Reversible actuation ability upon light stimulation of the smart systems with controllably grafted graphene oxide with poly (glycidyl methacrylate) and PDMS elastomer: Effect of compatibility and graphene oxide reduction on the photo-actuation performance

polyme s A icle Re e sible Ac ua ion Abili y upon Ligh S imula ion o he Sma Sys ems wi h Con ollably G a ed G aphene Oxide wi h Poly (Glycidyl Me hac yla e) and PDMS Elas ome : E ec o Compa ibili y and G aphene Oxide Reduc ion on he Pho o-Ac ua ion Pe o mance Jose Osicka 1ID , Mi osla M lik 1ID , Ma ke a Ilciko a 2,*, Ba bo a Hanuliko a 1, Pa el U banek 1ID , Michal Sedlacik 1,*ID and Ja osla Mosnacek 2,3 ID 1Cen e o Polyme Sys ems, Uni e si y Ins i u e, Tomas Ba a Uni e si y in Zlín, T ida T. Ba i 5678, 760 01 Zlín, Czech Republic; [email p o ec ed] (J.O.); [email p o ec ed] (M.M.); [email p o ec ed] (B.H.); [email p o ec ed] (P.U.) 2Polyme Ins i u e, Slo ak Academy o Sciences, Dúb a ska ces a 9, 845 41 B a isla a, Slo akia; [email p o ec ed] 3Cen e o Ad anced Ma e ials Applica ion, Slo ak Academy o Sciences, Dúb a ska ces a 9, 845 11 B a isla a, Slo akia *Co espondence: [email p o ec ed] (M.I.); [email p o ec ed] (M.S.); Tel.: +421-232-294-347 (M.I.); +420-576-038-027 (M.S.) Recei ed: 20 June 2018; Accep ed: 26 July 2018; Published: 28 July 2018   Abs ac : This s udy is ocused on he con ollable educ ion o he g aphene oxide (GO) du ing he su ace-ini ia ed a om ans e adical polyme iza ion echnique o glycidyl me hac yla e (GMA). The success ul modi ica ion was con i med using TGA-FTIR analysis and TEM mic oscopy obse a ion o he polyme shell. The simul aneous educ ion o he GO pa icles was con i med indi ec ly ia TGA and di ec ly ia Raman spec oscopy and elec ical conduc i i y in es iga ions. Enhanced compa ibili y o he GO-PGMA pa icles wi h a polydime hylsiloxane (PDMS) elas ome ic ma ix was p o en using con ac angle measu emen s. P epa ed composi es we e u he in es iga ed h ough he dielec ic spec oscopy o p o ide in o ma ion abou he polyme chain mobili y h ough he ac i a ion ene gy. Dynamic mechanical p ope ies in es iga ion showed an excellen mechanical esponse on he dynamic s imula ion a a b oad empe a u e ange. The mal conduc i i y e alua ion also con i med he u he pho o-ac ua ion capabili y p ope ies a ligh s imula ion o a ious in ensi ies and p o ed ha composi e ma e ial consis ing o GO-PGMA pa icles p o ide sys ems wi h a signi ican ly enhanced capabili y in compa ison wi h nea GO as well as nea PDMS ma ix. Keywo ds: g aphene oxide; educ ion; SI-ATRP; pho o- esponsi e ma e ial; ligh -s imuli ma e ial; dielec ics; poly (glycidyl me hac yla e); dynamic mechanical analysis 1. In oduc ion Sma ma e ials belong o a g oup o ma e s. Such physical p ope ies can be changed upon ex e nal s imulus i.e., elec ic [ 1 – 4 ] o magne ic ield [ 5 – 8 ], pH [ 9 – 12 ], empe a u e [ 13 – 16 ], o ligh [ 17 – 20 ]. The sys ems exhibi ing e e sible pho o-ac ua ion and ligh - esponsi e p ope ies a e i al o he esea ch communi y only du ing he las decade while he es o he abo e men ioned p ope ies ha e been pa o he esea ch communi y o e he pas 30 yea s. The e o e, he e a e s ill Polyme s 2018,10, 832; doi:10.3390/polym10080832 www.mdpi.com/jou nal/polyme s Polyme s 2018,10, 832 2 o 14 many d awbacks in his opic like s abili y o he sys ems o e en pe o mance, which e e sibly con ac s o elonga es he polyme composi e sample upon ligh s imula ion. Ma e ials exhibi ing his phenomenon can ind u iliza ion in a ious sys ems con olling he damping p ope ies [ 21 ], sensing [ 22 ], o hap ic displays [ 23 ]. The e o e, he b oad applica ions belong o he ield o elec onic [24], ci il enginee ing [25], o medicine [26], espec i ely. In hese applica ions, he g aphene oxide (GO) pa icles as a pa o sma sys ems we e p ope ly in es iga ed due o hei unique p ope ies, i.e., good dispe sibili y in he su ounding media [ 27 ], possible pos - unc ionaliza ion [ 28 ], a e easily educed, and, he e o e, p o ide unabili y o he elec ical conduc i i y [ 29 ]. The e a e a ious app oaches ega ding how o educe he GO pa icles such as ea men wi h hyd azine [ 30 ], educ ion in he acidic en i onmen [ 31 ], o simul aneous educ ion o GO du ing he su ace-ini ia ed a om ans e adical polyme iza ion (SI-ATRP) [32]. Due o he high equi emen s in he abo e men ioned applica ions on he inal ma e ial and om he mechanical and s abili y poin o iew, he u iliza ion o poly (dime hyl siloxanes) PDMS is e y equen [ 33 ]. Such PDMS ma e ial can be ei he ailo ed by c oss-linking densi y o using he addi ion o silicone oil and a cu ing agen . Howe e , he e is s ill a lack o compa ibili y o PDMS wi h common ille s such as MWCNT, g aphene, o e en GO and, he e o e, such ille s need o be modi ied in o de o imp o e compa ibili y and dispe sibili y as well as o e all p ope ies o p epa ed composi e ma e ials. The e a e a ious echniques o modi ica ion using su ac an s [ 34 ], bu such sys ems a e a he ins able o uncon olled polyme iza ion om he su ace, which signi ican ly changes he p ope ies o ille [ 35 ] and, he e o e, he SI-ATRP app oach seems o be a e y con enien me hod o su ace modi ica ion using a a ie y o monome s [ 27 , 32 , 36 , 37 ] o copolyme s [ 38 ], which signi ican ly imp o es he compa ibili y while he basic physical p ope ies such as mechanical o elec ical a e a ec ed only negligibly. The e o e, his a icle is ocused on he SI-ATRP o glycidyl me hac yla e (GMA) om he su ace o GO pa icles in o de o imp o e hei compa ibili y wi h PDMS. Success ul modi ica ion o GO by sho polyme chains was p o ed using TEM and TGA-FTIR measu emen s. The compa ibili y, mechanical, dielec ic, and pho o-ac ua ion p ope ies we e in es iga ed when special aim was concen a ed on he e ec o ligh in ensi y on he inal pho o-ac ua ion pe o mance. 2. Ma e ials and Me hods G aphi e (powde , <20 µ m, syn he ic), sul u ic acid (H 2 SO 4 , 95%–98%), sodium ni a e (NaNO 3 , ≥ 99%), po assium pe mangana e (KMnO 4 , 97%), hyd ogen pe oxide (H 2 O 2 , 29.0–32.0 w %), α -b omoisobu y yl b omide (BiBB, 98%), ie hylamine (TEA, ≥ 99%), glycidyl me hac yla e (GMA, 98%), e hyl α -b omoisobu y a e (EBiB, 98%), N,N,N 0 ,N”,N”-pen ame hyldie hylene iamine (PMDETA, ≥ 99%), coppe b omide (CuB , ≥ 99%), anisole (99%), and die hyl e he ( ≥ 99%) we e all pu chased om Sigma Ald ich and we e used as ecei ed. The g aphene oxide was ab ica ed om g aphi e powde by a modi ied Humme s me hod [ 39 ]. The p oduc was sepa a ed in a high-speed cen i uge (So all LYNX 4000, The mo Scien i ic, Wal ham, MA, USA) ope a ing a 10,000 pm o 20 min a 25 ◦ C. The cleaning ou ine was based on he dispe sion o he GO in 0.1 M HCl and hei e–sepa a ion in a cen i ugal ield. The p ocedu e was epea ed wi h dis illed wa e se e al imes un il he pH has eached a alue o 7. A e wa d, he pa icles we e lyophilized in o de o emo e he esidual amoun o wa e a e pu i ica ion and emo e he b own powde ha was ob ained. The ini ia o BiBB was immobilized, acco ding o he p ocedu e desc ibed in de ail elsewhe e [ 32 ]. Two a ious polyme iza ions om he su ace o GO pa icles in o de o p epa e poly (glycidyl me hac yla e)-modi ied GO (GO-PGMA and GO-PGMA-2), we e pe o med by he ollowing p ocedu e. The mola a io o eac an s [GMA]:[EBiB]:[CuB ]:[PMDETA] was [100]:[1]:[1]:[4] and [100]:[1]:[1]:[2] while anisole (50 ol. %) was used as a sol en . The p esence o oxygen was minimized by degassing he sys em by se e al eeze-pump- haw cycles and a e he las cycle by illing he sys em wi h a gon. Las ly, he CuB ca alys was added unde a gon low and polyme iza ion was ca ied ou a 60 ◦ C o 4 h and a 50 ◦ C o 12 h o polyme iza ions pe o med Polyme s 2018,10, 832 3 o 14 wi h 4:1 and 2:1 a io o PMDETA o CuB , espec i ely. The p oduc was pu i ied by il a ion using DMF, ace one, and die hyl e he and d ied using lyophiliza ion. 1 H nuclea magne ic esonance (NMR) spec a we e eco ded a 25 ◦ C using an ins umen (400 MHz VNMRS Va ian, Tokyo, Japan) wi h deu e a ed chlo o o m (CDCl 3 ) as a sol en . The 1 H NMR was used o de e mine he monome con e sion om he a io o a ea o peaks assigned o PGMA o he a ea o peaks assigned o bo h PGMA and GMA (Figu e 1). The mola mass and polydispe si y (Ð) o PGMA chains we e in es iga ed using gel pe mea ion ch oma og aphy (GPC) on he GPC ins umen (PLGPC220, Agilen , Hachioji, Japan) equipped wi h GPC columns (Wa e s 515 pump, wo PPS SDV 5 lm columns (diame e o 8 mm, leng h o 300 mm, 500 Å + 105 Å)) and a Wa e s 410 di e en ial e ac i e index de ec o empe ed o 30 ◦ C. The nea GO and GO wi h a g a ed PGMA polyme laye we e obse ed using a ansmission elec on mic oscope (TEM, JEM-2100Plus, Jeol, Tokyo, Japan). The samples o he TEM analysis we e p epa ed by dispe sing he pa icles in ace one using mechanical s i ing o 5 and 2 min o sonica ion and d opping he esul an suspension on o a coppe g id. The Raman Shi (3 scans, esolu ion o 2 cm −1 ) we e collec ed on a Nicole DXR (Nicole , Rhinelande , WI, USA) using an exci a ion wa eleng h o 532 nm. The in eg a ion ime was 30 s while he lase powe on he su ace was se o 1 mW. The powde s unde in es iga ion we e comp essed o he o m o pelle s (diame e o 13 mm, hickness app 1 mm). The pelle s we e used o elec ical conduc i i y measu emen s using a wo-poin me hod (Kei hley 6517B, Cle eland, OH, USA). The con ac angle (CA) alues we e e alua ed om he s a ic sessile d op me hod on he pelle s ca ied ou on a Su ace Ene gy E alua ion sys em equipped wi h a CCD came a (Ad ex Ins umen s, B no, Czech Republic). A d ople (5 µ L) o PDMS was ca e ully d ipped on o he su ace and he CA alue was eco ded. The p esen ed CA esul s a e he a e age alues om 10 independen measu emen s. The he mo-oxida ion decomposi ion o he samples was on-line moni o ed using a he mog a ime ic analyze (TGA) ope a ing in an oxygen a mosphe e coupled wi h FTIR wi h a help o Nicole iS10 equipped wi h TGA-IR module (The mo Scien i ic, Wal ham, MA, USA). In he Figu e 2, he highligh ed bands a e hose whe e he FTIR signal was collec ed in o de o p o e he p esence o he a ious componen s in he GO-based powde s. The composi es con aining a ious amoun o GO-based pa icles we e p epa ed using he ollowing s anda d p ocedu e: PDMS (Sylga d 184, A lan a, GA, USA) was mixed wi h silicone oil and subsequen ly a c oss-linke was added in a ios o PDMS: silicone oil: c oss-linke 7/3/1 and, las ly, 0.1 ol. % o he pa icles was added be o e he cu ing. In he case o he nea PDMS ma ix, we u he in es iga ed he same a io o PDMS in his pape . Silicone oil and a c oss-linke was used bu wi hou he addi ion o he pa icles. In he case o all samples, he mix u es we e degassed using a acuum o en in he ou cycles a 10 mba a oom empe a u e and hen placed in o he o en and cu ed a an ele a ed empe a u e se o 60 ◦C o 6 h. The he mal conduc i i y was measu ed by one side con ac me hod using he TCi model (C-Te m Technologies, Vancou e , BC, Canada). The iscoelas ic p ope ies o bo h he nanocomposi e and pu e polyme ma ix we e s udied h ough he dynamic mechanical analysis (DMA) in ensile mode. All measu emen s we e pe o med a a linea iscoelas ic egion. The measu emen was done a 1 Hz in he empe a u e ange om − 150 o 150 ◦ C. To p o ide in o ma ion abou how he modi ica ion o he GO wi h PGMA g a s in luences he s ain o he ma e ials, a dependence o he s o age and loss moduli was plo ed agains he change in he leng h ∆ L, i.e., pa ame e speci ied in he expe imen al pho o-ac ua ion in es iga ions. The measu emen s we e pe o med a 1 Hz and a 25 ◦ C. The dielec ic spec oscopy anged om a empe a u e o − 150 o 100 ◦ C and anged in equency om 10 −1 o 107Hz, which we e employed o in es iga e he polyme chains dynamics. The glass ansi ion p ocess was e alua ed h ough ac i a ion ene gies calcula ed om he A henius equa ion (Equa ion (1)) in o de o see he e ec o modi ica ion on he elaxa ion p ocesses in he PDMS based composi es. β= ∞expEa kBT, (1) Polyme s 2018,10, 832 4 o 14 whe e E a is he ac i a ion ene gy, ∞ is he p e-exponen ial ac o , Tis he modynamic empe a u e, and kBis he Bol zmann cons an . In o de o p ope ly in es iga e he polyme chains dynamics, he loss pe mi i i y need o be ecalcula ed o he loss modulus. This ecalcula ion was based acco ding o Equa ion (2) [40]. M∗=1 ε∗ M0=ε0 ε02+ε00 2 M00 =ε00 ε02+ε00 2 (2) whe e ε * is complex pe mi i i y and ε0 and ε ” a e ela i e pe mi i i y and loss pe mi i i y, espec i ely. M* is he complex dielec ic modulus and M 0 and M” a e s o age and dielec ic loss moduli, espec i ely. Polyme s 2018, 10, x FOR PEER REVIEW 4 o 14 whe e Ea is he ac i a ion ene gy, 𝑓 ∞is he p e-exponen ial ac o , T is he modynamic empe a u e, and kB is he Bol zmann cons an . In o de o p ope ly in es iga e he polyme chains dynamics, he loss pe mi i i y need o be ecalcula ed o he loss modulus. This ecalcula ion was based acco ding o Equa ion (2) [40]. 22 22 * *1                   M M M (2) whe e ε* is complex pe mi i i y and ε′ and ε″ a e ela i e pe mi i i y and loss pe mi i i y, espec i ely. M* is he complex dielec ic modulus and M′ and M″ a e s o age and dielec ic loss moduli, espec i ely. Figu e 1. Rep esen a i e 1 H NMR spec um om il e ed polyme iza ion mix u e o glycidyl me hac yla e pe o med wi h [GMA]:[EBiB]:[CuB ]:[PMDETA] a io o [100]:[1]:[1]:[4] a 60 °C o 4 h. The monome con e sion was 43%. The pho o-ac ua ion abili y o bo h he ma ix and composi e samples was in es iga ed using he mal mechanical analysis (TMA, Me le Toledo, Columbus, OH, USA), which was p e iously published [15]. Red LED diode (Luxeon Rebell, Philips, Ams e dam, he Ne he lands) was used o i adia ion. I adia ion was applied o 10 s a 627 nm wi h 6, 9, and 12 mW ligh sou ce in ensi y unde 10% p e-s ain o he samples. The maximum alue o ac ua ion is cha ac e ized by a change in sample leng h du ing he exposi ion o ligh , ΔL = (L0 − L)/L0, whe e L0 is he leng h o non-i adia ed sample and L is he leng h o an i adia ed sample. Figu e 1. Rep esen a i e 1 H NMR spec um om il e ed polyme iza ion mix u e o glycidyl me hac yla e pe o med wi h [GMA]:[EBiB]:[CuB ]:[PMDETA] a io o [100]:[1]:[1]:[4] a 60 ◦ C o 4 h. The monome con e sion was 43%. The pho o-ac ua ion abili y o bo h he ma ix and composi e samples was in es iga ed using he mal mechanical analysis (TMA, Me le Toledo, Columbus, OH, USA), which was p e iously published [ 15 ]. Red LED diode (Luxeon Rebell, Philips, Ams e dam, he Ne he lands) was used o i adia ion. I adia ion was applied o 10 s a 627 nm wi h 6, 9, and 12 mW ligh sou ce in ensi y unde 10% p e-s ain o he samples. The maximum alue o ac ua ion is cha ac e ized by a change in sample leng h du ing he exposi ion o ligh , ∆ L= (L 0− L)/L 0 , whe e L 0 is he leng h o non-i adia ed sample and Lis he leng h o an i adia ed sample. Polyme s 2018,10, 832 5 o 14 3. Resul s and Discussion Success ul polyme iza ion o GMA om he su ace o GO was con i med by a ious echniques such as 1 H NMR, GPC, TEM, and TGA-FTIR. The con e sion o GMA was calcula ed o be 43% and 46%, acco ding o 1 H NMR spec a and he mola mass and Ð o PGMA chains de e mined om GPC we e 5900 g · mol −1 and 1.28 and 6100 g · mol −1 and 1.26 o he GO-PGMA 1 and GO-PGMA 2, espec i ely, i he expe imen al mola mass wi h he heo e ical one. Fu he mo e, om he TEM in es iga ion, he 2D na u e o he nea GO pa icles (Figu e 2a) can be clea ly seen. Mo eo e , he 2D s uc u e was also obse ed in he case o GO-PGMA while he p esence o he PGMA chains exhibi a he lossy-like s uc u es, which p o ided subs an ial coa ing o he GO pa icle (Figu e 2b). The change in he eac ion mix u e o GO modi ica ion (Figu e 2c) does no lead o a signi ican change in he mo phology and p o ides nea ly he same mo phology han he p e ious one (Figu e 2b). Polyme s 2018, 10, x FOR PEER REVIEW 5 o 14 3. Resul s and Discussion Success ul polyme iza ion o GMA om he su ace o GO was con i med by a ious echniques such as 1H NMR, GPC, TEM, and TGA-FTIR. The con e sion o GMA was calcula ed o be 43% and 46%, acco ding o 1H NMR spec a and he mola mass and Ð o PGMA chains de e mined om GPC we e 5900 g·mol−1 and 1.28 and 6100 g·mol−1 and 1.26 o he GO-PGMA 1 and GO-PGMA 2, espec i ely, i he expe imen al mola mass wi h he heo e ical one. Fu he mo e, om he TEM in es iga ion, he 2D na u e o he nea GO pa icles (Figu e 2a) can be clea ly seen. Mo eo e , he 2D s uc u e was also obse ed in he case o GO-PGMA while he p esence o he PGMA chains exhibi a he lossy-like s uc u es, which p o ided subs an ial coa ing o he GO pa icle (Figu e 2b). The change in he eac ion mix u e o GO modi ica ion (Figu e 2c) does no lead o a signi ican change in he mo phology and p o ides nea ly he same mo phology han he p e ious one (Figu e 2b). Figu e 2. TEM images o (a) nea GO; (b) GO-PGMA; and (c) GO-PGMA-2. The TGA-FTIR echnique u ilizing he on-line moni o ing o he FTIR spec a du ing he mal decomposi ion o he nea GO (Figu e 3a,b), GO wi h bonded ini ia o (Figu e 3c,d), and GO-PGMA (Figu e 3e, ) pa icles was employed o u he p o e he success ul coa ing o GO wi h PGMA chains. In his case, he TGA spec a o he le side o Figu e 3 co espond o he FTIR spec a on he igh side o Figu e 3. Fo he nea GO pa icles and GO wi h an ini ia o , he de ailed desc ip ion was al eady published elsewhe e [41]. Howe e , he ollowing desc ip ion is no el o GO-PGMA pa icles. I can be clea ly seen ha he pa icles peak a ound 200 °C, which co esponds o oxygen- con aining g oups ha dec ease as side in o ma ion o p o e he pa ial educ ion o he GO-PGMA pa icles. Mo eo e , he p esence o he success ul coa ing is ema kable om Figu e 3e when, in he ange om 250 o 450 °C, we obse ed wo peaks bo h co esponding o he he mal decomposi ion o PGMA. A simila ange o PGMA decomposi ion was also ound in he case o modi ica ion o ca bonyl i on [42] as well as in he case o GO-PGMA modi ied h ough SI-ATRP whe e he mass loss in Figu e 3e is e y simila o he ollowing e e ence [27]. In case o GO-PGMA-2, he TGA-FTIR scan looked nea ly iden ical because, om he s uc u al poin o iew, he FTIR spec a in Figu e 3 ep esen he collec ion o he signal du ing he pe iod highligh ed in Figu e 3e by a cyan colo . Speci ic abso p ion bands we e ound a 1722 cm−1 (ca bonyl), 1318 cm−1 C-O-C s e ching, 2961, and 2791 cm−1 (alkyl ib a ions). Fu he mo e, he sha p peak a 750 cm−1 is based on an epoxy ing abso p ion and, he e o e, con i ms he p esence o PGMA polyme chains g a ed on he su ace o GO. G aphene oxide educ ion is a e y impo an ac o om i s applicabili y poin o iew. I he ma e ial has a highe elec ic conduc i i y, he he mal conduc i i y is highe . The he mal ene gy edis ibu ion in he sample is a c ucial ac o o he inal pho o-ac ua ion pe o mance. In addi ion, he composi e ma e ial upon i s de o ma ion can show a sensing capabili y only i ce ain esis i i y o he ma e ial is eached. The e o e, he high conduc i i y o he inal composi e is e y impo an . This is simila ly obse ed in he s udy by Geo gousiss e al. [43]. The e o e, he conduc i i y and Raman spec oscopy (Figu e 4) we e in es iga ed o p o e he deg ee o educ ion o GO and Figu e 2. TEM images o (a) nea GO; (b) GO-PGMA; and (c) GO-PGMA-2. The TGA-FTIR echnique u ilizing he on-line moni o ing o he FTIR spec a du ing he mal decomposi ion o he nea GO (Figu e 3a,b), GO wi h bonded ini ia o (Figu e 3c,d), and GO-PGMA (Figu e 3e, ) pa icles was employed o u he p o e he success ul coa ing o GO wi h PGMA chains. In his case, he TGA spec a o he le side o Figu e 3co espond o he FTIR spec a on he igh side o Figu e 3. Fo he nea GO pa icles and GO wi h an ini ia o , he de ailed desc ip ion was al eady published elsewhe e [ 41 ]. Howe e , he ollowing desc ip ion is no el o GO-PGMA pa icles. I can be clea ly seen ha he pa icles peak a ound 200 ◦ C, which co esponds o oxygen-con aining g oups ha dec ease as side in o ma ion o p o e he pa ial educ ion o he GO-PGMA pa icles. Mo eo e , he p esence o he success ul coa ing is ema kable om Figu e 3e when, in he ange om 250 o 450 ◦ C, we obse ed wo peaks bo h co esponding o he he mal decomposi ion o PGMA. A simila ange o PGMA decomposi ion was also ound in he case o modi ica ion o ca bonyl i on [ 42 ] as well as in he case o GO-PGMA modi ied h ough SI-ATRP whe e he mass loss in Figu e 3e is e y simila o he ollowing e e ence [ 27 ]. In case o GO-PGMA-2, he TGA-FTIR scan looked nea ly iden ical because, om he s uc u al poin o iew, he FTIR spec a in Figu e 3 ep esen he collec ion o he signal du ing he pe iod highligh ed in Figu e 3e by a cyan colo . Speci ic abso p ion bands we e ound a 1722 cm −1 (ca bonyl), 1318 cm −1 C-O-C s e ching, 2961, and 2791 cm −1 (alkyl ib a ions). Fu he mo e, he sha p peak a 750 cm −1 is based on an epoxy ing abso p ion and, he e o e, con i ms he p esence o PGMA polyme chains g a ed on he su ace o GO. G aphene oxide educ ion is a e y impo an ac o om i s applicabili y poin o iew. I he ma e ial has a highe elec ic conduc i i y, he he mal conduc i i y is highe . The he mal ene gy edis ibu ion in he sample is a c ucial ac o o he inal pho o-ac ua ion pe o mance. In addi ion, he composi e ma e ial upon i s de o ma ion can show a sensing capabili y only i ce ain esis i i y o he ma e ial is eached. The e o e, he high conduc i i y o he inal composi e is e y impo an . This is simila ly obse ed in he s udy by Geo gousiss e al. [ 43 ]. The e o e, he conduc i i y and Raman spec oscopy (Figu e 4) we e in es iga ed o p o e he deg ee o educ ion o GO and a iously educed GO-PGMA pa icles. The in ensi ies a ios (I D /I G ) we e ound o be 0.9 o nea GO (Figu e 4a) Polyme s 2018,10, 832 6 o 14 and 1.08 and 1.26 o GO-PGMA 1 (Figu e 4b) and GO-PGMA 2 (Figu e 4c) co esponding o he de e mined conduc i i ies o 1.2 × 10 −8 , 5 × 10 −7 , and 2.3 × 10 −3 S · cm −1 , espec i ely. The a ios indica e a signi ican and con ollable educ ion du ing he SI-ATRP p ocess, which is e y p omising o u he indus ial applica ions. Compa ibili y o he ille wi h a ma ix is a c ucial ac o o imp o emen o he physical as well as mechanical p ope ies o he inal composi e ma e ial. Inhomogenei y p esen in he sample due o he weak compa ibili y can be mainly esponsible o mechanical ins abili ies du ing a epea able mechanical load o , in he case o ma e ials wi h desi ed elec ical o he mal conduc i i ies, can lead o hei su e ed pe o mances. The e o e, he con ac angle alues o PDMS d ops, as he elas ome ic ma ix used in his s udy, on o he su ace o pelle s p epa ed om he nea GO o GO-PGMA pa icles, which we e in es iga ed (Figu e 5). I can be clea ly seen ha he con ac angle o nea GO was de e mined o be 49.9 ◦± 3.2 ◦ , which showed ela i ely poo compa ibili y while he modi ica ion o he GO wi h sho polyme chains o PGMA dec eased he con ac angle o 40.1 ◦± 1.3 ◦ and, he e o e, imp o ed he we abili y be ween he PDMS and GO-PGMA su ace due o he p esence o he alipha ic polyme backbone. In his case, he in luence o a ious conduc i i ies was no p o en and con ac angles we e in he ange o e o . Howe e , he con ac s angles we e no so low as was p e iously ound by ou esea ch g oup o PMMA o PBMA g a s [36]. Polyme s 2018, 10, x FOR PEER REVIEW 6 o 14 a iously educed GO-PGMA pa icles. The in ensi ies a ios (ID/IG) we e ound o be 0.9 o nea GO (Figu e 4a) and 1.08 and 1.26 o GO-PGMA 1 (Figu e 4b) and GO-PGMA 2 (Figu e 4c) co esponding o he de e mined conduc i i ies o 1.2 × 10−8 S·cm−1, 5 × 10−7 S·cm−1, and 2.3 × 10−3 S·cm−1, espec i ely. The a ios indica e a signi ican and con ollable educ ion du ing he SI-ATRP p ocess, which is e y p omising o u he indus ial applica ions. Compa ibili y o he ille wi h a ma ix is a c ucial ac o o imp o emen o he physical as well as mechanical p ope ies o he inal composi e ma e ial. Inhomogenei y p esen in he sample due o he weak compa ibili y can be mainly esponsible o mechanical ins abili ies du ing a epea able mechanical load o , in he case o ma e ials wi h desi ed elec ical o he mal conduc i i ies, can lead o hei su e ed pe o mances. The e o e, he con ac angle alues o PDMS d ops, as he elas ome ic ma ix used in his s udy, on o he su ace o pelle s p epa ed om he nea GO o GO-PGMA pa icles, which we e in es iga ed (Figu e 5). I can be clea ly seen ha he con ac angle o nea GO was de e mined o be 49.9° ± 3.2°, which showed ela i ely poo compa ibili y while he modi ica ion o he GO wi h sho polyme chains o PGMA dec eased he con ac angle o 40.1° ± 1.3° and, he e o e, imp o ed he we abili y be ween he PDMS and GO-PGMA su ace due o he p esence o he alipha ic polyme backbone. In his case, he in luence o a ious conduc i i ies was no p o en and con ac angles we e in he ange o e o . Howe e , he con ac s angles we e no so low as was p e iously ound by ou esea ch g oup o PMMA o PBMA g a s [36]. Figu e 3. TGA analysis (a,c,e) wi h on-line moni o ing o he FTIR spec a (b,d, ) o nea GO (a,b); GO-inicia o , and (c,d) and GO-PGMA (e, ) pa icles. Figu e 3. TGA analysis ( a , c , e ) wi h on-line moni o ing o he FTIR spec a ( b , d , ) o nea GO ( a , b ); GO-inicia o , and (c,d) and GO-PGMA (e, ) pa icles. Polyme s 2018,10, 832 7 o 14 Polyme s 2018, 10, x FOR PEER REVIEW 7 o 14 Figu e 4. Raman spec a o he nea GO (a) GO-PGMA 1; (b) GO-PGMA 2; and (c) pa icles and co esponding chemical s uc u es. Figu e 5. Images om CCD came a o he 5 µL PDMS d ople s on he nea GO (a) and GO-PGMA (b). In o de o show how he op ical p ope ies o he composi es we e changed a e adding a ious ille s, he images o nea PDMS as well as he GO-based composi es we e pe o med (Figu e 6a). I can be seen ha he bes op ical p ope ies had a nea PDMS. Howe e , he modi ica ion using he SI-ATRP app oach p o ided he composi es wi h be e dispe sed ille in compa ison o he nea GO due o he ac ha nea GO/PDMS composi es seem o be o highe anspa ency wi h ela i ely big agglome a es and less uni o m ille dispe sion compa ed o he GO-PGMA g a ed pa icles. In addi ion, he change o he con ac angles be ween he wa e and composi es is nea ly negligible and is mo e a ec ed by he modi ica ion han he ime o s o age (Figu e 6b). This means ha he p ope ies ha we e changing o e 7 days did so negligibly. The con ac angle o nea as-p epa ed PDMS and a e 7 days o s o age is 105.4° and 105.1°, espec i ely. Simila esul s we e ound o o he composi es whe e he as-p epa ed GO-PGMA 1 a e 7 days o s o age show con ac angles o 98.7° and 98.2°, espec i ely. The longe g a s p o ided composi es wi h a sligh ly lowe con ac angle o 97.4° and 96.8° o as-p epa ed GO-PGMA 2 and a e 7 days o s o age, espec i ely, due o he highe amoun o he hyd ophilic epoxy g oups p esen ed on he GO-PGMA 2 pa icles su ace. The lowe con ac angle was obse ed o nea GO, which was expec ed due o he p esence o hyd oxyl, ca boxyl, and epoxy g oups on i s su ace. The e o e, showing con ac angle o 87.7° and 87.1° o as-p epa ed GO composi e a e 7 days o he s o age, espec i ely. Figu e 6. (a) Images o he nea PDMS and p epa ed composi es and (b) Images om CCD came a o he 5 µL wa e d ople s on he nea PDMS and a ious composi es. Line 1 ep esen s measu emen s o as-p epa ed samples while line 2 ep esen s he measu emen s o he samples a e 7 days o s o age a RT. Figu e 4. Raman spec a o he nea GO ( a ) GO-PGMA 1; ( b ) GO-PGMA 2; and ( c ) pa icles and co esponding chemical s uc u es. Polyme s 2018, 10, x FOR PEER REVIEW 7 o 14 Figu e 4. Raman spec a o he nea GO (a) GO-PGMA 1; (b) GO-PGMA 2; and (c) pa icles and co esponding chemical s uc u es. Figu e 5. Images om CCD came a o he 5 µL PDMS d ople s on he nea GO (a) and GO-PGMA (b). In o de o show how he op ical p ope ies o he composi es we e changed a e adding a ious ille s, he images o nea PDMS as well as he GO-based composi es we e pe o med (Figu e 6a). I can be seen ha he bes op ical p ope ies had a nea PDMS. Howe e , he modi ica ion using he SI-ATRP app oach p o ided he composi es wi h be e dispe sed ille in compa ison o he nea GO due o he ac ha nea GO/PDMS composi es seem o be o highe anspa ency wi h ela i ely big agglome a es and less uni o m ille dispe sion compa ed o he GO-PGMA g a ed pa icles. In addi ion, he change o he con ac angles be ween he wa e and composi es is nea ly negligible and is mo e a ec ed by he modi ica ion han he ime o s o age (Figu e 6b). This means ha he p ope ies ha we e changing o e 7 days did so negligibly. The con ac angle o nea as-p epa ed PDMS and a e 7 days o s o age is 105.4° and 105.1°, espec i ely. Simila esul s we e ound o o he composi es whe e he as-p epa ed GO-PGMA 1 a e 7 days o s o age show con ac angles o 98.7° and 98.2°, espec i ely. The longe g a s p o ided composi es wi h a sligh ly lowe con ac angle o 97.4° and 96.8° o as-p epa ed GO-PGMA 2 and a e 7 days o s o age, espec i ely, due o he highe amoun o he hyd ophilic epoxy g oups p esen ed on he GO-PGMA 2 pa icles su ace. The lowe con ac angle was obse ed o nea GO, which was expec ed due o he p esence o hyd oxyl, ca boxyl, and epoxy g oups on i s su ace. The e o e, showing con ac angle o 87.7° and 87.1° o as-p epa ed GO composi e a e 7 days o he s o age, espec i ely. Figu e 6. (a) Images o he nea PDMS and p epa ed composi es and (b) Images om CCD came a o he 5 µL wa e d ople s on he nea PDMS and a ious composi es. Line 1 ep esen s measu emen s o as-p epa ed samples while line 2 ep esen s he measu emen s o he samples a e 7 days o s o age a RT. Figu e 5. Images om CCD came a o he 5 µ L PDMS d ople s on he nea GO ( a ) and GO-PGMA ( b ). In o de o show how he op ical p ope ies o he composi es we e changed a e adding a ious ille s, he images o nea PDMS as well as he GO-based composi es we e pe o med (Figu e 6a). I can be seen ha he bes op ical p ope ies had a nea PDMS. Howe e , he modi ica ion using he SI-ATRP app oach p o ided he composi es wi h be e dispe sed ille in compa ison o he nea GO due o he ac ha nea GO/PDMS composi es seem o be o highe anspa ency wi h ela i ely big agglome a es and less uni o m ille dispe sion compa ed o he GO-PGMA g a ed pa icles. In addi ion, he change o he con ac angles be ween he wa e and composi es is nea ly negligible and is mo e a ec ed by he modi ica ion han he ime o s o age (Figu e 6b). This means ha he p ope ies ha we e changing o e 7 days did so negligibly. The con ac angle o nea as-p epa ed PDMS and a e 7 days o s o age is 105.4 ◦ and 105.1 ◦ , espec i ely. Simila esul s we e ound o o he composi es whe e he as-p epa ed GO-PGMA 1 a e 7 days o s o age show con ac angles o 98.7 ◦ and 98.2 ◦ , espec i ely. The longe g a s p o ided composi es wi h a sligh ly lowe con ac angle o 97.4 ◦ and 96.8 ◦ o as-p epa ed GO-PGMA 2 and a e 7 days o s o age, espec i ely, due o he highe amoun o he hyd ophilic epoxy g oups p esen ed on he GO-PGMA 2 pa icles su ace. The lowe con ac angle was obse ed o nea GO, which was expec ed due o he p esence o hyd oxyl, ca boxyl, and epoxy g oups on i s su ace. The e o e, showing con ac angle o 87.7◦and 87.1◦ o as-p epa ed GO composi e a e 7 days o he s o age, espec i ely. Polyme s 2018, 10, x FOR PEER REVIEW 7 o 14 Figu e 4. Raman spec a o he nea GO (a) GO-PGMA 1; (b) GO-PGMA 2; and (c) pa icles and co esponding chemical s uc u es. Figu e 5. Images om CCD came a o he 5 µL PDMS d ople s on he nea GO (a) and GO-PGMA (b). In o de o show how he op ical p ope ies o he composi es we e changed a e adding a ious ille s, he images o nea PDMS as well as he GO-based composi es we e pe o med (Figu e 6a). I can be seen ha he bes op ical p ope ies had a nea PDMS. Howe e , he modi ica ion using he SI-ATRP app oach p o ided he composi es wi h be e dispe sed ille in compa ison o he nea GO due o he ac ha nea GO/PDMS composi es seem o be o highe anspa ency wi h ela i ely big agglome a es and less uni o m ille dispe sion compa ed o he GO-PGMA g a ed pa icles. In addi ion, he change o he con ac angles be ween he wa e and composi es is nea ly negligible and is mo e a ec ed by he modi ica ion han he ime o s o age (Figu e 6b). This means ha he p ope ies ha we e changing o e 7 days did so negligibly. The con ac angle o nea as-p epa ed PDMS and a e 7 days o s o age is 105.4° and 105.1°, espec i ely. Simila esul s we e ound o o he composi es whe e he as-p epa ed GO-PGMA 1 a e 7 days o s o age show con ac angles o 98.7° and 98.2°, espec i ely. The longe g a s p o ided composi es wi h a sligh ly lowe con ac angle o 97.4° and 96.8° o as-p epa ed GO-PGMA 2 and a e 7 days o s o age, espec i ely, due o he highe amoun o he hyd ophilic epoxy g oups p esen ed on he GO-PGMA 2 pa icles su ace. The lowe con ac angle was obse ed o nea GO, which was expec ed due o he p esence o hyd oxyl, ca boxyl, and epoxy g oups on i s su ace. The e o e, showing con ac angle o 87.7° and 87.1° o as-p epa ed GO composi e a e 7 days o he s o age, espec i ely. Figu e 6. (a) Images o he nea PDMS and p epa ed composi es and (b) Images om CCD came a o he 5 µL wa e d ople s on he nea PDMS and a ious composi es. Line 1 ep esen s measu emen s o as-p epa ed samples while line 2 ep esen s he measu emen s o he samples a e 7 days o s o age a RT. Figu e 6. ( a ) Images o he nea PDMS and p epa ed composi es and ( b ) Images om CCD came a o he 5 µ L wa e d ople s on he nea PDMS and a ious composi es. Line 1 ep esen s measu emen s o as-p epa ed samples while line 2 ep esen s he measu emen s o he samples a e 7 days o s o age a RT. Polyme s 2018,10, 832 8 o 14 In es iga ions o dielec ic p ope ies (Figu e 7) is e y impo an due o he ac ha , wi h he help o measu emen in a b oad empe a u e ange and equency-dependen pe mi i i y, i is possible o calcula e E a o he glass ansi ion and T g , which p o ides in o ma ion abou he polyme chain lexibili y in he p esence o GO pa icles. In ou s udy, howe e , he p epa ed composi es exhibi ed a a he s ong elec ical esponse o he applied elec ic ield and, he e o e, ob ained ε0 and ε ”exhibi ed elec ode pola iza ion and we e no sui able o E a calcula ion [ 40 ]. The e o e, he exp ession o M 0 and M” was used, which was mainly M” acco ding o Equa ion (2). The e o e, his quan i y was also used o he in e p e a ion o he dielec ic spec a in Figu e 5. He e he peak a ound − 120 ◦ C indica ing he p esence o Tgcan be seen o all in es iga ed samples. Polyme s 2018, 10, x FOR PEER REVIEW 8 o 14 In es iga ions o dielec ic p ope ies (Figu e 7) is e y impo an due o he ac ha , wi h he help o measu emen in a b oad empe a u e ange and equency-dependen pe mi i i y, i is possible o calcula e Ea o he glass ansi ion and Tg, which p o ides in o ma ion abou he polyme chain lexibili y in he p esence o GO pa icles. In ou s udy, howe e , he p epa ed composi es exhibi ed a a he s ong elec ical esponse o he applied elec ic ield and, he e o e, ob ained ε′ and ε″ exhibi ed elec ode pola iza ion and we e no sui able o Ea calcula ion [40]. The e o e, he exp ession o M′ and M″ was used, which was mainly M″ acco ding o Equa ion (2). The e o e, his quan i y was also used o he in e p e a ion o he dielec ic spec a in Figu e 5. He e he peak a ound −120 °C indica ing he p esence o Tg can be seen o all in es iga ed samples. Figu e 7. 3D plo s o he dielec ic p ope ies o he nea PDMS ma ix, (a) nea GO-PDMS; (b) GO- PGMA 1; (c) and GO-PGMA 2; (d) All a 0.1 ol. % con en in PDMS. F om he posi ion o he maxima o his peak a a ious empe a u es, he Ea o Tg was calcula ed acco ding o Equa ion (1) and esul s a e lis ed in Table 1. I can be clea ly seen ha he highes Ea o 45.70 kJ·mol−1 was ound o nea PDMS by ollowing he nea GO composi e wi h Ea o 36.57 kJ·mol−1. The sample GO-PGMA 1 wi h 0.1 olume pe cen age o pa icles o lowe conduc i i y possess only a sligh dec ease in Ea showing an imp o ed PDMS chain mobili y a e modi ica ion while he sample GO-PGMA 2 wi h same pa icle loading. Howe e , wi h signi ican ly highe conduc i i y possesses signi ican ly be e chain mobili y and, las ly, he lowes Ea o 23.80 kJ·mol−1 u he enhanced he pho o-ac ua ion capabili y. These esul s indica e ha he p esence o he GO-PGMA pa icles in he composi e signi ican ly imp o es he lexibili y o he PDMS chains due o he ac ha he ene gy necessa y o he polyme chain mo emen is lowe . As i will be shown below, hese esul s we e also con i med by he in es iga ion o DMA and pho o-ac ua ion pe o mance since he esul s om hese expe imen s well-co ela es wi h hese dielec ic in es iga ions. Figu e 7. 3D plo s o he dielec ic p ope ies o he nea PDMS ma ix, ( a ) nea GO-PDMS; ( b ) GO-PGMA 1; (c) and GO-PGMA 2; (d) All a 0.1 ol. % con en in PDMS. F om he posi ion o he maxima o his peak a a ious empe a u es, he E a o T g was calcula ed acco ding o Equa ion (1) and esul s a e lis ed in Table 1. I can be clea ly seen ha he highes E a o 45.70 kJ · mol −1 was ound o nea PDMS by ollowing he nea GO composi e wi h E a o 36.57 kJ · mol −1 . The sample GO-PGMA 1 wi h 0.1 olume pe cen age o pa icles o lowe conduc i i y possess only a sligh dec ease in E a showing an imp o ed PDMS chain mobili y a e modi ica ion while he sample GO-PGMA 2 wi h same pa icle loading. Howe e , wi h signi ican ly highe conduc i i y possesses signi ican ly be e chain mobili y and, las ly, he lowes E a o 23.80 kJ · mol −1 u he enhanced he pho o-ac ua ion capabili y. These esul s indica e ha he p esence o he GO-PGMA pa icles in he composi e signi ican ly imp o es he lexibili y o he PDMS chains due o he ac ha he ene gy necessa y o he polyme chain mo emen is lowe . As i will be shown below, hese esul s we e also con i med by he in es iga ion o DMA and pho o-ac ua ion pe o mance since he esul s om hese expe imen s well-co ela es wi h hese dielec ic in es iga ions. Polyme s 2018,10, 832 9 o 14 Table 1. Ac i a ion ene gies o a glass ansi ion p ocess o pu e PDMS and PDMS composi es wi h a iously conduc ing pa icles. Sample Code Ea(kJ·mol−1) o Tg(−120 ◦C) pu e PDMS 45.70 0.1 ol % nea GO/PDMS 36.57 0.1 ol % GO-PGMA 1/PDMS 31.32 0.1 ol % GO-PGMA 2/PDMS 23.80 Dynamic mechanical p ope ies (Figu e 8) a e one o he mos c ucial ac o s in luencing he applicabili y o ma e ials as pho o-ac ua ion sys ems. Re e sible con ac ion/elonga ion o he sample by ligh s imula ion is a a he dynamic p ocess and, he e o e, in es iga ion upon dynamic condi ions is e y impo an . As can be seen in Figu e 8a, he s o age moduli below T g we e nea ly he same o all in es iga ed samples. The i s di e ence can be seen abo e T g when he lowes s o age modulus was ob ained o nea PDMS and was ollowed by he GO-PGMA sample. The highes alues we e obse ed o samples con aining nea GO pa icles. A simila si ua ion occu s abo e he mel ing egion when he nea GO possessed he highes s o age modulus. This obse a ion can be explained by possible co alen bonding be ween he PDMS and hyd oxyl g oups o GO pa icles [ 44 ]. Since he amoun o he hyd oxyl g oups signi ican ly dec eased due o bo h he modi ica ion wi h PGMA chains and he educ ion o he GO (clea ly seen om Figu es 3and 4), he mechanical esponse is mos ly based on he good compa ibili y o he GO-PGMA pa icles wi h he PDMS. F om he empe a u e dependence o he an δ (Figu e 8b), i can be seen ha he peak o an δ o he sample con aining GO-PGMA dec eased when compa ed wi h pu e PDMS o PDMS illed wi h nea GO, which indica ed enhanced compa ibili y o GO-PGMA wi h he PDMS ma ix. Ye , he absolu e alue o an δ a e all ansi ions was highe o GO-PGMA han o PDMS ma ix and PDMS con aining nea GO due o he ac ha physical en anglemen s o PGMA sho polyme chains p o ide mo e lexible s uc u e han in he case o GO wi h possible co alen bonding o he PDMS. Composi es consis ing o a ious GO-PGMA wi h di e en conduc i i ies show nea ly he same mechanical beha io . The di e ences we e in he ange o e o . The e o e, only he one consis ing o GO-PGMA pa icles wi h highe conduc i i ies a e shown in Figu e 8. The e o e, i can be s a ed ha GO-PGMA/PDMS composi e p o ides a sys em wi h enhanced damping and also wi h imp o ed lexibili y o he composi e sys em, which well-co ela es wi h dielec ic s udies and which is in he same ime highly sui able o he pho o-ac ua ion poin o iew. Polyme s 2018, 10, x FOR PEER REVIEW 9 o 14 Table 1. Ac i a ion ene gies o a glass ansi ion p ocess o pu e PDMS and PDMS composi es wi h a iously conduc ing pa icles. Sample Code Ea (kJ·mol−1) o Tg (−120 °C) pu e PDMS 45.70 0.1 ol % nea GO/PDMS 36.57 0.1 ol % GO-PGMA 1/PDMS 31.32 0.1 ol % GO-PGMA 2/PDMS 23.80 Dynamic mechanical p ope ies (Figu e 8) a e one o he mos c ucial ac o s in luencing he applicabili y o ma e ials as pho o-ac ua ion sys ems. Re e sible con ac ion/elonga ion o he sample by ligh s imula ion is a a he dynamic p ocess and, he e o e, in es iga ion upon dynamic condi ions is e y impo an . As can be seen in Figu e 8a, he s o age moduli below Tg we e nea ly he same o all in es iga ed samples. The i s di e ence can be seen abo e Tg when he lowes s o age modulus was ob ained o nea PDMS and was ollowed by he GO-PGMA sample. The highes alues we e obse ed o samples con aining nea GO pa icles. A simila si ua ion occu s abo e he mel ing egion when he nea GO possessed he highes s o age modulus. This obse a ion can be explained by possible co alen bonding be ween he PDMS and hyd oxyl g oups o GO pa icles [44]. Since he amoun o he hyd oxyl g oups signi ican ly dec eased due o bo h he modi ica ion wi h PGMA chains and he educ ion o he GO (clea ly seen om Figu es 3 and 4), he mechanical esponse is mos ly based on he good compa ibili y o he GO-PGMA pa icles wi h he PDMS. F om he empe a u e dependence o he an δ (Figu e 8b), i can be seen ha he peak o an δ o he sample con aining GO-PGMA dec eased when compa ed wi h pu e PDMS o PDMS illed wi h nea GO, which indica ed enhanced compa ibili y o GO-PGMA wi h he PDMS ma ix. Ye , he absolu e alue o an δ a e all ansi ions was highe o GO-PGMA han o PDMS ma ix and PDMS con aining nea GO due o he ac ha physical en anglemen s o PGMA sho polyme chains p o ide mo e lexible s uc u e han in he case o GO wi h possible co alen bonding o he PDMS. Composi es consis ing o a ious GO-PGMA wi h di e en conduc i i ies show nea ly he same mechanical beha io . The di e ences we e in he ange o e o . The e o e, only he one consis ing o GO-PGMA pa icles wi h highe conduc i i ies a e shown in Figu e 8. The e o e, i can be s a ed ha GO-PGMA/PDMS composi e p o ides a sys em wi h enhanced damping and also wi h imp o ed lexibili y o he composi e sys em, which well-co ela es wi h dielec ic s udies and which is in he same ime highly sui able o he pho o-ac ua ion poin o iew. Figu e 8. Dependence o he s o age modulus (a) and an δ (b) o b oad empe a u e ange o nea PDMS (black solid line) and o PDMS composi es con aining 0.1 ol % o nea GO ( ed dash do line) and GO-PGMA 2 (blue dashed line). In o de o in es iga e he mechanical p ope ies o he p epa ed composi es, dependence on he change in he leng h ∆L in he ange o po en ial pho o-ac ua ion on he iscoelas ic moduli we e measu ed. Va ious na u es o he ille can p o ide he sys em wi h mul iple mechanical pe o mances a he s ain de o ma ion ob ained du ing ligh -s imula ion. As can be seen in Figu e Figu e 8. Dependence o he s o age modulus ( a ) and an δ ( b ) o b oad empe a u e ange o nea PDMS (black solid line) and o PDMS composi es con aining 0.1 ol % o nea GO ( ed dash do line) and GO-PGMA 2 (blue dashed line). In o de o in es iga e he mechanical p ope ies o he p epa ed composi es, dependence on he change in he leng h ∆ Lin he ange o po en ial pho o-ac ua ion on he iscoelas ic moduli we e measu ed. Va ious na u es o he ille can p o ide he sys em wi h mul iple mechanical pe o mances