Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 2: Contact Line Pinning

Abstract

Pinning of droplets on solids is an omnipresent wetting phenomenon that attracts intense research interest. Unlike in classical wetting, pinning effects in a novel wetting problem where droplets are confined onto the substrates by elastic films have hardly been investigated. Here, following our study in an accompanying paper (part 1) on the static mechanics of nanoscale blisters confined between a two-dimensional elastic sheet and its substrate, we investigate in this part the pinning behaviors of such blisters by using atomic force microscopy. The blisters’ lateral retention forces are shown to scale almost linearly with their contact lines and to increase until saturation upon increasing their resting times. Our analysis reveals a mechanism of microdeformation of the substrate at the contact line. The creep of the microdeformation is found to cause the time-dependent pinning, which is evidenced by residual fine ridge structures left by blisters after their spread after long resting times.

Time-Dependent Pinning of Nanoblisters Confined by Two-Dimensional Sheets. Part 1: Scaling Law and Hydrostatic Pressure

“…[1][2][3][4][5][14][15][16]20 Such blisters have typical lateral sizes from a few nanometers to micrometers and may be formed through the aggregation of adsorbed molecules on the interface surfaces due to the vdW attraction between them. Although it is difficult to directly determine the substance inside the blisters, we conclude from the observation of residual wetting ridges after depinning the blisters (see part 2 17 ) that for our sample it is at least liquid. Indeed, studies have suggested that absorbed liquid water is the most likely candidate rather than other possibilities of trapped air or hydrocarbon.…”

“…Spontaneously formed blisters are frequently observed between different 2D materials and their substrates. − ,− , Such blisters have typical lateral sizes from a few nanometers to micrometers and may be formed through the aggregation of adsorbed molecules on the interface surfaces due to the vdW attraction between them. Although it is difficult to directly determine the substance inside the blisters, we conclude from the observation of residual wetting ridges after depinning the blisters (see part 2) that for our sample it is at least liquid. Indeed, studies have suggested that absorbed liquid water is the most likely candidate rather than other possibilities of trapped air or hydrocarbon. ,,− ,, In particular, a study by Cao et al showed that the number density and the sizes of the nanoblisters are both reduced for graphene–graphite interfaces prepared at lower relative humidity .…”

“…To this end, in this two-part work, we investigate both the static mechanics and dynamics of nanoscale blisters confined between a 2D elastic sheet and its substrate. Before we report our study on the pinning/depinning behaviors of such blisters in an accompanying paper (part 2), 17 here in this part, which also serves as a basis for the analyses in part 2, we investigate the morphology characteristics and hydrostatic pressures of the blisters. We first study the shape characteristics of the blisters by using atomic force microscopy (AFM) characterization and by a mechanics analysis.…”

Mechanical Mapping of Nanoblisters Confined by Two-Dimensional Materials Reveals Complex Ridge Patterns

“…Such blisters are indeed frequently seen between 2D materials and their substrates. − Although being considered as contaminations that affect device performances and therefore cleaning methods of them are of great importance, − , blisters confined by 2D materials also attract research interests from both fundamental and applied perspectives. For example, analyzing their morphology allows us to study the mechanical and interfacial properties of the capping 2D materials. ,, Blisters enclosing liquids benefit understanding a novel wetting phenomenon known as elastic-wetting. , Moreover, the high internal pressure of 2D material blisters inspires high-pressure chemistry within them, , and their potential for strain engineering is also explored. − …”

“…This is because high-resolution pixel-by-pixel force curve measurements are commonly quite time-consuming, although a fast method of doing so has been reported . In addition, a relatively large indentation force during the measurement may remove , or damage , the blisters.…”