Presentation on theme: "Kinetic/Optical Properties of Colloids"— Presentation transcript:
1Kinetic/Optical Properties of Colloids PhD Halina Falfushynska
2Motion Thermal motion Techniques for measuring colloidal sizes Brownian Motion on the microscopic scaleDiffusion and translation on the macroscopic scaleTechniques for measuring colloidal sizesSedimentation (under gravitational or applied field)Colligative PropertiesScattering techniques
3George Gabriel Stokes (1851) Albert Einstein (1905) Robert Brown (1827)Brownian motionGeorge Gabriel Stokes (1851)Albert Einstein (1905)Brownian motion was discovered by the biologist Robert Brown in He was studying pollen particles floating in water under the microscope, and he observed minute particles within vacuoles in the pollen grains executing the jittery motion that now bears his name. Full explanation by Einstein.Stokes ( ) was an Irish mathematician and physicist. He was a fellow at Pembroke college, but was kicked out for marrying in years later he was allowed back in. The oldest of the trio Lord Kelvin, James Clerk Maxwell and Stokes who made Cambridge famous in the19th century was appointed Lucasian professor of Mathematics.PecletMainz
4Sedimentation Potential Sedimentation Of A Single Particle Generates a Potential
5Stokes LawStokes' law, for the frictional force – also called drag force – exerted on spherical objects with very small Reynolds numbers (e.g., very small particles) in a continuous viscous fluid.Fd is the frictional force – known as Stokes' drag – acting on the interface between the fluid and the particle (in N),μ is the dynamic viscosity (N s/m2),R is the radius of the spherical object (in m), andvs is the particle's settling velocity (in m/s).
6Calculate the fall or settling velocity (Vt) for the given details through Stoke's Law formula. Acceleration of Gravity (g) = 25 m/s2 Particle Diameter (d) = 15 m Density of Medium (ρm) = 5 kg/m4 Particle Density (ρp) = 10 kg/m3 Viscosity of Medium (μ) = 20 kg/m-sVt = gd2 (ρp - ρm)/18μ
7Problem Vt = gd2 (ρp - ρm)/18μ Find the largest possible diameter for water drops falling in air with a velocity where Stoke’s law can be used In the calculation. Giver: density of air 1.2 kg/m3, μ – 1.8×10-5 kg/(m×s)Vt = gd2 (ρp - ρm)/18μ
8A terminal velocity is reached Where m – mass of particle- specific volume of colloidal particle- solvent densityf – particle frictional factor
9Stokes Law In the limit of Slow particle motion Dilute colloidal suspensionsSolvent is considered as a continuum of viscosity
10The Frictional FactorThe frictional factor in a given medium is obtained from Stokes Law – solvent viscosityR- particle radiusf, is a measure of the resistance to movement of a molecule; this resistance is a function of both the size and the shape of the molecule
11The Frictional Factor D – diffusion coefficient S – sedimentation coefficient
12Frictional Factors Frictional factors depend on the particle shape f increases asParticle asymmetry increasesDegree of interaction with solvent increasesDefine the frictional ratio, f/fo.Ratio of the f value of the particle to that of an unsolvated sphere.
13Poiseuille's Law Calculation In the case of smooth flow (laminar flow), the volume flowrate is given by the pressure difference divided by the viscous resistance. This resistance depends linearly upon the viscosity and the length, but the fourth power dependence upon the radius is dramatically different.
15Sedimentation of colloids buoyant massThe bigger the particles the faster they sediment
16Sedimentation Under gravity Balance method – cumulative mass of settling particles is obtained as a function of timePractical lower limit is about 1 micronUnder centrifugal forceHigh Field – up to 4 x 105g is applied.Displacement of boundary is monitored with timeUnder low fieldMeasure concentration profile in the tube as a function of position.
18Erythrocyte sedimentation rate Sedimentation rate or is the rate at which red blood cells sediment in a period of one hour.To perform the test, anticoagulated blood is placed in an upright tube, known as a Westergren tube. The rate at which the red blood cells fall is measured and reported in mm/h.The ESR is governed by the balance between pro-sedimentation factors, mainly fibrinogen, and those factors resisting sedimentation, namely the negative charge of the erythrocytes (zeta potential).
19When an inflammatory process is present, the high proportion of fibrinogen in the blood causes red blood cells to stick to each other. The red cells form stacks called 'rouleaux,' which settle faster. Rouleaux formation can also occur in association with some lymphoproliferative disorders in which one or more immunoglobulin are secreted in high amounts.The ESR is increased by any cause or focus of inflammation. The ESR is increased in pregnancy, inflammation, anemia or rheumatoid arthritis, and decreased in sickle cell anemia and congestive heart failure. The basal ESR is slightly higher in females.
20DiffusionDiffusion is one of several transport phenomena that occur in nature. A distinguishing feature of diffusion is that it results in mixing or mass transport without requiring bulk motion. There are two ways to introduce the notion of diffusion: either a phenomenological approach starting with Fick’s laws and their mathematical consequences, or a physical and atomistic one, by considering the random walk of the diffusing particles
21Fick’s Laws of Diffusion The diffusion flux is proportional to the minus gradient of concentrations. It goes from regions of higher concentration to regions of lower concentration.
22DiffusionFrom the atomistic point of view, diffusion is considered as a result of the random walk of the diffusing particles. In molecular diffusion, the moving molecules are self-propelled by thermal energy. Random walk of small particles in suspension in a fluid was discovered in 1827 by Robert Brown.
24Diffusion and Frictional Factors The diffusion coefficient of a suspended particle is related to f via the Einstein EquationFor spherical particleswhere D is the diffusion constant; μ is the mobility"; T is the absolute temperaturekB is Boltzmann's constant; × 10-23 m2 kg s-2K-1
25Diffusion of ions through a membrane the flux is equal to mobility×concentration×force per gram ion. This is the so-called Teorell formula.The force under isothermal conditions consists of two parts:Diffusion force caused by concentration gradient: Electrostatic force caused by electric potential gradient: Here R is the gas constant, T is the absolute temperature, n is the concentration, the equilibrium concentration is marked by a superscript "eq", q is the charge and φ is the electric potential.
26Measurement of Diffusion Coefficients Free boundary methodsa boundary between two solutions of different concentrations is formed in a cylindrical cellDetermine the evolution of the concentration distribution with time.
27Measurement of Diffusion Coefficients Taylor Dispersion methodsNMR TechniquesPulsed gradient spin echo experiments (PGSE)Diffusion oriented spectroscopy (DOSY)
28Intensity of transmitted radiation related to solution turbidity () Intensity of transmitted radiation related to solution turbidity ()
29Nobel Prize for Chemistry for his work on the heterogeneous nature of colloidal solutions.
31Light Scattering and Colloidal Sizes Size and shapes of colloidal systems can be obtained from scattering measurementsAdvantages of Light ScatteringAbsoluteNo perturbations of systemPolydispersed systemsFast
32Molar Masses from Scattering Obtain the Rayleigh ratio at 90
33The Faraday-Tindall effect 30ºThe distilled solution of absent, solve by water in different ratioCrab nebulosityOpal
34Tooth opalescenceLight for the dental technician is essential, especially when it comes to aesthetics. In a healthy tooth light effects manifest themselves from inside. Separate layers of tissues react for the light at different angles. Interestingly, the structure of dentin and enamel differently behave to the light. Especially noticeable light blue opalescent glow enamel