Experimental and theoretical estimation of the Hansen solubility parameters of paramylon esters based on the degrees of substitution and chain lengths of their acyl groups.

Paramylon is a natural hydrophilic polysaccharide produced in the pyrenoids of euglenoids, and esterification may render paramylon hydrophobic. Esterification imparts not only thermoplasticity, but also potential compatibilities with other polymer resins and fillers. However, the dependence of the compatibility on the structure of the polymer ester has not yet been systematically studied. To estimate the affinities between paramylon esters and hydrophobic organic solvents/resins, the dependences of their Hansen solubility parameters, which are association indices, on the degrees of substitution and chain lengths of the ester groups were investigated. Experimental and theoretical investigations were conducted using the dissolution and Fedors methods, respectively. Esterification decreased the solubility parameter from 49 (paramylon) to approximately 18 MPa1/2 (paramylon esters), indicating that the potential affinities of paramylon esters for hydrophobic organic solvents/polymers increased. A multiple regression analysis was also performed to investigate the effects of acyl chain length and degree of substitution with acyl groups on the solubility parameter. The solubility parameters of the paramylon derivatives were continuously variable from hydrophilic to -phobic. Hence, esterification with various acyl groups may control the hydrophobicities of paramylon esters, enhancing their miscibilities with various hydrophobic organic solvents and resins.

Synthesis of Multiblock Copolymer Composed of Biodegradable Poly(butylene succinate) and Poly(2-pyrrolidone): Impact of Each Block Length on the Mechanical Properties.

A series of multiblock copolymers comprising a systematic combination of biomass-originated and biodegradable poly(butylene succinate) (PBS) and poly(2-pyrrolidone) (PA4) units is synthesized with various mean degrees of polymerization (mDP) of each unit. Despite the inherent immiscibility of PBS and PA4, multiblock structure allows to mix the two components in the solution-cast films from solution. The mechanical properties of the cast films are highly dependent on the mDP of each unit, as demonstrated by tensile tests. The film of the copolymer with the lowest mDP of each unit (PBS: 17, PA4: 10) is transparent and exhibits extremely high elongation at break (> 400%) and high tensile stress (39.5 MPa) with strain hardening. The films with 50% or higher crystallinity are brittle and opaque, while a decrease in crystallinity can result in higher elongation, as revealed by wide-angle X-ray diffraction measurements.

Effect of the Alumina Particle Filler Structure and Particle Size on the Dielectric Constant and Dielectric Loss in the Millimeter-Wave Band.

The sixth-generation communication system (6G) is the next-generation communication system and is expected to be operational in 2030. The following areas will use 6G: the frequency band employed in 6G is expected to be 100 GHz or higher, necessitating additional reduction of the dielectric constant and dielectric loss in the substrate material. In this study, we examined the effects of compounding various phases of alumina with different shapes and crystal phases on the dielectric constant and dielectric loss of cyclo-olefin polymer (COP) compounds. It was confirmed that the smaller the particle size, the higher the effect on the dielectric loss. The dielectric loss decreased from 1.6 × 10-3 of COP to 1.2 × 10-3 when the smallest filler was added at 30 wt %.

Novel Approaches to In-Situ ATR-FTIR Spectroscopy and Spectroscopic Imaging for Real-Time Simultaneous Monitoring Curing Reaction and Diffusion of the Curing Agent at Rubber Nanocomposite Surface.

Here, we propose a novel attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy method for simultaneously monitoring the curing reaction and the diffusion behavior of curing agents at the surface of rubber in real-time. The proposed scheme was demonstrated by fluorine rubber (FKM) and FKM/carbon nanotube (CNT) nanocomposites with a target curing agent of triallyl-isocyanurate (TAIC). The broadening and the evolution of the C=O stretching of TAIC were quantitatively analyzed to characterize the reaction and the diffusion. Changes in the width of the C=O stretching indicated the reaction rate at the surface was even faster than that of the bulk as measured by a curemeter. The diffusion coefficient of the curing agent in the course of heating was newly calculated by the initial increase in the absorbance and our model based on Fickian diffusion. The diffusion coefficients of TAIC during curing were evaluated, and its temperature and filler dependency were identified. Cross-sectional ATR-FTIR imaging and in situ ATR-FTIR imaging measurements supported the hypothesis of the unidirectional diffusion of the curing agent towards the heated surface. It was shown that our method of in situ ATR-FTIR can monitor the degrees of cure and the diffusion coefficients of curing agents simultaneously, which cannot be achieved by conventional methods, e.g., rheological measurements.

Improving thermal and mechanical properties of biomass-based polymers using structurally ordered polyesters from ricinoleic acid and 4-hydroxycinnamic acids.

Biomass-based copolymers with alternating ricinoleic acid and 4-hydroxycinnamic acid derivatives (p-coumaric acid, ferulic acid, and sinapinic acid) exhibit a repeating structure based on soft and hard segments, derived from ricinoleic and 4-hydroxycinnamic acids, respectively. To achieve this alternating sequence, copolymers were synthesised by the self-condensation of hetero-dimeric monomers derived by the pre-coupling of methyl ricinolate and 4-hydroxycinnamic acid. The glass transition temperature (T g) was observed to increase as the number of methoxy groups on the main chain increased; the T g values of poly(coumaric acid-alt-ricinoleic acid), poly(ferulic acid-alt-ricinoleic acid), and poly(sinapinic acid-alt-ricinoleic acid) are -15 °C, -4 °C, and 24 °C respectively, 58 °C, 69 °C, and 97 °C higher than that of poly(ricinoleic acid). The polymers were processed into highly flexible, visually transparent films. Among them, poly(sinapinic acid-alt-ricinoleic acid) bearing two methoxy groups on each cinnamoyl unit, is mechanically the strongest polymer, with an elastic modulus of 126.5 MPa and a tensile strength at break of 15.47 MPa.

Nonuniform functional group distribution of carbon nanotubes studied by energy dispersive X-ray spectrometry imaging in SEM.

Functionalization is a key technique to improving the dispersibility of carbon nanotubes (CNTs) in solvents and polymer matrices for producing versatile CNT-based materials. Therefore, a robust and efficient characterization method is required to confirm that the functionalization on the CNT surface is spatially uniform. Although several imaging techniques for transmission electron microscopes can characterize the spatial localization of elements chemically bound to an isolated CNT surface, they are unsuitable for examinations on a practical scale because of their limited scanning area. Here, we present high spatially resolved energy dispersive X-ray spectrometry (EDS) imaging of functionalized single-walled CNTs (SWCNTs) in scanning electron microscopy (SEM). Highly sensitive EDS detection and drift-free operation enables our technique to image the light elements of SWCNTs with sufficient spatial resolution (<10 nm). We describe an experimental visualization of the spatial distribution of the functionalization on individual SWCNT bundle structures and discuss the CNT de-bundling mechanism via surface modification and the uniformity of the CNT dispersion state.

Nondestructive real-space imaging of energy dissipation distributions in randomly networked conductive nanomaterials.

For realization the new functional materials and devices by conductive nanomaterials, how to control and realize the optimum network structures are import point for fundamental, applied and industrial science. In this manuscript, the nondestructive real-space imaging technique has been studied with the lock-in thermal scope via Joule heating caused by ac bias conditions. By this dynamical method, a few micrometer scale energy dissipations originating from local current density and resistance distributions are visualized in a few tens of minutes due to the frequency-space separation and the strong temperature damping of conductive heat components. Moreover, in the tensile test, the sample broken points were completely corresponding to the intensity images of lock-in thermography. These results indicated that the lock-in thermography is a powerful tool for inspecting the intrinsic network structures, which are difficult to observe by conventional imaging methods.

Correction: Carbon nanotube-copper exhibiting metal-like thermal conductivity and silicon-like thermal expansion for efficient cooling of electronics.

Correction for 'Carbon nanotube-copper exhibiting metal-like thermal conductivity and silicon-like thermal expansion for efficient cooling of electronics' by Chandramouli Subramaniam and Kenji Hata et al., Nanoscale, 2014, 6, 2669-2674.

Quantitative evaluation of carbon nanomaterial releases during electric heating wire cutting and sawing machine cutting of expanded polystyrene-based composites using thermal carbon analysis.

Field measurements were conducted at a facility where expanded polystyrene-based carbon nanomaterial composites, namely, carbon nanotube and carbon black composites, were cut with an electric heating wire cutter or a circular sawing machine. The aerosol particles released during the cutting of the composites were measured using real-time aerosol monitoring, gravimetric analysis, thermal carbon analysis, and scanning electron microscopic observations. This study had two major goals: (1) to quantitatively evaluate the concentrations of airborne carbon nanomaterials during the cutting of their composites; (2) to evaluate the capability of thermal carbon analysis to quantify airborne carbon nanomaterials in the presence of expanded polystyrene-derived particles. The results of thermal carbon analysis showed that the concentrations of elemental carbon (an indicator of carbon nanomaterials) for all the respirable dust samples in both cutting processes were less than the limit of detection (∼2 µg/m3), which is nearly equivalent to or lower than the occupational exposure limits for carbon nanotubes (1 to 50 µg/m3). For total dust, which includes particles larger than respirable size, although the elemental carbon concentrations during heating wire cutting were low (<3 µg/m3), those during sawing machine cutting were up to 58 µg/m3. In scanning electron microscopic observations, micron-sized particles composed of or including carbon nanotubes were detected only in aerosol particles collected during the sawing machine cutting. Therefore, heating wire cutting is considered preferable. This study demonstrated that thermal carbon analysis can quantify airborne carbon nanomaterials in the presence of expanded polystyrene-derived particles.

Designing Neat and Composite Carbon Nanotube Materials by Porosimetric Characterization.

We propose a porosimetry-based method to characterize pores formed by carbon nanotubes (CNTs) in the CNT agglomerates for designing neat CNT-based materials and composites. CNT agglomerates contain pores between individual CNTs and/or CNT bundles (micropore < 2 nm, mesopores 2-50 nm, and macropores > 50 nm). We investigated these pores structured by CNTs with different diameters and number of walls, clarifying the broader size distribution and the larger volume with increased diameters and number of walls. Further, we demonstrated that CNT agglomerate structures with different bulk density were distinguished depending on the pore sizes. Our method also revealed that CNT dispersibility in solvent correlated with the pore sizes of CNT agglomerates. By making use of these knowledge on tailorable pores for CNT agglomerates, we successfully found the correlation between electrical conductivity for CNT rubber composites and pore sizes of CNT agglomerates. Therefore, our method can distinguish diverse CNT agglomerate structures and guide pore sizes of CNT agglomerates to give high electrical conductivity of CNT rubber composites.

Influence of matching solubility parameter of polymer matrix and CNT on electrical conductivity of CNT/rubber composite.

We report a general approach to fabricate elastomeric composites possessing high electrical conductivity for applications ranging from wireless charging interfaces to stretchable electronics. By using arbitrary nine kinds of rubbers as matrices, we experimentally demonstrate that the matching the solubility parameter of CNTs and the rubber matrix is important to achieve higher electrical conductivity in CNT/rubber composite, resulting in continuous conductive pathways leading to electrical conductivities as high as 15 S/cm with 10 vol% CNT in fluorinated rubber. Further, using thermodynamic considerations, we demonstrate an approach to mix CNTs to arbitrary rubber matrices regardless of solubility parameter of matrices by adding small amounts of fluorinated rubber as a polymeric-compatibilizer of CNTs. We thereby achieved electrical conductivities ranging from 1.2 to 13.8 S/cm (10 vol% CNTs) using nine varieties of rubber matrices differing in chemical structures and physical properties. Finally, we investigated the components of solubility parameter of CNT by using Hansen solubility parameters, these findings may useful for controlling solubility parameter of CNTs.

Elastomeric thermal interface materials with high through-plane thermal conductivity from carbon fiber fillers vertically aligned by electrostatic flocking.

Electrostatic flocking is applied to create an array of aligned carbon fibers from which an elastomeric thermal interface material (TIM) can be fabricated with a high through-plane thermal conductivity of 23.3 W/mK. A high thermal conductivity can be achieved with a significantly low filler level (13.2 wt%). As a result, this material retains the intrinsic properties of the matrix, i.e., elastomeric behavior.

Controlling exfoliation in order to minimize damage during dispersion of long SWCNTs for advanced composites.

We propose an approach to disperse long single-wall carbon nanotubes (SWCNTs) in a manner that is most suitable for the fabrication of high-performance composites. We compare three general classes of dispersion mechanisms, which encompass 11 different dispersion methods, and we have dispersed long SWCNTs, short multi-wall carbon nanotubes, and short SWCNTs in order to understand the most appropriate dispersion methods for the different types of CNTs. From this study, we have found that the turbulent flow methods, as represented by the Nanomizer and high-pressure jet mill methods, produced unique and superior dispersibility of long SWCNTs, which was advantageous for the fabrication of highly conductive composites. The results were interpreted to imply that the biaxial shearing force caused an exfoliation effect to disperse the long SWCNTs homogeneously while suppressing damage. A conceptual model was developed to explain this dispersion mechanism, which is important for future work on advanced CNT composites.

Carbon nanotube-copper exhibiting metal-like thermal conductivity and silicon-like thermal expansion for efficient cooling of electronics.

Increasing functional complexity and dimensional compactness of electronic devices have led to progressively higher power dissipation, mainly in the form of heat. Overheating of semiconductor-based electronics has been the primary reason for their failure. Such failures originate at the interface of the heat sink (commonly Cu and Al) and the substrate (silicon) due to the large mismatch in thermal expansion coefficients (∼300%) of metals and silicon. Therefore, the effective cooling of such electronics demands a material with both high thermal conductivity and a similar coefficient of thermal expansion (CTE) to silicon. Addressing this demand, we have developed a carbon nanotube-copper (CNT-Cu) composite with high metallic thermal conductivity (395 W m(-1) K(-1)) and a low, silicon-like CTE (5.0 ppm K(-1)). The thermal conductivity was identical to that of Cu (400 W m(-1) K(-1)) and higher than those of most metals (Ti, Al, Au). Importantly, the CTE mismatch between CNT-Cu and silicon was only ∼10%, meaning an excellent compatibility. The seamless integration of CNTs and Cu was achieved through a unique two-stage electrodeposition approach to create an extensive and continuous interface between the Cu and CNTs. This allowed for thermal contributions from both Cu and CNTs, resulting in high thermal conductivity. Simultaneously, the high volume fraction of CNTs balanced the thermal expansion of Cu, accounting for the low CTE of the CNT-Cu composite. The experimental observations were in good quantitative concurrence with the theoretically described 'matrix-bubble' model. Further, we demonstrated identical in-situ thermal strain behaviour of the CNT-Cu composite to Si-based dielectrics, thereby generating the least interfacial thermal strain. This unique combination of properties places CNT-Cu as an isolated spot in an Ashby map of thermal conductivity and CTE. Finally, the CNT-Cu composite exhibited the greatest stability to temperature as indicated by its low thermal distortion parameter (TDP). Thus, this material presents a viable and efficient alternative to existing materials for thermal management in electronics.

Green, scalable, binderless fabrication of a single-walled carbon nanotube nonwoven fabric based on an ancient Japanese paper process.

We propose a fabrication method for carbon nanotube (CNT) nonwoven fabrics based on an ancient Japanese papermaking process where paper is made from natural plant fibers. In our method, CNT nonwoven fabrics are made by a scalable process of filtering binder-free, aqueous suspensions of CNTs. The aqueous suspension of these entangled single-walled carbon nanotube (SWNT) aggregates enabled smooth filtration through a cellulose filter with large pores (8 µm). The "wet SWNT cakes," which were composed solely of SWNT and water and obtained after filtration, were press-dried to fabricate an SWNT nonwoven fabric. This environmentally friendly process employs water and the raw CNT material alone. Moreover, the scalability of this process was demonstrated by manufacturing a large area (A3, 30 × 42 cm; thickness: 40-150 µm), self-supporting SWNT nonwoven fabric with a density of 0.4 g/cm(3), a basis weight of 0.2 g/m(2) , a porosity of 63%, and a specific surface area of 740 m(2)/g. This SWNT nonwoven fabric is anticipated to find application as functional particle-supported sheets, electrode materials, and filters.

Mechanically durable and highly conductive elastomeric composites from long single-walled carbon nanotubes mimicking the chain structure of polymers.

By using long single-walled carbon nanotubes (SWNTs) as a filler possessing the highest aspect ratio and small diameter, we mimicked the chain structure of polymers in the matrix and realized a highly conductive elastomeric composite (30 S/cm) with an excellent mechanical durability (4500 strain cycles until failure), far superior to any other reported conductive elastomers. This exceptional mechanical durability was explained by the ability of long and traversing SWNTs to deform in concert with the elastomer with minimum stress concentration at their interfaces. The conductivity was sufficient to operate many active electronics components, and thus this material would be useful for practical stretchable electronic devices.