MIT 3 051J - Lecture 12: Biomaterials Characterization in Aqueous Environments (10 pages)

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Lecture 12: Biomaterials Characterization in Aqueous Environments



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Lecture 12: Biomaterials Characterization in Aqueous Environments

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Pages:
10
School:
Massachusetts Institute of Technology
Course:
3 051j - Materials for Biomedical Applications

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1 3 051J 20 340J Lecture 12 Biomaterials Characterization in Aqueous Environments High vacuum techniques are important tools for characterizing surface composition but do not yield information on surface structure or chemistry in a water based environment Aqueous based methods for surface characterization are limited Here we will consider three common techniques 1 water contact angle studies surface reconstruction a water absorption b surface chemistry analysis advancing a receding a droplet volume r advancing b receding cos f1 cos 1 f 2 cos 2 Cassie s eqn use to determine fraction of surface area of components 1 2 f1 f2 1 droplet volume 2 3 051J 20 340J 2 in situ ellipsometry degree of hydration of a film Ellipsometric angles and thickness df refractive index nf 3 layer model nwater nf df n f f water nwater f material nmaterial where fwater and fmaterial are volume fractions nsub 3 3 051J 20 340J 3 Atomic Force Microscopy or Surface Force Microscopy imaging method that exploits intermolecular interactions between a small atomic probe and molecules on surface He Ne laser position sensitive photodetector Au coated Si Si3N4 SiO2 cantilever spring const k 0 1 1N m atomic Si Si3N4 C tip sample surface piezoelectric transducer Scan area 1 1 nm2 to 250 250 m2 z range 8 m force range 10 13 10 6N piezo controlled sample stage Intermolecular potential curve U r short range ion ion repulsion Force generated F U z r Long range attractive van der Waals H bonding electrostatic dipole dipole 4 3 051J 20 340J Operation Modes 1 Contact mode short range Tiny cantilever deflections detected by photodiode array Tip rastered over sample surface at fixed force via photodetectorz piezo feedback loop generates topographical image analogous to stylus on a record player Good for hard samples can drag soft materials force applied nN x y resolution 1 z resolution 1 Photo removed for copyright reasons Contact mode images of TiO2 rutile film surface No contrast at low resolution flat surface



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