Elastocapillarity: Adhesion and Wetting in Soft Polymeric Systems
Z Cao and MJ Stevens and AV Dobrynin, MACROMOLECULES, 47, 6515-6521 (2014).
We have developed a generalized model of particle-substrate interactions describing both adhesion and wetting behavior. Using a combination of the molecular dynamics simulations and scaling analysis we have shown that the crossover between adhesion and wetting-like behavior for a particle with size R-p and shear modulus Gp interacting with a substrate of shear modulus G(s) is determined by the dimensionless parameter beta proportional to gamma*(G* R-p)W--2/3(-1/3), where G* = GpGs/(G(p) + G(s)) is the effective shear modulus, W is the work of adhesion between particle and substrate, and y* = Wg, + yp(14) + yspe is the effective surface tension of the particle/substrate system with yp and y, being surface tensions of particle and substrate, ysp - surface tension of the particle-substrate interface, and beta proportional to gamma*(G* R-p). This parameter fi is proportional to the ratio of elastocapillary length gamma*/G* and contact radius a, beta proportional to gamma*(G* R-p). In the limit of small values of the parameter fi < 1, when the contact radius a is larger than the elastocapillary length gamma*/G*, our model reproduces Johnson, Kendall, and Roberts results for particle adhesion on elastic substrates (adhesion regime). However, in the opposite limit, ag > 1 (a < y*/G*), the capillary forces play a dominant role and determine particle-substrate interactions (wetting regime). Model predictions are in a very good agreement with simulation and experimental results.
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