Origin of Buckling Phenomenon during Drying of Micrometer-Sized Colloidal Droplets

Abstract

The origin of the buckling of micrometer-sized colloidal droplets during evaporation-induced self-assembly (EISA) has been elucidated using electron microscopy and small-angle neutron scattering. Doughnut-like assembled grains with varying aspect ratios are formed during EISA at different physicochemical conditions. It has been revealed that this phenomenon is better explained by an existing hypothesis based on the formation of a viscoelastic shell of nanoparticles during drying than by other existing hypotheses based on the inertial instability of the initial droplets and hydrodynamic instability due to thermocapillary forces. This conclusion was further supported by the arrest of buckling through modification of the colloidal interaction in the initial dispersion.

Phenomenology and control of buckling dynamics in multicomponent colloidal droplets

“…In drying systems, the loss of solvent induces self-assembly (without external aids) of the colloidal particles into hierarchical order (maximum concentration at the surface). [6][7][8] The interactions lead to agglomeration of particles which acts as precursor to the formation of an elastic membrane (shell) at the surface. 4 The shell undergoes viscoelastic transition which leads to the buckling instabilities in the droplet.…”

“…9,10 The phenomenon of buckling can be manipulated by varying the concentration, size, type, and distribution of the particles in the dispersion. 7,11,12 Rate of drying plays a key role in the invagination process eventually leading to spherical or non-spherical (dough-nut shaped) structures in the droplet. 12 Controlled buckling can be exploited to manufacture custom-tailored materials which have widespread industrial applications (pharmaceuticals, cosmetics, detergents, coatings, etc.).…”

Porous nano-structured micro-granules from silica-milk bi-colloidal suspension: Synthesis and characterization

“…This indeed indicates the significant role of inter-particle interaction in morphological transformation. It should be mentioned that in some of the previous works [24][25]27,[29][30][31][47][48][49][50][51][52][53][54], using single-component colloidal suspension, it was indicated that the spherical shape of droplet is retained even in the granule because of isotropic drying at slow drying rate. It has also been discussed that the formation doughnut shape is a consequence of anisotropic drying and shell buckling when drying rate is fast enough.…”

E. coli imprinted nano-structured silica micro-granules by spray drying: Optimization of calcination temperature

“…These include spray drying [3], freeze-drying [4], porogenation [5,6], micro-emulsion formation [7], gas-blowing techniques [8], phase separation [9] etc. Synthesis of micro-granules through drying of suspension-droplets is a well established process that can produce micrometric composite granules in a single step through evaporation-induced assembly [10][11][12][13][14][15]. Such assembly process is a quick and efficient bottom-up approach for realizing multi-functional composite micro-granules.…”