States of matter - Phases. Physical Bases of Dental Material Science 2. Fluids. Viscosity (h) INTERACTIONS = REPULSIVE ATTRACTIVE ) * !

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1 tates of matter - Phases T solid liquid gas definite volume stable shape Physical Bases of Dental Material cience 2. tructure of matter Liquids, solids, liquid crystals Highlights: v Viscosity v Water and saliva v Crystals - apatite v Polymorphism v Crystal defects v Amorphous materials v Liquid crystals (Material found in Medical Biophysics!) E-book Chapters: 4, 5 Medical Biophysics I/ Problems: Chapter 1.: 22, 23, 32, 33, 34, 35 1 Fluids versus olids indefinite shape: hape does not recover after deformation, lack of restoring forces. definite shape: hape recovers after deformation, due to restoring forces. Fluids REPULIVE INTERACTION = ATTRACTIVE Viscosity (h) F=? Fluidity (1/h) F s F = F s particle movement versus inter-particle bonds hort range, dynamic order isotropic F=? (later: Hagen-Poiseuille law) Newton s law of viscosity: Fs = h A Dh viscosity (coefficient of internal friction) [h] = Pa s Another form of Newton s law:! "#$%& Fs =h A Dh ) * shear stress velocity gradient 3! "#$%& = () * 4 1

2 Which one has higher viscosity? Rotational viscometer: h < h 5 6 Figure schematically shows the structure of a rotational viscometer. The inner cylinder is still and the outer is rotated. The radius of the outer cylinder R = 2.2 cm, the inner cylinder r = 1.2 cm. The cylinder s height is h = 10 cm. The tested liquid between cylinders is glycerine. Layer thickness is Dy = R r = 1cm. Calculate the force that is necessary for uniform rotation of the cylinder does 90 revolutions per minute? (viscosity of the glycerine h = 1500 mpas. The flow is laminar.) Newton s law of viscosity: Fs = h A Dh h ~ is the slope (constant) material h (mpas) air 0,019 (20 C) water 1 (20 C) saliva substitute (UA patent) 2 10 glycerol 1500 (20 C) ethyl methacrylate monomer 0,5 (25 C) h ethylene glycol dimethacrylate monomer zinc phosphate 3,4 (25 C) (25 C) zinc oxide -eugenol (37 C) silicone (37 C) Dh 7 8 2

3 h depends on: material quality temperature h depends on: 1. shear forces/velocity gradient (mpas) liquids Newtonian fluids Non-Newtonian fluids i.e. water, oil pseudoplastic i.e. saliva, blood polycarboxylate cements, elastomer impression materials dilatant i.e. dental composite resins 9 10 Bingham-fluid: F aliva mucin /Dh pseudoplastic liquid h depends on: 2. time of mechanical stress Thixotropic fluid: h Rheopex fluid: t some dental impression materials saliva substitutes: h Not to confuse them with dilatant and pseudoplastic fluids! t

4 olid materials (crystal = solid body) crystalline policrystalline single crystal single crystal amorphous polycrystalline crystallites or grains Metal microscope anisotropic «isotropic 13 Apatite 14 quartz Polymorphism OH- : hydroxyapatite F- : fluorapatite cristobalite tridymite io2 Ca10(PO4)6(X)2 Examples: hexagonal ioncrystal Ca5(PO4)3X carbon (C) Tin (n) fullerene Dentin, bone: nm x 6 nm crystals Enamel: nm x 30 nm crystals nanotube diamond 15 graphite polymorphism of elements = allotropy 16 4

5 Crystal defects point defects thermal defect vacancy (chottky-defect) interstitial defect n e - = N e kt No. of chottkydefects Frenkel-defect Frenkel-pair 0.9 ev energy is necessary to produce a vacancy in copper. a) How many percnt is the ratio of vacancies in the crystal at 1000 C? n = N e e - kt Impurity (dopant) (alloys!!) substitutional impurity atom interstitial impurity atom Generation and diffusion of point defects: Line defects edge dislocation screw dislocation edge dislocation screw dislocation Thermal defects in biomolecules: n = N e e - kt planar defects dislocations in titanium alloy No. of broken H-bonds

6 Lattice defects strongly influence the! Al2O3 i.e. mechanical i.e. optical + Cr3+ Fe2+ + V2+ +Ti4++Fe2+ i.e. chemicl Ca10(PO4)6(OH)2 Ca10(PO4)6F2 hydroxyapatite NaI + Tl NaI i.e. electronic fluorapatite Lower solubility in acids. doped semiconductors cintillation crystals for detecting X-ray and gamma rays. 21 Emits light when irradiated by X-ray! 22 v (Medical Biophysics I/3.4.2.) Amorphous materials = glass, glassy materials Liquid crystals (extreme high viscosity, thus flow is extremely slow) hard materials isotropic i.e. glass, synthetic resins, wax, asphalt,... anisodimensional molecules center of mesophasic mass partially ordered structure Translational order Orientational order fluid optically anisotropic structure can change according to environment temperature can change the order: thermotropic liquid crystals concentration: lyotropic liquid crystals molecular axis many defects no defined shape (flows) pitch drop experiment short distance order smectic translational + orientational order nematic only orientational order cholesteric only orientational order (twisted nematic)

7 LCD (electro-optical effect) Contact thermography (thermo-optical effect) incident unpolarized light 1. polarizer orienting layer liquid crystal molecules orienting layer 2. polarizer exiting light 25 no exiting light 26 Lyotropic liquid crystals lamellar liposome 27 7