Suppressing Crack Formation in Particulate Systems by Utilizing Capillary Forces

Abstract

Cracks, formed during the drying of particulate films, can reduce the effectiveness or even render products useless. We present a novel, generic approach to suppress crack formation in thin films made from hard particle suspensions, which are otherwise highly susceptible to cracking, using the capillary force between particles present when a trace amount of an immiscible liquid is added to a suspension. This secondary liquid preserves the particle cohesion, modifying the structure and increasing the drying rate.Crack-free films can be produced at thicknesses much greater than the critical cracking thickness for a suspension without capillary interactions, and even persists after sintering. This capillary suspension strategy is applicable to a broad range of materials including suspensions of metals, semiconductive and ceramic oxides or glassy polymeric particles and can be easily implemented in many industrial processes since it is based on well-established unit operations. Promising fields of application include ceramic foils and printed electronic devices.1

Shrinkage and dimensional accuracy of porous ceramics derived from capillary suspensions

“…A more homogeneous shrinkage between the top and the bottom is not only consistent with a better shape accuracy but also with a more homogeneous drying stress within the suspension [35]. This is consistent with the results of Schneider et al [34] where cracking was reduced. This confirms our previous results and emphasizes the benefits of capillary suspensions in terms of shape accuracy, molding behavior and defect-free drying.…”

“…Therefore, this work emphasizes the strengths of ceramic capillary suspension route as an accurate, low cost, widely applicable variable fabrication method for porous ceramics. We anticipate possible application in various fields, like membranes or filters [34], lightweight construction materials [24], biomedical devices, gas diffusers, thermal insulators or catalyst carriers.…”

“…As mentioned earlier, the high deviations probably result from inaccuracies during demolding as well as from shearing failure. The bottom shrinkage is mainly controlled by the substrate adhesion, whereas the top shrinkage is dominated by particle mobility and orientation [33,34]. The strong decrease in shrinkage of the top while the bottom remains uniform means a substantially lower difference between the top and bottom radii and, therefore, an increasing shape accuracy.…”

Fractal approaches to characterize the structure of capillary suspensions using rheology and confocal microscopy

“…This effect can be used as a simple method to tune the flow behavior of suspensions that would otherwise require the addition of rheology control agents, surfactants or other additives [7]. Capillary suspensions can be used for various applications such as precursors for ceramic or glass filters with high porosity and simultaneously small pore size [8–10], porous polymeric or hybrid membranes [11, 12] improved polymer blends [13–15], slurries for battery electrodes or printable electronics with accurately molded edge shape, good charge transfer properties and reduced resistivity [16–18], crack-free films [19], thermal interface materials [20], carbon slurries from renewable sources used for energy generation [21], the preparation of novel food products [22, 23] or as 3D printing paste formulations [24, 25].…”

Effect of surrounding polydimethylsiloxane frame and substrate on drying behavior of aqueous alumina suspensions

“…Dozens of methods have been developed to avoid cracking during drying. Those methods are mostly achieved in four ways: (i) enhancing the strength of the body, (ii) releasing or reducing the capillary stress, (iii) avoiding the substrate constraint, and (iv) combining at least two ways mentioned above . Some methods are usually accomplished by adding polymeric binders, surfactants or soft particles into the suspensions.…”