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This study is an attempt to improve the thermal properties of polyacrylamide (PAAm) membrane using graphene oxide (GO) and reduced graphene oxide (rGO) as a static modifier and phase change material micro-capsules (mPCMs) as a dynamic modifier at the same time. Fourier transform infra-red spectroscopy, X-ray diffraction and transmission electron microscopy were applied to prove GO and rGO synthesis. Dynamic heat transfer simulation apparatus and the transient heat transfer model were used to study the transient temperature behavior of the samples. Scanning electron microscopy and differential scanning calorimetry were also used to study the morphological properties and thermal behavior of hydrogels containing mPCMs. The addition of GO and rGO to the PAAm matrix increased thermal conductivity 2 and 2.5 times more than pure PAAm. Moreover, studying the transient temperature rates and mathematical simulations for PAAm containing GO and rGO revealed that rGO had better performance than GO in improving thermal properties. These hybrid nanocomposites increased the thermal conductivity of the fabrics thanks to the presence of rGO nanosheets and heat absorption capacity by mPCMs. It was also found that the presence of rGO improved the heat absorption performance of mPCMs to some extent. This long-awaited improvement in the thermal properties of the hydrogel membrane can be potentially harnessed to enhance user comfort in protective clothing.

Microstructure, rheological properties and their relationships of PA6/NBR/nano-clay nanocomposite have been investigated. Scanning electron microscopy (SEM) and transmission electron microscopy imaging techniques were used to study micro-structure. The nano-clay dispersion was measured by small angle X-ray diffraction. Frequency sweep, steady shear, startup shear transient, and startup shear free transient experiments were carried out to study rheological characteristics of nanocomposite. SEM micrograph revealed that nano-clay decreased the size of rubber droplets to a half in comparison with samples without nano-clay. Storage modulus of nanocomposite containing 7% wt nano-clay exhibited frequency independent behavior because of physical network which formed in matrix, in contrast to pure PA6 which showed terminal storage modulus at low frequencies. Shear thinning at high shear rates was observed by addition of rubber to PA6 matrix caused by deformation of rubber droplets. Nano-clay orientation in shear flow field accelerated non-Newtonian behavior in steady shear experiment. Transient shear viscosity studies were used for measurement the strength of nanoclay physical network. It was found that network breakdown is more stress consuming factor in comparison with nano-particle orientation and hydrodynamic forces. Elongation transient viscosity studies showed that critical Hencky strain for linear-nonlinear viscoelastic transition shifted to higher strains by increasing nano-clay concentration.

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