Frontally polymerized foams: thermodynamic and kinetical aspects of front hindrance by particles

This jou nal is © The Royal Socie y o Chemis y 2023 Ma e . Ho iz., 2023, 10, 2989–2996 | 2989 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 COMMUNICATION Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online View Jou nal | View Issue 2990 | Ma e . Ho iz., 2023, 10, 2989–2996 This jou nal is © The Royal Socie y o Chemis y 2023 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. Communica ion Ma e ials Ho izons Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online This jou nal is © The Royal Socie y o Chemis y 2023 Ma e . Ho iz., 2023, 10, 2989–2996 | 2991 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). Ma e ials Ho izons Communica ion Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online 2992 | Ma e . Ho iz., 2023, 10, 2989–2996 This jou nal is © The Royal Socie y o Chemis y 2023 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. Communica ion Ma e ials Ho izons Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online This jou nal is © The Royal Socie y o Chemis y 2023 Ma e . Ho iz., 2023, 10, 2989–2996 | 2993 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. Ma e ials Ho izons Communica ion Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online 2994 | Ma e . Ho iz., 2023, 10, 2989–2996 This jou nal is © The Royal Socie y o Chemis y 2023 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 Open Access A icle. Published on 09 May 2023. Downloaded on 2/16/2024 10:22:57 AM. This a icle is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed Licence. View A icle Online This jou nal is © The Royal Socie y o Chemis y 2023 Ma e . Ho iz., 2023, 10, 2989–2996 | 2995 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. Re e ences 1 Q. Li, H.-X. Shen, C. Liu, C.-F. 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