Optical microscopy Theoretical background Galina Kubyshkina

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1 Optical microscopy Theoretical background Galina Kubyshkina Elektromaterial Lendava d.d., Slovenia

2 Crystalline materials presence of a unit (cell), which is periodically repeated in space regular structure (lattice) have short and long range ordering anisotropy of properties have certain melting and crystallization temperature Typical features Figure 1. Examples of different crystal lattices 2

3 Amorphous materials Typical features do not have lattice irregular structure have short range ordering only isotropy of properties do not have certain melting (crystallization) temperature exhibit glass transition Figure 2. Polymorphism: crystalline and amorphous structure of SiO2 3

4 Polymers Molecular mass (weight) ATOMIC NUMBER SYMBOL Figure 3. D.I. Mendeleyev periodic table of the chemical elements 5 10,811 B BORON ELEMENT NAME RELATIVE ATOMIC MASS While non-polymeric substances have an exact molecular mass, for polymers they are ranging from about 25000g/mol to g/mol or even higher. 4

5 Polymers Molecular mass (weight) distribution and average molecular weight Relative Number of Chains Figure 4. Molecular mass distributions of the same polymer from two different sources Relative Number of Chains Bimodal PA6 Monomodal PA log (Molecular mass) Figure 5. Molecular mass distributions of mono- and bimodal PA6 Polymer is characterized by: molecular mass (weight) distribution average molecular weight average molecular weight: M n N M = i N weight-average molecular weight: M w i i i N M = i N 2 i 5

6 Polymers Molecules and supramolecular structures linear molecule branched molecule cross-linked molecules packages lamellas globule, tangle spherulite shish-kebab structure Figure 6. Examples of polymeric molecules and supramolecular structures 6

7 Polymers Structure of semicrystalline polymer crystal region amorphous material amorphous region crystalline material Figure 7. Semicrystalline polymer structure semicrystalline material 7

8 Morphology investigation methods Microscopy * Morphology means the object s structure and also shape, size, position relationship of it s elements either on the surface or inside IR-microscopy Optical microscopy UV-microscopy X-rays microscopy Electron microscopy others Wavelength decrease 8

Optical microscope Basic definitions Optical microscope an optical device that produces a magnified image of objects (or their elements) too small to be seen with the naked eye.

9 Optical microscope Basic definitions Optical microscope an optical device that produces a magnified image of objects (or their elements) too small to be seen with the naked eye. Microscope magnification: Γ = Γobj Γoc = x* Γobj = 6,3 100x* objective magnification Γoc = 7 15x* ocular magnification Figure 8. Optical microscope component parts * - typical range of magnifications 9

10 Optical microscope Microscope optical scheme Figure 9. Microscope optical scheme 10

11 Optical microscope Markings on objectives Contrast method Designation of objective Magnification / aperture + special properties Tube length / cover slip thickness Magnification color code Immersion liquid Figure 10. Standard markings on microscope objectives 11

$Summary illumination distribution (diffraction pattern of two points) others 12 resolution increase IR-microscopy wavelength decrease Resolution of an optical microscope is limited due to the wave$

12 Optical microscope Resolution Optical microscopy UV-microscopy X-rays microscopy Electron microscopy Figure 11. Summary illumination distribution (diffraction pattern of two points) others 12 resolution increase IR-microscopy wavelength decrease Resolution of an optical microscope is limited due to the wave properties of light (diffraction) and theoretically amount around 0.2 mkm E illumination ro the distance between two points

13 Optical microscope Light pass transmitted light reflected light Figure 12. Light pass scheme 13

Optical microscope Transmitted and reflected light

14 Optical microscope Transmitted and reflected light Transmitted-light microscopy is used for transparent objects investigation. Reflected-light microscopy is used for opaque objects investigation. Figure 13. Transparent film. Brightfield transmitted- (left) and brightfield reflected-light (right) Figure 14. Opaque fiber. Brightfield transmitted- (left) and brightfield reflected-light (right) 14

$Optical microscopy Contrast methods The object structure can be investigated only if its elements reflect or absorb the light in different ways or differ from each other by refractive index.$

15 Optical microscopy Contrast methods The object structure can be investigated only if its elements reflect or absorb the light in different ways or differ from each other by refractive index. That is why the used contrast method should be chosen according to the properties of the object. Polymers are examined by both transmitted- and reflected-light microscopy. All contrast methods common today are employed. 15

16 analogy: Contrast methods Brightfield Transmitted light transparent object with inclusions analogy: Reflected light Used for investigation of transparent objects with absorbing inclusions (for example, tissues). opaque object Used for investigation of opaque objects which reflect the light well (for example, metals) Hoffman contrast 16

Contrast methods Darkfield analogy: Used for investigation of

of brightfield method, but diffuse the light well.

17 Contrast methods Darkfield analogy: Used for investigation of objects with nonabsorbent inclusions that are invisible by means of brightfield method, but diffuse the light well. diffused light objective field of vision cone of illumination darkfield condenser Figure 15. Mixed plastic with aluminium inclusion and shrink holes. Brightfield reflected- (left) and darkfield reflected-light (right) 17

$invisible by means of brightfield because they differ from the surroundings only in refractive index.$

18 Contrast methods Phase contrast transparent object Figure 16. Phase contrast method principle scheme idea: Used for investigation of transparent and colorless elements that are invisible by means of brightfield because they differ from the surroundings only in refractive index. Thus light intensity does not change and only phase shifts take place. phase shifts invisible amplitude changing visible Figure 17. Mix of Polypropylene and HDPE. Phase contrast 18

transparent object ray condenser objective birefringent lens jack Figure 18.

19 Contrast methods Differential interference contrast (DIC) Used for investigation of transparent and colorless elements that are invisible by means of brightfield. transparent object ray condenser objective birefringent lens jack Figure 18. DIC contrast method principle scheme Figure 19. Carbon fiber-reinforced plastic. Reflected light DIC idea: path-length difference invisible brightness visible 19 Figure 20. Biostructure. Transmitted light DIC

20 Contrast methods Fluorescence Figure 21. Crack in polymer Used for structure investigation of objects that exhibit natural fluorescence and non- fluorescent objects put in a fluorescent dye. If under certain conditions polymer exhibits fluorescence, this can be utilized to make crystalline structure visible. 20

Contrast methods Polarization Used for investigation of anisotropic objects Pure polymers hardly absorb any light so brightfield transmitted

Partially crystalline polymers are optically anisotropic.

21 Contrast methods Polarization Used for investigation of anisotropic objects Pure polymers hardly absorb any light so brightfield transmitted light method is not very useful for them. From the other hand, polymers develop partially crystalline or amorphic structures. Partially crystalline polymers are optically anisotropic. For this reason polarization is the most common contrast method for the examination of polymers. Figure 22. PA6 fiber. Brightfield transmitted-light (left) and polarized transmitted-light (right) Figure 23. PA6. Polarized transmitted-light 21

propagation direction wave propagation direction direction of particles oscillation

22 Polarization Waves: mechanical analogy transverse wave longitudinal wave Mechanical examples: λ λ wave propagation direction direction of particles oscillation propagation direction wave propagation direction direction of particles oscillation Important difference: transverse waves are capable of polarization while longitudinal are not 22

23 Polarization Light wave Figure 24. Scheme of the light wave 23

24 Polarization Polarization of light waves and its mechanical analogy Figure 25. Polarization of light waves, its mechanical analogy and scheme of polarized light microscope 24

25 Specimen preparation Microtome HM 355 S 30º specimen Figure 26. Microtome HM 355 S Key parameters: knife Velocity of cutting Knife position 16º 25

26 Specimen preparation The procedure immersion oil pincers 5 6 glass needle weight cover glass needle 26 26

27 Specimen preparation Possible problems furrows folds injuries incomplete slice ragged edges bubbles 27

28 Specimen preparation Magnifications and problems with focusing 2.5x10 20x10 5x10 10x10 50x10 100x10 28

29 Optical microscopy Another possibilities The following metrological data can be received: linear sizes angular sizes areas of different elements particles (elements) size distribution Also may be performed: using different filters to transform the picture combination with thermal analysis 29

30 Optical microscope system Architecture AxioCam HRc digital camera Axiokcop 2 MAT microscope LTS350 heating/freezing stage TMS 94 control system Figure 27. Equipment position (left) and the system principal architecture 30

31 Optical microscope Axioscop 2 MAT Digital Camera AxioCam HRc(color) 1 st step adapter 2 nd step objective Real image is invisible for the eye, but visible for the camera. Figure 28. Camera fixation scheme ocular Virtual image is visible for the eye, but invisible for the camera. 31

32 Optical microscope Axioscop 2 MAT silver block sensor Figure 30. A temperature profile programmed with TMS 94 control system Figure 29. LTS340 heating/freezing stage: general look (up) and a view from within (down) 32 TMS 94 control system and LTS350 heating/freezing stage

33 Optical microscope Axioscop 2 MAT TMS 94 control system and LTS350 heating/freezing stage An example of cooling rate influence on structure formation slow cooling fast cooling 33

34 Optical microscopy use in quality control Key for success? Why is the certain product competitive on the market name technology design quality 34

35 Optical microscopy use in quality control Quality assurance appropriate choice of raw materials technological conditions quality control prediction 35

36 Optical microscopy use in quality control Quality control Quality control embraces: materials the monitoring of incoming materials input the control of the manufacturing processes technological process check of products produced output product 36

37 Optical microscopy use in quality control Raw materials raw materials polymer itself reduce the price modifiers, additives, fillers processing aids provide certain properties prepared raw materials 37

38 Optical microscopy use in quality control Dispersed fillers Key variables affecting the performance: shape size distribution These parameters strongly influence: irregular shape idealized shape mechanical properties processability aesthetic properties 38

39 Optical microscopy use in quality control Particles shape and size distribution Can be estimated: size shape how the particles behave to each other (agglomerate) Can be measured: size distribution 39

40 Optical microscopy use in quality control Particles size distribution 40

Optical microscopy use in quality control Surface

Brightfield reflected light roughness of the surface

41 Optical microscopy use in quality control Surface quality estimation and defects control Can be estimated: Figure 31. Different polymeric products surface. Brightfield reflected light roughness of the surface texture covering integrity mold surface quality Surface defects may be found: cracks lack of material small deformations 41

Optical microscopy use in quality control Defects and inclusions show local difference in light reflectance /absorption. That is used to find the embedded flows or unnecessary inclusions.

42 Optical microscopy use in quality control Defects and inclusions show local difference in light reflectance /absorption. That is used to find the embedded flows or unnecessary inclusions. Also the distribution of additives may be controlled. Figure 32. Mixed plastic with aluminium inclusion and shrink holes. Brightfield reflected- (left) and darkfield reflected-light (right). Technological process leaves specific patterns. Once these are understood, the process parameters (temperature, pressure, time) can be varied to improve product quality. Figure 33.Crack. Fluorescence. Figure 34.Shrinkage cavity. Polarized transmitted light. 42 Distribution of particles and embedded flows control

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