The subject of colloid chemistry. Why are so different the colloids? Classification, characterization of colloid systems.

Transcription

1 Colloid chemistry for pharmacists The subject of colloid chemistry. Why are so different the colloids? Classification, characterization of colloid systems. Dr Berka Márta, associate professor Bányai István professor Univ. of Debrecen, Dep. of Colloid- and Environmental Chemistry 1. lecture 1

2 Reading Barnes, GT, Gentle, IR: Interfacial Science A, Oxford UP. ISBN , 2005 Cosgrowe T.: Colloid science Blackwell Publishing ISBN: , 2005 Erbil, H. Y.: Surface Chemistry Blackwell, ISBN , 2006 Pashley, R. M.: Applied Colloid & Surface Chemistry Wiley&Sons, ISBN X, 2004 McCash, E. M.: Surface Chemistry Oxford UP. ISBN , 2001 (2007) Crowe, J.:Chemistry for the Biosciences Oxford UP. ISBN ,

3 Exam, requirements Written test one test in an exam period (2 possibilities) (50-60% mark 2; 61-75% mark 3; 76-85% mark 4; >85% mark 5.) Slides 3

4 Place of colloid science 1. partly physical chemistry not the chemical composition is important the states are independent of the composition 2. partly physics the physical properties are important basic law of physics are used 3. partly biology the biological matters are colloids the mechanisms of living systems surface chemistry (enzymes) perfomation disappear, stability, interaction with external field, force colloid science biology physical chemistry biochemistry organic chemistry chemistry physics The word colloid was derived from the Greek, kolla for glue (1862), distinguish colloids from crystalloids such as sugar and salt. Colloids have been studied by scientists since the early 1800's. The early part of the 20th century saw a number of major developments in both chemistry and physics, some of which had direct influences on the study of colloids. A number of methods for studying colloidal particles were developed, including diffusion, electrophoresis, and scattering of visible light and X-rays. 4

5 Homogeneous, heterogeneous? Homogeneous: isotropic. (5% solution) heterogeneous, Gibbs phases rule Homogeneous one isotropic phase continuum? point like? In case of a colloid system the properties depend of the sampling scale. pv = nrt P + F = C + 2 Gold sol Michael Faraday 1857; Gustav Mie 1908 It is not distinguishable by appearance. Soup, jelly, milk, beer, bread, pudding-pie, fog, smoke, smog, soils, toothpaste, blood, mayonaise, whip, opal, solution of soap, etc. Heterogeneous more phase Colloids can not be classified as homogeneous or heterogeneous system tenzides Aerogel, frozen smoke liogel 5 Xerogel, modern opal

6 1. Definition of colloid state history: Solution and suspension theory, homogeneous-heterogeneous 2. Ultramicroscope, dark field microscope R. Zsigmondy Nobel price: 1925 The colloidal state "for his demonstration of the heterogenous nature of colloid solutions and for the methods he used, which have since become fundamental in modern colloid chemistry" They examined two types of colloids, After cooling one of them jellify, form a gelatin like matter and other type forms crystals they found that this behavior is in relation with the diffusibility that is with the size. He saw some illuminating particles and their conclusion was that this particles had interface so the system must be heterogeneous nature If he had examined a gelatin solution he would have explained that the colloids must be homogeneous systems. This experiment was the first evidence for that the Brown motion is a thermal motion and the Boltzmann-Maxwell kinetic gas theory 6

7 Homogeneous, heterogeneous? Why are not the colloids heterogeneous? Colloids don t obey the rule of Gibbs because the effect of interface between the phases can not be neglected. S/V surface molecules/ total nano the effect of surface can not be ignored 10 % R<10 nm nanotechnology 1 % 0.1 % F = C P+ The phase rule enabled the identification of the number of variables (or degree of freedom) depending on the system composition and conditions. It is generally written as F=C-P+2 where F is the number of possible independent changes of state or degrees of freedom. C is the number of independent chemical constituents and P the number of phases present in the system Increasing specific surface area and surface energy E-7 1.0E-6 1.0E-5 1.0E-4 1.0E-3 1.0E-2 1.0E-1 1.0E+0 R,cm kolloid Surface molecules/total molecules gold sol 7

8 Subject of colloid chemistry: systems consist of particles in size of 1nm 500 nm. (more phases system in which the surface plays a significant role) Homogeneous Atoms, small molecules colloid system smoke Heterogeneous systems (macroscopic phases) macromolecules fog m Homogeneous colloid microscopic heterogeneous 6 10 nm micelles virus pollen, bacterium 8

9 Submicroscopic discontinuity blocks: molecules sûrûség property sûrûség property particles Forming a disperse system by breaking of β phases (any kind of phases except from 2 gas) A: two homogeneous phase form a heterogeneous system D: two component form a homogeneous solution, particles are smaller than 1 nm x W. Ostwald: the colloidal state is independent on the chemical forms Aladár Buzágh : submicroscopic discontinuities x length 9

10 Coherent and incoherent systems Incoherent systems Fluid phase characters Particles moves individually (the cohesive forces attraction is weaker than the thermal energy) Coherent systems solid phase characters (crosslinking by covalent or interparticle forces) (the cohesive forces attraction is stronger than the thermal energy) network structure (the anisometry helps the formation of network ) Intermediate systems (semisolids) concentrated emulsions, suspensions, liofil solutions creams, pastes, gels (thixotropy); sol-gel transformation. 10

11 Type of colloids on the basis of structure colloids Incoherent (fluid) Solid-like consistency Coherent, gel Colloidal Dispersions sols Macromol. solutions Association Colloids Colloidal solutions Porodin (porous) Reticular Spongoid lyophobic lyofhilic lyophilic (IUPAC) gold sol, micro emulsion Gelatin solution, polyelectrolyte tenzid, soap, detergent inorganic catalyzer; fibroids, gel from fibrous molecules: gum, rubber, viscose, natural synthetic fibers, muscle-fibers; spongoid are formed from thin lamellas or films 11

12 Type of colloidal dispersions (sols) categorized by inner/outer phases aerosols liosols xerosols L/G liquid aerosol: fog, mists, spray, perfumes, pesticides S/G solid aerosol, solid in gas: smoke, colloidal powder Complex, smog G/L gas liosol, gas bubbles in liquid (sparkling water, foam, whipped cream) L/L liquid liosol, liquid droplets in liquid, emulsion S/L solid liosol, solid particles in liquid (gold sol, toothpaste, paint, ink) G/S bubbles in solid, solid foam: polystyrene foam L/S solidified emulsion: opals, pearls S/S solidified sols: pigmented plastics, stained glass 12

13 Macromolecules The probably shape and weight of some molecules Illustration of a polypeptide macromolecule Macromolecules are much larger than the solute in a solution, the properties of these particles depend on their size and shape! 13

14 Association colloids Surfactant (soap and detergent) amphiphilic spherical micelle Micelles are the simplest of all self-assembly structures 14

15 gels (coherent systems) Solid-like consistency Gel for example gelatin, collagen, pectin. Gelatin may be used for food as a stabilizer, thickener, or texturizer in foods such as ice cream, jams, yogurt, cream cheese, margarine; it is used, as well, in fat-reduced foods to simulate the mouth feel of fat and to create volume without adding calories. Pharmaceutical capsules in order to make their contents easier to swallow, microcapsule, for photographic films, hair styling cream. ( sol-gel: blood- coagulated blood, milk -sour cream) 15

16 Fundamental forces and energy Gravitational forces tending to settle or raise particles depending on their density relative to the solvent. Colloidal particles are to small to settle out of solution due to the gravity) Viscous drag force Arises as a resistance to motion, since the fluid has to be forced apart as the particle moves through it Kinetic energy of particles, Brownian motion The kinetic random motion will dominate the behavior of small particles if there is not attractive or repulsive force between them. Van der Waals force, a ubiquitous attractive force in nature, electromagnetic in origin Electrostatic repulsion between similarly charged particles Most materials when dispersed on water selectively adsorb ions from solution, and hence become charged. 16

17 Stability Thermodynamic Stable (true solutions): lyophilic colloids G solution < G initial, (ΔG=ΔH-TΔS) Macromolecular solution, association colloids give true solution in thermodynamic sense with the medium which surround them.this is entropic and enthalpic stabilization Not stable: Lyophobic colloids G sol > G initial Sols, of large specific surface area (ratio of surface to volume) Kinetic - Stable (unchanged within the examination ) - Unstable 17

18 Characterization of colloids Buzágh gh: colloidal state parameters 1. Dispersity (or size distribution) Monodispersed, isometric (spheres with the same radius) Heterodispersed, anisometric (rod, plate) 2. Morphology: shape as spheres, cubes, plates, rods etc., inner structure as crystal or amorphous. 3. Spatial distribution 4. Interparticle interaction 18

19 Dispersity (or size distribution) Heterodispersed systems The average diameters Number, surface and volume weighted diameters Polydispersity. Colloidal systems are polydisperse with regard to their size or/and shapes, to a greater or lesser extent. 19

20 d Average diameters The mean and the standard deviation are used to represent for polydispersed systems The arithmetic mean is relevant any time several quantities add together to produce a total. The arithmetic mean answers the question, "if all the quantities had the same value, what would that value have to be in order to achieve the same total?" Arithmetic mean d d φ i i = φi The mean diameter Φ the weighting factor i index the class or fraction Φ the multiplier may be number, surface, volume, intensity, credit etc.. hence number weighted, surface weighted, mass weighted, etc. 20

21 Number average Φ is the factor by which the contribution of the constituent is proportional in the measured property. In case of number average the weighting factor is the number in class. Number average is often referred to as simply the average or mean. Φ=N the weighting factor is number in class Example: colligative properties yield number averages. stb. diameters: 1, 2, 3, 4, 5, 6, 7, 8, 9,10 φ = i d N Ni Li 55 = = = N 10 i 5.5 Number of class, N i =1 N i = 10 The total number of particles The length of the string 55 is the same from the original spheres and from spheres of average 21 size

22 Calculation of the number average Properties, d i, diameter, N i the weighting factor, number Sample: L d N L Li dini = = = = = = N N N i i 4 N 1 =2, d 1 =1; N 2 =1, d 2 =10 L N=3, d N =4 The average diameter: 4. meaning: 3 pieces with length of d N =4 together give the same length (L) than the original string The number is known and remain valid for the average spheres 22

23 Other weighted averages The measurement of colligative properties results number average The numbers or diameter are not known or there is not any tool for their determination. It is known the correlation between the volume and surface, V/S (the constants are neglected!): L S = d N 2 i i i hence V = d N 3 i i i V / S = d ( = 9,8)? N 1 =2, d 1 =1; N 2 =1, d 2 =10 We can measure the total volume and total surface and calculate the diameter. What kind of diameter is V/S? 23

24 Surface weighted averages When the numbers are not known, For example the number of drops in a mug of milk. d?( = 9,8) >> d N ( = 4) d? ( = 9,8) d2( = 10) Comparing the definition of arithmetic mean it can be seen, that the weighting factor is the surface S weighting factor x x φ i i = φi d S V V d S d N ~ = = = = = 9.8 S S S d N i i i i i i i i i 1 2 if d i and N i known S/d s2 = 1.06 pieces V/d s3 = 1.06 pieces 1.06 pieces of d~9.8 spheres have the same total volume and surface as the origin ones. The number changed! d N < d S 24

25 Mass weighted averages When the numbers are not known, for example particles in a sack of powder. Sample: We got a sack from the previous spheres. We select them by sieve, measure their weights and calculate an effective diameter. N 1 =?, d 1 =1; N 2 =?, d 2 =10 W But what kind of??? d? dw + dw dw i W + W W = = 1 2 i i x x φ i i = φi This is a volume or mass weighted average 25

26 Mass weighted averages When the numbers are not known. From the original system d w ( = 9,98) d ( = 10) 2 d W W 4 = dw i i di Ni W = d N = i i i W/d w3 = ps In this average the larger particles dominate. (for example the center of mass.) if d i and N i known The number changed! dn < ds < dw 26

27 Why we need the different average? The different experimental method perceive the polydispersity systems with different way. They are sensitive for different properties of the fractions so they result different averages. N 1 =2, d 1 =1; N 2 =1, d 2 =10 d N = 4 d S = 9,8 d W = 9,98 Φ=N Φ=S Φ=W (more dozens average exist) x x φ i i = φi The average does not say anything from the details Beside the average we have to give the average deviation or the polydispersity, PD for characterize the distribution. PD = d / d 2.5 w N 27

28 Polydispersity d d w N 1 Example: 1, M A = 1, N A = 100, M B =100, N B =1 2, M A = 1, N A = 100, M B =100, N B =100 3, M A = 1, N A = 1, M B =100, N B =100 1) 2) M / M = 25 W M / M = 2 W 3) M / M = 1.01 W N N N M n NM i = Ni i M M molar mass, W weight, N number w WM ( NM) M NM = = = W N M N M 2 i i i i i i i i i i i i 28

29 Polydispersity xn < xs < xw PD xw = 1 x N M NM 2 i i w = NM i i M n NM i = Ni i Sample: A M= 1, B M= pcs A + 1pc B 100 pcs A pcs B 1 pc A pcs B M W = = 50, M W = = 99, M W = = M N = = 1, M N = = 50, M N = = M / M = 25 W N M / M = 2 W Number or pc~ piece; pcs pieces N M / M = 1,01 W N 29

30 Polydispersity Sample A: M= 100, B: M= pcs A + 1pc B 100 pcs A pcs B 1 pc A pcs B M / M = 5050 /198 = 25 W N M / M = 9999 / 9902 = 1,01 W N M / M = 9902 / 5050 = 2 W N M molar mass, W weight, N number Only the ratio of the molar masses is important, not their absolute values pc~ piece; pcs pieces 30

31 Normal distribution, cumulative function 100 % mean + σ σ = 15 mean ± σ ~ 68 % The Φ cumulative distribution function describes probabilities for a random variable to fall in the intervals of the form (0, x) or (-, x). 16 mean - σ x f(x) probability density function is "bell"- shaped, and is known as the Gaussian function, it describes the relative likelihood for this random variable to occur at a given point 31

32 Normal distribution, dφ f x x dx ( ) = ( ) frequency function 1 ( x x) f( x) = exp 2 2πσ 2σ 2 ( x x) 2 dϕ 2 σ = ϕ where parameter is the mean (location of the peak) and σ 2 is the variance (the measure of the width of the distribution). The distribution with and is called the standard normal. x ± σ 68% 32

33 Determination of sizes Sieve 25 micron-125 mm Wet sieve 10mikron-100 mikron Microscope 200 nm-150 mikron Ultramicroscope 10 nm -1 mikron Electron microscope 1 nm- 1 mikron Sedimentation d>1 micron (colloidal particles are to small to settle out of solution due to the gravity) Centrifuge d<5 micron Light scattering 1 nm- some microns 33

34 2. Morphology (shape, inner structure) 1. Prolate (a>b), 2. oblate (a<b), 3. rod, 4. plate, 5. coil Irregular particle, equivalent radius 34

35 3. Spatial distribution, ordered structure Homogeneous Diffuse (or exponential) Heterogeneous Ordered Special behavior nematic smectic tactoid The diffuse distribution or Boltzmann distribution law says that if the energy associated with some state or condition of a system is ε then the frequency with which that state or condition occurs, or the probability of its occurrence, is proportional to exp ( ε/kt), where T is the system s absolute temperature and where k is the Boltzmann constant, 35