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LUND UNIVERSITY Particle characterization Chapter 6 1 LUND UNIVERSITY Why determinate particle size • List three things that you know will be affected by particle size 2 LUND UNIVERSITY My three things • • • Delivery of particles to the lungs Solubility of active pharmaceutical compounds Bulk density 3 LUND UNIVERSITY What do you want to characterize Particle • Size • Morphology • Material properties – Porosity – Density – Hardness/elasticity(later) • Surface properties – Chemical composition – Surface energy – Roughness Powder • Particle distribution • Flowability/cohesion • Specific surface • Density • Porosity • Air content • Water content (later) 4 LUND UNIVERSITY Size and Morphology Describe these two particle collections QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. 5 LUND UNIVERSITY Size and Morphology Different descriptive terms for particles Particle form spherical, ellipsoid, granular, blocky, flaky, platy,prismodal, rodlike, acicular, needle shaped, fibrous irregular,dendrites, irregular, agglomerates But also particle surface Smooth, spotty, rough, porous, with cracks, hairy 6 LUND UNIVERSITY Size and Morphology Measurement of particle size • Reduce to known geometry – Volume • • • – Area • • • A= Projected a rea P=Perimeter d=equivalent diameter• S=surface area V=volume – Cubes Spheres Ellipsoids Circles Squares Ellipses Lengths • • Characteristic lengths Feret and Martin diameters Relate to the geometry – Fit into the geometry – Have equal Volume or Area – Have equal properties 7 LUND UNIVERSITY Size and Morphology Descriptors based on diameters of circles dcirc=Diameter of circumscribed minimum circle dinsc=Diameter of inscribes maximum circle deq=Diameter of the circle having same area as projection area of particle Shape descriptor:Circularity deq/dcirc 8 LUND UNIVERSITY Size and Morphology More descriptors according to the same principles Namn Definition Formula Volume diameter Diameter of a sphere having the same volume as the particle 3 d V 6 Surface diameter Diameter of a sphere having the same surface as the particle S d 2 Surface volume diameter Diameter of a sphere having the same surface to volume ratio as the particle Projected area diameter Diameter of the circle having the same area as the projection area of particle Perimeter diameter Diameter of the circle having the same perimeter as the projection peramiter of particle dsv dv3 /6d 2s 2 d A 4 P d 9 LUND UNIVERSITY Size and Morphology Feret and Martin diameter Df0 Dm0 • • • The Feret diameter the distance between two tangents to the contour of the particle in a well defined orientation. The Martin diameter, is the length of a line that divide the area of the particle into two equal halves. Normally measured – Mean= the mean over several orientations – Y=largest – X=smallest – Elongation= Y/X 10 LUND UNIVERSITY Size and Morphology Unrolled diameter • The mean chord length through the center of gravity of the particle E(dg) 1 2 d d g g 0 11 LUND UNIVERSITY Size and Morphology Diameter Defined from equal properties Drag diameter • Diameter of a sphere having the same resistance to motion as the particle in a fluid of the same viscosity and the same speed Free-falling diameter • Diameter of a sphere having the same density and the same freefalling speed as the particle in a fluid of the same density and viscosity Stoke diameter • The free falling diameter of a particle in the laminar flow region Aerodynamic diameter • the diameter of a sphere of unit density (1g/cc) that has the same gravitational settling velocity as the particle in question. 12 LUND UNIVERSITY Size and Morphology Stoke diameter • Brownian motion D msolvent*g • kT 6a For small particles <0.5m Brownian motions counteract gravitational forces and the system will be stable For larger particles 2d 2 g v 18 a 2a 2 g v 9 mpart*g • Density matching will hinder sedimentation 13 LUND UNIVERSITY Size and Morphology Diameter Defined from equal properties contin.. Equivalent light-scattering diameter • Diameter of the sphere giving the same intensity of light scattering as that of a particle, obtained by the lightscattering method Sieve diameter • The diameter of the smallest grid in a sieve that the particle will passe through 14 LUND UNIVERSITY Size and Morphology From descriptors • • • Elongation: L/B or dferet(max)/dferet (min) Circularity: for example dins/dcirc Sphericity (Wandells): 2 2 dv S p ds dv 15 LUND UNIVERSITY Size and Morphology Form descriptors • Form factors: f/k will describe the form S p f * da2 Vp k * d • 3 a Space Filling Factor: The ratio between the area of a circumscribed rectangle or circumscribed circle of the image and that of the particle eg A/LB eller 4A/πr2 16 LUND UNIVERSITY Material properties Density • • • True particle density: The density of the material Apparent particle density: Density of the particle when inner porosity is included Effective or aerodynamic particle density: Density if outer porosity is included. Related to the density that a air or gas stream will measure. 17 LUND UNIVERSITY Surface properties Particle surface • • Properties – Roughness of the surface – Composition – Surface energy Influences – Stability – Total area – Particle size reduction – Adsorption of other substances to the surface – Aggregation – Release of adsorbed material 18 LUND UNIVERSITY Surface properties To evaluate surfaces properties • • • • • ESCA, XPS - Composition FTIR - Composition AFM- Surface morphology and surface energy Raman microscopycomposition Electron microscopy Surface morphology Evaluation of Ascorbyl Palmitate-loaded NLC Gel using Atomic Force Microsco V.Teeranachaideekul.1,2, S. Petchsirivej3,4 , R.H. Müller1, V.B. Junyaprasert2 19 LUND UNIVERSITY Surface properties To evaluate surface energy - Contact angles L/V S/V S/V • • • Gives information on how easily a liquid wets a surface. Low contact angle with water for hydrophilic surfaces. Contact angle hysteresis: – Chemically heterogeneous surface. – Surface roughness. – Surface porosity – Surface changes when wetted. 20 LUND UNIVERSITY Assignments particles Task • • • Test and compare two different techniques for size determinations (half a day) – Microscopy – Light scattering Answer the questions in the assignment description on a seminar (Tue 28 Apr 13.15) As usuell hand in a short technical note 21 LUND UNIVERSITY Assignments particles Practical issues • • • Do the assignment in groups of three Use our sample or your own Microscopy use the microscope to take picture but do the major part of the analyses afterwards Image J is a free program 22 LUND UNIVERSITY Size distribution Particle size distribution • • Why is the mean value not enough to describe particle size distributions How can we describe the distribution – Based on what properties – Based on what type of statistic distribution 23 LUND UNIVERSITY Size distribution Type of distributions • • Different type of diameters Different type of distribution – Number (0) – Length (1) – Area (2) – Volume (3) – Weight (w) =V* • • • How will these differ from one another? How do you calculate the mean particle size Can you transfer mean particle size between the different distributions? 24 LUND UNIVERSITY Size distribution Average particle size Number mean length diameter d(1,0) dL dN d dS dN d dV dN d dL dw d Number mean surface diameter d(2,0) 2 2,16 3 Number mean volume diameter d(3,0) Weighted mean length diameter d(3,0) Length surface mean diameter d(2,1) Length volume mean diameter d(3,1) Surface Volume mean diameter d(3,2) weight moment mean diameter d(4,3) d dS d dL dV dL d dV d dM 2,29 2,33 2,45 dS 2,57 dW 2,72 25 LUND UNIVERSITY Size distribution Different distributions 0,8 0,7 distribution 0,6 N L S V 0,5 0,4 0,3 0,2 0,1 0 1 2 3 size 26 LUND UNIVERSITY Size distribution Type of statistic distribution QuickTime™ and a decompressor are needed to see this picture. Normal distribution QuickTime™ and a decompressor are needed to see this picture. Log Normal Rosin–Rammler (Weibull) Distribution QuickTime och en -dekomprimerare krävs för att kunna se bilden. d n q exp d 27 LUND UNIVERSITY Size distribution Special properties of log distributions • • • If the number is log distributed so is the length, surface, and volume With the same geometric mean deviation Hatch-Choate relationships will transfer one type of mean diameter into another 28 LUND UNIVERSITY Size distribution Description of particle size distribution • Mean diameter – Standard mean, – Geometric mean ln dg dN *ln x • variability • Standard deviation – Geometric standard deviation ln g dN(ln x ln x )2 / N Skewness N – IQCS (D75% Dg ) (Dg D25% ) (D 75% Dg ) (Dg D25% ) 0 5 10 15 20 25 30 35 1 (x i - x) 3 n 3/2 1 2 (x i - x) n 29 40 LUND UNIVERSITY Powder Specific surface • • • Surface per weight Factors that increase surface area – Decrease in particle size – Increase in surface roughness – Inner porosity (if available) Method dependent parameter – Permeatry – Gas adsorption – Gas diffusion – Porosimetery • Importance – Dissolution – Chemical reactions – Adsorption of other molecules – Flow though particle beds 30 LUND UNIVERSITY Powder Density, air content and porosity • • • Density (b)= weight of powder/Volume of powder Air content= air in pores(entrapped air) and air in between particles (void air) Porosity • • In particle Between particles 31 LUND UNIVERSITY Powder Flow properties and powder density • • Angle of repose Bulk density – Tapping density Flow character Angle Very good <20 Good 20-30 Ok Carrs indextapped poured density Carr sin xdes tapped density – poured density tapped density Hausner Hausner ratioration – Poor 30-34 Very poor Extremely poor >40 Carrs index 5-15 12-16 18-21 25-35 33-38 >40 32