During the deformation stage of latex film formation, a close-packed array of particles is consolidated to form a structure with volume fraction unity. There are a number of different possible driving forces to achieve this. Proposed mechanisms range from surface tension between polymer particles and either water or air to capillary forces at the water-air interface. We review the different driving forces and the literature supporting them. A recent model we have proposed predicts the conditions under which each mechanism operates. Experiments in the literature correlate well with our model, although the need for experiments with well-defined values for the critical parameters is highlighted.

The first systematic and quantitative experimental study of the influences on lateral drying in colloidal films is reported. The time until water recedes from the edge of a drying thick film of a waterborne colloidal dispersion, called the open time, was measured as a function of several controllable parameters. Magnetic resonance microscopy, using a specially designed probe, noninvasively provides a direct and quantitative measurement of the concentration of water as a function of vertical and lateral position. Images were obtained from drying films of latices with known values of thickness, particle size, and surface tension, which are neatly encapsulated in an expression for the reduced capillary pressure, p c. A strong increase in the open time was found over a relatively narrow range of p c values. Larger particles, slower evaporation rates, and thinner films encourage more uniform lateral drying with a delay in drying from the edges. This observation is consistent with a recent model (Routh, A. F.; Russel, W. B. AIChE J. 1998, 44, 2088) based on the lubrication approximation. The experiments and the modeling point to a way of achieving control over the lateral drying processes of waterborne colloids.

in Wiley Online Library (wileyonlinelibrary.com) Controlling the final shape resulting from evaporation of pinned droplets containing polymer, is important in the fabrication of P-OLED displays by inkjet printing. Typically, a coffee -ring shape arises, due to the pinning and associated outward capillary flow. For operational reasons, this is undesirable -a flat topography is required. The aim of this work is to understand the important groups governing the shape, to provide a practical guide to ink selection. The theory presented is based on a thin-film lubrication model. The governing equations are solved numerically and continuously track the lateral progression of a liquid/gel front. A large capillary number or large ratio of initial to maximal polymer volume fraction can suppress the coffee-ring. White light interferometry is used to confirm these findings experimentally.

Boron removal from and reinsertion into the framework of a HAMS-1B (H-[B]-ZSM-5) borosilicate molecular sieve was studied by a combination of wet chemistry and 11 B solid-state NMR (SSNMR) spectroscopy. Uncalcined HAMS-1B shows only tetrahedral boron. However, three boron species are observed in the NMR spectra of as-prepared and then calcined HAMS-1B-3: tetrahedral framework boron ( [4] B fr ), trigonal framework boron ( [3] B fr ), and nonframework trigonal boron ( [3] B NF ). A picture has emerged as to the origins of these three species. Trigonal boron species are formed via hydrolysis by reaction with the water formed from water release and water formed by oxidation and removal of the template during calcination. [3] B NF is confirmed to be due to free boric acid formed by complete removal of boron from the framework. The trigonal boron species are readily removed from the framework by slurrying in water or mild acid solutions. Tetrahedral boron remains at a concentration about equal to that in the calcined sieve, indicating that it is more difficult to remove. The extent of boron removal and reinsertion is pH dependent. Boron is removed to a greater extent at low pH and can be reinserted when pH is increased. Boron reinsertion into the framework is proven by 11 B SSNMR of a series of 10 B-11 B exchanged borosilicate zeolites. Surprisingly, when boron is reinserted it enters as tetrahedral boron, not trigonal boron, thus reversing the partial hydrolysis and removal during calcination.