Inducing electrical conductivity by tuning the phase-separated morphology and carbon nanotube network in bi-phasic polymer blends with free and grafted (co)polymers

We present novel routes to tune the phase-separated morphology and the percolated network of multiwalled carbon nanotubes (MWNTs) in 60/40 PMMA/PαMSAN LCST blends. The rheological and dielectric properties were monitored during phase separation to probe the morphological development and the MWNT network build-up. The steady-state microstructure of the phase-separated blends was verified by (S)TEM imaging. By altering the sample preparation method from melt to solution mixing, the improved dispersion of MWNTs reduced the rheological and electrical percolation threshold from 2 wt% in melt mixed blends to 0.5 wt% in solution mixed blends. Different novel compatibilizers were employed in order to stabilize and refine the blend morphology, including short PS-Br polymers, long SH-functionalized PMMA polymers and short PS-PMMA block-copolymers with distinct molecular weight and asymmetry. The interfacial segregation of the (co)polymers during phase separation resulted in different morphologies based on the ability of the (co)polymer to entangle with the blend components, the presence of steric hindrance and the (co)polymer asymmetry compared to the curvature of the blend interface. The kinetic competition between the migration of the (co)polymers to the blend interface and the migration of the MWNTs to the energetically preferred PαMSAN phase governed the MWNT localization. They ended up either in the continuous PαMSAN phase, at the blend interface or in the dispersed PMMA phase, thereby giving rise to different paths for charge transfer. Irrespective of the compatibilizer type, the electrical percolation threshold of solution mixed blends was further reduced from 0.5 wt% to 0.15 wt% in presence of 2 wt% of compatibilizer. As an alternative, chemically grafting the different compatibilizers onto the surface of the MWNTs further tuned the localization of the MWNTs and the formation of conductive pathways in one of the phases or along the blend interface. This allowed the formation of a percolated 0.15 wt% MWNT network at reduced compatibilizer concentrations of 0.1 wt% or less without severely affecting the intrinsic conductivity of the MWNTs. However, the limited amount of compatibilizer, combined with the interfacially localized MWNTs, exhibited less refinement ability as compared to 2 wt% of isolated compatibilizer (see Figure 1). Our novel routes could steer the development of polymer blends with tailor-made morphologies and highly specific percolated networks of conductive nanofillers at ultra-low concentrations.Posterstatus: publishe

Uniquely developing tunable morphologies and carbon nanotube localization in bi-phasic polymer blends by compatibilizer grafting

The concentration of conducting fillers for rendering a continuous conductive pathway is referred to as the ‘electrical percolation threshold’. In this regard, the high aspect ratio of multiwalled carbon nanotubes (MWNTs) enables electrical percolation at lower concentrations. [1] Multiple successful attempts to reduce the electrical percolation threshold of MWNTs in insulating polymeric matrices are present in literature. We recently combined phase separation of polymer blends with selectively localized MWNTs [2] along with morphology refinement and stabilization by long random or block copolymers [3, 4] to reduce the electrical percolation threshold of MWNTs in PMMA/PαMSAN blends. We now present novel routes to simultaneously control the morphology and carbon nanotube network in phase separating 60/40 PMMA/PαMSAN blends. Hereto, different (co)polymers, including short PS polymers, long PMMA polymers and short PS-PMMA block copolymers with distinct molecular weight and asymmetry, are chemically grafted onto the surface of MWNTs. The intrinsic conductivity of the compatibilizer-grafted carbon nanotubes decreased by a decade due to the grafting procedure, thereby largely maintaining the beneficial electrical properties of MWNTs. In the blends, chemical grafting of (co)polymers onto the MWNTs simultaneously refined the blend’s morphology and steered the MWNT localization, as discerned from the dielectric relaxation spectra, thereby leading to some fascinating phenomena assisting long-ranged MWNT charge transfer at ultralow concentrations. In this regard, phase inversion, as verified by TEM images, leads to localization of MWNTs in the PαMSAN matrix with finely dispersed PMMA droplets, which facilitated charge transfer as connection or restriction points for the MWNT network in the matrix. The presence of interfacial MWNTs along the interface of small PMMA droplets further supports a continuous network of MWNTs in the blends. By chemical grafting, we could reduce the electrical percolation threshold of MWNTs from 0.5 wt% to 0.15 wt% in presence of very low compatibilizer concentrations (0.1 wt% instead of 2 wt% in the ungrafted case). We can thus conclude that a droplet-matrix morphology with tunable MWNT localization either in the matrix phase and/or at the blend interface is an effective alternative to bi-continuous morphologies for developing conductive blends. [1] I. Alig et al., Polymer, 53(1), 4-28 (2012) [2] S. Bose at al., Applied Materials and Interfaces, 2(3), 800-807 (2010) [3] A. Bharati at al., Polymer, 79, 271-282 (2015) [4] A. Bharati et al., Polymer, 108, 483-492 (2017)Conference talkstatus: publishe

Predicting the localization and interconnectivity of carbon nanotubes in compatibilized bi-phasic polymer blends

Broadband dielectric spectroscopy (BDS) is often used to probe the electrical percolation threshold (EPT) of multiwalled carbon nanotubes (MWNTs) in polymeric systems. In this regard, phase separation of polymer blends with selectively localized MWNTs and stabilization of the cocontinuous morphology by block and random copolymers are valuable tools to reduce the EPT. We now present novel routes to simultaneously tune the phase-separated morphology and MWNT network in 60/40 PMMA/PαMSAN blends and thereby reduce the EPT. We developed a method based on BDS to successfully predict the localization and interconnectivity of MWNTs in the resulting conductive blends and validated our predictions by (S)TEM images. An improved dispersion and hence overall connectivity of MWNTs in solution mixed blends compared to melt mixed blends was discerned by comparing the electrical properties in the blends to that in equivalent PMMA and PαMSAN monophasic nanocomposites, thereby decreasing the EPT from 2 wt% in melt mixed blends to 0.5 wt% in solution mixed blends. Morphology stabilization and refinement were achieved by employing novel types of compatibilizers in solution mixed blends, including short PS-Br polymers and long PMMA-SH polymers, which further reduced the EPT from 0.5 wt% MWNTs to 0.15 wt% MWNTs in presence of 2 wt% of compatibilizer. The kinetic competition between the migration of the compatibilizers to the blend interface and the migration of the MWNTs to their energetically preferred PαMSAN phase during phase separation, gave rise to different MWNT localization, either in the PMMA phase, in the PαMSAN phase or at the interface, depending on the polymer compatibilizer. This in turn resulted in disparate interfacial polarization peak characteristics. The amount of entrapped polymer between adjacent MWNTs in the microcapacitor assembly was estimated by the dielectric interlayer model. The gap spacing of the microcapacitors, on the other hand, was deduced from the relaxation time of charge migration by fluctuation-induced tunnelling. Both these parameters allow to model the interfacial capacitance of the various MWNT microcapacitor networks in the compatibilized bi-phasic blends.status: publishe

A generalized mechano-statistical transient network model for unravelling the network topology and elasticity of hydrophobically associating multiblock copolymers in aqueous solutions

In this contribution, we unravel the transient network topology and elasticity of micellar networks formed by hydrophobically associating multiblock copolymers in aqueous solutions. Unlike studies on conventional triblock copolymers bearing hydrophobic blocks as end groups, our research focuses on alternating poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) multiblock copolymers having multiple hydrophobic PPO blocks along the chain. We adopt a combinatorics approach to extend and generalize the mechano-statistical transient network model developed by Annable et al. for telechelic triblock copolymers [ Journal of Rheology, 1993, 37, 695] to multiblock copolymers. The model allows one to predict the concentration dependent elasticity of networks formed by multiblock copolymers with known molecular characteristics by using knowledge of the micellar network microstructure. The spatial distribution of the hydrophobic nodes is inferred from Small-Angle X-ray Scattering (SAXS) by converting the structure factor to the radial distribution function. The number of closely neighboring micellar cores between which an elastic bridge can be formed (nm) is calculated by spherical integration of the radial distribution function up to a distance of the radius of gyration of an intermediate soluble PEO block. Using the evolution of nm with concentration as an input for the model, the predictions show good agreement with experimental elasticity data, as inferred from the plateau modulus in linear shear rheology. The network evolves from loop-dominated, poorly elastic with cross-linking nodes with low functionality at low concentrations to bridge-dominated, highly elastic with higher node functionalities at more elevated concentrations. It is anticipated that our generalized mechano-statistical transient network model can also be used for equally spaced, multisticker associating polymers forming networks by multifunctional interactions other than micellar aggregation

Technische prestatie uitkomst in de stal

Vleeskuikenhouders die uitkomst in de stal als innovatief concept omarmen, geven aan dat ze positieve effecten zien op de productie, lager antibioticagebruik en minder ziektegevoeligheid. Deze veronderstelde positieve effecten ten opzichte van uitkomen in de broederij en het vervolgens transporteren van eendagskuikens is nu wetenschappelijk onderzocht

Technische prestatie uitkomst in de stal

Vleeskuikenhouders die uitkomst in de stal als innovatief concept omarmen, geven aan dat ze positieve effecten zien op de productie, lager antibioticagebruik en minder ziektegevoeligheid. Deze veronderstelde positieve effecten ten opzichte van uitkomen in de broederij en het vervolgens transporteren van eendagskuikens is nu wetenschappelijk onderzocht

Phase behavior of medium-length hydrophobically associating PEO-PPO multiblock copolymers in aqueous media

Hypothesis The micellization of block copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) is driven by the dehydration of PPO at elevated temperatures. At low concentrations, a viscous solution of isolated micelles is obtained, whereas at higher concentrations, crowding of micelles results in an elastic gel. Alternating PEO-PPO multiblock copolymers are expected to exhibit different phase behavior, with altered phase boundaries and thermodynamics, as compared to PEO-PPO-PEO triblock copolymers (Pluronics®) with equal hydrophobicity, thereby proving the pivotal role of copolymer architecture and molecular weight. Experiments Multiple characterization techniques were used to map the phase behavior as a function of temperature and concentration of PEO-PPO multiblock copolymers (ExpertGel®) in aqueous solution. These techniques include shear rheology, differential and adiabatic scanning calorimetry, isothermal titration calorimetry and light transmittance. The micellar size and topology were studied by dynamic light scattering. Findings Multiblocks have lower transition temperatures and higher thermodynamic driving forces for micellization as compared to triblocks due to the presence of more than one PPO block per chain. With increasing concentration, the multiblock copolymers in solution gradually evolve into a viscoelastic network formed by soluble bridges in between micellar nodes, whereas hairy triblock micelles jam into liquid crystalline phases resembling an elastic colloidal crystal

Applicability of the Foodtexture Puff Device for rheological characterization of viscous food products

The Foodtexture Puff Device (FPD) is a noncontact rheological measurement device, which applies an air pulse on the sample and measures the subsequent deformation of the sample surface with a laser distance sensor. The deformation behavior is considered as a measure for the rheological properties of the sample. The applicability of this device was studied for use on viscous food products with a broad range of rheological characteristics. In this study, sugar and fat-based systems with a viscosity range of respectively 0.001–6.1 Pa.s and 0.01–5.9 Pa.s were tested. Comparison of the FPD with classical rheological analyses showed that the maximum deformation created by the FPD is strongly correlated to the viscosity. Hence, the FPD is well suited for measurements on sugar-based and fat-based systems. It is capable of providing accurate, noncontact, fast, easy and nondestructive rheological measurements on food products.status: publishe

Applicability of the Foodtexture Puff Device for rheological characterization of viscous food products

The Foodtexture Puff Device (FPD) is a noncontact rheological measurement device, which applies an air pulse on the sample and measures the subsequent deformation of the sample surface with a laser distance sensor. The deformation behavior is considered as a measure for the rheological properties of the sample. The applicability of this device was studied for use on viscous food products with a broad range of rheological characteristics. In this study, sugar and fat-based systems with a viscosity range of respectively 0.001-6.1Pa.s and 0.01-5.9Pa.s were tested. Comparison of the FPD with classical rheological analyses showed that the maximum deformation created by the FPD is strongly correlated to the viscosity. Hence, the FPD is well suited for measurements on sugar-based and fat-based systems. It is capable of providing accurate, noncontact, fast, easy and nondestructive rheological measurements on food products. Practical ApplicationsThe FPD is a new, noncontact rheological measurement device that can be used for a wide range of food products, including sugar solutions, fruit purees and concentrates, oils and fats, molten chocolate, batter, soft pastry, among others. Furthermore, more solid food products like dough can be measured accurately. The device outputs a displacement signal over time from which information can be extracted. For simple behaviors, this can be performed based on one or a few characteristic values derived from the signal. For more complex foodstuff, the signal as a whole can be used, and techniques such as partial least squares can be used to create a calibration curve that translates the full displacement signal over time into the desired rheological values. Seen the fact that measurement time is short, the FPD is suitable for in-line as well as for R&D applications and can replace classical devices that are often time consuming and require sample preparation