The dielectric properties of nanocomposites of polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymers containing organically modified clay nanoparticles featuring controlled spatial orientation at the nanoscale: isotropic, totally oriented and partially oriented, have been investigated and correlated with the nanocomposite morphologies. A slow dielectric relaxation process attributed to elastomer chains with reduced mobility confined at nanoparticle/polymer interphase was observed in all the nanocomposites and was found to be dependent on the orientation of nanoclay and polystyrene (PS) domains, the location of clay tactoids as well as the PS block fraction. A dielectric "interfacial" glass transition temperature T gi assigned to this characteristic relaxation was estimated to occur at temperatures ranging between 6 °C and 35 °C depending on the nanocomposite, which is much higher than the bulk rubber phase glass transition temperature, normally lower than -40 °C for the studied block copolymers. Interestingly, the highest T gi were associated with the nanocomposites featuring random or partial orientation and/or selective location of nanoparticles in the rubber phase.
I) IntroductionIn nanocomposite materials, controlled orientation of certain anisotropic nanoparticles such as nanoclay 1,2 , carbon nanotubes 3 and recently boron nitride nanotubes and nanosheets 4,5 is very beneficial for a wide spectrum of applications requiring excellent mechanical, electrical and/or thermal properties.For example, in the case of mechanical reinforcement, the alignment of nanoclay was reported in several publications to induce an improved mechanical strength in the alignment direction 6 . In the specific case of nanodielectrics, more efficient electron scattering and consequently higher breakdown strength perpendicular to the nanoparticles alignment direction were reported 2,7,8,9 . Simultaneously, nanoparticle alignment was shown to reduce dielectric losses in the direction perpendicular to the main plane of the M A N U S C R I P T
A C C E P T E D ACCEPTED MANUSCRIPT3 aligned nanoparticles 2 . This controlled orientation can be obtained using a wide range of techniques 3 although spatial alignment of nanoparticles according to 2D and 3D patterns is still a challenging field of study 10 .In applications requiring tuned spatial distribution of nanoparticles, the use of block copolymers can be really an asset due to the different nanoscale morphologies these materials present 11,12,13,14,15,16 . To probe the effect of tailored morphology and orientation of such designed nanocomposites on their polymer-filler interactions and implicitly on their final performance, techniques such as broadband dielectric spectroscopy (BDS) are often required 17 .In fact, the performance of polymer nanocomposites in general is governed by the interphase region 18,19 which consists mainly of a bound layer where the motion of macromolecular chains is strongly restricted affecting several properties including dielectric and m...
