ISSN:
1042-7147
Schlagwort(e):
Healing
;
Interdiffusion
;
Fracture
;
Interface
;
Diffusion coefficient
;
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Maschinenbau
Notizen:
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.
Zusätzliches Material:
18 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pat.1994.220050901
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