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Ci e his: Ma e . Ho iz., 2023,
10, 2989
F on ally polyme ized oams: he modynamic and
kine ical aspec s o on hind ance by pa icles†
Pe Lepcio,
a
John Dague e-B ad o d,
b
Anna Ma ia C is ado o,
c
Ma kus Schue e
c
and Alan J. Lesse *
b
F on al polyme iza ion (FP) is a sol en - ee, ene gy-efficien p ocess
whe e a sel -p opaga ing polyme iza ion eac ion wi h a cha ac e is ic
sha p empe a u e g adien a he on head p opaga es h ough he
esin o p o ide he cu ing condi ions. I elies on he en halpic
balance, which sp eads he eac ion o un eac ed esin in he
neighbo hood. The e o e, he FP is sensi i e o he p esence o
non- eac i e olumes, such as bounda ies, ille s, o o he addi i es,
ha e ain hea om he on bu p oduce no en halpy in e u n.
On he o he hand, he on ’s high empe a u e could be used o
ini ia e o he p ocesses, such as oaming, inco po a ing hem in o a
simple single-s ep ab ica ion p ocedu e. This s udy used silica
pa icles o wo diffe en sizes (14 nm and 200–300 nm) in an
epoxy-based FP oam as a ep esen a i e ille o p obe he con-
s ain s imposed by non- eac i e addi i es. The p esence o pa i-
cles isibly hinde ed he on p opaga ion, inc eased he oam
densi y and e en co up ed he on al egime in some cases. We
show ha p ehea ing o chemical composi ion changes a e iable
app oaches o add ess he ille s’ ad e se e ec s. Fu he mo e, we
p esen e idence ha he educed eac ion en halpy caused by
silica nanopa icles, was balanced by he lowe hea capaci y o ou
model sys em. A he same ime, he on hind ance was a ibu ed
o changes in eac ion kine ics and he hea dis ibu ion a ound he
on . These esul s se up essen ial na a i es o he design and
p ac ical applica ions o on ally polyme ized oams wi h non-
eac i e ille s.
1. In oduc ion
F on al polyme iza ion (FP) is a special polyme iza ion p ocess
whe e once ini ia ed a one loca ion, can p opaga e om he
ini ia ion si e h ough he olume o he uncu ed esin ia he
exo he m gene a ed du ing he cu e. As he cu ing p oceeds,
he e ol ing excess hea locally sel -ini ia es he eac ion in
nea by egions. This p ocess is epea ed un il he p opaga ing
polyme iza ion c ea es a on wi h a cha ac e is ic sha p
empe a u e g adien . These cu ing condi ions a e a mo e
ene gy efficien han he mal cu ing
1
while no suffe ing om
he sho po -li e o chemically cu ed o mula ions.
2
A he
same ime, he sol en - ee FP condi ions gene a e minimum
was e and offe speci ic unique p ope ies compa ed o bulk
polyme iza ion, such as highe con e sion, be e mechanical
pe o mance, o chemical esis ance.
3
Mo eo e , he on
could ini ia e o he p ocesses such as in-si u syn hesis o
nanopa icles
4
o oaming.
5
These pa ame e s make he FP a
good candida e o en i onmen ally iendly and sus ainable
p ocessing me hods, especially in combina ion wi h g een
chemis ies.
6,7
a
Cen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology,
Pu kyn
ˇo a 656/123, 612 00 B no, Czech Republic
b
Uni e si y o Massachuse s Amhe s , 120 Go e no s D i e, Amhe s , MA 01003,
USA. E-mail: [email p o ec ed]
c
BASF Polyu e hanes, Elas og ans 60, Lem oe de, 49448, Ge many
†Elec onic supplemen a y in o ma ion (ESI) a ailable: The suppo ing in o ma-
ion ile con ains addi ional da a wi h a on al egime co up ed by pa icles, a
aw DSC cu e, and empe a u e p o iles o he illed samples. See DOI: h ps://
doi.o g/10.1039/d2mh01553
Recei ed 21s Decembe 2022,
Accep ed 9 h May 2023
DOI: 10.1039/d2mh01553
sc.li/ma e ials-ho izons
New concep s
This manusc ip es ablishes basic na a i es o designing and imple-
men ing ille s in on ally polyme ized (FP) oams. New undamen al
insigh s in o he he modynamics and kine ical effec s induced by mic o-
and nanopa icles o on al polyme iza ion a e p esen ed. FP oams a e
a o ed o ene gy-efficien cu ing, high con e sion, and good mechanical
pe o mance. Howe e , adding pa icles o an FP o mula ion may
equi e adjus men s o main ain he on al egime o polyme iza ion
by es o ing he en halpic balance. The h ee main phases o FP a e he
p ehea ing ahead o he on , he on head wi h maximum
empe a u e, and he hea e en ion a e he on passes. All h ee
p ocesses a e signi ican ly affec ed by he p esence o pa icles. We
demons a e new design s a egies add essing hese challenges
p e en ing his ield om u he expansion. Ei he he o mula ion
could be p ehea ed be o e he ini ia ion, he eac ion a e can be
accele a ed by adding mo e ini ia o , o he eac ion en halpy migh be
inc eased by adjus ing he monome composi ion. These esul s open a
way owa d inno a i e composi e and nanocomposi e FP oams. This new
class o ma e ials can combine simple and efficien p ocessing,
ligh weigh s uc u e, mechanical obus ness, and ad anced p ope ies,
such as he mal o elec ical conduc i i y, in oduced by unc ional
nano ille s.
Ma e ials
Ho izons
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The on al egime is go e ned by he en halpic balance
be ween hea gene a ion, consump ion, and losses o he
en i onmen and simul aneous p ocesses.
2
The he e ogeneous
ma e ials nea he eac ion on may abso b and e ain he
excess eac ion en halpy while p oducing no eac ion en halpy
in e u n. Hence, he FP is sensi i e o bounda y condi ions and
un eac i e olume, e.g., ille s. E en a iny a ia ion o ac i a-
ion ene gy may ha e a p ominen effec on he on eloci y
and limi he maximum con en o un eac i e addi i es eligible
o achie ing he FP condi ions.
8
Insufficien , slow, o une en
hea e olu ion causes he on o cool down and decele a e; i
may esul in inge ing o e en dis up he sel -p opaga ion.
9,10
This could also o igina e om he inc eased c oss-linking
densi y o slowe diffusion in he sys em.
2
On he o he hand,
oo la ge excess hea p omo es sel -ini ia ion, and he eac ion
becomes mo e simila o s anda d bulk polyme iza ion.
11
Nanopa icles and o he nanoma e ials ep esen a speci ic
ca ego y o ille s wi h p onounced in e acial effec s.
12
They a e
a o ed o nano ein o cemen ,
13
unc ional addi i a ion,
14,15
and, gene ally, a simple modi ica ion o p ope ies.
16
Da yan,
e al. epo ed an almos negligible effec o silica nanopa icles
(NPs) on he on p opaga ion and empe a u e o PMMA/me hyl
me hac yla e solu ion up o he concen a ion co esponding o
he NP agg ega ion limi .
17
On he o he hand, la ge o agg e-
ga ed pa icles caused a a mo e p onounced on hind ance.
In e es ingly, Da yan, e al. also documen ed an imp o ed NP
dispe sion a e he FP. A s ong shea ield is usually equi ed o
achie e a good NP dispe sion, e.g.,ina winsc ewex ude
18
o
ul asonica ion-induced ca i a ion.
19,20
Nanosilica pa icles we e
also ound o s abilize he on and supp ess inge ing.
9
Such
obse a ion has g ea p ac ical impo ance because he quali y o
NP dispe sion di ec ly in luences he ma e ial p ope ies.
21
Fo
ins ance, he mechanical and he mal p ope ies s em om he
immobilized and us a ed polyme laye adso bed a ound he
NPs
22
ha expe ience he nanocon inemen effec .
23
Finally, nanocomposi e oams ep esen a b oad ca ego y o
ligh weigh ma e ials. NPs and o he nano ille s a e o en used
o con ol he oam mo phology, educing he cell size h ough
enhanced cell nuclea ion
24–26
o in oducing unc ional p ope -
ies such as elec ic conduc i i y.
27
Howe e , NPs also ha e a
complex e ec on mechanical de o ma ion and ac u e due o
he combined nanocon inemen e ec om so and s i
inclusions ep esen ed by he oids and he nanopa icles.
26
In he only p e ious a emp known o he au ho s, he FP has
been deployed o ab ica e polyme oams by including a
physical blowing agen in o a s anda d FP o mula ion.
5
The
mo phology o FP oams was con olled by he concen a ion
and ype o he blowing agen . A he same ime, he empe a-
u e and iscosi y g adien a he on head esul ed in a
p ominen aniso opy o he oam cells.
5
We no e ha his
single-s ep p ocedu e migh be be e sui ed o ab ica ing
aniso opic oams a a la ge scale han he empla ing p o-
cesses.
28
None heless, he apo iza ion o a physical blowing
agen e ained hea om he on , comp omising i s s abili y.
5
This ac o limi s he e sa ili y o his app oach, especially in
combina ions wi h o he non- eac i e addi i es.
Ins ead, an exo he mic chemical blowing agen may p o e a
mo e iable solu ion o achie ing low oam densi y and a high
polyme iza ion a e. The cu en s udy p esen s on ally poly-
me ized oams based on a he mose ing epoxy esin. An
azodica bonamide-based blowing agen s a ed he oaming
nea he polyme iza ion empe a u e, and wo sizes o silica
pa icles (14 nm and 200–300 nm) we e used as ep esen a i e
ille . The pa icles caused an appa en on hind ance man-
i es ed by a slowe on p opaga ion a e and inc eased oam
densi y. A de ailed insigh in o he he modynamics by modu-
la ed DSC sugges ed ha he nanopa icles lowe ed he eac-
ion hea . Ye , i was coun e ed by he educed hea capaci y o
he nano- illed o mula ion. Thus, he c ucial ole in he on
hind ance was a ibu ed o eac ion kine ics and hea dis ibu-
ion a ound he on . The mal imaging was used o e alua e
he on empe a u e g adien s, o sepa a e he con ibu ions
in h ee egions – p ehea ing ahead o he on , he on head
wi h maximum empe a u e, and he hea e en ion a e he
on passes. All h ee egions we e signi ican ly a ec ed by he
p esence o pa icles. The p esen ed esul s se up basic na a-
i es o he design and implemen a ion o nanopa icles in o
he on ally polyme ized oams.
2. Ma e ials and me hods
Ma e ials
The basic FP o mula ion used in his s udy is a pa en ed
echnology o he BASF company and he Uni e si y o Massa-
chuse s Amhe s . The main componen s we e he 3,4-epoxy-
cyclohexylme hyl 3,4-epoxycyclohexaneca boxyla e (ECC, Sigma
Ald ich, Ge many) and bisphenol A diglycidyl e he (DGEBA,
Olin Epoxy, USA) monome s in he a io o 60 : 40. I u he
con ained 2.5% o he p-(oc yloxyphenyl)phenyliodonium hexa-
luo oan imona e (IOC, Geles , USA) pho oini ia o , 2.5% o he
1,1,2,2- e aphenyl-1,2-e hanediol (Sigma Ald ich, Ge many),
0.5% o he azodica bonamide based RAZ-P oaming agen
(Reedy Chemicals, USA), and 1% o he DC-193 s abilize
(Dow Silicon, USA). The 3% IOC and 70 : 30 ECC : DGEBA
samples we e a ied om he basic FP o mula ion by adjus ing
he IOC concen a ion and he monome a io, espec i ely.
Silica pa icles wi h an a e age size o 14 nm and 200–300 nm
we e supplied om Sigma Ald ich (Ge many) and used as
ob ained.
Sample p epa a ion
All componen s o he FP o mula ion we e mixed and s i ed
o 1 hou a 60 1C. Pa icles we e hen added and homogenized
wi h a B anson Soni ie 450 (USA) o 4 minu es a 20% du y
cycle and he powe se o 6. The o mula ion was pou ed in o a
2200 p e-cu ubbe mold placed on a PTFE shee and
ini ia ed by a ho solde ing i on (Welle WP 80, 80 W, 24 V,
se poin 250 1C). The on p opaga ed in he ho izon al di ec-
ion wi h no uppe bounda y.
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Cha ac e iza ion
The oam densi y was measu ed using wa e as a wo king
medium wi h a pycnome e . The eac ion en halpy was
measu ed by a DSC Q200 (TA Ins umen s, USA) in he me ic
pans a a hea ing amp o 10 1Cmin
1
. Modula ed DSC
(M-DSC) was pe o med wi h he same ins umen a he
hea ing amp o 2 1Cmin
1
, modula ion ampli ude o 0.5 1C,
and a pe iod o 60 s. The ille concen a ion was e alua ed
by TGA (Q50, TA Ins umen s, USA) om he esidual weigh
a e a 10 minu e hold a 700 1C. The esul s we e co ec ed
on he un illed o mula ion’s esidual weigh o 0.48%.
Magellan 400 (FEI, Czech Republic) collec ed he SEM images
using a seconda y elec on de ec o on gold-coa ed samples
a he accele a ion ol age o 2 kV.
The mal imaging was pe o med wi h a FLIR A325sc
he mal came a on a on p opaga ing h ough a 1 500
mold. The maximum empe a u e and empe a u e p o iles
we e analyzed using he FLIR ools OEM so wa e. The
p ehea ing and cooling a e was e alua ed by a linea i o
7 diffe en spo s in he ange o 37.5–100 1Cand401C
beyond he on empe a u e, espec i ely. F on eloci y
was calcula ed om he peak empe a u e ime and he
known dis ance o he selec ed poin s.
3. Resul s and discussion
The oam densi y is a basic p ope y ha can be ela ed o he
enginee ing p ope ies o he oam h ough mic omechanics as
well as o he physical p ope ies. These will be discussed in a
sepa a e publica ion, and i is no he ocus o he cu en
in es iga ion. Fo he model sys em p esen ed he ein, i was
es ablished as 0.569 g cm
3
(Fig. 1). These FP oams ea u e a
ough skin laye nea he bounda ies wi h a ela i ely smoo h
su ace on op and he skin laye oughness on he bo om
being a unc ion o he subs a e he oam is gene a ed on. In
con as , he ac ual densi y o he oamed co e is much lowe .
Adding silica pa icles isibly hinde s he on p opaga ion
and inc eases he densi y o he oams. 1 ol% o he 14 nm
silica nanopa icles slow he eac ion o he poin ha he on
canno o m a labo a o y empe a u e. Only a iny a ea nea
he ho ip is cu ed (Fig. S1, ESI†). In his case, he on al
egime can only be achie ed by p ehea ing he o mula ion in
an o en o 60 1C be o e he ini ia ion. These esul s con adic
Da yan’s conclusions ha nanopa icles ha e negligible
impac on he on p opaga ion.
17
Two s a egies a e employed o b ing he illed oams’
densi ies down o he le el o he basic o mula ion. Fi s ly,
he eac ion a e is enhanced by inc easing he IOC ini ia o
Fig. 1 F on ally polyme ized oams. SEM images o he po osi y in pa allel ( op igh ) and pe pendicula (middle igh ) di ec ions espec i e o he on
p opaga ion. The densi y o he selec ed samples measu ed by a pycnome e (middle le ). Images o he p opaga ing on in ime (bo om).
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concen a ion om 2.5 o 3%, assuming ha he o al eac ion
en halpy emains nea ly unchanged hanks o he high mono-
me con e sions achie ed by on al polyme iza ion.
3
Secondly,
he eac ion en halpy is boos ed by adjus ing he monome
a io om 60 : 40 o 70 : 30 ECC : DGEBA. We no e ha he
densi ies o un illed oams also dec ease in bo h cases (Fig. 1).
The c i ical pa ame e o all FP chemis ies is main aining
he on ’s en halpic balance. Thus, he eac ion en halpies a e
measu ed by DSC (Fig. S3 le , ESI†). An en i e DSC cu e o he
s anda d FP oam o mula ion is displayed in Fig. S3 (ESI†)
igh . I was p e iously epo ed ha he eac ion en halpy
iola es he simple ule o mix u e.
2
Ins ead, he mix u e
p ope ies a e p edic ed o lie be ween an uppe bound de ined
by he weigh ed a i hme ic mean (WAM) and a lowe bound
based on each componen ’s weigh ed ha monic mean (WHM).
2
Mo eo e , he empe a u e amp es and he small eac ion
olume used o his measu emen migh no cap u e he
on al condi ions, ye we assume ha he eac ion en halpies
scale acco dingly. None heless, he en halpy eco ded o he
70 : 30 ECC:DGEBA sample (508 J g
1
) is nea ly iden ical o he
basic o mula ion (516 J g
1
) while he 3% IOC has e en lowe
alue (486 J g
1
, Fig. S3 le , ESI†). In e es ingly, his end is
discon inued in he samples illed wi h 0.1% o 200–300 nm
umed silica. Ins ead, hei en halpies scale in he o de Basic
o mula ion (437 J g
1
)o3% IOC (477 J g
1
)E70 : 30 ECC :
DGEBA (469 J g
1
), co esponding well o hei densi ies
(Fig. 1).
While hese esul s appea con using, he e a e se e al
p ocesses going on simul aneously, which he s anda d DSC
canno dis inguish. Mo eo e , he baseline o he hea low
cu e shi s as he hea capaci y changes h oughou he eac-
ion. On he o he hand, a modula ed DSC (M-DSC) can
sepa a e he con ibu ions o e e sible and i e e sible en hal-
pies (Fig. 2). Repea ing he es se e al imes while omi ing
a ying componen s o he o mula ion iden i ies he indi i-
dual peaks (Fig. S2, ESI†). The h ee mos p onounced p o-
cesses a e associa ed wi h he ECC and DGEBA polyme iza ion,
which shall be ea ed sepa a ely,
29
and he decomposi ion o
he oaming agen (Fig. 2). Glass ansi ion, ECC e apo a ion
peak, and he changes in hea capaci y h oughou he eac ion
(Fig. 2) a e ecognized in he much weake e e sible hea low
signal.
Polyme iza ion is he i s p ocess s a ing a he lowes
empe a u e (a ound 80 1C). The glass ansi ion, which ollows
a 97 1C o he s anda d o mula ion, is expec ed in his ange
o an epoxy esin.
30
An i e e sible exo he mic peak o oaming
appea s wi h a maximum a 116.9 1C. Finally, he ligh e and
mo e eac i e ECC monome ceases eac ion a oughly 160 1C,
while he hea ie and less eac i e DGEBA monome eac s
un il oughly 220 1C. The esul s co ela e well wi h he
expec a ion ha he hea ie monome ’s eac ion is slowe han
he ligh e one’s.
29
The e e sible en halpy peak a 116.3 1Cis
a ibu ed o he ECC e apo a ion (boiling poin 170 1C)
because i is s ill p esen e en in he absence o he oaming
agen . Ye , i is p obably no coincidence ha his peak aligns
nea he maximum o he highly exo he mic oaming (Fig. 2).
Fu he expe imen s a e pe o med wi h he 3% IOC sample
because he s anda d o mula ion canno on ally polyme ize
in he p esence o pa icles a he es ed bounda y condi ions.
Adding 1 ol% o 14 nm silica nanopa icles is a ep esen a i e
example p obing he effec o illing. The eco ded en halpies
( o al, e e sible, i e e sible), glass ansi ion, and hea capa-
ci y a 50 1C o bo h samples a e lis ed in Table S1 (ESI†). The
esul s a e qui e sensi i e o he p ecise composi ion and he
monome a io, which is affec ed by he ECC e apo a ion upon
p ocessing. The e o e, he illed and un illed samples a e
p epa ed om a single ba ch and p ocessed oge he o achie e
high p ecision. No ably, he un illed o mula ion is also ul a-
sonica ed, al hough i has no p ac ical meaning beyond main-
aining he same p ocessing condi ions. Silica nanopa icles
sligh ly in luence he i e e sible en halpy (Fig. S4 le , ESI†).
The eco ded change o 18.7 J g
1
ep esen s a dec ease o
3.1%, exceeding he expec a ion based on he simple olume
eplacemen (Table S1, ESI†). While he onse o polyme iza ion
is sligh ly hinde ed, he exo he mic oaming peak is mo e
p onounced (Fig. S4 le , ESI†). A possible explana ion is he
nanopa icle’s capabili y o ca alyze he decomposi ion o he
oaming agen ,
31
bu i could also inc ease due o he delayed
cu ing.
32
The inal pa o he ECC and DGEBA eac ions a e
p ac ically independen o he illing (Fig. S4 le , ESI†).
The T
g
o he 3% IOC is obse ed a a lowe empe a u e
(95 1C, Fig. S4 igh , ESI†) han in he s anda d o mula ion
(97 1C, Fig. 2) due o i s as e cu ing. The illing was indiffe en
o T
g
wi hin he expe imen al e o , keeping he alue o 95 1C
( he de ice’s empe a u e accu acy is 0.05 1C and he em-
pe a u e p ecision is 0.1 1C). The peak a ibu ed o ECC
e apo a ion is also p onounced by adding nanopa icles
(Fig. S4 igh , ESI†), p esumably due o he pa icle nuclea ion
effec , which eases he monome e apo a ion. None heless, he
mos p onounced diffe ence is he shi o he illed sample’s
baseline owa ds highe (less nega i e) le els o he e e sible
hea low (Fig. S4 igh , ESI†). The baseline ep esen s he hea
Fig. 2 To al, e e sible, and i e e sible hea low cu e o he FP o -
mula ion ob ained by he modula ed DSC. The inse shows an enla ged
de ail o he e e sible hea low in he ange o he eac ion.
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consumed by he sample’s hea ing and di ec ly co esponds o
i s hea capaci y. The upshi mani es s a d op in he hea
capaci y o he illed sample om 1.927 J g
1
K
1
(measu ed a
50 1C) o 1.775 J g
1
K
1
, because i equi es less en halpy o
hea ing. Silica and o he oxidic nanopa icles adhe e well o
hyd ophilic ma ices,
33
leading o he well-known nano ein o -
cemen effec ,
23
inc eased iscosi y,
34
and he s iffening o he
o mula ion. In u n, a lowe hea capaci y is gene ally expec ed
om a mo e solid-like ma e ial due o he supp essed inne
mo ion. None heless, i is essen ial o highligh ha he lowe
hea capaci y ully compensa es he losses in cu ing en halpy
caused by he olume eplacemen . This p inciple may explain
he p e iously epo ed ze o effec o nanopa icle addi i es on
on al polyme iza ion a low pa icle concen a ions.
17
The in eg al hea cu es, i.e., he hea cu es in eg a ed o e
he empe a u e (Fig. 3), clea ly documen his phenomenon.
The p ocess s a s wi h a hea consump ion equi ed o he
ini ial hea -up, and he end only u ns upwa ds o become
exo he mic a he eac ion onse (92.7 and 90.7 1C o he illed
and un illed samples, espec i ely). The eac ion en halpy con-
ibu es he same hea as equi ed o he ini ial hea ing phase
a a ound 110 1C. This poin ma ks he minimum empe a u e
which mus be heo e ically eached by he on ’s head o
sus ain he on . Though, he hea e en ion and losses push
his poin o highe empe a u es in eal samples. None heless,
he eac ion con inues un il he maximum excess hea is
ob ained nea he empe a u e whe e he ECC s ops eac ing
wi h a dis inc shoulde a ound he oaming empe a u e
(Fig. 3). Finally, he hea consump ion phase is eco e ed when
he eac ion en halpy is (nea ly) exhaus ed.
The in eg al cu es o he illed and un illed samples a e
nea ly iden ical up o app ox. 125 1C, while a disc epancy
de elops abo e his empe a u e (Fig. 3). The illed o mula ion
e ol es mo e excess hea pe uni weigh , which could be
dis ibu ed in o he neighbo ing a eas o p opaga e he on .
The impo ance o he lowe ed hea capaci y is supe io o he
educed eac ion en halpy (Table S1, ESI†). I is unclea how
much his conclusion ela es o his speci ic case and could be
gene alized o o he nano- illed FP o mula ions. None heless,
he esul s seemingly disapp o e ou ini ial obse a ion ha
nanopa icles hinde he on p opaga ion while suppo ing
he conclusion o Da yan, e al.
17
An appa en d awback o he
low en halpy-low capaci y case is i s highe sensi i i y o bounda y
condi ions. The bounda ies ake away he same amoun o hea
(a a gi en empe a u e), ye he illed o mula ion mus dona e i
by eac ing la ge mass/ olume han he un illed one. Ne e -
heless, a po en ial explana ion o he obse ed diffe ence may
be ound in he cu ing kine ics. F ee- adical polyme iza ion o
ac ylics, used by Da yan, e al.,
17
gene ally p o ide a as e cu ing
eac ion han ca a onically polyme ized epoxies used in his s udy.
Mo eo e , Da yan, e al. used a simple on al polyme iza ion,
bu he azodica bonamide oaming agen decomposi ion may
also in e ac wi h he nanopa icles.
31
Indeed, ou u he e i-
dence sugges s ha he hind ance effec should be ela ed o
kine ics a he han he modynamics, as ini ially assumed.
The kine ics a e assessed by he mal imaging o he p opa-
ga ing on o e a dis ance o 500 . The maximum empe a u e
sensed by he came a in he whole he mal image (Fig. 4 le )
and empe a u e p o iles a se e al ixed poin s (Fig. 4 igh ) a e
e alua ed. The peak empe a u e imes o he indi idual
poin s a e combined wi h hei known dis ance o ob ain he
on eloci y (Fig. S6 le , ESI†). The mal imaging con i ms
he subjec i e obse a ion o pa icles slowing down he p o-
paga ing on . Bo h samples illed wi h 1 ol% o silica
yield a simila d op in on eloci y. I alls by 25–28% om
3.2 mm s
1
o he un illed o mula ion o 2.3 and 2.4 mm s
1
o 14 nm and 200–300 nm pa icles, espec i ely. Polyme -
adso bing pa icles con ibu e o he physical c oss-linking.
35
Highe c oss-linking densi y slows down he di usion and,
hus, he on p opaga ion.
2
Howe e , scaling wi h he pa icle
size and su ace a ea would be expec ed in such a case, which
con adic s he cu en esul s.
The on empe a u e (Fig. S6 igh , ESI†) is calcula ed om
he a e age maximum empe a u e eco ded by he he mal
came a a he s eady on p opaga ion phase (Fig. 4 le ). We
no e ha he spa ial esolu ion o he mal imaging is insuffi-
cien o e alua e he empe a u e o indi idual pa icles. Mo e-
o e , no o he echnique known o au ho s is a ailable o
moni o empe a u e p o iles a nanoscale p ecision inside
he o mula ion du ing he eac ion. The e o e, no local em-
pe a u e a ia ion nea he silica su ace was conside ed. The
on head o he 3% IOC o mula ion aises he empe a u e
om ambien condi ions (B18 1C) o he maximum o 253.9 1C
in abou 6–7 s. Silica educes he on empe a u e o 236.7 and
238.6 1Cmms
1
o 14 nm and 200–300 nm pa icles, espec-
i ely (Fig. S6 igh , ESI†). The d op by 17.2/15.3 1C co esponds
o oughly 7% o he o al empe a u e change expe ienced a
he on head (B234 1C).
The eco ded on empe a u es misma ch he expec a ion
based on he M-DSC measu emen (Fig. 3), whe e he illed
samples p oduce la ge excess en halpy. This obse a ion
migh be pa ially ela ed o he M-DSC expe imen al se up,
which alls ou o he FP condi ions, and he hea dis ibu ion
a ound he on , as ou u he esul s sugges .
Fig. 3 In eg al cu es compa ing he hea consump ion and e olu ion o
he FP o mula ions as a unc ion o empe a u e.
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The ini ial hea ing a e ahead o he on (Fig. S7 le , ESI†)
is e alua ed in he ange o 37.5–100 1C acco ding o he M-DSC
esul s (Fig. 3). While he un illed o mula ion hea s up a he
a e o 86.6 1Cs
1
, he silica- illed samples show he a e o 48.1
and 53.3 1Cs
1
o he 14 nm and 200–300 nm pa icles,
espec i ely. This a ia ion by 44.5/38.5% exceeds he simple
expec a ion based on he di e en on eloci ies whe e he
change caused by pa icles is only 25–28% (Fig. S6 le , ESI†). I
sugges s ha he silica- illed o mula ions s a o p ehea
u he ahead o he on , hus, hea ing a la ge olume while
consuming mo e hea om he on head.
The pos -cu ing cu es a e i ed wi h a linea eg ession a
40 1C beyond he peak empe a u e (Fig. S7 igh , ESI†). This
app oach migh be a li le o e simplis ic, ye i p o ides a
single-pa ame e cha ac e is ic ha could be easily used o
compa e diffe en samples. The 3% IOC, 1 ol% silica 14 nm,
and 1 ol% silica 200–300 nm samples’ cooling a es a e 4.2,
2.2, and 2.4 1Cs
1
, espec i ely. Hence, he slowe cooling a e
o he illed o mula ions u he es ains he on head om
he hea supply since i is mo e e ained behind he on .
Finally, we es ed whe he he shea g adien a he on
head could push pa icles. This could inc ease he pa icles’
local concen a ion ahead o he on and magni y he pa icle-
induced effec s. The e o e, se e al specimens collec ed om
si es o an FP sample a a ying dis ances om he ini ia ion
poin a e es ed by TGA (Fig. S7, ESI†). The esidual weigh s a e
co ec ed by he esidual weigh o un illed ma ix e e ence
and ecalcula ed o olume a ios acco ding o he silica
densi y. No signi ican a ia ion in pa icle concen a ion is
ound o ei he 14 nm o 200–300 nm pa icles, sugges ing no
such e ec aking place ega dless o he pa icle size (Fig. S7,
ESI†).
4. Conclusion
Adding pa icles o a FP o mula ion may equi e adjus men s
o main ain he on al egime o polyme iza ion. Ei he he
o mula ion could be p ehea ed be o e he ini ia ion, he eac-
ion a e can be accele a ed by adding mo e ini ia o , o he
eac ion en halpy migh be inc eased by adjus ing he mono-
me composi ion. The lowe eac ion en halpy o he illed
samples is coun e ed by hei educed hea capaci y, leading
o a g ea e excess en halpy as eco ded by modula ed DSC. On
he o he hand, he mal imaging e eals slowe p ehea ing,
on p opaga ion, and cooling a es o he illed o mula ions.
I sugges s ha he excess ene gy sp ead in o a la ge a ea/
olume ahead o he on while mo e hea is e ained
behind i .
These esul s ollow he same end as he change in on
empe a u e and eloci y, ye he a e a ied by a diffe en
ela i e a io han he o he p ope ies. I sugges s ha he
on eloci y is no he only con ibu ion o he o he changes.
Finally, he on capabili y o push pa icles was es ed wi h no
e idence o such beha io . The cu en esul s se up essen ial
na a i es o he design and p ac ical applica ions o on ally
polyme ized oams wi h non- eac i e ille s. Fu he wo k shall
ocus on he aniso opic p ope ies o hese ma e ials and he
mo phological changes caused by he pa icula ille s.
Fig. 4 Maximum empe a u e ( op le ) and empe a u e p o iles o he nea un illed 3% IOC sample a selec ed ixed poin s ( op igh ) o he on al
polyme iza ion eco de by he mal imaging (bo om). Tempe a u e p o iles o he illed samples can be ound in Fig. S5 (ESI†).
Communica ion Ma e ials Ho izons
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Con lic s o in e es
A pa en WO 2022/087097 A1 owned by BASF company and he
Uni e si y o Massachuse s Amhe s p o ec s he basic FP
oam o mula ion.
Acknowledgemen s
This wo k was suppo ed by he F on al Polyme iza ion o
Mic ocellula Foams (NORA) p ojec suppo ed by BASF com-
pany h ough he No heas Resea ch Alliance (NORA).
P. Lepcio acknowledges he GF21-43070L p ojec suppo ed
by GA C
ˇR.
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