4(%3)3 - Ecole nationale supÃ©rieure de chimie de Montpellier

More documents

Recommendations

Info

the lower stiffness and fracture toughness of PDMS compared to matrix polymer. In a furthermodification to above work, PDMS was employed as the matrix polymer while containing two differentsets of microcapsules 25 . One set of microcapsules contained a PDMS copolymer with active sites forcrosslinking while the other kind contained a high molecular weight vinyl functionalized PDMS along withplatinum catalyst (initiator capsule). Up to 75% healing efficiency was achieved with 10 wt% resincapsules and 5 wt% catalyst capsules.Encapsulation of epoxy resin in microcapsules as healing agent is also one of the alternativesinvestigated 26,69-71 . However to accomplish healing, a latent hardener has to be incorporated into thematrix. Upon rupture of the microcapsule, the epoxy would seep into the crack and polymerizes due tocontact with embedded hardener thus closing the crack. This approach shares the same advantage asthe PDMS/catalyst system that the healing material generated during the healing process is identical asthe matrix material itself chemically. This result in the deviation of tear path in the healed sample fromthat of the virgin tear path, resulting in greater than 100 % healing efficiencies. The epoxy/hardenersystem, first reported in 2007 71 employed an imidazole-metal complex as a latent hardener. Thesolubility of CuBr 2 (2-MeIm) 4 hardener complex in epoxy ensured a homogeneous distribution all over thematrix and thus capable of curing epoxy at any point in the matrix. The reported diameter range of themicrocapsules was 30 – 70 µm with encapsulated epoxy resin. The incorporation of the hardener and theepoxy microcapsules did not impact the mechanical properties of the matrix as such though fracturetoughness was found to be increased slightly. Using 10 wt% epoxy microcapsules and 2 wt% latenthardener, an impressive 111% healing efficiency was reported however the approach failed to qualify asa true autonomous healing system. The obvious reason is the inherent need to heat the samplesbetween 130 o C – 170 o C to initiate the curing of the epoxy resin. To make this approach fullyautonomous, the imidazole-metal complex hardener was replaced with low-temperature mercaptanhardener 34 in conjunction with a tertiary amine catalyst, encapsulated in microcapsules and embeddedalong with epoxy filled microcapsules in an epoxy matrix 35 . The microcapsules used for bothcomponents, were based on the melamine-formaldehyde due to instable nature of mercaptan hardener.The benzyldimethyl amine catalyst was infiltrated into mercaptan filled microcapsules in a secondarystep, since being basic in nature the catalyst couldn’t be incorporated during the microencapsulationprocedure which is performed in acidic medium. A healing efficiency of 104.5% was reported forspecimens containing 5 wt% (2.4 wt % each) capsules at 20 o C (Figure – 1.11a). It was observed thatmaximum healing occurred when the ratio of two microcapsules set is near 1:1. A minimum of 12 hours13
was required to reach healing efficiency beyond 100 %. A novel feature of this work was theachievement of healing at temperature as low as -10 o C with an efficiency of 86% (Figure – 1.11b).Figure – 1.11: Self-healing process based on epoxy/mercaptan system, a) Influence of capsules concentration onfracture toughness of the materials, b) Influence of temperature on healing efficiencies with time.Solvent induced self-healing comprises the earliest known works in the field of self-healing. Firstreported in early 80s, the approach involved the heating of thermoplastic polymers (for example:PMMA) and simultaneous sealing of cracks with solvents like ethanol, methanol and carbontetrachloride 72-77 . The healing mechanism involved wetting of the polymer surface and swelling of thebulk polymer material, which led to reptation and interlocking of the chains across the crack plane torecover mechanical properties of the virgin material and heal the crack. Immersion of polymerspecimens in these solvents reduced the glass transition (T g ) of the polymer, thereby facilitating thehealing procedure to occur at room temperature or slight heating. However due to high degree ofswelling, the healed samples had lower strengths than the original ones. The solvent strategy wascombined with encapsulation technique in 2007 by Caruso et al. in a work where the solvent wasencapsulated and embedded into an epoxy matrix 78 . A significant number of solvents were investigatedand first screened for their healing ability by manually injecting them onto a crack plane of a fracturedepoxy specimen in reference tests mimicking the delivery of solvent to the crack by a ruptured capsule.The study showed a correlation between the healing efficiency and the solvent polarity (Figure – 1.12a).Five aprotic polar solvents exhibited the highest healing efficiencies namely: nitrobenzene, NMP, DMA,DMF, and DMSO. These solvents have dielectric constants ranging from 32 to 47. However, therelationship of polarity with healing efficiency could not be explained. On both extremes of the polarityspectrum, non polar solvents like cyclohexane, hexanes and protic polar solvents like formamide, and14
Page 1: THESISPRESENTED ATNATIONAL GRADUATE
Page 4 and 5: As the human civilization progress
Page 6 and 7: CHAPTER - 1 SELF-HEALING POLYMERIC
Page 8: 8.1.5 Atomic Force Microscopy …
Page 11 and 12: Synthetic engineering materials in
Page 13 and 14: esponse to a specific external stim
Page 15 and 16: The first work based on this approa
Page 17 and 18: een prepared from urea-formaldehyde
Page 19 and 20: monomer systems. The addition of EN
Page 21: Figure - 1.10: Self-healing process
Page 25 and 26: In addition to above works, some ot
Page 27 and 28: that have been identified to be tak
Page 29 and 30: part of the chapter, these material
Page 31 and 32: Figure - 1.17: Self-healing of the
Page 33 and 34: commercialized under tradenames; Nu
Page 35 and 36: joined together at temperature high
Page 37 and 38: Inspired by these findings, the fir
Page 39 and 40: temperature greater than 80 o C in
Page 41 and 42: Figure - 1.27: Sulfur chemistry bas
Page 43 and 44: A different kind of sulfur chemistr
Page 45 and 46: Figure - 1.29: Dynamic covalent che
Page 47 and 48: cracks. The recovered droplets afte
Page 49 and 50: 23 White, S. R. et al. Autonomic he
Page 51 and 52: 65 Taber, D. F. & Frankowski, K. J.
Page 53 and 54: 107 Kushner, A. M., Vossler, J. D.,
Page 55: 148 Park, J. S., Kim, H. S. & Hahn,
Page 58 and 59: The value of subscripts “n”,
Page 60 and 61: The formation of spherical micelles
Page 62 and 63: the micelle assembly showed the pre
Page 64 and 65: gain onto the electrodes by buildin
Page 66 and 67: The resistance R can be further exp
Page 68 and 69: empty-tower velocity U only depends
Page 70 and 71: This apparent morphological switchi
Page 72 and 73:
In a further qualitative analysis,
Page 74 and 75:
noteworthy and though its feasibili
Page 76 and 77:
Furthermore within this range, lowe
Page 78 and 79:
Figure - 2.22: Scanning Electron Mi
Page 80 and 81:
While the resistance measurements g
Page 82 and 83:
In conclusion, a self-healing membr
Page 84 and 85:
23 Giacomelli, F. C., Riegel, I. C.
Page 86 and 87:
micelles enabled the membrane to se
Page 88 and 89:
The second class is represented by
Page 90 and 91:
To avoid the probable clogging of t
Page 92 and 93:
181614SP2 - iNumber of Particles121
Page 94 and 95:
1000900800y = 3E+06xR² = 0,9911y =
Page 96 and 97:
very high value of 1.5 g.l -1 . Thi
Page 98 and 99:
Since the only change in the membra
Page 100 and 101:
100Retention (%)8060400,100,20,40,6
Page 102 and 103:
Page 104 and 105:
(Figure - 3.20). A cursory look at
Page 106 and 107:
When compared to poly(styrene) NPs,
Page 108 and 109:
Page 110 and 111:
REFERENCES1 Metzler, R. & Klafter,
Page 112 and 113:
46 Bemporad, D., Luttmann, C. & Ess
Page 114 and 115:
In this chapter, preparation of 3D
Page 116 and 117:
obtain complex macromolecular archi
Page 118 and 119:
The polymerization was conducted at
Page 120 and 121:
proceeds, lesser monomer is availab
Page 122 and 123:
mg/ml),the micelles’ hydrodynamic
Page 124 and 125:
Figure - 4.15: The monolayer and mu
Page 126 and 127:
monolayer of micelles and topmost l
Page 128 and 129:
The presence of the dispersed micel
Page 130 and 131:
Heating the multilayer micelle asse
Page 132 and 133:
stable zipping of the micelles. Mul
Page 134 and 135:
24 Moad, G., Rizzardo, E. & Thang,
Page 136 and 137:
The concept of nano-gel based self-
Page 138 and 139:
Figure - 5.4: Size distribution of
Page 140 and 141:
In a typical process, the two compo
Page 142 and 143:
Figure - 5.10: 1HNMR spectra obtain
Page 144 and 145:
The 1 HNMR spectrum obtained for th
Page 146 and 147:
REFERENCES1 White, S. R. et al. Aut
Page 148 and 149:
healing ability shown by the membra
Page 150 and 151:
7. PERSPECTIVESBeing the first such
Page 153 and 154:
8. MATERIALS & METHODSThis chapter
Page 155 and 156:
8.1.3 PEG Filtration MeasurementsTh
Page 157 and 158:
addition of TEOS due to formation o
Page 159 and 160:
solution was ultrasonicated for 15
Page 161 and 162:
Triethylamine (TEA) (Sigma-Aldrich
Page 163 and 164:
To prepare the monolayer assembly o
Page 165 and 166:
was added followed by addition of 0
Page 168 and 169:
ELABORATION OF SELF-HEALING POLYMER
Page 170 and 171:
ELABORATION DES MEMBRANES POLYMERES
show all

4(%3)3 - Ecole nationale supÃ©rieure de chimie de Montpellier

Create successful ePaper yourself

Delete template?

Save as template?