Dry spreading

Sieve the sample through a 27-pm mesh, wash with distilled water, purify with acetone, and dry at 100°C. The final result is a dry powder, which is used to make uncovered dry spreads. 

Color and Appearance. Transfer ca 10g of the wet sample as received, to a Buchner funnel and apply suction until the sample is almost dry. Spread the material on a large watch glass and place in an oven at 70-75° for at least 4 hrs or until constant wt is obtd. Take four 0.5-mg portions, each from different sections of the sample and spread them over an area of 2 sqcm on a glass microscopic slide. Examine the material using a magnification of ca 30 times... 

SQUEEZE THE CASEIN ALMOST DRY. SPREAD OUT THE CHEESE CLOTH TO LET THE CASEIN DRY. 

In order for pure ammonium nitrate to be detonated by a dynamite cap, it must be very dry. Spread it out under a heat lamp or in rhe sun. When eomplcccly dry, store it in tightly closed plastic bags. 

Filter the chromous acetate on a Buchner funnel and wash with four 50-ml portions of ice-cold air-free water. (Water may be freed from dissolved air by bubbling nitrogen or by shaking with a little ether as in Experiment 40). Pour one portion on as soon as the other has drained and see that the wash water is distributed over the whole precipitate. Then wash with 75 ml of alcohol and 75 ml of ether and suck dry. Spread the precipitate on a piece of paper to let all the ether evaporate then weigh the yield. It should be about 75 per cent of theoretical and should be a light brick-red powder. 

Fig. 3.1. The final pancake profile in dry spreading The thickness e(S) is constant except in an edge region of width i,.

Fig. 3.2. Detailed form of the advancing profile in dry spreading of a completely wetting fluid. The cross-over thickness / is of order a/0.

These considerations are important for a discussion of dry spreading on a random surface (i.e., when 5 is slightly modulated from point to point) for more details see de Gennes (1985b) and Joanny (1985). 

In Chapter 3 entitled Dry spreading of liquids on solids (originally the last lecture) the general phenomenon of surface wetting by liquids with different spreading coefficients is examined in its most basic aspects. The specific case of polymer melts is also taken into consideration here we are confronted with many new possibilities either an anomalous slippage of the melt at the wall surface or in some other cases an anomalous sticking of the chains to the wall. 

The comparison between the dry spreading of a liquid and that of a polymer is given in Table 2. Some parameters in Table 2 are still being examined currently by others. Recent experiments(65a) on a model system (silicone oil on a potential surface of silicon oxide) and the latest work by Daillant et a/.(6Sb) v ith X-ray reflectivity have confirmed the theory proposed by Joanny and de Gennes(59) and the existence of a thin precursor film. 

The dry spreading of polymer solution(66) more complex than that of either the pure liquid or a polymer melt. Assuming the polymer does not adsorb on the surface, the dry spreading of a semidilute solution (from a good solvent) of neutral, flexible chains on a solid surface can be summarized as follows. 

L. Leger, A. M. Guinet-Picard, H. Hervet, D. Ausserre, and M. Erman, Dry spreading of polymer liquids on solid surfaces Role of long-range forces, precursor film profiles, and specific polymeric effects, in New Trends in Physics and Physical Chemistry of Polymers (L. H. Lee, ed.). Plenum Press, New York (1989). 

Suck the silica gel dry, spread it in the hood on aluminum foil to form a layer about 2-3 cm thick, and let it air-dry overnight. Move silica gel into a clean, suitable, heat-resistant container and heat it in an oven at 140-160°C overnight. Store in a tightly closed container until use. 

Dry Spreading of Polymer Liquids on Solid Surfaces Role of Long Range Forces, Precursor Film Profiles and... 

The comparison between the dry spreading of a liquid and that of a polymer is given in Table 2. Some parameters in 2 are still being... 

DRY SPREADING OF POLYMER LIQUIDS ON SOLID SURFACES ROLE OF LONG RANGE FORCES, PRECURSOR FILM PROFILES AND SPECIFIC POLYMERIC EFFECTS... 

Spreading over saturated porous substrate than in the case of dry spreading, (2) experimentally determined values of the effective lubrication coefficient, (o, agree well with the aforementioned theoretical estimations. However, precision of experimental determination of this parameter does not allow us to extract more information about effective viscosity of the porous substrate. 

---