are the most popular methods. Electrically conductive nanomaterials, such as carbon black, [11] planar graphene, [12] carbon nanotube (CNT), [13] carbon nanofiber (CNF), [14] gold nanowires, [15] conductive polymer, [16] silver nanowires, [17] and silver flakes, [18] have been widely studied for the piezoresistive sensing applications both in stand-alone form and by dispersing into flexible polymers. Several review papers have summarized the state of the art of current research on highly flexible nanocomposites. [19][20][21] When used in standalone form, such as CNT bucky papers, these nanoparticles can provide superior electrical conductivity, but are lacking in flexibility. [22] The more practical approach is to disperse nanoparticles within a flexible polymer, such as PDMS, [23,24] polyimide, [25] and polyurethane. [26] It has been reported that a small amount of CNTs or CNFs dispersed in polymer can significantly enhance the electrical conductivity by orders. Among those, CNF is two orders of magnitude cheaper than its counterparts CNT and graphene. [14] Multiple key parameters, including electrical conductivity, sensitivity, sensing range, durability, and manufacturing cost and complexity, can impact on the performance of nanocomposite sensors. Advanced manufacturing technologies, such as etching and photolithography, have been employed to create critical microstructures in nanocomposites, resulting in novel pressure and strain sensors, though the manufacturing cost and scalability are often criticized. [24,27] Recently, graphene/ PDMS nanocomposites have shown good sensitivity with gauge factor of 61.3 and detectability of up to 20% tensile strain, but manufacturing requires freezing at −50 °C and heat treatment at 750 °C. [28] In terms of sensor performance, obtaining an optimum combination of sensitivity and sensing range is challenging. High gauge factors in the order of 1000 were obtained using a woven mesh configuration of graphene/polymer but this material only achieved up to 6% strain. [29] A graphene film was made in an easy single step process, and showed gauge factor of 1000 but its failure strain was only at 2% strain. [30] In general, highly flexible nanocomposites result in the trade-off of piezoresistive sensitivity. For example, Qin et al. reported that flexible nanocomposites using reduced graphene oxide and polyimide had the maximum stretching and compression sensing capability up to 50% strain with low gauge factors of 0.712 and 1, respectively. [25] Majority of the works on sensor A polydimethylsiloxane (PDMS)/carbon nanofiber (CNF) nanocomposite with piezoresistive sensing function is presented. Excellent electrical conductivity is achieved by dispersing the CNFs into PDMS. A facile, low cost, and scalable fabrication procedure allows the sensors to be made in different shapes. The piezoresistive sensors show repeatable response up to 30% tensile strain. In addition, the characterization of sensing mechanism using an in situ mechanical testing system within a scanning electron microscope...

Three water-soluble polymers containing linear alkyl monool, 1,2-diol, and 1,2,3-triol groups, mostly on the primary amines of polyethylenimine, were synthesized, characterized, and tested for their ability to recover boric acid. The boron-binding capacities of these polymers and the backbone polyethylenimine were determined by titration, ultrafiltration, and inductively coupled plasma/ atomic emission spectroscopy analysis. At low boron concentrations, the 1,2,3-triol polymer performed better than the 1,2-diol, whereas at high boron concentrations, the 1,2-diol outperformed the 1,2,3-triol.11 B-NMR spectroscopy and retention studies with various salt concentrations indicated that boron interacted with these two polymers by means of ion pairing with the protonated amines and by borate ester formation. For the monool and the polyethylenimine backbone, the mechanism for boron binding was ion pairing only. These polymers are under consideration for the selective recovery and recycling of enriched boric acid used in the primary coolant loop of pressurized water nuclear reactors.

Here, we report all-polymer polysiloxane composites that overcome the long-standing processing problems of silica-reinforced silicone rubbers. Polystyrene fillers are dispersed with styrene/dimethylsiloxane symmetric diblock and triblock copolymers that control the filler morphology, filler−matrix interactions, and filler−filler interactions. Surprisingly, the composites not only rival the traditional silica-reinforced polysiloxane in mechanical properties of cured materials but also have better processability and stability than the silica-filled compound before curing. Large amplitude oscillatory shear experiments demonstrate that the triblock copolymer addition strongly affects the rheological properties. We hypothesize that the bridges and entangled loops that were formed by the triblock copolymer can connect different PS domains to provide additional reinforcement. The aging effect that originates from PDMS chain adsorption on the filler particle surface is also avoided because of the thermodynamic repulsion between PS and PDMS phases.

Here we report microphase-separated poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) as a reinforcing filler in PDMS thermosets that overcomes the long-standing problem of aging in the processing of silicareinforced silicone. Surprisingly, PS-b-PDMS reinforced composites display comparable mechanical performance to silica-modified analogs, even though the modulus of PS is much smaller than that of silica and there is no evidence of percolation with respect to the rigid PS domains. We have found that a few unique characteristics contribute to the reinforcing performance of PS-b-PDMS. The strong selfassembly behavior promotes batch-to-batch repeatability by having well-dispersed fillers. The structure and size of the fillers depend on the loading and characteristics of both filler and matrix, along with the shear effect. The reinforcing effect of PS-b-PDMS is mostly brought by the entanglements between the corona layer of the filler and the matrix, rather than the hydrodynamic reinforcement of the PS phase.

This article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future. ARTICLE HISTORY