Free volume distribution during consolidation and coalescence of latex films

The focus of the work is the effect of molecular architecture on free volum e distribution during consolidation and coalescence of aqueous latex emulsi ons. Two series of model emulsion polymers, iso-butyl methacrylate (i-BMA) and normal-butyl methacrylate (n-BMA) dispersions with varying level of tri methylolpropanetriacrylate (TMPTA) crosslinker, are studied. Coatings are c haracterized by positron annihilation lifetime spectroscopy (PALS), and ato mic force microscopy (AFM). Formation of coherent brittle films without sig nificant interdiffusion is achieved by consolidation below the glass transi tion temperature (T-g). Consolidation, or ordering/compaction of films foll owing water evaporation at temperatures below the MFFT, results in a decrea se in the relative free volume element size, tau (3), as measured by PALS. An increase in the characteristic relaxation time for the consolidation pro cess is evident as TMPTA levels and corresponding gel fraction increase. co nsolidation below T-g is accompanied by physical aging. Coalescence and int erdiffusion are achieved by annealing films at or above T-g. Annealed coati ngs show a decrease in T-g and an increase in PALS free volume attributed t o erasure of physical aging in combination with the action of the surfactan t (sodium dodecyl sulfate) as a plasticizer.