*2.2.2. Bio-ferroelectric nanocomposites*

The double layered bio-ferroelectric composites were fabricated layer-by-layer via the solution casting method. The first layer consisted of chitosan-cellulose bio-polymers and the second layer consisted of the bio-polymers mixed with strontium titanate (STO) particles. To fabricate the said first layer, small solutions of chitosan and cellulose (i.e., 85 v%Ch-15 v%Cel and 75 v%Ch-25 v%Cel) were synthesized and transferred in the petri dishes for the dry process. The purpose of the second layer was to prevent the nanoparticles from settling and passing through the still soft first polymeric film. Hence, for the second layer, the same amount of small solutions was synthesized, this time with different STO amounts, i.e., 10 and 20 wt%; the goal was to analyze their effect in the electrical properties of the resulting biocomposites. Thereafter, these solutions were transferred onto their corresponding first layer of chitosan-cellulose followed by a second drying process to remove any residual water from the polymeric matrix.

The dispersion of nanoparticles within a given matrix has always been an issue, as proven in a prior research [11]. Therefore, to enhance such dispersion in the matrix we reduced the size of the particles using a varioplanetary high energy ball mill. To find the optimal time in which we could reduce the particle size to the smallest possible, the particle size was determined at different milling times using the Scherrer equation [12, 13]. Afterwards, the particle size was computed at different milling times to select the most time-efficient operation, i.e., maximum size reduction at minimal time. The overall technique had been successfully implemented to reduce the size of compound particles in previously published works [14, 15].
