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Author: Jin Kuk Lee Publisher: ISBN: Category : Glass transition temperature Languages : en Pages : 315
Book Description
The surface dynamics of thin polymer films were tailored via tethering a fraction of the chains to the supporting substrate. This fractionally tethered state was called a "partially tethered film". A partially tethered film was prepared by coating an untethered chain layer on top of a tethered chain layer, followed by annealing. The tethered chain layers for this study had values of grafting density smaller than 0.15 chains/nm2. This low grafting density provided better miscibility between untethered and tethered chains, as compared to previous work with densely grafted brushes, therefore allowing the untethered chains to penetrate to the substrate region. Partially tethered films had slower surface fluctuation dynamics than did corresponding untethered reference films. These tailored surface dynamics after partial tethering were indicated by variations in surface relaxation time measured with X-ray photon correlation spectroscopy. Using the hydrodynamic continuum theory, the surface relaxation behavior of each sample was rationalized. However, since the hydrodynamic continuum theory hypothesizes a homogeneous viscous layer, it is not perfectly applicable to partially tethered films. To address this problem, the surface dynamics of the partially tethered film were described with models designed to account for various effects. A confinement effect due to the covalent bonds between the polymer layer and the substrate was described by modeling the hydrodynamics of a layer adjacent to the substrate and containing a substantial fraction of tethered chains as being extremely slow. The surface dynamics of a partially tethered film for which surface relaxation could still be observed was explained using a two-layer model composed of a top layer of untethered chains moving essentially like bulk untethered chains on top of the bottom layer with very slow dynamics designed to capture the effect of tethering. For sufficiently thick films this model looks very much like that already described by others for the flow of solvent past a solvent swollen layer of adsorbed polymer chains. However, as the partially tethered film becomes thinner, a more complicated model is required. At the least, the thickness of the layer with very slow hydrodynamics has to be varied as a fitting parameter and can become as large as the entire film thickness in some cases. We attribute this behavior to a "neighboring layer" effect. That is, the dynamics of the nominally untethered top layer are slowed by the influence of the practically immobile lower layer. The width of the interface between the top region of nearly pure untethered chains and the bottom region rich in tethered chains apparently plays an important role. When the degree of interpenetration between the two regions is altered by varying miscibility between the tethered and untethered chains, through the control of molecular weights or the segment-segment exchange interaction parameter, [chi], the surface dynamics can be strongly impacted. The relationship of the glass transition temperatures (T [subscript g]) of the tethered and untethered chains to one another was yet another parameter found to influence the tethering effect. When an oligiomeric untethered chain was used, the plasticization of the overall film by the low T[subscript g] untethered material dominated in determining the surface dynamics in the range of temperatures studied. More realistically accounting for all these effects requires a gradient model envisioning a gradual change in dynamical properties with depth into the film.
Author: Jin Kuk Lee Publisher: ISBN: Category : Glass transition temperature Languages : en Pages : 315
Book Description
The surface dynamics of thin polymer films were tailored via tethering a fraction of the chains to the supporting substrate. This fractionally tethered state was called a "partially tethered film". A partially tethered film was prepared by coating an untethered chain layer on top of a tethered chain layer, followed by annealing. The tethered chain layers for this study had values of grafting density smaller than 0.15 chains/nm2. This low grafting density provided better miscibility between untethered and tethered chains, as compared to previous work with densely grafted brushes, therefore allowing the untethered chains to penetrate to the substrate region. Partially tethered films had slower surface fluctuation dynamics than did corresponding untethered reference films. These tailored surface dynamics after partial tethering were indicated by variations in surface relaxation time measured with X-ray photon correlation spectroscopy. Using the hydrodynamic continuum theory, the surface relaxation behavior of each sample was rationalized. However, since the hydrodynamic continuum theory hypothesizes a homogeneous viscous layer, it is not perfectly applicable to partially tethered films. To address this problem, the surface dynamics of the partially tethered film were described with models designed to account for various effects. A confinement effect due to the covalent bonds between the polymer layer and the substrate was described by modeling the hydrodynamics of a layer adjacent to the substrate and containing a substantial fraction of tethered chains as being extremely slow. The surface dynamics of a partially tethered film for which surface relaxation could still be observed was explained using a two-layer model composed of a top layer of untethered chains moving essentially like bulk untethered chains on top of the bottom layer with very slow dynamics designed to capture the effect of tethering. For sufficiently thick films this model looks very much like that already described by others for the flow of solvent past a solvent swollen layer of adsorbed polymer chains. However, as the partially tethered film becomes thinner, a more complicated model is required. At the least, the thickness of the layer with very slow hydrodynamics has to be varied as a fitting parameter and can become as large as the entire film thickness in some cases. We attribute this behavior to a "neighboring layer" effect. That is, the dynamics of the nominally untethered top layer are slowed by the influence of the practically immobile lower layer. The width of the interface between the top region of nearly pure untethered chains and the bottom region rich in tethered chains apparently plays an important role. When the degree of interpenetration between the two regions is altered by varying miscibility between the tethered and untethered chains, through the control of molecular weights or the segment-segment exchange interaction parameter, [chi], the surface dynamics can be strongly impacted. The relationship of the glass transition temperatures (T [subscript g]) of the tethered and untethered chains to one another was yet another parameter found to influence the tethering effect. When an oligiomeric untethered chain was used, the plasticization of the overall film by the low T[subscript g] untethered material dominated in determining the surface dynamics in the range of temperatures studied. More realistically accounting for all these effects requires a gradient model envisioning a gradual change in dynamical properties with depth into the film.
Author: Dongping Qi Publisher: ISBN: Category : Languages : en Pages : 230
Book Description
Studies show that dynamical properties of ultra-thin polymer films deviate from those of bulk materials. Despite some controversial issues, there is growing evidence indicating that the interfacial properties play a key role for observed dynamical anomalies. However, how and how much the interfacial properties affect the average dynamics of the nanometer scale systems are still elusive. In this work, we developed several novel techniques to investigate near-free-surface dynamics of thin polymer films. We studied surface dynamics of glassy i-PMMA films using a nano surface hole relaxation technique: a strong substrate property dependence and an unexpected molecular weight dependence were observed; we found that a local Tg of ~40K below bulk Tg could be assigned to the surface region. We used nano gold particle embedding to study PS surface dynamics: enhanced surface dynamics and weak temperature dependence were observed for the surface region; a depth profile with the nm resolution was observed; viscous liquid-like and soft solid-like properties were observed in the first 5.5nm and next 3.3 nm regions in PS films; no molecualr weight dependence was found in glassy PS films. We built a low level noise measurement system to study the thermal polarization noise in PVAc films: cooperative rearranging dynamics were evidenced; the noise power spectral density (PSD) is found to fluctuate around a certain average level without discernable peak shift; we observed some relatively big jumps or fluctuations in successive integrated PSD's, which indicate some energy exchange between different microscopic domains in glassy polymer systems. We developed a novel nano rheology AFM technique to study the near-free-surface dynamics of thin polymer films: enhanced near-free-surface dynamics with weak temperature dependence are observed for PVAc films, which is similar with the PS case.
Author: Wolfgang Knoll Publisher: John Wiley & Sons ISBN: 3527638490 Category : Science Languages : en Pages : 1107
Book Description
Very thin film materials have emerged as a highly interesting and useful quasi 2D-state functionality. They have given rise to numerous applications ranging from protective and smart coatings to electronics, sensors and display technology as well as serving biological, analytical and medical purposes. The tailoring of polymer film properties and functions has become a major research field. As opposed to the traditional treatise on polymer and resin-based coatings, this one-stop reference is the first to give readers a comprehensive view of the latest macromolecular and supramolecular film-based nanotechnology. Bringing together all the important facets and state-of-the-art research, the two well-structured volumes cover film assembly and depostion, functionality and patterning, and analysis and characterization. The result is an in-depth understanding of the phenomena, ordering, scale effects, fabrication, and analysis of polymer ultrathin films. This book will be a valuable addition for Materials Scientists, Polymer Chemists, Surface Scientists, Bioengineers, Coatings Specialists, Chemical Engineers, and Scientists working in this important research field and industry.
Author: Stephen J. Grunzinger Publisher: ISBN: Category : Polymers Languages : en Pages : 444
Book Description
In a separate study, tensile elongation of water-plasma-treated polyisoprene caused the surface to become more hydrophilic, consistent with exposure of underlying polar groups in the increased surface area. The hydrophobicity of the polymer surface returned when the strain was released. This reversibility damped out slowly over several cycles, but could be recovered by allowing the sample to relax in air.
Author: Chunhua Li Publisher: ISBN: 9781109852875 Category : Polymers Languages : en Pages : 84
Book Description
Polymer thin films play an increasingly important role in various technological applications, including coatings, adhesives and lithography. These applications require polymers to meet diverse performance criteria. For example, viscosity and other rheological properties are critical in the applications of thin film coatings.
Author: Publisher: Springer ISBN: 3540696857 Category : Technology & Engineering Languages : en Pages : 193
Book Description
Most of the untreated surfaces of polymers used in industry are not hydrophilic but hydrophobic. It is, therefore, difficult to bond these nonpolar polymer sur faces directly to other substances like adhesives, printing inks, and paints because they generally consist of polar compounds. On the other hand, polymer surfaces generally adsorb proteins when brought into direct contact with a bio logical system, resulting in cell attachment or platelet aggregation. The protein adsorption and attachment of biological components trigger a subsequent series of mostly adverse biological reactions toward the polymeric materials. Therefore, the technologies for surface modification of polymers or regulation of the polymer surface interaction with other substances have been of prime importance in polymer applications from the advent of polymer industries. Some of the technologies have been directed to introduction of new function alities onto polymer surfaces. The new functionalities introduced include improved surface hydrophilicity, hydrophobicity, bio compatibility, conductivi ty, anti-fogging, anti-fouling, grazing, surface hardness, surface roughness, adhesion, lubrication, and antistatic property. Theoretically, there is a large dif ference in properties between the surface and the bulk of a material and only the outermost surface is enough to be taken into consideration when the sur face properties are concerned. However, this is not the case for polymer surfaces, as the physical structure of the outermost polymer surface is generally not fixed but continuously changing with time due to the microscopic Brownian motion of polymer segments.
Author: Jin Kuk Lee
Author: Jin Kuk Lee
Author: Dongping Qi
Author: Wolfgang Knoll
Author: Zahra Fakhraai
Author: Stephen J. Grunzinger
Author: JD ANDRADE (ED.)
Author: Chunhua Li
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Author: 
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