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

2

INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)

3

Laser

Detector

Focal Plane

Pinhole to eliminate

Out-of-focus light

INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)

4

Laser

Detector

Focal Plane

Pinhole to eliminate

Out-of-focus light

INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM)

5

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)

6

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

7

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

8

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

9

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

10

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)

11

EXAMPLE 2: SURFACTANT LEACHING

12

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

13

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

14

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

15

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

16

Y

Z

Grape JuiceAcrylic Polymer

Spatial differentiation of grape juice is possible!

EXAMPLE 3: OPTICAL SECTIONING OF STAINED LATEX FILMS BY CLSM

17

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?

18

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

19

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)

20

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

21

● 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

22

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

23

THANK YOU!

24

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:

Wenjun.wu@Arkema.com