14-08-2013
Preparation of galactomannan based ionic gel and its nanocomposite gel with MWCNT having self-healing and solvent responsive healing property Kamalesh Prasad, * Mukesh Sharma, Dibyendu Mondal and Chandrakant Mukesh Marine Biotechnology and Ecology Discipline, CSIR-Central Salt & Marine Chemicals Research Institute, G. B Marg, Bhavnagar-364002 (Gujarat), India, Phone No : +91-278-2567760. Fax No. +91-278-2567562 Email: kamlesh@csmcri.org / drkamaleshp@gmail.com
Herewith we report the preparation of guar gum ion gels and its nanocomposite ion gels with multiwalled carbon nanotubes (MWCNT) in 1-butyl-3-methylimidazolium chloride. The gels upon complete bisection or upon fracture on the surfaces self-healed at room temperature without any external stimuli. Further, the bisected gels also showed healing ability in presence of three polar aprotic solvents namely, acetone, N,N-dimethylformamide and dimethylsulfoxide. However, the gels did not heal in the presence of acetonitrile. The gels could be adhered to human finger muscles and they remained attached on the fingers for long time. The natural polysaccharide, guar gum (GG ) is a galactomannan extracted from the seed of the leguminous shrub Cyamopsis tetragonoloba and consists of (1→ →4)-linked β-D-mannopyranose main chain with a branched α-D-galactopyranose unit at C-6 (Fig. 1a)
Designing of self healable bio mimicking gel systems The gelation of GG (10% w/v) was achieved by heating-cooling process (Prasad et al., 2009; Mine et al., 2010). In a typical procedure, GG (0.10 g) was dissolved in BmimCl (1.0 g) by heating at 80 - 100 °C for 1 h under argon atmosphere (the optimized molar ratio of GG repeating units to BmimCl was 1:27.7). Similarly the nanocomposite gel of GG with MWCNT was prepared by adding 10% of GG in BmimCl containing 0.2% of MWCNT followed by heating at 80 – 100 °C for 1 h under argon atmosphere. After the respective viscous solutions were cooled to room temperature, it gave formation of the gels. In order to study the interactions among the IL, MWCNT and GG, the respective gels were processed to powder form by adding isopropyl alcohol (IPA) followed by drying.
Figure 4. Healing of guar gum-BmimCl and guar gum-BmimCl/ MWCNT nanocomposite gel in the presence of acetone at room temperature
Proposed schematic mechanism for the acetone induced healing phenomenon
Figure 1: Self-healing of bisected (a) guar gum-BmimCl ionic gel and (b) guar gum-BmimCl/MWCNT nanocomposite gel.
Cation-π π interaction between ionic liquid and MWCNT as observed in TEM analyses
Figure 2: TEM image of (A) pure MWCNT (B) BmimCl functionalized MWCNT and (C) interaction of guar gum and BmimCl with MWCNT.
Figure 3 : Evaluation of thixotropic behaviour by hysteresis loop measurements (A) guar gum-BmimCl gel and (B) guar gum-BmimCl / MWCNT nanocomposite gel Carbohydr. Polym. 2013, 98, 1025-1030
Figure 5 Evaluation of thixotropic property by hysteresis loop experiment for (A) Guar gum-BmimCl and (B) Guar gum-BmimCl/MWCNT nanocomposite gel
Figure 6. Self-healing in guar gumBmimCl/MWCNT nanocomposite gel as characterized by dynamic recovery of the storage modulus (G´) upon induced relaxation
RSC-Advances 2013 : DOI:10.1039/C3RA42454E
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