Multiwalled Carbon Nanotube Reinforced Epoxy Nanocomposites for

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Multiwalled Carbon Nanotube Reinforced Epoxy Nanocomposites for Vibration Damping Anand Joy, Susy Varughese, Sankaran Shanmugam, and Prathap Haridoss ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b01865 • Publication Date (Web): 23 Jan 2019 Downloaded from http://pubs.acs.org on January 24, 2019

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ACS Applied Nano Materials

Multiwalled Carbon Nanotube Reinforced Epoxy Nanocomposites for Vibration Damping Anand Joy1, Susy Varughese2, Sankaran Shanmugam1, and Prathap Haridoss1* 1Department

of Metallurgical and Materials Engineering, IIT Madras, Chennai 600036, India

2Department

of Chemical Engineering, IIT Madras, Chennai 600036, India Abstract

Multiwalled carbon nanotubes (CNT) are used as reinforcement in epoxy modified with adduct, i.e. block

co-polymer

acrylonitrile

of

carboxyl-terminated

(CTBN)

and

diglycidyl

butadiene ether

of

bisphenol A (DGEBA). Microstructure analysis reveals uniform

dispersion

of

a

phase

with

spherical

morphology in a continuous phase. The mean diameter of the spherical particles increased with CNT and adduct content. At 30 wt% adduct, adding CNT results in exceptional growth of spherical particles. Loss factors in the first two modes were determined by using

free

vibration

test

in

cantilever

mode.

Significant increase in loss factor is obtained for the epoxy nanocomposites modified with 30 wt% adduct and at all wt.% CNTs (i.e. 0.5, 1 and 2.5). Vibration damping mechanism in this nanocomposite is likely due 1

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to relative sliding of spherical particles during dynamic loads, which dissipates energy. The reduction in the distance between spherical particles as well as the reduction in the elastic modulus of continuous phase facilitate relative sliding.

Keywords:

Carbon

nanotube,

Epoxy,

Damping,

Nanocomposite, CTBN, Phase separation, Polymer blend, Vibration isolation

*Corresponding author: Dr. Prathap Haridoss; Email: [email protected]

1

Introduction Vibration damping is a highly demanding and challenging

problem

encountered

by

design

engineers

and

material

scientists. Structures exposed to vibration leads to fatigue loading which causes unanticipated failure [1]. In passenger carriers,

such

as

automobiles,

aircraft

etc.,

vibration

causes noise and unfavourable motions to the passenger [2, 3]. In a material system, vibration damping occurs via energy dissipating events known as vibration damping mechanisms [4]. These mechanisms are essentially restoration of structures ranging from atomic or molecular level to macro level [5]. Dominance of a mechanism over the other possible mechanisms depends

on

many

internal

and

2

external


factors.

Internal

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factors

include

presence

of

point

defects,

dislocations,

grain boundaries, reinforcement material etc. [5]. External factors

include

temperature,

frequency,

input

stress

or

strain and preload [6]. Damping can be achieved by active or passive methods [3, 7, 8]. Inherent material properties are utilized to achieve passive damping [3]. Surface damping treatment is a passive damping treatment which is easy to apply, less complex, compact and relatively cheap [3]. It is broadly classified into free layer damping and constrained layer damping [9]. In free layer damping, a damping material is applied on to either one or both the sides of the structure. Under dynamic loads the damping material undergo cyclic tension and compression deformation. In constrained layer damping, a metal plate known as “constraining layer” is applied to the damping material. Whenever

dynamic

loads

are

applied,

the

damping

layer

undergoes shear deformation due to the constraining of metal plate. In both of these treatments, the damping material is either spray coated or adhesive bonded to the base structure. Performance of surface damping treatment depends on thickness and stiffness of the adhesive layer too [5, 10]. Which can be avoided if the damping material itself has adhesive property. Epoxy is a thermosetting polymer well known for its adhesive properties [11, 12]. However, they exhibit poor vibration damping characteristics [13]. One of the initial studies to improve

the

vibration

damping 3

of

epoxy


was

done

by

the


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incorporation of continuous glass fibre and graphite fibre [14]. This study revealed the dependence of loss factor on type and orientation of fibre. Shape memory alloys such as TiNi embedded epoxy composites exhibited loss factor around 0.2 above austenite finish temperature in the free vibration analysis [15]. Blending of epoxy with carboxylterminated butadiene-acrylonitrile amine-terminated

(CTBN)

[16–20]

liquid

butadiene-acrylonitrile

rubber

and

[21,

22]

(ATBN)

rubber improves vibration damping. A loss factor of 0.084 compared to 0.037 of neat epoxy was obtained for 25 wt% CTBN modified epoxy composites in free vibration analysis [17]. Liquid rubber modified epoxy systems are characterized with two phase morphology. In this, the spherical rubber particles are dispersed in the continuous epoxy matrix [23]. Since the deformation of rubber particles under vibratory loads is restrained

by

the

rigid

epoxy

matrix,

a

significant

improvement in vibration damping is not observed. However, vibration

damping

in

these

materials

can

be

improved

significantly by reducing the gap between the rubber particles in epoxy matrix. The inter connected phase structure exhibited higher

damping

structure

[21].

compared

to

distributed

Increasing

the

liquid

spherical rubber

domain content

increases the size of distributed spherical domains [24]. As a result the distance between spherical domains decreases. However, this is still not sufficient to get significant improvement in vibration damping.

4


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In this work, we report a high damping composite based on epoxy reinforced with multiwalled carbon nanotube (CNT) and modified with an adduct of epoxy and CTBN. Adduct is a copolymer of epoxy resin and CTBN [25]. Significant improvement in vibration damping is observed beyond a certain level of adduct content. Mechanism of vibration damping is predicted by microstructure analysis. A unique microstructure formation due

to

the

reaction

epoxy/adduct/CNT behaviour,

induced

composite

which

is

phase

results

explained

separation in

based

a on

peak

in

the

damping

microstructure

analysis of the composite.

2 2.1

Experimental Details Materials

Araldite GY 257 is a low viscose (viscosity at 25 oC is 450 650 mPa·s) epoxy resin based on bisphenol–A modified with an aromatic

glycidyl

ether

(DGEBA).

Aradur

polyamidoamine (PAMAM) hardener (viscosity at 25

140 oC

is

a

is 10000

- 25000 mPa·s). Both were purchased from Huntsman Company, Mumbai, India. CTBN liquid rubber with acrylonitrile content of 26 % (Hypro 1300×13) and number average molecular weight of 3150 was purchased from CVC thermoset specialties, NJ, USA. Mixing ratio of resin to hardener is 2:1 by weight. CNT was synthesized in house using arc discharge technique as

5



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reported earlier [26, 27]. The average diameter of CNT was 15.2 ± 5.5 nm and length was around 1 µm.

2.2

Nanocomposite fabrication

Adduct of DGEBA and CTBN was prepared by stirring 40 phr CTBN in DGEBA at 120

oC

for 4 h under slow Nitrogen purge. The

reaction is shown in Figure 1. Carboxyl group of CTBN reacts with epoxide group of DGEBA to form DGEBA – CTBN – DGEBA adduct and the chain extends further as reaction proceeds (Figure S1 in supporting information) [20, 28].

Figure 1: Reaction between DGEBA and CTBN to form adduct

Appropriate amount of adduct was added to DGEBA and stirred using a magnetic stirrer for 30 min. CNTs were dispersed in epoxy by solution mixing technique [29]. Based on the cost, availability and also on the results from previous studies [30,

31]

ethanol

was

selected

as

solvent.

CNT

was

ultrasonicated in ethanol using a bath type ultrasonicator 6


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(CREST ultrasonics, NJ, USA) at 25 kHz and 132 kHz operated in

parallel

for

10

min

to

break

the

agglomerates.

This

dispersion was added to the blend of adduct and DGEBA and stirred for 30 min using a magnetic stirrer. Increase in the level (by volume) after the addition of CNT/ethanol dispersion was noted. After this, the dispersion was placed on a hot plate and heated at 85

◦C

till the volume level reduces to

the initial level. PAMAM hardener was then added with 2:1 resin to hardener ratio by weight. It was mixed using a magnetic stirrer for 15 min. After degassing, this mixture was injected to a Teflon mould lined with silicone rubber using a hand operated plunger. This enabled proper handling of the injection pressure to address the higher viscosity of the mixture. Size of the mould was 200 mm in length 10 mm in width and 4 mm in thickness. Details about the injection process

is

given

in

section

S.2.

information. Curing was done at 100

oC

in

the

supporting

for 1 h and then at

room temperature for 7 days. Nanocomposite with 10, 20, 30 wt% of adduct and 0.5, 1, 2.5 wt% CNT were fabricated. Samples were coded as EAxCy where E stands for cross linked epoxy matrix, A is for the adduct, x is the wt% of adduct, C is for the CNT and y is wt% of CNT.

2.3

Characterization and testing Test for vibration damping was conducted according to

ASTM E756-05 [10]. Nanocomposites in Oberst beam configuration 7



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(damped on one side) were tested to find the damping ratios at different modes of vibration. Aluminum of thickness 2 mm was chosen as the base material and 2 mm thick nanocomposite layer was cast on to this. The beam dimension was 200 mm × 10 mm (length × width) (Figure S3). The free length was 180 mm. An initial tip displacement was given to the beam using an impact hammer (Model 5800B4, DynapulseTM, Dytran Instruments) and

the

tip

displacement

was

recorded

using

a

Dytran

accelerometer having sensitivity 100 mV/g. The frequency range of

the

accelerometer

was

5

to

10000

Hz.

The

weight

of

accelerometer was 2 g and the weight of the beams was around 20 g. The weight of the accelerometer is relatively small. Hence, the effect of mass of accelerometer on the response of the beams is negligible. Further, no bending was observed due to the attachment of accelerometer to the beams. NI 9234 data acquisition system of ’National Instruments’ was used to acquire signals through m+p SO analyser application. The results were obtained as amplitude vs. frequency, called as frequency response function (FRF). Minimum five samples were tested in each configuration. In the given length two modes were excited. Loss factors in this two modes were obtained by half power bandwidth method. From this the loss factors of the nanocomposites

were

calculated

by

using

Ross–Kerwin–Ungar

(RKU) equations [32] given in the ASTM standard specified above. Average value of loss factor with standard deviation was plotted against adduct and CNT content.

8


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The density of the nanocomposites were found out using fluid displacement technique. Weight in air and weight in water of the samples for each composition were determined using Sartorius CP124S weighing balance. At least five samples were tested and the average value with standard deviation was plotted against CNT content. The evolution of two phase morphology was analysed by placing

a

small

drop

of

the

sample

on

a

glass

slide

immediately after adding PAMAM hardener. Stirring for 1 min was

carried

out

to

ensure

proper

mixing.

This

was

characterized by phase contrast microscopy (PCM) in Olympus IX71 inverted optical microscope. Images were taken at regular intervals

of

fractured

by

time.

The

bending

nanocomposite

for

samples

microstructure

were

analysis.

cryo The

fractured surfaces were sputter coated with gold and viewed under FEI Quanta 400 FEG scanning electron microscope (SEM). The

microstructure

developed

in

the

nanocomposites

were

analysed. The average diameter with standard deviation of the spherical domains was measure using ImageJ software. Elastic moduli of each phase in the nanocomposite was determined using Park NX10 atomic force microscope (AFM) in contact mode.

9



3 3.1

Results and Discussion Free Vibration damping

The FRFs of composite beams in Oberst condition are shown in Figure 2. Damped natural frequency (ωd) in the first and second modes are varying with respect to adduct and CNT content. This variation is significant in the second mode and is shown in Table 1. Damped natural frequencies in mode 2 (ωd2) of the nanocomposite beams with adduct modifier are slightly lower than that of neat epoxy beam. The beams with

Figure 2: Frequency response function of neat epoxy and nanocomposites. Two modes were excited for 180 mm free length

10


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30 wt % adduct at all wt % of CNT have the lowest ωd2. The variation in ωd2 is attributed to the effects of damping. Damped natural frequency varies with damping ratio (ζ) as given by; d  n 1   2 where ωn is the undamped (ζ = 0) natural frequency. As the damping increases the natural frequency of the damped system decreases. However ωd2 of nanocomposites without adduct modifier are higher than that of neat epoxy. This is attributed to the increase in flexural rigidity of these

beams.

Natural

frequency

rigidity (EI) as, n    n L 

2

varies

with

the

flexural

EI l L4 , given by Euler - Bernoulli

beam theory. Here L is the beam length, E is elastic modulus, I is the second moment of inertia of cross section with respect to bending axis and ρl is the mass per unit length. For cantilever beam β1L = 1.875, β2L = 4.694 gives the first two natural frequencies.

Table 1: Variation of mode 2 natural frequency with adduct and CNT content

CNT content (wt %) 0 0.5 1 2.5

Damped natural frequency in mode 2 (Hz) Adduct content (wt %) 0 10 20 30 257 ± 4

245 ± 5.3

242 ± 5

264 ± 10 268 ± 4.5 263.5 ± 4.7

244 ± 2 245 ± 4.6 248 ± 5

252 ± 4.7 255 ± 4 252 ± 4

11


240 ± 5.4 230 ± 4 226 ± 5 231 ± 6


Loss

factors

in

mode

1

(η1)

and

Page 12 of 42

mode

2

(η2)

of

the

nanocomposites are shown in Figure 3(a) and 3(b). Addition of adduct to epoxy improved the loss factor in both the modes. Two distinct trends in the variation of loss factor with the addition of CNT have observed. In nanocomposites with 10 and 20 wt% adduct, incorporation of CNT has no effect or slightly reduced the loss factor in both the modes. Similar results were

reported

in

previous

studies

[24,

33].

Whereas

in

nanocomposites with 30 wt% adduct, the incorporation of CNT increased the loss factor significantly. In mode 1, EA30C1 exhibited highest loss factor, with an increase of 119 % from that of the neat epoxy. In mode 2, EA30C0.5 exhibited highest loss factor, with an increase of 98 % from that of the neat epoxy. Earlier studies reported 13 % increase in loss factor for epoxy reinforced with 0.5 wt % CNT and 32 % increase for 2.5 wt 3: % CNT 34].inCompared to mode these, a significant Figure Loss [8, factor mode 1 and 2 are calculated improvement in according vibrationto damping is obtained for the from the FRFs ASTM E756–05 [10] and shown in nanocomposites discussed in this study. (a) and (b) respectively Loss factor calculation using RKU equations depends on the density of the damping material. Hence, the effect of addition of adduct and CNT to epoxy on the density of the final nanocomposite

was

tested

and

is

shown

in

Figure

4.

The

variation in the density of nanocomposite with 10, 20 and 30 wt% adduct is well within the limits of standard deviation of that of neat epoxy, which has a density of 1118.2 ± 9.3 kg/m3.

12


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In nanocomposites with 10 and 20 wt% adduct, with the incorporation of CNT, negligible variation in density is observed. However, the addition of CNT to the nanocomposites with 30 wt% adduct resulted in the lowest density among all the nanocomposites. EA30C0.5 has the lowest density which is 2.5 % lower than that of neat epoxy. This reduction will not affect significantly in the calculation using RKU equations.

13



Page 14 of 42

Significant improvement in vibration damping was obtained especially when CNT is incorporated to epoxy modified with 30 wt% adduct. Vibration damping mechanisms need to be examined to

substantiate

energy

this

dissipating

improvement. events,

such

Damping as

occurs

various

through

relaxation

processes of polymer chains [35, 36], interfacial movements

Figure 4: Variation of density of the nanocomposite [6,

8,

37,

adduct and CNT content. 38],with inter-tube sliding in CNT

[39–43]

etc.

Detailed microstructure analysis of the nanocomposites using SEM and PCM was done to formulate the mechanism of vibration damping.

14


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3.2 3.2.1

Microstructure analysis Reaction induced phase separation

One of the factors that contribute to vibration damping in material systems is the microstructure developed during the processing. PCM images in Figure 5 were taken 1 min after adding the cross linking agent. The presence of spherical domains structures were characterized in the initial stages of cross linking (Figure 5(a)). More number of spherical domains

appeared

as

time

progressed

due

to

the

phase

separation (Figure 5(b)). These domains grow in size (Figure 5(c) and 5(d)). However, the growth is hindered as viscosity increases due to cross linking. Previous studies suggest that the phase separation in the blend

of

epoxy

and

adduct

can

occur

either

by

spinodal

decomposition [20, 21] or by nucleation and growth [44–46]. Phase separation by spinodal decomposition results in cocontinuous

and

interconnected

phase

structure

[21,

47].

Whereas, the morphology as a result of nucleation and growth, is spherical domains distributed in continuous phase [48, 49]. Similar morphology is obtained in the nanocomposites of this study (Figure 5(a) – 5(d)). Hence, it is believed that the phase separation occurs by nucleation and growth mechanism.

15



Page 16 of 42

3.2.2

Particle size and distribution of CNT

SEM

images

showing

variation

in

microstructure

of

nanocomposites with respect to adduct and CNT content are shown in Figure 6. A continuous phase and a dispersed phase with spherical morphology are observed. Average diameter of the dispersed phase with standard deviation corresponding to each adduct and CNT content are shown in Figure 6. It is found that

the

average

diameter

increased

with

adduct

and

CNT

content. A significant increase is observed with 0.5, 1 and 2.5 wt% CNT and 30 wt% adduct. The observed diameter of adduct in EA30C0 is around 0.99 ± 0.16 µm, which has increased to 65 ± 25.8 µm in EA30C0.5 due to the presence of 0.5 wt% CNT.

16


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Higher rate of curing is expected at lower adduct and CNT contents. This results in higher viscosity which restricts

Figure 5: Phase contrast optical microscope images of cross linking of EA30C0, 1 min after adding PAMAM (a), images (b), (c) and (d) were taken successively. Time stamps are provided with each image the coalescence of adduct particles [16]. Cross linking rate decreases as the adduct and CNT content increases. This allows the growth as well as coalescence of adduct particles for an extended period of time [44]. Hence, the diameter of spherical adduct particles increases with adduct and CNT content. Such a trend has been reported earlier [20, 50–52]. Substantial

increase

in

the

diameter

of

spherical

domains was observed when CNT is added to epoxy with 30 wt% adduct (Figure 6). Morphology evolution of EA10C0.5 and EA30C0.5 nanocomposites are shown in Figure 7. These images were taken 17



20, 30 and 40 min after adding PAMAM cross linking agent. The

18


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black dots marked in Figure 7 are CNT aggregates. In EA10C0.5

19



these dots are well distributed in the matrix. Whereas in

20


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EA30C0.5 most of these dots are situated on the surface of the

21



spherical domains. This is again substantiated with the SEM

22


Page 22 of 42

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images shown in Figure 8. In EA20C1, the CNTs are found in the

23



continuous epoxy phase (Figure 8 (a) – 8(d)). In EA30C2.5 the

24


Page 24 of 42

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irregular areas of spherical adduct phase (Figure 8(e)) were

25



Page 26 of 42

magnified (Figure 8 (f)). CNTs are found to be protruding out

Figure

7:

Morphology

evolution

of

EA10C0.5

and

EA30C0.5

nanocomposites after 20, 30 and 40 min of adding cross linking agent

26


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Figure 8: SEM images of EA20C1 and EA30C2.5 nanocomposite. CNTs are found in the continuous phase (a and c). Images (b) and (d) are magnified view of CNTs in (a) and (c) respectively. In image (e), the spherical domains have few irregular Figure 6: SEM micrographs of fracture surfaces. Average areas. One such area is magnified (b). On further analysis diameter with standard deviation of the second phase we could see CNTs protruding out from the spheres (h) particles is given the box from the surface of these domains (Figure 8 (h)). Growth of nuclei

occurs

through

two

mechanisms;

diffusion

of

the

monomers (here adduct and DGEBA molecules) from the bulk, and surface reactions [53]. It is believed that the presence of CNTs on the surface of the growing particles enhances the diffusion of monomers from the bulk by acting as defects on the surface of the growing spherical adduct particles. This also results in the reduction of available number of DGEBA molecules for cross linking. Thus, the nuclei experience less resistance towards growth. This might be the reason for the substantial

increase

of

spherical

domain

size

in

CNT

reinforced epoxy nanocomposites modified with 30 wt% adduct. The DGEBA molecules left outside form the continuous phase.

27



Page 28 of 42

The amount of continuous phase in 30 wt% adduct modified nanocomposites have reduced significantly (Figure 6). This also reveals that the number of DGEBA molecules available for cross linking was quite less as a result of its diffusion to the spherical particles.

3.3 Vibration damping mechanism AFM scanning of the samples was conducted and the elastic modulus of points 0.05 µm apart along a line was calculated using Hertzian model. Figure 9 shows the variation of elastic modulus of four compositions with distance along the line of scan. An abrupt increase in elastic modulus indicates the presence of continuous phase.

28

Figure

9:

Variation


of

elastic

distance along the sample surface

modulus

with

scanning

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Which is marked with dashed circles. The continuous phase in EA30C0.5 has very low elastic modulus compared to the other three nanocomposites shown in Figure 9. This is due to the diffusion

of

DGEBA

molecules

into

the

spherical

adduct

particles. Which resulted in the reduction of number DGEBA molecules available for cross linking with PAMAM. Hence, it is determined that the continuous phase in EA30C0.5, EA30C1 and EA30C2.5 is highly flexible. As a result, energy is dissipated as heat during frictional sliding of spherical particle with respect to the matrix as well as between themselves. A reduction in loss factor was obtained for 10 and 20 wt% adduct

modified

nanocomposites.

Whereas

a

significant

improvement is obtained for nanocomposites with 30 wt% adduct. The gap between distributed spherical adduct particles in 30 wt% adduct modified nanocomposites is lesser than that in 10 and 20 wt% adduct modified nanocomposites (Figure 6). AFM analysis also revealed that the continuous phase in 30 wt% adduct

modified

compared

to

nanocomposites

that

in

10

and

has 20

lower wt%

elastic adduct

modulus modified

nanocomposites. This implies that compared to 10 and 20 wt% adduct

modified

nanocomposites,

30

wt%

adduct

modified

nanocomposites facilitate relative sliding. This dissipate more energy and results in higher loss factor. The loss factor in mode 2 is found to be higher than that in mode 1 (Figure 3). At a particular excitation frequency 29



Page 30 of 42

some mechanisms dominate and the damping is proportional to the quantity of energy dissipated by these mechanisms. Hence, higher modes can give higher damping ratio if the mechanism active at the higher modes are capable of dissipating more amount of energy. Similar results were reported in previous studies [8, 34]. Mode 2 occurred at higher frequency (250 Hz) compared to mode 1 (30 Hz). More relative sliding might occur between

spherical

particles

and

matrix

as

well

as

with

themselves. This could dissipate more energy. This led to higher loss factor in mode 2 compared to that in mode 1. A prominent decrease in loss factor in both the modes is observed for EA30C2.5 nanocomposite. Agglomeration of CNTs can occur

since

its

amount

is

more

in

this

nanocomposite.

Diffusion into spherical adduct particles would be difficult for the agglomerated CNTs. Hence, a fraction of CNTs are retained in the continuous phase. This reduces the flexibility of the continuous phase. As a result loss factor decreases.

4

Conclusions Nanocomposites of CNT reinforced epoxy, modified with

adduct of epoxy and CTBN, were fabricated and tested for vibration damping properties. In the first mode, epoxy with 1 wt% CNT and 30 wt% adduct exhibited highest loss factor. An increase of 119 % compared to that of neat epoxy is obtained. In the second mode, epoxy with 0.5 wt% CNT and 30 wt% adduct 30


Page 31 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


exhibited highest loss factor. An increase of 98 % compared to that of neat epoxy is obtained. Significant improvement in loss factor is obtained for 30 wt% adduct modified epoxy nanocomposites reinforced with CNT. Which is as a result of the modification of microstructure of the nanocomposites when CNTs were incorporated to it. Larger spherical adduct particles were formed as a result of phase separation. Diffusion of DGEBA molecules to spherical adduct particles reduced the elastic modulus of continuous phase. Under the application of dynamic loads these particles slide relative to each other. This is facilitated by the increased flexibility of continuous phase. Energy is dissipated as heat during the frictional sliding of spherical particle with respect to the matrix as well as between themselves. CNTs played

major

role

in

developing

a

microstructure

which

enhanced the vibration damping.

5

Acknowledgement

The authors gratefully acknowledge Prof. S. Raja, Department of

Chemical

Sciences,

IISER,

Kolkata

for

the

technical

discussions and the Naval Research Board (NRB) of Government of

India

for

the

funding

support

DNRD/05/4003/NRB/333).

Supporting Information 31


(Project

number:


Page 32 of 42

Synthesis of adduct, Fabrication of nanocomposite

References [1] DA Saravanos and JM Pereira. Effects of Interply Damping Layers on the Dynamic Characteristics of Composite Plates. AIAA journal, 30(12):2906–2913, 1992.

[2] Maksim

Kireitseu,

Advanced

David

Hui,

Shock-resistant

Nanoparticle-reinforced

and

and

Geoffrey

Vibration

Composite

Tomlinson. Damping

Material.

of

Composites

Part B: Engineering, 39:128–138, 2008.

[3] Ioana C Finegan and Ronald F Gibson. Recent Research on Enhancement of Damping in Polymer Composites. Composite Structures, 44:89–98, 1999.

[4] R Chandra, SP Singh, and K1 Gupta. Damping Studies in Fibre

Reinforced

Composites

–

A

Review.

Composite

structures, 46(1):41–51, 1999.

[5] Ahid D Nashif, David IG Jones, and John P Henderson. Vibration damping. John Wiley & Sons, 1985.

[6] Jonghwan Suhr and Nikhil A Koratkar. Energy Dissipation in

Carbon

Nanotube

Composites:

A

Review.

Materials Science, 43:4370–4382, 2008. 32


Journal

of

Page 33 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[7] Mohan D Rao. Recent Applications of Viscoelastic Damping for Noise Control in Automobiles and Commercial Airplanes. Journal of Sound and Vibration, 262:457– 474, 2003.

[8] Himanshu Damping

Rajoria

and

Enhancement

Nader Using

Jalili. Carbon

Passive Nanotube

Vibration –

Epoxy

Reinforced Composites. Composites Science and Technology, 65:2079–2093, 2005.

[9] DIG Jones, AD Nashif, and ML Parin. Parametric Study of Multiple-layer Damping Treatments on Beams. Journal of Sound and Vibration, 29(4):423–434, 1973. [10] ASTM E756-05(2010). Standard Test Method for Measuring Vibration-damping

Properties

of

Materials.

In

ASTM

International, West Conshohocken, PA, 2010.

[11] Budhe, S., Banea, M.D., De Barros, S. and Da Silva, L.F.M., An Updated review of Adhesively Bonded Joints in Composite Materials. International Journal of Adhesion and Adhesives, 72:30 – 42, 2017.

[12] Kosmann, J., Klapp, O., Holzhüter, D., Schollerer, M.J., Fiedler, A., Nagel, C. and Hühne, C., Measurement of Epoxy Film Adhesive Properties in Torsion and Tension Using Tubular Butt Joints. International Journal of Adhesion and Adhesives, 83:50 – 58, 2018. Special issue on joint design.

33



[13] D.

Ratna,

Chakraborty.

N.R.

Manoj,

Novel

L.

Epoxy

Page 34 of 42

Chandrasekhar,

Compositions

for

and

B.C.

Vibration

Damping Applications. Polymers for Advanced Technologies, 15:583–586, 2004.

[14] Roger M Crane and John W Gillespie Jr. Characterization of the Vibration Damping Loss Factor of Glass and Graphite Fibre

Composites.

Composites

science

and

technology,

40(4):355–375, 1991.

[15] Dong-Ying Ju and Akira Shimamoto. Damping Property of Epoxy Matrix Composite Beams with Embedded Shape Memory Alloy Fibres. Journal of Intelligent Material Systems and Structures, 10:514–520, 1999.

[16] CW Wise, WD Cook, and AA Goodwin. CTBN Rubber Phase Precipitation in Model Epoxy Resins. Polymer, 41:4625– 4633, 2000.

[17] G Mansour, K Tsongas, and D Tzetzis. Investigation of the Dynamic Mechanical Properties of Epoxy Resins Modified with Elastomers. Composites Part B: Engineering, 94:152– 159, 2016.

[18] Raneesh Konnola and Kuruvilla Joseph. Effect of Side-wall Functionalization of Multi-walled Carbon Nanotubes on the Thermo-mechanical

Properties

of

Epoxy

Advances, 6:23887–23899, 2016. 34


Composites.

RSC

Page 35 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[19] YT Wang, CS Wang, HY Yin, LL Wang, HF Xie, and RS Cheng. Carboxyl-terminated

Butadiene-acrylonitrile-Toughened

Epoxy/carboxyl-modified Thermal

and

Carbon

Mechanical

Nanotube

Properties.

Nanocomposites: Express

Polymer

Letters, 6, 2012. [20] H.

S.

Y.

Hsich.

Thermodynamically

Reversible

and

Irreversible Control on Morphology of Multiphase Systems; Part 2 Morphology Control by Spinodal Decomposition and Nucleation

and

Growth.

Journal

of

Materials

Science,

26:3209–3222, Jun 1991.

[21] Keizo

Yamanaka,

Yasushi

Takagi,

and

Takashi

Inoue.

Reaction-induced Phase Separation in Rubber-modified Epoxy Resins. Polymer, 30:1839–1844, 1989.

[22] N Chikhi, S Fellahi, and M Bakar. Modification of Epoxy Resin

Using

Reactive

Liquid

(ATBN)

Rubber.

European

Polymer Journal, 38:251 – 264, 2002.

[23] D Verchere, H Sautereau, JP Pascault, SM Moschiar, CC Riccardi, and RJJ Williams. Rubber-modified Epoxies. (I) Influence of Carboxyl-terminated Butadiene-acrylonitrile Random Copolymers (CTBN) on the Polymerization and Phase Separation Processes. Journal of Applied Polymer Science, 41:467–485, 1990.

35



Page 36 of 42

[24] D Verchere, JP Pascault, H Sautereau, SM Moschiar, CC Riccardi, and RJJ Williams. Rubber-modified Epoxies. II. Influence of the Cure Schedule and Rubber Concentration on the Generated Morphology. Journal of Applied Polymer Science, 42:701–716, 1991.

[25] D Verchere, H Sautereau, JP Pascault, SM Moschiar, CC Riccardi, and RJJ Williams. Miscibility of Epoxy Monomers with Carboxyl-terminated Butadiene-acrylonitrile Random Copolymers. Polymer, 30(1):107–115, 1989.

[26] A. Joseph Berkmans, S. Ramakrishnan, Gaurav Jain, and Prathap Haridoss. Aligning Carbon Nanotubes, Synthesized Using

the

Arc

Discharge

technique,

During

and

After

Synthesis. Carbon, 55:185–195, 2013.

[27] M.

Jagannatham,

S.

Sankaran,

and

Prathap

Haridoss.

Electroless Nickel Plating of Arc Discharge Synthesized Carbon Nanotubes for Metal Matrix Composites. Applied Surface Science, 324:475–481, 2015.

[28] Lulu Wang, Yefa Tan, Haitao Wang, Li Gao, and Chufan Xiao. Investigation

on

Fracture

Behaviour

and

Mechanisms

of

DGEBF Toughened by CTBN. Chemical Physics Letters, 699:14– 21, 2018. [29] Kai Ke, Yu Wang, Xi-Qiang Liu, Jun Cao, Yong Luo, Wei Yang, Bang-Hu Xie, and Ming-Bo Yang. A Comparison of Melt

36


Page 37 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and Solution Mixing on the Dispersion of Carbon Nanotubes in a Poly-(vinylidene fluoride) Matrix. Composites Part B: Engineering, 43:1425–1432, 2012.

[30] Kin-tak Lau, Mei Lu, Chun-ki Lam, Hoi-yan Cheung, Fen-Lin Sheng, and Hu-Lin Li. Thermal and Mechanical Properties of Single-walled Carbon Nanotube Bundle Reinforced Epoxy Nanocomposites:

The

Role

of

Solvent

for

Nanotube

Dispersion. Composites science and technology, 65:719–725, 2005.

[31] Young Seok Song and Jae Ryoun Youn. Influence of Dispersion States of Carbon Nanotubes on Physical Properties of Epoxy Nanocomposites. Carbon, 43:1378– 1385, 2005.

[32] D Ross, EE Ungar, and EM Kerwin. Structural damping. ASME, pages 49–88, 1959. [33] Garima Tripathi and Deepak Srivastava. Effect of Carboxylterminated

Poly

(Butadiene-co-acrylonitrile)

(CTBN)

Concentration on Thermal and Mechanical Properties of Binary Blends of Diglycidyl ether of bisphenol-a (DGEBA) Epoxy

Resin.

Materials

Science

and

Engineering:

A,

443:262–269, 2007.

[34] Abhinav Alva and S Raja. Damping Characteristics of Epoxyreinforced

Composite

with

37

Multiwall


Carbon

Nanotubes.


Page 38 of 42

Mechanics of Advanced Materials and Structures, 21:197– 206, 2014.

[35] J

Heijboer.

Secondary

Loss

Peaks

in

Glassy

Amorphous

Polymers. Molecular basis of transitions and relaxations, Gordon and Breach, London, page 75, 1978.

[36] F Garwe, A Sch¨onhals, H Lockwenz, M Beiner, K Schro¨ter, and E Donth. Influence of Cooperative α Dynamics on Local β Relaxation during the Development of the Dynamic Glass Transition

in

Poly

(n-alkyl

methacrylate)

s.

Macromolecules, 29:247–253, 1996.

[37] X Zhou, Eungsoo Shin, KW Wang, and CE Bakis. Interfacial Damping

Characteristics

of

Carbon

Nanotube-based

Composites. Composites Science and Technology, 64:2425– 2437, 2004. [38] Nikhil A Koratkar, Jonghwan Suhr, Amit Joshi, Ravi S Kane, Linda S Schadler, Pulickel M Ajayan, and Steve Bartolucci. Characterizing Energy Dissipation in Single-walled Carbon Nanotube

Polycarbonate

Composites.

Applied

physics

letters, 87:063102, 2005.

[39] John Cumings and A Zettl. Low-friction Nanoscale Linear Bearing Realized from Multiwall Carbon Nanotubes. Science, 289:602–604, 2000.

38


Page 39 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


[40] Paul Tangney, Steven G Louie, and Marvin L Cohen. Dynamic Sliding

Friction

between

Concentric

Carbon

Nanotubes.

Physical Review Letters, 93:065503, 2004.

[41] Aleksey

N

Bearings:

Kolmogorov

and

Interlayer

Vincent

Sliding

H

in

Crespi.

Smoothest

Multiwalled

Carbon

Nanotubes. Physical Review Letters, 85:4727, 2000.

[42] Quanshui Nanotubes

Zheng as

and

Qing

Gigahertz

Jiang.

Multiwalled

Oscillators.

Carbon

Physical

Review

Letters, 88:045503, 2002.

[43] Jos´e

L

Rivera,

Clare

McCabe,

and

Peter

T

Cummings.

Oscillatory Behaviour of Double-walled Nanotubes under Extension: A Simple Nanoscale Damped Spring. Nano Letters, 3:1001–1005, 2003.

[44] CB Bucknall and IK Partridge. Phase Separation in Crosslinked

Resins

Containing

Polymeric

Modifiers.

Polymer

Engineering & Science, 26:54–62, 1986.

[45] Jong-Pyng Chen and Yu-Der Lee. A Real-time Study of the Phase-separation Process during Polymerization of Rubbermodified Epoxy. Polymer, 36(1):55–65, 1995.

[46] Jeremy

H

Influence

Klug on

and the

James

C

Seferis.

Performance

39

of


Phase

Separation

CTBN-toughened

Epoxy


Page 40 of 42

Adhesives. Polymer Engineering & Science, 39:1837–1848, 1999.

[47] Hak Soo Lee and Thein Kyu. Phase Separation Dynamics of Rubber/Epoxy Mixtures. Macromolecules, 23:459–464, 1990.

[48] A

Vazquez,

AJ

Rojas,

HE

Adabbo,

J

Borrajo,

and

RJJ

Williams. Rubber Modified Thermosets: Prediction of the Particle Size Distribution of Dispersed Domains. Polymer, 28(7):1156–1164, 1987. [49] SM Moschiar, CC Riccardi, RJJ Williams, D Verchere, H Sautereau, and JP Pascault. Rubber-modified Epoxies. III. Analysis of Experimental trends through a Phase Separation Model. Journal of Applied Polymer Science, 42(3):717–735, 1991.

[50] Reza Bagheri and Raymond A Pearson. Role of Particle Cavitation

in

Rubber

Toughened

Epoxies:

1.

Microvoid

Toughening. Polymer, 37:4529–4538, 1996.

[51] Bobby Russell and Richard Chartoff. The Influence of Cure Conditions on the Morphology and Phase Distribution in a Rubber-modified

Epoxy

Resin

using

Scanning

Electron

Microscopy and Atomic Force Microscopy. Polymer, 46:785– 798, 2005.

[52] Raju Thomas, Sebastien Durix, Christophe Sinturel, Tolib Omonov,

Sara

Goossens,

Gabriel 40


Groeninckx,

Paula

Page 41 of 42 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Moldenaers, and Sabu Thomas. Cure kinetics, Morphology and Miscibility of Modified DGEBA – based Epoxy Resin – effects of a Liquid Rubber Inclusion. Polymer, 48:1695–1710, 2007.

[53] Tadao Sugimoto. Monodispersed particles. Elsevier, 2001.

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Multiwalled Carbon Nanotube Reinforced Epoxy Nanocomposites for

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