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1.
Langmuir ; 36(4): 837-843, 2020 Feb 04.
Artigo em Inglês | MEDLINE | ID: mdl-31898908

RESUMO

Use of a plasma-polymerized (pp) layer under a polyurethane (PU) coating on aluminum dramatically improves the corrosion resistance. Compared to conventional polymer coatings, pp coatings are highly cross-linked, have better adhesion to substrates, and result in lower emission of volatile organic contents. Although past research has focused on the properties of comparatively thick pp films and on the use of pp films alone to protect metals, we consider here very thin pp coatings as a primer layer to improve corrosion resistance. Electrochemical impedance spectroscopy combined with salt spray lab tests show that the corrosion resistance of a PU coating on top of a pp coating from hexamethyldisiloxane (HMDSO) is much better than that of a PU coating directly on Al 3003. The relatively poor pull-off adhesion between PU and pp-HMDSO is readily addressed using a gradient coating by depositing a pp maleic anhydride layer over the pp-HMDSO coating or by modifying the surface composition of the pp-HMDSO coating with N2 plasma. X-ray photon spectroscopy analysis of the failure interface from pull-off tests makes clear that failure does not occur at the interface between the pp coating and the metal substrate. Field tests show the performance of the coating system with PU on a gradient coating on Al 3003 to be superior to that of a coating system of PU on chromate-treated Al 3003.

2.
ACS Appl Mater Interfaces ; 11(3): 3555-3564, 2019 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-30592199

RESUMO

A challenge of broad interest in both materials science and biology is the study of interfaces that are buried within a structure, particularly multilayer structures. Despite the enormous costs of corrosion and many decades of corrosion research, details of the mechanisms of various sorts of corrosion are still not clear, in part due to the difficulty in interrogating the interface between the corroding metal and an organic coating, which is typically used to mitigate corrosion. Generally, the performance of such coatings is evaluated by visual inspection after exposure or by modeling impedance data, which is a process not straightforwardly connected to physical interface structures. "Rocking-curve" X-ray scattering measurements provide a means of probing such interfaces due to the ability of X-rays to penetrate materials. Here, variations in the morphology of an interface between a protective coating and a metal substrate due to exposure to an electrolyte are derived from analysis of rocking-curve data in conjunction with atomic force microscopy imaging of the outer coating surface. The interfaces of cross-linked epoxy coatings with aluminum are irreversibly changed after 12 h of contact between the electrolyte solution and the face of the coating. The character of this change varies with the molecule used to cross-link the coating. Since X-ray off-specular scattering is sensitive to changes on the nanometer scale, it is also able to register interface degradation on time scales shorter than those probed by many other techniques, potentially expediting the evaluation of coatings for protection against degradation of the interface.

3.
Anal Chem ; 90(22): 13427-13433, 2018 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-30346135

RESUMO

Surface layer matrix-assisted laser desorption ionization mass spectrometry imaging (SL-MALDI-MSI) is a powerful new surface sensitive imaging technique to establish surface component localization of multicomponent polymer materials. This study demonstrates the ability of SL-MALDI-MSI to image defects from foreign materials, material absence, mechanical scribing, and solvent perturbation at the surface of low-molecular-weight poly(methyl methacrylate) and polystyrene thin films. The surface specificity of the SL-MALDI-MSI technique is validated by imaging polystyrene on poly(methyl methacrylate) bilayer films; only polystyrene ions are detected from the surface of the unperturbed polystyrene layer. A key process enabling SL-MALDI-MSI is the solvent-free sublimation of matrix and salt uniformly on the sample's surface.

4.
Langmuir ; 34(33): 9634-9644, 2018 08 21.
Artigo em Inglês | MEDLINE | ID: mdl-30036069

RESUMO

The search continues for means of making quick determinations of the efficacy of a coating for protecting a metal surface against corrosion. One means of reducing the time scale needed to differentiate the performance of different coatings is to draw from nanoscale measurements inferences about macroscopic behavior. Here we connect observations of the penetration of water into plasma polymerized (PP) protective coatings and the character of the interface between the coating and an oxide-coated aluminum substrate or model oxide-coated silicon substrate to the macroscopically observable corrosion for those systems. A plasma polymerized film from hexamethyldisiloxane (HMDSO) monomer is taken as illustrative of a hydrophobic coating, while a PP film from maleic anhydride (MA) is used as a characteristically hydrophilic coating. The neutron reflectivity (NR) of films on silicon oxide coated substrates shows that water moves more readily through the hydrophilic PP-MA film. Off-specular X-ray scattering indicates the PP-MA film on aluminum is less conformal with the substrate than is the PP-HMDSO film. Measurements with infrared-visible sum frequency generation spectroscopy (SFG), which probes the chemical nature of the interface, make clear that the chemical interactions between coating and aluminum oxide are disrupted by interfacial water. With this water penetration and interface disruption, macroscopic corrosion can occur much more rapidly. An Al panel coated with PP-MA corrodes after 1 day in salt spray, while a similarly thin (∼30 nm) PP-HMDSO coating protects an Al panel for a period on the order of one month.

5.
Langmuir ; 33(31): 7818-7825, 2017 08 08.
Artigo em Inglês | MEDLINE | ID: mdl-28719214

RESUMO

Tip enhanced Raman spectroscopy (TERS) has been established as a powerful, noninvasive technique for chemical identification at the nanoscale. However, difficulties, including the degradation of probes, limit its use in liquid systems. Here TERS probes for studies in aqueous environments have been demonstrated using titanium nitride coatings with an alumina protective layer. The probes show enhancement in signal intensity as high as 380% in liquid measurements, and the probe resonance can be tuned by varying deposition conditions to optimize performance for different laser sources and types of samples. This development of inexpensively produced probes suited for studies in aqueous environments enables its wider use for fields such as biology and biomedicine in which aqueous environments are the norm.


Assuntos
Análise Espectral Raman , Óxido de Alumínio , Lasers , Água
6.
Phys Rev Lett ; 118(16): 167801, 2017 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-28474912

RESUMO

If you mix lines and circles, what happens at the edge of the mixture? The problem is simply stated, but the answer is not obvious. Twenty years ago it was proposed that a universal topological driving force would drive cyclic chains to enrich the surface of blends of linear and cyclic chains. Here such behavior is demonstrated experimentally for sufficiently long chains and the limit in molecular weight where packing effects dominate over the topological driving force is identified.

7.
Langmuir ; 32(22): 5623-8, 2016 06 07.
Artigo em Inglês | MEDLINE | ID: mdl-27172089

RESUMO

The scaling of the thickness, hs, of a densely grafted polymer brush of chain length N and grafting density σ swollen in vapor agrees quantitatively with the scaling reported by Kuhl et al. for densely grafted brushes swollen in liquid. Deep in the brush, next to the substrate, the shape of the segment concentration profile is the same whether the brush is swollen by liquid or by vapor. Differences in the segment concentration profile are manifested primarily in the swollen brush interface with the surrounding fluid. The interface of the polymer brush swollen in vapor is much more abrupt than that of the same brush swollen in liquid. This has implications for the compressibility of the swollen brush surface and for fluctuations at that surface.

8.
Soft Matter ; 12(24): 5372-7, 2016 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-27222250

RESUMO

The surface height fluctuations of a layer of low molecular weight (2.2k) untethered perdeuterated polystyrene (dPS) chains adjacent to a densely grafted polystyrene brush are slowed dramatically. Due to the interpenetration of the brush with the layer of "untethered chains" a hydrodynamic continuum theory can only describe the fluctuations when the effective thickness of the film is taken to be that which remains above the swollen brush. The portion of the film of initially untethered chains that interpenetrates with the brush becomes so viscous as to effectively play the role of a rigid substrate. Since these hybrid samples containing a covalently tethered layer at the bottom do not readily dewet, and are more robust than thin layers of untethered short chains on rigid substrates, they provide a route for tailoring polymer layer surface properties such as wetting, adhesion and friction.

9.
Phys Rev Lett ; 113(22): 225702, 2014 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-25494077

RESUMO

The contributions of chain ends and branch points to surface segregation of long-branched chains in blends with linear chains have been studied using neutron reflectometry and surface-enhanced Raman spectroscopy for a series of novel, well-defined polystyrenes. A linear response theory accounting for the number and type of branch points and chain ends is consistent with surface excesses and composition profile decay lengths, and allows the first determination of branch point potentials. Surface excess is determined primarily by chain ends with branch points playing a secondary role.

10.
Phys Rev Lett ; 111(6): 068303, 2013 Aug 09.
Artigo em Inglês | MEDLINE | ID: mdl-23971618

RESUMO

The dynamics of thermally stimulated surface fluctuations of 100 nm thick films of long-branched polymers are measured for the first time. In contrast to comparable films of linear or cyclic chains that show no change in viscosity upon confinement, films of 6-pom, 6-star, and 6-end end-branched stars show viscosities, inferred from x-ray photon correlation spectroscopy, as much as 100 times higher than in the bulk. This difference varies in magnitude with chain architecture. Branching has a profound effect on confinement, even for these unentangled chains.

11.
ACS Appl Mater Interfaces ; 5(8): 2976-84, 2013 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-23560512

RESUMO

We demonstrate, using neutron reflectivity, that the width of a nonequilibrium interface between an organo-soluble aromatic polyimide film and triacetate cellulose (TAC) support film created by spin-coating or solution-casting can be broadened in a controllable way using a "swelling agent" in the deposition process. In a favorable case, the adhesion, as measured by T-peel tests, can be increased by a factor of 7 by adjustment of the solvent composition. The morphologies of the TAC fractured surfaces after peeling tests measured by AFM reveal that broadening of the interfacial width causes an interconnected network in the interface, leading to a sharp increase in the interfacial adhesion. Differences in the chemistry (solubility) of the materials being deposited do make a difference in the effectiveness of this strategy of using a "swelling agent". For one polyimide, a 3-fold increase in adhesion can be obtained by optimizing the deposition temperature, but this approach for improving adhesion is less effective than that of adding "swelling agent". The formation of robust interfaces of this type is important because of the critical roles that multilayer films containing polymers with special properties and tailored structures play in applications as diverse as computer displays, photovoltaic devices, and polymeric electronics. The "swelling agent" strategy makes it possible to produce polymer multilayer structures in a cost-effective way with roll-to-roll mass production using direct solution coating.

12.
J Am Soc Mass Spectrom ; 24(1): 74-82, 2013 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-23192702

RESUMO

[M + Ag](+) ions from cyclic and linear polystyrenes and polybutadienes, formed by matrix-assisted laser desorption ionization (MALDI), give rise to significantly different fragmentation patterns in tandem mass spectrometry (MS(2)) experiments. In both cases, fragmentation starts with homolytic cleavage at the weakest bond, usually a C-C bond, to generate two radicals. From linear structures, the separated radicals depolymerize extensively by monomer losses and backbiting rearrangements, leading to low-mass radical ions and much less abundant medium- and high-mass closed-shell fragments that contain one of the original end groups, along with internal fragments. With cyclic structures, depolymerization is less efficient, as it can readily be terminated by intramolecular H-atom transfer between the still interconnected radical sites (disproportionation). These differences in fragmentation reactivity result in substantially different fragment ion distributions in the MS(2) spectra. Simple inspection of the relative intensities of low- versus high-mass fragments permits conclusive determination of the macromolecular architecture, while full spectral interpretation reveals the individual end groups of linear polymers or the identity of the linker used to form the cyclic polymer.


Assuntos
Poliestirenos/química , Espectrometria de Massas por Ionização e Dessorção a Laser Assistida por Matriz/métodos , Espectrometria de Massas em Tandem/métodos , Butadienos/química , Elastômeros/química , Modelos Moleculares
13.
ACS Appl Mater Interfaces ; 3(9): 3375-83, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21875044

RESUMO

Tailoring the structure of films deposited by plasma-enhanced chemical vapor deposition (PECVD) to specific applications requires a depth-resolved understanding of how the interface structures in such films are impacted by variations in deposition parameters such as feed position and plasma power. Analysis of complementary X-ray and neutron reflectivity (XR, NR) data provide a rich picture of changes in structure with feed position and plasma power, with those changes resolved on the nanoscale. For plasma-polymerized octafluorocyclobutane (PP-OFCB) films, a region of distinct chemical composition and lower cross-link density is found at the substrate interface for the range of processing conditions studied and a surface layer of lower cross-link density also appears when plasma power exceeds 40 W. Varying the distance of the feed from the plasma impacts the degree of cross-linking in the film center, thickness of the surface layer, and thickness of the transition region at the substrate. Deposition at the highest power, 65 W, both enhances cross-linking and creates loose fragments with fluorine content higher than the average. The thickness of the low cross-link density region at the air interface plays an important role in determining the width of the interface built with a layer subsequently deposited atop the first.


Assuntos
Gases/química , Nanoestruturas/química , Clorofluorcarbonetos , Clorofluorcarbonetos de Metano/química , Flúor/química , Espectroscopia Fotoeletrônica , Polímeros/química
14.
Scanning ; 27(1): 44-8, 2005.
Artigo em Inglês | MEDLINE | ID: mdl-15712757

RESUMO

The measurement of lateral force in response to small amplitude lateral oscillations of a sample using a scanning probe microscope (X-modulation) is presented as an effective means of identifying key qualitative differences in the nanomechanical behavior of solid surfaces. To study the surface behavior in detail, it is critical that the instrument have sufficient flexibility. Computer-assisted measurement automation achieved using LabVIEW makes an X-modulation experiment more flexible and convenient. Even though further refinement of the modulation technique is necessary in both theory and experiment to obtain a complete picture, the systematic approach made possible by this sort of instrumentation is valuable for the study of mechanical properties of the surface.

15.
J Colloid Interface Sci ; 261(2): 273-82, 2003 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-16256532

RESUMO

The surfactants sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) displace human serum albumin (HSA) from loosely packed self-assembled monolayers (SAM) of hydrophobic alkyl chains by different means. Removal of HSA is of interest because previous work has suggested that the adsorption of HSA to such loosely packed SAMs may be sufficiently tenacious to offer opportunities for surface passivation. While HSA remains on the surface after exposure to SDS and rinsing, no protein remains after exposure to CTAB and rinsing. X-ray reflectivity and X-ray photoelectron spectroscopy measurements indicate that CTAB molecules remain interdigitated in the loosely packed SAM after rinsing, suggesting that CTAB is more effective in removing the HSA because it interacts more strongly with the SAM.


Assuntos
Compostos de Cetrimônio , Albumina Sérica/farmacocinética , Dodecilsulfato de Sódio , Tensoativos , Adsorção , Cetrimônio , Compostos de Cetrimônio/química , Eletroquímica , Humanos , Tensoativos/química
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