Relevant methodology for characterization of radiation exposed polymeric materials

1. Relevant methodology forcharacterization of radiationexposed polymeric materials Dr. Cornelia Vasile Reims, France, September, 12 – 17, 2016

2. TL-IRMP This project has been funded with support from the European Commission. This publication reflects the views only of the author(s). Polish National Agency for the Erasmus+ Programme and the European Commission cannot be held responsible for any use which may be made of the information contained therein. Date: Oct. 2017

3. Outlines Surface properties • Classification • Principles and information obtained: • Composition: ATR-FTIR, XPS • Morphology: AFM, SEM, optical microscopy • Wettability: Contact Angle measurements • Oxidation: Chemiluminescence Bulk Properties • Mechanical Properties - Commonly used methods and Nano Mechanical Testing of Materials • Thermal Properties: DSC, TG, Special methods: Ultra Fast Scanning Calorimetry, AC- chip calorimetry, Nano-TA • Other methods

4. The most important properties of the polymer surfaces • Surface composition, • Free surface energy -: the energy associated with the intermolecular forces at the interface between two media <the surface energy per unit area equals the surface tension> —called also free surface energy., • Wettability -Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. • Roughness - arithmetical mean or maximum height mean spacing of profile irregularities and profile bearing length ratio (tp). • Zeta potential - the potential difference existing between the surface of a solid particle immersed in a conducting liquid (e.g. water) and the bulk of the liquid. • Dynamics of polymer surfaces and aging behaviour

5. Wetting transition - A wetting transition corresponds to a certain change in contact angle.  • Adhesion - the action or process of adhering to a surface or object • Barrier properties - the term used for the function of sealing contents from outside factors (oxygen, nitrogen, carbon dioxide, water vapors)to avoid quality degradation. • Friction and wear - force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other; • Wear and tear- is damage that naturally and inevitably occurs as a result of normal wear or aging. • Biocompatibility- describes the property of a material being compatible with living tissue. Biocompatible materials do not produce a toxic or immunological response when exposed to the body or bodily (biological) fluids. • Bioadhesion-  the phenomenon where natural and synthetic materials adhere to biological surfaces.  Biocompatibility and Bioadhesionare indispensable for developing new biomaterials, therapies and technological applications, such as biosensors.

6. Surface properties play an important role in a number of applications of polymeric materials such as: • wetting, • printing, • adhesive bonding, • membranes, • biomedical devices, etc.

7. SURFACE ANALYSIS TECHNIQUES

8. Indirect Methods: • Free surface energy determination by contact angle methods; • Nanoindentation • Differential thermal analysis (DTA), • Differential scanning calorimetry (DSC); • Molecular mass and molecular mass distribution Methods used to determine specific surface property are: Composition: AES/SAM, XPS, SEM/EDX, SIMS; Chemistry: XPS, ATR-FTIR/RAMAN, SIMS; Morphology/Topography: SEM, AFM/STM, Nanoindentation – mechanical properties determination (i.e. stiffness, deformability, adhesion, friction)

9. Schematic representation of the measurement of forces between particles and surfaces. (a) Particle detachment and peeling forces - adhesion measurements; (b) peeling measurements (adhesive tapes, material fracture and crack propagation); (c) direct measurement of a force as a function of surface separation (spring or a balance); (d) contact angle measurement (for testing wettability and stability of surface films); (e) equilibrium thickness of thin free films (soap films, foams); (f) equilibrium thickness of thin adsorbed film; (long-range repulsive forces stabilizing wetting films)

10. (g) interparticles spacing in liquids (colloidal suspensions, paints, pharmaceutical dispersions) (nuclear magnetic resonance (NMR), light scattering, X-rays and neutron scattering) ; (h) sheet-like particle spacing in liquids (microstructure of soaps and biological membranes)

11. Comparison between the possibilities offered by the analysis techniques in the study of polymer surfaces EDX -Energy-dispersive X-ray spectroscopy

12. Depth profiling techniques determine the composition of one or more components of a film as a function of depth SIMS - Secondary Ion Mass Spectroscopy PS,150 kGy - surface oxidation >10 nm while only ≈ 3 nm depth offered by plasma or corona-discharge treatment. Static (locally destructive technique), Dynamic, Time of Flight-Secondary Ion Mass Spectrometry (very small amount removed)

13. Advantages • detection of large organic molecules up to several thousands of mass units, (II) fast data acquisition with a Time of Flight (ToF) analyzer and (III) obtained chemical information out of the top few angstroms layer of material. The SIMS imaging was recently developed

14. . ANALYTICAL INFORMATION OBTAINED USING SIMS: • - Mass spectrum - identifies the elemental and ion composition of the uppermost layer of 10 to 20 Å of analyzed surface. Libraries of static SIMS spectra give the guide to the results interpretation. - Depth profile - the primary ions penetrate to a depth of ~ 3 nanometers below the surface. Depth resolution of a few Å is possible.- Secondary ion mapping - measures the lateral distribution of elements and molecules on the surface. Lateral resolution is less than 100 nm for elements and 0.5 µm for large molecules. • Careful spectral interpretation combined with fragmentation pathways (e.g. on pyrolysis/electron impact mass spectrometry) allows different classes of polymers to be distinguished as well as individual members of one class to be identified, and also modification/exposure changes performed in polymer materials (radiation exposure)

15. ATR-FTIR identify the molecular species through their vibration states - outermost atomic layers, generally from 1000 Å up to 1 µm; but generally, penetration depth ranges from 40 Å to 3 µm Attenuated total reflection (ATR)-Fourier Transform Infrared Spectroscopy CR–39 polymer n2>>n1 Evanescent wave, is an oscillating electric and/or magnetic field which does not propagate as an electromagnetic wave but whose energy is spatially concentrated in the vicinity of the source (oscillating charges and currents).

16. ATR-FTIR and Raman spectroscopyidentify the molecular species through their vibration states, chemical bond information and molecular orientation. • Non-destructive –Very little sample preparation is necessary. • The gamma irradiation resulted in the formation of hydroxyl (mainly hydroperoxides and alcohols) (3350 cm-1) and carbonyl groups (mainly ketones, esters and acids) (1740 cm-1) which were detected by infrared spectroscopy in the 3200–3600 cm-1 and 1900–1500 cm-1 region, respectively. The carbonyl and hydroxyl indices indices usually increase with the absorbed dose

17. Samples irradiated with X-rays emit photo-electrons XPS - X-ray photoelectron spectroscopy XPS photoemission process (a) and characteristic shape of a photoelectron peak, with contribution from the inelastic scattering background (b). The photoemission peaks in the XPS spectra allow identification of all elements, except H and He.

18. XPS information and applications C‒C < C‒O < C=O < O‒C=O < O‒(C=O) O‒. • The change in binding energy is known as chemical shift. BE increases: • XPS - survey spectrum • XPS core level spectra: intensities, shake-up satellites, depth profiles, valence band spectra = information about atomic, chemical and structural composition of macromolecular surfaces. • XPS is conducted without special preparation of the samples, but the procedure is carried out in an ultrahigh vacuum environment (10-9 torr), therefore biomaterial samples must be in dry state. • Applications include: liquid/solid interfaces, impurity segregation, polymer coatings, transfer films, thin film chemistry.

19. Since the energy levels in materials are quantified, the resulting energy spectrum consists of discrete peaks associated to the electronic energy states of the sample. The peaks of a photoelectron spectrum are grouped in three categories: peaks due to photoemission from the core levels of the atom, those due to photoemission from the valence level and those due to Auger emission.

20. Scanning probe microscopy (SPM) OM (A) Surface imaging technique classification according to measurable size. STM indicates Scanning tunneling microscopy, SPMs - Scanning probe microscopies, TEM - transmission electron spectroscopy, SEM - scanning electron microscopy, OM - Optical microscopy; SFA - Surface force apparatus; (B) Surface force technique classification, according to the strength of interactions;

21. An AFM uses a cantilever with a very sharp tip to scan over a sample surface. As the tip approaches the surface, the close-range, attractive force between the surface and the tip cause the cantilever to deflect towards the surface. Detection MethodA laser beam is used to detect cantilever deflections towards or away from the surface. By reflecting an incident beam off the flat top of the cantilever, any cantilever deflection will cause slight changes in the direction of the reflected beam. A position-sensitive photo diode (PSPD) can be used to track these changes. The resulting cantilever deflection (and the subsequent change in direction of reflected beam) is recorded by the PSPD. ImagingAn AFM images the topography of a sample surface by scanning the cantilever over a region of interest. The raised and lowered features on the sample surface influence the deflection of the cantilever, which is monitored by the PSPD. AFM can generate an accurate topographic map of the surface features. AFM Principle

23. AFM images of the Pristine PMMA samples: (a) - unirradiated; irradiated with electron fluencies: (b) - 4x1014 e/cm2, (c) - 4x1015 e/cm2 and (d) - 1x1016 e/cm2

24. Information Fully characterization of polymer films at nanoscale: • film morphology and topographical features : imaging, roughness of surface (RMS is calculated as the Root Mean Square of a surfaces measured microscopic peaks and valleys.) • mechanical properties (i.e. stiffness, deformability, adhesion, friction), • electrical and • thermal properties (i.e., glass-transition, melting and crystallization temperatures), etc.

25. SEM Emissions produced performing SEM analysis (a); SEM images of MoO3 nanostructures (b) (A–E) Deposited in the pin-to-pin electrode configuration, (F–H) deposited in the pin-to-plate electrode configuration; (I) porous networks of MoO3 deposited in the pin-to-plate configuration

26. Emissions related to SEM operation and features to examine /information obtained High vacuum prevents study of biological samples – ESEM environmental scanning electron microscopes developed for hydrated samples

27. SEM needs the optimal preparation of the sample. Therefore embedded liquids and gases in the sample must be removed by appropriate treatment (e.g. storage at elevated temperatures or in vacuum). • The surface of non-conductive samples has to be sputtered with a thin conductive layer. For these reasons noble metals like gold, palladium and platinum serve as the typical coating materials. • In the case of x-ray analysis the sample is analyzed according to its composition and can therefore not be coated with above-mentioned metals but with carbon. Many thin polymer films - though non-conductive in bulk - can be imaged without coverage by a conducting material.

28. - surface energetics,- roughness, - heterogeneity, - surface dynamics-advancing angle- receding angle. - “contact angle hysteresis”. the difference between these two values. Indirect Methods: Contact Angle measurements - allows to monitor the behavior of solid-liquid interfaces

29. Surface tensions at the contact between liquid and solid phases. (b) acid-base component of the free surface energy  vs epoxidized lignin (LER) content in izotactic polypropylene - based composites, exposed to different irradiation sources

30. Four commonly used methods of contact angle (surface tension) measurement are: sessile drop, tilting plate, captive bubble, and Wilhelmy plate technique. • Three liquids are necessary: water, and dimethylformamide – polar and bromo-naphthalene as non-polar

31. Chemiluminescence- emission of ultraviolet, visible or infrared radiation from a molecule or atom as the result of the transition of an electronically excited state. • [A] + [B] → [◊] → [Products] + light • [◊] + F C + F* - fluorophore F + Light The time dependent CL intensity variations with the treatment temperature for EB irradiated EVA copolymer Measurement temperatures: (■) 200 oC; (●) 210 oC; (▲) 220 oC OOT- onset oxidation time • Decay curves of chemiluminescence Coupling of several methods in surface properties investigation is highly recommended for the achievement of reliable results in sample investigations

32. Bulk Properties Radiation treatment of polymers may lead in fact to cross-linking and/or chain scission reactions, depending on the chemical nature of the polymer and irradiation conditions. These will change bulk properties: • chemical composition and structure, • average molecular weight, • solubility, • mechanical properties (Young’s modulus, flexural modulus, tensile, impact (strength or energy), hardness, fatigue, etc.), • electric and optical properties, • crystallinity, • transition temperatures (mainly glass transition related to Vicat softening point and brittleness temperature), melting and crystallization, degradation temperatures, • gas permeability across a polymer film or membranes, • water absorption, • melt viscosity and rheological properties, • polymer stability under aging (natural and accelerated), biological factors, thermal, UV resistance, weathering (environmental stress)

33. Tensile properties: tensile strength, elongation at break, Young moduli - Uniaxial tensile tests; Hardness or microhardness (Vicker, Shore) Long term creep tests in tension (2.5 MPa), Tension creep tests predict long term deformation behaviour Bending resistance Impact strength and energy: Izod and Charpy with/without notch; Short- and long-term mechanical behaviour (stress-deformation, fatigue life, fatigue-propagation, low-speed impact, durability, fracture behaviour) Tension creep tests predict long term deformation behaviour Mechanical Properties Static Mode: quasi-static conditions, i.e. when the imposed stresses and strains are constant or change only slowly

34. Mechanical Properties Dynamic mode: Stress analysis involves the use of the frequency-dependent dynamic moduli of the polymers. The polymer is subjected to a sinusoidal stress σ of amplitude σo and frequency ω, i.e. σ = σ0 sin ωt. the strain response e to the imposed sinusoidal stress can be described as ε = ε0 sin (ωt − δ) where δ is the phase angle. The sinusoidal stress  and corresponding strain ε response for a linear viscoelastic material. The imposed stress and the material response do not coincide, and the phase angle δ is the difference between the two curves.

35. σ = Eε, but E is a function of the frequency ω. Because the stress and strain are not in phase, E must be treated as a complex function: E* = E’+E” E’ (storage modulus) and E″ (elastic) are the in-phase and out-of-phase components of the modulus. The phase angle δ can be expressed as follows: tgδ =E”/E’. Tan δ is commonly called the loss tangent or damping factor. The mechanical properties of nanomaterials as deformed under periodic forces such as dynamic modulus, loss modulus and mechanical damping or internal friction At very high frequencies (ω = 104−108 cycles s−1 or Hz) rubber is very stiff with a glass-like modulus.

36. . Nano Mechanical Testing of Materials The MML NanoTest™ system is a fully flexible nano-mechanical property measurement system, offering a complete range of nanomechanical and nanotribological tests, including nanoindentation, nano-scratch and wear, nano-impact and fatigue, elevated temperature nanoindentation and indentation in fluids. It is capable of measuring hardness, modulus, toughness, adhesion and many other properties of thin films and other surfaces or solids such as nano-scratch and nanowear testing (for abrasive/sliding wear resistance and adhesion strength of coatings), fatigue wear and accelerated wear testing)

37. The technique consists of performing a contact mode scan of an area of a cantilever test structure as well as of an area that does not deform. The bending moment in the test cantilever changes continuously with the position of the applied force, allowing both the stress and strain to change even though the force remains constant. Elastic modulus can be determined. This testing method can be performed by any AFM capable of scanning in the contact mode without requiring specialized software. Contact scanning mode AFM for nanomechanical testing

38. Second order transitions and relaxation phenomena: Tl,l– translation of the entire macromolecule; Tg – glass transition; Tg,g; T (Ta and Tc); T branching point movement; T - groups Tg- polymer transitions from a hard, glassy material to a soft, rubbery material. Change in specific volume, changes in heat capacity: heat flow, specific heat cp (J/mol K). First order transitions: Melting and Crystallization: enthalpy, thermal capacity, crystallization kinetics; Standard methods: HDT heat deflection temperature- bending under load; Softening temperature – VICAT Thermal stability: characteristic temperatures, (onset temperature, temperature corresponding to the maximum mass loss rate or peak temperature, temperature corresponding to a certain mass loss as 5 wt%, 10 wt% or even 50 wt%), mass losses and energy of the process(es) or other kinetic parameters as criteria for thermal stability. Thermal Properties

39. Principle of conventional DTA and DSC DTA and DSC DTA and DSC

40. The glass transition temperature depends mainly on a molecular weight, branching, crystallinity, amount and type of additives and traces of solvents/water. Tgdepends also on irradiation dose of polymers Different properties can be obtained if the polymer is irradiated below or above its glass transition temperature Differential Scanning Calorimetry; Thermal Mechanical Analysis; Dynamic Mechanical Analysis.

41. % Crystallinity =[ ΔHf/ΔH°f ] × 100

42. Effect of increase in crystallinity on different polymer properties [40]

43. Thermal properties evaluated from DSC thermograms for PLA, PLA/ATBC and PLA/CH samples ATBC – tributyl o-acetyl citrate ; CH - chitosan

44. Thermal methods of investigation • DSC: Differential Scanning Calorimeter - The DSC measures the energy absorbed or released from a sample as a function of time or a temperature. DSC is useful to make the measurements for melting points, heats of reaction, glass transition, heat capacity and purity determination. • (MTDSC) Modulated Thermal DSC - a relatively new technique, is successfully used to study miscibility of polymer blends, interface, physical ageing, and latex structure. It is able to separate complex transitions into more easily interpreted components and directly measure heat capacity changes from a single experiment. MTDSC measures reversing and non-reversing heat flow signals, which reveal thermal behaviour such as the glass and melting transitions, and physical ageing and crystallisation, etc.

45. PDSC: Pressure Differential Scanning Calorimeter- The Pressure DSC allows for experiments to run under pressure up to 1000 PSI (Pounds per square inch) using various gases. This allows for samples to be tested under the conditions they will be exposed to during processing and or use. DSCE: External Differential Scanning Calorimeter - The DSC-E is a flexible instrument allowing for DSC and DTA cells to be interchanged on one easy to operate unit. Cells simply plug in and the software automatically configures the system for each cell type. AC-chip calorimetry A differential AC-chip calorimeter is capable to measure the glass transition in nanometer thin films. Due to the differential set-up pJ/K sensitivity is achieved. Heat capacity can be measured for sample masses below one nanogram. The calorimeter allows for the frequency dependent measurement of complex heat capacity in the frequency range from 1 Hz to 1 kHz; Ultra Fast scanning calorimetry - To study phase-transition kinetics on submillisecond time scale a set of new membrane gauges for ultrafast scanning nanocalorimetry were constructed. Controlled ultrafast cooling, as well as heating, up to 106 K/s was attained. .

46. Ultra Fast scanning calorimetry To study phase-transition kinetics on submillisecond time scale Controlled ultrafast cooling, as well as heating, up to 106 K/s was attained. The maximum cooling rate is inversely proportional to the radius of the heated region, which was in the range 10–100 μm for different gauges. The minimum heat capacity was 3 nJ/K. The new calorimetric cells in combination with common differential scanning calorimetry (DSC) were applied for the measurements of superheating in a set of linear polymers. A power law relation between the superheating and the heating rate was observed in the broad heating rate range 10−2 to 105 K/s.

47. Nano-TA Nano-TA:is a Localized Thermal Analysis technique which combines the high spatial resolution imaging capabilities of atomic force microscopy with the ability to obtain understanding of the thermal behaviour of materials with a spatial resolution of sub-100 nm. Nano-TA is a surface technique, essentially different from DSC, which is a bulk characterization method. The DSC runs investigating melting and crystallization were conducted at heating/ cooling rates of 3 °C/min, while during the Nano-TA experiments the tip was heated extremely fast (600 °C/min). This difference might account for the ability of Nano-TAto detect polymer re-organization phenomena on the sample surface which are not evident in larger volume samples heated at slower rates during the DSC experiments.

48. The melting behavior of Graphene nanoplatelets (xGnP) as a novel nano-reinforcement filler in poly(lactic acid)(PLA)/poly(ethylene glycol)(PEG) blends PLA/xGnP-1 composites was further analyzed using nano-TAin order to investigate possible connections between agglomeration of xGnP and polymer molecular weight which were not evidenced by the DSC analysis Nano-TA curves for (a) PLA L210S/xGnP-1 and (b) PLA L209S/xGnP-1 composites containing different amounts (% wt) of xGnP-1

49. . The onset of melting transition (Tmo). nano-TA revealed three major differences in the melting behavior of the different molecular weight PLA and their composites with xGnP-1: Lower temperatures were also recorded for the onset of melting transition, linear increases of deflection with temperature, the deflections recorded were lower than the deflection measured for the neat • . DMA results indicated a smaller extent of improvement in storage modulus in the case of composites prepared with the lower molecular weight polymer. It is likely that xGnP-1 dispersed better in PLA L210S, which was better nucleated by the nanoplatelets, generating more polymer crystallites and fewer regions in which xGnP-1 agglomerated. In the PLA/xGnP-1 systems studied, more uniform crystalline structures would lead to higher probabilities that the nano-TA tip encounters polymer spherulites rather than regions where xGnP-1 agglomerates.

50. Spider silk • Spider silks, are evenly spun, which provides a model natural fibre with superb combinations of strength and toughness. • The yield strain, under ambient conditions is usually about 2%. Other parameters of yield stress, post-yield modulus, and stress and strain to break, are dependent upon the detailed composition and morphology of the silk polymer at a nanometer scale