MATERIALS
SCIENCE
Flexible
biomimetic
block
copolymer
composite
for
temper
ature and long-w
ave infrared sensing
Tae Hyun
Kim
1
, Zhun
Zhou
1
, Yeong
Suk
Choi
2
*, Vincenzo
Costanza
1
, Linghui
Wang
1
,
Joong
Hwan Bahng
1
, Nicholas
J. Higdon
1,3
, Youngjun
Yun
2
, Hyunbum
Kang
2
, Sunghan
Kim
2
,
Chiar
a Daraio
1
*
Biological
compounds
often
provide
clues
to advance
material
designs.
Replica
ting their
molecular
structur
e
and functional
motifs
in artificial
materials
offers
a blueprint
for unpr
ecedented
functionalities.
Here, we
report
a flexible
biomimetic
thermal
sensing
(BTS)
polymer
that is designed
to emula
te the ion transport
dy-
namics
of a plant
cell wall component,
pectin.
Using
a simple
yet versatile synthetic
procedur
e, we engineer
the
physicochemical
properties
of the polymer
by inserting
elastic fragments
in a block
copolymer
architectur
e,
making
it flexible
and stretchable.
The thermal
response
of our flexible
polymer
outperforms
current state-
of-the-art
temper
ature sensing
materials,
including
vanadium
oxide,
by up to two orders
of magnitude.
Thermal
sensors
fabrica
ted from these
composites
exhibit
a sensitivity
that exceeds
10 mK and operate
stably
betw
een 15° and 55°C,
even under
repea
ted mechanical
deforma
tions.
We demons
trate the use of our
flexible
BTS polymer
in two-dimensional
arrays for spatiotempor
al temper
ature mapping
and broadband
infra-
red photodetection.
Copyright
© 2023 The
Authors,
some
rights
reserved;
exclusive licensee
American
Associa
tion
for the Advancement
of Science.
No claim to
original
U.S. Government
Works. Distributed
under
a Creative
Commons
Attribution
NonCommer
cial
License
4.0 (CC BY-NC).
INTR
ODUCTION
Organic
electronic materials are emerging
as competitiv
e alterna-
tives to conventional
silicon-based
microelectronics because
of
their low-cost manufa
cturing
(
1
,
2
) and multifunctionality
(
3
,
4
).
The ability to tailor their properties
at the molecular
level makes
themappealing
forarangeofsensing
applications,suchaswearable
and implantable
devices,
which require specific
characteristics that
are difficult
to achieve with inorganic
compounds,
like flexibility
andstretchability
.Theincreasingdemand
forall-organic
electronic
devices
hasledtothedevelopments
ofagrowingnumber
ofsoftand
active materials for a variety
of physical (
5
,
6
) and biochemical
sensors
(
7
,
8
), paralleled by the advancements
in elastic substrates
andconductors
(
9
,
10
), aswellasintheirfabricationandintegration
strategies (
11
,
12
).
Organic
thermal
sensors
have also been proposed
for remote
health care, robotics,
andenvironmental
and industrial monitoring
applications (
10
,
13
). However, thermal
sensing
devices
relying on
organic
materials are often limited
by their response
performance,
whichisnotyetcompar
abletotheirinorganic
counterparts.
Several
approaches have been suggested to improve materials
’
response
to
temperature, for example,
by using inorganic
fillers, nanocompo-
sites, volume expansion,
or the use of transistor-type
devices
for
signal amplifica
tion (
14
–
17
).
However, these strategies generally
involvecomplexfabricationstepsanddevicearchitectur
es,function
in narrow temperature ranges, or provide limited
response.
Toovercometheselimitations,itisnecessary
todeveloporganic
materials that intrinsically
present high thermal
response
and flex-
ibility in a relatively simple scaffold that can be fabricated to scale
with reproducible
performance.
However, the ability to design new
materials depends
on understanding
the fundamental
transport
mechanism
and structural dynamics
in organic
molecules
(
18
,
19
)
and on linking
these properties
to their functional
characteristics.
Although
promising
advances
have been made, for example,
with
first principle
simulations and data-driven approaches (
20
,
21
),
thefieldisstilllackingpredictivemodels
forthedesignandsynthe-
sis of such materials. One approach to design new materials is to
gain insights
from building
blocks found in biological
matters
and to emulate their structures in synthetic
materials.
Recentinvestigationsofplantcellwallcomponents
reported
that
pectin,
a structurally and functionally
complex acid-rich
polysac-
charide
(
22
), has a remarkable
response
to temperature (
23
–
25
).
Pectin consists mostly of repeating units of
D
-galacturonic acid
(Fig. 1A). At neutral pH, the
D
-galacturonic acid units of low-
ester pectin form ionic bridges
with Ca
2+
, creating an
“
egg-box
”
complex in which cations are encapsula
ted (
26
,
27
). Increasing
the temperature of a Ca
2+
–
cr oss-link
ed pectin results in an expo-
nential
increase in ionic conduction
(
23
,
24
). However, pectin is
most abundantly
found in agricultur
al products,
e.g., fruit peels,
and its chemical
composition
is directly influenced
by climate,
plantorigins,
andextractionmethods
(
28
). Hence,devices
fabricat-
edwithpectin,asasensing
element,
presentinconsis
tentelectronic
properties
and demons
trate poor structural stability.
Here, we introduce a new flexible biomimetic
thermal
sensing
(BTS) polymer
that emulates the structure and functional
motifs
of pectin. The synthetic
BTS polymer
composite
exhibits superior
thermal
sensitivity
whilealsobeingmechanically
robustandflexible
(Fig. 1B). The basic architectur
e consists of an ABA-type
triblock
copolymer,
synthesized
through reversible addition-fr
agmenta
tion
chaintransfer(RAFT)
polymeriza
tion(fig.S1A),whichisaversatile
living radical polymeriza
tion method
used to engineer
structures
with intrinsic
mechanical
flexibility
(thermoplas
tic elastomers),
suitable
for organic
electronic materials (
29
–
31
).
1
Division
of Engineering
and Applied
Science,
California
Institute of Technology
,
Pasadena,
CA 91125,
USA.
2
Samsung
Advanced
Institute
of Technology
(SAIT),
Samsung
Electronics,
Suwon
16678,
South
Korea.
3
Division
of Chemis
try and
Chemical
Engineering,
California
Institute
of Technology
, Pasadena,
CA 91125,
USA.
*Corresponding
author.
Email:
yeongsuk.choi@samsung.com
(Y.S.C.);
daraio@
caltech.edu
(C.D.)
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
1 of 9
SCIENCE
ADVANCES
|
RESEARCH
ARTICLE
RESUL
TS
Design
of the flexible
BTS
polymer
To mimic
pectin
’
s
temperature response,
we conceptualize
the
polymer
architectur
e by reducing
the complex pectin structure to
a simpler
backbone,
bearing
only the minimally
required cues for
thedesiredfunctions.
Wehypothesize
thatthecarboxyl
groups,hy-
droxyl groups, and the conforma
tion of sugar pockets are all essen-
tialcomponents
withinthe
D
-galacturonicacidthatchelatedivalent
cationsforming
theegg-box
complex(
26
,
32
). IntheABAarchitec-
ture,the
“
A
”
blocksrepresenttwoflanking
hydrophilicregions,dis-
playing motifs that can bind with divalent
cations, composed
of
random
placement
of 2-hydroxyethyl acrylate (HEA)
and acrylic
acid (AA). Upon chelating with divalent
cations, the A blocks
present a temperature response
mechanism
similar
to that of
pectin (Fig. 1C). However, the cationic interactions result in a
“
pseudo-cr
oss-link,
”
forming
a hard segment
with high glass tran-
sition temperature (
T
g
) (
33
). To add mechanical
flexibility, the
polymer
is further
modified
by introducing
low-
T
g
polymer
mole-
cules as soft segments.
Poly(
n-
butyl
acrylate), with low glasstransi-
tion temperature (
T
g
<
−
50°C)
(
34
), is inserted
in the middle
block
“
B,
”
to serve as an elastic strand in the network
and to make the
polymer
membrane stretchable
(Fig. 1D). In ethanol,
the synthe-
sized polymer
exists in colloidal
states with an average particle
di-
ameterof96.9nm(Fig.1Bandfig.S1B).Thehydrophilic-lipophilic
balance
value of the hydrophilic A block, calculated on the basis of
Davies
’
method,
is 13.03, corresponding
to the oil-in-w
ateremulsi-
fier range (table S1).
Fig.
1. Biomimetic
design
of the flexible
BTS
polymer.
(
A
) Schema
tic illustration of the plant cell wall structur
e and of pectin.
(
B
) Design
of the ABA-type
block co-
polymer,
with
m
= 5,
n
= 5,
p
= 100, and
r
= 85.7. The hydrophilic
A block,
rich in carboxyl
(red) and hydroxyl (blue)
groups, is designed
to electrostatically
interact with
metallic
cations.Thehydrophobic
B block,
composed
ofpoly(
n
-butyl
acrylate),isdesigned
to providemechanical
flexibility
and stretchability
tothenetwork.
Asshownin
the particle
size measur
ement
(bottom
right),
the synthesized
polymer
exists in a colloidal
state in ethanol
due to phase
separation. (
C
) Hypothesized
mechanism
gov-
erning
the temper
ature response
of the synthetic
block copolymer.
Rearrangement
of the potential
wells at low and high temper
ature in which
the cations are confined
(top). When
an external
electric
field is applied,
temper
ature rises cause
an increase in ion migration through the hydrophilic
channels
formed
between the colloidal
particles
in the polymer
matrix (bottom).
(
D
) Mechanical
flexibility
and stretchability
of the synthetic
block copolymer.
The dried pectin
film is prone to tear aftera slight
bending
deforma
tion (left), whereas the composite
polymer
is robust to repeated stretching
motions
because
of the soft B block (right).
The polymer
is stretched
300%
from its original
shape.
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
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To verify the functional
roles of the polymer
moiety
relating to
the temperature-dependent
ion transport,
we first characterize the
structuralcomponents
oftheas-synthesized
blockcopolymer,
using
gelpermeation chromatography(GPC)andnuclear
magnetic
reso-
nance (NMR)
measurements
(fig. S2). The synthesized
polymer
shows a weight-average molecular
weight (
M
w
) of 113,600
g/mol
with a dispersity
of 1.08. This is similar
to the
M
w
of natural
pectin but with a much narrower weight distribution
(
35
). The
monomer
feed ratio of the hydrophilic
(hard) and hydrophobic
(soft) segments
is 1:5 (tables S2 and S3).
Adding
divalent
calcium
ions into the flexible BTS polymer
sol-
utionresultsinacloudyappearance,revealinganetwork
formation
through ionic cross-links.
The cross-link
ed solution
is cast on a
plastic sheet and dried to remove the remaining
solvent (Fig. 2A).
During
this process, the mixture is monitor
ed in situ using attenu-
atedtotalreflectance
–
F
ouriertransform
infrared(ATR-FTIR)
spec-
troscopytoexamine
thefilmformationbehavior.Thecharacteristic
peaks clearly elucidate structures of the designed
polymer
(Fig. 2B
and table S4) and the presence of water contained
inside (fig. S3).
While the solvent evaporates, the neighboring
chains of the block
copolymer
form interpolymer
complexes (IPCs) between the AA-
HEA functional
groups. This interaction between the carbonyl
oxygen
and hydrogen of the hydroxyl group (hydrogen bonding)
is suggested by the thermogr
avimetric
analysis (TGA)
profile
(Fig.2C)(
36
). Here,theIPCsmayplayaroleinaggregatingthecol-
loidalparticles
toformiontransport
channels
betweentheinteract-
ingAblocks(Fig.1C).Atelevatedtemperatures,thenumber
ofions
overcoming
theenergybarrierincreases,whichleadstoahigherdif-
fusion constant and hopping
rate between the coordina
tion sites
through the absorption
of thermal
energy and the polymer
’
s seg-
mental
motion.
Under an applied
electric
field, the probability
of
ions moving forward becomes
favorable, generating a net current
flow through the polymer
network.
The maximum
amount
of AA
that can be involved in IPC formation is calculated as 86.13%
(table S6).
To interrogate the importance
of chemical
composition
within
the A block, series of copolymers
with varying
ratio of AA to HEA
are synthesized
(Fig. 2D and table S7). The polymer
film with even
proportion
of carboxyl-to-hydr
oxyl groups demons
trates the
highest activation energy
and temperature response.
Modifying
Fig.
2. Film
forma
tion
beha
vior
and
component
analy
sis of the block
copolymer.
(
A
) Digital
images
of the cross-link
ed block copolymer
solution
drop-cas
ted on a
flexible plastic substrate. The amount
of cross-linking
metal
ions used for all tests is fixed to 100% unless
otherwise
stated. a.u., arbitrary units; EtOH, ethanol.
(
B
) Time
series
of ATR-FTIR
spectra after polymer
deposition.
During
1 hour of air dry, ethanol
starts to evapor
ate, and subsequently
, water is absorbed
and saturated by the
hygroscopic
regions
in the polymer
matrix.
*
Peak assignments
of the ATR-FTIR
spectra (table
S4). (
C
) TGA profile of the polymer
film before and after washing
in DI
water. Titration analysis is performed
to determine
the percent of IPC formed
in the composite
film based
on the amount
of bounded
metal
ions after wash. Inset:
Corresponding
FTIR spectra of the films. (
D
) Arrhenius
plot of different block copolymers.
Activation energy
compar
ed between different polymer
films with varying
ratio of carboxyl
to hydroxyl functional
groups (type 1:
m
= 5,
n
= 5,
p
= 100; type 2:
m
= 4,
n
= 7,
p
= 100; type 3:
m
= 10,
n
= 0,
p
= 100). Inset: Corresponding
thermal
response
of each type of polymer
compar
ed. Measur
ements
are performed
using the electrode design
fabricat
ed in fig. S6B with an AC voltage
bias of 300 mVat 200 Hz.
(
E
) Relation between the concentr
ation of metal
ions in the composite
film and the amount
of water adsorbed.
Weight percentage
of the polymer,
Ca
2+
, and water is
calcula
ted on the basis of the TGA profile and the coupled
gas-phase
FTIR spectra of the dried polymer
films (fig. S5) with varying
amount
of CaCl
2
(table
S5). A linear
relationship
is observ
ed between the CaCl
2
concentr
ation and water absorbed
by the composite
film. (
F
) Impedance
spectra of the polymer
film with and without
Ca
2+
.
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
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this ratio to approximately 1:2 results in a >7-fold
decrease in re-
sponse,
while films consisting of only the carboxyl
groups lead to
aresponse
depletion.
Theresult revealsthat bothhydroxyland car-
boxyl groups collectiv
ely play important
roles in chelation of Ca
2+
and the subsequent
formation of the egg-box
–
type
interactions
analogous
to the coordina
tion environment
in pectin.
Moreover,
the high temperature response
can be explained
by the high-
energy barrier created by strong binding
forces between these side
chains and calcium
ions.
By varying
the concentr
ation of ions, the films are further
pro-
filed using TGA-FTIR
to verify components
from gas-phase
diffu-
sion (figs. S4 and S5). The linear relationship
(
R
2
= 0.987) between
Ca
2+
concentr
ation and water in the film indicates that water ab-
sorption
ismainlycausedbymetalions(Fig.2E).Last,toinvestigate
the conducting
species within the polymer
matrix, electrochemical
impedance
spectroscopy analysis is performed.
Polymer
films with
and without
Ca
2+
are prepared, and the system
’
s conductivity
as a
function
of AC frequency
is measured (Fig. 2F). The conductance
profileofthefilmwithnometalionsisflatuntil10kHz,whereasthe
onewithCa
2+
showsanincrease below100Hzduetoelectrodepo-
larizationfollowedbyaplateau.Thisrevealsthatcalcium
cationsare
the major transporting
charge carrier of the system.
Char
acteriza
tion
of the flexible
BTS
polymer
To characterize the temperature response,
we fabricate an array of
circularly shaped
interdigita
ted electrodes on a flexible plastic sub-
strate and drop cast and dry 5 μl of the cross-link
ed BTS polymer
solution
on the electrodes
’
surface (fig. S6, A and B). After mount-
ingthesamples
onacustom-built
thermal
cycler,theoutputcurrent
ismeasuredwhileapplying
anACvoltageof300mVat200Hz.The
alternating signals enable stable measurements
over time, reducing
the possibility
of ionic charge depletion
caused by DC bias. Here,
300 mV is chosen
on the basis of the minimum
level of current
(to avoid self-joule
heating) that could be stably read from the
sensorconsidering
thesignalnoiseflooratroomtemperature(RT).
The hydration state of organic
materials closely correlatesto the
ionic transport
and the material
’
s mechanical
properties
(
37
). To
monitor
the effect of water in the polymer
’
s performance,
we
dried the films under various
conditions
and repeat the measure-
ments(Fig.3A).Whenthepolymer
filmisfullyhydrated,arelative-
ly low temperature response
is observed. Under these conditions,
conduction
through water channels
domina
tes the transport,
sup-
pressing the effectof ions, which is mainly responsible
for the large
temperature-dependent
impedance
changes.
Asthefilmisdried,re-
moving unbound
water from the chain, the response
increases
markedly, indicating the growing portion
of Ca
2+
-mediated trans-
port (
25
). However, further
dehydration results in a decreased re-
sponse
due to loss of conduction
paths. A maximum
root mean
square (RMS) current response
(
I
45°C
/
I
15°C
) of 80.04 A/A is exhib-
ited over the defined
temperature range. Such normaliza
tion ap-
proach has been adopted
to compar
e between state-of-the-art
thermal
sensing
materials, characterized
under different measure-
mentconditions.
Bymeasuring
theoutputcurrentatconstanttem-
peratureinair,asensing
resolution
oflessthan8.68mKisobtained
with negligible
hysteresis (fig. S6, C and D). Compared to the state-
of-the-art
thermal
sensing
materials,including
vanadium
oxide(
38
,
39
), inorganic
devices
(
40
–
42
),
andnaturalpectinproducts(
23
,
24
),
the overall temperature response
of the resulting
flexible BTS
polymer
composite
is orders of magnitude
higher (Fig. 3B).
To evaluate the materials
’
response
as a function
of excitation
frequency
, we measure the samples
’
impedance
spectrum
between
1 Hz and 5 MHz using 300 mV (Fig. 3C). At lower frequencies,
in
which the transport
is mainly induced
by ion migration, change
of
temperature results in a large variation of current. A maximum
current response
of over 160 A/A is evident
around 20 Hz. At fre-
quencies
above the charge relaxation, transporting
ions within the
polymer
are not able to follow the alternating electric
field (polari-
zationdomina
ted)andnolongercontribute
tothetemperature-de-
pendent
conduction
behavior.
After conditioning
the polymer
film to its optimal
hydration
status, cyclic stability
is evaluated by heating the sensor from 15°
to 45°C for 6 hours while monitoring
the current. Before measure-
ments, a thin layer of parylene-C
is conformally
coated around the
device to serve as a moisture barrier and electrical
insulation. The
deviceshowshighstability(Fig.3Dandfig.S7)withminimum
var-
iation in current response,
lying within the ±2.39%
fluctuation
boundary
over 100 cycles of continuous
use.
Tocharacterizetheeffectofmechanical
solicitations,thesensors
are compressed or bent at different pressures and curvatures. Al-
though
aslightdecreaseinconduction
isobservedduringcompres-
sion (fig. S8), the average temperature error converted from the
difference in current read-out,
with and without
loading,
is less
than0.11°Cuptoapressureof250kPa(Fig.3E).Thisdemons
trates
that the sensor response
is relatively insensitiv
e to strain. Under
bending
deforma
tions, an even lower temperature error is detected
(Fig.3F).Totestwhether
thestraininsensitivity
persistsafterrepet-
itive mechanical
loading,
we subject
the samples
to 100 cycles of
bending
(bending
radius = 1.6 mm) or compression
(to a
maximum
pressure of 25 kPa). The current remains
similar
to
thatoftheas-fabrica
tedsamples,
indicatinghighmechanical
stabil-
ity and elastic recovery. In contrast, dehydrated pectin films are
brittle and prone to tear (Fig. 1D).
Spatiotempor
al temper
ature mapping
Weexemplify
theapplicability
ofourflexibleBTSpolymer
compos-
iteforspatiotempor
altemperaturemapping
andlong-waveinfrared
(IR) photodetection.
First, we create a flexible temperature sensing
sheet, consisting of a 10 by 10 array of uniformly
spaced sensors,
placed 1 cm apart (Fig. 4A). We attach the sensor matrix on a cir-
cular glass plate with a point heat source located on its center and
monitor
the thermal
gradient evolving across the glass surface in
real time. The continuous
heat flowalong the plate
’
s radius is visu-
alized in atime-dependent
temperature map (Fig. 4B), obtained
by
measuring
and interpola
ting the current variation on five polymer
sensors.
High temperature response,
paired with its flexibility
and
compliance,
offers opportunities
in various
engineering
applica-
tions,suchasbatteries,packaging
ofperishable
items,andwearable
thermometers
that require continuous
spatial monitoring
of tem-
perature over three-dimensional
surfaces.
Broadband
long-w
ave IR sensing
Next, we experimentally
demons
trate an uncooled,
long-wave IR
sensor that can detect thermal
radiation across a wide spectral
range(Fig.5A).Toreducethermal
lossviaheatconduction,
wefab-
ricateelectrodesonathinpolyimide
(PI)membrane(2μm)(fig.S9,
Aand B).To measure theresponsivity
(Δ
I
/
P
), the entire devicewas
placedinahermetically
sealedchamber
withazincselenide
(ZnSe)
transmission
window(fig.S9C).Thesensorwasbiasedat1VACat
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
4 of 9
SCIENCE
ADVANCES
|
RESEARCH
ARTICLE
200 Hz to increase the sensor
’
s signal-to-noise
ratio, ensuring
no
excessive self-hea
ting caused by joule dissipation (fig. S10). Moni-
toring the current change
as a function
of applied
power at 8.5-μm
wavelength,
we observe an exponential
increase in current, follow-
ing an Arrhenius
behavior (Fig. 5B). To investigate the spectral re-
sponsivity
of the sensor,
we vary the wavelength
of the incident
IR
with an applied
power of 4 mW. The sensor responsivity
is closely
correlated to the spectral features of the polymer
absorption
spec-
trum, in which the characteristic peaks are located (8 to 14 μm)
(Fig. 5C). Last, we use our sensor to detect IR-emitting
objects
nearRT.Withahandwavingmotion
abovethesensor,acorrelating
currentvariationisdetected
(Fig.5D).Currentdecreaseisobserved
whenthehandiscoveredwithasheetofpaper.Werepeatthemea-
surement with an IR reflective aluminum
sheet to verify whether
this behavior is induced
by thermal
radiation. The aluminum
layer blocks
the irradiation emitted
not only from the hand
(movie S1) but also from the surrounding
environment,
resulting
in a further
decrease in sensor current.
DISCUSSION
The results presented
here demons
trate a biomimetic
approach to
design
a thermally
responsiv
e polymer
for organic
electronics.
Inspired by the functional
motifs in the pectin-Ca
2+
complex, we
create a block copolymer
that demons
trates an extremely high
thermal
response
with a sensing
resolution
of below 10 mK. By
using a versatile synthetic
procedure, we also show the ability to
tailor physicochemical
properties
that enables
optimiza
tion of the
material
’
s temperaturesensitivity
andendowsmechanical
flexibility
and stretchability
. Additional
functionalities
can be introduced
by
tailoring
the polymer
architectur
e and its side chains,
for example,
increasing its electrical
conductivity
, response
time, or IR absorp-
tion spectrum
for diverse thermal
sensing
platforms.
The resulting
materialisstableundercyclicloading
andinsensitiv
etomechanical
solicitations, extending
its capability
and potential
use for wearable
sensors
and consumer
electronics. In particular,
these aspects
have
promise to affect technological
advances
in the medical
or health
care field that can allow continuous
and noninvasiv
e personalized
monitoring
of minute
pathophysiological
thermal
stresses caused
by disruption
in homeos
tasis, infection,
inflamma
tory responses,
and mental
stresses or sleep deprivation.
Although
ourBTSpolymer
hasshownpromising
results,several
challenges
androomfor improvements
remain.Because
ofitsnon-
linear, exponential
response
to temperature and hydration-depen-
dent sensitivity
, a precalibration curve needs to be acquired before
initial measurements,
and care must be taken during
sensor
Fig.
3. Char
acteriza
tion
of the flexible
BTS
polymer
sensor.
(
A
) Current variation as a function
of temper
ature, measur
ed between 15° and 45°C with an applied
voltage
of 300 mVat 200 Hz (bottom)
and the corresponding
current response
calcula
ted at different hydration levels (top). Darker blue lines represent higher
hydration,
andlighter
bluelinesrepresentlowerhydration.Inset:Device
schema
ticandconfigur
ationforelectrical
measur
ement.
(
B
) Response
comparison
betweenstate-of-the-art
temper
ature sensing
materials
and devices,
normalized
with signals
at 15°C. (
C
) Frequency-dependent
current measur
ed between 1 Hz and 5 MHz at varying
temper-
atures(top)andthecorresponding
currentresponse
calcula
tedwhen300mVwasapplied
(bottom).
Maximum
response
of161.3isobtained
at17.8Hz.(
D
) Cyclicstability
testover100cycles
ofcontinuous
temper
atureoscillationbetween15°and45°C.(
E
) Temper
atureerrorextractedfromthethermal
sensor
asafunction
ofnormal
pressure
and (
F
) bending
strain (curvature). All plots represent data from polymer
solution
cross-link
ed with 100% concentr
ation of CaCl
2
.
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
5 of 9
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RESEARCH
ARTICLE
packaging.
In addition,
an alternative synthesis
procedure such as
the continuous
polymeriza
tion method
will allow us to reduce
batch-to-ba
tch variation and enable mass production.
Last, it will
beofinteresttofurtherinvestigatethetransport
mechanism
supple-
mented
by molecular
dynamic
simulations to further
delineate the
thermal
sensing
behavior of the system to potentially
improve the
materialsensitivity
,dynamic
range,oreventhemechanical
features
by modifying
the polymer
composition
and coordina
ting
metal ions.
Interests on realizing
all-organic
electronic devices
with func-
tionalities
that their inorganic
counterparts
cannot
provide are on
the rise. While many organic
electronic components
such as sub-
strates, electrodes, and transistors have been developed,
advance-
ment and mechanis
tic understanding
of the organic
sensory
elements
have not progressed in parallel. To bridge this gap and
to fully optimize
the specific
features of our flexible BTS polymer,
further
mechanis
tic studies accompanied
by molecular
dynamic
simulations to delineate the exact origin of the high thermal
re-
sponse
should
be followed. We anticipa
te that our material and
designconcept
canbeusedforfundamental
studiesofiontransport
mechanisms
in the form of such simplified
polyelectrolytes, which
canbegeneralizedtodifferentionicconducting
polymeric
systems.
MATERIALS
AND
METHODS
Materials
HEA,
tert
-butyl
acrylate(
t
-BA),
n
-butyl
acrylate(
n
-BA) monomers,
and a dual-functional
chain transfer agent (CTA)
S
,
S
-dibenzyl
tri-
thiocarbona
te (DBTTC) were purchased
from Sigma-Aldrich.
DBTTC was used to expedite
the synthesis
of the ABA polymer
for multistep processing
(
43
). Azobis
(isobutyr
onitrile)
(AIBN),
a
radical initiator, was purchased from Sigma-Aldrich
and recrystal-
lized from methanol
before use.
Synthetic
procedur
e of the ABA
block
copolymer
ABA-type
block copolymers
were prepared via RAFT polymeriza-
tion (fig. S1A). During
the entire polymer
synthesis
process, the
resulting
material was characterized
using GPC and NMR (
1
H
NMR) (fig. S2) (
44
). First, N
2
-purged
HEA
1
(1.16 g, 10 mmol)
and
t
-BA
2
(1.28 g, 10 mmol) were dissolved in 2 ml of dimethyl-
formamide
(DMF),
followed by DBTTC
3
(29 mg, 0.1 mmol).
The
mixture was further
purged
with N
2
for 3 min. Next, AIBN (0.81
mg, 5 μmol) was added into the reactor and lastly stirred at 75°C
under inert N
2
atmospher
e. The reactor was cooled
down and
vented to air. The residual
monomers
(
t
-BA and HEA) were
removed by vacuum, following precipitation in 100 ml of cold
diethyl
ether that resulted
in a yellow oil of bis[p(
t
-BA
10
-
r
-
HEA
10
)] trithiocarbona
te (macro-CTA). The yield of polymeriza-
tion monitor
ed using
1
H NMR was 80% (2.02 g). Next, the
macro-CTA was mixed
with N
2
-purged
n
-BA
4
(12.8 g, 100
mmol)
and AIBN (0.81 mg, 5 μmol), along with 15 ml of DMF.
ThemixturewaspurgedagainunderN
2
for3min,followedbystir-
ring at 75°C under N
2
atmospher
e. The reactor was cooled down
and vented to air. Residual
n
-BA was removed by vacuum to yield
aprotected
formofABAblockcopolymer,
p[(
t
-BA
5
-
r
-HEA
5
)-
b
-(
n
-
BA)
100
-
b
-(
t
-BA
5
-
r
-HEA
5
)]
r
. Here, a conversion rate of 81% was
achieved (11.24 g). Last, 1 g of the protected
polymer
was dissolved
in 3 ml of dichloromethane
(DCM)
and combined
with 3 ml of tri-
fluoroacetic acid (TFA). The deprotection
reaction was carried
out
at RT and stirred overnight.
DCM and TFA were removed by
vacuum after precipitating the polymer
in cold diethyl
ether. As a
result, a highlysticky yellow oil asthe final form of the deprotected
ABA block copolymer,
p[(AA
5
-
r
-HEA
5
)-
b
-(
n
-BA)
100
-
b
-(AA
5
-
r
-
HEA
5
)]
r
, was produced.
The conversion of
tert
-butyl
groups into
AAwas confirmed
using
1
H NMR from the deprotected
block co-
polymer
(100% conversion to AA form).
Polymer
char
acteriza
tion
The size of the colloidal
particle
formed
in ethanol
was measured
usingazetapotential
andparticle
sizeanalyzer
(Otsuka
Electronics,
ELSZ-2000)
at RT (Fig 1B and fig. S1B). After dissolving
the
samples
in deuterated DCM (CD
2
Cl
2
), NMR spectrawere obtained
using Bruker Ascend
500 (500 MHz). Spectral analysis was per-
formed
using Topspin
3.2 software. GPC was carried
out in
Fig. 4. Temper
ature
sensing
array based
on flexible
BTS
polymer.
(
A
) Schema
tic diagram of aflexible thermal
sensor
for large-ar
ea, multipixel
temper
ature mapping.
The sensor
is placed on top of a glass plate where a heat source in the middle
is used to generate a thermal
gradient
across the surface. Inset: Time versus temper
ature
profile of the heat source (top) and the measur
ed temper
ature value from each sensor
(bottom).
(
B
) Spatiotempor
al reconstruction
of the temper
ature evolution
across
the glass plate. Data are extracted from five sensor
pixels
along
the radius of the glass slide.
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
6 of 9
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|
RESEARCH
ARTICLE
tetrahydrofuran on two MZ-gel
(10 μm) columns
composed
of
styrene-divinylbenzene
copolymer
(Analysentechnik)
connected
inserieswithaminiDA
WNTREOS
multiangle
laserlightscattering
detector.
Thefilmformationoftheblockcopolymer
wasmonitor
ed
in situ from the composite
mixtures using ATR-FTIR
spectroscopy
using a Nicolet
iS50 FTIR spectrometer.
The synthesized
block co-
polymer
was dissolved in ethanol
(1 mg/1 ml) with metal ions (0.3
M), mixed,
placed on top of the ATR module,
and continuously
dried in air at 22°C under 23% relative humidity
. The ATR-FTIR
spectra were obtained
as a function
of time. Table S5 summarizes
the composition
of the tested mixtures.
TGAwas carried
out on dried composite
films (20 mg) using a
Discovery TGA (Thermo
Fisher Scientific)
with the following set-
tings:ramprate,10°C/min;
temperaturerange,30°to650°C;andN
2
flow rate, 10 ml/min.
For material identifica
tion, TGA-FTIR
mea-
surements
were performed
in parallel to TGA to analyze
the gas-
phase FTIR spectra using a Nicolet
iS50 FTIR spectrometer.
The
spectrometer
was equipped
with an auxiliary
experiment
module,
composed
of an optional
mercury cadmium
telluride
detector,
a
10-cm path-length
nickel-plated aluminum
flow cell, and an inte-
grated digital temperature controller. After the integrated digital
controller reached a constant 130°C temperature, FTIR spectra
werecollected
every5minbetween0and65min.Foreachmeasure-
ment, atotal of 32 scans were averaged with 4 cm
−
1
resolution.
Im-
pedance
spectroscopy analysis was performed
using an impedance
analyzer
(Zurich
Instruments
MFIA).
AC frequency
was swept
between 1 and 100 MHz (100 points)
with a voltage biased at 1 V.
Percentage
of IPC formed
in the polymer
film was calculated
using the AA-Ca
2+
titration method
with the assumption
that two
AA functional
groups are involved to form a coordina
tion bond
with a single Ca
2+
. To begin with, the total amount
of AA and
metal ions (100% CaCl
2
) in the polymer
solution
mixture was cal-
culated (table S6). Next, the TGA and FTIR spectrum
of the com-
posite film was measured before and after washing with deionized
(DI) water (Fig. 2C). To completely
rinse out the unbound
metal
ions from the polymer
matrix, the film was soaked in 200 cm
3
of
DI water excessively with continuous
stirring (120 rpm) at RT for
72 hours and dried. The proportion
of Ca
2+
bound to the polymer
wascalculatedbysubtractingtheweightpercentage
betweenthetwo
TGAprofilesat550°C,whichcorresponds
totheresidualcontent
of
metal ions (chelated Ca
2+
with AA = 11.62%,
free Ca
2+
= 88.38%).
The free and bound
Ca
2+
ions were recognized
from the FTIR
Fig.
5. IR sensor
based
on flexible
BTS
polymer.
(
A
) Schema
tic of the fabrica
ted long-w
ave, thermal
IR detector.
(
B
) Current as a function
of IR power irradiated at a
wavelength
of8.5
μ
m. Inset:Representa
tivecurrentprofileduring
a4-speriod
ofIRexposur
einairwithdifferentpower.Currentismeasure
dusinganapplied
voltage
of1
V at 200 Hz. (
C
) Responsivity
of the IR detector
at different wavelengths.
Inset: Wavelength-dependent
absorption
intensity
of the block copolymer.
(
D
) Real-time
de-
tection
of thermal
radiation generated by a hand wave motion.
Covering the hand with a sheet of paper,
the rise in current is reduced
due to limited
transmission
of
irradiation power. Covering the hand with an aluminum
sheet,
no change
or decrease in current is observ
ed due to IR reflection.
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
7 of 9
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ARTICLE
spectra (inset of Fig. 2C) at 1640 and 1560 cm
−
1
, respectiv
ely. On
thebasisofthenumber
ofCa
2+
ionsboundtothepolymer
film,the
percentage
of AA used to from IPCs was estimated as 86.13%
(table S6).
Device
fabrica
tion
The block copolymer
was dissolved in anhydrous ethanol
at a con-
centration of 0.15 g/ml. Simultaneously
, metal ion salt (CaCl
2
) was
dissolved in anhydrous ethanol
at a concentr
ation of 0.3 M. The
ionically
cross-link
ed polymer
solution
was obtained
by mixing
the two solutions
at a volume ratio of 1:2. To fabricate the flexible
temperaturesensors,
athinsheetofpolyesterterephthala
te(PET;20
μm) was washed and attached to a 4-inch (100 mm) silicon wafer.
On top, a layer of photoresist was spin-coa
ted and patterned
using
thestandard
lithographyprocess.Thesurfacewasthen treatedwith
O
2
plasma(Plasma-Therm
SLR720)followedbyTi/Auevaporation
(CHA Mark 40 electron beam evaporator) with a thickness
of 200/
1000Å.Theentiresheetwasimmersed
inacetoneformetallift-off,
exposing
thecircularlyshapedinterdigita
tedelectrodes(
D
=4mm,
30 μm wide with 20-μm spacing). Last, the PET sheet with the pat-
terned electrodes was released,
rinsed,
and dried for use. Next, a
total of 5 μl of cross-link
ed polymer
solution
was drop cast on top
of each sensing
pixel and dried at RT for 1 hour. To test different
hydration status for optimal
temperature response,
the composite
polymer
was further
dehydrated using dry air and sealed using a
permeable
PI tape. For cyclic studies, a thin layer of parylene-C
(2
μm; ParaTech LabTop 3000 Parylene
coater) was conformally
coated around the devices
to prevent water absorption
or evapora-
tion. External
electrical
connection
was made using an anisotropic
conductiv
e film or an electrical
probe set. The cross-sectional
view
of the fabrication process is shown in fig. S6A.
The IR bolometers
were fabricated following similar
steps but
with slight modifica
tions. An 8-inch (200 mm) glass wafer was
cleaned
in piranha solution
for 30 min, rinsed using DI water,
and dried under a nitrogen stream. The dried wafer was then
plasma-tr
eated. PI solution
[10 weight % in dimethyla
cetamide
(DMAc)]
was spin-coa
ted to a thickness
of 2 μm and baked on a
hot plate at 250°C for 60 min to cure the resin and fully remove
the trapped DMAc
in the film. Using a hard mask, a 100-nm-
thick Au was thermally
evaporated on the PI film to form the
same interdigita
ted electrode design used above and rinsed using
DI water, followed by a complete
dry step. For handling
purpose,
a guiding
layer of PI tape was placed on the wafer surface and cut
into pieces with a knife. Last, each PI film containing
a single elec-
trode design was released
and attached on a custom-made
plastic
holder with an opening
at its center for air suspension
(membr
ane
structure).Atotalof5μlofcross-link
edpolymer
solution
wasdrop
cast on top of the sensing
pixel and dried at RT for 1 hour.
Figure S9A illustrates the entire device fabrication process.
Experimental
setup
A measurement stage was built to evaluate the temperature sensor
(figs.S7AandS8A).Thesystemwascomposed
ofaPeltier-Element
(model
Qc-31-1.4-8.5m)
connected
to a custom circuit board for
controlledsampleheatingandcooling.
Thesensors
wereconnected
through electrical
probes, and signals were measured using an im-
pedance
analyzer
(Zurich
Instruments
MFIA).
During
measure-
ments,
the temperature of the Peltier block was continuously
monitor
ed with a Pt100 platinum resistance thermometer,
which
wascalibratedbyaFLIRthermal
camera(model
A655sc).
Formul-
tiple cyclic tests, we generated atemperature sinewave between 15°
and 45°C through the dedicated control board.
ForIRmeasurement,thebolometer
wasplacedinahermetically
sealed chamber
(MPS-PT
, Micro Probe System, Nextron Corp.)
with a zinc selenide
(ZnSe)
transmission
window (68-503,
Edmund
Optics).
Figure S9C illustrates the optical
setup. A
quantum
cascade
laser (QCL;
MIRcat-QT Mid-IR
Laser) was
used to apply IR radiation to the device at various
wavelengths.
The beam size of the QCL was 4.8 mm in diameter.
The power of
the emitted
IR was calibrated using a power meter (PM16-401,
Thorlabs)
or an IR detector
(PVMI-4TE,
VIGO System). For both
temperature and IR measurements,
RMS current and phase from
the impedance
analyzer
were continuously
logged and visualized
using a custom software (Python,
LabVIEW).
Supplementary
Materials
This
PDF
file includes:
Figs. S1 to S10
Tables S1 to S7
References
Other
Supplementary
Material
for this
manuscript
includes
the follo
wing:
Movie S1
REFERENCES
AND
NOTES
1. S. R. Forrest, The path to ubiquitous
and low-cost organic
electron
ic appliances
on plastic.
Nature
428
, 911
–
918
(2004).
2. A. N. Sokolov, M. E. Roberts,
Z. Bao, Fabrication of low-cost electronic biosensors.
Mater.
Today
12
, 12
–
20
(2009).
3. H. Ling, S. Liu, Z. Zheng,
F. Yan, Organic
flexible electron
ics.
Small
Methods
2
,
1800070
(2018).
4. J. Kang, J. B.-H. Tok, Z. Bao, Self-healing
soft electronics.
Nat. Electr
on.
2
, 144
–
150
(2019).
5. B. C.-K. Tee, A. Chortos,
A. Berndt,
A. K. Nguyen, A. Tom, A. McGuir
e, Z. C. Lin, K. Tien, W.-
G. Bae, H. Wang, P. Mei, H.-H. Chou,
B. Cui, K. Deisser
oth, T. N. Ng, Z. Bao, A skin-inspir
ed
organic
digital
mechanor
eceptor.
Science
350
, 313
–
316
(2015).
6. I. You, D. G. Mackanic,
N. Matsuhisa,
J. Kang, J. Kwon,
L. Beker, J. Mun, W. Suh, T. Y. Kim, J. B.-
H. Tok, Z. Bao, U. Jeong,
Artificial
multimodal
receptors
based
on ion relaxation dynamics.
Science
370
, 961
–
965
(2020).
7. N. Wang, A. Yang, Y. Fu, Y. Li, F. Yan, Functionalized
organic
thin film transistors for bio-
sensing.
Accounts
Chem.
Res.
52
, 277
–
287
(2019).
8. M. Y. Lee,H. R.Lee, C. H. Park, S. G.Han, J. H.Oh, Organic
transistor-based
chemical
sensors
for wearable bioelectr
onics.
Accounts
Chem
Res.
51
, 2829
–
2838
(2018).
9. T. Sekitani,
T. Someya, Stretchable,
large-ar
ea organic
electronics.
Adv. Mater.
22
,
2228
–
2246
(2010).
10. J. Wang, M.-F. Lin, S. Park, P. S. Lee, Deformable
conductors
for human
–
ma
chine interfa
ce.
Mater. Today
21
, 508
–
526
(2018).
11. S. Wang, J. Xu, W. Wang, G.-J. N. Wang, R. Rastak, F. Molina-Lopez,
J. W. Chung,
S. Niu,
V. R. Feig, J. Lopez,
T. Lei, S.-K. Kwon,
Y. Kim, A. M. Foudeh,
A. Ehrlich,
A. Gasperini,
Y. Yun,
B.Murmann,
J.B.-H.Tok,Z.Bao, Skinelectronicsfromscalable
fabrication
ofanintrinsically
stretchable
transistor array.
Nature
555
, 83
–
88
(2018).
12. H. Lim, H. S. Kim, R. Qazi, Y. Kwon,
J. Jeong,
W. Yeo, Advanced
soft materials,
sensor
in-
tegrations, and applica
tions of wearable flexible hybrid
electronics in healthcar
e, energy
,
and environment.
Adv. Mater.
32
, e1901924
(2020).
13. Y. H. Lee, O. Y. Kweon,
H. Kim, J. H. Yoo, S. G. Han, J. H. Oh, Recent advances
in organic
sensors
for health
self-monitoring
systems.
J. Mater. Chem.
C
6
, 8569
–
8612
(2018).
14. X.Ren,K.Pei,B.Peng,Z.Zhang,
Z.Wang,X.Wang,P.K.L.Chan,
Alow-opera
ting-po
werand
flexible active-matrix organic-tr
ansistor temper
ature-sensor
array.
Adv. Mater.
28
,
4832
–
4838
(2016).
15. T. Q. Trung, S. Ramasundar
am, B. Hwang, N. Lee, An all-elas
tomeric
transpar
ent and
stretchable
temper
ature sensor
for body-a
ttachable
wearable electron
ics.
Adv. Mater.
28
,
502
–
509
(2016).
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
8 of 9
SCIENCE
ADVANCES
|
RESEARCH
ARTICLE
16. Y. Yamamoto,
S. Harada, D. Yamamoto,
W. Honda,
T. Arie, S. Akita, K. Takei, Printed
mul-
tifunctional
flexible device
with an integrated motion
sensor
for health
care monitoring.
Sci. Adv.
2
, e1601473
(2016).
17. T. Yokota, Y. Inoue,
Y. Terakawa, J. Reeder,
M. Kaltenbrunner,
T. Ware, K. Yang, K. Mabuchi,
T. Murakawa, M. Sekino,
W. Voit, T. Sekitani,
T. Someya, Ultraflexible, large-ar
ea, physio-
logical
temper
ature sensors
for multipoint
measur
ements.
Proc. Natl. Acad.
Sci. U.S.A.
112
,
14533
–
14538
(2015).
18. H. Bronstein, C. B. Nielsen,
B. C. Schroeder,
I. McCulloch,
The role of chemical
design
in the
performance
of organic
semiconductors.
Nat. Rev. Chem.
4
, 66
–
77
(2020).
19. M.Fahlman,
S.Fabiano,
V.Gueskine,
D.Simon,
M.Berggre
n,X.Crispin,
Interfa
cesinorganic
electronics.
Nat. Rev. Mater.
4
, 627
–
650
(2019).
20. S. Mogura
mpelly
, O. Borodin, V. Ganesan,
Computer
simula
tions of ion transport
in
polymer
electrolyte
membr
anes.
Annu.
Rev. Chem.
Biomol.
7
, 1
–
23 (2015).
21. P. Friederich,
A. Fediai, S. Kaiser,
M. Konrad, N. Jung, W. Wenzel,
Toward design
of novel
materials
for organic
electronics.
Adv. Mater.
31
, 1808256
(2019).
22. A. Peaucelle,
S. Braybrook, H. Höfte,
Cell wall mechanics
and growth control in plants:
The
role of pectins
revisited.
Front. Plant
Sci.
3
, 121 (2012).
23. R. D. Giacomo,
C. Daraio, B. Maresca, Plant nanobionic
materials with a giant temper
ature
response
mediate
d by pectin-Ca2
+
.
Proc. Natl. Acad.
Sci. U.S.A.
112
, 4541
–
4545
(2015).
24. R. D. Giacomo,
L. Bonanomi,
V. Costanza,
B. Maresca, C. Daraio, Biomimetic
temper
ature-
sensing
layer for artificial
skins.
Sci. Robot.
2
, eaai9251
(2017).
25. V.Costanza,
L.Bonanomi,
G.Mosca
to,L.Wang,Y.S.Choi,C.Daraio, Effectofglycerolonthe
mechanical
and temper
ature-sensing
properties
of pectin
films.
Appl.
Phys.
Lett.
115
,
193702
(2019).
26. G. T. Grant, E. R. Morris,
D. A. Rees, P. J. C. Smith,
D. Thom,
Biological
interactions
between
polysaccharides
and divalent
cations: The egg-box
model.
FEBS
Lett.
32
, 195
–
198
(1973).
27. D. A. Powell, E. R. Morris,
M. J. Gidley, D. A. Rees, Conforma
tions and interactions
of pectins
.2. Influence
of residue
sequence
on chain associa
tion in calcium
pectate gels.
J. Mol. Biol.
155
, 517
–
531
(1982).
28. B. R. Thakur,
R. K. Singh,
A. K. Handa,
M. A. Rao, Chemis
try and uses of pectin
—
A
review.
Crit. Rev. Food Sci.
37
, 47
–
73
(1997).
29. K. Matyjasze
wski, J. Xia, Atom transfer
radical
polymeriza
tion.
Chem.
Rev.
101
,
2921
–
2990
(2001).
30. S. Yamago,
Precision
polymer
synthesis
by degener
ative transfer
controlled/living
radical
polymeriza
tion using organotellurium,
organos
tibine,
and organobismuthine
chain-
transfer
agents.
Chem.
Rev.
109
, 5051
–
5068
(2009).
31. G. Moad,
E. Rizzardo,
S. H. Thang,
Toward Living
Radical
Polymeriza
tion
(2008),
vol. 41 of
Accounts
of Chemical
Researc
h
.
32. L. Cao, W. Lu, A. Mata, K. Nishinari,
Y. Fang, Egg-box
model-based
gelation of alginate and
pectin:
A review.
Carbohyd.
Polym.
242
, 116389
(2020).
33. J. Furukaw
a, A theory
of pseudo
cross-link.
Polym.
Bull.
7
, 23
–
30
(1982).
34. E. A. DiMarzio,
J. H. Gibbs,
Glass temper
ature of copolymers.
J. Polym.
Sci.
40
,
121
–
131
(1959).
35. M. Y. Sayah, R. Chabir,
H. Benyahia, Y. R. Kandri,
F. O. Chahdi,
H. Touzani,
F. Errachidi,
Yield,
esterifica
tion degree and molecular
weight evalua
tion of pectins
isolated fromorange and
grapefruit
peels under
different conditions.
PLOS ONE
11
, e0161751
(2016).
36. G. A. Mun, V. V. Khutory
anskiy,
G. T. Akhmetkalieva,
S. N. Shmako
v, A. V. Dubolazo
v,
Z. S. Nurkeeva, K. Park, Interpolymer
complexe
s of poly(acrylic acid) with poly(2-hydrox-
yethyl acrylate) in aqueous
solutions.
Colloid
Polym.
Sci.
283
, 174
–
181
(2004).
37. J. W. H. Schymk
owitz, F. Rousseau,
I. C. Martins,
J. Ferkinghoff-Borg,
F. Stricher,
L. Serrano,
Prediction
of water and metal
binding
sites and their affinities
by using the Fold-X force
field.
Proc. Natl. Acad.
Sci. U.S.A.
102
, 10147
–
10152
(2005).
38. B. Wang, J. Lai, H. Li, H. Hu, S. Chen,
Nanostr
uctured vanadium
oxide thin film with high
TCR at room temper
ature for microbolometer.
Infrared Phys. Techn.
57
, 8
–
13 (2013).
39. J. Dai, X. Wang, S. He, Y. Huang,
X. Yi, Low temper
ature fabrication
of VOx thin films for
uncooled
IR detectors
by direct current reactive magnetr
on sputtering
method.
Infrared
Phys. Techn.
51
, 287
–
291
(2008).
40. J. Kim, M. Lee, H. J. Shim, R. Ghaffari, H. R. Cho, D. Son, Y. H. Jung, M. Soh, C. Choi, S. Jung,
K. Chu, D. Jeon, S.-T. Lee, J. H. Kim, S. H. Choi, T. Hyeon, D.-H. Kim, Stretchable
silicon
nanoribbon
electronics for skin prosthesis.
Nat. Commun.
5
, 5747 (2014).
41. J. Park, M. Kim, Y. Lee, H. S. Lee, H. Ko, Fingertip
skin
–
inspir
ed microstructur
ed ferroelectric
skins discriminate
static/dynamic
pressure and temper
ature stimuli.
Sci. Adv.
1
,
e1500661
(2015).
42. R. C. Webb, A. P. Bonifas,
A. Behnaz,
Y. Zhang,
K. J. Yu, H. Cheng,
M. Shi, Z. Bian, Z. Liu, Y.-
S. Kim, W.-H. Yeo, J. S. Park, J. Song,
Y. Li, Y. Huang,
A. M. Gorbach, J. A. Rogers, Ultrathin
conformal
devices
for precise and continuous
thermal
characteriza
tion ofhuman
skin.
Nat.
Mater.
12
, 938
–
944
(2013).
43. H. U. Kang, Y. C. Yu, S. J. Shin, J. H. Youk, One-step synthesis
of block copolymers
using a
hydroxyl-
functionalized
trithiocarbonate
RAFT agent
as a dual initiator for RAFT poly-
merizati
on and ROP.
J. Polym.
Sci. Part Polym.
Chem.
51
, 774
–
779
(2013).
44. D. G. Hawthorne,
G. Moad,
E. Rizzardo,
S. H. Thang,
Living
radical
polymerizatio
n with
reversible addition
−
fr
agmenta
tion chain transfer
(RAFT):
Direct ESR observa
tion of inter-
mediate
radicals.
Macromolecules
32
, 5457
–
5459
(1999).
45. W. Wang, Q. Zhang,
Synthesis
of block copolymer
poly (n-butyl
acrylate)-b-poly
styrene by
DPE seeded
emulsion
polymerization
with monodisperse
latex particles
and morphology
of self-assembly
film surface.
J. Colloid
Interf.
Sci.
374
, 54
–
60
(2012).
46. A. M. Kubo,
L. F. Gorup,
L. S. Amaral, E. Rodrigues-Filho,
E. R. de Camargo,
Heterogeneous
microtubules
of self-assembled
silver and gold nanoparticles
using alive biotempla
tes.
Mater. Res.
21
, e20170947
(2018).
47. E. Vargün,
A. Usanmaz,
Polymeriza
tion of 2-hydr
oxyethyl acrylate in bulk and solution
by
chemical
initiator and by ATRP method.
J. Polym.
Sci. Part Polym.
Chem.
43
,
3957
–
3965
(2005).
48. D. Tang, B. A. J. Noordo
ver, R. J. Sablong,
C. E. Koning,
Metal-fr
ee synthesis
of novel bio-
based
dihydr
oxyl-termina
ted aliphatic polyesters as building
blocks
for thermoplas
tic
polyure
thanes.
J. Polym.
Sci. Part Polym.
Chem.
49
, 2959
–
2968
(2011).
Ackno
wledgments:
We acknowledge
the critical
support
and infrastructure provided for this
work by The Kavli Nanoscience
Institute at Caltech.
We would
like to thank
C. Heo and the
Process Technology
Group at SAIT for technical
support
during
IR device
fabrica
tion; S. Han,
M. S. Jang, and B. Min at the Korea Advanced
Institute of Science
and Technology
(KAIST)
for
advice
on the IR measur
ements;
and H. B. Moon,
Y. H. Jang, and N. Kim at Nextron Corp. for use
oftheMicroProbeSystem.
Funding:
Thisworkwassupported
bytheSamsung
Electron
icsSAIT,
GRO Program (C.D.),
and by the Schwartz/Re
isman
Collabor
ative Science
Program (C.D.).
Author
contributions:
T.H.K., Z.Z., V.C., L.W., and C.D. conceiv
ed the idea and designed
the
research. Z.Z., Y.S.C., and J.H.B. synthesized
the block copolymer.
T.H.K., Z.Z., Y.S.C., and S.K.
performed
the particle
size analysis, NMR, GPC, ATR-FTIR,
TGA-FTIR,
and the titration
experiments
for material characteriza
tion and analyzed
the data. N.J.H. provided technical
support
during
the FTIR analysis. T.H.K. designed
and fabrica
ted the temper
ature sensor.
T.H.K.,
V.C., and L.W. built the custom
measur
ement
stage for thermal
characteriza
tion, conducted
electrical
measur
ements,
carried
out mechanical
tests on the block copolymer,
and analyzed
the data. T.H.K., Y.S.C., Y.Y., and H.K. designed
and fabricate
d the IR detector.
T.H.K. performed
the IR measur
ements
and analyzed
the data. C.D. supervised
the project. T.H.K., Y.S.C., and C.D.
cowrote the manuscript.
All authors
commented
on the manuscript.
Competing
inter
ests:
T.H.K., Z.Z., Y.S.C., V.C., L.W., and C.D. are the named
inventors
on the patent assigned
to
Samsung
Electron
ics Co Ltd. and the California
Institute of Technology
regarding
the
biomimetic
block copolymer
and its applica
tion for temper
ature and IR sensing.
Applica
tion
number:
US20220056188A1
(2022-02-24).
Status: Pending.
T.H.K., Z.Z., Y.S.C., V.C., L.W., and C.D.
are the named
inventors on the issued
patent number
US11492420B2,
granted
to Samsung
Electronics Co. Ltd. and the California
Institute of Technology
regarding
composites
and IR
absorbers
(2022-11-08).
Status:Active.V.C.,C.D.,andZ.Z.arethenamed
inventors
onthepatent
assigned
to the California
Institute ofTechnology
regarding
the ABA-type
blockcopolymers
for
temper
ature sensing
and flow meters.
Applica
tion number:
US20200353729A1
(2020-11-12).
Status: Pending.
V.C. and C.D. are the named
inventors
on the issued
patent number
US10345153B2,
granted
to the California
Institute of Technology
regarding
gel-based
thermal
sensors
(2019-07-09).
Status: Active. C.D. is currentlyaffiliated with Meta Reality Labs. The other
authors
declare that they have no competing
interests.
Data and
materials
availability:
All
data needed
to evalua
te the conclusions
in the paper
are present in the paper
and/or
the
Supplementary
Materials.
Submitted
22 July 2022
Accepted
9 January
2023
Published
10 February
2023
10.1126/sciadv.ade0423
Kim
et al.
,
Sci. Adv.
9
, eade0423
(2023)
10 February
2023
9 of 9
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