涂层中疏水优化检测方案(表面张力仪)

Application Report Protective polymer coating Application report： AR218e Industry section： Construction Author： Hubert Lechner Method： Force Tensiometer-K12 Keywords： polymer， anti-graffiti coating， wettability， dynamic contact angle， Wilhelmy， surface free energy polymer， anti-graffiti coating， wettability， dynamic contact angle， Wilhelmy， surface free energy Optimization of Anti-graffiti Coatings Based on Silicon-Hybrid Systems Abstract Many monuments， made of stone， are degraded due to air pollution and human vandalism such as graffiti. Damage fromgraffiti also concerns present-day architecture as once soiled， these surfaces must be restored by repainting， sandblastingor washing with solvents. Such treatments change the look of the surface due to the physical degradation and are alsolabor intensive. Besides， it is useless because new graffiti appears some days later at the same place. An alternative method is permanent protection of external surfaces by coating them with transparent polymer films withlow wettability and good weathering resistance. One possible solution can be a solvent-free film forming emulsion containing crosslinkable reactive polysiloxane [SIL] andpolytetrafluoroethylene [PTFE]. With these stabilized emulsions (which also contain various non-ionic and anionicsurfactants and a catalyst) a film can be obtained with polysiloxane-polytetrafluoroethylene semi-interpenetratingpolymer network [semi IPN SIL/PTFE]. The proper design of semi IPN SIL/PTFE leads to a polymer film which showsexcellent features of both polymers (high permeability of gases and vapors of SIL as well as low wettability of bothpolymers). Several parameters like morphology， water vapor permeability， resistance to salts， frost resistance， UV resistance， dynamiccontact angle and surface free energy have to be tested for optimizing SIL/PTFE ratio for best protective coatings inpractice. Experimental For water wettability evaluation， dynamic contact angle[DCA] measurements were made with a KRUSS ProcessorTensiometer K12 with software K121 using Wilhelmymethod at 25℃. Samples were prepared by coating glasscover slides with tested emulsion and drying them over48 hours. For detection of wetted length and dynamiccontact angle samples were immersed and withdrawn ina liquid of known surface tension. For calculation ofwetted length n-hexane as totally wetting liquid wasused. Speed of movement wass constant at about4mm/min. Advancing and receding contact angles [ACAand RCA] were calculated by using regression method i.e.elimination of buoyancy by extrapolationntozeroimmersion depth. Surface free energy values [SFE] were obtained on thebasis of DCA measurements for water and benzyl alcoholusing thegeometric meanapproach (Owens-Wendtequation). Results The following results from DCA determination with waterwere obtained for different ratios of PTFE content in semiIPN consisting of SIL/PTFE applied in the form of anaqueous dispersion： PTFEwt% 0 26 35 45 55 65 75 100 ACA1 92，0 93，5 95，6 98，0 105，0 109，6 114，1 116，0 RCA[] 83，9 83，4 85，7 82，3 88，9 89，3 90，2 92，0 For surface free energy， the following values have beencalculated based on advancing contact angles of waterand benzyl alcohol： PTFE wt% 0 26 35 45 55 65 75 100 SFE[mN/m1 17，3 16，8 16，5 14，1 13，6 13，1 13，0 12，8 disperse part 3，9 4，0 6，0 8，4 10，1 10，6 10，8 11，5 polarpart 13，4 12，8 10，5 5，7 3，5 2，5 2，3 1，3 SFE for PTFE content in semiIPN SIL/PTFE Knowing the different molecular structure of PTFE andSIL it is clear that in such aqueous coating formulationsincreasing PTFE/SIL ratio results in increaseddwatercontact angle and decreased SFE value. As one can see， even below a ratio 50/50 % the disperse part is biggerthan the polar part， which means dispersion-typeattraction already dominates over polar-type ones. Results of DCA and SFE determination were in goodagreement with ESCA measurements and mechanicalapplicationttests..This allow/sspreselection(oftheformulation of semi IPN SIL/PTFE that will show goodprotective behavior in practice. ( Literature ) ( [1] M. Zielecka， 3"d Internationa l Conference Advances In Coating Technology， A CT 1998， Katowice ( P L)， Paper N°19 ) ( [2\ D.K.Owens， R .C. Wendt： J.Appl.Polymer S ci. 1 3 (1969)，1741-1747 ) KRUSS GmbH|iBorsteler Chaussee Hamburg|Germany|www.kruss.de|