1
Syne gy be ween bo on ni ide o g aphene 1
nanopla ele s and i(bu yl)e hylphosphonium 2
die hylphospha e ionic liquid as lub ican 3
addi i es o iiso idecyl imelli a e oil 4
José M. Liñei a del Río, En ique a R. López, Jose a Fe nández* 5
Labo a o y o The mophysical P ope ies, Na oma G oup, Depa men o Applied Physics, 6
Facul y o Physics, Uni e si y o San iago de Compos ela, 15782, San iago de Compos ela, 7
Spain 8
*Co esponding au ho . 9
E-mail add ess: jose a. e [email protected] (J. Fe nandez) 10
11
2
ABSTRACT: In his wo k, he syne gy be ween an ionic liquid (IL) and nanopa icles as 12
addi i es o lub ican s was s udied. Fo his pu pose, ou dispe sions based on g aphene 13
nanopla ele s, GnPs, o nanopa icles o hexagonal bo on ni ide, h-BN, wi h o wi hou he IL 14
i(bu yl) e hylphosphonium die hylphospha e in an es e ype base oil, iiso idecyl imelli a e 15
(TTM), we e p epa ed and ibologically analyzed as po en ial nanolub ican s. The mass 16
concen a ion o he nanoaddi i es is 0.1 w %, whe eas o he IL i is 2 w %. The p epa ed 17
blends we e s able o h ee weeks. New densi y and iscosi y alues show ha bo h p ope ies 18
sligh ly inc ease wi h he addi ion o IL and/o nanopa icles. T ibological es s we e pe o med 19
unde a no mal load o 20 N o TTM, he ou dispe sions and he TTM + 2 w % IL mix u e. 20
Wi h espec o base oil, a maximum ic ion educ ion o 33% was achie ed o TTM/IL/GnP 21
nanodispe sion. The bes an iwea pe o mance also co esponds o his same nanodispe sion 22
wi h a wea ack wid h educ ion o 44% and a s ong dec ease o he a e age c oss sec ional 23
a ea o 65%, bo h espec o hose ob ained wi h he nea oil. In he case o wea sca dep h, he 24
maximum educ ion is 32% o TTM/IL/h-BN nanodispe sion. In addi ion, he alues o 25
oughness o wo n su aces es ed wi h bo h TTM/IL/GnP and TTM/IL/h-BN nanodispe sions 26
a e lowe han hose co esponding o he nea oil, o he TTM/IL mix u e and o hose o he 27
co esponding bina y dispe sions. Hence, posi i e syne gies be ween he IL and GnP o h-BN 28
as addi i es o TTM we e ound. Con ocal Raman mic oscopy demons a es ibo ilm 29
o ma ion and mending e ec on wo n su aces. 30
31
KEYWORDS: es e ; ionic liquid; lub ican ; nanoaddi i es; ic ion: wea 32
33
3
1. In oduc ion 34
Recen calcula ions o he impac o ic ion and wea indica e ha 23% (119 EJ) o he 35
o al ene gy consump ion in he wo ld akes place in ibological con ac s (lub ica ed o no 36
lub ica ed solid su aces). 20% (103 EJ) o o al consump ion is used o o e come ic ion and 37
3% (16 EJ) o emanu ac u e wo n pa s and spa e equipmen due o wea and ela ed aul s [1]. 38
The use o nano echnology in he de elopmen o mo e e icien lub ican s will educe no only 39
hese expenses bu also CO2 emissions. In ac , he addi ion o a e y low quan i y o 40
nanopa icles o lub ican s can imp o e hei ibological pe o mance. Nanopa icle addi i es 41
ha e supe io ibological p ope ies o adi ional solid lub ican addi i es [2]. Nanolub ican s 42
a e s able colloidal suspensions o nanome ic ma e ials wi h a e y low concen a ion (usually 43
lowe han 1 w %) in con en ional lub ican s. Hexagonal bo on ni ide (h-BN) based 44
nanolub ican s lead o be e an i ic ion/an iwea capabili ies compa ed o hose o se e al base 45
oils [3-7]. h-BN, conside ed an en i onmen ally iendly ma e ial [8], is he so es and mos 46
lub icious polymo ph o BN [9], ha ing a lamella c ys alline s uc u e in which an de Waals 47
o ces exis be ween shee s [10]. Mo eo e , g aphene nanopla ele s (GnP) ha e been s udied as 48
nanoaddi i es [11-13] imp o ing ic ional and an iwea cha ac e is ics as well as ex eme 49
p essu e p ope ies, compa ed o hose o some base luids. Chang and Baek [14] ha e ecen ly 50
summa ized he eco iendly g een syn hesis p ocedu es o GnP. 51
On he o he hand, good ibological pe o mance has been epo ed o ionic liquids 52
(IL) s udied as nea lub ican s [15-20]. Mo eo e , he use o nanoaddi i es o ionic liquids as 53
base oils can imp o e hei ibological beha io [21,22]. Howe e , ILs a e s ill expensi e and 54
he cu en di ec ion is o ocus he esea ch on he use o ionic liquids as addi i es [23]. In his 55
ein, ILs based on phosphonium ca ions ha e shown a good pe o mance as addi i es o 56
biodeg adable oils, among o he lub ican s, o s eel/s eel con ac s [23-26]. 57
4
Mo eo e , one o he main p oblems when using nanopa icles as addi i es is he poo 58
s abili y o he esul ing nanodispe sions. The use o dispe san s o chemical unc ionaliza ion 59
o he nanopa icles a e solu ions unde conside a ion. Besides, by combining desi ed p ope ies 60
o ionic liquids and o nanopa icles, be e s abili y and highe e iciency can be achie ed 61
[22,27,28]. Such hyb id o mula ions some imes exhibi in e es ing posi i e syne gies [29], bu 62
he in es iga ions on he combined e ec s o ILs and uncoa ed nanopa icles as oil addi i es 63
a e s ill e y sca ce [30-33]. 64
Sena o e e al. [30] s udied dispe sions o a polyalkylene glycol base oil wi h bo h 1-65
e hyl-3-me hylimidazolium ace a e and g aphene oxide (GO) as addi i es a wo empe a u es 66
(298.15 K and 353.15 K) inding ic ion educ ions up o 17% a 298.15 K whe eas a 353.15 67
K no educ ion was ound. Fo he lowes GO concen a ion, a 298.15 K he wea educ ion 68
was 22% while o 353.15 K no educ ion was ob ained. On he o he hand, o he highes GO 69
concen a ion he wea educ ions we e excellen a bo h empe a u es. Sanes e al. [31] ound 70
ha he p esence o 1-oc yl-3-me hylimidazolium e a luo obo a e enhances he load-ca ying 71
and su ace sepa a ing abili y o g aphene, leading o an unmeasu able wea , when bo h 72
addi i es a e dispe sed in an isopa a inic base oil, whe eas o a SAE 10W30 ully o mula ed 73
oil, no posi i e syne gies we e ound o he same addi i es. Howe e , e a luo obo a e ILs a e 74
no ecommended in ibology applica ions due o hei eac i i y wi h wa e leading o he 75
p oduc ion o co osi e hyd ogen luo ide acid [34-36]. Ami il e al. [32] concluded ha he 76
addi ion o he IL ihexyl e adecylphosphonium bis(2,4,4- ime hylpen yl)phosphina e (1 77
w %) and nanopa icles o hexagonal bo on ni ide (0.05 w %) in a chemically modi ied palm 78
olein ime hylolp opane es e , sligh ly dec eases bo h wea (app oxima ely 3.4%) and ic ion 79
(5%) wi h espec o he base oil. Finally, Li e al. [33] in es iga ed he syne gis ic e ec s o 2-80
me cap obenzo hiazola e based ILs and Mo nanopa icles in a polye hylene glycol base oil 81
obse ing excellen ic ion- educ ion and an i-wea pe o mance a 100 °C, bu no a 20 °C. 82
5
Hence, as no clea conclusion can be ound, mo e s udies on IL and nanoaddi i es syne gies 83
a e needed. 84
In o de o gain a deepe knowledge on he combined e ec s o ILs and uncoa ed 85
nanopa icles as oil addi i es, in his wo k we ha e analyzed he syne gies o 86
i(bu yl)e hylphosphonium die hylphospha e, [P4,4,4,2][C2C2PO4], wi h hexagonal bo on ni ide 87
(h-BN) nanopa icles and wi h g aphene nanopla ele s (GnPs) using iiso idecyl imelli a e 88
(TTM) as base oil. The e is no p e ious esea ch on he ibological syne gies o bo h g aphene 89
nanopla ele s and ILs as addi i es o base oils. Recen ly, Oulego e al. [37] ha e de e mined he 90
bac e ial oxici y o se en phosphonium ILs p e iously analyzed as lub ican addi i es. These 91
au ho s conclude ha he IL i(bu yl)e hylphosphonium die hylphospha e, [P4,4,4,2][C2C2PO4], 92
was he leas oxic o all he ILs es ed. The main ad an ages o imelli a e es e s a e low 93
ola ili y, good he mal s abili y, good s abili y o oxida ion, high ilm s eng h, good low 94
empe a u e p ope ies, high lashpoin s and good hyd oly ic s abili y. T imelli a e es e s a e 95
used as special y lub ican s including comp esso luids, wo s oke oils, g eases o chain oils 96
[38]. 97
98
2. Expe imen al sec ion 99
2.1. Ma e ials 100
The iiso idecyl imelli a e sample (TTM, CAS Numbe : 72361-35-4, Fig. 1) was 101
p o ided by Ve kol. This oil has been cha ac e ized by in a ed spec oscopy (IR) wi h a FTIR 102
Va ian 670-IR spec ome e . The spec um (Fig. 2) shows he ollowing peaks: a s ong peak 103
a 1726 cm-1, which co esponds o he s e ching ib a ion o es e ca bonyl (C=O), wo weak 104
peaks a ound 1574 and 1607 cm-1 ha a e associa ed wi h he C-H s e ching in-o plane ing, 105
some peaks appea a ound 1305–1240 cm−1 ela ed o C–O(H) s e ching and C–O–(H) bending 106
ib a ions, a peak a 1102 cm-1, which can be assigned o he (C–O–C) single bond s e ching 107

6
ib a ion and some peaks a 2956 cm-1, 2927 cm-1 and 2871 cm-1 which co espond o ca bon–108
hyd ogen g oups: (CH3) asymme ic s e ching, (CH2) asymme ic s e ching and (CH3) 109
symme ic s e ching espec i ely [39,40]. 110
O O
O
O
O
O
111
112
Fig. 1. Chemical s uc u e o iiso idecyl imelli a e (TTM). 113
114
Fig. 2. The FTIR spec um o iiso idecyl imelli a e (TTM) base oil. 115
Mo eo e , his base oil was also analyzed by high pe o mance liquid ch oma og aphy, 116
HPLC, coupled wi h a quad upole o hogonal accele a ion ime-o - ligh mass spec ome e 117
(mic oTOF-Q™) which is equipped wi h an elec osp ay ioniza ion sou ce (ESI). The base oil 118
was dissol ed in isop opanol (5:250) and analyzed in isoc a ic mode. As can be seen in Fig. 3, 119
7
a wide peak appea s, which may be due o small impu i ies simila o iiso idecyl imelli a e. 120
The mass spec um (Fig. 4) o he oil, shows ha he mass o he molecula ion co esponds o 121
TTM (molecula weigh 757.63 g·mol-1 and molecula o mula: C48H84O6). Mo eo e , his 122
spec um shows ano he weak peak wi h a molecula weigh close o ha o TTM; his ac may 123
be owing o he loss o some hyd ogen a oms in he molecule. To he bes o ou knowledge no 124
p e ious mass spec a o his ype o es e s ha e been epo ed. The TTM kinema ic iscosi y 125
a 40ºC and i s iscosi y index a e 317 cS and 74, espec i ely [24]. 126
127
Fig. 3. HPLC ch oma og am o he iiso idecyl imelli a e sample. 128
129
Fig. 4. Mass spec um o TTM ( e en ion ime 4.0 min). 130
Hexagonal bo on ni ide powde s (h-BN, CAS Numbe : 10043-11-5) ha e a pu i y o 131
99.5 %, an a e age pa icle size o 70 nm and a speci ic a e age a ea o 19.4 m2/g as indica ed 132
In ensi y
Time/min
In ensi y
m/z
8
by he manu ac u e (Ioli ec, GmbH, Ge many, lo MNC018001). An aliquo o he powde 133
sample has p e iously been cha ac e ized [41]. Disc-like shaped mo phology was ob ained o 134
h-BN nanopa icles wi h T ansmission Elec on Mic oscopy (TEM) [41]. G aphene 135
nanopla ele s powde s (GnP, CAS numbe 1034343-98-0) o a pu i y o 99.5% wi h an a e age 136
pa icle diame e o 15 µm and a hickness o 11-15 nm, we e also p o ided by Ioli ec. An 137
aliquo o his GnP sample was used in a p e ious wo k [11] whe e i s p ope ies a e desc ibed. 138
T i(bu yl)e hylphosphonium die hylphospha e ([P4,4,4,2][C2C2PO4], Cyphos 169, CAS 139
Numbe : 20445-94-7, Fig. 5) was kindly p o ided by Cy ec Indus ies Inc. (US) wi h a pu i y 140
o 96.3%. I s kinema ic iscosi y a 40ºC and he iscosi y index a e 225 cS and 82 [24], 141
espec i ely. FTIR and Raman spec a o his IL a e shown in Figs. S1 and S2 espec i ely. A 142
band wi h h ee peaks a 2873, 2927 and 2958 cm-1 due o he me hylene bonds o he alipha ic 143
chains can be obse ed in Fig. S1. FTIR spec um also shows a single peak a 1148 cm-1 ha 144
can be assigned o he P=O bond. The ull spec um is e y simila o ha p e iously epo ed 145
o he same IL by He nández Ba ez e al. [42]. A WITec alpha300R+ con ocal Raman 146
mic oscopy was used o ob ain he Raman spec um o he IL. We a e no awa e o any p e ious 147
Raman spec um o his IL epo ed in he li e a u e. 148
149
Fig. 5. Chemical s uc u e o i(bu yl)e hylphosphonium die hylphospha e, 150
[P4,4,4,2][C2C2PO4]. 151 152
2.2. P epa a ion o he nanolub ican s 153
Fou dispe sions we e p epa ed apa om a mix u e o TTM and [P4,4,4,2][C2C2PO4] 154
wi h a concen a ion o 2 w % o he IL. Two-s ep me hod was used o make he 155
nanodispe sions TTM + 0.1 w % h-BN and TTM + 0.1 w % GnP. To p epa e TTM + 2 w % 156
9
IL + 0.1 w % h-BN and TTM + 2 w % IL + 0.1 w % GnPs nanodispe sions, a p ocedu e simila 157
o ha used by Sanes e al. [31] was employed. Fi s ly, h-BN o GnP nanopowde s we e added 158
o he IL. Secondly, his ensemble is mechanically mixed in an aga e mo a o 5 min and 159
subsequen ly mixed wi h he base oil (TTM). The ou nanodispe sions we e sonica ed o 4 160
hou s by ul asound in a Fishe b and ba h, ope a ing in con inuous shaking mode wi h an 161
e ec i e powe o 180 W and a sonica ion equency o 37 kHz. The weigh pe cen age o all 162
he blends was de e mined by using a Sa o ius balance (model MC 210P) wi h a eadabili y o 163
0.01 mg. The mass concen a ion o he nanopa icles was chosen due o good ibological 164
pe o mance ob ained in ou p e ious esea ch [11,43]. S abili y o he nanodispe sions we e 165
analyzed by isual obse a ion and he measu emen o he e ac i e index along ime by using 166
a Me le Toledo Re ac ome e RA-510M. I s measu ing cell is an in e ed cone-shaped ca i y, 167
wi h s ainless s eel walls. The base o his cone is a polished su ace o a sapphi e p ism, on 168
which he nanolub ican is placed. In addi ion, in o de o analyze he in e ac ions among he 169
componen s o he nanodispe sion he FTIR Va ian 670-IR spec ome e was used. 170
2.3. The mophysical Measu emen s 171
Densi y and dynamic iscosi y o he lub ican s we e measu ed om 278.15 o 373.15 172
K and a a mosphe ic p essu e wi h a o a ional S abinge iscome e SVM 3000 om An on 173
Paa (G az, Aus ia) which inco po a es a ib a ing ube densime e [44]. This de ice has 174
p e iously been desc ibed in de ail [45,46]. The expanded unce ain ies (k = 2) a e 1% o 175
dynamic iscosi y, 0.0005 g⋅cm-3 o densi y and 0.02 K o he empe a u e om 288.15 o 176
378.15 K and 0.05 K ou side his ange. 177
2.4. T ibological Tes s 178
Ro a ional ic ion es s we e pe o med wi h a CSM S anda d ibome e wo king in a 179
ball-on-disc con igu a ion [43] o he base oil, he TTM + IL mix u e and he ou 180
nanodispe sions a oom empe a u e (~23ºC) unde he ollowing condi ions: load o 20 N 181
16
Table 3. Mean alues o he ic ion coe icien , μ, and o he wid h, WTW, dep h, WTD, and 267
c oss-sec ion a ea o he wea ack and hei espec i e s anda d de ia ions o all lub ican s. 268
Dispe sion
µ
σ
WTW/µm
σ/µm
WTD/µm
σ/µm
A ea/µm2
σ/µm2
TTM 0.1253 0.0043 344 22 1.29 0.42 274 17
TTM+ 0.1 w % h-BN 0.1076 0.0035 246 20 0.95 0.25 120 18
TTM+0.1 w % GnP 0.1036 0.0060 242 21 1.23 0.19 142 12
TTM+ 2 w % IL 0.1077 0.0096 234 18 1.21 0.37 140 14
TTM+2 w % IL+ 0.1 w % h-BN 0.1019 0.0043 223 19 0.88 0.51 120 12
TTM+2 w % IL+ 0.1 w % GnP 0.0836 0.0048 194 16 1.19 0.34 110 16
269
270
Fig. 9. Mean ic ion coe icien ,
µ
, ob ained o all he s udied lub ican s. 271
As can be seen in Table 3, he wea ob ained wi h all he p epa ed dispe sions is lowe 272
han o he base oil wi hou addi i es. The mean wea ack wid h educ ion anges om 28% 273
( o he TTM/h-BN nanodispe sion) o 44% ( o he TTM/IL/GnP nanodispe sion), he 274
imp o emen s in he mean wea ack dep h ange om 5% ( o he TTM/GnP nanodispe sion) 275
o 32% ( o TTM/IL/h-BN nanodispe sion) whe eas he dec ease o he a e age c oss sec ional 276
a ea (Fig. 10) is excellen o all he cases anging om 56% ( o he TTM/GnP mix u e) o 277
66% ( o TTM/IL/GnP nanodispe sion). Consequen ly, he nanodispe sions con aining ILs 278
p o ide be e ibological p ope ies han he TTM/IL mix u e and he co esponding 279

17
nanodispe sion wi hou IL. On he o he hand, he ic ion and wea educ ions o he 280
TTM/IL/h-BN nanodispe sion (19% and 32% espec i ely) a e signi ican ly be e han hose 281
ob ained by Ami il e al. [32] o an es e /IL/h-BN lub ican (5% and 3.4%) and hose ob ained 282
by Sena o e e al. [30] a 298. 15 K o a glycol/IL/GO nanodispe sion (17% and 22%). 283
284 Fig. 10. WTW and ans e sal a ea ob ained o all he s udied lub ican s. 285
In Fig. 11 a signi ican educ ion can be obse ed in he 3D p o iles o he wea acks 286
ob ained lub ica ing he con ac wi h he TTM/IL/GnP nanodispe sion in compa ison wi h ha 287
co esponding o nea oil. P o iles o he ans e sal a eas and 3D p o iles o wo n su aces o 288
all he s udied lub ican s a e shown in Fig. 12, whe e he educ ions o he sca s a e clea ly 289
obse ed, especially o he TTM + 2 w % IL + 0.1 w % GnP nanodispe sion. 290
18
291 Fig. 11. 3D p o iles (Con ocal 10x) o he wea acks o he discs lub ica ed wi h (a) TTM 292
base oil (b) nanolub ican o med by TTM + 2 w % IL + 0.1 w % GnP 293
294 Fig. 12. a) 3D Su ace opog aphy o wea acks and b) C oss sec ion p o iles o wea acks 295
o he all he s udied lub ican s a oom empe a u e. 296
Di e en mechanisms ha e been iden i ied o explain he ole o nanopa icles as 297
lub ican addi i es. These mechanisms a e classi ied in wo di e en ca ego ies: di ec e ec 298
19
o he nanopa icle on he su ace (ball bea ing and ibo ilm o ma ion) and su ace 299
enhancemen e ec s (mending and polishing e ec s) [49,50]. As ega ds he ole o ionic liquid, 300
he main mechanism is he o ma ion o ibo ilm. In o de o be e unde s and he mechanisms 301
unde lying in he p esen samples, we ha e pe o med measu emen s o oughness, SEM and 302
Raman mic oscopy. 303
The oughness o he wo n su ace, Ra, was de e mined acco ding o he s anda d ISO 304
4287, applying a Gaussian il e wi h a long wa eleng h cu -o o 0.25 mm. As p esen ed in 305
Table 4, he oughness alues o he wo n su ace, Ra, co esponding o TTM+IL, TTM+h-BN 306
and TTM+GnP a e 8.8, 8.3 and 7.9 nm espec i ely. Taking in o accoun ha he oughness 307
alue o he wo n su ace o TTM base oil was 19.7 nm, we can conclude ha he p esence o 308
he chosen IL p oduces he o ma ion o p o ec i e ibo ilms whe eas he nanoaddi i es can 309
lead o mending, polishing o ibo ilm o ma ion e ec s. The smoo hes su ace co esponds 310
o he disc lub ica ed wi h he TTM/IL/GnP nanodispe sion (Ra = 7.0 nm) ollowed by he one 311
lub ica ed wi h he mix u e TTM/IL/h-BN (Ra =7.5 nm). Thus, posi i e syne gies be ween he 312
IL and he bo h nanoaddi i es we e ound. 313
Table 4. Roughness pa ame e , Ra, o wo n su aces o he di e en analyzed nanolub ican s. 314
Lub ican
Ra / nm
σ / nm
Gaussian Fil e / mm
TTM base oil
19.7
1.2
0.25
TTM +h-BN
8.29
0.64
0.25
TTM + GnP
7.91
0.55
0.25
TTM +IL
8.82
0.52
0.25
TTM +IL+ h-BN
7.47
0.51
0.25
TTM +IL+ GnP
7.02
0.46
0.25
Mo eo e , SEM mic og aphs o wea acks a e lub ica ion wi h all he s udied 315
lub ican s based on TTM we e pe o med. Fig. 13 (especially Fig. 13b) shows ab asi e wea 316
sc a ches o he sca co esponding o he nea oil whe eas o he sca s co esponding o he 317
i e addi i a ed TTM oils, plas ic de o ma ion and smoo he su aces we e ound in ag eemen 318
wi h oughness alues. Addi ionally, o he nanolub ican TTM/IL/GnP an impo an dec ease 319
20
in wea sca wid h is obse ed in compa ison wi h he base oil TTM as seen in Fig. 13a. These 320
esul s con i m he wea measu emen s analyzed wi h he 3D p o ilome e . 321
322
323
Fig. 13. SEM mic og aphs a) 700x and b) 5000x o he wo n discs a e ibological es s o 324
he s udied nanolub ican s. 325
100 µm
100 µm100 µm
100 µm
100 µm
100 µm
10 µm
10 µm
10 µm
10 µm
10 µm
10 µm
b)
a)
21
Elemen al mapping and Raman spec a o he h ee addi i es (Figs. S2-S4) and o he 326
wo n su aces lub ica ed wi h TTM and wi h he i e addi i a ed TTM oils (Figs. S5-S8 and 327
14) we e eco ded wi h a con ocal Raman mic oscope a a wa eleng h o 532 nm in o de o 328
know he ole ha nanopa icles and he ionic liquid play in he educ ion o su ace wea o 329
discs. An impo an ibo ilm is e idenced due o a signi ican p esence o IL (blue colo ) in he 330
mapping o he wo n su ace lub ica ed wi h he TTM/IL mix u e. (Fig. S6). On he o he hand, 331
he Raman spec um o he h-BN powde s (Fig S4) exhibi s a cha ac e is ic band a 1367 cm-1 332
[51] ha is due o he E2g phonon mode, simila o he G band in g aphene o g aphene 333
de i a i es [11]. The spo s o bo on ni ide nanopa icles (Fig. S7) on he wo n su ace 334
lub ica ed wi h TTM/h-BN dispe sion, as well as oughness educ ion could indica e he 335
occu ence o mending e ec . 336
The spec um o he GnP nanopowde s (Fig. S3) shows wo cha ac e is ic bands a ound 337
1350 cm-1 (D-band) and a 1580 cm-1 (G-band) [11]. The i s one is a esul o he b ea hing 338
modes o sp2 a oms in ings whe eas he G-band is due o he bond s e ching o all pai s o sp2 339
a oms in ings and chains [11,52]. On he wo n su ace lub ica ed wi h TTM/GnP dispe sion 340
(Fig. S8) he p esence o a eas whe e he spec um coincides wi h ha o GnP can be obse ed 341
(Fig S3). Taking his las esul in o accoun , as well as he oughness and SEM images i can 342
be concluded ha he e is a p esence o mending and ibo ilm e ec s. 343
Fig. 14a, co esponding o he nanolub ican TTM/IL/h-BN, shows he p esence o he 344
IL (blue) and h-BN (g een) on he wo n su ace. The h ee spec a in Fig. 14a ag ee wi h he 345
Raman spec um o he nea IL (Fig. S2), wi h hose o he wo n su ace lub ica ed wi h TTM 346
(Fig. S5) and o h-BN [41] nanopowde s. The Raman analyses o TTM/IL/GnP on he sca 347
su ace a e shown in Fig. 14b whe e ed and blue show he p esence o GnP o TTM and IL, 348
espec i ely. In his igu e, he ca bon spec um ag ees wi h he spec um o he wo n su ace 349
lub ica ed wi h TTM (Fig. S5) and ha o he GnP nanopowde s (Fig S3), p esen ing he peaks 350

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co esponding o he D and G-bands, as well as an addi ional band (2D band) which indica es 351
he p esence o GnP. Mo eo e , he IL spec um o Fig. 14b coincides wi h ha o he pu e IL 352
(Fig. S2). Fu he mo e, i has been ound ha he GnP nanoaddi i es a e placed along se e al 353
u ows on he wo n su ace. The e o e, mending e ec akes place also esul ing in a smoo he 354
su ace. F om he mappings in Fig. 14, i can be concluded ha he IL plays a mo e impo an 355
ole o TTM/IL/h-BN han o TTM/IL/GnP, due o i s s onge concen a ion in he ibo ilm 356
o he wo n su ace. Taking in o accoun Raman, SEM and oughness esul s i can be 357
concluded ha o bo h nanodispe sions he main ibological mechanisms a e he o ma ion o 358
he IL and nanopa icle ibo ilms, as well as he mending e ec due o nanopa icles. Thus, 359
posi i e syne gies be ween he nanoaddi i es and he IL we e ound. 360
361
362
23
363
Fig. 14. Raman spec a and elemen al map o he wo n su ace ob ained wi h he 364
nanolub ican a) TTM + 2 w % IL + 0.1 w % h-BN and b) TTM + 2 w % IL + 0.1 w % GnP 365
366
4. Conclusions 367
In his wo k he ollowing ea u es we e achie ed: 368
1. Dispe sions based on g aphene nanopla ele s, GnPs, o nanopa icles o hexagonal 369
bo on ni ide, h-BN, wi h o wi hou he IL i(bu yl) e hylphosphonium 370
die hylphospha e in an es e ype base oil, iiso idecyl imelli a e (TTM), we e 371
p epa ed. Th ee weeks a e hei p epa a ion, none o he dispe sions showed signs o 372
ins abili y. 373
2. Ro a ional ibological es s we e pe o med wi h a CSM s anda d ibome e unde a 374
no mal load o 20 N, he con ac pai being AISI52100/AISI52100. The mean ic ion 375
coe icien s ob ained lub ica ing he con ac wi h each one o he dispe sions a e lowe 376
han he co esponding ones using TTM wi hou addi i es. Wi h espec o ha ob ained 377
wi h he nea oil, he maximum educ ion o he ic ion coe icien is 33%, eached wi h 378
he TTM/IL/GnP nanodispe sion. We should poin ou ha he e is no p e ious s udy o 379
GnP dispe sions combined wi h bo h IL and base oil. 380
24
3. Wea was e alua ed in e ms o he wid h (WTW), he dep h (WTD) and c oss-sec ion 381
a ea o he wea ack, as well as he oughness o he wo n su ace. In compa ison o 382
hose ob ained wi h he nea oil, he maximum educ ions o mean WTW (44%), he 383
mean ans e sal a ea (66%) and he mean oughness (65%) co espond o he 384
TTM/IL/GnP nanodispe sion whe eas ha o he mean WTD (32%) is ob ained wi h 385
TTM/IL/h-BN. T ibo ilm o ma ion was con i med by con ocal Raman mic oscopy on 386
he wo n su aces. The esul s ob ained o TTM/IL/h-BN a e be e han he only 387
p e ious s udy wi h dispe sions Palm Olein TMP Es e /IL/h-BN a oom empe a u e 388
[32]. 389
4. F om he abo e esul s, i can be concluded ha posi i e syne gies be ween he IL and 390
h-BN o GnP as addi i es o TTM a e ound. 391
Decla a ion o compe ing in e es 392
None. 393
Acknowledgmen s 394
I is a pleasu e o hank D . Al edo Amigo and D . Ma ía J. G. Guima ey (bo h om Applied 395
Physics Depa men , Uni e si y o San iago de Compos ela) o kindly allowing o use a 396
e ac ome e and p o ide us unpublished da a, espec i ely. Au ho s acknowledge Ve kol and 397
Cy ec Sol ay G oup o p o iding us he TTM and IL samples espec i ely. Au ho s would like 398
o hank he use o RIAIDT-USC analy ical acili ies, especially o M . Ezequiel Vázquez o 399
his use ul ad ice. This wo k was suppo ed by MINECO and he ERDF p og amme h ough 400
ENE2014-55489-C2-1-R and ENE2017-86425-C2-2-R p ojec s, and by he Xun a de Galicia 401
(ED431E 2018/08, ED431D 2017/06 and GRC ED431C 2016/001). These unde s also 402
inanced he acquisi ion o he 3D Op ical P o ile (UNST15-DE-3156). 403
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