Carbon Nanotubes In Polycarbonate Research Articles

Diffusivity and solubility of HF gas in polymers and nanocomposites used for automated handling containers of silicon substrates in microelectronic industry

Thermoplastic boxes with internal clean mini-environment (ISO 14644–1:2015, class 2–3), called Front Opening Unified Pods (FOUP), are widely used in microelectronic fabrication for transport and handling of silicon substrates (named wafers) in order to minimize the negative impact of contaminants on integrated circuits. As a type of airborne molecular contaminants (AMC), hydrogen fluoride (HF) outgassed from freshly processed wafers and sorbed (adsorption and absorption) on/in FOUP's walls and then becomes a potential source for subsequent HF cross-contamination. Thin polymeric films which were comprised of available commercial FOUP materials were prepared by hot pressing. They were neat polymers (polycarbonate (PC), Entegris Barrier Materials (EBM)) and nanocomposites (polycarbonate/carbon powder (PCCP), polycarbonate/carbon nanotubes (PCCNT), and EBM/carbon nanotubes (EBMCNT)). The sorption and desorption kinetics of HF in polymers were experimentally established at ultralow HF concentration (part-per-billion-volume, ppbv) and cleanroom conditions (atmospheric pressure, 20 °C and 40%RH); such conditions mimicking fabrication process conditions. Having a polar group in polymeric chains, the PC, PCCP and PCCNT showed a higher affinity to HF rather than EBM and EBMCNT, which resulted in significantly increasing HF diffusivity (nearly two orders of magnitude, 10−10 versus 10−12 cm2.s−1) and HF solubility. The presence of embedded CNT in nanocomposites (PCCNT and EBMCNT) exhibited a significant increase of both HF diffusivity and solubility. Interestingly, based on desorption curves, it was determined that the sorbed HF in nanocomposites made with CNT was composed of two types (i) fixed-HF inside cylindrical voids of CNT and (ii) mobile-HF in polymeric bundle-chains. In addition, the obtained HF transport coefficients were applied as input data in numerical simulation model to simulate the HF concentration profiles and the evolution of HF uptake in FOUP walls in different scenarios.

ТЕПЛОПРОВІДНІСТЬ ПОЛІМЕРНИХ МІКРО- І НАНОКОМПОЗИТІВ НА ОСНОВІ ПОЛІКАРБОНАТУ ТА СТУПІНЬ КРИСТАЛІЧНОСТІ ПОЛІМЕРНОЇ МАТРИЦІ

The data of studies of the thermal conductivity coefficient of polymer composites "polycarbonate-carbon nanotubes or aluminum particles" are presented. The results of determining the degree of crystallinity of the polymer matrix of these composites are submitted. The existence of a relationship between the specified thermal conductivity coefficient and the degree of crystallinity is shown.

Predictive Optimization of Electrical Conductivity of Polycarbonate Composites at Different Concentrations of Carbon Nanotubes: A Valorization of Conductive Nanocomposite Theoretical Models.

Polycarbonate—carbon nanotube (PC-CNT) conductive composites containing CNT concentration covering 0.25–4.5 wt.% were prepared by melt blending extrusion. The alternating current (AC) conductivity of the composites has been investigated. The percolation threshold of the PC-CNT composites was theoretically determined using the classical theory of percolation followed by numerical analysis, quantifying the conductivity of PC-CNT at the critical volume CNT concentration. Different theoretical models like Bueche, McCullough and Mamunya have been applied to predict the AC conductivity of the composites using a hyperparameter optimization method. Through multiple series of the hyperparameter optimization process, it was found that McCullough and Mamunya theoretical models for electrical conductivity fit remarkably with our experimental results; the degree of chain branching and the aspect ratio are estimated to be 0.91 and 167 according to these models. The development of a new model based on a modified Sohi model is in good agreement with our data, with a coefficient of determination for an optimized design model. The conductivity is correlated to the electromagnetic absorption (EM) index showing a fine fit with Steffen–Boltzmann (SB) model, indicating the ultimate CNTs volume concentration for microwave absorption at the studied frequency range.

Long-term performance and durability of polycarbonate/carbon nanotube nanocomposites

Due to their good mechanical properties, low density, and ease of processing polymer nanocomposites are of interest for a multitude of applications in the automotive, electronics, and leisure industry. Besides having an impact on short-term mechanical performance of polymers, the addition of nanoreinforcements can have also a significant effect on long-term properties such as the resistance to static (creep) and cyclic (fatigue) loadings. However, despite its significance there is a shortage of long-term mechanical performance data for thermoplastic-based polymer nanocomposites. Reason being that existing characterization methods for long-term performance and durability are time consuming and limited in their applicability. Here, an engineering approach to predict long-term time-to-failure of polycarbonate/carbon nanotube (PC/CNT) nanocomposites is presented based on short-term experimentation with an application to both creep and fatigue. Results showed that the addition of CNTs had an opposite effect on two important long-term failure mechanisms. Addition of CNTs lead to improvements in durability in the plasticity-controlled failure regime, whereas it had an adverse effect in the slow crack growth-controlled regime, meaning that in the latter regime nanocomposite performance was significantly less than that of the neat polymer matrix.

Performance evaluation of the senergy polycarbonate and asphalt carbon nanotube solar water heating collectors for building integration

Senergy building integrated solar thermal collectors aim to reduce costs of solar water heating systems by utilizing polymer materials and offsetting costs of conventional roofing construction components. Carbon nanotubes can be added to polymer materials to improve their thermal, optical and mechanical properties. Two working prototypes; one Polycarbonate Carbon Nano-Tube (PCNT) collector and one Asphalt Carbon Nano-Tube (ACNT) collector; have been tested using the solar simulator facility at Ulster University and their performances compared. The PCNT collector is single glazed and uses a twinwall sheet to act as both the solar absorptive surface and the heat transfer fluid channeling element. The ACNT collector is unglazed and has an asphalt based absorber with embedded serpentine copper tubing to channel the heat transfer fluid. Tests were conducted with 800 W m−2 illumination intensity and for water inlet temperatures between from 23 °C and 47 °C. The PCNT collector achieved 62% maximum collection efficiency compared to 45% for the ACNT collector. The heat loss coefficients were 6.0 and 8.1 W m−2 K−1 respectively. The performance of the PCNT collector was similar to benchmark values for single glazed collectors with selective absorber surfaces. The ACNT collector responded very slowly and performance was lower than a typical unglazed solar water heater with non-selective absorber due to the high thermal resistance between the absorber surface and the serpentine tubing.

Electrical and melt rheological characterization of PC and co‐continuous PC/SAN blends filled with CNTs: Relationship between melt‐mixing parameters, filler dispersion, and filler aspect ratio

ABSTRACTElectrical and melt rheological properties of melt‐mixed polycarbonate (PC) and co‐continuous PC/poly(styrene–acrylonitrile) (SAN) blends with carbon nanotubes (CNTs) are investigated. Using two sets of mixing parameters, different states of filler dispersion are obtained. With increasing CNT dispersion, an increase in electrical resistivity near the percolation threshold of PC–CNT composites and (PC + CNT)/SAN blends is observed. This suggests that the higher mixing energies required for better dispersion also result in a more severe reduction of the CNT aspect ratio; this effect was proven by CNT length measurements. Melt rheological studies show higher reinforcing effects for composites with worse dispersion. The Eilers equation, describing the melt viscosity as function of filler content, was used to fit the data and to obtain information about an apparent aspect ratio change, which was in accordance with measured CNT length reduction. Such fitting could be also transferred to the blends and serves for a qualitatively based discussion. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 79–88

Effects of injection molding conditions on the electrical properties of polycarbonate/carbon nanotube nanocomposites

Polycarbonate/Carbon nanotube (PC/CNT) nanocomposites containing various CNT contents (0–5 wt%) were prepared by injection molding. The effects of CNT contents, injection speed (V) and injection temperature (T) on the electrical resistivity of the PC/CNT nanocomposites were investigated. It was found that the tensile strength of nanocomposites was enhanced slightly with increased CNT contents, and the tensile modulus was 29% greater after the 5 wt% CNT addition, but the brittle tendency became stronger. Aside from tensile properties, the electrical resistivity of the nanocomposites dropped 12 orders of magnitude after the 5 wt% CNT addition. Also, there was a tendency that the electrical resistivity was lower in the case of higher injection temperature and lower injection speed. Scanning electron microscope (SEM) images and the distribution of surface layer electrical resistivity, clearly showed a notable influence by surface layer microstructures on the electrical resistivity, and the injection conditions affected both the value of the maximum electrical resistivity and the position where it occurred. This study offers an alternative green and simple molding process to prepare conductive PC nanocomposites and to achieve the industrialization of PC/CNT nanocomposite products which can be used in electromagnetic shielding and anti‐static fields. POLYM. COMPOS., 37:3245–3255, 2016. © 2015 Society of Plastics Engineers

High strain rate behavior of multi-walled carbon nanotubes–polycarbonate composites

Multi-walled carbon nanotubes–polycarbonate composites (MWCNT–PC) were prepared by a two-step method of solvent casting followed by compression molding and their dynamic impact strength was studied. Split Hopkinson Pressure Bar (SHPB) was deployed as the instrument for impact testing of the composite samples. The impact tests were performed under varying strain rates ranging from 1096 to 4017/s. The present studies report the stress–strain behavior of MWCNT–PC composites under a high strain rate of 2000–2600/s. A comparison of stress at various strains ranging from 5% to 20% was done by varying MWCNT concentration in the range 0.1, 0.5, 1, 2 and 5wt.% in PC. Stress tolerance of these composites was studied to analyze effectiveness of small amounts of carbon nanotubes (CNTs) for impact/stress absorption in comparison to pure PC samples. It was found that the stress behavior for specific strains varies with concentration of CNTs in polycarbonate. At very low (about 0.1wt.%) and high concentrations (about 5wt.%) of carbon nanotubes the stress did not vary much as compared to pure PC for the above mentioned strain range. At concentration levels of 0.5, 1 and 2wt.% CNTs, the impact absorption (nearly 105MPa) increased by 10–20% as compared to pure PC (nearly 90MPa) depending upon the amount of strain in the samples. The role of functionalized CNTs in impact studies was also studied by using 0.5wt.% and 2wt.% functionalized MWCNT. The use of functionalized CNTs was found to result in reduced impact absorption (nearly 95MPa) as compared to as-synthesized CNTs (nearly 105MPa). The effect of concentration of CNTs on impact strength of MWCNT–PC composites was analyzed by studying the SEM images of composite samples after impact.

Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate

The electrical and electromagnetic interference shielding effectiveness (EMI SE) properties of multi-walled carbon nanotubes/polycarbonate (MWCNT/PC) composites are investigated. The composites were prepared by diluting masterbatch (15 wt.% MWCNT) using a Haake mixer and then injection-molded into a dog-bone mold. Various MWCNT alignments were created by changing operating conditions. Electrical resistivity measurements were carried out at three different areas at both parallel and perpendicular to the flow direction. The results showed higher resistivity and percolation threshold at higher alignments in both parallel and perpendicular to the flow direction. By applying Ohm’s law it was seen that after percolation, the field emission mechanisms are more important at higher orientations. Higher MWCNT alignments were observed in areas with higher resistivities, and this was verified using SEM, TEM and Raman spectroscopy techniques. Additionally, EMI SE measurements were done on compression-molded samples at different concentrations and thicknesses. The results showed that both EMI SE by reflection and absorption increased with increase in MWCNT loading and shielding material thickness.

Rheological properties and percolation in suspensions of multiwalled carbon nanotubes in polycarbonate

This paper is concerned with several issues related to the rheological behavior of polycarbonate/multiwalled carbon nanotube nanocomposites. The composites were prepared by diluting a masterbatch of 15 wt.% nanotubes using melt-mixing method, and the dispersion was analyzed by SEM, TEM, and AFM techniques. To understand the percolated structure, the nanocomposites were characterized via a set of rheological, electrical, and thermal conductivity measurements. The rheological measurements revealed that the structure and properties were temperature dependent; the percolation threshold was significantly lower at higher temperature suggesting stronger nanotube interactions. The nanotube networks were also sensitive to the steady shear deformation particularly at high temperature. Following preshearing, the elastic modulus decreased markedly suggesting that the nanotubes became more rigid. These results were analyzed using simple models for suspensions of rod-like particles. Finally, the rheological, electrical, and thermal conductivity percolation thresholds were compared. As expected, the rheological threshold was smaller than the thermal and electrical threshold.

A Microstructure-Level Material Model for Simulating the Machining of Carbon Nanotube Reinforced Polymer Composites

A continuum-based microstructure-level material model for simulation of polycarbonate carbon nanotube (CNT) composite machining has been developed wherein polycarbonate and CNT phases are modeled separately. A parametrization scheme is developed to characterize the microstructure of composites having different loadings of carbon nanotubes. The Mulliken and Boyce constitutive model [2006, “Mechanics of the Rate Dependent Elastic Plastic Deformation of Glassy Polymers from Low to High Strair Rates,” Int. J. Solids Struct., 43(5), pp. 1331–1356] for polycarbonate has been modified and implemented to capture thermal effects. The CNT phase is modeled as a linear elastic material. Dynamic mechanical analyzer tests are conducted on the polycarbonate phase to capture the changes in material behavior with temperature and strain rate. Compression tests are performed over a wide range of strain rates for model validation. The model predictions for yield stress are seen to be within 10% of the experimental results for all the materials tested. The model is used to study the effect of weight fraction, length, and orientation of CNTs on the mechanical behavior of the composites.

Attenuation of electromagnetic waves by carbon nanotube composites

Experiments on polycarbonate/single-walled carbon nanotube composites were performed to explore the potential of carbon nanotubes in attenuating electromagnetic waves. According to the results of these experiments a distinct effect is present. The effect is dependent on the tubular filler properties and on the morphology of the composite. At a loading of 5.4 wt% single-walled carbon nanotubes in polycarbonate an attenuation of the field of 47 dB could be detected, which corresponds an attenuation of the power of 99.998%.

Dispersion of Carbon Nanotubes in Polycarbonate and Its Effect on the Composite Properties

The effect of the dispersion state of carbon nanotubes in polycarbonate on the rheological, mechanical and electrical properties of melt-extruded compounds is presented. The dispersion state was monitored by means of grey values distribution histograms of optical micrographs of the composites. Increasing the processing residence time, and hence the deformation induced by the surrounding polymer, increased the level of dispersion of CNTs in the matrix. This, in turn, resulted in a large improvement of the CNTs reinforcement effect and decreased composite electrical resistivity. Rheological behaviour is in agreement with these observations.

Studies on the Dispersion of Carbon Nanotubes in Polycarbonate

AbstractWe investigated the dispersion of carbon nanotubes in a polycarbonate matrix under varying flow conditions to determine the most efficient dispersion parameter. Distributive mixing was investigated by a flow digitization technique as well as electrical conductivity of the materials. Residence time distribution (RTD) was obtained from an integral of the area under an absorbance‐time curve. Total shear strain rate was obtained by multiplying RTD by shear rate. The area ratio of the filler (Ar) was determined by an image analysis technique where fillers less than 0.36μm were counted as unoccupied area. Area ratio decreased with increasing total shear strain rate, while volume resistivity decreased with decreasing area ratio. We observed an optimum value of Ar for conductivity. Increasing barrel temperature did not have a dramatic effect on dispersion. It was observed that the dominant dispersion parameters were shear rate and RTD.

Dispersion and alignment of carbon nanotubes in polycarbonate

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber-spinning apparatus. The effects of mixing time and fiber draw rates on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw rate was greater than 70 m/min. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.

Dispersion and Alignment of Carbon Nanotubes in Polycarbonate

AbstractDispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber spinning apparatus. The effects of mixing time and fiber draw ratios on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw ratio was greater than 7. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties.