from a hydrogel with a mesh size of 0.5 nm. Reproduced with permission.40 Copyright 2012, The Royal Society of Chemistry. c) Droplets of water on carbon nanotubes coated with cross-linked, thermoresponsive pNIPAAm. Reproduced with permission.46 Copyright 2011, Elsevier. d) Fluorescent image of the longitudinal tissue contacts created using pNIPAAm-coated silicone microgrooves. Reproduced with permission.47 Copyright 2011, American Chemical Society. e) Controlled release of drugs through a pH-responsive iCVD polymer layer. Reproduced with permission.49 Copyright 2012, American Chemical Society.

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pNIPAAm has been a subject of deep investigation due to its thermo-responsive properties.44–46 This polymer has a lower critical solution temperature (LCST) of approximately 32 °C. Below the LCST, pNIPAAm is hydrophilic and adopts a random coil configuration in water. Above the LCST, the polymer chains undergo a discontinuous phase change and collapse into a globular form. pNIPAAm homopolymer and cross-linked copolymer films were recently deposited by iCVD. Cross-linking is necessary to prevent dissolution of films in water. In addition, cross-linked films with a graded, NIPAAm-rich surface composition demonstrated a more rapid thermal response than cross-linked films exhibiting homogeneous compositions.44 Figure 2c shows droplets of water on multi-walled carbon nanotubes coated with cross-linked iCVD pNIPAAm. When the system temperature is increased from 25 to 40 °C, the static water contact angle increases from 50 ° to 135 ° due to the change in polymer chain configuration.46 Below the LCST, the hydrophilic amide groups of NIPAAm are exposed to the surface and can interact with water, above the LCST, the amide groups are inter- and intrachain bonded. As a result, only the hydrophobic isopropyl groups interact with water. This configuration change also has been found to influence protein adsorption kinetics. Above the LCST of the film, simple monolayer adsorption is observed, while below the LCST, protein diffuses into the swollen hydrogel.45 The thermoresponsive properties of pNIPAAm were used to create guides for the growth of longitudinal tissue constructs; a fluorescent image of one such construct is shown in Figure 2d.47 The constructs were formed by seeding cells on PDMS microgrooves coated with conformal layers of iCVD pNIPAAm. The temperature-dependent swelling and change in hydrophilicity of the pNIPAAm allowed the tissue constructs to be easily retrieved from the substrates.

iCVD has also been used to deposit pH-responsive poly(2-(diisopropylamino) ethyl methacrylate) (PDPAEMA).48 Deposition of PDPAEMA on a rough substrate yields a surface that can reversibly change its wetting state from superhydrophobic to superhydrophilic. This surface is interesting because when the surface amino groups are protonated at high pH, it can interact easily with anionic biological materials. pH-responsive polymers have also been used to create a controlled drug delivery system as depicted in Figure 2e.49 The assembly process involves loading a drug into the pores of a nanoporous Si matrix, and then using iCVD to cap the pores with a thin, pH-responsive copolymer film. Drug release from this device was more than four times faster at pH 7.4 than at pH 1.8. The key advantage of this approach is that application of the polymer film does not degrade the drug; the iCVD process does not require harmful solvents or high temperatures and is independent of the surface chemistry and pore size of the nanoporous matrix.

4. Selective Permeation

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

The possibility of creating materials that allow or block the selective permeation of gases, vapors, and liquids is an active research field, with applications in biotechnology, microfluidics, and the electronics and energy industries.

If current trends persist, the next generation of electronic devices, including solar cells and displays, will be stretchable, light-weight, and flexible. In order to achieve functional devices with these properties, electronic components need to be deposited on non-rigid substrates (e.g., polymers, paper); however, these components are sensitive to oxygen and water vapor, and non-rigid substrates are poor barriers against them. Therefore, the enabling technology for the commercialization of non-rigid, nonplanar devices is the creation of barrier layers, which limit the permeation of oxygen and water vapor while maintaining the mechanical properties of the substrate. The most promising barrier layers to date are multilayers in which thin, glass-like coatings are alternated with organic polymers. Sandwiching the glass-like layers in between polymeric layers improves the flexibility of the stack and planarizes the surface of the substrate. In particular, iCVD has been used to fill the pores of the substrate50, 51 and offers a microscopically flat surface for the deposition of the subsequent inorganic layer.52 A new process, initiated-plasma-enhanced CVD (iPECVD),53 yielded liquid-like depositions – a meniscus was observed when the coating was deposited inside a trench (see Figure 3a i). This type of deposition can be desirable for planarization and pore filling.52 Tuning the deposition conditions can result in a conformal coating (Figure 3a ii) and very unconformal (Figure 3a iii). The multilayers can be easily deposited from the vapor phase because CVD techniques can be coupled to deposit inorganic (SiOx, SiNx) and polymer layers (acrylate, silicone) sequentially. Excellent barrier properties were obtained from multilayers deposited by hot-wire CVD coupled with iCVD54–58 or PECVD coupled with iCVD. The pore-filling properties of iCVD coatings have also been demonstrated to be useful for dye-sensitized solar cells.59, 60 The liquid electrolyte in these devices was substituted with an iCVD polymer. Complete pore filling of 12 μm thick titania was achieved and resulted in enhanced cell performance.

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Figure 3. a) Deposition of iPECVD polymer coating inside silicon wafer trenches. Depending on the deposition conditions, the process can yield a liquid-like (i), conformal (ii), or non-conformal coating (iii). Reproduced with permission.52 Copyright 2012, American Institute of Physics. b) Microfluidic channel for a lung assisted device. Reproduced with permission.66 Copyright 2012, Springer. c) Hydrophobicity-based separation of molecules (Mes/Phl) of the same size is achieved by narrowing the pores of a polycarbonate (PC) membrane with iCVD polymers and coating with various functional layers. F5 and F9 indicate membranes coated with a single fluorocarbon layer yielding different pore sizes. X5 indicates a membrane coated with a single poly(divinyl benzene) (pDVB) layer and XF5 is a membrane coated with a bilayer of pDVB and a fluoropolymer. Reproduced with permission.67 Copyright 2011, American Chemical Society. d) Schematic depicting antifouling properties of a RO membrane covered with an iCVD zwitterionic coating. Reproduced with permission.28 Copyright 2011, American Chemical Society.

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Barrier properties were also demonstrated with single-layer polymers deposited by iCVD. Hard and impermeable, yet flexible, polymer coatings were obtained from copolymers of iCVD MA and aminostyrene.61 Reaction of the amine and anhydride functionalities resulted in a massively cross-linked network. Elastic moduli exceeding 20 GPa were obtained for these films; these values are significantly higher than typical polymer moduli (≈0.5–5 Gpa). The oxygen permeability observed for the cross-linked iCVD coating was also lower than those of commercial permeation barrier coatings. Another barrier polymer deposited by iCVD consisted of pGMA. The dissolution rate of pGMA-coated sodium chloride particles (≈355 μm) in aqueous solution was found to be reduced by an order of magnitude compared with uncoated NaCl.62

iCVD fluoropolymer coatings can also serve as excellent liquid barriers. Fluoropolymer barrier coatings were used in PDMS-based microfluidic devices. These devices have the potential to provide superior control over mixing as compared to traditional batch reactions. For an optimal performance, the microchannels need to be impermeable to liquids. However, PDMS, the most common substrate used in microfluidics, can swell in different solutions. Masking the underlying PDMS with a vapor-deposited fluorocarbon barrier film eliminates the possibility of swelling and prevents hydrophobic recovery due to the low glass transition temperature of PDMS. The ability of such films to prevent absorption of low-molecular-weight molecules and resist swelling in organic solvents was recently demonstrated by Riche et al.63 Use of this fluorocarbon coating enables synthesis of nanomaterials that are difficult to produce using conventional batch reactions. Coated devices were used for more than 24 h without exhibiting signs of degradation or delamination.64

Selectively permeable coatings and materials are necessary for many biomedical applications, including lung devices. These devices need to be permeable to gases (e.g., CO2 and O2) but impermeable to liquids to prevent leakage of blood. Such selectivity has been demonstrated using free-standing iCVD membranes.65 These membranes were also integrated into microfluidic devices possessing a vascular network, as shown in Figure 3b.66 iCVD coatings have also been used to enhance selective permeation of commercially available membranes. For example, hydrophobicity-based separation was achieved by coating the pores of a polycarbonate membrane with a conformal fluoropolymer coating.67 In particular, membranes with small fluorinated pores (10 nm) exhibited an effective cutoff based on the polar surface area of the molecules; limited correlation was observed with solute size (Figure 3c). Surface modification can also be used to prevent membrane fouling. A zwitterionic coating deposited on reverse osmosis membranes using iCVD exhibited superior antifouling performance compared with to bare membranes (Figure 3d).28

5. Conclusions and Perspectives

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information

iCVD polymer films have been successfully integrated into many different applications. This versatility is enabled by the ability to easily tune the chemical properties for each application. In addition, the capability of coating delicate, flexible, and nonplanar substrates enables the use of iCVD in applications for which wet chemistry methods are not possible.

Continued development of CVD methods is essential to ensure industrial implementation. Ledermann et al.68 demonstrated the use of HWCVD to deposit device quality amorphous silicon (a-Si:H) films for solar cells. This technique is also commonly used to obtain PTFE-like films with high chemical stability.69, 70 Practical industrial application, however, demands continuous operation, and the carbonization and fluorination of the catalyzer surface were found to cause significant reduction of the deposition rate. To remedy this problem and clarify the decomposition mechanism, a tungsten catalyzer was installed in the same chamber to remove the carbonized surface of the NiCr catalyzer.71 Lewis et al.72 have demonstrated the commercial viability of iCVD to synthesize PTFE films, achieving a deposition rate higher than that obtained with HWCVD. Process scale-up has also been demonstrated with iCVD and is necessary to meet demand, as well as to offer high performance products. Figure 4 shows several different iCVD coating systems, including a mid-size production batch coater (20 in. × 30 in. coating area) (Figure 4a), a large production batch coater with a door 1.2 m wide (Figure 4b), and a roll-to-roll web coating system (30 in. width) (Figure 4c). Another technique, filament-assisted chemical vapor deposition (FACVD), allows for the operation of either HWCVD or iCVD depending on the desired film properties. This technology incorporates a heated zone to fragment chemical precursors for subsequent deposition on a two- or three-dimensional surface. Operating at lower filament and substrate temperatures than conventional HWCVD, FACVD can deposit organic, inorganic, and hybrid materials on a variety of substrates.73, 74 In summary, iCVD is a versatile, rapidly growing (Figure 4d) process for fabricating polymer thin films. Continued implementation of this method will have a significant impact on the next generation of functional surfaces and devices.

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Figure 4. a–c) Commercial scale iCVD reactors. a) A mid-size production batch coater (20 × 30 in. coating area), b) a large production batch coater with a door 1.2 m wide, and c) a roll-to-roll web coating system (30 in. width). d) Evolution of iCVD publications over time. Panel a and c reproduced with permission.72 Copyright 2009, Elsevier.

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Biographical Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information
Thumbnail image of

Jose Luis Yagüe obtained his B.S. degree in Chemistry from IQS University, Barcelona in 2004. He received his Ph.D. degree in Materials Science from the same institution in 2010 under the supervision of Prof. Salvador Borrós. He is currently a Postdoctoral Associate in Prof. Karen K. Gleason's group at Massachusetts Institute of Technology, Chemical Engineering Department. His research interests include chemical vapor deposition of polymer thin films, surface patterning, nanofabrication, and biosensors.

Biographical Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information
Thumbnail image of

Anna Maria Coclite received her B.S. and M.S. degrees in Chemistry with the highest honors from the University of Bari, Italy in 2004 and 2006, respectively, and her Ph.D. degree in Chemical Science from the same institution in 2010 under the supervision of Professor Riccardo d'Agostino. She is currently a Postdoctoral Associate in Professor Karen K. Gleason's group at Massachusetts Institute of Technology, Chemical Engineering Department. Her current research interests include thin films deposition, nanotechnology, and surface chemistry.

Biographical Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information
Thumbnail image of

Christy D. Petruczok received her B.S. degree in chemical engineering from Clarkson University in 2008 and her M.S. degree in chemical engineering practice from MIT in 2011. She is currently a Ph.D. candidate in the laboratory of Professor Karen K. Gleason. Ms. Petruczok is a recipient of the Barry M. Goldwater Scholarship and National Science Foundation Graduate Research Fellowship. Her research interests include the synthesis of polymer films for sensing applications.

Biographical Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Tailored Surfaces and Interfaces
  5. 3. Functional, Responsive Surfaces for Biotechnology
  6. 4. Selective Permeation
  7. 5. Conclusions and Perspectives
  8. Acknowledgements
  9. Biographical Information
  10. Biographical Information
  11. Biographical Information
  12. Biographical Information
Thumbnail image of

Dr. Karen K. Gleason is the Alexander and I. Michael Kasser Professor of Chemical Engineering at MIT and has authored more than 250 publications. She is a recipient of the NSF Presidential Young Investigator, the ONR Young Investigator, the Printed Electronics Europe Best Technical Development Materials Award, and the AIChE Process Development Research Award. At MIT, Prof. Gleason has served as an Executive Officer of Chemical Engineering, an Associate Director for the Institute of Soldier Nanotechnologies, and an Associate Dean of Engineering for Research. She cofounded GVD Corporation, headquartered in Cambridge, MA, with manufacturing facilities in Greenville, SC.