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.

.Chem. Rev., 2002, 102 (11), pp 4093–4138

Zeolite: silicalite

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

Solvent molecules can act as templates

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

Cited over 10,200 times

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.

Size of MCM 41 pores can be controlled by process conditions

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!!!!!!

Traditional ionic surfactants used in mesoporous materials templation

Traditional non-ionic surfactants used in mesoporous materials templation

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

Phase separation: surfactants

Phase separation: surfactants

Adv. Mater 1999, Brinker

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

Published in: Avelino Corma; Chem. Rev. 1997, 97, 2373-2420.

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.

Plane-projection of CDF (a), respective TEM image fragment (b) and its simulation (c).

Electronic density maps and bicontinuous cubic structure of MCM-48

Chem. Mater., 1996, 8, 1141

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

Making Hybrid Materials: Class 2C(Templating) Shown here with block copolymer

Polymer phase separation templation of macropores

Chem. Rev., 2011, 111 (2), pp 765–789

How organic templates can control porosity of materials

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