Materials Characterization W. Marshall Ming Department of Chemistry, Georgia Southern University Statesboro, GA 30460, USA [email protected]; (912)478-5043

Characterization Techniques for Materials Morphology/structure Particle characters

• Microscopy (SEM/TEM/AFM) • Particle size analyzer

MW&MWD (polymer)

• Size exclusion chromatography (SEC) • MALDI-ToF MS

Chemical composition & molecular structure

• NMR • FTIR/Raman • Mass spectrometry

Physical properties Thermal properties Solid-state properties Mechanical properties Surface properties Rheology/viscoelasticity …

• • • • • •

DSC/TGA/DMA WAXD/SAXS Tensile, impact tester… XPS/SIMS, Contact angle goniometer Rheometer …

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Particle Size Analyzer Dynamic light scattering

Malvern Nano ZS

Acrylic polymer latex

Scanning Electron Microscopy (SEM)

Energy-dispersive X-ray spectroscopy (EDX)

• Sample prep often required (sputtering) • High vacuum needed (except ESEM)

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SEM Images of Electrospun PEG Fibers (Group II)

SEM Images of Electrospun PEG Fibers (Group II) Elemental mapping

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Transmission Electron Microscopy (TEM)

• Sample prep required (staining/microtoming) • Very high vacuum needed

Atom Force Microscopy (AFM)

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AFM Image of a Standard Grid (Group II)

• Sample often examined as is, at ambient conditions • Various interactions can be probed

MW & MWD (for Polymer) Size exclusion chromatography (SEC) • Also called Gel Permeation Chromatography (GPC) • Determine MW&MWD in the range of 102-106

Equivalent spheres (excluded volume): • Higher MW, larger sphere • Lower MW, smaller sphere

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SEC (GPC) Molecules of different sizes are eluted through a column of porous particles (typically crosslinked polystyrene, 10-104 nm): Larger molecules are swept through unhindered, while small molecules are retarded in the pores.

MW in the range of 102-106

SEC (GPC) Measurements

Following MW increase

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MW & Chemical Information MALDI-ToF MS (Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry) • A soft ionization technique (the other: Electrospray ionization, ESI) • No polymer fragmentation (good for qualitative MW analysis) • May discriminate against high MW species (not best for MWD analysis) • Can be used to analyze chemical identity

Nobel Prize in Chemistry (2002)

MALDI-ToF MS

• Formation of a 'Solid Solution': o Analyte completely isolated in matrix o Lead to stable desorption of analyte • Matrix Excitation: o Laser beam focusing causes rapid vibrational excitation of matrix o Localized disintegration of ‘solid solution’, followed by ejection of the clusters (analyte, matrix and cations) o Matrix molecules evaporate away from the clusters to leave the free analyte in the gas-phase • Analyte Ionization: o One cation is attached to the analyte (regardless of MW), forming [M+X]+ (X= H, Na, K, etc). o Ions are then extracted into mass spectrometer for analysis.

Typical matrix molecules

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MALDI-ToF MS Sample plate Extraction grids

Attenuator Prism

Reflector Timed ion detector selector

Linear detector Reflector

Laser

Collision cell Camera Pumping

Pumping

MALDI-ToF MS Spectrum

Polystyrene of low PDI m/z (z = 1)

Distance between peaks m/z: 104 Styrene repeating unit

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MALDI-ToF MS Some drawbacks • Ionization efficiency is dependent on MW of polymers: more difficult for higher-MW chains Discrimination against high MW • Not suitable for quantitative analysis (MWD) • Fingerprint analysis limited to MW < 5,000, despite up to 106-MW) polymer can be detected

Chemical Composition of Polymer FTIR

To identify chemical composition

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Chemical Composition of Polymer 1H

and 13C NMR

• Peak broadening for polymers (compared to small molecules) • Chemical shifts are sensitive to chemical environmental changes • 1H-NMR: quantitative analysis • Many other applications…

Thermal Property Characterization Differential Scanning Calorimetry (DSC)

Rate dependent

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Glass Transition of Polymers Glass transition: • Modulus decay of 3 - 4 orders of magnitude over a 20 to 40°C range

Glassy

Tg Rubbery

• Viscosity drops nearly 10 orders

Rubbery flow

Viscous flow (l)

Tg > Troom

Plastic materials

Tg < Troom

Rubbery materials

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