Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy
Silicone polymers are frequently used as cushions and inserts between load bearing parts. In this capacity, they must act to position their associated parts and distribute mechanical force as appropriate. One type of failure is specific to silicones that are filled with high surface area particulates for purposes of tailoring the polymer compressive properties. Additives such as fumed silicon oxide are presumed to have a high degree of surface interaction with the polymer matrix, thus causing the polymer to stiffen and to display greater dimensional stability as a function of temperature. However, it has been observed that the compressive behavior of these materials is not always invariant over long times. There is evidence that suggests changes in humidity and temperature can irreversibly alter the silicone-filler interaction, thereby changing the overall characteristics of parts made from such materials. As before, changes in compressive or shear stability can have serious effects on the ability of these materials to effectively position precision parts or distribute high mechanical loads. We approach the analysis of the filled systems by creating controlled layers of silicone polymers attached to silicon oxide substrates. Straight chain vinyl-silicone polymers identical to those used in the formulation of pads for stockpile systems are chemically appended to a substrate surface, and cross-linked to form a three dimensional network. This type of structure serves as a model of silicone polymer coating a silicon oxide filler particle. We study these model systems first by using Atomic Force Microscopy (AFM) to image the samples with nanometer resolution, and then by measuring the forces of interactions between single model silica filler particles and polymer-coated surfaces. We use normal longitudinal force AFM to measure adhesion, and a relatively newly developed technique, lateral force AFM, to determine the frictional forces between the silica particles and the polymer films. Lateral force AFM is a sophisticated technique that involves observing the torsional deflections of a cantilever that is scanned across a surface perpendicular to the normal mode deflection. For a carefully calibrated system, this gives information on the dynamic frictional component of the particle/polymer interaction. Both force-measuring techniques utilize colloidal silicon oxide probes ranging from 0.6 {micro}m to 2.0 {micro}m in diameter. These probes replace the standard sharp AFM tip on the cantilever with a spherical bead (Figure 1) and are used to examine interactions between the bead material and the sample surface.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 920487
- Report Number(s):
- UCRL-TR-231783; TRN: US0805322
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
ADDITIVES
ADHESION
ATOMIC FORCE MICROSCOPY
BEARINGS
COATINGS
FILLERS
HUMIDITY
MICROSCOPY
PARTICULATES
POLYMERS
PROBES
RESOLUTION
SHEAR
SILICA
SILICON OXIDES
SILICONES
STABILITY
STOCKPILES
SUBSTRATES
SURFACE AREA