Fast crystal growth at the surface of organic glasses

Caleb Brian, Lei Zhu, Ye Sun, Dani Musumeci, Zahra Fakhraai, Lian Yu, Mark Ediger (UW-Madison)

Juan de Pablo (U.Chicago), Jamie Forrest (U.Waterloo)

NSF (Chemistry, Solid State Chemistry, Materials Genone Initiative)

1

Outline •  Fast crystal growth at the surface of

organic glasses •  Surface crystals grow up rather than

down •  Fast diffusion at the surface of organic

glasses •  Glass surfaces appear to be in

equilibrium •  High surface mobility accounts for fast

surface crystal growth 2

“Whereas in many metallic glasses nucleation has been observed to be enhanced at the surface, growth rates are usually quite comparable with those in the bulk.” Koster (Mat. Sci. & Eng. 1988, 97, 233)      

[For silicate glasses,] “The crystal growth velocities of crystals in the volume and of the surface layer in the glass volume, as well as of isolated crystals on the glass surface are equal.” Diaz-Mora et al. (J. Non-Crystalline Solids 2000, 273, 81)

Growth in bulk vs. growth at free surface

glass crystal glass ub

us

u b

crystal

3  

Organic glasses can grow crystals faster at the free surface than in the bulk

Cl

Indomethacin(IMC)

N

CO2H

O

O

Fast growth emerges near Tg

Observed in dry N2 and vacuum

Log

u, m

/s

T, K

Crystal growth rate of IMC (α polymorph)

surface bulk

T

Wu, T.; Yu, L. J. Phys. Chem. B 2006, 100, 15694; Pharm. Res. 2006, 23, 2350

g

4  

Surface crystals rise upward while growing laterally

a

c

1500nm

200µm  

b

2µm

α IMC growing at Tg – 2 K Cl

N

CO2H

O

Indomethacin (IMC)

O

upward growth

SEM by D. Musumeci Ye Sun, M. Ediger, L. Yu et al. PNAS 2011, 108, 5990 5  

1µm

2µm

Cross-sectional views by SEM          

crystal

glass (cross-section)

Surface crystals may be only “skin deep”

6  

Surface crystal growth can be inhibited with a nanocoating

Wu, Sun, Li, de Villiers, and Yu. Langmuir 2007, 23, 5148

200µm 200µm

Uncoated IMC glass

7 d at 40 ºC

Coated with 10 nm gold or 2–30 nm polymer

7 d at 40 ºC

15 mm

PDDA

PDDA + + + + +

+ + + + + - - - - -

Layer-by-layer coating of

polyelectrolytes  

PSS

+- +- +- + - - +

+ + + + + - - - - -

PSS - - - - -

IMC glass

7  

Log

u s (m

/s)

Cordierite: 2MgO·2Al2O3·5SiO2 Anorthite: CaO·Al2O3.2SiO2    

OTP

Log ub (m/s)

us = ub

Many organic glasses show fast surface crystal growth, while some inorganics do not

NIF

O NO2

H N CH3

OCH3

CH3

H3CO O

O

N O

OH

O

Cl IMC

N

CBZ O NH2

Me

OMe

OMe

MeO

Cl

O

R

S

 O

O

GSF

8  

Explanations for fast surface crystal growth  

(1) Tension from crystal growth is relaxed at surfaces (Schmelzer et al. 1993)

Crystal is denser

       

(2) Surface mobility and opportunity for upward growth (Sun et al. 2011)

Model 2 better explains data on organic glasses: upward growth and inhibition by nanocoating 9  

Outline •  Fast crystal growth at the surface of

organic glasses •  Surface crystals grow up rather than

down •  Fast diffusion at the surface of

organic glasses •  Glass surfaces appear to be in

equilibrium •  High surface mobility accounts for fast

surface crystal growth 10

0 µm 3 µm

3 µm

0 µm

Gold Nano-Particle Embedding on the Surface of Polymeric and Low Molecular Weight Glassformers

Gold on PS, Tg+50K, 24hours Gold on TNB, Tg-9 K, 180 sec.

Daley, Fakhraai, Ediger, Forrest, Soft Matter (2012) 11

Surface flow and particle embedding happen on different timescales

• Surface flow has a weaker T dependence than embedding – attribute to surface diffusion • Embedding controlled by bulk viscosity • Daley, et al. Soft Matter 2012.

Tg-9 K

12

Depletion layer observed several hundred nanometers from particle

Tg-9 K

13

1µm

2µm

Cross-sectional views by SEM          

crystal

glass (cross-section)

Note presence of depletion layers next to crystals growing at the free surface

14  

Surface diffusion can be measured directly via decay of an imprinted grating (related work on polymers by Russell,

Dhinojwala, and Johannsmann)

Zhu et al., Phys. Rev. Lett. (2011)

Atomic force microscope Visible light microscope

15

Sub-Tg grating decay is caused by surface diffusion (Mullins model)

Zhu et al., Phys. Rev. Lett. (2011)

293 K 1 µm

16

Surface diffusion is MUCH faster than bulk diffusion

Zhu et al., Phys. Rev. Lett. (2011)

107

17

Simulations verify interpretation of grating decay as surface diffusion

Malshe, Ediger,Yu, de Pablo, J. Chem. Phys. (2011) 18

Additional measurements on nifedipene glasses – Brian, Yu J. Phys. Chem. A 117:13303 (2013)

19

Fast surface diffusion appears to be quite general for organic glasses (data from Lian Yu lab)

Zhang, Yu (unpublished)

7-9 orders of magnitude at Tg

20

Aging for up 10 days has no impact on surface diffusion => surface is at

“equilibrium” while bulk is not

21 Brian, Yu J. Chem. Phys. 140, 054509 (2014)

Outline •  Fast crystal growth at the surface of

organic glasses •  Surface crystals grow up rather than

down •  Fast diffusion at the surface of organic

glasses •  Glass surfaces appear to be in

equilibrium •  High surface mobility accounts for

fast surface crystal growth 22

High surface mobility correlates well with large surface crystal growth rates

Brian, Yu J. Phys. Chem. A 117:13303 (2013)

Zhang, Yu (unpublished)

23

Liquid fluidity terminates fast surface crystal growth

•  Hasebe et al., J. Phys. Chem. B (2014) 24

Bulk

Surface

•  Organic glasses can grow crystals much faster at the free surface than in the interior  •  Crystals grow upward while spreading

laterally  

•  The phenomenon is caused by high surface mobility  

•  Nano-coatings can inhibit the process •  Do all organic glasses show fast surface

crystal growth? •  Why observed only for organic glasses (so

far)? Do other glasses not have surface mobility?

Summary

25