Structure and Dynamics of Glycerol in Gamma-Alumina Nano-pores

G. Campos-Villalobos

…or why glycerol can move faster under confinement? G. Campos-Villalobos

The Classical Picture of Confined Liquids

The equilibrium and transport properties of liquids geometrically confined in nano-sized pores are dramatically different to those in the bulk state

Low mobility

1

Phase Transitions

L

The Curious Case of Glycerol

Temperature

Volume Liquid

Crystal

Glass (1)

Glass (2)

TmTg(1)Tg(2)

Glycerol is a glass-former

Cometics Bio-Inks Heterogeneous Catalysis

2

The Curious Case of Glycerol

3

The Curious Case of Glycerol

3

The Curious Case of Glycerol

3

The Curious Case of Glycerol

3

Model Systems

⇢conf =Mglycerol

Vpore

A measure of the pore saturation

Pore size

Glycerol in Gamma-Alumina

4

{100} hydroxylated facet exposed to the liquid. CLAYFF force-field

Gamma-Alumina

GlycerolOPLS-AA

T = 300K

Order and Symmetry Breaking at Interfaces

(a) (b) (c)Reduction of Pore Saturation

Fully saturated pore Bubble Adsorbed liquid films

⇢conf

5

(a)(b)

(c)

Order and Symmetry Breaking at Interfaces

-30 -20 -10 0 10 20 300

1

2

3

ρconf = 1.2ρconf = 1.0

-30 -20 -10 0 10 20 30-2

0

2

4

ρconf = 0.8ρconf = 0.6

-20 -10 0 10 200

1

2

3

ρ(z

) / ρ

bulk

ρconf = 0.4

-20 -10 0 10 20-2

0

2

4

W(z

) / k

BT

-10 -5 0 5 10

z / Å

0

1

2

3

-10 -5 0 5 10

z / Å

-2

0

2

4

lz = 60 Å

lz = 40 Å

lz = 20 Å

Fully saturated pore

Bubble

Adsorbed liquid films

Formation of discrete molecular layers close to the surface

6

Order and Symmetry Breaking at Interfaces

In-plane ordering

7

Interfacial Effects

The number of HB per molecule is spatially-dependent

8

Interfacial Effects

0.4 0.6 0.8 1 1.2

ρconf / g cm-3

0.6

0.7

0.8

0.9

1

n* H

B/O

H

lz = 60 Å

lz = 40 Å

lz = 20 Å

(a)(b)

(c)

Fully saturated pore

Bubble

Adsorbed liquid films

HB change with confinement length and density

9

Consequences on the Dynamics: HB Networks

0.4 0.6 0.8 1 1.2

ρconf / g cm-3

0

1

2

3

4

τ* H

B

lz = 60 Å

lz = 40 Å

lz = 20 Å

t = 0

r < rHB

r > rHB

HB lifetime

t = ⌧HB

10

Consequences on the Dynamics: Diffusion

-30 -20 -10 0 10 20 300369

ρconf = 1.2ρconf = 1.0

-20 -10 0 10 200246

D||(z

) / D

bulk

ρconf = 0.8ρconf = 0.6

-10 -5 0 5 10z / Å

0

1

2

3

ρconf = 0.4

lz = 60 Å

lz = 40 Å

lz = 20 Å

(a)(b)

(c)

Fully saturated pore

Bubble

Adsorbed liquid films

Local diffusion coefficient

11

Consequences on the Dynamics: Diffusion

-30 -20 -10 0 10 20 300369

ρconf = 1.2ρconf = 1.0

-20 -10 0 10 200246

D||(z

) / D

bulk

ρconf = 0.8ρconf = 0.6

-10 -5 0 5 10z / Å

0

1

2

3

ρconf = 0.4

lz = 60 Å

lz = 40 Å

lz = 20 Å

Local diffusion coefficient

12

Dconf =⌦Dk (z)

↵=

RlzDk (z) ⇢ (z) dzRlz⇢ (z) dz

Consequences on the Dynamics: Diffusion

0.4 0.6 0.8 1 1.2

ρconf / g cm-3

0

1

2

3

4

5

D*

lz = 60 Å

lz = 40 Å

lz = 20 Å

Global diffusion coefficient

Enhanced molecular self-diffusion in confinement

13

Outlook

1 2 3

The solid imposes a heterogeneity in the liquid, causing the structural and

dynamical properties to acquire a spatial dependence

The formation of interfaces with the solid and vacuum regions is found profoundly

affect the kinetics of breaking and re-formation of hydrogen

bonds

A necessary condition for the enhancement in the molecular diffusion is the partial saturation

of the pores

Acknowledgements

Alessandro Patti

Flor R. Siperstein

Carmine D'Agostino

THANK YOU!