When Polymers Meet: SelfAssembled Amphiphilic 

Diblock Copolymers

CANDYCE COLLINS, DR. KATIE WEIGANDT, DR. AVANISH 

BHARATI

AUGUST 3 RD ,2019

NIST-SURF

1
Self-Assembly 

Self-Assembly in micelles:

Hydrophilic tail

Hydrophobic head

2

Song, Xianyu et. Al. (2018). 

Molecular crystals 

Micelles 

Colloids

Lipid bilayers 
How does diblock ratio and solvent quality effect the shape and size of 

particles? 

What does self-assembly have to do 

with this research? 

3

PEO block PLLA
Nucleation and Growth

Nucleation/growth

Sonication CrystallizationDriven Self 

Assembly (CDSA) 

Solvent-induced crystallization 

at 550C: 

Crystallization in solution 

Block B

soluble insoluble

block A block B

Amorphous corona

(flexible chains)

Crystalline core

(folded chains)

Poly-dispersed 

structures

(pre-seed)

Polymer solution

Near crystallization temperature slowly alter the solvent quality to a good solvent for the corona and theta solvent for the crystallizing core

PEO block PLLA

4
Experimental Conditions 

• Solvent quality 

◦ THF/D2O 

◦ Acetone/D2O (forms a homogeneous mixture at all experimental temperatures 

and compositions – inferred from Dynamic Light Scattering and Small-angle Neutron 

Scattering)

✔

✗

Conditions/Parameters varied: 

5
Nucleation/growth

Sonication CrystallizationDriven Self 

Assembly (CDSA) 

Sonication

6

Mono-dispersed 

structures

(seed)
Dynamic Light Scattering (DLS) 

Conditions Hydrodynamic

radius in nm [r]

% Polydispersity

(in size)

Pre Seeds ~ 450 ~ 45

Seeds ~ 80.0 ~ 8.0

D – Diffusion constant

ΚB – Boltzmann’s constant

T – Temperature 

η – Viscosity (solvent)

r – Radius of the spherical particle

7
Small-Angle Neutron Scattering (SANS)

8

Neutron beam source  sample  2D detector and reads the information with intensity (l, q) and momentum transfer (q)

Monica Castellanos, et. Al.(2016)
100

101

102

103

104

 I(q) (cm

-1

)

2 3 4 5 6

0.01

2 3 4 5 6

0.1

2 3 4

 q (Å

-1

)

 PreSeed 2K-20K

 Seed 2K-20K

1D Small-Angle Neutron Scattering (SANS) 

Preseeds vs seeds

Sonication resulted in smaller structures.

9

-1 -4

Temperature: 55°C

Solvent: 10 wt % Acetone to D2O
100

101

102

103

104

 I(q) (cm

-1

)

2 3 4 5 6

0.01

2 3 4 5 6

0.1

2 3 4

 q (Å

-1

)

 Seed 2K-5K

 Seed 2K-10K

 Seed 2K-20K

SANS on Seeds 

Increasing the block asymmetry

resulted in particles of different

shapes.

Effect of block ratio: 

10

-1

-2

-4

Temperature: 55°C

Solvent: 10 wt % Acetone to D2O
100

101

102

103

104

 I(q) (cm

-1

)

2 3 4 5 6

0.01

2 3 4 5 6

0.1

2 3 4

 q (Å

-1

)

 Seed 1K-10K

 Seed 2K-20K

100

101

102

103

104

 I(q) (cm

-1

)

2 3 4 5 6

0.01

2 3 4 5 6

0.1

2 3 4

 q (Å

-1

)

 Seed 1K-5K

 Seed 2K-10K

Small PLLA in highly asymmetric blocks do not undergo self-assembly 

Effect of PLLA length for a fixed block ratio 

SANS on Seeds 

PLLA length effects the shape of particles 

Block ratio of 1:5 Block ratio of 1:10

11

Temperature: 55°C

Solvent: 10 wt % Acetone to D2O

-1

-1

-2
Crystallization-Driven Self Assembly (CDSA): 

Tuning aspect ratio

Basic idea:

Aim: Long fairly 

Mono-dispersed structures

Minimize self-nucleation of micelles

Minimize the propensity of seeds to attach and grow

Promote stable seeds and epitaxial growth of polymers on 

seeds 

Add polymer 

solution

Longer particles

Good solvent for PEO corona and marginal to bad solvent for PLLA core 

Nucleation/growth

Sonication

CrystallizationDriven Self 

Assembly (CDSA) 

Thank you 

Seeds

✔
Effective concentration: ~5-10 mg/mL

Solvent: 10 wt % Acetone to D2O

SANS data on Seeds and CDSA: Choosing the 

appropriate temperature

0.1

1

10

100

1000

 I(q) (cm

-1

)

2 3 4 5 6

0.01

2 3 4 5 6

0.1

2 3 4

 q (Å

-1

)

 Seed 1K-5K at 55°C

 CDSA_1K-5K at 0°C

 CDSA_1K-5K at 20°C

 CDSA_1K-5K at 40°C

The shape of the particle is unaffected at 400C

Seeds (1K-5K) vs CDSA (1:1)

13
3x10-1

4

5

6

7

 I(q) (cm

-1

)

0.01

2 3 4 5 6 7 8 9

0.1

2

 q (Å

-1

)

 PEO polymer Seeds 1K-10K

 CDSA 1K-10K

Seed response is similar to that of PEO of the corresponding length: no self-assembly occurs 

SANS data on Seeds and CDSA for short and 

highly asymmetric diblocks

CDSA temperature is 40°C

14
On-going and Future Research 

•Preparing seeds and CDSA for 1K-7.5K and 2K-15K to form 1D particles with

varying aspect ratio.

•In the future, the findings will provide a toolbox of particles with varying aspect

ratio to answer the fundamental questions relevant to the flow behavior of soft

materials.

15
Acknowledgements

NCNR:

Julie Borchers 

Joe Dura

Katie Weigandt

Avanish Bharati

Ryan Murphy

Elizabeth Kelley 

SURF Fellows NCNR Soft Matter Group

Fayetteville State University:

Cevdet Akbay

Zhiping Luo

Gibin George

16
17
Facilitate the formation of 1-dimensional rod-like structures

Decrease the thickness to broaden the accessible length

18

Currently used 

PEO/PLLA DOP

= 5:1 (block ratio)

Reference samples

Only PLLA polymer PEO with increasing Mn as in the diblocks

Increasing the length of PEO block for fixed PLLA block 

Block ratio (10:1) and Block ratio (20:1)

Procured

Increase l

c more 

rapidly than V

Procured

CANDYCE COLLINS, KATIE WEIGANDT, AVANISH 

BHARATI

AUGUST 2ND,2019
19