Polymer surface energy values

Surface Energy Values from Selected Polymers... 

The surface forces apparatus (Section 2.3) enables the estimation of a surface energy term, Fq (Eq. 9), providing sufficiently smooth surfaces can be produced. In recent years Chaudhury, Pocius and colleagues have made a valuable contribution to the field of adhesion by developing the technique to study energies of adhesion and of surface energies of polymers [81-85]. These SFA results provide alternatives to values based on traditional destructive tests or contact angle measurements. 

Israelachvili and his colleagues have used the SEA to study the interactions between surface layers of surfactant and of other molecules representing functionalised polymer chains, adhesion promoters or additives. Typically a monolayer of the molecule concerned is deposited onto cleaved mica sheets. The values of surface energies obtained from the JKR equation (Eq. 18) throw some interesting light on the nature and roughness of surface layers in contact. 

It is observed that the total surface energy increases with grafting (Table 5). The values become almost double for PEgDBM3. The increased surface energy of the grafted polymer comes mostly from the polar compo-... 

On the other hand, the values for g13 or g23 are positive, with a few exceptions. In other words, the adsorption processes of water and of protein onto polymer surfaces are for the most part thermodynamically unfavorable. The negative values of gs are the result of a remarkable decrease in free energy when adsorptive water molecules are driven back to the bulk water system, as seen... 

So far a number of important conclusions can be summarised. The SFM signal (deflection of the cantilever) results from a combination of surface and deformation forces. The total surface force between a SFM tip and a polymer surface includes adhesion and capillary forces, Fs=Fadh+Fcap. For polymer surface, it can be estimated to Fs 15 nN. Lower values might be expected for nonwettable and lower energy surfaces. The surface force is balanced by forces from the surface deformation, Fd, and from the deflection of the cantilever, Fc. In order to monitor a signal in contact SFM, the deformation forces must exceed the total surface forces, Fc=Fd - Fs. E.g., a net repulsive force of 0.4 nN will be monitored by 1 nm deflection of a Si cantilever with the following parameters E=50 GPa, 1= 100 pm,b=30 pm, h=4 pm, k=0.4 N/m. 

Fluorinated polymers are considered high value-added materials, due to their outstanding properties which open up various applications [1-9]. Such polymers exhibit high thermostability and chemical inertness, low refractive index and coefficient of friction, good water and oil repellence, low surface energy and valuable electrical properties. In addition, they are non-sticky and resistant to UV, ageing, and to concentrated mineral acids and alkalies. 

---