http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Graphene-polymer nanocomposites for structural and functional applications

Tribology of polymers: Adhesion, friction, wear, and mass-transfer

Highly sensitive sensor arrays are in high demand for prospective applications in remote sensing and imaging. Measuring microscopic deflections of compliant micromembranes and cantilevers is developing into one of the most versatile approaches for thermal, acoustic and chemical sensing. Here, we report on an innovative fabrication of compliant nanocomposite membranes with nanoscale thickness showing extraordinary sensitivity and dynamic range, which makes them candidates for a new generation of membrane-based sensor arrays. These nanomembranes with a thickness of 25–70 nm, which can be freely suspended over large (hundred micrometres) openings are fabricated with molecular precision by time-efficient, spin-assisted layer-by-layer assembly. They are designed as multilayered molecular composites made of a combination of polymeric monolayers and a metal nanoparticle intralayer. We demonstrate that these nanocomposite membranes possess unparalleled sensitivity and a unique autorecovering ability. The membrane nanostructure that is responsible for these outstanding properties combines multilayered polymer/nanoparticle organization, high polymer-chain orientation, and a pre-stretched state.

/pdf/freely-suspended-nanocomposite-membranes-as-highly-sensitive-2xrgx5egg3.pdf

Freely suspended nanocomposite membranes as highly sensitive sensors

The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

/pdf/elastic-moduli-of-ultrathin-amorphous-polymer-films-285qxquj7l.pdf

Elastic Moduli of Ultrathin Amorphous Polymer Films

The approach developed for the microindentation of layered elastic solids was adapted to analyze atomic force microscopy probing of ultrathin (1–100 nm-thick) polymer films on a solid substrate. The model for analyzing microindentation of layered solids was extended to construct two- and tri-step graded functions with the transition zones accounting for a variable gradient between layers. This “graded” approach offered a transparent consideration of the gradient of the mechanical properties between layers. Several examples of recent applications of this model to nanoscale polymer layers were presented. We considered polymer layers with elastic moduli ranging from 0.05 to 3000 MPa with different architecture in a dry state and in a solvated state. The most sophisticated case of a tri-layered polymer film with thickness of 20–50 nm was also successfully treated within this approach. In all cases, a complex shape of corresponding loading curves and elastic modulus depth profiles obtained from experimental data were fitted by the graded functions with nanomechanical parameters (elastic moduli and transition zone widths) close to independently determined microstructural parameters (thickness and composition of layers) of the layered materials.

/pdf/nanomechanical-probing-of-layered-nanoscale-polymer-films-1dzouqctl4.pdf

Nanomechanical probing of layered nanoscale polymer films with atomic force microscopy

Polymer tribology is a fast growing area owing to increasing applications of polymers and polymer composites in industry, transportation, and many other areas of economy. Surface forces are very important for polymer contact, but the real origin of such forces has not been fully investigated. Strong adhesive interaction between polymers leads to an increase in the friction force, and hence, the asperities of the material may be removed to form wear particles or transfer layers on the counterface. The theory of polymer adhesion has not been completely elucidated yet and several models of adhesion have been proposed from the physical or chemical standpoints. This paper is focused on the research efforts on polymer adhesion with emphasis on adhesion mechanisms, which are very important in the analysis of polymer friction and wear.

/pdf/adhesion-and-surface-forces-in-polymer-tribology-a-review-lss3qez6pv.pdf

Adhesion and surface forces in polymer tribology—A review

http://polysurf.mse.gatech.edu/wp-content/uploads/2010/08/EPJMulti2004.pdf

Some aspects of AFM nanomechanical probing of surface polymer films

Surface phenomena and the structure of polymers affect essentially their tribological characteristics, the adhesion of polymers to solids being one of the dominating factors. The latter is explained, in particular, by the adsorption (chemisorption) of the functional groups, variations in the polymer crystallinity and morphology, constrained molecular mobility, and catalytic effects of the additives on the reactions occurring in the contact zone. It is shown how load, sliding velocity, and temperature affect friction. Different modes of wear of polymers and friction transfer are considered.

Alexander Kovalev

Papers

Tribology of polymers: Adhesion, friction, wear, and mass-transfer

Nanomechanical probing of layered nanoscale polymer films with atomic force microscopy

Adhesion and surface forces in polymer tribology—A review

Some aspects of AFM nanomechanical probing of surface polymer films

Adhesion and friction of polymers