Transcript Diapositiva 1

LA SPETTROSCOPIA VIBRAZIONALE
NELLA CARATTERIZZAZIONE DEI MATERIALI:
PRINCIPI ED APPLICAZIONI
Pellegrino Musto
Istituto di Chimica e Tecnologia dei Polimeri, CNR
Spettroscopia RAMAN - Principi
Elastic Scatter
no change in wavelength of light
laser
1,000,000
photons
1 photon
Inelastic Scatter
lower wavelength light
La radiazione incidente interagisce con i moti rotovibrazionali della molecola. L’analisi
spettrale della luce diffusa, sotto forma di uno spettro Raman, fornisce informazioni
chimiche e strutturali della sostanza in esame
Metanolo - CH3OH
Vibrazione CO at 1035 cm-1
Deformazione CH 2 a 1453 e 1470 cm-1
Stretch simmetrico e antisimmetrico CH3 a 2836 e 2945 cm-1
2836.4
2945.1
OH a 3361cm-1 Hydrogen Bonding Broadens and Lowers Freq.
15000
5000
3361.3
1453.5
1469.5
1035.3
10000
0
500
1000
1500
2000
cm-1
2500
3000
3500
2000
4000
800
1000
1200
1400
1641.5
1439.5
CH2 Wag split by correlation field*
In-phase Twist
1294.2
Asymmetric C-C Stretch
0
1600
>C=C<
CH2 Scissor in Fermi Resonance with 1st
overtone of CH2 Rock (IR); Interaction is
decreased in presence of conformation
disorder (ie., Gauche structures)
1461.6
1415.4
(residual CH3)
CH2 Rock
6000
1369.4 Umbrella
8000
1128.3
C-C Stretch
10000
1062.5 Symmetric
12000
1264.1
1168.3
876.0
Spettro RAMAN PE dettagli
Advantages of Raman spectroscopy
• Raman spectroscopy is:
- Non destructive
- Non invasive
- Fast
• Raman measurements can be carried out :
- On solids, powders, liquids, gas, organics, inorganics, etc.
- Without any preparation
- At ambient Temperature
- At atmospheric Pressure
A Raman spectrometer can be coupled to:
• a confocal microscope:
- high spatial resolution
- depth discrimination
- small quantities
Volume down to ~1µm3
• a fiber-coupled probe:
- for in-situ analysis (e.g. deposition chamber, glove box, reaction cell, etc)
- for industrial process monitoring (e.g. polymerization, etc)
- for Art and Forensic applications
Information accessed by Raman
Qualitative and quantitative information
Direct insight in all parameters that can influence molecular vibrations
Intensity
Band position
Band Position
shift
• Band Position :
- Qualitative studies
- Identification of functional groups
- Chemometric analysis
• Band Intensity:
- Concentration (% level)
- Molecular orientation (polarized)
Band
Width
• Band Shift :
- Stress and strain measurement
Raman shift
• Band width :
- Amorphous/Crystalline phases
Application to polymer science
• Raman spectroscopy has found profound applications in the field of
Polymer Science.
• For industrial analytical purposes, Raman can be used to:
– confirm incoming product for QC
– identify contaminants appearing during Production
– monitor production of product
• Raman is sensitive to functional groups. Example:
– Polymers with a C=O group  band at 1650-1750 cm-1
– Polymers with C-H  band at 2800-3200 cm-1
– Monomer with C=C  band at 1650 cm-1: can be used for monitoring
polymerization reaction
Identification of polymers
Thanks to Raman’s high chemical selectivity, it is possible to study many
different types of polymers.
10000
8000
Nylon6
6000
Kevlar
Pstyrene
4000
PET
Paper
Ppropylene
PE/EVA
PE
2000
0
500
1000
1500
2000
2500
3000
3500
PET:Polyethylene terephthalate
EVA: ethylene-vinyl acetate (copolymer)
Spectral databases
?
- Use existing databases
- Over 1500 spectra of
minerals, polymers, drugs,
pigments, semiconductors, etc
- Build up your own library
- Spectral ID software allows you to search
through database to identify unknown samples
Spectroscopy
Microscopy
Spatial Information
Optical, AFM, etc.
Hyperspectral
Imaging
Chemical Information
IR, Raman,
Fluorescence, etc.
Chemical and Spatial
Information
Chemical Images
Chemical and
spatial
distribution
Concentration or
Abundance
Statistical Sample
Morphology
Statistical Sample
Heterogeneity
Depth profiles on multilayered polymers
polyethylene
Depth (µm)
20
Nylon
40
60
polyethylene
30
40
Length X (µm)
50
60
1000
1100
1200
1300
1400
1500
1600
Wavenumber (cm-1)
Sample of 75µm thickness
Consists of 2 polyethylene layers with a sandwiched Nylon layer
Analyzed without any need for cross section cut !
Effetto della fluorescenza
Virtual
state
Effetto della fluorescenza
Spectrum Polluted by Fluorescence
200
180
Raman signals
intensity (counts)
160
140
120
Fluorescence
background
100
80
60
40
20
500
1000
1500
2000
Raman shift (D cm-1)
2500
3000
Effetto della fluorescenza
35000
30000
Intensity (a.u.)
A careful and adequate
choice
of
the
laser
wavelength
enables
to
counteract the emission of
fluorescence of the coloured
polymer
25000
633 nm
20000
15000
10000
5000
500
1000
1500
2000
2500
3000
Wavenumbe r (cm-1)
25000
70000
20000
Intensity (a.u.)
Intensity (a.u.)
60000
532 nm
50000
40000
15000
785 nm
10000
30000
5000
20000
0
10000
500
1000
1500
2000
Wavenumbe r (cm-1)
2500
3000
500
1000
1500
2000
Wavenumbe r (cm-1)
2500
3000
Effetto della fluorescenza
Spettri Raman di un polimero a con eccitazione a 632 nm (He-Ne) e 785 nm (diodo)
Lecture 3
SECOND PART
The basic types of vibration
Type
Stretching
Bending
In-plane
Torsion
Out-of-plane
-
Schematic
-
+
-
-
+
Symbol
n
d
g
t
minimum number
of atoms
2
3
4
4
minimum number
of bonds
1
2
3
3