skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy

Abstract

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 stockpilemore » 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.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
920487
Report Number(s):
UCRL-TR-231783
TRN: US0805322
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, 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

Citation Formats

Ratto, T, and Saab, A. Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy. United States: N. p., 2007. Web. doi:10.2172/920487.
Ratto, T, & Saab, A. Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy. United States. doi:10.2172/920487.
Ratto, T, and Saab, A. Mon . "Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy". United States. doi:10.2172/920487. https://www.osti.gov/servlets/purl/920487.
@article{osti_920487,
title = {Evaluation of Polymer-Filler Interaction Characteristics by Force Microscopy},
author = {Ratto, T and Saab, A},
abstractNote = {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.},
doi = {10.2172/920487},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Apr 23 00:00:00 EDT 2007},
month = {Mon Apr 23 00:00:00 EDT 2007}
}

Technical Report:

Save / Share:
  • In the present work, we study, via force microscopy, the basic physical interactions of a single bead of silica filler with a PDMS matrix both before and after exposure to gamma radiation. Our goal was to confirm our results from last year, and to explore force microscopy as a means of obtaining particle-scale polymer/filler interactions suitable for use as empirical inputs to a computational model consisting of an ensemble of silica beads embedded in a PDMS matrix. Through careful calibration of a conventional atomic force microscope, we obtained both normal and lateral force data that was fitted to yield adhesion,more » surface shear modulus, and friction of a 1 {micro}m silica bead in contact with PDMS layers of various thickness. Comparison of these terms before and after gamma exposure indicated that initially, radiation exposure lead to softening of the PDMS, but eventually resulted in stiffening. Simultaneously, adhesion between the polymer and silica decreased. This could indicate a serious failure path for filled PDMS exposed to radiation, whereby stiffening of the bulk polymer leads to loss of compressive elastic behavior, while a decrease in polymer filler adhesion results in an increased likelihood of stress failure under load. In addition to further testing of radiation damaged polymers, we also performed FEA modeling of silica beads in a silicone matrix using the shear modulus and adhesion values isolated from the force microscopy experiments as model inputs. The resulting simulation indicated that as a polymer stiffens due to impinging radiation, it also undergoes weakening of adhesion to the filler. The implication is that radiation induces a compound failure mode in filled polymer systems.« less
  • The fundamental purpose for SKEET is to provide a means of simulating and evaluating OTEC platform SKSS performance. This evaluation capability may be employed in the process of a design review, comparison of alternative concepts, operational planning, establishing risk and reliability criteria and a host of other applications. However, the central requirement is that SKEET have the capability to predict the excursions on motions of the platform and loads on the SKSS as a result of environmental effects under a range of operational conditions. The principal elements which should be represented by the SKEET model include: environment (wind, current, waves);more » vessel/CWP configuration; mooring system (including anchor/soil and electrical riser cable interactions); and dynamic positioning system effects. Findings are summarized of the following two tasks that have been undertaken to formulate a definition of the requirements of SKEET: Task III - identify and classify the physical characteristics and phenomena and evaluate interaction effects; and Task IV - establish mooring performance criteria. The objective of Task III was to define the range of physical parameters that must be incorporated into SKEET and to make an assessment of the most appropriate manner in which to incorporate each of those parameters. The objective of Task IV was to define the required outputs from SKEET. (WHK)« less
  • The OH modules for the DO end calorimeter are being tested by supporting a load to simulate the MH, IH, and EM modules. This test structure, the MH filler, is inserted into the previously assembled OH modules, and then loaded with hydraulic jacks. The maximum test load applied by the jacks is 78,600 lb, which is via the two downstream jacks at 130% of the nominal load. Bill Cooper's memo of 9/10/90 is include as appendix C. This note presents calculations for the AISC maximum allowable stresses/loads of the various parts of the testing assembly. Furthermore, calculations show that themore » actual test load is less than the AISC allowable.« less
  • Microcharacterization studies were performed on weld-metal microstructures of a Ni-base filler metal. Specimens were taken from the fusion zone and the weld-metal heat-affected zone of transverse- and spot-Varestraint welds. The filler metal was first deposited onto a steel substrate by hot-wire, gas tungsten arc welding before specimen removal. Optical microscopy indicates the crack morphology is intergranular and is along high-angle, migrated grain boundaries. At low magnifications, scanning electron microscopy reveals a relatively smooth fracture surface. However, at higher magnifications the grain faces exhibit microductility. Analytical electron microscopy reveals high-angle, migrated grain boundaries decorated with MC (Ti, Cr) and M{sub 23}C{submore » 6} (Cr, Ni, Fe) precipitates ranging from 10 to 200 n. Auger electron spectroscopy of pre-strained Gleeble specimens fractured in situ revealed internal ductility-dip cracks decorated with magnesium aluminate (MgAl{sub 2}O{sub 4}) spinel particles (1,000 nm).« less
  • No abstract prepared.