Effect of particle adsorption rates on the disproportionation process in pickering stabilised bubbles

Abstract

The degree of shrinkage of particle stabilised bubbles of various sizes, in a polydisperse bubble dispersion, has been investigated in the light of the finite adsorption times for the particles and the disproportionation kinetics of the bubbles. For the case where the system contains an abundance of particles we find a threshold radius, above which bubbles are stabilised without any significant reduction in their size. Bubbles with an initial radius below this threshold on the other hand, undergo a large degree of shrinkage prior to stabilisation.As the ratio of the available particles to the bubbles is reduced, it is shown that the final bubble size, for the larger bubbles in the distribution, becomes increasingly governed by the number of particles, rather than their adsorption time per se. For systems with "adsorption controlled" shrinkage ratio, the final bubble distribution is found to be wider than the initial one, while for a "particle number controlled" case it is actually narrower. Starting from an unimodal bubble size distribution, we predict that at intermediate times, prior to the full stabilisation of all bubbles, the distribution breaks up into a bimodal one. However, the effect is transient and an unimodal final bubble size distribution is recovered once again, when all the bubbles are stabilised by the particles.-3-1

Evolution of bubble size distribution in particle stabilised bubble dispersions: Competition between particle adsorption and dissolution kinetics

“…Interestingly, in a distribution of bubble sizes with enough particles present to stabilise all the bubbles at their initial size, it is the small bubbles with a radius below a characteristic value R * that suffer the largest degree of gas loss. Bubbles much larger than R * , although these only become completely stabilised later on, actually suffer very little shrinkage prior to doing so [44]. However, the shrinkage rates of different sized bubbles in the system occurs more of less independently.…”

“…Our preliminary theoretical results, for the evolution of bubble size distributions under such circumstances, indicates that the depletion of nanoparticles at the early stages of the process, due to their adsorption onto the surface of smaller bubbles, leaves the larger bubbles with very few remaining particles towards the end of the process. Consequently, even the larger bubbles which normally would have been stabilised without much shrinkage, now undergo a large degree of gas loss [44].…”

“…Indeed in dilute bubble dispersions, the dissolution process may become the dominant short term instability mechanism, overtaking coalescence. In a recent paper [44], we have theoretically analysed the consequences of finite time durations for the transport of a sufficient number of particles onto the surface of newly created bubbles produced under quiescent conditions [44]. Examples of such processes are bubbles generated in situ as in fermentation, through ultrasound cavitation [19] or even gentle bubbling of gas into the food product.…”

Development of a theoretical model for obtaining the whipped emulsions from a dry fat-containing mixture and its experimental verification

“…The stability of foams using the solid particle can persist for several months [5]. It depends on the speed of adhesion of solid particles [6], contact angle [7]. In food systems they use cellulose [5], micro gels particles [8].…”

“…At pressure of fat mixture feed 0.2×10 6 Pa and diameter of the nozzles 1.5×10 -3 m, we received fatty particles of average diameter (5…10)×10 -6 m. Recovery of a dry fat-containing mixture and whipping allows obtaining whipped emulsions with foaming capacity of 400±16 %, foam stability of 99±1 % and the yield shear stress of 550±28 Pa. The magnitude of foaming capacity and yield shear stress is significantly lower than the values of indicators of whipped emulsions, received in the sequential process of formation.…”