key concepts
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Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 13: Using surfactants to template materials. Key concepts. Surfactants are amphiphiles with polar head groups and non-polar tails (like soap molecules) Surfactants can be cationic, anionic, or neutral. - PowerPoint PPT PresentationTRANSCRIPT
Physics and Chemistry of Hybrid Organic-Inorganic Materials
Lecture 13: Using surfactants to template materials
Key concepts• Surfactants are amphiphiles with polar head groups and non-polar tails
(like soap molecules)• Surfactants can be cationic, anionic, or neutral.• Surfactants can be small molecules or block- copolymers.• Surfactants in water or organic solvents will organize into liquid crystalline
like structures with two phases (or more).• Hybrid monomers can be polymerized in one or the other of these phases.• The structure of the surfactant templates the growth of the hybrid
material.• Once the polymerization is done, the surfactant can be calcined or
extracted out, leaving pores where the surfactant phase resided.• The resulting materials are highly ordered on nm to 10 nm length scales
with hierarchical structures. (MCM 41, MCM 48• Structures include gyroid, double gyorid, hcp, cubic and more.
Templating of structures and pores in hybrids, inorganics and organics
In templating, you build a material around some molecule, macromolecules or liquid crystal
Opals were used as templates for inverse opals and photonic solids (described in an earlier lecture).
At high concentrations, surfactants organize into multi-phase structures that can template structures.
This is the mechanism Nature uses to make hybrids like Nacre and bone.
Solvent molecules can act as templates
Depending on compliance of network, porosity may be retained or completely lost
Imprinting is also a kind of
pore templating
C. Lin, A. Joseph, C.K. Chang, Y.C. Wang, Y.D. Lee Anal. Chim. Acta, 481 (2003), p. 175
Surfactant phase diagrams: oil + water + soap
cylinders
lamellae: stacked 2D layers
dispersed spheres of Ain body centered cubic array in continuous phase of B.
micelles
First model for surfactant templating: assumes liquid crystal occupies entire solution
A few nanometers in diameter
1) n-Hexadecyltrimethylammonium bromide (2.5 g, 0.007 mol) was dissolved in deionized water (50 g)2) To this surfactant solution, 13.2 g of aqueous ammonia (32 wt.%, 0.25 mol) and 60.0 g of absolute ethanol (EtOH, 1.3 mol) were added and the solution was stirred for 15 min (250 rpm).3) TEOS (4.7 g, 0.022 mol, freshly distilled) was added at one time resulting in a gel. 4) After stirring for 2 h the white precipitate was filtered and washed with 100 ml of deionized water and 100 ml of methanol. 5) After drying overnight at 363 K, the sample was heated to 823 K (rate:1 K min−1) in air and kept at that temperature for 5 h.
Synthesis of MCM-41 spheres
Microporous and Mesoporous Materials, 1999, 27, 207–216
Synthesis of MCM-41 silica spheres
Microporous and Mesoporous Materials, 1999, 27, 207–216
X-ray diffraction pattern of an MCM-41 sample prepared in heterogeneous medium with n-hexadecylpyridinium chloride as template.
TEM image of the honeycomb structure of MCM-41 and a schematic representation of the hexagonal shaped one-dimensional pores.
A close look at the structure shows that it is made of small amorphous silica particles
Just like the silica in living sponges> 1 nm in size
X-Ray Diffraction (XRD)
These materials show peaks at very small angles = larger structures than are typical in crystalline materials
The Mobil patent was duplicating something already in the literatureSomebody did not do a careful literature search!!!!!!
Using other phase separations to control how particles aggregate
Surfactants
Polymers
Block copolymers
Hydrophilic Phase
Hydrophobic PhaseMonomers are often dissolve in this phase
Hydrolyzed monomers and polymers are often dissolve in this phase
Polymers are not very soluble in each other and will phase separate like oil and water
Larger structures
Smallerstructures
Liquid crystal forms then monomer enters and reacts
Monomer starts reacting and interacting with surfactant as the liquid crystal forms
Pore models of mesostructures with symmetries of (A) p6mm, (B) Ia3Ad, (C) Pm3An, (D) Im3Am, (E) Fd3Am, and (F) Fm3Am.
MCM-41
FDU-12SBA-16
SBA-1
FDU-2
MCM-48
Structure of SBA-1 or SBA-6 observed as an electron density and described either in terms of a clathrate structure or as a surface enveloping the micellar templating agents Nature, 2000, 408, 449
Electron micrographs of SBA-1 and SBA-6 along [100]
What are some of these materials and what do they look like (SBA-Santa Barbara.
HREM images of CMK-4 along the three zone axes [100], [110] and [111] together with a representation of the carbonaceous surface.
J. Phys. Chem. B, 2002, 106, 1256
Tools for hierarchical materials structures
Phil. Trans. R. Soc. A 28 April 2009 vol. 367 no. 1893 1587-1605
• Surfactants are amphiphiles with polar head groups and non-polar tails (like soap molecules)
• Surfactants can be cationic, anionic, or neutral.• Surfactants can be small molecules or block- copolymers.• Surfactants in water or organic solvents will organize into liquid crystalline
like structures with two phases (or more).• Hybrid monomers can be polymerized in one or the other of these phases.• The structure of the surfactant templates the growth of the hybrid material.• Once the polymerization is done, the surfactant can be calcined or
extracted out, leaving pores where the surfactant phase resided.• The resulting materials are highly ordered on nm to 10 nm length scales
with hierarchical structures. (MCM 41, MCM 48• Structures include gyroid, double gyorid, hcp, cubic and more.
Summary