lecture2

lecture2 - bulk 1 3.051 J / 20 .340 J Lecture 2:...

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Unformatted text preview: bulk 1 3.051 J / 20 .340 J Lecture 2: Biomaterials Surfaces: Physics The surface of a material strongly dictates its performance in vivo . Surface Properties Influencing Cell Adhesion Wettability Crystallinity Roughness Composition Electrical Charge Mobility Whats so special about a surface? Surface vs. Bulk 10 15 atoms 1. Inherently Small # of Atoms 1 cm 3 material ~ 10 23 atoms Requires special characterization tools 2. Enhanced Mobility bulk D = D exp(-E a /kT) fewer bonds gradient in density D surf >> D bulk ~1 nm Facilitates rate-limited processes (phase transformations, crystallization, corrosion) 2 3.051 J / 20 .340 J Example: Devitrification of calcium phosphate glass CaO-P 2 O 5-SiO 2 (44:40:15) Crystallization initiates at surface E a,cry powder size (kcal/mol) ( m) 75 < 44 108 297-590 from J.-S. Lee et al., J. Thermal Anal. Cal. 56 (1999) 137. 3. Higher Energy State Atoms/molecules with unsatisfied (dangling) or strained bonds High reactivity and susceptibility to adsorbates Quantifying Surface Energy loss of bonds at a surface attraction towards bulk = areal contraction force Surface tension , , is the work required to create unit surface area at constant T,P and composition. Consider a simple soap film experiment: dx dG = SdT + VdP + dA L f (force) wire frame = G f d x f = = A T P n 2 Ldx 2 L , , where G = Gibbs free energy, A = area ? 3 3.051 J / 20 .340 J Surface Tensions of Example Materials Material T ( C) P E 2 3 6 soda-lime-silicate ( l ) 1350 Al 2 O 3 1850 TiC 1100 Teflon (PTFE) 20 Silicone (PDMS) 20 (dyn/cm) 1 dyn/cm = 1 mJ/m 2 19 = 1 erg/cm 2 20 P M M A 2 4 1 P E O 2 4 3 W a t e r 2 7 3 FeO 1400 580 Ti ( l ) 1660 1550 -Fe (bcc) 1400 1900 350 w/ T 950 sv H sublim 1190 lv H vapor Trends: high materials: (>200 dyn/cm) metals, carbides, oxides low materials: polymers, organics Why? Consider the nature of bonds Surface tension is a measure of degree of cohesion....
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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lecture2 - bulk 1 3.051 J / 20 .340 J Lecture 2:...

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