Due to their atomically excellent structure and sp2-hybridization, carbon nanotubes (CNTs) have exceptional mechanical, thermal, and electrical properties. Single-walled CNTs (swCNTs) have recently gained interest as an intriguing host for the nanoscale confinement of fluids, with a variety of unexpected phenomena such as spontaneous filling, frictionless mass transport, unusual phase diagram etc[1]. The majority of these phenomena are still under debate and require experimental confirmation. However, it is challenging in this field to find experimental methods sensitive enough to carry out measurements at the level of individual nanotubes. The electronic properties of swCNTs are demonstrated to be sensitive to their diameter, defects, doping, adsorbates, and environment via swCNT field effect transistors (swCNT-FETs)[2], [3].In this contribution, we show that individual carbon nanotube field effect transistors (CNTFET) are the perfect tool for achieving this goal, enabling for the first time to accurate identification of water confined inside the nanotube. By investigating the electrical performances of several unopened and opened CNTFETs submitted to different atmosphere and temperature treatments, such as dry air, humidity, secondary vacuum, and current annealing, we demonstrate that it is possible to distinguish between water being outside and inside of the nanotube, just outside, or the nanotube free from water. Hence, we found that secondary vacuum and current annealing both shift the threshold gate voltage of opened swCNTs towards more negative values, however, the secondary vacuum had no effect on closed swCNTs compared to current annealing. In conclusion, the current annealing process is essential to distinguish water adsorbed outside from water confined inside swCNT. We demonstrate that this behavior is uniform across all devices’ metallicities, assuming that the nanotube’s surface has been pre-cleaned using current annealing. We will also discuss the mechanism behind the coupling of electronic transport and the presence of water.Our findings open up the possibility of using CNTFET to address long-standing issues in the nanofluidic community regarding the behavior of water confinement at the nanoscale, and also to use them for reliable, sensitive, and selective chemical and biological sensors.Reference:[1] T. A. Pascal, W. A. Goddard, and Y. Jung, “Entropy and the driving force for the filling of carbon nanotubes with water,” Proc. Natl. Acad. Sci., vol. 108, no. 29, pp. 11794–11798, 2011, doi: 10.1073/pnas.1108073108.[2] D. Cao et al., “Electronic sensitivity of carbon nanotubes to internal water wetting,” ACS Nano, vol. 5, no. 4, pp. 3113–3119, 2011, DOI: 10.1021/nn200251z.[3] I. Heller, A. M. Janssens, J. Männik, E. D. Minot, S. G. Lemay, and C. Dekker, “Identifying the mechanism of biosensing with carbon nanotube transistors,” Nano Lett., vol. 8, no. 2, pp. 591–595, 2008, DOI: 10.1021/nl072996i.

We explore the impact of three water-soluble polyelectrolytes (PEs) on the flow of concentrated suspensions of poly(N-isopropylacrylamide) (PNIPAm) microgels with thermoresponsive anionic charge density. By progressively adding the PEs to a jammed suspension of swollen microgels, we show that the rheology of the mixtures is remarkably influenced by the sign of the PE charge, PE concentration and hydrophobicity only when the temperature is raised above the microgel volume phase transition temperature Tc, namely when microgels collapse, they are partially hydrophobic and form a volume-spanning colloidal gel. We find that the original gel is strengthened close to the isoelectric point, attained when microgels are mixed with cationic PEs, while PE hydrophobicity rules the gel strengthening at very high PE concentrations. Surprisingly, we find that polyelectrolyte adsorption or partial embedding of PE chains inside the microgel periphery occurs also when anionic polymers of polystyrene sulfonate with high degree of sulfonation are added. This gives rise to colloidal stabilization and to the melting of the original gel network above Tc. Contrastingly, the presence of polyelectrolytes in suspensions of swollen, jammed microgels results in a weak softening of the original repulsive glass, even when an apparent isoelectric condition is met. Our study puts forward the crucial role of electrostatics in thermosensitive microgels, unveiling an exciting new way to tailor the flow of these soft colloids and highlighting a largely unexplored path to engineer soft colloidal mixtures.

Fundamental understanding of the macroscopic properties of polymer nanocomposites (PNCs) remains difficult due to the complex interplay of microscopic dynamics and structure, namely interfacial layer relaxations and three-dimensional nanoparticle (NP) arrangements. The effect of surface modification by alkyl methoxysilanes at different grafting densities has been studied in PNCs made of poly(2-vinylpyridine) and spherical 20 nm silica NPs. The segmental dynamics has been probed by broadband dielectric spectroscopy and the filler structure by small-angle X-ray scattering and reverse Monte Carlo simulations. By combining the particle configurations with the interfacial layer properties, it is shown how surface modification tunes the attractive polymer–particle interactions: bare NPs slow down the polymer interfacial layer dynamics over a thickness of ca. 5 nm, while grafting screens these interactions. Our analysis of interparticle spacings and segmental dynamics provides unprecedented insights into the effect of surface modification on the main characteristics of PNCs: particle interactions and polymer interfacial layers.

Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.

An experimental program is oriented to the mechanical behaviour of the Interfacial Transition Zone (ITZ) exposed to leaching, for a single mix. Leaching kinetics of the degraded depth, measured through grey level on cross sections, reveals a maximum gap of 10 % between ITZ and bulk cement paste. ITZ, with a main thickness of 15 µm suffers a significant decalcification, which is reflected on the mechanical properties of the bond. Grey level, Calcium/Silicon (Ca/Si) molar ratio and Young’s modulus in the degraded zone present similar evolution. Effect of ITZ causing cracking and then debonding is noticed, through chemical analysis, image observation and mechanical tests.