When a suspension freezes, a compacted particle layer builds up at thesolidification front with noticeable implications on the freezing process. In adirectional solidification experiment of monodispersed suspensions in thinsamples, we evidence a link between the thickness of this layer and the sampledepth. We attribute it to an inhomogeneity of particle density induced by thesample plates. A mechanical model enables us to relate it to the layerthickness with a dependency on the sample depth and to select the distributionof particle density that yields the best fit to our data. This distributioninvolves an influence length of sample plates of about nine particle diameters.These results clarify the implications of boundaries on suspension freezing.They may be useful to model polydispersed suspensions since large particlescould play the role of smooth boundaries with respect to small ones.
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