RESINOGRAPHY 



interpretive information from transmitted fabricating interface may be unknown — 



light. for example, with commercial fibers, foils, 



By reflected light, interference patterns laminates and moldings, 



(polarization figures) are being studied on The internal texture may be entirely dif- 



ore minerals, but such a study on resins is ferent from the external one. The problem 



to date onl}^ suggested. of representing the interior of the specimen 



Electron Microscope. High polymers, may be very difficult. Since the area needed 



alone or simply formulated with plasticizers, is small, a small part of a fracture surface 



curing agents and/or stabilizers are com- may be sufficiently flat (Figures 5B, 6, 14). 



posed generally of very small particles For such purposes fracturing is generally 



(Types II and I). Such particles are smaller simple when the sample is cooled to brittle- 



than the wavelengths of light and, for this ness. Even a film can be fractured in a planar 



reason, are not observable with a light micro- section if the substance can be obtained as 



scope. A stream of electrons at a potential of a liquid and used as an adhesive between 



55 kv has a wavelength of about 0.05 A halves of two L-shaped pieces of sheet iron 



and even though the numerical aperture of or steel. After the "adhesive" is hardened 



an electron lens is extremely low (about and cold-embrittled it is usually fractured 



0.02) a resolution as relatively poor as 100 A by holding one "leg" of the composite L in 



is more than ample to separate colloidal a vise and striking the other leg sufficiently 



particles (Type II) . Electron microscopes, of with a hammer. The fracture-surface is then 



or over 50 kv in potential, somewhat cor- replicated as usual. 



rected in astigmatism, clean and in good op- In a corollary manner a replica can be 



eration, can resolve distances of 20 to 10 A made of a single microtomed surface of fibers, 



or, perhaps, smaller. This kind of resolution foils, films or other soft materials. Grooves 



should resolve macromolecular particles will probably appear in the replica but these 



(Type I) of above approximately 20,000 in are readily related to microscopic nicks in 



molecular weight. The remaining problem is even the best cutting edge. A glass cutting 



to obtain adequate contrast in the bound- edge and a cantilever rocking microtome 



aries or among loci of influence. may be preferred to rotary microtome and 



If the sm-face of a high polymer or its a steel knife, 

 resin is to be examined electron microscop- Mounting specimens for microtomy is 

 ically, a negative, positive, or pseudo replica even more important in electron microscopy 

 will probably serve the purpose (Figures 5B, than in light microscopy. Special precautions 

 6, 10, 11, 14). In any kind of replication of may have to be taken to avoid distortion, 

 a high polymeric material, the primary repli- chattering and other effects. A very success- 

 eating medium must not modify or stick ful method for fibers is to treat them w^ith a 

 to the material. Therefore, replicating media synthetic rubber latex before embedding in 

 are generally limited to aqueous media, such methacrylate (4) (Figure 12, left). 

 as a "solution" of gelatin, methyl cellulose The most direct method of examining a 

 or polyvinyl alcohol. Control samples of the high poljoner is to cast it into a film which 

 replicating and photographic media should is sufficiently thin for electron microscopy 

 be compared with the electron micrograph (Figure 4). This presupposes that the speci- 

 of the specimen. men is obtainable in a fluid state, which will 



A "surface" of a polymer is generally an flow to a thin film and cure or dry to a film 



interface of the polymer with air, liquid or which is self-supporting and able to with- 



solid, and the electron microscopical image stand the incidence of the electron beam, 



must be considered as such even when the Linseed oil cast on water can be prepared 



535 



