Perfluorinated Polyether Research Articles

Mitigating substrate effects of van der Waals semiconductors using perfluoropolyether self-assembled monolayers.

The properties of transition metal dichalcogenides (TMDCs) are critically dependent on the dielectric constant of substrates, which significantly limits their application. To address this issue, we used a perfluorinated polyether (PFPE) self-assembled monolayer (SAM) with low surface energy to increase the van der Waals (vdW) gap between TMDCs and the substrate, thereby reducing the interaction between them. This resulted in a reduction in the subthreshold swing value, an increase in the photoluminescence intensity of excitons, and a decrease in the doping effect by the substrate. This work will provide a new way to control the TMDC/dielectric interface and contribute to expanding the applicability of TMDCs.

A Perfluoropolyether Microfluidic Device for Cell-Based Drug Screening with Accurate Quantitative Analysis.

Microfluidic drug screening technologies have been extensively explored to evaluate the pharmacology and therapeutic implications of promising chemical compounds in multiplexed physiological microenvironments in vivo. However, conventional poly(dimethylsiloxane) microchips are susceptible to adsorption by hydrophobic molecules on channel surfaces and permeation in the matrix. These can significantly compromise the drug availability and accuracy of dose-dependent quantitative analyses. Here, we prepared a perfluorinated polyether (PFPE) microchip via digital light processing 3D printing as a quantitative drug screening platform for precise concentration-dependent pharmaceutical assays. Cells cultured on PFPE microchips exhibited excellent viability with a spread morphology as well as superior proliferative capability. Importantly, PFPE constructions with a low surface energy significantly prevented the nonspecific molecular adsorption into their surfaces or permeation into the matrix. In particular, the PFPE multibranched channel preserved the concentration of the pharmaceutical drug during the perfusion process and generated a linear concentration gradient, resulting in a dose-dependent chemotherapeutic effect. We suggest that the biocompatible and nonadsorbing PFPE microchannel can provide a cell-based drug screening platform for concentration-dependent quantitative analyses.

Reducing the contact time of impacting water drops on superhydrophobic surfaces by liquid-like coatings

Surfaces that can rapidly shed impacting drops are important for a wide range of applications, including anti-icing, dropwise condensation and miniaturized drones. Previous strategies to reduce the contact time of impacting drops are primarily based on engineering superhydrophobic surfaces through introducing secondary textures, either macroscopic or nanoscopic, or constructing specifically designed nanotextures. Here, a facile and effective approach is demonstrated to reduce the contact time of superhydrophobic surfaces by simply replacing the widely used perfluorosilane (i.e., trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane, PFOS) coating with liquid-like perfluorinated polyether (PFPE) surface chemistry. Though their apparent contact angles are comparable, the PFPE-coated superhydrophobic surface exhibits a reduction of contact time up to 26% compared to the PFOS-coated counterpart, attributed to enhanced retraction speed on the former surface. Remarkably, while a classical inertial model predicts a merely 3% difference in retraction time between the PFPE- and the PFOS-coated surfaces, a drastic reduction of retraction time by 12–32% is observed. The improved retraction dynamics on the liquid-like surface is suggested to be caused by the low contact angle hysteresis and enhanced interface slippage on the liquid-like coating. This study offers a general strategy to enhance dynamic liquid repellency of superhydrophobic surfaces for diverse applications.

Study on the formulations for Topical Skin Protectant against Liquid-Phase Chemical Warfare Agents

Chemical warfare agents(CWA) such as nerve agents and vesicating agents show lethality by skin contamination. Skin protection, therefore, is one of the top priorities to deal with the growing threat from CWA. In an attempt to develop the most effective topical skin protectant(TSP), candidate substances including PFPE(perfluorinated polyether), PTFE(polytetrafluoroethylene), glycerin, and polysaccharides were evaluated in forms of various formulations against nerve agent simulant DMMP(dimethylmethyl phosphonate) penetration. The protective efficacy of the formulation against DMMP penetration was estimated as the onset time of color change of the KM9 chemical agent detection paper. Based on this study, it was found that several PFPE- and glycerin-based formulations exhibit remarkably superior efficacy as a protective cream. This protective cream is expected to be used as TSP for military application after further research.

Biocompatible amphiphilic Janus nanoparticles with enhanced interfacial properties for colloidal surfactants

Emulsions in which water droplets are dispersed in fluorocarbon oil phase (W/F emulsions) serve as effective means to encapsulate bioactives and precisely execute reactions in confined space due to the gas permeability, chemical inertness, and biocompatibility offered by the continuous phase. While molecular surfactants consisting of perfluorinated polyether (PFPE) and polyethylene glycol (PEG) have been used to stabilize these emulsions, these surfactants cannot effectively prevent coalescence and cross-contamination between the neighboring droplets. Herein, we present Janus nanoparticles (F-SiO2-PEG) as biocompatible colloidal surfactants to achieve excellent stability in W/F emulsions. By utilizing monolayered wax colloidosomes as templates, we show that Janus silica nanoparticles with two distinctive surface wetting properties can be synthesized in high purity. Moreover, we demonstrate that additional PEGylation of these Janus particles allows these colloidal surfactants to strongly adhere at the W/F interface, granting excellent emulsion stability compared to the equivalent randomly functionalized nanoparticles and prevent non-specific adsorption of proteins. As the strategy outlined in this work is general, we anticipate that it can be further extended to prepare Janus particles with tailored interfacial properties for biomedical, cosmetics, and pharmaceutical applications involving emulsions.

Tribological tests of micro-arc oxidation coatings in environmentally safe lubricants

This study is devoted to wearing resistance of MAO-coatings formed on aluminum alloys 2024 (Al-Cu-Mg) and 7075 (Al-Zn-Mg-Cu) at the friction in pair with steel 100Cr6 in environmentally safe lubricants and represents a generalization and analysis of tests’ results. Investigations were conducted using two methods: reciprocating sliding on the “ball-on-disk” friction scheme and unidirectional sliding on the “pin-on-disk” friction scheme. As environmentally lubricants were used some base oils like polyalphaolefin (PAO), polyethylene glycol (PEG), Silicon Oil, perfluorinated polyether (PFPE) and diisotridecyl adipate ether (DITA). Tests on the first friction scheme allowed us to determine the maximal value of load for investigated friction pairs and tests on the second friction scheme showed their antifriction properties in different lubricants and in the mode of the greasing starvation. There was revealed that MAO-coatings formed on alloy 7075 at high contact pressures demonstrate a friction coefficient lower than on alloy 2024. Some problems of the used “pin-on-disk” scheme is discussed also for improving the tests’ results data.

Smooth Perfluorinated Surfaces with Different Chemical and Physical Natures: Their Unusual Dynamic Dewetting Behavior toward Polar and Nonpolar Liquids

The effects of surface chemistry and the mobility of surface-tethered functional groups of various perfluorinated surfaces on their dewetting behavior toward polar (water) and nonpolar (n-hexadecane, n-dodecane, and n-decane) liquids were investigated. In this study, three types of common smooth perfluorinated surfaces, that is, a perfluoroalkylsilane (heptadecafluoro-1,1,2,2-tetrahydrooctyl-dimethylchlorosilane, FAS17) monomeric layer, an amorphous fluoropolymer film (Teflon AF 1600), and a perfluorinated polyether (PFPE)-terminated polymer brush film (Optool DSX), were prepared and their static/dynamic dewetting characteristics were compared. Although the apparent static contact angles (CAs) of these surfaces with all probe liquids were almost identical to each other, the ease of movement of liquid drops critically depended on the physical (solidlike or liquidlike) natures of the substrate surface. CA hysteresis and substrate tilt angles (TAs) of all probe liquids on the Optool DSX surface were found to be much lower than those of Teflon AF1600 and FAS17 surfaces due to its physical polymer chain mobility at room temperature and the resulting liquidlike nature. Only 6.0° of substrate incline was required to initiate movement for a small drop (5 μL) of n-decane, which was comparable to the reported substrate TA value (5.3°) for a superoleophobic surface (θ(S) > 160°, textured perfluorinated surface). Such unusual dynamic dewetting behavior of the Optool DSX surface was also markedly enhanced due to the significant increase in the chain mobility of PFPE by moderate heating (70 °C) of the surface, with substrate TA reducing to 3.0°. CA hysteresis and substrate TAs rather than static CAs were therefore determined to be of greater consequence for the estimation of the actual dynamic dewetting behavior of alkane probe liquids on these smooth perfluorinated surfaces. Their dynamic dewettability toward alkane liquids is in the order of Optool DSX >> Teflon AF1600 ≈ FAS17.

An investigation of fretting wear behaviour of nickel coatings for electrical contacts application in dry and lubricated conditions

Fretting remains a major cause of connector failure and can impair reliability of complex system. Much work is devoted to minimise the effects of cyclic displacements in the contact interface. One of the options is to choose proper materials for the final layer and eventually select an underlayer. Another option is to apply a lubricant compatible with the electrical function of the connecting device. Its effect must be the reduction of friction with the preservation of conduction. In this work we have investigated the properties of nickel electrodeposited on cuprous coupons submitted to an imposed sine displacement fretting test (1Hz, 25μm, 2.5N). The contacts are of the sphere on plane type. The plating conditions are shown to have a large effect on the microstructure, roughness and composition of the nickel coatings. Consequently the fretting behaviours of the compared coating are different. Fretting degradation is evaluated for our application as the number of cycles for which the build-up of oxidised debris gives a value of electrical resistance superior to a threshold. During the fretting test the rough nickel with large grains is observed to be prone to very high friction and partial slip. Fretting of the smoother coating with small grains is characterised by gross slip. Contacts were lubricated with solutions of perfluorinated polyether (PFPE). It is shown that a strong friction reduction takes place and that the fretting degradation is postponed. Surface analysis shows that fluorine is grafted in the interface and protects the interface. The electrodeposition process and the properties of the nickel coating are shown to have an effect on the lubricant behaviour in the contact interface. These results show the strong potential of lubricated nickel for applications in the field of electrical devices.

Inelastic scattering of OH radicals from organic liquids: isolating the thermal desorption channel

Inelastic scattering of OH radicals from liquid surfaces has been investigated experimentally. An initially translationally and rotationally hot distribution of OH was generated by 193 nm photolysis of allyl alcohol. These radicals were scattered from an inert reference liquid, perfluorinated polyether (PFPE), and from the potentially reactive hydrocarbon liquids squalane (C30H62, 2,6,10,15,19,23-hexamethyltetracosane) and squalene (C30H50, trans-2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene). The scattered OH v = 0 products were detected by laser-induced fluorescence. Strong correlations were observed between the translational and rotational energies of the products. The high-N levels are translationally hot, consistent with a predominantly direct, impulsive scattering mechanism. Impulsive scattering also populates the lower-N levels, but a component of translationally relaxed OH, with thermal-desorption characteristics, can also be seen clearly for all three liquids. More of this translationally and rotationally relaxed OH survives from squalane than from squalene. Realistic molecular dynamics simulations confirm that double-bond sites are accessible at the squalene surface. This supports the proposition that relaxed OH may be lost on squalene via an addition mechanism.

Deformation of nanostructures on polymer molds during soft UV nanoimprintlithography

Soft nanoimprint lithography (soft NIL) relies on a mechanical deformation of a resist by apatterned polymer used as a mold. Here, we report on the investigation of the nanopatternfidelity of the high pressure imprint process based on a perfluorinated polyether (PFPE)soft mold material. The perfluorinated polyether material was found to be well suited totransfer the mold pattern into the resist by a direct imprinting process at low cost.Moderate deformations of the polymer mold structures occurring during the high pressureimprint are systematically studied. Features of decreased size are found to be moresensitive to pattern distortions. An optimized pattern design with increased structuredensity and constant pattern ratio is developed to minimize deformation effects.Imprints performed on the basis of these design rules result in reduced deformationsand repeal their size dependence. The improved pattern transfer, especially forsmall structural elements, turns the direct and cost-effective soft UV-NIL into aninteresting technique also for patterning tasks in the lower nanometer range.

A geometrical optimization of a magneto-rheological rotary brake in a prostheticknee

Magneto-rheological (MR) fluids have been successfully introduced to prosthetic devices.One such device is a biomechanical prosthetic knee that uses MR fluids to activelycontrol its rotary stiffness. The brake is rotational, utilizing the MR fluid in shearmode. In this study, the geometrical design of the MR brake is addressed. Thisincludes the design of the magnetic circuit and the geometry of the fluid chamber.Mathematical models are presented that describe the rotary torque of the brake.A novel perfluorinated polyether (PFPE)-based MR fluid is introduced, whoseproperties are tailored for the prosthetic knee. On-state and off-state rheologicalmeasurements of the MR fluid are presented. The finite element method is used toevaluate the magnetic flux density in the MR fluid. The design is formulated as anoptimization problem, aiming to maximize the braking torque. A parametricstudy is carried out for several design parameters. Subsequently, a multi-objectiveoptimization problem is defined that considers three design objectives: the field-inducedbraking torque, the off-state rotary stiffness and the weight of the brake. Trade-offsbetween the three design objectives are investigated which provides a basis forinformed design decisions on furthering the success of the MR prosthetic knee.

Stereodynamics at the Gas−Liquid Interface: Orientation and Alignment of CO2 Scattered from Perfluorinated Liquid Surfaces

Rotational orientation/alignment dynamics of CO(2) scattered from a perfluorinated polyether (PFPE) liquid surface has been investigated via direct absorption experimental studies and theoretical molecular dynamics (MD) simulations. Experimentally, polarization modulation of a single mode diode laser is combined with lock-in detection to measure circular/linear IR polarizance due to CO(2) scattering from the surface at theta(inc) = 60 degrees and E(inc) = 10.6(8) kcal/mol and probed over a series of final scattering angles. The differential absorption intensities are related through Fano-Macek theory to the three lowest multipole moments (A(0), A(2+), and O(1-)) which describe collisionally induced orientation and alignment at the liquid surface. The total scattering population reflects both trapping-desorption (TD) and impulsive scattering (IS) components, with a strong positive anisotropy in the M(J) distribution that indicates preferential CO(2) scattering from the surface with a forward (i.e., "topspin") sense of end-over-end tumbling. Theoretical trajectory simulations provide 3D CO(2) flux and J state distributions scattering from fluorinated self-assembled monolayers (F-SAMs) and are compared with experimental results as a function of final rotational state. Specifically, trends in the theoretical orientation/alignment moments are in remarkable agreement over the full range of J states but with values consistently overpredicted by nearly 2-fold, which may reflect a higher level of local ordering for F-SAMS vs a gas-PFPE liquid interface.

Determination of the Electron Escape Depth for NEXAFS Spectroscopy

A novel method was developed to determine carbon atom density as a function of depth by analyzing the postedge signal in near-edge X-ray absorption fine structure (NEXAFS) spectra. We show that the common assumption in the analysis of NEXAFS data from polymer films, namely, that the carbon atom density is constant as a function of depth, is not valid. This analysis method is then used to calculate the electron escape depth (EED) for NEXAFS in a model bilayer system that contains a perfluorinated polyether (PFPE) on top of a highly oriented pyrolitic graphite (HOPG) sample. Because the carbon atom densitites of both layers are known, in addition to the PFPE surface layer thickness, the EED is determined to be 1.95 nm. This EED is then used to measure the thickness of the perfluorinated surface layer of poly(4-(1H,1H,2H,2H-perfluorodecyl)oxymethylstyrene) (PFPS).

Dynamics of Inelastic Scattering of OH Radicals from Reactive and Inert Liquid Surfaces

The inelastic scattering of gas-phase OH radicals from a liquid hydrocarbon and a liquid perfluorinated polyether (PFPE) has been investigated. The surfaces examined were the potentially reactive, branched hydrocarbon squalane (C30H62, 2,6,10,15,19,23-hexamethyltetracosane) and the inert PFPE Krytox 1506 (F−[CF(CF3)CF2O]14ave−CF2CF3). Superthermal OH was formed by 355-nm laser photolysis of a low pressure of HONO above the liquid surface. Laser-induced fluorescence (LIF) was used to determine the relative yields and nascent translational and rotational distributions of OH (v′ = 0). The time-of-flight profiles from both liquids can be resolved, at least empirically, into two components. The dominant, faster component is consistent with direct, inelastic scattering. It has a higher average translational energy from PFPE than from squalane. This faster OH also has a higher Boltzmann-like rotational temperature for PFPE (655 ± 45 K) than for squalane (473 ± 27 K), in both cases considerably hotter than the incoming OH. For both liquids, there is also a slower component, with characteristics consistent with a thermalized, trapping-desorption mechanism. This is a higher proportion for squalane (0.22 ± 0.02) than for PFPE (0.09 ± 0.01). These results are consistent with squalane being the “softer” surface, exhibiting more efficient momentum transfer than PFPE, and more able to temporarily trap OH. Relative to PFPE, around half (0.49 ± 0.04) of the OH molecules that collide with squalane are lost, presumably due to reaction forming H2O. These results are compared with previous studies of the scattering of inert gas species from both squalane and PFPE. The reactive branching fraction of OH on squalane is discussed in the context of previous observations of enhanced reactivity at the gas−liquid interface.

Cellular responses to novel, micropatterned biomaterials

AbstractTwo UV-curable polymers, i.e., a star-shaped poly(ethylene glycol) (PEG) and a linear perfluorinated polyether (PFPE), are investigated as novel biomaterials in a systematic study of the cellular responses to surface chemistry, topography, and elasticity. Based on the wettability it was expected that the two novel biomaterials were too hydrophilic or -phobic, respectively, to support cell adhesion. Indeed, no cell adhesion was observed on the smooth, unstructured elastomers, whereas the materials showed no cytotoxicity. However, when the materials bear defined, topographic patterns (prepared by UV-based imprinting), cells do react strongly to the surfaces; they adhere, spread, and change their shape depending on the geometry of the features. Typically, cells were found to align along line patterns and "float" on pillar structures. It should be noted that the chemistry of the surface is not altered by the imprinting process, hence, there are no biofunctional molecules present at the surface to aid the cell adhesion. Finally, a remarkable effect of elasticity on the cellular behavior was discovered. Thus, the three parameters of chemistry, topography, and elasticity were investigated in- and interdependently, and it was found that the biomaterials may lose their resistance to protein adsorption and cell adhesion depending on the surface topography.

Quantum State-Resolved CO2 Collisions at the Gas−Liquid Interface: Surface Temperature-Dependent Scattering Dynamics

Energy transfer dynamics at the gas-liquid interface are investigated as a function of surface temperature both by experimental studies of CO2 + perfluorinated polyether (PFPE) and by molecular dynamics simulations of CO2 + fluorinated self-assembled monolayers (F-SAMs). Using a normal incident molecular beam, the experimental studies probe scattered CO2 internal-state and translational distributions with high resolution infrared spectroscopy. At low incident energies [Einc = 1.6(1) kcal/mol], CO2 J-state populations and transverse Doppler velocity distributions are characteristic of the surface temperature (Trot approximately Ttrans approximately TS) over the range from 232 to 323 K. In contrast, the rotational and translational distributions at high incident energies [Einc = 10.6(8) kcal/mol] show evidence for both trapping-desorption (TD) and impulsive scattering (IS) events. Specifically, the populations are surprisingly well-characterized by a sum of Boltzmann distributions where the two components include one (TD) that equilibrates with the surface (TTD approximately TS) and a second (IS) that is much hotter than the surface temperature (TIS > TS). Support for the superthermal, yet Boltzmann, nature of the IS channel is provided by molecular dynamics (MD) simulations of CO2 + F-SAMs [Einc = 10.6 kcal/mol], which reveal two-temperature distributions, sticking probabilities, and angular distributions in near quantitative agreement with the experimental PFPE results. Finally, experiments as a function of surface temperature reveal an increase in both sticking probability and rotational/translational temperature of the IS component. Such a trend is consistent with increased surface roughness at higher surface temperature, which increases the overall probability of trapping, yet preferentially leads to impulsive scattering of more highly internally excited CO2 from the surface.

Water Adsorption on Lubricated Carbon Surface

The fundamental properties of adsorption, i.e., molecular mobility and interaction energy between lubricants, water, and overcoats, are investigated for perfluorinated polyether (PFPE) lubricants on carbon surfaces in order to design mechanically reliable magnetic storage devices. The interaction between PFPE molecules and water molecules on carbon surfaces in dry and humid environments is analyzed using nuclear magnetic resonance (NMR). Two NMR spectrum peaks of water on carbon surfaces on which the PFPE diol is coated are observed when humid air of 90% relative humidity (RH) is introduced. One peak at a low chemical shift corresponds to the adsorbed water on the carbon surface. The other peak at a high chemical shift shows sorbed water molecules in the PFPE diol film. Minimum molecular mobility is observed for OH groups, i.e., adsorption sites, in dry air. However, the molecular mobility increases because of the lubricant desorption when humid air is introduced. The increased spin-lattice relaxation time (T1) for the proton in the OH group reveals the desorption phenomena. Adsorption energies between the adsorbates (lubricants and water) and the adsorbent (carbon powder) are measured using a flow micro-calorimeter. When water vapor is introduced, the negative heat of adsorption is observed, which indicates the lubricant desorption caused by the water molecules.

Water Adsorption on Lubricated Surfaces for Magnetic Storage Devices

In order improve the design of tribologically reliable magnetic storage devices, the fundamental properties of adsorption - molecular mobility and interaction energy between lubricants, water, and overcoats — are investigated for perfluorinated polyether (PFPE) lubricants on carbon surfaces. The interaction between the PFPE molecules and water molecules on the carbon surfaces in dry and humid environments is analyzed by using Nuclear Magnetic Resonance (NMR). Two NMR spectrum peaks of water on carbon surfaces on which the PFPE diol is coated are observed when humid air of 90% RH is introduced. One peak at a low chemical shift corresponds to the adsorbed water on the carbon surface. The other peak at a high chemical shift shows sorbed water molecules in the PFPE diol film. Minimum molecular mobility is observed for OH groups, i.e. adsorption sites, in the dry air. However, the molecular mobility increases because of the lubricant desorption when the humid air is introduced. Adsorption energies between the adsorbates (lubricants and water) and the adsorbent (carbon powder) are measured by using a flow micro-calorimeter. When water vapor is introduced, the negative heat of adsorption is observed, which indicates the lubricant desorption caused by the water molecules. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Surface-induced dissociation of diphenyl ether

The primary fragmentation of diphenyl ether and further secondary dissociation of its fragments have been studied by surface-induced dissociation (SID). In a tandem linear time-of-flight mass spectrometer, the dissociation of ions is studied as a function of the collision energy with a liquid perfluorinated polyether (PFPE) surface. In a tandem quadrupole instrument, an alkyl terminated (C 18) and a perfluoroalkyl terminated (FC 10) self-assembled monolayer surface have been used. The differences in the spectra obtained with the TOF and quadrupole instruments are attributed to the different time frames available for observation of the fragments. Deconvolution of the collision energy resolved SID spectra of diphenyl ether shows that above 50 eV collision energy, the energy deposition efficiency is similar in the two experimental set-ups, in spite of the different geometries. Ion/surface reactions are observed upon collisions of the diphenyl ether radical cation with the C 18 surface but not with the FC 10 surface The rearrangement fragments, obtained from perdeuterated diphenyl ether, C 11D 10 + and C 11D 9 +, react with both the C 18 and FC 10 surface. Hydrogen exchange with the surface combined with hydrocarbon loss from C 12D 10O +, C 11D 10 +, and C 11D 9 + is observed.

Characterization of Perfluorinated Polyether (PFPE) Disk Drive Lubricants

We report the XPS characterization of perfluorinated polyether (PFPE) samples used as lubricants for magnetic disk drive heads. Survey and high resolution C, O, and F spectra were obtained for eight different polyether formulations using a monochromatic AlKα source. Sample charging was evident in the samples, and was minimized throughout by the use of thin films of the samples and data collection under a metallic screen.