Michael F. Smolin J. R. Williams School Painesville, Ohio E. M. Srnolinl Diamond Alkali C o m, ~ a n, v Painesville, Ohio
I I1
Film Carting- on Water
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T h e solution casting of fi~nisof common plastics on wat,er, a technique that has not heen drscribed in the literatwe, o m provide a simple, rapid met,hod for classroonl demonstr:ltion of the formatinu of transparent films. Student,s also can use this t,ei:hnique without such rquipnient as drying ovms, film boxes, or "doctor knives." Solutions of readily avnilahle polymers are mark np in volatile, water-solnhle organic solvents. I'lasticizers and other organic-soluhle, compatible additjives may he included in t,he solntion for flexibility or added strength. I n general, polymer conzent~mt,ionsof 2 0 % an! suital>le for the preparation of fairly uniform films that are thick enough for strength and large enough for measuring or for use in orientation experiments. Solutions more dilute than 20% produce fihns too thin to handle readily. This cannot be corrected by increasing the volume of solution used, as t,l~is:~lTrnt,s the size of the film, not its thirlincss.
Solveuts must he hoth wat,er-soluble and volatile. The ones found most suitable in the work described were methylethyl ketone and tetrahydrofuran. Subsitution of a water-soluhle, low-volatility solvent such as dimet.hylformaniide or dimethylacetamide resulted in the formation of strings of polymer and no films. Volatile, hut water-insoluhle, solvents such as toluene or methylcyclohexane, yielded sticky films that reqnired a long time hefore they could be removed from t,he surface of the water. Even then, the films were of poor quality. A dense solvent, such as the chlorinated hydrocarhonn, caused the polymer solutiou to sink so that fihn could not he isolated. The formation of films a t the surface of wnt,cr occurs when the solvent from the lower surface of the film dissolves and t,he solvrnt at. t,he npper surfare of the 'Please direct aorrrspc,ndeitr;eto this author. SOKENSON, W. It., .*NU (:.LMPBELI,, T. \V., i ' P r e p a ~ . ~ Methti~e ods of Polymer Chemislry," Intersciewe Publishem (division of John Wiley $ Sons,Itla.), N e r Yo*, 1961, pp. 27-29.
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lournol o f Chemiml
Education
film evaporates siniultan?ously. Thcsc processes are rapid enough so that Formation of the film is almost instantaneous. Equipmat and dfale~.ials: A pneumatic trough, or similar pan, a thermometer or glass rod, a syringe (preferably polyethylene or polypropyleoe), polystyrene (Dow 666), copolymer of vinyl
chloride nnd vinyl acetate (Diamond Alkali Ca. OM-80), dioctyl phthslate (DOP), methylethyl ketone, tr1r;hydrofuran (THF), tolwnr, dimetbylacetmnide, c:,y?jrlahexnne.
Solutions of the pnly(viny1 chloride co-vinyl acetate) re made up in concentrations ranging from 1C&3070 in methylethyl ketone and THF. Plasticizer (DOP) is added (20% of the weight of the copolymer) in order tan emure film flexibility. Polystyrene solutions are made up in nlethylethyl ketone and THF, again in concentrations ranging from 10-30%. When small drops of the polymer soh~t~ion are placed on the surface of water in a pneumatic trough, the solution spreads out rapidly t,o cover the surface smoothly and uni-
formly. The solutions are taken up in a 2.5 co s y r i n g e approximately 1.5 cc for a 20% solution. 2.0 cc for a 30yo solution is deposit,ed in a sweeping motion on a center line of the long axis of a water-filled pneumatic trough 9 X 15 X 25/8 in. The film X forms immediately. I t can be readily removed by lifting carefully with a thcrmomet,er or glass rod along one edge of the long axis. I t should he plnccd on a paper towel to absorh the droplets of mnt,w. Tt may then be cut to any desired size. Polystyrene films are normally quit,e brittle unless "oriented:" Orientation is accomplished by placing t,he film sample on a support after it is dry, weighting it, and heating it,. The support we used consisted of a length of in. od sl.ainless steel tuhing bent to form a square with 4'/* in. sides. The protmding end of t,he t,uhing is clamped to a ring stand. All four sides of t,hc film are evrnly weight,ed with flat jawed paper clips. Heat from a small hot plate placed about 3 in. below the filni rauses visually npparent biaxial orientat,ion of the film whirl1 res~~It,s it1 mn~:ligreater flexibility.
