NOVEL APPLICATIONS OF CONFOCAL MICROSCOPY … · Confocal Raman Microscopy (CRM) Confocal Laser...
Transcript of NOVEL APPLICATIONS OF CONFOCAL MICROSCOPY … · Confocal Raman Microscopy (CRM) Confocal Laser...
ARKEMA COATING RESINS
NOVEL APPLICATIONS OF
CONFOCAL MICROSCOPY
TECHNIQUES IN COATINGS
RESEARCH
DOUG MALL
FOR DR. WENJUN WU
9/20/2018
Wood Coatings & Substrates Conference 2018
OUTLINE
Introduction
● Confocal Raman Microscopy (CRM)
● Confocal Laser Scanning Microscopy (CLSM)
Coatings problems investigated:
● Example 1: Component distribution in paint films
● Example 2: Surfactant leaching on paint surface
● Example 3: Stain adsorption, penetration and stain removal
Summary
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INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)
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Laser
Detector
Focal Plane
Pinhole to eliminate
Out-of-focus light
INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)
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Laser
Detector
Focal Plane
Pinhole to eliminate
Out-of-focus light
INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)
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Laser
Detector
Focal Plane
Pinhole to eliminate
Out-of-focus light
INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)
Advantages: combines a high resolution confocal microscope with sensitive Raman spectroscopy
● Depth profiling: tracking of individual species vs. depth
● Quantification: Raman intensity scales linearly with concentration
• Quantification by band area or intensity ratio
● Spatial distribution: lateral mapping and depth profiling
• Material stratification, segregation or migration can be identified and dealt with
Limitations: limited to clear/transparent samples
● Raman intensity is weak
• Difficulties: sample fluorescence, baseline shifts and/or overlapping peaks
● 3D data acquisition by lateral scanning and depth profiling is time consuming
• Limited application in non-transparent samples (pigmented coatings)
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Laser
Detector
Focal Plane
Pinhole to eliminate
Out-of-focus light
INTRODUCTION: CONFOCAL LASER SCANNING MICROSCOPY (CLSM)
High sensitivity and chemical specificity
● Compared to CRM, perform real-time 3D imaging using reflection or fluorescence
contrast with greatly improved speed and spatial resolution
Non-invasive spatial-spectral analysis
● Multispectral fluorescence imaging using spectral signatures of either intrinsically
fluorescent molecules or fluorescent markers
• Successful applications in (pre)clinical studies
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Ref.: Mayes P, Dicker D, Liu Y, El-Deiry W. “Noninvasive vascular imaging in
fluorescent tumors using multispectral unmixing”. Biotechniques. Oct 2008;
45:459–460, 461–464.
Red: vascular; Green: avascular
EXAMPLES: ANALYZE COATING SYSTEMS USING CRM AND CLSM
Coating problems investigated and CRM data analysis techniques● Example 1: Component distribution
• Intensity ratio analysis for quantification of a styrenated additive (SA) in acrylic paint
● Example 2: Surfactant leaching
• 2nd derivative analysis to enhance subtle spectral features
● Example 3: Stain penetration and stain removal
• CLSM: utilize fluorescence of grape juice for visualization/quantification of stain penetration into latex film
• CRM: utilize fluorescence of grape juice in semi-quantitative characterization of pigmented coatings
Acrylic Latexes, Styrenated Additive (SA) and Paint Samples● Paint formulation: 35% volume solids (VS), 31% pigment volume concentration (PVC)
Stain: Welch’s Concord Grape Juice
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Latex ID AP1 AP2
Paint ID Paint I-SA Paint I Paint II
Case Study Example 1 Example 2 & 3 Example 3
EXAMPLE 1: COMPONENT DISTRIBUTION BY RAMAN INTENSITY RATIO
Distribution of styrene-containing additive (SA) in acrylic paint
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Strong rutile TiO2
stretching and
bending transitions
in 650 to 100 cm-1
All intensities decrease progressively
due to depth attenuation as CRM
probes deeper into non-transparent
coating film
Paint I-SA
EXAMPLE 1: ANALYSIS OF SA DISTRIBUTION IN ACRYLIC PAINT FILM
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3060 cm-1: aromatic C-H stretching
1598 cm-1: aromatic ring motion
989 cm-1: aromatic bending and ring
breathing
1727 cm-1: carbonyl C=O stretching
SA Concentration(wt%)SA
Latex
A
A⇒
ph
C=O
I
I=
Paint I-SA
EXAMPLE 1: UNIFORM SPATIAL DISTRIBUTION OF STYRENATED ADDITIVE (SA)
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EXAMPLE 2: SURFACTANT LEACHING
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Surfactant migration and surface enrichment has been reported for many anionic and nonionic surfactants in latex films
● Surfactant migration in latex films have been detected by AFM, XPS, CRM, and
contact angle measurements
Unsightly streaking defect caused by leaching of water soluble species is a common field complaint of exterior paints
● Analyzing leachate from pigmented paint systems
EXAMPLE 2: SURFACTANT LEACHING CONFIRMED BY 2ND DERIVATIVE ANALYSIS
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0.72 phm C14-C16 alpha-olefin sulfonate used in emulsion polymerization of acrylic polymer
Raman transitions 2920 ~ 2925 cm-1 correspond to the C-H stretching of -(CH2)n-
Water rinse
0 – top surface
2 µm
4 µm
6 µm
8 µm
10 µm
Red: 0 ~ 4 µm
Green: 4 ~ 8 µm
2nd derivative
Paint I
EXAMPLE 3: STAIN ADSORPTION, PENETRATION AND STAIN REMOVAL
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Stain resistance and stain removal are desirable properties of interior wall paints
● Stain Resistance
• Stain resistance - ability to withstand discoloration caused by contact with liquids, oils and grease,
and solid particulates
● Washability or Stain Removal
• Washability - relative ease and completeness of removal of a specific soilant from a coating
surface by scrubbing using a sponge and a non-abrasive cleanser
Cleaner stain removal
Better washability
Higher stain resistance
Paint I Paint II
EXAMPLE 3: PROPERTIES OF CONCORD GRAPE JUICE
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Physical properties
● Solids content = 16.2%
• Sugar content: 15.2% (45 gram/296 mL)
● Surface tension = 59.5 ± 0.06 mJ/m2
● Color compounds
• Monomeric and polymeric anthocyanins
● pH = 3.36
Emission of Diluted Grape Juice (in water)
grape juice stain
Red at pH < 3 Violet at pH = 7~8
532 nm excitation
EXAMPLE 3: CLSM VISUALIZATION OF STAIN PENETRATION IN LATEX FILMS
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Y
Z
Grape JuiceAcrylic Polymer
Spatial differentiation of grape juice is possible!
EXAMPLE 3: OPTICAL SECTIONING OF STAINED LATEX FILMS BY CLSM
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surface 1.0 µm 2.0 µm 2.5 µm depth
Polymer
Acrylic Polymer AP2: grape juice via paper towel, 2hr staining
Surface
(grape juice)
Polymer film
(Blue area)
Substrate
surface 2 µm depth 10 µm depth
Acrylic Polymer AP2: after sponge wash using Formula 409
Polymer film
(Blue area)
substrate
1.5 µm
EXAMPLE 3: FLUORESCENCE AND RAMAN SPECTRA OF GRAPE JUICE
Can we use fluorescence envelop in Raman Spectra to analyze stain concentration and penetration depth?
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Grape juice specific Raman transition? ● Grape juice specific Raman transition undetectable
● Fluorescence dominates Raman spectrum
EXAMPLE 3: FLUORESCENCE IN RAMAN SPECTRA OF STAINED PAINT FILMS
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Fluorescence envelop 4146 – 3071 cm-1: “high frequency curvature”
● Area under fluorescence envelop normalized to C-H stretching area 3075 – 2798 cm-1
● Intensity ratio proportional to grape juice conc.
Grape juice (pink)Paint I Stained and water rinsed (red)Paint I Un-stained (blue)
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Stained and Water Rinsed
Paint I
∆∆∆∆E = 5.7
Paint II
∆∆∆∆E = 0.7
12 µm
6 µm
EXAMPLE 3: SEMI-QUANTITATIVE ANALYSIS OF STAIN ADSORPTION & PENETRATION
Higher surface conc.
Greater penetration
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● Paint I vs. Paint II
• Paint I: more juice residue (adhesion/adsorption)
• Paint I: deeper penetration with longer staining time
• Paint II: lower surface concentration
• Paint II: slight increase of surface conc. of grape juice but no significant change of penetration depth
Paint I Paint II
EXAMPLE 3: STAINING AND STAIN PENETRATION INCREASES WITH STAINING TIME
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EXAMPLE 3: MECHANICAL SCRUBBING REMOVES MORE STAIN THAN WATER RINSE
Sponge washing more effectively removed
the grape juice stain than just a water rinse
The minimum (10~12 µµµµm) in intensity ratios
was unchanged by sponge washing
● Once penetration occurred, staining depth unchanged by mechanical sponge scrubbing
● Film erosion not a mechanism for stain removal
Water Rinsed
Water Rinsed
Sponge Washed
SUMMARY
CRM and CLSM offer chemical specificity and high resolution spatial analysis
● Powerful tools for determining chemical composition and component distribution
● Examples demonstrate usefulness and advantage of these confocal scanning techniques
● Sophisticated analyses using confocal techniques are in harmony with results from industrial standard test methods and provide greater insight into practical coatings problems
Coatings problems investigated and data analysis techniques
● Example 1: Component distribution
• Uniform spatial distribution of styrenated additive in acrylic paint, quantified by Raman intensity ratio
● Example 2: Surfactant leaching
• Surface enrichment of polymerization surfactant on paint film, confirmed by 2nd derivative analysis
● Example 3: Stain penetration and stain removal
• Direct visualization of stain penetration in latex films by CLSM
• Semi-quantitative analysis of stain adsorption, penetration and removal using fluorescence envelop in Raman spectra
Continued method development is needed in order to expand applications of confocal scanning techniques in coatings research
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THANK YOU!
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Acknowledgment:
Dr. Wenjun Wu (ACR-Cary)
Jeffrey Schneider (ACR- Cary)
Dana Garcia (Arkema – KoP)
Prof. Steve Severtson (UMN)
Dr. Gang Pu
Dr. Jilin Zhang
Contact: