Surface Restructuring Behavior Research Articles

Structural Reorganization and Fibrinogen Adsorption Behaviors on the Polyrotaxane Surfaces Investigated by Sum Frequency Generation Spectroscopy.

Polyrotaxanes, such as supramolecular assemblies with methylated α-cyclodextrins (α-CDs) as host molecules noncovalently threaded on the linear polymer backbone, are promising materials for biomedical applications because they allow adsorbed proteins possessing a high surface flexibility as well as control of the cellular morphology and adhesion. To provide a general design principle for biomedical materials, we examined the surface reorganization behaviors and adsorption conformations of fibrinogen on the polyrotaxane surfaces with comparison to several random copolymers by sum frequency generation (SFG) vibrational spectroscopy. We showed that the polyrotaxane (OMe-PRX-PMB) with methylated α-CDs as the host molecule exhibited unique surface structures in an aqueous environment. The hydrophobic interaction between the methoxy groups of the methylated α-CD molecules and methyl groups of the n-butyl methacrylate (BMA) side chains may dominate the surface restructuring behavior of the OMe-PRX-PMB. The orientation analysis revealed that the orientation of the fibrinogen adsorbed on the OMe-PRX-PMB surface is close to a single distribution, which is different from the adsorption behaviors of fibrinogen on other polyrotaxane or random copolymer surfaces.

In Situ Probing the Surface Restructuring of Antibiofouling Amphiphilic Polybetaines in Water.

Antibiofouling materials have a wide range of applications in biomedical devices and marine coatings. Due to the amphiphilic nature of proteins and organisms, amphiphilic materials have been designed to resist their unspecific adsorption. Surface restructuring behavior of amphiphilic materials in water is believed to play a key role in the antibiofouling mechanisms. In this work, the surface structures of several amphiphilic polybetaine coatings in water have been probed in situ using sum frequency generation (SFG) vibrational spectroscopy. These are novel polybetaines constructed from functionalized polynorbornenes. The polybetaines with oligo(ethylene glycol) (OEG), octyl (C8), or fluorinated (F13) side chains exhibit different surface restructuring behaviors upon contacting water due to their different surface hydrophobicity. The OEG and C8 chains were present and ordered at the water interface, while the F13 chain withdrew from water. The hydrophilic betaine group extended into the water and formed hydrogen bonds with water molecules. The surface restructuring of these materials detected using SFG can be well correlated to their antibiofouling performance, providing an understanding of their antibiofouling mechanisms.

The molecular surface conformation of surface-tethered polyelectrolytes on PDMS surfaces

Surface properties of polymer materials are important for many applications such as biomedical materials, marine antifouling coatings, polymer membranes for biological and chemical molecule separations, and polymer adhesives. Surface properties are highly dependent on molecular surface structures. Presently, surface polymerization is one of the most effective methods to tailor and optimize molecular surface structures of many polymers. Herein, the surface structure of polydimethylsiloxane (PDMS) is modified by tethering polyelectrolytes (PEs) through surface-initiated ultraviolet (UV) polymerization. Using dimethylacrylamide, acrylic acid, and [2-(methacryloyloxy)ethyl]dimethyl(3-sulfopropyl)ammonium as monomers, cationic, anionic, and zwitterionic PEs are grafted onto PDMS surfaces using the “graft-from” method. Successful grafting of PEs onto PDMS surfaces has been verified by several analytical techniques, including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle measurement. In particular, sum-frequency generation (SFG) vibrational spectroscopy has been employed to probe the molecular structure of modified PDMS surfaces in both the dry and hydrated states. It was found that in air, the surface dominating –Si–CH3groups of unmodified PDMS segregate to the PDMS surface along with the grafted PEs. These methyl groups have similar orientations to those on the unmodified PDMS surface: they more or less stand up on the surface, along the surface normal. Upon exposure to water, only SFG signals from the surface-tethered PE chains on the modified PDMS surface are observed, showing a substantial surface restructuring behavior. More details regarding such surface restructuring behavior can be deduced through SFG data analysis. With numerous PDMS applications in aqueous environments, it is of particular importance to modify its surface structures and characterize such surface structures in aqueous environments in situ.

Comparison of surface structures of poly(ethyl methacrylate) and poly(ethyl acrylate) in different chemical environments

Sum frequency generation (SFG) vibrational spectroscopy has been applied to investigate and compare the chemical structures of poly(ethyl methacrylate) (PEMA) and poly(ethyl acrylate) (PEA) in air, in water, and in a non-polar solvent, FC-75. SFG spectra from both polymer surfaces in air are dominated by vibrational modes from the ester ethyl side groups. The average orientation of these ester ethyl groups on the two polymer surfaces is slightly different. In water, the two polymers show markedly different restructuring behavior. The ester ethyl side chains on the PEMA surface in water reorient to tilt more toward the surface, yet remain ordered. Such a restructuring of the PEMA surface in water is reversible. However, no SFG signal was detected from the PEA/water interface, showing that the surface of PEA becomes disordered upon contacting water, and this process is irreversible. SFG results collected from the C=O range indicate that hydrogen bonding is observed for both polymer/water interfaces, but the order of C=O at the PEA/water interface is much lower than that at the PEMA/water interface. Supplemental experiments support our hypothesis that the PEA surface becomes rough and loses order gradually as it interacts with water. We have demonstrated, for the first time, that the loss of surface structural order is due to the interaction between soft PEA chains with water molecules followed by reorganization of the polymer backbone. This causes the polymer surface to become rough and disordered. However, the surface structures of PEMA and PEA in FC-75 are similar and are also similar to those in air. This indicates that not only T(g), but also the contacting medium plays an important role in determining the surface restructuring behavior of polymer materials.

Surface Restructuring Behavior of Various Types of Poly(dimethylsiloxane) in Water Detected by SFG

Surface structures of several different poly(dimethylsiloxane) (PDMS) materials, tetraethoxysilane-cured hydroxy-terminated PDMS (TEOS-PDMS), platinum-cured vinyl-terminated PDMS (Pt-PDMS), platinum-cured vinyl-terminated poly(diphenylsiloxane)-co-poly(dimethylsiloxane) (PDPS-co-PDMS), and PDMS-co-polystyrene (PDMS-co-PS) copolymer in air and water have been investigated by sum frequency generation (SFG) vibrational spectroscopy. The SFG spectra collected from all PDMS surfaces in both air and water are dominated by methyl group stretches, indicating that all the surfaces are mainly covered by methyl groups. Other than surface-dominating methyl groups, some -Si-CH2-CH2- moieties on the Pt-PDMS surface have also been detected in air, which are present at cross-linking points. Information about the average orientation angle and angle distribution of the methyl groups on the PDMS surface has been evaluated. Surface restructuring of the methyl groups has been observed for all PDMS surfaces in water. Upon contacting water, the methyl groups on all PDMS surfaces tilt more toward the surface. The detailed restructuring behaviors of several PDMS surfaces in water and the effects of molecular weight on restructuring behaviors have been investigated. For comparison, in addition to air and water, surface structures of PDMS materials mentioned above in a nonpolar solvent, FC-75, have also been studied. By comparing the different response of phenyl groups to water on both PDPS-co-PDMS and PS-co-PDMS surfaces, we have demonstrated how the restructuring behaviors of surface phenyl groups are affected by the structural flexibility of the molecular chains where they are attached.

Surface-restructuring behavior of aged PTFE irradiated by a high-flux nitrogen ion beam

Polytetrafluoroethylene (PTFE) was irradiated by a high-flux nitrogen ion beam. The influence of experimental parameters was investigated by varying ion beam energy from 2 to 20 keV with the same flux of 1.4×10 17 ions/cm 2. XPS, SEM, AFM, and wettability were employed to study structures and properties of the treated PTFE samples. All of the as-irradiated samples were aged in air for 1 year. After aging, five chemical bonds, CF 3, CF 2, CF, CO, and carbon bonds were observed on the surfaces of the aged samples. The intensities of various chemical bonds changed with increasing ion beam energy. The surface-restructuring behavior was observed on the surfaces of the aged samples irradiated by ion beam with energies of 2 and 5 keV. The surface roughness and water droplet contact angle of the aged PTFE samples irradiated with 2 and 5 keV ion beams improved obviously, and those of the aged PTFE samples irradiated with 10 and 20 keV ion beams kept basically no change. The experimental results suggest that the ion beam energy strongly affected the surface chemical bond, microstructure, and wettability of the aged PTFE samples.

Morphology and chemical structure of poly(methyl methacrylate) surfaces and interfaces: restructuring behavior induced by the deposition of SiO 2

The surface morphology, molecular structure, and the surface restructuring behavior after the deposition of a SiO 2 layer on poly(methyl methacrylate) (PMMA) have been investigated by using atomic force microscopy (AFM) in contact mode and sum-frequency generation (SFG) vibrational spectroscopy. AFM images show that the surface of PMMA is quite flat and sporadically contains dendritic features, which are micro-crystalline structures of PMMA. From the SFG measurements, the ester methyl groups of PMMA are pointed away from the surface plane at least in the surface region. By depositing a SiO 2 film, the SFG signal intensity is significantly reduced, indicating that the CO and the ester methyl groups are aligned nearly parallel to the surface plane.

Effect of aging on surface chemical bonds of PTFE irradiated by low energy Ti ion

Polytetrafluoroethylene (PTFE) was irradiated by low energy titanium ion in a metal vapor vacuum arc (MEVVA) implanter. The samples were irradiated with 80keV Ti ion with fluences from 5×1015 to 5×1017 Ti/cm2, respectively. Transportation of Ion in Matters (TRIM) code was employed to simulate Ti ion irradiation. The as-irradiated samples were investigated by ESCA, SEM and wettability. As increasing ion fluence, various chemical bonds and irradiation-damaged surfaces were observed. The water droplet contact angel of PTFE samples increased gradually with ion fluence. All the as-irradiated PTFE samples were aged in air for 1 year. After aging the surface-restructuring behavior was observed on the surfaces of the samples irradiated with ion fluence equal to or less than 5×1016 Ti/cm2, which resulted in decrease of the droplet contact angle of these samples. The surface roughness change of the aged samples, which were measured by atomic force microscopy (AFM), was consistent with the droplet contact angle change. The experimental results revealed that Ti ion fluence closely affected the surface chemical bond, morphology and wettability, as well as the aging stability of the as-irradiated PTFE samples.

Influence of aging on the morphology and wettability of polytetrafluoroethylene implanted by high-fluence carbon ion

Polytetrafluoroethylene (PTFE) was implanted by 40 keV carbon ion in a Metal Vapor Vacuum Arc (MEVVA) implanter. The influence of implantation parameters was studied by varying ion fluence from 5×10 15 to 5×10 17 ions/cm 2. Characterization of the as-implanted samples was performed by electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), and wettability. With increasing ion dose, various chemical bonds and irradiation-damaged structures were observed, and droplet contact angle of the samples increased gradually. All the as-implanted PTFE samples were aged in air for 1 year. After aging the surface-restructuring behavior was observed on the surfaces of the samples implanted with ion fluences equal to or less than 5×10 16 ions/cm 2. The experimental results revealed that ion fluence strongly affected the surface chemical composition, morphology, and wettability of the as-implanted samples, as well as the aging stability.

Aging Stability of the Morphology and Wettability of Titanium-Implanted Polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was implanted by titanium ions in a MEVVA (MEtal Vapour Vacuum Arc) implanter. The influence of implantation parameters was studied by varying the ion dose over a wide range. The samples were implanted with 40 keV Ti ions with doses from 5 × 1015 to 5 × 1017 Ti/cm2, and investigated by ESCA, XRD, SEM, and wettability. All the as-implanted PTFE samples were aged in air for one year. After aging the surface-restructuring behavior was observed on the samples implanted with doses of 5 × 1015, 1 × 1016, and 5 × 1016 Ti/cm2. The water contact angle of all the aged samples decreased to a certain extent except for the sample implanted with a dose of 5 × 1017 Ti/cm2. The experimental results suggest that the surface chemical bond, morphology, wettability, and aging stability of as-implanted PTFE samples exhibited fairly strong dependence on the ion dose.

Effect of aging on the morphology and wettability of polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) was implanted in vacuum by argon ions. The influence of experimental parameters was studied by varying ion energy from 2 to 20 keV with the same dose of 1.4×10 17 ions/cm 2. The ion energy strongly affected the surface composition, microstructure, and wettability of PTFE. All as-implanted PTFE samples were aged in air for 1 year. After aging, the surface-restructuring behavior was observed on the surface of samples implanted with ion energy of 2 and 5 keV. The water contact angle of aged samples implanted with ion energy of 5 and 10 keV decreased up to 22° and 11°, respectively.