Transcription of Surface Tension of Polymers - MIT
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Surface Tension of Polymers - MIT
June 29, 20051 Surface Tension of PolymersAbhinandan AgrawalHatsopoulos Microfluids LaboratoryDepartment of Mechanical EngineeringMassachusetts Institute of TechnologyJune 29, 20052 Physical origin of Surface Tension / Surface energy Unhappy molecules at the Surface : they aremissing half their attractive interactions Unbalanced forces for the molecules at the Surface lead to additional energy The additional free energy at the Surface is known as surfaceenergy This is the fundamental reason behind liquids adjusting their shapes to expose the smallest possible areaExamples of minimal surfaces spherical shape of dry hair vs. sticky wet hairJose Bico, Nature, 2004 June 29, 20053 Mechanical definition: as a Surface energy Supply of energy is necessary to create surfacesdWdA = (mJ/m2)specific free energy or Surface Tension =Specific Surface energy of a material is the excess energy per unit area due to the existence of the free surfaceJune 29, 20054 Estimation of Surface Tension based on intermolecular forcesUU/2 Surface Tension is then of order For van derWaalstype interactions, At a temperature of 25 oC, kTis equal to
Specific surface energy of a material is the excess energy per unit area due to the existence of the free surface. June 29, 2005 4 Estimation of surface tension based on intermolecular forces U U/2 ... Zisman plot for PMMA using various testing liquids. June 29, 2005 18 2c.
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