A hydrophobic and biocompatible transdermal device has been developed from 2-hydroxyethyl methacrylate (HEMA) grafted carnboxymethyl guar gum (CMG)-functionalized multi-walled carbon nanotube (MWCNT) in situ composite membranes. The developed composites may be used for sustained delivery of diclofenac sodium. Supreme matrix-MWCNT interaction at 0.5 and 1 wt% MWCNT concentrations induces excellent copolymer-adsorbed fibrillar orientation of MWCNT compared to that at 2 and 3 wt%. It successively leads to efficient encapsulation and more sustained release of the drug molecules at these compositions (65% vs. 17% at 1 wt%). Analyses show that the releases are dominated by the viscoelastic relaxation behavior (power law indices 0.75 and 0.80 and extremely high Deborah numbers) of the devices. Conversely, for the latter, the releases are comparatively less sustained and more swelling controlled (indices are 0.5 and 0.6 and low Deborah numbers). However, all devices have significantly increased the half life period of the drug molecules (2.5 h vs. 47 h at 1 wt%). This journal is © the Partner Organisations 2014.