Styrene/2-ethylhexyl acrylate/methacrylic acid (Sty/EHA/MAA) coalescence and response-driven mobility of sodium dodecyl sulfate (SDS) in colloidal films. 22. A spectroscopic study

The surface morphology of coalesced latex films is a key parameter for understanding coalescence processes and physical and chemical properties of the resulting films. These studies focus on molecular aspects of colloidal film surfaces. Specifically, the distribution and orientation of a commonly used surfactant, sodium dodecyl sulfate (SDS), in films obtained from colloidal dispersions of poly(styrene/ ethylhexyl acrylate/methacrylic acid) (Sty/EHA/MAA) and the effect of covalent and ionic entities incorporated into these films are examined. Apparently, the presence of covalently bonded species, such as diacetone acrylamide/adipic dihydrazide (DAAM/ADDH), or ionic species, such as Ca(OH)(2)/NH4OH, can effectively immobilize or mobilize SDS molecules during coalescence. Furthermore, molecular orientation of SDS is also influenced causing structural rearrangements near the film-air (F-A) interface. Upon coalescence at 25 degreesC, the -SO3-Na+ moieties take a preferentially parallel orientation, whereas at 60 degreesC they are randomized. Upon further annealing at 90 degreesC, -SO3-Na+ moieties regain parallel orientation, to become random at 120 degreesC. This reorganization is affected by the presence of ionic species, H2O, and cross-linkers to which SO3-Na+ groups respond via structural changes from being fully to partially hydrated. Overall, the coalescence of colloidal particles is affected by the presence of minute quantities of active components, which significantly influence surface film morphologies. These studies also show that the response of individual components stimulated by external conditions may lead to specific surface properties and new morphological features.