Experimental Techniques in Characterizing Polymer Adsorption Matthew Herbert

Overview Background Theory Experimental Techniques Adsorption vs. absorption Applications Theory Common conformations Adsorption Isotherm Experimental Techniques Infrared Spectroscopy (IR) Forward Recoil Spectrometry (FRES) Neutron Scattering (NS) Quartz Crystal Microbalance (QCM)

Adsorption vs. Absorption Adsorption: Physical adherence or bonding of ions and molecules onto the surface of another phase Physiosorption Chemisorption Absorption: The incorporation of a substance in one state into another of a different state. adsorbate adsorbate adsorbate adsorbate adsorbate adsorbent adsorbent adsorbent adsorbent G. Glockner. Polymer Characterization by Liquid Chromatography. Journal of Chromatography Library – Volume 34. p74-92

Applications Friction and Lubrication Mineral processing, petroleum, paper industry Stabilization or flocculation of colloidal dispersions Inks, cosmetics, processed food Biomedical Applications Protein interaction (enamel, nacre), drug delivery, etc. Colloid and Surface Chemistry Laboratory. http://www.chem.cuhk.edu.hk/NgaiToGroup/research.html http://www.timron-inc.com/teknote_Jan2001.html

Overview Background Theory Experimental Techniques Adsorption vs. absorption Applications Theory Common conformations Adsorption Isotherm Experimental Techniques Infrared Spectroscopy (IR) Forward Recoil Spectrometry (FRES) Neutron Scattering (NS) Quartz Crystal Microbalance (QCM)

Conformations Polymer adsorption occurs when there is a favorable adsorption energy of the polymer over that for a solvent molecule. Xs = (Us-Up)/kT Xs = dimensionless energy parameter Us = adsorption energy of solvent segment Up = adsorption energy of polymer segment Homopolymers (a) Each segment is equally attracted to interface End-functionalized homopolymers (b) Special end-functional group that grafts to interface Diblock copolymers (c) Specific block group in chain is attracted to interface G. Glockner. Polymer Characterization by Liquid Chromatography. Journal of Chromatography Library – Volume 34. p74-92 Karim, A., Kumar, S. Polymer Surfaces, Interfaces and Thin Films. P181-200

Adsorption Isotherm Functional relationship between adsorbate and adsorbent in the adsorption process. Described in terms of surface excess (amount of adsorbed polymer per interfacial area) vs. bulk volume fraction of adsorbing species (bulk solution concentration) Γ = adsorbed amount Encyclopedia of polymer science: http://onlinelibrary.wiley.com/doi/10.1002/0471440264.pst014.pub2/pdf

Overview Background Theory Experimental Techniques Adsorption vs. absorption Applications Theory Common conformations Adsorption Isotherm Experimental Techniques Infrared Spectroscopy (IR) Forward Recoil Spectrometry (FRES) Neutron Scattering (NS) Quartz Crystal Microbalance (QCM)

Infrared Spectroscopy 3 basic components Radiation source Monochromator or interferometer (FTIR) Detector Measuring absorption of incident IR radiation as a function of… Change in frequency of monochromatic beam wrt time (IR) All frequencies examined simultaneously (FTIR) A=εbc Beers-Lambert Law: Absorption = molecular absortivity (ε) x path length of source beam (b) x sample concentration (c) http://www.exova.ca/index.php?option=com_content&view=article&id=1148 Infrared Spectroscopy. http://www.prenhall.com/settle/chapters/ch15.pdf http://intermediateorgchemistry.co.uk/spectroscopy.htm

Infrared Spectroscopy 1. Adsorption mechanism 2. Relative adsorbed concentration with respect to a calibration curve of known polymer concentration Γ = amount adsorbed ∆C = change in concentration V = known volume of adsorbate A = surface area of adsorbent ν = wavenumber λ = wavelength C. Blachier et al., Journal of Colloid and Interfac Science 336 (2009) 599-606 Infrared Spectroscopy. http://www.prenhall.com/settle/chapters/ch15.pdf

Forward Recoil Spectrometry (Elastic Recoil Detection) Measures loss of energy between incident He ions and recoiled nuclei Edet = detected energy Q = total number of incident ions N(x) = H and D concentration at given depth σ(E1,θ) = scattering cross section evaluated at E1 E1 = energy before recoil collision Ω = detector solid angle δEdet = energy width of a channel dEdet/dx = effectivestopping cross section of H or D K = kinematic factor for forward scattering t = depth Energy detected = K(incident energy – energy lost on inward path) – energy lost on outward path – energy lost passing through filter R.J. Composto et al., Materials Science and Engineering R 38 (2002) 107-180 M.H. Rafailovich et al., Hyperfine Interactions 62 (1990) 45-53 Karim, A., Kumar, S. Polymer Surfaces, Interfaces and Thin Films. P181-200

J. Genzer et al., Polymer 40 (1999) 4223-4228 Neutron Scattering Q = scattering vector (change in neutron momentum) Nj = neutron refractive index of medium j Nd = atomic number density B = coherent scattering length P(z) = scattering length density λ = neutron wavelength J. Genzer et al., Polymer 40 (1999) 4223-4228 http://users.ox.ac.uk/~dgbuck/people/bucknall/research/NR.htm D.G. Bucknall et al., “Neutron Reflection Studies of Polymer-polymer Interfaces”. Polymers and Surfaces: A Versatile Combination. 1998.

Quartz crystal microbalance Measures change in oscillating frequency of a quartz crystal disk as a function of mass. Cf = crystal calibration constant fq = resonant frequency of quartz pq = quartz density vq = quartz volume mf = foreign mass J.C. Munro et al., Macromolecules 2004, 37, 925-938 http://www.directindustry.com/prod/stanford-research-systems/quartz-crystal-microbalances-7218-54640.html http://large.stanford.edu/courses/2007/ph210/hellstrom2/

Extended List of Techniques What adsorption information can this technique provide? Infrared Spectroscopy Adsorption mechanism, concentration of adsorbed polymer (with respect to known calibration curve) Forward Recoil Spectroscopy Depth vs. concentration profile of hydrogen and deuterium (labelling polymer with deuterium required for contrast) Neutron Scattering Depth vs. concentration profile (labelling polymer with deuterium provides contrast) Quartz Crystal Microbalance Adsorbed mass (∆f) , viscoelastic properties (∆D) Nuclear Reaction Analysis Depth vs. concentration profile Electron Spin Resonance Surface coverage information Rutherford Backscattering Spectrometry concentration vs. depth profile for heavier elements Secondary Ion Mass Spectrometry surface composition Ellipsometry layer thickness, composition, surface roughness

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