The surface structure of UV exposed poly-dimethylsiloxane (PDMS) insulator studied by slow positron beam

Study on surface structure of plasma‐treated polydimethylsiloxane (PDMS) elastomer by slow positron beam

“…The structure of this inorganic layer is denser than the PDMS chains. () After the formation of silica‐like layer, the positrons with low incident energy have a higher possibility of diffusing or being scattered back into vacuum, resulting in a sharply decreased formation possibility of p ‐Ps near sample surface. Moreover, this inorganic surface layer hardly contains free volumes.…”

“…To return the surface to its pretreatment hydrophobic character, the LMW siloxanes will diffuse through silica‐like layer covering the sample surface. () Due to the blocking effect of silica‐like layer, a number of LMW species accumulates beneath the inorganic layer, resulting in an increased S t value . Compared with 3‐min–treated sample, the 5‐minute one forms a thicker silica‐like layer, of which the blocking effect on migration of LMW species is more remarkable.…”

“…() Cracking of the silica‐like layer allows for a direct path for LMW siloxanes to migrate to the surface, resulting in a faster hydrophobic recovery rate than the uncracked one. () The recovered surface hydrophobicity is a superficial property, because the LMW species covers only the PDMS topmost, masking permanent changes deeper in the material . Hence, some valuable information can be lost, due to shortcomings of traditional surface characterizations.…”

“…14,16,19 The recovered surface hydrophobicity is a superficial property, because the LMW species covers only the PDMS topmost, masking permanent changes deeper in the material. 20 Hence, some valuable information can be lost, due to shortcomings of traditional surface characterizations. For example, X-ray photoelectron spectroscopy (XPS) can only provide chemical states information in a depth less than 10 nm.…”

Effect of Ultraviolet Absorber on Photo-Degradation of Epoxy Coating Studied by Slow Positron Beam

“…3, the S value of non-irradiated sample increases with increasing incident energy until 2 keV. Similar to most polymers, this is ascribed to the back scattering and back diffusion of the positrons and positro- nium (Ps) from or near the sample surface [11]. The formation possibility of p-Ps decreases, thus resulting in a low S parameter.…”