Mechanisms of Particle Deformation During Latex Film Formation

Abstract

The aim of this article is to review the literature dealing with the deformation step in the phenomenon of film formation from a latex. It will be shown that the situation of this problem in the literature is quite confusing. The article will be divided in two parts. The first will recall the classical theories proposed in the past to account for the deformation of latex particles in the film formation process, namely the dry sintering theory by Dillon et al., Brown's capillary theory, the wet sintering theory by Vanderhoff et al., and the surface layer theory by Sheetz. The second part will deal with following works which were all attempts to experimentally verify and/or improve the main theories.One can distinguish three steps in the process of film formation from a latex (/, 2). i) In the first step, water evaporates at a constant rate until a stage is reached where particles form a dense packing of spheres. The solid volume fraction, for a latex monodispersed in size, is then close to 0.74. An additional condition for high packing fraction is sufficient colloidal stability. Otherwise, a less ordered structure with lower polymer volume fraction will result. ii) At the beginning of the second step, particles show at the surface of the latex, and the rate of water evaporation decreases. Forces start to act which ensure the deformation of the particles in such a way that polymeric material fills all the space. Acting forces have to surmount the mechanical resistance of the particles against deformation. The spheres are transformed into rhombic dodecahedra. A rhombic dodecahedron has 12 rhombic faces, and 14 vertices of two types. Six vertices correspond to 4-fold axes, and 8 to 3-fold axes. It is not easy to draw this polyhedron. A schematic representation can be found in reference 3. They can also be observed in beautiful freeze fracture micrographs of poly(butyl methacrylate) latex films (4). At this stage, interfaces between particles still exist (5). For latexes, the compaction/deformation step is favorable from a thermodynamical point of view

Drying Patterns of Dispersions and Solutions

“…[160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176] Three processes from the dispersions into the film have been proposed: (1) close-packing processes of polymer colloids by evaporation of solvent, (2) deformation of the particles followed by disappearing voids, although the original particles are still distinguishable, and (3) continuous film formation by the diffusion of polymer across particle boundaries. Cracking patterns of the films induced by the shrinkage during dryness were also investigated for the paste layers of clay, sand, and water deposited on a rigid substrates.…”

Latex Barrier Thin Film Formation on Porous Substrates

“…This capillary pressure deforms the polymer particles to fill the void space between them. 13,11,12,14 In the third stage, the individual particles coalesce into a film. Polymer chains interdiffuse across particle−particle boundaries, and the individual particles become indistinguishable.…”

“…17,4 After coalescence is complete, the film has its final toughness and strength. 13,[18][19][20][21]14 The physical and mechanical properties of the film are dependent on the extent to which the latex particles coalesce and fuse together. 22 Coalescence of polymer beads into a film is thermodynamically favorable because the thin film has less surface area than the individual particles; thus, the thin film has a lower state of free energy than the same mass of individual particles.…”

Preferred partitioning: the influence of coalescents on the build-up of mechanical properties in acrylic core–shell particles (I)

“…[2][3][4] A number of methods are available to probe the degree of film formation, for example by diffusion wave spectroscopy, 5 magnetic resonance imaging (MRI)-profiling, 6 fluorescence resonance energy transfer (FRET)-techniques, 7,8 microscopic techniques, 9 and neutron scattering. 10 The drawback of all these techniques is that they do not provide information on the development of the mechanical properties of the coating film, which are crucial for the performance.…”