NOVEL APPLICATIONS OF CONFOCAL MICROSCOPY TECHNIQUES IN COATINGS RESEARCH

Transcription

1 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

2 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

3 INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM) Pinhole to eliminate Out-of-focus light Detector Laser Focal Plane 3

4 INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM) Pinhole to eliminate Out-of-focus light Detector Laser Focal Plane 4

5 INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM) Pinhole to eliminate Out-of-focus light Detector Laser Focal Plane 5

6 INTRODUCTION: CONFOCAL RAMAN MICROSCOPY (CRM) Pinhole to eliminate Out-of-focus light Laser Focal Plane Detector 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

7 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 Red: vascular; Green: avascular Ref.: Mayes P, Dicker D, Liu Y, El-Deiry W. Noninvasive vascular imaging in fluorescent tumors using multispectral unmixing. Biotechniques. Oct 2008; 45: ,

8 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 2 nd 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) Latex ID AP1 AP2 Paint ID Paint I-SA Paint I Paint II Case Study Example 1 Example 2&3 Example 3 Stain: Welch s Concord Grape Juice 8

9 EXAMPLE 1: COMPONENT DISTRIBUTION BY RAMAN INTENSITY RATIO Distribution of styrene-containing additive (SA) in acrylic paint Paint I-SA Strong rutile TiO 2 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 9

10 EXAMPLE 1: ANALYSIS OF SA DISTRIBUTION IN ACRYLIC PAINT FILM Paint I-SA 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 A A SA Latex = I I ph C=O SA Concentration(wt%) 10

11 11 EXAMPLE 1: UNIFORM SPATIAL DISTRIBUTION OF STYRENATED ADDITIVE (SA)

12 EXAMPLE 2: SURFACTANT LEACHING 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 12

13 EXAMPLE 2: SURFACTANT LEACHING CONFIRMED BY 2 ND DERIVATIVE ANALYSIS Paint I 0 top surface 2 µm 4 µm 6 µm 8 µm 10 µm 2 nd derivative Red: 0 ~ 4 µm Green: 4 ~ 8 µm Water rinse 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 -(CH 2 ) n - 13

14 EXAMPLE 3: STAIN ADSORPTION, PENETRATION AND STAIN REMOVAL 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 14

15 EXAMPLE 3: PROPERTIES OF CONCORD GRAPE JUICE Physical properties Solids content = 16.2% Sugar content: 15.2% (45 gram/296 ml) Surface tension = 59.5 ± 0.06 mj/m 2 Color compounds Monomeric and polymeric anthocyanins ph = 3.36 Emission of Diluted Grape Juice (in water) 532 nm excitation grape juice stain Red at ph < 3 Violet at ph = 7~8 15

16 EXAMPLE 3: CLSM VISUALIZATION OF STAIN PENETRATION IN LATEX FILMS Acrylic Polymer Y Grape Juice Z Spatial differentiation of grape juice is possible! 16

17 EXAMPLE 3: OPTICAL SECTIONING OF STAINED LATEX FILMS BY CLSM Acrylic Polymer AP2: grape juice via paper towel, 2hr staining Polymer surface 1.0µm 1.5µm 2.0µm 2.5 µm depth Substrate Polymer film (Blue area) Surface (grape juice) Acrylic Polymer AP2: after sponge wash using Formula 409 substrate Polymer film (Blue area) surface 2 µm depth 10 µm depth 17

18 EXAMPLE 3: FLUORESCENCE AND RAMAN SPECTRA OF GRAPE JUICE Grape juice specific Raman transition? Grape juice specific Raman transition undetectable Fluorescence dominates Raman spectrum Can we use fluorescence envelop in Raman Spectra to analyze stain concentration and penetration depth? 18

19 EXAMPLE 3: FLUORESCENCE IN RAMAN SPECTRA OF STAINED PAINT FILMS Fluorescence envelop cm -1 : high frequency curvature Area under fluorescence envelop normalized to C-H stretching area cm -1 Intensity ratio proportional to grape juice conc. Grape juice (pink) Paint I Stained and water rinsed (red) Paint I Un-stained (blue) 19

20 EXAMPLE 3: SEMI-QUANTITATIVE ANALYSIS OF STAIN ADSORPTION & PENETRATION 12 µm Higher surface conc. Greater penetration Paint I E = µm Paint II E = 0.7 Stained and Water Rinsed 20

21 EXAMPLE 3: STAINING AND STAIN PENETRATION INCREASES WITH STAINING TIME Paint I Paint II 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 21

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 µm) 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 22

23 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 2 nd 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

24 Acknowledgment: THANK YOU! Dr. Wenjun Wu (ACR-Cary) Jeffrey Schneider (ACR- Cary) Dana Garcia (Arkema KoP) Prof. Steve Severtson (UMN) Dr. Gang Pu Dr. Jilin Zhang Contact: 24