Characterization of microcapsule adhesion on cellulose film by a flow chamber and AFM

He, Yanping; Bowen, James; Liu, Min; Smets, Johan and Zhang, Zhibing (2013). Characterization of microcapsule adhesion on cellulose film by a flow chamber and AFM. In: 9th European Congress of Chemical Engineering, 21-25 Apr 2013, The Hague, The Netherlands.



Perfume microcapsules have attracted a great deal of attention from industries to be incorporated in household products (e.g. detergent), and then provide a pleasant scent to the consumers after laundry process. To realise this, it is essential for the microcapsules to deposit on fabric surface. Therefore it is important to understand their adhesion at the interface and then develop a strategy to enhance the deposition of microcapsules on fabric surface.

In this study, a parallel-plate flow chamber with a video camera was built to investigate the deposition of perfume microcapsules on a cellulose film in aqueous solution and the adhesion was quantified by measuring the surface area occupied by the microcapsules before and after a fluid flow. Moreover, individual microcapsules were used to test adhesion on cellulose films by AFM colloidal probe technique. The cellulose film was then modified with a polyelectrolyte (PE) bearing positive charges and amine groups in order to increase the adhesion of microcapsules on the cellulose. The extent of deposition and adhesion of perfume microcapsules on cellulose films determined by the flow chamber and AFM were compared, and the adhesion mechanisms have been proposed.

It has been found that the surface area of a cellulose film occupied by microcapsules was approximately 10% after a fluid flow of 3 min with a wall shear stress of 0.0395 Pa in the flow chamber. After the PE with a concentration of 0.1% (wt. %) was applied to the cellulose for 30 min, the corresponding deposition ratio of the microcapsules was increased to 90%.

The average pull-off force between single microcapsules and a cellulose thin film was 2.3 ± 1.0 nN for a contact time of 0.01 s, and was increased to 58 ± 31 nN after the PE (0.1 wt%) was applied to the cellulose for 30 min. The adhesion was also found to increase with increasing time to 10 s.

Microcapsules are supposed to be displaced from the fabric surface by rolling motion in the flow chamber and the torque balance on a particle demonstrated that the particle displacement from a flat surface is directly correlated with the adhesion between the two surfaces, which agrees with the correlation observed between the two techniques used in this study. Moreover, the adhesion was further investigated as a function of surface charges of microcapsules and PE, ionic strength and pH of the suspending liquid by AFM; it is proposed that bridging forces resulting from the extension of cellulose chains dominate the adhesion between the microcapsule and un-modified cellulose film; electrostatic attraction helps to capture the microcapsule to the modified cellulose film with PE and then hydrogen bonding as well as bridging forces play important roles to contribute to the adhesion when they were separated.

It is believed that the flow chamber device can be used to provide a quick evaluation of adhesion between other microparticles on a flat surface, whilst the AFM can be used to generate in-depth understanding of the mechanisms underlying the adhesion.

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