MIL-HDBK-17-1F Volume 1,Chapter 3 Evaluation of Reinforcement Fibers (i)Secondary lon Mass Spectroscopy(SIMS)-uses a controlled sputtering process with accelerated ions to remove surface atomic layers for direct analysis by mass spectroscopy.SIMS can be used to identify surface molecules and determine their concentrations. (j)Infrared Spectroscopy(IRS)or Fourier Transform IRS(FTIRS)-absorption vibrational spectros- copy technique to obtain molecular information about surface composition.IRS yields both quali- tative and quantitative information relating to the chemical composition of surface molecules.The quality of the IR analysis depends on the fiber composition and is directly related to the care taken during sample preparation. For fibers with diameters between 0.015 and 0.03 mm,no sample preparation is required if an IR mi- croscope is available to examine fibers directly.Organic fibers may be pressed (up to 1000/m) into a film of fiber grids. (k)Laser Raman spectroscopy-absorption/vibrational spectroscopic technique which complements IR and is relatively simple to apply.Little or no sample preparation is necessary.Fibers can be oriented in the path of the incident beam for direct analysis.Fiber sample must be stable to the high intensity incident light and should not contain species that fluoresce. (1)Contact angle and wetting measurements-provide an indirect measurement of fiber surface free energy for use in predicting interfacial compatibility and thermodynamic equilibrium with matrix materials.Contact angle and wetting measurement information can be obtained by direct meas- urement of contact angle,mass pick-up,or surface velocity.Measurement of contact angles on small diameter fibers(<10 microns)is difficult if done optically.If a fiber's dimensions are known, a simple force balance may be used to determine the contact angle by measuring the force in- duced by immersing the fiber into a liquid of known surface free energy.The apparatus usually employed for this test is the Wilhelmy balance(Reference 3.2.4(a)). Contact angles 0 also may be measured indirectly by the micro-Wilhelmy technique (References 3.2.4(b-e)).A single fiber is partially immersed in a liquid and the force exerted on the fiber due to the surface tension of the liquid is measured.The contact angle is determined from the relation- ship F CyLv cose where F is the force measured corrected for buoyancy,C is the circumference of the fiber,and YLv is the surface tension of the liquid.The results may be used to determine the fiber surface free energy and the contributions of polar and dispersive components to the free en- ergy (References 3.2.4(c)and(d)). (m)Physisorption and chemisorption measurements -adsorption of inert gas or organic molecules can be used to measure fiber surface area.To obtain accurate estimates of surface area,it is important that there is complete monolayer coverage of the surface,that the area occupied by the adsorbed gas is known and that significant amounts of the gas are not taken up in micropores. Additional complications arise when the adsorption of organic molecules is used in place of gas adsorption,since it may be necessary to know the orientation of the adsorbed molecules to calcu- late surface area.Adsorption may also occur only at specific active sites and,if solutions are used,solvent molecules may be adsorbed as well. The chemical reactivity of fiber surfaces can be determined by oxygen chemisorption and desorption measurements.Topographical changes (e.g.,pores,cracks and fissures)caused by surface treatments often can be readily detected by adsorption measurements.Flow microcalorimetry is a useful technique for directly measuring heats of adsorption(Reference 3.2.4(f)). (n)Thermal desorption measurements-desorption of volatile products from fibers by heat treatment in vacuo.Thermal gravimetric analysis (TGA),gas chromatography (GC),mass spectroscopy (MS).infrared spectroscopy(IRS)analysis or combinations of pyrolysis GC/MS or TGA/IRS may be used to identify components desorbed from fiber surfaces.Below 150C,CO,NH,CH and various organic molecules are observed depending upon the fiber type. 3-4MIL-HDBK-17-1F Volume 1, Chapter 3 Evaluation of Reinforcement Fibers 3-4 (i) Secondary Ion Mass Spectroscopy (SIMS) - uses a controlled sputtering process with accelerated ions to remove surface atomic layers for direct analysis by mass spectroscopy. SIMS can be used to identify surface molecules and determine their concentrations. (j) Infrared Spectroscopy (IRS) or Fourier Transform IRS (FTIRS) - absorption vibrational spectros￾copy technique to obtain molecular information about surface composition. IRS yields both quali￾tative and quantitative information relating to the chemical composition of surface molecules. The quality of the IR analysis depends on the fiber composition and is directly related to the care taken during sample preparation. For fibers with diameters between 0.015 and 0.03 mm, no sample preparation is required if an IR mi￾croscope is available to examine fibers directly. Organic fibers may be pressed (up to 1000/m2 ) into a film of fiber grids. (k) Laser Raman spectroscopy - absorption/vibrational spectroscopic technique which complements IR and is relatively simple to apply. Little or no sample preparation is necessary. Fibers can be oriented in the path of the incident beam for direct analysis. Fiber sample must be stable to the high intensity incident light and should not contain species that fluoresce. (l) Contact angle and wetting measurements - provide an indirect measurement of fiber surface free energy for use in predicting interfacial compatibility and thermodynamic equilibrium with matrix materials. Contact angle and wetting measurement information can be obtained by direct meas￾urement of contact angle, mass pick-up, or surface velocity. Measurement of contact angles on small diameter fibers (< 10 microns) is difficult if done optically. If a fiber's dimensions are known, a simple force balance may be used to determine the contact angle by measuring the force in￾duced by immersing the fiber into a liquid of known surface free energy. The apparatus usually employed for this test is the Wilhelmy balance (Reference 3.2.4(a)). Contact angles θ also may be measured indirectly by the micro-Wilhelmy technique (References 3.2.4(b-e)). A single fiber is partially immersed in a liquid and the force exerted on the fiber due to the surface tension of the liquid is measured. The contact angle is determined from the relation￾ship F = CγLV cosθ where F is the force measured corrected for buoyancy, C is the circumference of the fiber, and γLV is the surface tension of the liquid. The results may be used to determine the fiber surface free energy and the contributions of polar and dispersive components to the free en￾ergy (References 3.2.4(c) and (d)). (m) Physisorption and chemisorption measurements - adsorption of inert gas or organic molecules can be used to measure fiber surface area. To obtain accurate estimates of surface area, it is important that there is complete monolayer coverage of the surface, that the area occupied by the adsorbed gas is known and that significant amounts of the gas are not taken up in micropores. Additional complications arise when the adsorption of organic molecules is used in place of gas adsorption, since it may be necessary to know the orientation of the adsorbed molecules to calcu￾late surface area. Adsorption may also occur only at specific active sites and, if solutions are used, solvent molecules may be adsorbed as well. The chemical reactivity of fiber surfaces can be determined by oxygen chemisorption and desorption measurements. Topographical changes (e.g., pores, cracks and fissures) caused by surface treatments often can be readily detected by adsorption measurements. Flow microcalorimetry is a useful technique for directly measuring heats of adsorption (Reference 3.2.4(f)). (n) Thermal desorption measurements - desorption of volatile products from fibers by heat treatment in vacuo. Thermal gravimetric analysis (TGA), gas chromatography (GC), mass spectroscopy (MS), infrared spectroscopy (IRS) analysis or combinations of pyrolysis GC/MS or TGA/IRS may be used to identify components desorbed from fiber surfaces. Below 150°C, CO, NH , CH and various organic molecules are observed depending upon the fiber type