Due to the wide applications of three-dimensional graphene (3DG) foam in bio-sensors, stretchable electronics, and conductive polymer composites, predicting its mechanical behavior is of paramount importance. In this paper, a novel multiscale finite element model is proposed to predict the compressive modulus of 3DG foams with various densities. It considers the effects of pore size and structure and the thickness of graphene walls on 3DG foams’ overall behavior. According to the scanning electron microscope images, a unit cell is selected in the microscale step to represent the incidental arrangement of graphene sheets in 3DG foams. After derivation of equivalent elastic constants of the unit cell by six individual load cases, the whole unit cell is considered an equivalent element. The macroscale model is prepared by defining a representative volume element (RVE), containing a sufficient number of the equivalent elements. Assigning a stochastic local coordinate system for each equivalent element in the macro RVE provides a model that could be utilized for elastic modulus estimation of 3DG foams in macroscale. To investigate the correspondence between the theoretical results and experimental data, 3DG foams were synthesized with four densities, and their compressive behavior were evaluated. The mass densities of the prepared foams were 5.36, 8.50, 9.37, and 11.5 mg cm−3, and the corresponding measured elastic modulus for each were 6.4, 10.7, 16.9, and 29.1 kPa, respectively. The predicted modulus by the proposed model for the synthesized foams were 6.1, 13.1, 15.6 and 21.7 kPa, respectively. The results show that the maximum divergence between estimated values and experimental data is less than 25%, confirming the high capability of the model in the estimation of 3DG foams’ properties.

In this study, graphene aerogel (GA) was used to improve the multifunctionality of epoxy resin, which is essential for its application in integrated circuits and semiconductors. To this end, a scalable method with a high capacity for producing large-size GA with desirable quality was proposed for GA synthesis. The synthesized GA was utilized to produce epoxy nanocomposites by infiltrating epoxy resin into its macro-pores. The flexural modulus of the GA/epoxy nanocomposite was investigated experimentally, and the results indicated a 30% increase with respect to the pure epoxy. The electrical conductivity of the nanocomposite reached an exceptional value of 0.7 S/m, which is 13 orders of magnitude greater than the electrical conductivity of pure epoxy. Moreover, the measured thermal conductivity for pure epoxy and GA/epoxy nanocomposites were 0.23 and 0.40 W/mK, respectively. The percentage of thermal conductivity improvement per filler content was over 101, among the highest values attained by different filler types in polymer nanocomposites. This study demonstrates that the proposed method can simultaneously increase epoxy polymers’ mechanical, electrical, and thermal properties with a low nanomaterial concentration, which could greatly benefit applications requiring highly multifunctional epoxy polymers.

Optical tweezers are proven and indispensable micro-manipulation tools. It is very common to use an immersion-assisted high NA objective for optical trapping of micrometer-sized beads. However, such objectives suffer from low working depth range. Here we show, both by theory and experiment, that a dry objective can be utilized for optimal trapping of even sub-micrometer objects. For the first time, to the best of our knowledge, we were able to stably trap polystyrene beads with radii of 270 and 175 nm in 3D using an objective with numerical aperture of 0.9.

In this study, graphene aerogel (GA) was utilized to improve the multifunctionality of epoxy resin, which is highly necessary in its applications in integrated circuits and semiconductors. A scalable method with high capability for production of large size GA with desirable quality was proposed for GA synthesis. The synthesized GA was utilized to produce epoxy nanocomposite by epoxy resin infiltration in its macro-pores. Flexural modulus of the GA/epoxy nanocomposite was experimentally investigated and the results showed 30% increase with respect to the pure epoxy. The electrical conductivity of the nanocomposite reached to remarkable amount of 0.7 S/m, which is 13 orders of magnitudes more than the electrical conductivity of the neat epoxy. Moreover, the measured thermal conductivity for pure epoxy and GA/epoxy nanocomposites were 0.23 and 0.40 W/mK, respectively. The percentage of thermal conductivity enhancement per filler content is more than 101, which is in the top range of the reached values by various filler types in polymer nanocomposites. The proposed method could simultaneously increase the mechanical, electrical and thermal properties of epoxy polymer, and could be greatly beneficial for applications that need epoxy polymer with high multifunctionality.