The interdiffusion of polymer chains during film formation from direct mini-emulsified deuterated and protonated polystyrenes (DPS = mol wt 150 000 and 185 000; HPS = mol wt 150 000 and 200 000) was characterized by small-angle neutron scattering (SANS) and tensile strength measurements. Films containing 6 mol % deuterated particles were annealed at several temperatures above Tg for various periods of time. The average interpenetration depth of deuterated polystyrene chains depended on the one-fourth power of the annealing time up to the reptation time, r, shifting to the one-half power after the reptation time. The center of mass diffusion coefficients from the SANS data were 2.4 X 10-16 cm2/s for Mn = 150 000 and 1.5 X 10-16 cm2/s for Mn = 185 000 at an annealing temperature of 135 °C. The diffusion activation energies of the present system were 52 ± 4 kcal/mol for the temperature range 125 < T < 155 °C. Full tensile strength was achieved at a penetration depth of 90-100 A, which is comparable to 0.81 times the radius of gyration of the whole polystyrene chain (86 A for Af" = 150 000) predicted theoretically. Finally, latex samples containing 1.5 wt % cosurfactants showed a faster interdiffusion rate especially at t > r and a smaller activation energy than the corresponding pure latex sample.

The interdiffusion of polymer chains across a polymer–polymer interface, and subsequent fracture to re‐create the interface is reviewed. In particular, films formed via latex coalescence provide a very large surface area. Of course, latex film formation is a very important practical problem. Healing of the interface by interdiffusion is treated using the de Gennes reptation theory and the Wool minor chain reptation model. The self‐diffusion coefficients of polystyrene and the polymethacrylates obtained by small‐angle neutron scattering, SANS, direct non‐radiative energy transfer, DET, and other techniques are compared. Reduced to 150,000 g/mol and 135°C, both polystyrene and poly(methyl methacrylate) have diffusion coefficients of the order of 10−16−10−17 cm2/sec. Variations in the diffusion coefficient values are attributed to the experimental approaches, theoretical treatments and molecular weight distribution differences. An activation energy of 55 kcal/mol was calculated from an Arrhenius plot of all polystyrene data reduced to a number‐average molecular weight of 150,000 g/mol, using an inverse square molecular weight conversion method. Interestingly, this is in between the activation energies for the α and β relaxation processes in polystyrene, 84 and 35 kcal/mol, respectively. Fracture of polystyrene was considered in terms of chain scission and chain pull‐out. A dental burr apparatus was used to fracture the films. For low molecular weights, chain pull‐out dominates, but for high molecular weights, chain scission dominates. At 150,000 g/mol, the energy to fracture is divided approximately equally between the two mechanisms. Above a certain number average molecular weight (about 400,000 g/mol), the number of chain scissions remains constant at about 1024 scissions/m3. Energy balance calculations for film formation and film fracture processes indicate that the two processes are partly reversible, but have important components of irreversibility. From the interdiffusion SANS data, the diffusion rate is calculated to be about 1 Å/min, which is nine orders of magnitude slower than the dental burr pull‐out velocity of about 0.8 cm/sec.