Self-assembled nanostructures soft and hard matter

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Hands-On Nano-Technology course Nano-Science Center University of Copenhagen Self-assembled nanostructures soft and hard matter One-day workshop, August 12, 2004 Division of Physical Chemistry 1,

00 Arrival, coffee Lecture on self-assembled nanostructures Group 1: How to make nanostructures in a test tube. X-ray. (Anna) Group 2: Mesoporous silica synthesis. Electron microscope.

1 Hands-On Nano-Technology course Nano-Science Center University of Copenhagen Self-assembled nanostructures soft and hard matter One-day workshop, August 12, 2004 Division of Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University Sweden Anna Svensson Katarina Flodström Schedule Arrival, coffee Lecture on self-assembled nanostructures Group 1: How to make nanostructures in a test tube. X-ray. (Anna) Group 2: Mesoporous silica synthesis. Electron microscope. (Katarina) Lunch at Ideon Group 1: Mesoporous silica synthesis. Electron microscope. (Katarina) Group 2: How to make nanostructures in a test tube. X-ray. (Anna) Lecture hall F Lecture hall F Physical Chemistry 1, level -1 Physical Chemistry 1, level +2 Ideon restaurant (5 min walk, the lunch costs 60 SEK) Physical Chemistry 1, level +2 Physical Chemistry 1, level -1

Self-assembled nanostructures soft and hard matter The aim of today s workshop is to give you hands-on experience with two kinds of nanostructured materials: Soft matter = liquid crystalline phases

2 Self-assembled nanostructures soft and hard matter The aim of today s workshop is to give you hands-on experience with two kinds of nanostructured materials: Soft matter = liquid crystalline phases Self-assembled structures with long-range order, where the molecules are in a liquid state. Hard matter = mesoporous silica Liquid crystalline phases can be used as templates to create hard matter, in this case mesoporous silica. Amphiphilic molecules - surfactants The basic unit in self-assembled structures is an amphiphilic molecule, also known as surfactants (SURFace ACTive AgeNTS) or detergents. Surfactants contain a hydrophilic (water-loving) and a hydrophobic (water-hating) part. The hydrophilic part, the headgroup, is a polar group which can be charged or uncharged. The hydrophobic part, the tail, is non-polar, e.g. a long hydrocarbon chain.

3 Self-assembly in water The hydrophilic part wants to be in contact with water, while the hydrophobic part does not. At a certain concentration the molecules will start to assemble and form aggregates, so called micelles. This is referred to as the critical micellar concentration, cmc. Water If the solvent is oil instead of water, a reversed micelle is formed. The hydrophilic part tries to avoid contact with oil. The hydrophobic part wants to be in contact with oil. Oil How does washing detergent work? Surfactants are present in many products, e.g. wash-up liquid, hair conditioners, food, pharmaceutics, paints etc. In the washing process, the surfactant molecules adsorb to the fat particle that is to be removed. The fat is dissolved by the micelle and transported away by water.

4 Examples of surfactants Ionic surfactant Sodium dodecylsulfate (SDS) CH 3 -(CH 2 ) 11 -SO 4 - Na + Nonionic surfactant Penta-ethyleneglycol mono n-dodecyl ether (C 12 E 5 ) CH 3 -(CH 2 ) 11 -O-(CH 2 CH 2 O) 5 -H Polymeric surfactant Pluronics Poly(EO)-poly(PPO)-poly(EO) H-(OCH 2 CH 2 ) n -(OCH 2 CH 2 CH 2 ) m -(OCH 2 CH 2 ) n -OH Addition of oil - emulsions Emulsions are mixtures of oil, water and surfactants. The surfactant molecules are situated at the oil-water interface. Addition of oil to a micellar solution: % oil micelle oil-in-water emulsion lamellar water-in-oil emulsion reversed micelle The drop size in an emulsion is 1-10 mikrometers. Emulsions are unstable and will eventually separate into oil and water. The drop size in a microemulsion is 10 nanometers. Microemulsions are thermodynamically stable and will not separate.

5 Nonionic surfactants are temperature sensitive Penta-ethyleneglycol mono n-dodecyl ether (C 12 E 5 ) CH 3 -(CH 2 ) 11 -O-(CH 2 CH 2 O) 5 -H When increasing the temperature, the molecules obtain higher thermal energy and a larger amount of configurational changes are possible. The polarity of the ethyleneoxide groups decreases. T Increased temperature - smaller headgroup Increasing temperature for nonionic surfactants gives larger aggregates and long-range order Increased temperature - smaller headgroup change of aggregate curvature! T Lamellar bilayers Elongated (wormlike) micelles Spherical micelles

Colloid chemistry. Lecture 10: Surfactants

Colloid chemistry. Lecture 10: Surfactants Colloid chemistry Lecture 10: Surfactants Applications of surfactants: cleaning/detergents (40%); textiles; cosmetics; pharmacy; paint; food; etc. Etymology Surfactant micelles surfactant molecule spherical