Dynamics of pristine graphite and graphene at an air‐water interface

Abstract

We examine the dynamics and morphology of graphitic films at an air-water interface in a Langmuir trough by varying interfacial surface coverage, by observing in situ interfacial structure, and by characterizing interfacial structure of depositions on mica substrates. In situ interfacial structure is visualized with Brewster angle microscopy and depositions of the interface are characterized with atomic force microscopy and field-emission scanning electron microscopy. Compression/expansion curves exhibit a monotonically decreasing surface pressure between consecutive compressions, but demonstrate a "rebound" of hysteretic behavior when the interface is allowed to relax between consecutive compressions. This dynamic results from a competition between consolidation of the interface via agglomeration of particles or the stacking of graphene sheets, and a thermally-driven relaxation where nanometer-thick particles are able to overcome capillary interactions. These results are especially relevant to applications where functional films with controlled conductivity and transparency may be produced via liquid-phase deposition methods. V C 2018 American Institute of Chemical Engineers AIChE J, 00: 000-000, 2018 Figure 3. Different microscopy methods used to characterize interfaces at different length scales. From left to right, BAM image at 11 mN/m, AFM image at 3 mN/m, FESEM image at 13 mN/m. [Color figure can be viewed at wileyonlinelibrary.com] AFM images taken from an interface deposited at 3 mN/m after a 15 h relaxation time. Mono-and few-layer graphene sheets are present between large islands of graphitic material. (b) AFM image (left) that reveals few-and mono-layer graphene sheets present at the interface at a surface pressure of 20 mN/m. A corresponding height trace (right) follows the red path indicated in image on the left.Figure 5. Compression curves for graphene interfaces. The upper left plot shows pre-relaxation and post-relaxation compression curves for a 2.5 h relaxation period, and the upper right plot shows the pre-relaxation and postrelaxation compression curves for a 15 h relaxation period. Pre-relaxation curves are plotted with red dashes, post-relaxation curves are plotted with blue dots. The bottom two plots contain the same data, but the postrelaxation curves have been shifted along both axes. The shift factors were obtained "by eye" to overlap the first compressions of the pre-relaxation and post-relaxation curve sets. The inset FESEM images (scale bars: 10 μm) were obtained fromdepositions at low Π (indicated by the black boxes). The images reveal that aggregates are present at all times and are surrounded to different degrees by micron and sub-micron particles. [Color figure can be viewed at wileyonlinelibrary.com] Figure 7. BAM images taken during each of the three compression cycles for both the pre-relaxation and postrelaxation interfaces.White areas indicate graphitic material. All images were taken with the barriers in a fully open state and show the evolution of the interface between cons...

Capillary force on an ‘inert’ colloid: a physical analogy to dielectrophoresis

“…1,2 These interactions can be exploited to drive colloidal self-assembly at interfaces, [3][4][5][6][7][8][9] which offers a promising route for the design of advanced two-dimensional (2D) materials. 2,10,11 Interparticle capillary forces generically result from interfacial deformations due to the presence of the particles. Since colloidal particles have negligible buoyant weight, they can deform an interface only by virtue of their shape [12][13][14][15] or wetting properties.…”

“…One potential way of suppressing these permanent quadrupoles would be to use molecularly thin colloids, such as the particles of graphene, molybdenum disulfide, and hexagonal boron nitride recently studied by Goggin et al 11 Planar particles do not possess undulated contact lines, yet do show evidence of interparticle interactions at interfaces. 10,11,60,61 On the other hand, further theoretical insight might be gained if we revisit the virtual work calculation for an inert colloid. Domínguez et al 29 had previously raised concerns with applying the principle of virtual work to capillary problems in unbounded domains.…”

“…One potential way of suppressing these permanent quadrupoles would be to use molecularly thin colloids, such as the particles of graphene, molybdenum disulfide, and hexagonal boron nitride recently studied by Goggin et al 11 Planar particles do not possess undulated contact lines, yet do show evidence of interparticle interactions at interfaces. 10,11,60,61 …”

Interference Provides Clarity: Direct Observation of 2D Materials at Fluid–Fluid Interfaces

“…25 However, AFM and SEM rely on deposition of material onto a solid substrate, which alters film morphology 8 and prohibits the study of key transition states involved in dynamic processes. Combinations of the above ex situ and in situ techniques have been used by us 20 and others 23 to study lateral interactions between graphene and graphite particles to find that these uncharged particles form metastable films at an air−water interface. We proposed that misaligned capillary multipoles could induce dynamic stabilization between agglomerated particles and that nanometer-thick graphene particles could spontaneously detach from aggregated structures due to a competition between weak attractive interactions and Brownian motion (i.e., thermal energy), which seeks to drive particles apart.…”

Janus Particles at Fluid Interfaces: Stability and Interfacial Rheology

“…The retarded VDW forces are short-ranged and typically extend over a range of tens of nanometers for micrometer-sized colloids [ 143 ], while an unexpected long-ranged attraction has been reported for interfacially-trapped particles [ 146 , 147 , 148 , 149 ]. This strong long-ranged attractive interaction has been attributed to capillary forces [ 139 , 150 , 151 , 152 , 153 , 154 , 155 , 156 , 157 , 158 , 159 , 160 ] resulting from the distortions imposed on the interface by the particles, represented in Figure 3 c [ 120 , 161 ]; an interfacial phenomena with no analogy in bulk aggregation. The interfacial distortions can originate from the weight of particles (gravity-driven capillary attraction for heavier or bigger particles) [ 162 ] or electrostatic stresses caused by the particles dipolar field (electrodipping) [ 158 , 163 ].…”