Crosslinking silica-based 

nanoporous networks under 

ambient conditions

Caleb Wigham

Ryan Murphy

Katie Weigandt

Yun Liu
Properties of Nanoporous Silica Networks

2

2

Catalysis - High Surface Area

High Porosity

Low Thermal Conductivity

Hydrophobic

Low Surface Energy and High 

Contact Angle

1

500 nm!

3

1. Zhang, H.; Gu, W.; Li, M.-J.; Fang, W.-Z.; Li, Z.-Y.; Tao, W.-Q. Influence of Environmental Factors on the Adsorption Capacity and Thermal Conductivity of Silica Nano-Porous Materials. 

J. Nanosci. Nanotechnol. 2015, 15 (4), 3048–3054.

2. https://news.softpedia.com/news/Omniphobic-Material-Repels-Any-Liquid-97625.shtml

3. Catal. Sci. Technol., 2016,6, 2465-2466
Building Nanoporous Silica Networks

TEOS + Water + Base

4

4. https://www.sciencedirect.com/science/article/pii/S002230931300522X#f0015 3

Tetraethyl orthosilicate

monomer
Removing the Solvent

4

Supercritical Drying

Freeze Drying

Ambient Pressure Drying (APD)

Advantages

• Lower Cost

• Fewer Synthesis Steps

• Easier Scalability

Disadvantages

• Harder to Control

• Destructive Capillary Forces
5

Ambient Pressure Drying

Air

Bond 

Breakage

ppcc =

2γγcos(θθ)

rrcc

Solvent

γγ = iiiiiiii iiiiiiiiiiii tt tt

rrcc = rr rr rr iiiiiiii iiiiiiii

ppcc = cc pp rc = 100 μm 

rc = 10 nm pc = 56 atm

pc = 0.0056 atm
New Synthetic Approach

6

Air

Solvent

Polymer Linkages 

Provide Flexibility
7

SiO2

NP

-OH

-OH

-OH -OH

-OH

-OH

-OH

-OH

-OH

Silica Nanoparticles

Toluene

Diisocyanate (TDI)

Our Approach 

Pluronic Block-Copolymer

Catalyst
Problems Encountered

8

Particle and Polymer Effects

Shape and Molecular Weight

Rate of Solvent Evaporation

Phase Separation Catalyst Addition Delay after Reaction

Slow Fast

Spherical Random Difunctional BlockCopolymer

0 Hours 2 Hours
Particle and Polymer Effects

9

Spherical

Random

Increasing Polymer Molecular Weight
What is SANS?

10 5. Monica Castellanos, Maria & Mcauley, Arnold & Curtis, Joseph. (2016). Investigating Structure and Dynamics of Proteins in Amorphous Phases Using Neutron Scattering. 

Computational and Structural Biotechnology Journal. 15. 10.1016/j.csbj.2016.12.004. 

P(Q)

S(Q)

P(Q): Form Factor – particle shape, size, dispersity

S(Q): Structure Factor – spatial distribution of particles, 

interactions between particles

5

qq =

4ππ

λλ sin(θθ)
SANS Before Solvent Evaporation

11

Df ≈ 1.6 to 2.0

2π/D

D ≈ 10-15 nm

2π/ξ

ξ ≈ 100-150 nm

Solvated 

Silica Particle 

Network
SANS After Solvent Evaporation

12

Do more significant structural 

changes occur at larger 

lengths (smaller q)? 

No major structural changes 

on the nanoscale 

Dried

Silica Particle 

Network

Df ≈ 1.6 to 1.9

2π/D

D ≈ 10-15 nm

2π/ξ

ξ ≈ 100-150 nm
Problems Encountered

13

Particle and Polymer Effects

Shape and Molecular Weight

Rate of Solvent Evaporation

Phase Separation Catalyst Addition Delay after Reaction

Slow Fast

Spherical Random Difunctional BlockCopolymer

0 Hours 1.5 Hours
Summary of Key Results

14

• Incubation time of ~2 hours 

greatly increases structural 

integrity

• Slow solvent evaporation 

dispenses stresses

• Optimum polymer additive 

molecular weight ~ 3800 g/mol

Slow Fast

0 hours 1.5 hours

1100 g/mol 3750 g/mol
Future Work

15

• Quantify effect of particle shape, size, and structure

• Mitigate phase separation using incubation times and 

solvent variations

• Use uSANS for larger length-scale probing

• Measure accessible surface area and thermal conductivity
Acknowledgements

16

• Ryan Murphy – Mentor

• Katie Weigandt - Co-Mentor

• Julie Borchers, Joe Dura – NCNR SURF Directors