Tchinga Ndalama and Deidre Hirschfeld

New Mexico Institute of Mining and Technology, Socorro, New Mexico

Analysis of the Effect of Surface Modification

on Polyimide Composites Coated With Erosion

Resistant Materials

NASA/CR—2003-212190

March 2003

https://ntrs.nasa.gov/search.jsp?R=20030032529 2018-05-15T15:55:27+00:00Z
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Tchinga Ndalama and Deidre Hirschfeld

New Mexico Institute of Mining and Technology, Socorro, New Mexico

Analysis of the Effect of Surface Modification

on Polyimide Composites Coated With Erosion

Resistant Materials

NASA/CR—2003-212190

March 2003

National Aeronautics and

Space Administration

Glenn Research Center

Prepared under Grant NAG3–2688
Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report contains preliminary

findings, subject to revision as

analysis proceeds.

The Propulsion and Power Program at

NASA Glenn Research Center sponsored this work.

Available electronically at http://gltrs.grc.nasa.gov

Trade names or manufacturers’ names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.
NASA/CRó2003-212190 1 

Analysis of the Effect of Surface Modification on Polyimide Composites Coated With 

Erosion Resistant Materials 

Annual Report PS-03-12 

Tchinga Ndalama and Deidre Hirschfeld 

New Mexico Institute of Mining and Technology 

Socorro, New Mexico 87801 

The aim of this research is to enhance performance of composite coatings through 

modification of graphite-reinforced polyimide composite surfaces prior to metal bond coat/ 

hard topcoat application for use in the erosive and/or oxidative environments of advanced 

engines. 

Graphite reinforced polyimide composites, PMR-15 and PMR-II-50, formed by sheet 

molding and pre-pregging will be surface treated, overlaid with a bond coat and then coated 

with WC-Co. The surface treatment will include cleaning, RF plasma or ultraviolet lightozone etching, and deposition of SiOx groups. These surface treatments will be studied in 

order to investigate and improve adhesion and oxidation resistance. 

The following panels were provided by NASA-Glenn Research Center(NASA-GRC): 

• Eight compression molded PMR-II-50; 6×6×0.125 in. 

• Two vacuum-bagged PMR-II-50; 12×12×0.125 in. 

• Eight compression molded PMR-15; 6×6×0.125 in. 

• One vacuum-bagged PMR-15; 12×12×0.125 in. 

All panels were made using a 12×12 in. T650-35 8HS (3K-tow) graphite fabric (Amaco 

Fabrics and Fibers Co., Austell, GA). A diamond-wafering blade, with deionized water as a 

cutting fluid, was used to cut PMR-II-50 and PMR-15 panels into 1×1 in. pieces for surface 

tests. The panel edges exhibiting delamination were used for the preliminary surface 

preparation tests as these would be unsuitable for strength and erosion testing. PMR-15 neat 

resin samples were also provided by NASA GRC. 

Surface profiles of the as-received samples were determined using a Dektak III 

Surface profile measuring system (Veeco Metrology Group, Santa Barbara, CA). Two 

samples of compression molded PMR-II-50 and PMR-15, vacuum-bagged PMR-II-50 and 

PMR-15 were randomly chosen for surface profile measurement according to ANSI/ASME 

B46.1, (American Society of Mechanical Engineers, New York, NY). Prior to each 

measurement, the samples were blasted with compressed air to remove any artifacts. Five 10 

mm-long scans were made on each sample. The short and long wavelength cutoff filter values 

were set at 100 and 1000 μm, diamond stylus radius was 12.5 microns. Table 1 is a summary 

of the arithmetic average roughness (Ra) and waviness (Wa) for the composite surfaces. 

Table 1: Arithmetic Average Roughness and Waviness for Graphite Reinforced 

PMR Composites 

Sample Ra (μm) Wa (μm) 

Compression molded PMR-II-50 0.46 4.70 

Vacuum-bagged PMR-II-50 2.11 6.30 

Compression molded PMR-15 0.31 0.54 

Vacuum-bagged PMR-15 2.22 4.73 
NASA/CRó2003-212190 2 

Contact angles of 0.03ml deionized water on the sample surfaces and FourierTransform Infrared (FTIR) spectra were used to characterize the effect of surface treatments. 

Additional tests were conducted on PMR-15 neat resins to study the effect of Kapton liners on 

steel dies used during molding. Parameters for plasma spraying zinc were also investigated. 

Cleaning and Plasma Etching 

Contamination is an inhibitor to adhesion between materials. Surface integrity must be 

maintained by appropriate handling during processing or by cleaning processes that remove 

contaminants from oxidation, the atmosphere, or processing residues. Cleaning can be as 

simple as washing in water or other solvents, light chemical etching to remove thin layers of 

the bulk material, or can be as complex as dry processes like plasma or laser assisted removal 

of organic contaminants [1,2]. 

Sixteen samples of vacuum-bagged PMR-II-50 were used in an experiment to 

investigate the effectiveness of cleaning method. Contact angles of 0.03 ml deionized water 

on the sample surfaces were used to characterize the effect of cleaning method (Table 2). 

Plasma etching was conducted using a Biorad RF Plasma Barrel Etcher Model PT 7100 

(Biorad, London, UK). Samples were etched in argon plasma for 2 minutes, under a pressure 

of 2 mbar at a radio-frequency power rating of 60 Watts. 

 Results showed that plasma etching had a significant effect on contact angle (Fig. 1). 

Table 2: Surface treatments on PMR-II-50 samples prior to contact angle measurements 

Treatment Samples 

No treatment 2 

Ultrasonic cleaned in methanol for 10 minutes 2 

Ultrasonic cleaned in acetone for 10 minutes 2 

Ultrasonic cleaned in methanol for 5 minutes then in acetone for 5 minutes 2 

Plasma etched 2 

Ultrasonic cleaned in methanol for 10 minutes then plasma etched 2 

Ultrasonic cleaned in acetone for 10 minutes then plasma etched 2 

Ultrasonic cleaned in methanol for 5 minutes then in acetone for 5 minutes 

and then plasma etched 

2 
NASA/CRó2003-212190 3 

Figure 1: Effect of cleaning/etching on contact angle of vacuum-bagged 

PMR-II-50. 

Similarly, sixteen pieces of vacuum-bagged PMR-15 were used to investigate the 

effect of cleaning method on contact angle (Table 3). Among the treatments, RF plasma 

etching had a significant effect on contact angle (Fig. 2). 

Table 3: Surface treatments on vacuum-bagged PMR-15 samples prior to contact angle 

measurements 

Treatment Samples 

As received 2 

Ultrasonic cleaned in methanol for 10 minutes 2 

Ultrasonic cleaned in acetone for 10 minutes 2 

Ultrasonic cleaned in methanol for 5 minutes then in acetone for 5 minutes 2 

Plasma etched for 2 minutes 2 

Ultrasonic cleaned in methanol for 10 minutes then plasma etched 2 

Ultrasonic cleaned in acetone for 10 minutes then plasma etched 2 

Ultrasonic cleaned in methanol for 5 minutes then in acetone for 5 minutes 

and then plasma etched 

2 

Acetone

Acetone +RF plasma

As received

Methanol

Methanol +Acetone

Methanol +Acetone + RFplasma

Methanol +RF plasma

RF plasma

20

30

40

50

60

70

80

90

Contact angle (Degrees)
NASA/CRó2003-212190 4 

Figure 2: Effect of cleaning/etching on contact angle of vacuum-bagged PMR-15. 

 

Ultraviolet light/Ozone (UV/Ozone) Etching 

A dual-purpose UV/Ozone reactor utilizing a low-pressure mercury lamp was 

constructed for UV/Ozone etching and UV induced chemical vapor deposition (Fig. 3). 

Vacuum-bagged PMR-II-50 samples were used in preliminary experiments to determine 

suitable ranges for UV/Ozone etching parameters. Prior to etching, samples were 

ultrasonically cleaned in acetone for 10 minutes, and then heated at 180 °C for 2 hours. The 

effect of distance between the UV lamp and sample surface on contact angle was investigated. 

Samples were UV/Ozone etched for 10 minutes under an oxygen flow rate of 50ml/min. 

Results showed that lower contact angles were achieved with a shorter distance (Fig. 4). 

Figure 3: UV/Ozone Reactor. 

Acetone

Acetone +RF plasma

Asreceived

Methanol

Methanol +Acetone

Methanol +Acetone +RF plasma

Methanol +RF plasma

RF plasma

0

10

20

30

40

50

60

70

Contact angle (degrees)

Heater

Silica 

precursor flask

Mass flow controller

N2

O2

Flow meter

Stainless steel cover

Sample-lamp distance

Heating tape

Sample holder

Flow meter

UV lamp

Exhaust

Bubbler
NASA/CRó2003-212190 5 

Figure 4: Effect of distance between PMR-II-50 sample and UV lamp. 

A 2-level factorial experiment was used to study the effect of exposure time and flow 

rate during UV/Ozone etching. Sample-lamp distance was set at 6 mm. Results showed that 

UV/Ozone etching has a statistically significant effect on the contact angle of PMR-II-50 

composites, and contact angle decreased with increase in oxygen flow rate (Fig. 5). 

Figure 5: Effect of UV/Ozone etching parameters on contact angle of PMR-II-50. 

Based on the results of the preliminary experiments, a three level factorial experiment 

was conducted to determine the effects of etching factors. Sample-lamp distance was set to 

6mm. Results showed that oxygen flow rate of 120 ml/min and exposure time of 24 min, 

produced the smallest contact angle of 50°. 

Further experiments were conducted to explore the effect of extended UV/Ozone 

treatment time on contact angle. In these experiments, oxygen flow rate was set at 

120 ml/min. Results showed that contact angle decreases with increasing exposure time 

(Fig. 6). Additional experiments are being conducted to optimize etching. 

100,10 100,20 50,10 50,20 Ultras. Clean.

75

70

65

60

55

50

45

40

Treatment {Oxygen flow rate (ml/min), Exposure time (min)}

Contact angle {Degrees}

6 16

50

60

70

Height (mm)

Contact angle (Degrees)
NASA/CRó2003-212190 6 

Figure 6: Effect of exposure time on contact angle of UV/Ozone etched PMR-II-50 

composites. 

In preliminary experiments using PMR-15, vacuum-bagged samples were 

ultrasonically cleaned in acetone for 10 minutes and heated at 180 °C for 2 hours. The effect 

of distance between the UV lamp and sample surface on contact angle was investigated. 

Samples were UV/Ozone etched for 10 minutes with an oxygen flow rate of 50ml/min. 

Results showed that low contact angles were achieved with short etching distance (Fig. 7). 

Figure 7: Effect of distance between PMR-15 sample and UV lamp. 

A 2-level factorial experiment was used to study the effect of exposure time and flow 

rate during UV/Ozone etching. Results showed that UV/Ozone etching has a statistically 

significant effect on the contact angle of PMR-15 composites, and contact angle decreased as 

both oxygen flow rate and exposure time increased (Fig. 8). 

6 16

30

35

40

45

Lamp-sample distance (mm) 

Contact angle (Degrees)

0

10

20

30

40

50

60

20 30 40 50 60 70 80 90 100

Exposure time (min)

Contact angle (degrees)
NASA/CRó2003-212190 7 

Figure 8: Effect of UV/Ozone etching parameters on contact angle of PMR-15. 

Based on the results of the preliminary experiments, a three level factorial experiment 

was conducted to explore etching factors. Results showed that oxygen flow rate of 

120 ml/min and exposure time of 24 min, yielded the lowest contact angle (Fig. 9). 

Figure 9: Effect of UV/Ozone etching parameters on contact angle of PMR-15. 

Results on experiments conducted to study the effect of longer UV/Ozone etch time on 

the contact angle of PMR-15 showed that contact angle decreases with increasing exposure 

time (Fig. 10). Results indicated that exposure time of 90 minutes are required to achieve 

contact angles similar to RF plasma etching. 

100,16 100,20 100,24 120,16 120,20 120,24 80,16 80,20 80,24

35

25

15

Treatment {Oxygen flow rate (ml/min), Exposure time (min)}

Contact angle {Degrees}

100,10 100,20 50,10 50,20 No treatment

60

50

40

30

20

10

Treatment {Oxygen flowrate (ml/min), Exposure time (min)}

Contact angle {Degrees}
NASA/CRó2003-212190 8 

Figure 10: Effect of UV/Ozone exposure time on contact angle of PMR-15. Oxygen flow rate 

was 120 ml/min. 

Plasma etching performance of an inductively coupled RF plasma reactor in the 

Chemical Engineering Department, New Mexico Institute of Mining and Technology, NM, 

was compared to that of the Biorad Barrel Etcher. The RF plasma reactor has the advantage 

that it can be used for chemical vapor deposition in addition to etching. It was found that 

samples etched using the RF plasma reactor in the Chemical Engineering Department yielded 

nearly 0° contact angles at 10-minute treatment time on both PMR-15 and PMR-II-50. 

Treatment parameters for the RF plasma reactor were: 10 minutes exposure time, 20 ml/min 

oxygen flow rate and 20ñ50 Watts RF power. On the other hand, samples etched in the Barrel 

Etcher yielded contact angles <30° for PMR-II-50 (Fig. 1) and <10° for PMR-15 at 2 minutes 

of treatment time (Fig. 2). 

An Avatar 360 FTIR system with an Omni Sampler ATR attachment (Thermo Nicolet, 

Madison, WI) was used to obtain the FTIR spectra of selected UV/Ozone and RF plasma 

etched composites. There was good correlation between the FTIR spectra of the as-received 

PMR-II-50 and PMR-15 composites, ultrasonically cleaned PMR-II-50 and PMR-15 

composites, and spectra of PMR-II-50 and PMR-15 resins in published literature [3ñ5]. The 

spectra of the as-received composites were used for comparison with the spectra of the etched 

composites. Both PMR-15 and PMR-II-50 composites that were UV/Ozone etched for 90 

minutes under an oxygen flow rate of 120 ml/min, and those that were RF plasma treated for 

10 minutes under an oxygen flow rate of 20 ml/min, were selected for FTIR analysis. The 

FTIR spectra of as-received PMR-15 and PMR-II-50 composites were compared to those of 

the surface treated composites to study the effect of surface treatment (Figures 11 and 12). 

Increased absorption in the 900 to 1100 cmñ1 and 1150 to 1300 cmñ1 ranges of infrared 

wavelength indicates a general increase in C-O-C moieties on the surface of PMR-II-50 and 

PMR-15 composites, respectively [6]. Additional evaluation using XPS is being conducted at 

the Center of Micro-Engineered Materials, University of New Mexico, Albuquerque, NM, 

and at NASA GRC. 

0

2

4

6

8

10

12

14

16

18

20

20 30 40 50 60 70 80 90 100

Exposure time (min)

Contact angle (degrees)
NASA/CRó2003-212190 9 

Figure 11: FTIR spectra of (a) as-received PMR-II-50 composite, (b) UV/Ozone etched PMRII-50 composite and (c) RF plasma etched PMR-II-50 composite. 

Figure 12: FTIR spectra of (a) as-received PMR-15 composite, (b) UV/Ozone etched PMR-15 

composite and (c) RF plasma etched PMR-15 composite. 

80

85

90

95

100

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumber (cm-1)

a

b

c

75

80

85

90

95

100

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumber (cm-1)

a

b

c
NASA/CRó2003-212190 10 

Chemical Vapor Deposition 

An inductively coupled RF plasma reactor in the Chemical Engineering Department, 

New Mexico Institute of Mining and Technology, was used for plasma-enhanced chemical 

vapor deposition (PE-CVD). Tetraethoxysilane (TEOS) and Tetramethoxysilane (TMOS) 

were used as silica precursors in order to compare their effectiveness for SiOx deposition. It is 

known that factors such as: RF power, substrate temperature, reactant flow rates and reactor 

pressure affect the deposition of SiO2 films [7]. Experiments were conducted to investigate 

the effect of silica precursor temperature and oxygen flow rate on SiOx deposition, because 

these factors could be controlled precisely. Because both TEOS and TMOS lose internal 

energy when subjected to low pressure, a heater was used to warm the silica precursors to 

enhance vaporization. A TMOS temperature of 4 °C was chosen because at this temperature, 

all frozen liquid was molten. Another higher temperature of 20 °C was chosen to study the 

effect of silica source temperature. Temperatures chosen for TEOS were 20 and 40 °C, for the 

same reasons. The flow rate of the silica source vapors was not determined. Oxygen flow rate 

was set at 20 ml/min and at 100 ml/min. 

PMR composite samples were ultrasonically cleaned in acetone for 10 minutes, then 

dried at 180 °C for 2 hours to volatilize the cleaning agent. The composite samples were next 

placed in the reactor and exposed to a 40-millitorr-oxygen atmosphere. An RF plasma was 

then lit for 10 minutes to etch the surfaces prior to the CVD process. A mixture of silica 

precursor vapor and oxygen was then introduced into the chamber for SiOx deposition. At the 

end of each deposition run (45 minutes), the vapor and oxygen supply to the chamber was 

shut off, and plasma power was switched off. FTIR spectra and contact angles of the films 

were obtained. 

A dual-purpose UV/Ozone reactor (Fig. 3) was used for ultraviolet light induced 

chemical vapor deposition (UV-CVD). Prior to chemical vapor deposition, the PMR 

composites were ultrasonically cleaned and dried, as in the previous PE-CVD experiments, 

then UV/Ozone etched for 24 minutes with an oxygen flow of 120ml/min. During deposition, 

a mixture of oxygen and silica precursor vapor was bled into the reactor for 45 minutes. 

Distance between lamp and sample was 6mm. Silica precursor temperature was set at 70 °C 

because oxygen gets saturated with TEOS vapor at this temperature and standard atmospheric 

pressure [8]. The same temperature was also used for TMOS. In the UV-CVD experiments, 

oxygen flow rate and substrate-temperature were varied to investigate their effects on SiOx

deposition. FTIR spectra and contact angles of the films were obtained. 

To evaluate the films deposited on PMR-II-50, FTIR and contact angle data of the 

films were compared with that of the as-received PMR-II-50 composite. For FTIR spectra, the 

amplitude of the peak due to Si-O-Si asymmetric stretching at 1030 to 1090 cmñ1

 was 

compared to (a) the absorption peaks of the substrate, at 1724, 1516, 1368 and 723cmñ1

(Fig. 13); and (b) the peaks due to impurities such as Si-OH deformation at 890 to 950cmñ1

and due to Si-C rocking at 750 to 840 cmñ1. 
NASA/CRó2003-212190 11 

Figure 13: FTIR spectrum of as-received PMR-II-50 composite. 

A clearly distinguishable Si-O-Si peak at 1030 to 1090 cmñ1, with minute peaks due to 

substrate and impurities indicated good film quality and coverage, as shown in Figures 14 and 

15. On the other hand, a Si-O-Si peak, with strong peaks due to the substrate and impurities in 

the spectrum, indicated poor film quality and coverage, as shown in Figures 16 and 17. This 

was confirmed by contact angle data, as shown in Fig. 18, where PE-CVD yielded films with 

lower contact angles than UV-CVD. 

Figure 14: FTIR spectrum of SiOx film on PMR-II-50 by PE-CVD using TMOS. 

85

90

95

100

2000 1800 1600 1400 1200 1000 800

Transmittance (Arbitrary units)

Wavenumbers (cm-1)

TMOS temp: 20o

C

O2

 flowrate: 20 ml/min

93

94

95

96

97

98

99

100

2000 1800 1600 1400 1200 1000 800

Transmittance (Arbitrary units)

Wavenumbers (cm-1)
NASA/CRó2003-212190 12 

Figure 15: FTIR spectrum of SiOx film on PMR-II-50 by PE-CVD using TEOS. 

Figure 16: FTIR spectrum of SiOx film on PMR-II-50 by UV-CVD using TMOS. 

Figure 17: FTIR spectrum of SiOx film on PMR-II-50 by UV-CVD using TEOS. 

94

95

96

97

98

99

100

101

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

Substrate temp: 90o

C

O2

 flowrate: 400 ml/min

92

93

94

95

96

97

98

99

100

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

Substrate temp: 90o

C

O2

 flowrate: 200 ml/min

92

93

94

95

96

97

98

99

100

2000 1800 1600 1400 1200 1000 800

Transmittance (Arbitrary units)

Wavenumbers (cm-1)

TEOS temp: 40o

C

O2

 flowrate: 100 ml/min
NASA/CRó2003-212190 13 

Figure 18: Effect of CVD treatment on contact angle of SiOx films on PMR-II-50. Treatment 

conditions are the same as specified in FTIR diagrams. 

The same strategy used to evaluate SiOx films deposited on PMR-II-50 was applied to 

PMR-15. FTIR spectra of as-received PMR-15 (Fig. 19) was compared to that of the 

deposited films (Figs. 20ñ23). Generally, SiOx films deposited by PE-CVD were of better 

quality(Figs. 20, 21) than films deposited by UV-CVD (Figs. 22, 23). Contact angle 

measurements confirmed this observation (Fig. 24). 

Figure 19: FTIR spectrum of as-received PMR-15 composite. 

90

92

94

96

98

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

As-received PE-CVD,

TEOS

PE-CVD,

TMOS

UV-CVD,

TEOS

UV-CVD,

TMOS

0

50

100

Treatment

Contact angle (degrees)
NASA/CRó2003-212190 14 

Figure 20: FTIR spectrum of SiOx film on PMR-15 by PE-CVD using TMOS. 

Figure 21: FTIR spectrum of SiOx film on PMR-15 by PE-CVD using TEOS. 

Figure 22: FTIR spectrum of SiOx film on PMR-15 by UV-CVD using TEOS. 

97

98

99

100

101

102

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

Substrate temp: 120o

C

O2

 flowrate: 200 ml/min

97.5

98

98.5

99

99.5

100

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

TEOS temp: 400

C

O2

 flowrate: 20 ml/min

94

95

96

97

98

99

100

101

102

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

TMOS temp: 4o

C

O2

 flowrate: 100 ml/min
NASA/CRó2003-212190 15 

Figure 23: FTIR spectrum of SiOx film on PMR-15 by UV-CVD using TMOS. 

Figure 24: Effect of CVD treatment on contact angle of SiOx films on PMR-15. Treatment 

conditions are the same as specified in FTIR diagrams. 

Contact angle data showed that TMOS yielded better films than TEOS on both 

PMR-15 and PMR-II-50, because CVD treatments with the former yielded lower contact 

angles than the latter. It is known that hydrocarbons have a low surface energy [6]. It is 

proposed that the presence of ñ OC2H5 groups in the films deposited by UV-CVD contributes 

to a low surface energy, resulting in large contact angles. This may be due to incomplete 

decomposition and hydrolysis of the silica precursors and the polysiloxane layers, 

respectively. Average thickness of PE-CVD deposited SiOx film was 1.4 μm, according to 

profilometry results. XPS analysis of the treated samples is currently underway at NASAGlenn Research Center and will elucidate the effect of deposition parameters used. 

95

96

97

98

99

100

2000 1800 1600 1400 1200 1000 800

Transmittance (arbitrary units)

Wavenumbers (cm-1)

Substrate temp: 120o

C

O2

 flowrate: 400 ml/min

As-received PE-CVD,

TEOS

PE-CVD,

TMOS

UV-CVD,

TEOS

UV-CVD,

TMOS

0

10

20

30

40

50

60

70

80

90

100

Treatment

Contact angle (degrees)
NASA/CRó2003-212190 16 

Effect of Kapton Liners on Molding PMR-15 Neat Resins 

Contact angle measurements and FTIR spectra were obtained for PMR-15 neat resins 

that were compression molded using steel dies with or without Kapton liners. Samples were 

not treated in any manner before testing. Contact angles and FTIR spectra of the two materials 

were different (Figs. 25ñ27). It is likely that some Kapton adheres to the polymer surface. 

Figure 25: Sessile drop of DI water on 

PMR-15 pressed with Kapton Liner. 

Contact angle: 94°. 

Figure 26: Sessile drop of DI water on 

PMR-15 (No Kapton). Contact angle: 83°.

In summary, the major differences in FTIR spectra are: 

• 1502 cmñ1 peak more intense on Kapton than the 1513 cmñ1 peak without: Benzene rings. 

• 1247 cmñ1 peak sharp on Kapton: C-O-C 

• 1114 cmñ1 peak sharp and intense on Kapton: C-O-C 

• 819 cmñ1 peak very intense on Kapton 

Figure 27: FTIR spectra of as-received compression molded PMR-15 resin samples. Solid 

Line is with Kapton Mold Liner and Dashed without. 

675 875 1075 1275 1475 1675 1875

Wavenumber (cm-1)

Transmittance 

Steel 

Kapton
NASA/CRó2003-212190 17 

Plasma Sprayed Coatings 

Experiments were conducted to investigate plasma spray parameters for zinc coatings. 

Aluminum substrates were used for the preliminary experiments. Cross sections of zinc 

coatings were examined using light microscopy for porosity and thickness. Photomicrographs 

of the cross sections were used to calculate porosity using SCION IMAGE software (Scion 

Corp., Frederick, MD). Average porosity of 1.4 percent was achieved for zinc on aluminum 

(Fig. 28). Because the polyimide composite substrates have different thermal properties than 

aluminum, it was expected that spray parameters would be different. Preliminary plasma 

spray experiments conducted using composite substrates yielded zinc coatings that were less 

than 2 percent porous (Figs. 29,30). Table 4 is a summary of the parameters used to plasma 

spray the coatings presented. Plasma spraying is being further optimized to achieve denser 

coatings. 

A preliminary investigation on the use of indentation hardness testing to optimize 

bond strength in terms of etching, deposition, and minor modification of plasma spray 

parameters has been conducted. Hardness indents using a Brinnel indenter were made on zinc 

coated PMR and debonded regions were measured using the profilometer. The 

standardization of the indentation technique is underway and should provide a screening 

method to characterize adhesion using a minimum sample size. After optimizing the 

indentation hardness adhesion, fracture toughness and conventional bond strength 

measurements will be used to confirm the results. 

Figure 28: Zinc coating on aluminum exhibiting average porosity of 1.4 percent. 

Figure 29: Zinc coating on PMR-15 composites exhibiting average porosity of 1.6 percent 
NASA/CRó2003-212190 18 

Figure 30: Zinc coating on PMR-II-50 composites exhibiting average porosity of 1.6 percent. 

Table 4: Plasma spray parameters for zinc coatings 

 Zinc on 

aluminum 

Zinc on PMR composites

Parameters 1.4% porous 1.6% porous 

Arc Amperage (A) 600 600 

Arc gas(psi) 100 100 

Auxiliary gas(psi) 45 55 

Powder gas(psi) 40 40 

Powder feeder rev (rpm) 2 2 

Gun velocity (mm/s) 523 523 

Powder nozzle stand off (mm) 13 13 

Substrate stand off (mm) 80 80 

Gun passes 80 80 

Accomplishments 

The following tasks and milestones have been achieved in the course of the project: 

• literature review of surface modification was conducted and continues to be monitored 

• an Omni Sampler ATR accessory for a Nicolet Avatar 360 FTIR (Thermal Nicolet, 

Madison, WI) were purchased 

• modification of PMR composite surfaces by RF plasma and UV/Ozone etching was 

investigated and optimized using contact angle and FTIR analyses 

• modification of PMR composite surface by RF plasma and UV induced chemical vapor 

deposition of silica films was explored using contact angle and FTIR analyses 

• the effect of Kapton liners, used during the processing of PMR-15, on surface chemistry 

was determined by contact angle and FTIR analyses 

• a Dektak III profilometer (Veeco Metrology Group, Santa Barbara, CA) and isolation 

table were purchased 
NASA/CRó2003-212190 19 

Future Work 

XPS analyses of the SiOx films is underway at NASA-GRC, which will elucidate the 

chemical composition of SiOx films effect of deposition parameters. Further XPS analyses 

will be conducted at the Center for Micro-Engineered Materials, University of New Mexico, 

Albuquerque, NM, to characterize chemical changes on the surfaces of plasma and UV/Ozone 

etched composites. 

Preliminary zinc bond coats on polyimide composites have been applied by 

atmospheric plasma spraying, using the standard sample preparation procedure followed at 

NASA-GRC and will provide a control for comparisons. Zinc and other metallic bond coats 

will be applied to surface modified PMR composites. The effect of surface modification on 

adhesion will be characterized by indentation testing, fracture toughness and bond strength. 

The last phase of the research will involve applying the WC-Co topcoat and performance 

testing (thermal cycling, oxidation and erosion testing) to optimize surface modification. 

References 

1. Matienzo L.J., Egitto F.D., ìAdhesion issues in electronic packaging,î Solid State 

Technology. (July 1995), 99ñ106. 

2. Ganesan G.S., Lewis G., Berg H.M., ìCharacterizing organic contamination in IC package 

assembly,î The International Journal of Microcircuits and Electronic Packaging. 17(2),

152ñ160, (1994). 

3. Allred R.E., Harrah L.A., Donnellan T.A., Williams T., Meilunas R., ìFiber finishes for 

improving interfacial thermo-oxidative stability in PMR-II-50 matrix composites,î Final 

Report for NASA Lewis Research Center, Cleveland, OH 44135. October 1993 to 

September 1996. 

4. Kim D.S., Lee J.R., ìCharacterization and properties of carbon/PMR-15 composites,î 

Polymers for Advanced Technologies. 6, 711ñ716, (1995). 

5. Conreur C., Francillette J., Laupretre F., ìSynthesis and processing of model compound of 

PMR-15 resin,î Journal of Polymer Science: Part A: Polymer Chemistry. 35, 123ñ136, 

(1997). 

6. Smith B., ìInfrared Spectral Interpretation: A Systematic Approach,î CRC Press LLC: 

Boca Raton (1999). 

7. Ceiler M.F. Jr, Kohl P.A., Bidstrup S.A., ìPlasma-enhanced chemical vapor deposition of 

silicon dioxide deposited at low temperatures,î Journal of the Electrochemical Society.

142(#6), 2067ñ2071, (1995). 

8. Klumpp A., Sigmund H., ìDeposition of high quality SiO2 layers from TEOS by excimer 

laser,î Applied Surface Science. 36, 141ñ149, (1989). 
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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NAG3–2688

25

Analysis of the Effect of Surface Modification on Polyimide Composites Coated

With Erosion Resistant Materials

Tchinga Ndalama and Deidre Hirschfeld

Composites; Polymers; Coatings

Unclassified -Unlimited

Subject Categories: 24 and 27 Distribution: Nonstandard

New Mexico Institute of Mining and Technology

801 Leroy Place

Socorro, New Mexico 87801

Project Manager, James K. Sutter, Materials Division, NASA Glenn Research Center, organization code 5150,

216–433–3226.

The implementation of polymer composites in the erosive/oxidative environment of advanced engines requires the use

of hard protective coatings. It has been proposed to utilize surface modification techniques to improve the adhesion of

the coating system. Experiments on graphite fiber reinforced polyimide composites, PMR-15 and PMR-II-50, overlaid

with a bond coat and then coated with WC-Co to optimize surface treatment, bond strength, erosion resistance, and

thermal stability are underway. Effectiveness of cleaning techniques and SiOx deposition using both RF plasma and

UV-ozone methods were determined using contact angle measurements and Fourier Transfer Infrared spectroscopy

(FTIR). Two sources of silica, tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS) were used as precursors.

Results indicate that RF Plasma etching is the most effective cleaning method for both composites and that TMOS

coatings yield the lowest contact angles.