【正文】 polymer film could easily form. Therefore, based on the experimental evidence it appears that the film formation mechanism of the novel latex is somewhat different to the conventional descriptions, because of the presence of clusters in the latex system.Moreover, as seen in Figure 5, in the final stages of the film formation process, a number of clusters appear to remain on the surface of the film. In the ESEM image the clusters appear brighter than the rest of the polymer film. This is believed to be caused by a difference in the working distance。 . the distance between beam exit point and cluster is shorter than the distance between beam exit point and polymer film.The accumulation of clusters on the surface of the latex specimens can beCopyright 2009 WILEYVCH Verlag GmbH amp。 Co. KGaA, Weinheim 124Macromol. Symp. 2009, 281, 119–125Figure 5.Lowmagnification ESEM image of a novel acrylic latex specimen in the final stage of the film formation process, showing accumulation of clusters on the surface of the drying film.explained by taking into consideration the Peclet number for latices.[22,23] For a latex system the Peclet number can be defined as:HEConclusionEnvironmental scanning electron micro scopy (ESEM) has proven to be a successful method for studying the process of the evolution of aqueous polymer dispersion into a dry film. The ESEM results revealed that there are differences in both the microstructures and the drying behaviour of the studied latex systems. The ESEM analysis revealed that the microstructure of the standardlow Tg system consisted of individual particles and upon evaporation a continuous film formed, whereas in the case of the standardhigh Tg latex the particles did not deform and/or coalesce, but formed wellordered arrays. However, in the case of the novel system the microstructure consisted of individual particles and clus ters and during evaporation a discontinuous film formed with voids present within its structure. Furthermore, it was found that in the final stages of the film formation processsome of the clusters accumulate on thePe 188。 D 。where H is the film thickness (m), E is the evaporation rate (m/s) and D is the diffusion coefficient (m2/s). The literature suggests that if Pe 0(1) then no surface accumulation is to be expected, but if Pe 1 then diffusion is weak and the particles will accumulate at the top of the surface during drying. D is taken as the StokesEinstein diffusion coefficient:kTD 188。 6pmRTaking m as water viscosity 10 3 Ns/m2,kT as 4 10 21 J and E as 3 10 8 m/s then,Pe 1011 H R。with both H and R in metres. Hence, if R (in this case the size of a cluster) is 5 10 6 m then to get uniform films, H has to be 2 10 6 m. Therefore, for the typicalsample film thickness, which is in the range of 200 mm, surface accumulation will be expected, which is in agreement with the experiments.surface of the latex specimens.[1] G. Danilatos, J. Microscopy 162, 1991, 391–402.[2] J. L. Keddie, P. Meredith, R. A. L. Jones, A. M. Donald, Langmuir 12, 1996, 3793–3801.[3] C. He, A. M. Donald, Langmuir 12, 1996, 6250–6256.[4] P. Meredith, A. M. Donald, J. Microscopy 181, 1996,23–35.[5] J. L. Keddie, P. Meredith, R. A. L. Jones, A. M. Donald,Macromolecules 28, 1995, 2673–2682.[6] A. M. Donald, C. He, P. Royall, M. Sferrazza, N. A. Stelmashenko, B. L. Thiel, Colloids amp。 Surf. A: Physico chem. Eng. Aspects 174, 2000, 37–53.[7] D. J. Stokes, Philos. Trans. R. Soc. Lond., A 361, 2003,2771–2787.[8] R. E. Cameron, A. M. Donald, J. Microscopy 173, 1994,227.[9] G. L. Brown, J. Polym. Sci. 22, 1956, 423.[10] J. W. Vanderhoff, Br. Polym. J. 2, 1970, 161.[11] S. S. Voyutakii, Z. M. Ustinova, J. Adhes. 9, 1977,39.[12] D. P. Sheettz, J. Appl. Polym. Sci. 9, 1965, 3759–3773.[13] E. M. Boczar, B. C. Dionne, Z. Fu, A. B. Kirk, P. M. Lesko, A. D. Koller, Macromolecules 26, 1993,5772.Copyright 2009 WILEYVCH Verlag GmbH amp。 Co. KGaA, Weinheim Macromol. Symp. 2009, 281, 119–125 125[14] M. A. Winnik, Curr. Opin. Colloid Interface Sci. 2,1997, 192–199.[15] J. L. Keddie, Mater. Sci. Eng. R21 (3) 1997.[16] A. F. Routh, W. B. Russel, Langmuir 15, 1999, 7762–7773.[17] P. A. Steward, J. Hearn, M. C. Wilkinson, Adv. Colloid Interface Sci. 86, 2000, 195–267.[18] P. Vandervorst, C. H. Lei, Y. Lin, O. Dupont, A. B. Dalton,Y. P. Sun, J. L. Keddie, Prog. Org. Coatings 75, 2006, 91–97.[19] T. Wang, C. H. Lei, A. B. Dalton, C. Creton, Y. Lin, K. A. S. Fernando, M. Manea, J. M. Asua, J. L. Keddie, Adv. Mater. 18, 2006, 2730.[20] ICI Plc, Private munication, 2006.[21] EU Directive 2004/42/CE.[22] A. F. Routh, W. B. Zimmerman, Chem. Eng. Sci. 59,2004, 2961–2968.[23] V. R. Gundabala, W. B. Zimmerman, A. F. Routh,Langmuir 20, 2004, 8721–8727.Copyright 2009 WILEYVCH Verlag GmbH amp。 Co. KGaA, Weinheim