Probing Macromolecular Dynamics and the Influence of Finite Size Effects

Sills, Scott; Overney, René M.

doi:10.1007/3-540-26910-x_4

Cited by 6 publications

(5 citation statements)

References 116 publications

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“…This procedure is called frequency− temperature superposition 24 and finally the activation energy E A can be extracted from an arrhenius plot of the shift factors E A . [12][13][14]25 In our case, the SAMs needed to be cooled down for the time constants to match the AFM excitation. It is helpful if all friction isotherms show the dissipation peak but it is not necessary because a master curve can also be built if this is not the case.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Therefore, measurements at different temperatures yield different peak velocities, or more generally, the velocity isotherms are shifted but can be transferred into a unique master curve by using a temperature dependent shift factor a T . This procedure is called frequency–temperature superposition and finally the activation energy E A can be extracted from an arrhenius plot of the shift factors E A . − , In our case, the SAMs needed to be cooled down for the time constants to match the AFM excitation. It is helpful if all friction isotherms show the dissipation peak but it is not necessary because a master curve can also be built if this is not the case …”

Section: Experimental Sectionmentioning

confidence: 99%

“…More specifically, this is done by combined temperature and velocity-dependent friction measurements on the monolayers and data analysis based on the frequency–temperature superposition model. This approach was demonstrated by Sills et al, − who used the transformation of friction–velocity isotherms into a single master curve that revealed activation energies E A of polymer systems. In our case, application of the frequency–temperature superposition model yields a characteristic energy barrier, which opens up a new route to understand frictional dissipation in SAM structures.…”

Section: Introductionmentioning

confidence: 99%

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Nanotribological Properties of Hexadecanethiol Self-Assembled Monolayers on Au(111): Structure, Temperature, and Velocity

et al. 2017

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Self-assembled monolayers (SAM) are promising building blocks for the optimization of a large variety of systems both on the nano- and on the microscale. Among other applications, SAM are often used as protective coating or friction modifiers. In this work, we have used hexadecanethiol SAM on Au(111) as a model system and studied the different mechanisms of energy dissipation during temperature and velocity dependent friction force microscopy (FFM). In a number of cases, the SAM remained stable during atomic force microscopy experiments and friction-velocity isotherms related dissipation to an activation energy. In other cases, friction experiments lead to an irreversible deterioration of the SAM. This can rather be associated with the general SAM structure that was analyzed by scanning tunneling microscopy and showed a large variety of potential breakdown points like, for example, grain boundaries, step edges, or substrate-related holes in the SAM.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: Experimental Sectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nanotribological Properties of Hexadecanethiol Self-Assembled Monolayers on Au(111): Structure, Temperature, and Velocity

et al. 2017

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“…The effects of nanoconfinement, free surfaces, and interaction with particles on the glass transition of polymers have been reviewed in recent years with no general consensus revealed. − Concerning particle-induced effects, there are observations that the segmental relaxation (α-relaxation) and glass transition temperature ( T g ) are largely unaffected by the presence of filler, despite significant levels of “bound” polymer enacted by high filler surface area and chemically modified interfaces. − Kumar, Gidley, and co-workers recently used differential scanning calorimetry (DSC) and dielectric relaxation spectroscopy to probe the influence of 15 nm diameter silica particles on the glass transition of poly(2-vinylpyridine). This system has strong attractive interactions between polymer and filler, but even at a very high filler volume fraction (ϕ) of 0.5 (62.5 wt % filler) they noted a T g increase of only about 5 °C.…”

Section: Introductionmentioning

confidence: 99%

Further Consideration of Viscoelastic Two Glass Transition Behavior of Nanoparticle-Filled Polymers

Robertson

Rackaitis

2011

Macromolecules

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Tsagaropoulos and Eisenberg [Macromolecules 1995, 28, 396; Macromolecules 1995, 28, 6067] reported a second loss tangent (tan δ) peak in temperature-dependent viscoelastic data for various un-cross-linked polymers filled with nanometer-sized silica particles. This peak, occurring at temperatures as much as 100 °C above the primary tan δ peak (glass-to-rubber softening transition), was ascribed to the glass transition of immobilized chains near the particles. This research is often cited as support for the existence of severely retarded segmental motion of polymer near the surfaces of small particles (glassy polymer shell). We offer a different interpretation of the results from Tsagaropoulos and Eisenberg, reinforced by our recent measurements on particle-filled polybutadiene and consideration of other literature data. Particles restrict the flow of some polymer chains, thus resulting in incomplete terminal relaxation, and partial cross-linking of unfilled polymers produces the same higher temperature tan δ peak. Polymer chains which are adsorbed onto filler surfaces are immobilized from a flow relaxation (chain diffusion/reptation) standpoint, but segmental relaxation (glass transition) is not substantially altered by small particles as a general rule.

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“…Using lock-in techniques, the modulation response, ∆x R , is analyzed relative to ∆x i . For a small (in-plane) lateral displacement for a sphere-plane geometry (assuming the absence of slip), the lateral stiffness of the contact k c,x is provided as [94][95][96]:…”

Section: Shear Modulation Force Microscopy (Sm-fm)mentioning

confidence: 99%

Friction and Surface Dynamics of Polymers on the Nanoscale by AFM

Schönherr

Tocha

Vancso

2008

Topics in Current Chemistry

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In this article the measurement and understanding of friction forces and surface dynamics ofpolymers on the one hand and the importance of molecular relaxation processes and viscoelasticityin polymers for advanced micro- and nanoscale applications on the other hand are discussed. Particularattention is paid to the nanoscale (surface) analysis by scanned probe microscopic approaches, includingatomic force microscopy (AFM), as a means to assess molecular relaxation processes that operateat a given temperature. Established AFM approaches, including lateral force and force modulationmicroscopy, are introduced and more recently developed techniques, such as torsional resonant modes,are briefly sketched. On the basis of the discussion of the techniques to measure friction and toprobe surface dynamics of polymers on the nanoscale, illustrative examples are reviewed. The examplesdiscussed address in particular the determination of values of the glass transition temperature (T g) and the difference of T gassessed in the bulk vs. at the free surface of polymers. Confinement and thin film effects on T g, but also on sub-T gtransitions and chain dynamics, are treated in detail. Finally, the mapping of multiphase systemsand anisotropic friction receive attention.

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Probing Macromolecular Dynamics and the Influence of Finite Size Effects

Cited by 6 publications

References 116 publications

Nanotribological Properties of Hexadecanethiol Self-Assembled Monolayers on Au(111): Structure, Temperature, and Velocity

Nanotribological Properties of Hexadecanethiol Self-Assembled Monolayers on Au(111): Structure, Temperature, and Velocity

Further Consideration of Viscoelastic Two Glass Transition Behavior of Nanoparticle-Filled Polymers

Friction and Surface Dynamics of Polymers on the Nanoscale by AFM

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