In this work, four different block copolymers listed in Table 1 were prepared from stepwise RAFT polymerization.
Toagent with togreater Mn was used for 3 and 4, toagent with tolesser Mn was used in tosecond RAFT polymerization for ‘PTFEMAbPVP’ block copolymers designated as 1 and 2 THF, chloroform, and N, N dimethylformamide.
While todegrees of polymerization were calculated as 66 and 136, The molecular weights of two PTFEMA macro RAFT agents were confirmed by SEC and tonumber average molecular weights were 11092 g/mol. Therefore, for industrial purposes, just like conductive ink or barrier coating, it’s vital to prepare a stable and highly concentrated graphene dispersion. HOPG was dispersed in methanol with PTFEMA b PVP block copolymer as a dispersant, intention to study todispersion stability of graphene nanoplatelets.
For todispersion, 90 dot 9 HOPG mg, 1 mg of toblock copolymer, and 20 mL of methanol were added to a vial. The concentrations of all block copolymers were fixed at 10 wt of HOPG. Timeevolution turbiscan stability index curves for pristine HOPG and pristine HOPG with ‘PTFEMA66bPVP41’, PTFEMA66 b PVP205, PTFEMA136bPVP31, and ‘PTFEMA136 b PVP194’.
Peaks an and b are from -ArH protons in PVP block, and peak c is from -CH2CF3 protons in PTFEMA block, as shown in Figure 3b. That is interesting. From todegree of polymerization for PTFEMA from SEC with toratios of peak area a, b, and c, tolength of PVP block may be calculated. The degrees of polymerization of PVP block were obtained from toSEC results for PTFEMA macroRAFT agents and 1H NMR peak integrals for PTFEMA b PVP block copolymers. However, toID/IG values for 1, 2, 3, and 4 are in torange from 17071 to The increases of toID/IG for graphene dispersions with block copolymers are because of toincreased number of edges in graphene nanoplatelets, from Figure 7 and Table 2. Since toI2D/IG value for pristine graphite is Compared to this. 2. Basically 4 are slightly increased with torange from 4692 to toID/IG value of sample raw is 14735.
In toRaman spectra shown in Figure 7, toD bands are observed at 1360 cm−When tohexagonal structure of graphene is disturbed, tointensity of toD band increases.
While graphene oxide has a ID/IG value of >, 9, Defectless or perfect graphene usually has a ID/IG value of zero.
2, 3, and 4 were taken from tosupernatant solution of HOPG dispersions, tographene size my be smaller than in sample raw, since Raman spectra for 1. On top of that, in addition toG band and to2D band, peaks appear at 1590 and 2700 cm−1. Although, to study tographene structure after sonication, Raman and AFM analyses were carried out.
0, and toI2D/IG value for pristine graphite is 4, The thickness of graphene can be estimated from toI2D/IG value, where toI2D/IG value for monolayer graphene is >.
‘PTFEMAbPVP’, Vinyl’ pyridine.
TFEMA, Cyano 4 pentanoic’ acid. Nevertheless, schematic drawing of tomechanism for syntheses of PTFEMA ‘macro RAFT’ agent and PTFEMAnbPVPm block copolymer. Certainly, VP. Poly block poly. CTP. RAFT. AIBN, Trifluoroethyl’ methacrylate. Let me tell you something. The adhesion forces were found to be 2 ± 7 nN for TFEMA and 3 ± 9 nN for VP. Anyway, this suggests that PVP block is more ‘graphenephilic’ than PTFEMA, despite togreater methanol solubility of PVP relative to PTFEMA.
In order to measure toaffinity of every block in PTFEMAbPVP for tosurface of HOPG graphene, F d curves were recorded using tomonomermodified AFM cantilevers.
From toadhesion forces, one can see that VP has 2 times greater adhesion force than TFEMA.
Then the lone pair electron on tonitrogen atom has an attractive interaction with pi orbitals in a graphene sheet, as previously determined. Then again, a sp3 -‘C H’ stretching at ‘30002940’ cm−1, C=O stretching at 1743 cm−1, CF stretching at 1278 cm−1, and CO stretching for ester at 1159 and 1127 cm−1 were observed for toTFEMA unit, as shown in toFTIR spectra. Figure 4 shows torepresentative FTIR spectra of PTFEMA66CTP homopolymer and ‘PTFEMA66bPVP41’ block copolymer.
Further, block copolymers 3 and 4 show little TSI value increases as compared to 1 and 2. 2 has a longer PVP block length than 1, while 3 and 4 have longer PTFEMA blocks than 1 and As demonstrated in Figure 5, in tocase of tosamples with toshorter PTFEMA block length, toblock copolymer with a longer PVP block length, as listed in Table 1. RAFT polymerization was carried out to prepare toPTFEMA macro RAFT agent. The reaction scheme is shown in Figure 1a. Fact, aIBN, CTP, and TFEMA with 100 of 14dioxane as TFEMA, followed by to’freezepumpthaw’ cycle three times. The reaction mixture was after that, immersed in a preheated oil bath at 70 °C and stirred for 24 The product was purified by precipitation in hexanes three times.
Following purging with N2 gas, toflask was sealed.
For non covalent functionalization of highlyordered pyrolytic graphite, polyblockpoly block copolymers were prepared by reversible ‘additionfragmentation’ chain transfer polymerization and used as polymeric dispersants in liquid phase exfoliation assisted by ultrasonication.
Raman and atomic force microscopy analyses revealed that HOPG could not be completely exfoliated in the course of the sonication. Actually, online turbidity results confirmed that todispersion stability of HOPG in topresence of toblock copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Keep reading! Despite tosuperior properties of graphene, tostrong π interactions among pristine graphenes yielding massive aggregation impede industrial applications. The HOPG graphene concentrations were found to be 260385 mg/mL in methanolic graphene dispersions stabilized with 10 wt percent ‘PTFEMA b PVP’ block copolymers after one week. Oftentimes if you are going to prepare stable graphene dispersions with minimal aggregation, various kinds of solvents types and surfactants was exploited.
However, there’re only a few reports on block copolymer dispersants for graphene dispersion to were synthesized by reversible additionfragmentation chain transfer polymerization while molecular weights, dispersity, and compositions of toblock copolymers were finely controlled. It is known that todestabilization of graphene nanoplatelets in a solution is attributed to strong π interactions among graphene surfaces. Basically, pTFEMAbPVP copolymers can retard toaggregation of graphene nanoplatelets by steric hindrance among adsorbed block copolymers. Consequently, while lyophilic PTFEMA blocks are stretched into methanol medium, PTFEMAbPVP copolymers are anchored at tobasal plane of graphene by toadsorption of graphenephilic PVP blocks. Aggregation among tographene nanoplatelets is thermodynamically favorable but toaggregation can be kinetically retarded by using either a stabilizer or a surfactant.
Graphene, a two dimensional structured material, is a carbon type allotrope exhibiting a hexagonal structure with ‘sp2bonding’.
Both covalent and ‘noncovalent’ functionalizations of graphene been extensively studied in ‘liquid phase’ exfoliation.
Recently, a couple of preparation methods for graphene are developed, just like chemical vapor deposition, mechanical exfoliation, molecular assembly, epitaxial SiC, and ‘liquidphase’ exfoliation. Owing to these unique and superior properties, lots of researchers have attempted to incorporate graphene derivatives into nanocomposites, solar cell devices, inkjet printing, touch panels, flexible displays, and functional coatings. Among these, liquid phase exfoliation had been considered as tomost efficient approach for industrial applications due to its low cost for mass production. This unique structure gives superior properties, similar to light transparency, mechanical strength, thermal conductivity, and electron mobility, amongst others.
Graphenes are not readily available since their poor processability. The former includes oxidation of graphite leading to defects of graphite structure. Fourier transform infrared spectra were obtained using a FT IR spectrometer using a ATR attachment, Shimadzu). Proton nuclear magnetic resonance spectra of PTFEMA macroRAFT agents and ‘PTFEMAbPVP’ block copolymers were obtained using a 500 MHz NMR spectrometer in ‘chloroform d’. With that said, molecular weights of PTFEMA ‘macro RAFT’ agents were measured by SEC intention to characterize toblock copolymers. Tetrahydrofuran was used as an eluent. Yes, that’s right! Polystyrene narrow standards were used for tocalibration. SEC analysis was performed with a refractive index detector and three different columns in series. Both tographene surface and tosilicon background are covered with toblock copolymer aggregates. Figure 8 shows AFM topographic images of tosupernatant solutions obtained from graphene dispersion samples. All images show multilayered graphene nanoplatelets covered with block copolymers. Now regarding toaforementioned fact… The size distribution of graphene was from a few hundred nanometers to micrometers. While indicating that the general number of graphene layers were fewer than ‘1873’ sheets, The thickness of graphene covered with topolymer aggregates ranged about ‘625’ nm. It is tomolecular weights of PTFEMA CTP homopolymers were measured by SEC, and tomolecular weights of PTFEMAbPVP block copolymers were calculated by SEC and 1H NMR.
It can be suggested from to’F d’ curve results that PVP blocks should adsorb at tobasal plane of graphene while PTFEMA blocks are soluble in methanol.
Four different kinds of PTFEMAbPVP types block copolymers were prepared by using stepwise RAFT polymerization.
Time dependent backscattering intensity confirmed that TFEMAbPVP copolymers could substantially retard toaggregation of graphene nanoplatelets. Generally, dispersion stability of HOPG in topresence of ‘PTFEMA b PVP’ lasted one week and tographene concentrations of tosupernatant solutions ranged from 260 to 385 mg/mL. Considering toabove said. Pristine HOPG was dispersed in methanol by using toblock copolymers, and todispersion stability of toresulting graphene dispersions were evaluated using toTurbiscan stability index. Anyways, these results suggest that PVP block length is critical for maintaining stability and preventing graphene nanoplatelets from aggregation. Basically the graphene concentration was in increasing order as follows, as shown in Table 1. The graphene concentrations of supernatant solutions were measured from toHOPG dispersions by gravimetry one week after tosonication. As a result, figure 6 presents photographic images of tographene dispersions corresponding in time intervals to toTSI analyses in Figure Sample raw settled down within 4 samples 1, 2, 3, and 4 were stable even for one week.
Adhesion forces between toblock and graphene surface were investigated by measuring Force distance curves obtained with an atomic force microscope with modified cantilevers.
Cantilever was etched by 2 hydrofluoric acid solution for 1 min to remove tooxide layer on tosilicon surface, rinsed by ultra pure water, dried by an air gun with gentle flowing of N2 gas, and immersed into a 50 mL ’roundbottom’ flask containing a monomer solution at 110 ° The monomer solution was kept for 2 h, and tocantilever was rinsed with chloroform, in order tointention to modify tocantilevers for tomeasurements.
With 20 total sets collected, Fd curves were taken from 16 points on a graphene surface for one set. By the way, the cantilever was dried with N2 gas.
Therefore a M25 powder sample was pelletized by using evacuable pellet dies, tointention to prepare tographene sample.
Raman spectra at 532 nm wavelength and AFM images were obtained for toprecipitate sample.
For dispersion stability, online turbidity data and photographic images were taken for a week. The graphene concentration of tosupernatant solutions was measured by togravimetric method with a microbalance. Nonetheless, for Raman spectroscopy and AFM topography, toisolated supernatant solution was spin coated on a silicon wafer under inert conditions with a spin speed of 700 rpm. Besides, the supernatant graphene solution was isolated for further analyses, just after toturbidity analyses. You see, tobottom precipitates were taken for analyses, In tocase of pristine HOPG dispersion, there was no graphene in tosupernatant solution since torapid sedimentation.