Colloid Chemistry Lecture #2 Association colloid 1 https://ilustracionmedica.wordpress.com/2014/08/27/fisicos-haciendo-medicina-john-tyndall/
Solution Classical vs. Colloid solution Tyndall effect Increased ion size NaBr At high c (3M 16 w%) 4M ( 20 w%) 5M ( 25 w%) J. Chem. Phys. 2016, 144, 204126. precipitation (e.g. inorganic chemistry) Classical state functions: Composition (x i, w% i, c i, c T,i etc.) (Colour, smell) T V P U H S G A Further state descriptors: Particle morphology Distribution Dispersity 2
Association (self-assembled) colloids In solution, tensides (molecules having polar and apolar sites) are associated by secondary chemical bond making micelles which are in chemical equilibrium with tenside solution (their formation is spontaneous process and they achieve thermodynamic stability). Transition between classical solution and sols Microheterogenous systems with at least two components equilibrium Micelle hydroapathetic hydrophilic Phys. Chem. Chem. Phys., 2014, 16, 8594. Sodium dodecyl sulfate (SDS) micelle J. Phys. Chem. B 2007, 111, 11722. 3
Classification of tensides I. According to their chemical structure: Nonionic tensides: Non dissociable hydrofil group(s) attached to hydroapathetic groups Anionic (anion active) tensides: Anionic group(s) attached to hydroapathetic groups Cationic (cation active) tensides: Cationic group(s) attached to hydroapathetic groups Amphoteric tensides: Zwitterionic group(s) attached to the hydroapathetic group hydrofil large µ (5D<µ) hydroapatic lipofil 4
Classification of tensides II. R: saturated and unsaturated hydrocarbon chain, # of carbon in the chain: 8-18 Counter ion: X + : Na +, K + Y - : Br -, Cl - 5
Classification of tensides III. According to their origin: Natural tensides: Ramnose lipid Soforose lipid Synthetic tensides: Optik 2016, 127, 2740. 6
Size, shape and structure of micelles Depending: Molecular structure of the tensides solvent c tensid c electrolyte temperature Dynamic equilibrium (Continuous exchange of tenside between the micelles and the solution, t exchange = few ns) Geometric parameters: a,b,t Aggregation number: average number of tenside in a micelle 7 PLoS ONE 2013, 8, e62488.
Classification of the association colloids Solvent: Micelles: In aqueous solution Inverse micelles: In nonaqueous solutions Size of aggregates are smaller than micelles In apolar solvent, only small HLB tensides can be dissolved Micelle Inverse micelle 8
Hydrophilic-lipophilic balance (HLB) Water solubility HLB scale (Nonionic tenside) Application Lipophilic Journal of Soil Science and Plant Nutrition, 2012, 12, 667. 9
Hydrophilic-lipophilic balance (HLB) ICI standard for selection of the optimal emulsifying agents Davies (HLB of the tenside): HLB molecule = 7 + H hydrophilic + H lipophilic HLB SDS = 7 + 38,7 + 12 0,475 = 40,0 Griffin method (for tenside mixtures): HLB = (HLB molecule,i w molecule,i ) Online: International Journal of Pharmaceutics 2008, 356, 44. http://www.firp.ula.ve/archivos/historicos/57_chap_davies.pdf http://www.al-nasir.com/www/pharmcalc/exec_calc.php?id=hlb Hydrophilic group -SO 4 Na + 38.7 -COO K + 21.1 -COO Na + 19.1 N (tertier amine) 9.4 sorbitane ester 6.8 Free ester 2.4 -COOH 2.1 free OH 1.9 -O- 1.3 Sorbitane OH 0.5 Lipophilic groups -CH- -0.475 -CH 2 - -0.475 CH 3 - -0.475 10 =CH- -0.475 H hydrophilic H lipophilic
Physical properties Physical chemical properties of association colloids I. Association colloids differ from classical solution at high concertation: Surface tension Specific and equivalent electric conductivity Osmotic pressure Decrease in vapor pressure Increase in Freezing point Micelle formation J. Colloid Interface Sci. 2012, 370, 102. Osmotic pressure Specific electric conductivity Eq. electric conductivity Surface tension Freezing point http://www.dataphysics.de/2/start/understanding-interfaces/basics/surfactants-and-critical-micelle-concentration-cmc/ CMC Concentration 11
Physical chemical properties of association colloids II. Surface tension (γ) Adsorption of tenside molecules at the air/solution interface Decrease in the surface tension compared to the neat solvent At c > CMC, there is no change in the tenside coverage at the interface since new tenside molecules are involve in the micelle formation. No change in the surface tension Specific and equivalent electric conductivity In the case of c < CMC: the ion concertation increasing with the adding ionic tensides to the solution, therefore the electric conductivity increases By the micelle formation, the ion mobility is decreased therefore the conductivity is only slightly increasing by adding tensides to the solution. Osmotic pressure, decrease in vapor pressure, increase in freezing point Colligative properties depends only from the ion concertation which is affected by the micelle formation 12
Critical micelle concentration (CMC) Other notation (IUPAC): c.m.c., cmc, c M Unit: mm (mmol/dm 3 ) mg/l (mg/dm 3 ) PLoS ONE 2011, 6, e19850. 13 Further cmc values: https://nvlpubs.nist.gov/nistpubs/legacy/nsrds/nbsnsrds36.pdf
Thermodynamic of the aggregation I. Equilibrium of the aggregate formation : G agg = RTlnK agg = RTln X n G agg = RTln X n Formation of aggregate from tenside solution: X n + nrtln X X n = 10 10 M (small, existence of the aggregates) X = 10 3 M = 1mM n > 50 (small aggregation number) G agg = RTln X n + nrtln(cmc) (typical CMC value) RTln(CMC): average molar free energy contribution of tenside molecule G agg = 57 kj mol + 50 17 kj mol kj 800 mol (K agg = 10 140 ) CMC = n X n K agg n[x] [X n ] + X X [X n ] 14 http://cdn.intechweb.org/pdfs/13118.pdf [X]
Thermodynamic of the aggregation II. Isothermal titration calorimetry (ITC) CMC determination of SDS by ITC Integration Frontiers in Microbiology, 2015, 6, 1049. CMC 15 Colloid Polym. Sci. 2011, 289, 3.
Factors changing CMC Accociaiton behavious depends on theintermoleculari nteractions: G agg = RTln X n G agg + RTln X n n + nrtln CMC = G agg = RTln(CMC) CMC decreases by increasing the carbon chain length (N C ) : lg CMC = a bn C tenside-tenside interaction increases The non ionic tenside has lower CMC value compared to the ionic tenside in the same size Smaller tenside-solvent interaction Higher the charge in the counterion smaller the CMC Larger tenside-counterion interaction CMC decreases by the decresing solvation of the counterion Smaller solvent-counterion interaction By adding electrolyte the CMC decreases lg CMC = a blgc electrolyte Smaller the dissociation of the ionic tenside Tenside-tenside interaction Tenside-solvent interaction Tenside-counterion interaction Solvent-counterion interaction Solvent-solvent interaction 16
Composition of Surface and bulky tenside solution 1dm 1dm 2 6,6 10-8 mol SDS 1dm High purity material with contaminated surface CMC(SDS)=8.2 mm A m (SDS)=0.25nm 2 =2.5 10-17 dm 2 V=1dm 3 A=1dm 2 Is there case when CMC does depend on the surface? 1dm 8,2 10-3 mol SDS 17
Interfacial structure of tenside solutions 7 nm 2 /SDS molecule 0.52 nm 2 /SDS molecule Monolayer coverage SDS Langmuir 2010, 26, 5462. DTAB C 12 E 10 A: a representative SDS in high surface concentration zone B: a representative SDS in low surface concentration zone Langmuir, 2014, 30, 10600. J. Phys. Chem. B 2011, 115, 2518. 18
Temperature effect on the solubility & micelle formation of ionic tensides By increasing the temperature the solubility of the ionic tensides will: Slightly increase At c tenside > CMC: rapidly increasing The average mass of the micelles decreases by the increasing temperature c tenside Saturated tenside solution + Solid tenside Saturated tenside solution + solid tenside + Micelles Micelles + Tenside solution tenside solution Krafft point T( C) https://www.stevenabbott.co.uk/practical-surfactants/cloud-krafft.php 19
Temperature effect of the solubility and micelle formation ability of nonionic tensides The CMC of nonionic tensides decreases by the increasing temperature The average mass of the micelle increases dramatically by the evaluation of the temperature At a characteristic temperature, the solubility of nonionic tensides drops After the size of micelle increased (cloudy), phase separation c tenside a b Micelle + Tenside solution Tenside solution CMC(T) T( C) Micelles Concentration of the micelle solution Two-phase system Concentration of the tenside solution Tenside solution Current Opinion in Colloid & Interface Science, 2016, 22, 23. 20 Physicochemical and Engineering Aspects 2001, 183 185, 95.
Analogy - solubility Formation of spatial discontinuation Concentrated NaCl solution (saturated 26% at 25⁰C) (3M 16 w%) 4M ( 20 w%) 5M ( 25 w%) J. Chem. Phys. 2016, 144, 204126. NaCl percolation network 21 https://www.tf.uni-kiel.de/matwis/amat/iss/kap_6/illustr/i6_2_2.html
Solubilisation Make a solution form a poorly soluble materials by means of tensides This is due to the micelle formation Spontaneous The formed solubilisatum can be either fluid or solid https://femina.hu/otthon/kezi_mosas/ Tenzid: Szolubilizátum: Apolar solubilisatum Amphiphatic solubilisatum Solubilisatum molecules adszorb on the surface of micelle Solubilisatum molecules inserted into the void of the nonionic tenzids 22
Phase equilibrium L lamellar phase; H 1 hexagonal phase (normal type); H 2 hexagonal phase (reversed type); I 1 isotropic solution (normal micelles); I 2 isotropic solution (reversed micelles); K liquid crystalline phase, presumably with rod-like reversed micelles (non-hexagonal packing Glycerine-monooleate Cetyl-trimethylammonium-bromide Biochemical Society Transactions, 2011, 39, 725. 23 Soft Matter, 2012, 8, 11022.
Applications Solubilizing agent Detergents Emulsifying agent Wetting and spreading agent Antifoaming agent Overall growth on a volume basis in the major world areas is expected to average almost 3% annually during 2015 20. https://www.ihs.com/products/chemical-surfactants-scup.html http://tudasbazis.sulinet.hu/hu/szakkepzes/kereskedelem-es-marketing/kereskedelmi-es-marketing-modulok/mososzerek/mososzerek-fogalma-osszetetele 24
Colloids http://kolloid.unideb.hu/wp-content/uploads/pharmacy/colloid1_intr.pdf 25
26