Synthesis of 3-D conducting polymers via

templating methods and application to

electrochromic devices

Jul 02, 2014

Shravan Tickoo(Advisor : Prof. Seokwoo Jeon)Flexible Devices & Metamaterials Laboratory

Department of Materials Science and Engineering

KAIST

Introduction

– Nobel Prize in Chemistry 2000

Alan J. Heeger

Alan G. MacDiarmid

Hideki Shirakawa

Conjugated polymer

Polyacetylene– oxidation with halogen vapor (doping) made

109 times more conductive than original

Electrochromic device can change

color by an electron transfer process

or by a sufficient electrochemical

potential reversibly

Application of conducting polymers

Electrochromic device

Sensor Transparent electrode

Battery

Introduction

Colloidal Self-Assembly

Y. A. Vlasov, et al., Nature 2001

Photolithography;

Woodpile Structure

S. Y. Lin, et al., Nature 1998

Proximity field

nanoPatterning

PNAS, 101, 12428 (2004)

New Material Property- Photonic band gap

- Antireflection

- Superhydrophobicity

High Capacity- Data storage devices

- 3D electrodes for energy devices

Advantage of three-dimensional structure

Objective

Timeline of Research Work

Synthesis of colloidal particles suitable for colloidal templating in the

size range of 200 nm to 300 nm . (Used : Silica spheres for the

experiment)

a) Highly mono-dispersed particles were desired.

b) Particles were grown and regrown to attain desired size

range and analyzed for mono-dispersion.

Preparation of colloidal templates using above grown particles

a) Colloidal templates were made, using above grown particles

on an ITO or FTO substrate.

b) It was done either by evaporation or spin-

coating method.

Timeline of Research Work

Infiltration of Conducting Polymers on the prepared templates .

(Used : PEDOT and PANI in the experiment )

a) Monomers used: E-DOT and Aniline.

b)Electropolymerization of the as-prepared samples was done by

chronopotentiometry(constant currents) mode.

Application to electrochromic devices

a) The prepared infiltrated templates were checked for apparent

color changes

b) The reason for color change was change in refractive index on

exertion of varying potential.

EDOT Aniline

Synthesis of Colloidal Particles

Particles were grown in steps, achieving range of 25-30 nm and

then regrown to size of 70-80 nm.

Particles of size: 70-80 nm Particles of size: 30 – 40 nm

(Images : FE-SEM was used to analyze these during expt.)

Synthesis of Colloidal Particles

Stober method was then employed to give the particles the

desired size range of 200 nm – 300 nm.

a) Maintaining the mono-dispersion was very much the

objective along with size.

(Image : FE-SEM)

b) Centrifugation of the given solution was done so that, now

less concentrated solutions like 1-10 wt % can be made

such that thickness of colloidal template can be monitored.

Thickness of Colloidal Template

The thickness of the colloidal template was monitored and

subsequently analyzed

a) 2 wt % b) 3 wt %

The objective was that infiltration of the polymer is easily achieved

thus different solutions were employed to monitor the thickness.

Alternatively spin coating method was also employed to make

templates of varying thickness. (Used : Thin layered templates were

made)

Well-ordered colloidal templates with variation of silica

concentration and solvents

a) Spin Coating Parameters : Speed : 1500 rpm

Time : 10 – 12 minutes

Top View : Cross-Section :

(Image Source : FE-SEM)

Well-ordered Structures

Infiltration of the Polymer

Infiltration of the polymer : PEDOT and PANI in 2 attempts.

Infiltration was done by electropolymerization. We usually

deployed constant current method.

The parameters deployed were : Current density : 0.3 mA/cm2

Time : 150 – 200 seconds

Etching the template : Diluted HF solution(1~5 wt%, 10-30 mins)

Infiltration attempt :

(Infiltration unsuccessful as structure

uneven)

Reason : Maybe lack of mono-dispersion

or thickness of layer.

Infiltration of the Polymer

Infiltration attempt :

(Infiltration relatively successful)

Reason : Employed initial coating of

PEDOT which resulted in

relatively ordered structure.

Still we could not get the apparent color change, we desired in the

device or the structure we wanted.

In order to get more regularized structure, we used ITO (indium tin

oxide) ,since we thought that ITO will render smooth structure and an

ordered colloidal template will form.

Infiltration of the Polymer

The PEDOT infiltration will give rise to a blue color in oxidized state

and transmissive color in neutral state.

Infiltration attempt 2 :

This time we used PANI (Polyaniline) as the infiltrating agent.

a) For maintaining the thickness, needed to infiltrate the template

spin coating method was deployed.

b) We used Stober method grown seeds and spin coated them at

an 1500 rpm.

(Infiltration attempt – PANI)

Infiltration of the Polymer

The spin coating is done in

desired way giving way to

well-ordered polymer and the

thickness of polymer is

controlled by

electropolymerization time

Conclusions and Proposals

We believe that achieving mono-dispersed particles and proper

thickness of template are the key to infiltrate conducting polymers

and thus color to the photonic crystals.

If mono dispersion and proper template thickness is achieved, we

wish to use a infiltrating agent such that which shows near-

transmissive color in both oxidized and neutral forms, such that we

could easily see the color change in the 3-D photonic crystals.

The color change is the defining property, on which the concept of

electrochromism is based.

We propose that, if subsequent time is put to find the requisite EC

polymer and proper infiltration is done, good quality 3-D photonic

crystals can be made, rendering to remarkable electronic

applications.

References

Kurtis D. Hartlen et al., Facile Preparation of Highly

Monodisperse Small Silica Spheres (15 to >200 nm) Suitable

for Colloidal Templating and Formation of Ordered Arrays,

Langmuir 2008, 24, 1714-1720

Reversible Full-Color Generation with Patterned Yellow

Electrochromic Polymers** Thiruvelu Bhuvana, Byeonggwan

Kim, Xu Yang, Haijin Shin, and Eunkyoung Kim* @

Angewante 2012

Tunable electrochromic photonic crystals

Su-Lan Kuai, Georges Bader, and P. V. Ashrit @ Applied

Physics Letters @ 2010

Conjugated Polymers : Synthesis and Application @ John

Reynolds 2009

THANK YOU !!!!!